Fast Ethernet technology, its features, physical layer, construction rules. Ethernet and Fast Ethernet equipment Why the fast ethernet network was created
We note the main features of the development of Ethernet networks and the transition to Fast Ethernet networks (IEEE 802.3u standard):
- - a tenfold increase in throughput;
- - preservation of the CSMA/CD random access method;
- - preservation of the frame format;
- - support for traditional data transmission media.
These features, plus the dual-speed and auto-sensing 10/100 Mbps support built into Fast Ethernet NICs and switches, allow for a seamless transition from Ethernet networks to faster Fast Ethernet networks, providing an advantageous legacy over other technologies. Another additional factor in successful market penetration is the low cost of Fast Ethernet equipment.
Fast Ethernet architecture
The structure of the Fast Ethernet layers (including the MII interface and the Fast Ethernet transceiver) is shown in fig. 13. Even at the development stage of the 100Base-T standard, the IEEE 802.3u committee determined that there is no universal signal coding scheme that would be ideal for all three physical interfaces (TX, FX, T4). If compared with the Ethernet standard, then there the encoding function (Manchester code) is performed by the PLS physical signaling layer (Fig. 5), which is located above the medium-independent interface AUI. In the Fast Ethernet standard, the coding functions are performed by the PCS coding sublayer located below the medium-independent MII interface. As a result, each transceiver must use its own set of coding schemes best suited to the respective physical interface, such as the 4V/5V and NRZI set for the 100Base-FX interface.
MII interface and Fast Ethernet transceivers. The MII (medium independent interface) interface in the Fast Ethernet standard is analogous to the AUI interface in the Ethernet standard. The MII interface provides communication between the negotiation and physical encoding sublayers. Its main purpose is to simplify the use of different types of environment. The MII interface requires further connection of a Fast Ethernet transceiver. A 40-pin connector is used for communication. The maximum distance along the MII interface cable must not exceed 0.5 m.
If the device has standard physical interfaces (for example, RJ-45), then the physical layer sublayer structure can be hidden inside the chip with a lot of logic integration. In addition, deviations in the protocols of intermediate sublayers in a single device are permissible, setting the main goal of increasing performance.
Physical Fast Ethernet interfaces
The IEEE 802.3u Fast Ethernet standard establishes three types of physical interface (Fig. 14, Table 6 Main characteristics of IEEE 802.3u Fast Ethernet standard physical interfaces): 100Base-FX, 100Base-TX and 100Base-T4.
100Base-FX. The standard of this fiber optic interface is completely identical to the FDDI PMD standard. The main optical connector of the 100Base-FX standard is Duplex SC. The interface allows a duplex communication channel.
- * - distance is achieved only in duplex communication mode.
- 100Base-TX. The standard of this physical interface assumes the use of unshielded twisted pair of category 5 or higher. It is completely identical to the FDDI UTP PMD standard. The physical RJ-45 port, as in the 10Base-T standard, can be of two types: MDI (network cards, workstations) and MDI-X (Fast Ethernet repeaters, switches). A single MDI port may be available on a Fast Ethernet repeater.
For transmission over a copper cable, pairs 1 and 3 are used. Pairs 2 and 4 are free. The RJ-45 port on the network card and on the switch can support 10Base-T mode, or the auto-negotiation function, along with 100Base-TX mode. Most modern network cards and switches support this feature via RJ-45 ports and, in addition, can work in full duplex mode.
100Base-T4. This type of interface allows you to provide a half-duplex communication channel over twisted pair UTP cat. 3 and above. It is the possibility of a company's transition from the Ethernet standard to the Fast Ethernet standard without a radical replacement of the existing cable system based on UTP cat.3 that should be considered the main advantage of this standard.
Unlike the 100Base-TX standard, where only two twisted pairs of cable are used for transmission, the 100Base-T4 standard uses all four pairs. Moreover, when the workstation and the repeater are connected via a direct cable, data from the workstation to the repeater goes through twisted pairs 1, 3 and 4, and in the opposite direction - through pairs 2, 3 and 4. Pairs 1 and 2 are used to detect collisions like the Ethernet standard . The other two pairs 3 and 4 alternately, depending on the commands, can pass the signal either in one or the other direction. Sending a signal in parallel over three twisted pairs is equivalent to the inverse multiplexing discussed in Chapter 5. The bit rate per channel is 33.33 Mbps.
Character encoding 8V/6T. If Manchester encoding were used, then the bit rate per twisted pair would be 33.33 Mbps, which would exceed the 30 MHz limit for such cables. An effective reduction in the modulation frequency is achieved if a three-level (ternary) code is used instead of a direct (two-level) binary code. This code is known as 8V/6T; this means that before transmission takes place, each set of 8 binary bits (character) is first converted according to certain rules into 6 triple (three-level) characters.
The 100Base-T4 interface has one significant drawback - the fundamental impossibility of supporting the duplex transmission mode. And if, when building small Fast Ethernet networks using 100Base-TX repeaters, it has no advantages over 100Base-T4 (there is a collision domain whose bandwidth is not more than 100 Mbps), then when building networks using switches, the disadvantage of the 100Base-T4 interface becomes obvious and very serious. Therefore, this interface has not received as much distribution as 100Base-TX and 100Base-FX.
Types of Fast Ethernet Devices
The main categories of devices used in Fast Ethernet are the same as in Ethernet: transceivers; converters; network cards (for installation on workstations/file servers); repeaters; switches.
transceiver- a two-port device covering the PCS, PMA, PMD and AUTONEG sublevels, and having, on the one hand, an MII interface, on the other, one of the media-dependent physical interfaces (100Base-FX, 100Base-TX or 100Base-T4). Transceivers are used relatively rarely, as are network cards, repeaters, switches with an MII interface.
Network Card. The most widely used today are network cards with a 100Base-TX interface to the PCI bus. Optional, but highly desirable, features of the RJ-45 port are 100/10 Mbps auto-configuration and duplex support. Most cards in production today support these features. There are also network cards with a 100Base-FX optical interface (manufacturers IMC, Adaptec, Transition Networks, etc.) - the main standard optical is the SC connector (ST is allowed) for a multimode optical fiber.
Converter(media converter) - a two-port device, both ports of which represent media-dependent interfaces. Converters, unlike repeaters, can operate in full duplex mode, except when there is a 100Base-T4 port. 100Base-TX/100Base-FX converters are common. Due to the general trends in the growth of broadband extended networks using single-mode FOCs, the consumption of optical transceivers per single-mode optical fiber has increased dramatically in the last decade. Converter chassis that combine multiple individual 100Base-TX/100Base-FX modules allow multiple fiber optic segments converging at a central node to be connected to a switch equipped with duplex RJ-45 (100Base-TX) ports.
Repeater. According to the parameter of maximum time delays during frame relay, Fast Ethernet repeaters are divided into two classes:
- - Class I. RTD double run delay must not exceed 130 watts. Due to less stringent requirements, repeaters of this class can have T4 and TX / FX ports, and can also be stacked.
- - Class II. Repeaters of this class are subject to more stringent requirements for delay on a double run: RTD
Switch- an important device of corporate networks. Most modern Fast Ethernet switches support 100/10 Mbps auto-configuration over RJ-45 ports and can provide full-duplex communication on all ports (with the exception of 100Base-T4). Switches may have special additional slots for installing an up-link module. Such modules can have optical ports such as Fast Ethernet 100Base-FX, FDDI, ATM (155 Mbps), Gigabit Ethernet, etc. as interfaces.
large switch manufacturers Fast Ethernet companies are: 3Com, Bay Networks, Cabletron, DEC, Intel, NBase, Cisco, etc.
Ethernet is the most widely used standard today. local networks. Total number of networks currently using
fast ethernet
Fast Ethernet technology is similar to traditional Ethernet technology in many ways, but it is 10 times faster. Fast Ethernet or 100BASE-T operates at 100 megabits per second (Mbps) instead of 10 for the traditional Ethernet option. 100BASE-T technology uses frames of the same format and length as Ethernet and does not require changes in upper layer protocols, applications, or network operating systems on workstations. You can route and switch packets between 10 Mbps and 100 Mbps networks without protocol translation and associated delays. Fast Ethernet technology uses the CSMA/CD MAC protocol to provide media access. Most modern Ethernet networks are built on a star topology, where the hub is the center of the network, and cables from the hub run to each computer. The same topology is used in Fast Ethernet networks, although the network diameter is somewhat smaller due to the higher speed. Fast Ethernet uses unshielded twisted-pair (UTP) cable as specified in the IEEE 802.3u specification for 100BASE-T. The standard recommends the use of category 5 cable with two or four pairs of plastic-sheathed conductors. Category 5 cables are certified for 100 MHz bandwidth. In 100BASE-TX, one pair is used for data transmission, the other pair for collision detection and reception.
The Fast Ethernet standard defines three modifications for working with different types of cables: 100Base TX, 100Base T4 and 100Base FX. Modifications 100Base TX and 100Base T4 are designed for twisted pair, and 100Base FX was designed for optical cable.
The 100Base TX standard requires two shielded or unshielded twisted pairs. One pair is for transmitting, the other for receiving. Two major cabling standards meet these requirements: Category 5 Unshielded Twisted Pair (UTP-5) and IBM Type 1 Shielded Twisted Pair.
The 100Base T4 standard has less restrictive cable requirements, as it uses all four pairs of an eight-core cable: one pair for transmit, one for receive, and the remaining two pairs work both for transmission and reception. As a result, in the 100Base T4 standard, data can be received and transmitted over three pairs. For 100Base T4 networks, Category 3-5 unshielded twisted pair and Type 1 shielded twisted pair cables are suitable.
The succession of Fast Ethernet and Ethernet technologies makes it easy to develop recommendations for use: Fast Ethernet is useful in those organizations that have widely used classic Ethernet, but today are in need of increased bandwidth. At the same time, all the accumulated experience with Ethernet and, in part, the network infrastructure is preserved.
For classic Ethernet, the network listening time is determined by the maximum distance that a 512-bit frame can travel over the network in a time equal to the processing time of this frame at the workstation. For an Ethernet network, this distance is 2500 meters. In a Fast Ethernet network, the same 512-bit frame will travel only 250 meters in the time it takes to process it at a workstation.
Fast Ethernet's main area of work today is workgroup and departmental networks. It is advisable to make the transition to Fast Ethernet gradually, leaving Ethernet where it does its job well. One obvious case where Ethernet should not be replaced by Fast Ethernet technology is when old personal computers with the ISA bus.
Gigabit Ethernet/
this technology uses the same frame format, the same CSMA/CD media access method, the same flow control mechanisms and the same control objects, yet Gigabit Ethernet is more different from Fast Ethernet than Fast Ethernet is from Ethernet. In particular, if Ethernet was characterized by a variety of supported transmission media, which gave reason to say that it could even work over barbed wire, then in Gigabit Ethernet, fiber optic cables become the dominant transmission medium (this, of course, is far from the only difference , but the rest will be discussed in more detail below). In addition, Gigabit Ethernet poses incomparably more complex technical challenges and places much higher demands on the quality of the wiring. In other words, it is much less versatile than its predecessors.
GIGABIT ETHERNET STANDARDS
Main efforts working group IEEE 802.3z aims to define physical standards for Gigabit Ethernet. She took the ANSI X3T11 Fiber Channel standard as a basis, more precisely, its two lower sublevels: FC-0 (interface and transmission medium) and FC-1 (encoding and decoding). The physical media-specific specification for Fiber Channel currently specifies 1.062 Gigabauds per second. In Gigabit Ethernet, this has been increased to 1.25 gigabytes per second. Considering the 8B/10B encoding, we get a data transfer rate of 1 Gbps.
Technologyethernet
Ethernet is the most widely used local area network standard today.
Ethernet is a networking standard based on the experimental Ethernet Network that Xerox developed and implemented in 1975.
In 1980, DEC, Intel, and Xerox jointly developed and published the Ethernet Revision II standard for a coaxial cable network, which became the latest version of the proprietary Ethernet standard. Therefore, the proprietary version of the Ethernet standard is called the Ethernet DIX standard, or Ethernet II, on the basis of which the IEEE 802.3 standard was developed.
Based on the Ethernet standard, additional standards were adopted: in 1995 Fast Ethernet (an addition to IEEE 802.3), in 1998 Gigabit Ethernet (section IEEE 802.3z of the main document), which in many ways are not independent standards.
To transfer binary information over a cable for all variants of the physical layer of Ethernet technology that provide a throughput of 10 Mbit / s, the Manchester code is used (Fig. 3.9).
In the Manchester code, a potential drop, that is, the front of the pulse, is used to encode ones and zeros. In Manchester encoding, each clock is divided into two parts. Information is encoded by potential drops that occur in the middle of each cycle. A unit is encoded by a low-to-high transition (rising edge of the pulse), and a zero is encoded by a reverse edge (rear edge).
Rice. 3.9. Differential Manchester encoding
The Ethernet standard (including Fast Ethernet and Gigabit Ethernet) uses the same media separation method, the CSMA/CD method.
Each PC operates on Ethernet according to the principle “Listen to the transmission channel before sending messages; listen when you send; stop working in case of interference and try again."
This principle can be deciphered (explained) as follows:
1. No one is allowed to send messages while someone else is already doing it (listen before you send).
2. If two or more senders start sending messages at about the same moment, sooner or later their messages will "collide" with each other in the communication channel, which is called a collision.
Collisions are easy to recognize because they always produce an interference signal that does not look like a legitimate message. Ethernet can recognize the interference and cause the sender to pause the transmission and wait a while before resending the message.
Reasons for the widespread and popularity of Ethernet (advantages):
1. Cheapness.
2. Great use experience.
3. Continued innovation.
4. Wealth of choice of equipment. Many manufacturers offer networking equipment based on Ethernet.
Disadvantages of Ethernet:
1. The possibility of message collisions (collisions, interference).
2. When the network is heavily loaded, the message transmission time is unpredictable.
TechnologyTokenring
Token Ring networks, like Ethernet networks, are characterized by a shared data transmission medium, which consists of cable segments connecting all network stations into a ring. The ring is considered as a common shared resource, and access to it requires not a random algorithm, as in Ethernet networks, but a deterministic algorithm based on the transfer of the right to use the ring to stations in a certain order. This right is conveyed using a frame of a special format called a token or token.
Token Ring technology was developed by IBM in 1984, and then submitted as a draft standard to the IEEE 802 committee, which based on it adopted the 802.5 standard in 1985.
Each PC works in Token Ring according to the principle “Wait for a marker, if it is necessary to send a message, attach it to the marker when it passes by. If the marker passes, remove the message from it and send the marker further.
Token Ring networks operate at two bit rates, 4 and 16 Mbps. Mixing of stations operating at different speeds in the same ring is not allowed.
Token Ring technology is a more sophisticated technology than Ethernet. It has fault tolerance properties. In the Token Ring network, network control procedures are defined that use ring-shaped feedback - the sent frame always returns to the sending station.
Rice. 3.10. Principle of TOKEN RING technology
In some cases, detected network errors are fixed automatically, for example, a lost token can be restored. In other cases, errors are only recorded, and their elimination is carried out manually by maintenance personnel.
To control the network, one of the stations acts as a so-called active monitor. The active monitor is selected during ring initialization as the station with the highest MAC address. If the active monitor fails, the ring initialization procedure is repeated and a new active monitor is selected. A Token Ring network can include up to 260 nodes.
A token ring hub can be active or passive. A passive hub simply interconnects ports internally so that stations connected to those ports form a ring. The passive MSAU does not perform signal amplification or resynchronization.
An active hub performs signal regeneration functions and is therefore sometimes referred to as a repeater, as in the Ethernet standard.
In general, the Token Ring network has a combined star-ring configuration. End nodes are connected to the MSAU in a star topology, and the MSAUs themselves are combined through special Ring In (RI) and Ring Out (RO) ports to form a backbone physical ring.
All stations in the ring must operate at the same speed, either 4 Mbps or 16 Mbps. Cables connecting a station to a hub are called lobe cables, and cables connecting hubs are called trunk cables.
Token Ring technology allows you to use various types of cable to connect end stations and hubs:
– STP Type 1 - shielded twisted pair (Shielded Twistedpair).
It is allowed to combine up to 260 stations into a ring with a length of branch cables up to 100 meters;
– UTP Type 3, UTP Type 6 - unshielded twisted pair (Unshielded Twistedpair). The maximum number of stations is reduced to 72 with drop cables up to 45 meters long;
– fiber optic cable.
The distance between passive MSAUs can be up to 100 m using STP Type 1 cable and 45 m using UTP Type 3 cable. The maximum distance between active MSAUs increases respectively to 730 m or 365 m depending on the type of cable.
The maximum length of a Token Ring ring is 4000 m. The restrictions on the maximum ring length and the number of stations in a ring in Token Ring technology are not as strict as in Ethernet technology. Here, these restrictions are mainly related to the turnaround time of the marker around the ring.
All timeout values on the network adapters of Token Ring network nodes are configurable, so you can build a Token Ring network with more stations and longer ring lengths.
Advantages of Token Ring technology:
Guaranteed message delivery
high data transfer rate (up to 160% Ethernet).
Disadvantages of Token Ring technology:
Requires expensive media access devices;
The technology is more difficult to implement;
2 cables are required (to increase reliability): one incoming, the other outgoing from the computer to the hub;
high cost (160-200% of Ethernet).
TechnologyFDDI
FDDI (Fiber Distributed Data Interface) technology is the first LAN technology in which the data transmission medium is a fiber optic cable. The technology appeared in the mid-80s.
FDDI technology is largely based on Token Ring technology, supporting a token-passing access method.
The FDDI network is built on the basis of two fiber optic rings, which form the main and backup data transmission paths between network nodes. Having two rings is the main way to increase resiliency in an FDDI network, and nodes that want to take advantage of this increased reliability potential should be connected to both rings.
In the normal mode of the network, data passes through all nodes and all sections of the cable only the primary (Primary) ring, this mode is called the Thru mode - “through”, or “transit”. The secondary ring (Secondary) is not used in this mode.
In the event of some kind of failure where part of the primary ring is unable to transmit data (for example, a cable break or node failure), the primary ring is merged with the secondary, forming a single ring again. This mode of network operation is called Wrap, that is, "folding" or "folding" rings. The folding operation is performed by means of concentrators and / or network adapters FDDI.
Rice. 3.11. IVS with two cyclic rings in emergency mode
To simplify this procedure, data on the primary ring is always transmitted in one direction (in the diagrams, this direction is shown counterclockwise), and on the secondary - in the opposite direction (shown clockwise). Therefore, when a common ring is formed from two rings, the transmitters of the stations still remain connected to the receivers of neighboring stations, which makes it possible to correctly transmit and receive information by neighboring stations.
The FDDI network can fully restore its operability in the event of single failures of its elements. With multiple failures, the network breaks up into several unrelated networks.
Rings in FDDI networks are considered as a common shared data transmission medium, so a special access method is defined for it. This method is very close to the access method of Token Ring networks and is also called the token ring method.
The differences in the access method are that the token retention time in the FDDI network is not a constant value. This time depends on the loading of the ring - with a small load, it increases, and with large overloads, it can decrease to zero. These access method changes only affect asynchronous traffic, which is not critical to small frame delays. For synchronous traffic, the token hold time is still a fixed value.
FDDI technology currently supports cable types:
– fiber optic cable;
– Category 5 unshielded twisted pair. The latest standard appeared later than the optical one and is called TP-PMD (Physical Media Dependent).
Optical fiber technology provides the necessary means for transmitting data from one station to another over an optical fiber and determines:
Use of 62.5/125 µm multimode fiber optic cable as the main physical medium;
Requirements for optical signal power and maximum attenuation between network nodes. For standard multi-mode cable, these requirements result in a distance limit between nodes of 2 km, and for single-mode cable, the distance increases to 10-40 km, depending on the quality of the cable;
Requirements for optical bypass switches and optical transceivers;
Parameters of optical connectors MIC (Media Interface Connector), their marking;
Use to transmit light with a wavelength of 1.3 nm;
The maximum total length of an FDDI ring is 100 kilometers, the maximum number of dual connected stations in the ring is 500.
FDDI technology was developed for use in critical areas of networks - on backbone connections between large networks, such as building networks, as well as for connecting high-performance servers to a network. Therefore, the main requirements, the developers had ( dignity):
- ensuring a high data transfer rate,
- fault tolerance at the protocol level;
- large distances between network nodes and a large number of connected stations.
All these goals have been achieved. As a result, FDDI technology turned out to be of high quality, but very expensive ( flaw). Even the introduction of a cheaper twisted-pair option has not greatly reduced the cost of connecting a single node to an FDDI network. Therefore, practice has shown that the main area of application of FDDI technology has become the backbone of networks consisting of several buildings, as well as networks of the scale of a large city, that is, the MAN class.
TechnologyFastethernet
The need for high-speed yet low-cost technology to connect powerful workstations to a network led in the early 90s to the creation of an initiative group that looked for a new Ethernet, a technology that was just as simple and effective, but operating at 100 Mbps .
Experts divided into two camps, which eventually led to the emergence of two standards adopted in the fall of 1995: the 802.3 committee approved the Fast Ethernet standard, which almost completely repeats 10 Mbps Ethernet technology.
The Fast Ethernet technology kept the CSMA/CD access method intact, leaving the same algorithm and the same time parameters in bit intervals (the bit interval itself decreased by 10 times). All the differences between Fast Ethernet and Ethernet are manifested at the physical level.
The Fast Ethernet standard defines three physical layer specifications:
- 100Base-TX for 2 pairs of UTP Category 5 or 2 pairs of STP Type 1 (4V/5V encoding method);
- l00Base-FX for multi-mode fiber optic cable with two optical fibers (4V/5V encoding method);
- 100Base-T4, operating on 4 pairs of UTP category 3, but using only three pairs for transmission at a time, and the remaining pair for collision detection (8B/6T encoding method).
l00Base-TX/FX standards can work in full duplex mode.
The maximum diameter of a Fast Ethernet network is approximately 200 m, and more accurate values depend on the specification of the physical environment. In the Fast Ethernet collision domain, no more than one class I repeater (allowing translation of 4V/5V codes to 8V/6T codes and vice versa) and no more than two class II repeaters (not allowing translation of codes) are allowed.
Fast Ethernet technology when working on twisted pair allows two ports to choose the most efficient mode of operation - 10 Mbps or 100 Mbps, as well as half-duplex or full-duplex mode due to the auto-negotiation procedure.
Gigabit Ethernet technology
Gigabit Ethernet adds a new 1000 Mbps step to the speed hierarchy of the Ethernet family. This stage allows you to effectively build large local networks, in which powerful servers and backbones of the lower levels of the network operate at a speed of 100 Mbps, and the Gigabit Ethernet backbone connects them, providing a sufficiently large margin of throughput.
The developers of Gigabit Ethernet technology have retained a large degree of continuity with Ethernet and Fast Ethernet technologies. Gigabit Ethernet uses the same frame formats as previous versions of Ethernet, operates in full duplex and half duplex modes, supporting the same CSMA/CD access method on a shared media with minimal changes.
To ensure an acceptable maximum network diameter of 200 m in half-duplex mode, the technology developers increased the minimum frame size by 8 times (from 64 to 512 bytes). It is also allowed to transmit several frames in a row, without freeing the medium, at an interval of 8096 bytes, then the frames do not have to be padded to 512 bytes. The remaining parameters of the access method and the maximum frame size remained unchanged.
In the summer of 1998, the 802.3z standard was adopted, which defines the use of three types of cable as a physical medium:
- multimode fiber optic (distance up to 500 m),
- single-mode fiber optic (distance up to 5000 m),
- double coaxial (twinax), through which data is transmitted simultaneously over two shielded copper conductors at a distance of up to 25 m.
An 802.3ab ad hoc group has been formed to develop a Gigabit Ethernet over Category 5 UTP variant and has already drafted a standard to operate over 4 UTP Category 5 pairs. Adoption of this standard is expected shortly.
Ease of installation.
A well-known and most widespread network technology.
Low cost network cards.
Possibility of implementation using various types of cable and cabling schemes.
Disadvantages of an Ethernet Network
Decreased real data transfer rate in a heavily loaded network, up to its complete stop, due to conflicts in the data transfer environment.
Difficulties in troubleshooting: when a cable breaks, the entire LAN segment fails, and it is quite difficult to localize a faulty node or network section.
Brief description of Fast Ethernet.
fast ethernet (Fast Ethernet) is a high-speed technology proposed by 3Com for the implementation of an Ethernet network with a data transfer rate of 100 Mbps, which retained to the maximum extent the features of 10-Mbit Ethernet (Ethernet-10) and implemented in the form of the 802.3u standard (more precisely, additions to the standard 802.3 as chapters 21 to 30). The access method is the same as Ethernet-10 - MAC layer CSMA/CD, which allows the use of the previous software and controls Ethernet networks.
All the differences between Fast Ethernet and Ethernet-10 are concentrated at the physical layer. 3 types of cable systems are used:
multimode FOC (2 fibers are used);
Network structure- hierarchical tree, built on hubs (like 10Base-T and 10Base-F), because no coaxial cable is used.
Network diameter Fast Ethernet is reduced to 200 meters, which is explained by a 10-fold reduction in the minimum frame length transmission time due to a 10-fold increase in transmission speed compared to Ethernet-10. However, it is possible to build large networks based on Fast technology Ethernet, thanks to the widespread adoption of low-cost, high-speed technologies, as well as the rapid development of switch-based LANs. When using switches, the Fast Ethernet protocol can operate in full duplex mode, in which there are no restrictions on the total length of the network, but only restrictions on the length of the physical segments connecting neighboring devices (adapter-to-switch or switch-to-switch) remain.
The IEEE 802.3u standard defines 3 Fast Ethernet physical layer specifications that are incompatible with each other:
100Base-TX - data transmission over two unshielded pairs of category 5 (2 pairs of UTP category 5 or STP Type 1);
100Base-T4- data transmission over four unshielded pairs of categories 3, 4, 5 (4 pairs of UTP category 3, 4 or 5);
100Base-FX- data transmission over two fibers of a multimode FOC.
What is the transmission time of the minimum (maximum) length frame (including the preamble) in bit intervals for a 10Mbps Ethernet network?
? 84 / 1538
What is PDV (PVV)?
PDV - the time during which the collision signal has time to propagate from the farthest node of the network - the time of a double turn (Path Delay Value)
PVV - reduction of the interframe interval (Path Variability Value)
What is the limit on PDV (PVV)?
PDV - no more than 575 bit intervals
PVV - when passing a sequence of frames through all repeaters, there should be no more than 49 bit intervals
How many bit intervals are sufficient safety margins for PDV? 4
When do you need to calculate the maximum number of repeaters and the maximum network length? Why not just apply the 5-4-3 or 4-hub rules?
When different types of transmission media
List the main conditions for the correct operation of an Ethernet network consisting of segments of various physical nature.
number of stations no more than 1024
the length of all branches is not more than the standard
PDV no more than 575
PVV - when passing a sequence of frames through all repeaters, there should be no more than 49 bit intervals
What is meant by segment base when calculating PDV?
Delays Introduced by Repeaters
Where is the worst-case collision of frames: in the right, left, or intermediate segment?
In the right - receiving
When is it necessary to calculate PDV twice? Why?
If the segment length is different at the remote edges of the network, since they have different base delay values.
Brief description of Token Ring LAN.
token ring (token ring) - A network technology in which stations can only transmit data when they own a token continuously circulating around the ring.
The maximum number of stations in one ring is 256.
The maximum distance between stations depends on the type of transmission medium (communication line) and is:
Up to 8 rings (MSAU) can be bridged.
The maximum network length depends on the configuration.
Purpose of network technology Token Ring.
The Token Ring network was proposed by IBM in 1985 (the first version appeared in 1980). The purpose of Token Ring was to network all types of computers manufactured by the company (from PCs to mainframes).
What international standard defines Token Ring network technology?
Token Ring is currently the IEEE 802.5 international standard.
How much bandwidth is provided on a Token Ring LAN?
There are two variants of this technology, providing data transfer rates of 4 and 16 Mbps, respectively.
What is an MSAU?
The MSAU hub is a self-contained unit with 8 slots for connecting computers using adapter cables and two end slots for connecting to other hubs using backbone cables.
Several MSAUs can be structurally combined into a group (cluster/cluster), within which subscribers are connected in a ring, which allows increasing the number of subscribers connected to one center.
Each adapter connects to the MSAU using two multidirectional links.
Draw the structure and describe the operation of a Token Ring LAN based on one (several) MSAUs.
One - see above
Several - (continued) ... The same two multidirectional communication lines included in the trunk cable can be connected to the MSAU in a ring (Fig.3.3), unlike a unidirectional trunk cable, as shown in Fig.3.2.
Each LAN node receives a frame from a neighboring node, restores signal levels to nominal levels, and passes the frame on to the next node.
The transmitted frame may contain data or be a marker, which is a special service 3-byte frame. The node that owns the token has the right to transmit data.
When a PC needs to transmit a frame, its adapter waits for the token, and then converts it into a frame containing data generated by the protocol of the appropriate level, and transmits it to the network. The packet travels across the network from adapter to adapter until it reaches the destination, which sets certain bits in the packet to confirm that the frame has been received by the destination and relays it on to the network. The packet continues to move through the network until it returns to the sending node, which checks the correct transmission. If the frame was transmitted to the destination without errors, the node passes the token to the next node. Thus, frame collisions are not possible on a token-passing LAN.
What is the difference between the physical topology of a Token Ring LAN and the logical one?
The physical token ring topology can be implemented in two ways:
1) "star" (Fig. 3.1);
The logical topology in all modes is a "ring". The packet is passed from node to node around the ring until it returns to the node where it originated.
Draw possible variants of the Token Ring LAN structure.
1) "star" (Fig. 3.1);
2) "expanded ring" (Fig. 3.2).
Brief description of the functional organization of the Token Ring LAN. See #93
The concept and functions of an active monitor in a Token Ring LAN.
When initializing a Token Ring LAN, one of the workstations is assigned as active monitor , which is assigned additional control functions in the ring:
temporary control in the logical ring in order to identify situations associated with the loss of the token;
generating a new token after token loss is detected;
formation of diagnostic frames under certain circumstances.
When an active monitor fails, a new active monitor is assigned from a variety of other PCs.
What mode (method) of passing the token is used in the Token Ring LAN with a speed of 16 Mbps?
To increase network performance in Token Ring at a speed of 16 Mbps, the so-called early token pass mode (Early Token Release - ETR), in which the RS transmits the token to the next RS immediately after the transmission of its frame. In this case, the next RS has the opportunity to transmit its frames without waiting for the completion of the transmission of the original RS.
List the types of frames used in the Token Ring LAN.
marker; data frame; completion sequence.
Draw and explain the format of the marker (data frame, termination sequence) of the Token Ring LAN.
Marker Format
KO - final limiter - [ J | K | 1 | J | K | 1 | PC | OO]
Data frame format
SPK - frame start sequence
BUT - initial delimiter - [ J|K| 0 |J|K| 0 | 0 | 0]
AP - access control - [ P|P|P|T|M|R|R|R]
UK - personnel management
AH - destination address
AI - source address
Data - data field
CS - checksum
PKK - a sign of the end of the frame
KO - final limiter
SC - frame status
Completion Sequence Format
The structure of the "access control" field in the LAN Token Ring frame.
UD- access control(Access Control) - has the following structure: [ P | P | P | T | M | R | R | R ] , where PPP - priority bits;
the network adapter has the ability to assign priorities to the marker and data frames by writing in the priority bit field of the priority level in the form of numbers from 0 to 7 (7 is the highest priority); The RS has the right to send a message only if its own priority is not lower than the priority of the token it received; T- marker bit: 0 for marker and 1 for data frame; M- monitor bit: 1 if the frame was transmitted by the active monitor and 0 otherwise; when the active monitor receives a frame with a monitor bit set to 1, the message or token has bypassed the LAN without finding a destination; RRR- reservation bits are used in conjunction with priority bits; The RS can reserve further use of the network by placing its priority value in the reservation bits if its priority is higher than the current value of the reservation field;
after that, when the transmitting node, having received the returned data frame, generates a new token, it sets its priority equal to the value of the reservation field of the previously received frame; thus, the token will be passed to the node that has set the highest priority in the reservation field;
The assignment of the priority bits (marker bit, monitor bit, reservation bits) of the access control field in the Token Ring LAN token. See above
What is the difference between MAC layer frames and LLC layer frames?
UK- personnel management(Frame Control - FC) defines the frame type (MAC or LLC) and the MAC control code; a one-byte field contains two areas:
Where FF- format (type) of the frame: 00 - for a frame of MAC type; 01 - for LLC level frame; (values 10 and 11 are reserved); 00 - unused reserve bits; CCCC- MAC MAC frame code (physical control field), which determines which type (defined by the IEEE 802.5 standard) MAC level control frames it belongs to;
Which field of the data frame indicates the belonging to the type of MAC (LLC)? In the CC field (see above)
The length of the data field in LAN Token Ring frames.
There is no special limitation on the length of the data field, although in practice it arises due to restrictions on the allowable time for network occupation by a single workstation and is 4096 bytes and can reach 18 KB for a network with a transfer rate of 16 Mbps.
What additional information and why does the LAN Token Ring frame end delimiter contain?
KO - the final limiter, containing, in addition to a unique sequence of electrical impulses, two more areas 1 bit long each:
tween bit (Intermediate Frame), which takes the values:
1 if this frame is part of a multipacket transmission,
0 if the frame is the last or only one;
detected error bit (Error-detected), which is set to 0 at the time of frame creation in the source and can be changed to 1 if an error is detected while passing through the network nodes; after that, the frame is relayed without error control in subsequent nodes until it reaches the source node, which in this case will retry the transmission of the frame;
How does the Token Ring network function if the "error detected bit" in the frame end delimiter is "1"?
after that, the frame is relayed without error control in subsequent nodes until it reaches the source node, which in this case will retry the transmission of the frame;
The structure of the "packet status" field of the Token Ring LAN data frame.
SC- (condition) frame status(Frame Status - FS) - a one-byte field containing 4 reserved bits (R) and two internal fields:
address recognition bit (indicator) (A);
packet copy bit (indicator) (C): [ ACRRACRR]
Since the checksum does not cover the SP field, each one-bit field in the byte is duplicated to ensure the validity of the data.
The transmitting node sets bits to 0 BUT And FROM.
The receiving node, after receiving the frame, sets the bit BUT in 1.
If, after copying the frame to the buffer of the receiving node, no errors were found in the frame, then the bit FROM also set to 1.
Thus, the sign of a successful frame transmission is the return of the frame to the source with bits: BUT=1 and FROM=1.
A=0 means that the destination station is no longer online or the PC has failed (turned off).
A=1 And C=0 means that an error occurred on the frame path from source to destination (this will also set the error detection bit in the trailing delimiter to 1).
A=1, C=1 and an error detection bit = 1 means that an error occurred on the return path of the frame from the destination to the source, after the frame was successfully received by the destination node.
What does the "address recognition bit" ("packet-to-buffer bit") value of 1 (0) indicate?- See above
The maximum number of stations in one Token Ring LAN is...?-256
What is the maximum distance between stations in a Token Ring LAN?
The maximum distance between stations depends on the type of transmission medium
(communication lines) and is:
100 meters - for twisted pair (UTP category 4);
150 meters - for twisted pair (IBM type 1);
3000 meters - for fiber optic multimode cable.
Advantages and disadvantages of Token Ring.
Advantages of Token Ring:
no conflicts in the data transmission medium;
guaranteed access time for all network users;
the Token Ring network functions well under heavy loads, up to 100% load, in contrast to Ethernet, in which the access time increases significantly already at a load of 30% or more; this is extremely important for real-time networks;
a larger allowable size of transmitted data in one frame (up to 18 KB), compared to Ethernet, ensures more efficient network operation when transferring large amounts of data;
the actual data transfer rate in a Token Ring network may turn out to be higher than in a regular Ethernet (the actual speed depends on the hardware features of the adapters used and on the speed of network computers).
Disadvantages of Token Ring:
higher cost of Token Ring network compared to Ethernet because:
more expensive adapters due to the more complex Token Ring protocol;
additional costs for the acquisition of MSAU concentrators;
the smaller size of the Token Ring network compared to Ethernet;
the need to control the integrity of the marker.
In which LANs there are no conflicts in the data transmission medium (guaranteed access time for all network users is provided)?
On a LAN with marker access
Brief description of FDDI LAN.
The maximum number of stations in the ring is 500.
The maximum length of the network is 100 km.
Transmission medium - fiber optic cable (twisted pair is possible).
The maximum distance between stations depends on the type of transmission medium and is:
2 km - for fiber optic multimode cable.
50 (40?) km - for fiber-optic single-mode cable;
100 m - for twisted pair (UTP category 5);
100 m - for twisted pair (IBM type 1).
Access method - marker.
The data transfer rate is 100 Mbps (200 Mbps for duplex transmission).
The restriction on the total length of the network is due to the limitation of the time for the complete passage of the signal around the ring to ensure the maximum allowable access time. The maximum distance between subscribers is determined by the attenuation of signals in the cable.
What does the abbreviation FDDI stand for?
FDDI (Fiber Distributed Data Interface) is one of the first high-speed LAN technologies.
Purpose of network technology FDDI.
The FDDI standard is focused on high data transfer rates - 100 Mbps. This standard was conceived to be as close as possible to the IEEE 802.5 Token Ring standard. Slight differences from this standard are determined by the need to provide higher data transfer rates over long distances.
FDDI technology involves the use of optical fiber as a transmission medium, which provides:
high reliability;
reconfiguration flexibility;
high data transfer rate - 100 Mbps;
long distances between stations (for multimode fiber - 2 km; for single-mode fiber when using laser diodes - up to 40 km; the maximum length of the entire network is 200 km).
How much bandwidth is available on an FDDI LAN?
First of all, it should be noted that two main types of intermediate devices are used to obtain complex Ethernet configurations from individual segments:
- Repeater hubs (hubs) are a set of repeaters and do not logically separate the segments connected to them in any way;
- Switches transfer information between segments, but do not transfer conflicts from segment to segment.
When using more complex switches, conflicts in individual segments are resolved on the spot, in the segments themselves, but do not propagate through the network, as in the case of using simpler repeater hubs. This is of fundamental importance for choosing an Ethernet network topology, since the CSMA / CD access method used in it assumes the presence of conflicts and their resolution, and the total length of the network is precisely determined by the size of the conflict zone, the collision domain. Thus, the use of a repeater hub does not divide the conflict zone, while each switching hub divides the conflict zone into parts. In the case of using a switch, it is necessary to evaluate the performance for each network segment separately, and when using repeater hubs, for the network as a whole.
In practice, repeater hubs are used much more often, since they are both simpler and cheaper. Therefore, in the future we will talk about them.
There are two main models used in selecting and evaluating an Ethernet configuration.
Model 1 Rules
The first model formulates a set of rules that a network designer must follow when connecting individual computers and segments:
- A repeater or hub connected to a segment reduces the maximum allowed number of subscribers connected to the segment by one.
- The full path between any two subscribers must include no more than five segments, four hubs (repeaters) and two transceivers (MAUs).
- If the path between subscribers consists of five segments and four hubs (repeaters), then the number of segments to which subscribers are connected should not exceed three, and the remaining segments should simply connect the hubs (repeaters) to each other. This is the already mentioned "5-4-3 rule".
- If the path between subscribers consists of four segments and three hubs (repeaters), then the following conditions must be met:
- the maximum length of the fiber optic cable segment 10BASE-FLconnecting hubs (repeaters) should not exceed 1000 meters;
- the maximum length of the fiber optic cable segment 10BASE-FLconnecting hubs (repeaters) with computers should not exceed 400 meters;
- computers can be connected to all segments.
If you follow these rules, you can be sure that the network will be operational. No additional calculations are required in this case. It is believed that compliance with these rules guarantees an acceptable amount of signal delay in the network.
When organizing the interaction of nodes in local networks, the main role is assigned to the link layer protocol. However, in order for the link layer to cope with this task, the structure of local networks must be quite specific, for example, the most popular link layer protocol - Ethernet - is designed for parallel connection of all network nodes to a common bus for them - a piece of coaxial cable. This approach, which consisted in the use of simple cable connection structures between computers on a local network, corresponded to the main goal that the developers of the first local networks set themselves in the second half of the 70s. This goal was to find a simple and cheap solution for connecting several dozen computers located within the same building into a computer network.
In the development of Ethernet technology, high-speed options have been created: IEEE802.3u/Fast Ethernet and IEEE802.3z/Gigabit Ethernet.
Fast Ethernet technology is an evolutionary development of classic Ethernet technology. Its main advantages are:
1) increase in the bandwidth of network segments up to 100 Mb/s;
2) preservation of the Ethernet random access method;
3) maintaining the star topology of networks and supporting traditional data transmission media - twisted pair and fiber optic cable.
These properties allow for a gradual transition from 10Base-T networks - the most popular Ethernet option to date - to high-speed networks that maintain significant continuity with well-known technology: Fast Ethernet does not require radical retraining of personnel and replacement of equipment in all network nodes. The official 100Base-T (802.3u) standard has established three different specifications for the physical layer (in terms of the seven layer OSI model) to support the following types of cabling:
1) 100Base-TX for two-pair UTP Category 5 unshielded twisted-pair cable or STP Type 1 shielded twisted-pair cable;
2) 100Base-T4 for 4-pair UTP Category 3, 4 or 5 unshielded twisted pair cable;
3) 100Base-FX for multimode fiber.
Gigabit Ethernet 1000Base-T, based on twisted pair and fiber optic cable. Since Gigabit Ethernet technology is compatible with 10 Mbps and 100 Mbps Ethernet, an easy transition to this technology is possible without investing heavily in software, cabling and staff training.
Gigabit Ethernet is an extension of IEEE 802.3 Ethernet that uses the same packet structure, format, and support for CSMA/CD protocol, full duplex, flow control, and more, while theoretically delivering a tenfold increase in performance. CSMA / CD (Carrier-Sense Multiple Access with Collision Detection - multiple access with carrier control and collision detection) is a technology for multiple access to a common transmission medium in a local computer network with collision control. CSMA/CD refers to decentralized random methods. It is used both in conventional networks such as Ethernet and in high-speed networks (Fast Ethernet, Gigabit Ethernet). Also called network protocol, which uses the CSMA/CD scheme. The CSMA/CD protocol operates at the data link layer in the OSI model.
Gigabit Ethernet - provides a transfer rate of 1000 Mbps. There are the following modifications of the standard:
1) 1000BASE-SX - Uses fiber optic cable with a light wavelength of 850nm.
2) 1000BASE-LX - Uses 1300nm fiber optic cable.
ComputerPress test laboratory tested 10/100 Mbit/s network cards of the Fast Ethernet standard for the PCI bus intended for use in workstations. The currently most common cards with a bandwidth of 10/100 Mbit / s were chosen, because, firstly, they can be used in Ethernet, Fast Ethernet and mixed networks, and, secondly, the promising Gigabit Ethernet technology ( throughput up to 1000 Mbps) is still most often used to connect powerful servers to the network equipment of the network core. It is extremely important what quality passive network equipment (cables, sockets, etc.) is used in the network. It is well known that if Category 3 twisted-pair cable is sufficient for Ethernet networks, then Category 5 is already required for Fast Ethernet. Signal scattering, poor noise protection can significantly reduce network throughput.
The purpose of testing was to determine, first of all, the index of effective performance (Performance / Efficiency Index Ratio - hereinafter P / E-index), and only then - the absolute value of throughput. P/E-index is calculated as the ratio of network card bandwidth in Mbps to the degree of CPU utilization in percent. This index is the industry standard for determining the performance of network adapters. It was introduced in order to take into account the use of CPU resources by network cards. The fact is that some manufacturers of network adapters are trying to achieve maximum performance by using more computer processor cycles to perform network operations. Minimal CPU usage and relatively high throughput are essential for mission-critical business, real-time, and multimedia applications.
Cards that are currently most often used for workstations in corporate and local networks were tested:
- D-Link DFE-538TX
- SMC EtherPower II 10/100 9432TX/MP
- 3Com Fast EtherLink XL 3C905B-TX-NM
- Compex RL 100ATX
- Intel EtherExpress PRO/100+ Management
- CNet PRO-120
- NetGear FA 310TX
- Allied Telesyn AT 2500TX
- Surecom EP-320X-R
The main characteristics of the tested network adapters are given in Table. one . Let us explain some of the terms that are used in the table. Automatic connection speed detection means that the adapter itself determines the maximum possible speed of operation. In addition, if auto-speed detection is supported, no additional configuration is required when switching from Ethernet to Fast Ethernet and vice versa. That is, the system administrator is not required to reconfigure the adapter and reload drivers.
Support for the Bus Master mode allows you to transfer data directly between the network card and the computer's memory. This frees up the CPU to perform other tasks. This property has become the de facto standard. No wonder all known network cards support the Bus Master mode.
Remote power on (Wake on LAN) allows you to turn on the PC over the network. That is, it becomes possible to service the PC during non-working hours. For this purpose, three-pin connectors are used on the system board and the network adapter, which are connected with a special cable (included in the package). In addition, special control software is required. Wake on LAN technology was developed by the Intel-IBM alliance.
Full duplex mode allows you to transfer data simultaneously in both directions, half duplex - only in one direction. Thus, the maximum possible throughput in full duplex mode is 200 Mbps.
The DMI (Desktop Management Interface) interface allows you to obtain information about the configuration and resources of a PC using network management software.
Support for the WfM (Wired for Management) specification ensures that the network adapter interacts with network management and administration software.
To remotely boot a computer OS over a network, network adapters are equipped with a special BootROM memory. This allows diskless workstations to be used effectively on the network. In most of the tested cards, there was only a socket for installing BootROM; the BootROM chip itself is usually a separately ordered option.
Support for ACPI (Advanced Configuration Power Interface) reduces power consumption. ACPI is a new technology that powers the power management system. It is based on the use of both hardware and software tools. Basically, Wake on LAN is an integral part of ACPI.
Proprietary performance enhancement tools allow you to increase the efficiency of the network card. The most famous of these are 3Com's Parallel Tasking II and Intel's Adaptive Technology. These tools are usually patented.
Support for major operating systems is provided by almost all adapters. The main operating systems include: Windows, Windows NT, NetWare, Linux, SCO UNIX, LAN Manager and others.
The level of service support is assessed by the availability of documentation, diskettes with drivers and the ability to download latest versions drivers from the company's website. The packaging also plays an important role. From this point of view, the best, in our opinion, are D-Link, Allied Telesyn and Surecom network adapters. But in general, the level of support turned out to be satisfactory for all cards.
Typically, the warranty covers the lifetime of the AC adapter (lifetime warranty). Sometimes it is limited to 1-3 years.
Test Methodology
All tests used the latest network card drivers downloaded from the respective manufacturer's Internet servers. In the case when the network card driver allowed any settings and optimizations, the default settings were used (except for the Intel network adapter). It should be noted that cards and corresponding drivers from 3Com and Intel have the richest additional features and functions.
Performance was measured using Novell's Perform3 utility. The principle of the utility is that a small file is copied from the workstation to a shared network drive server, after which it remains in the server's file cache and is repeatedly read from there during a specified period of time. This allows you to achieve memory-network-memory interaction and eliminate the impact of delays associated with disk operations. The utility parameters include initial file size, final file size, resizing step, and test time. The Novell Perform3 utility displays performance values with different file sizes, average and maximum performance (in KB/s). The following parameters were used to configure the utility:
- Initial file size - 4095 bytes
- Final file size - 65 535 bytes
- File increment - 8192 bytes
The testing time with each file was set to twenty seconds.
Each experiment used a pair of identical network cards, one running on the server and the other on the workstation. This does not seem to be in line with common practice, as servers typically use specialized network adapters that come with a number of additional features. But just in this way - the same network cards are installed both on the server and on workstations - testing is carried out by all known test laboratories in the world (KeyLabs, Tolly Group, etc.). The results are somewhat lower, but the experiment turns out to be clean, since only the analyzed network cards work on all computers.
Compaq DeskPro EN Client Configuration:
- processor Pentium II 450 MHz
- 512 KB cache
- RAM 128 MB
- hard drive 10 GB
- operating system Microsoft Windows NT Server 4.0c6aSP
- TCP/IP protocol.
Compaq DeskPro EP Server Configuration:
- Celeron processor 400 MHz
- RAM 64 MB
- hard drive 4.3 GB
- operating system Microsoft Windows NT Workstation 4.0 c c 6 a SP
- TCP/IP protocol.
Testing was done with computers connected directly with a UTP Category 5 crossover cable. During these tests, the cards were running in 100Base-TX Full Duplex mode. In this mode, the throughput is somewhat higher due to the fact that part of the service information (for example, confirmation of receipt) is transmitted simultaneously with useful information, the volume of which is estimated. Under these conditions, it was possible to fix quite high throughput values; for example, for a 3Com Fast EtherLink XL 3C905B-TX-NM adapter, an average of 79.23 Mbps.
Processor utilization was measured on the server using the Windows NT Performance Monitor utility; data was written to a log file. The Perform3 utility was run on the client so as not to affect the server's processor load. An Intel Celeron was used as the processor of the server computer, the performance of which is significantly lower than that of the Pentium II and III processors. Intel Celeron was used intentionally: the fact is that since the processor load is determined with a fairly large absolute error, in the case of large absolute values, the relative error turns out to be smaller.
After each test, the Perform3 utility places the results of its work in a text file as a data set of the following form:
65535 bytes. 10491.49 KBps. 10491.49 Aggregate KBps. 57343 bytes. 10844.03 KBps. 10844.03 Aggregate KBps. 49151 bytes. 10737.95 KBps. 10737.95 Aggregate KBps. 40959 bytes. 10603.04 KBps. 10603.04 Aggregate KBps. 32767 bytes. 10497.73 KBps. 10497.73 Aggregate KBps. 24575 bytes. 10220.29 KBps. 10220.29 Aggregate KBps. 16383 bytes. 9573.00 KBps. 9573.00 Aggregate KBps. 8191 bytes. 8195.50 KBps. 8195.50 Aggregate KBps. 10844.03 Maximum KBps. 10145.38 Average KBp.
The file size is displayed, the corresponding throughput for the selected client and for all clients (in this case there is only one client), as well as the maximum and average throughput over the entire test. The average values obtained for each test were converted from KB/s to Mbit/s using the formula:
(KB x 8)/1024,
and the value of the P / E index was calculated as the ratio of throughput to processor utilization in percent. Subsequently, the average value of the P/E index was calculated based on the results of three measurements.
When using the Perform3 utility on Windows NT Workstation, the following problem arose: in addition to writing to a network drive, the file was also written to the local file cache, from which it was subsequently read very quickly. The results were impressive, but unrealistic, since there was no data transmission per se over the network. In order for applications to perceive shared network drives as ordinary local drives, the operating system uses a special network component - a redirector that redirects I / O requests over the network. Under normal operating conditions, when writing a file to a shared network drive, the redirector uses the Windows NT caching algorithm. That is why when writing to the server, it also writes to the local file cache of the client machine. And for testing, it is necessary that caching is carried out only on the server. To prevent caching on the client computer, in Windows registry NT settings have been changed to disable caching by the redirector. Here's how it was done:
- Path to Registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Rdr\Parameters
Parameter name:
UseWriteBehind enables write-behind optimization for files being written
Type: REG_DWORD
Value: 0 (default: 1)
- Path to Registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Lanmanworkstation\parameters
Parameter name:
UtilizeNTCaching specifies whether the redirector will use the Windows NT cache manager to cache file contents.
Type: REG_DWORD Value: 0 (default: 1)
Intel EtherExpress PRO/100+Management Network Adapter
This card's throughput and CPU usage were almost the same as 3Com's. The window for setting the parameters of this map is shown below.
The new Intel 82559 controller installed on this card provides very high performance, especially on Fast Ethernet networks.
The technology that Intel uses in its Intel EtherExpress PRO/100+ card is called Adaptive Technology. The essence of the method is to automatically change the time intervals between Ethernet packets depending on the network load. As network traffic increases, the distance between individual Ethernet packets dynamically increases to reduce collisions and increase throughput. With a small network load, when the probability of collisions is small, the time intervals between packets are reduced, which also leads to an increase in performance. The benefits of this method should be most pronounced in large collisional Ethernet segments, that is, in cases where the network topology is dominated by hubs rather than switches.
New Intel technology, called Priority Packet, allows you to regulate the traffic passing through the network card, in accordance with the priorities of individual packets. This makes it possible to increase the data transfer rate for mission-critical applications.
Support for VLANs (IEEE 802.1Q standard) is provided.
There are only two indicators on the board - work / connection, speed 100.
www.intel.com
SMC EtherPower II 10/100 Network Adapter SMC9432TX/MP
The architecture of this card uses two promising technologies SMC SimulTasking and Programmable InterPacket Gap. The first technology is similar to 3Com Parallel Tasking technology. Comparing the test results for the cards of these two manufacturers, we can conclude on the degree of effectiveness of the implementation of these technologies. We also note that this network card showed the third result both in performance and in the P / E index, ahead of all cards except 3Com and Intel.
There are four LED indicators on the card: speed 100, transmission, link, duplex.
Company's main website: www.smc.com
The Ethernet network is the most widespread among standard networks. It appeared in 1972, and in 1985 became the international standard. It was adopted by the largest international standards organizations: IEEE Committee 802 (Institute of Electrical and Electronic Engineers) and ECMA (European Computer Manufacturers Association).
The standard is called IEEE 802.3 (read in English as "eight oh two dot three"). It defines multiple bus-type mono-channel access with collision detection and transmission control, i.e. with the already mentioned CSMA/CD access method.
Key features of the original IEEE 802.3 standard:
topology - bus;
transmission medium - coaxial cable;
Transfer rate - 10 Mbps;
The maximum length of the network is 5 km;
· maximum number of subscribers – up to 1024;
length of the network segment - up to 500 m;
· number of subscribers on one segment – up to 100;
· access method – CSMA/CD;
narrowband transmission, that is, without modulation (monochannel).
Strictly speaking, there are minor differences between the IEEE 802.3 and Ethernet standards, but they are usually ignored.
The Ethernet network is now the most popular in the world (more than 90% of the market), presumably it will remain so in the coming years. This was largely facilitated by the fact that from the very beginning, the characteristics, parameters, protocols of the network were open, as a result of which a huge number of manufacturers around the world began to produce Ethernet equipment that was fully compatible with each other.
In a classic Ethernet network, a 50-ohm coaxial cable of two types (thick and thin) was used. However, recently (since the beginning of the 90s), the most widely used version of Ethernet, which uses twisted pairs as a transmission medium. A standard has also been defined for use in a fiber optic cable network. Appropriate additions have been made to the original IEEE 802.3 standard to accommodate these changes. In 1995, an additional standard appeared for a faster version of Ethernet operating at a speed of 100 Mbps (the so-called Fast Ethernet, IEEE 802.3u standard), using twisted pair or fiber optic cable as a transmission medium. In 1997, a version for a speed of 1000 Mbit / s (Gigabit Ethernet, IEEE 802.3z standard) appeared.
In addition to the standard bus topology, passive star and passive tree topologies are increasingly being used. This assumes the use of repeaters and repeater hubs connecting different parts (segments) of the network. As a result, a tree-like structure can be formed on segments of different types (Fig. 7.1).
A classic bus or a single subscriber can act as a segment (part of the network). For bus segments, a coaxial cable is used, and for passive star beams (for connecting to a single computer hub), twisted pair and fiber optic cable are used. The main requirement for the resulting topology is that there are no closed paths (loops) in it. In fact, it turns out that all subscribers are connected to a physical bus, since the signal from each of them propagates in all directions at once and does not return back (as in a ring).
The maximum cable length of the network as a whole (the maximum signal path) can theoretically reach 6.5 kilometers, but practically does not exceed 3.5 kilometers.
Rice. 7.1. Classic Ethernet network topology.
The Fast Ethernet network does not provide a physical bus topology, only a passive star or passive tree is used. In addition, Fast Ethernet has much more stringent requirements for the maximum length of the network. After all, if the transmission rate is increased by 10 times and the packet format is preserved, its minimum length becomes ten times shorter. Thus, the allowable value of the double signal transit time through the network is reduced by a factor of 10 (5.12 µs versus 51.2 µs in Ethernet).
The standard Manchester code is used to transmit information on an Ethernet network.
Access to the Ethernet network is carried out according to the random CSMA / CD method, which ensures the equality of subscribers. The network uses packets of variable length.
For an Ethernet network operating at a speed of 10 Mbit / s, the standard defines four main types of network segments oriented to various information transmission media:
· 10BASE5 (thick coaxial cable);
· 10BASE2 (thin coaxial cable);
· 10BASE-T (twisted pair);
· 10BASE-FL (fiber optic cable).
The name of the segment includes three elements: the number "10" means a transmission rate of 10 Mbps, the word BASE - transmission in the base band (that is, without high-frequency signal modulation), and the last element - the allowable segment length: "5" - 500 meters, "2" - 200 meters (more precisely, 185 meters) or the type of communication line: "T" - twisted pair (from the English "twisted-pair"), "F" - fiber optic cable (from the English "fiber optic").
Similarly, for an Ethernet network operating at a speed of 100 Mbps (Fast Ethernet), the standard defines three types of segments, which differ in the types of transmission media:
100BASE-T4 (quad twisted pair);
· 100BASE-TX (dual twisted pair);
· 100BASE-FX (fiber optic cable).
Here the number "100" means a transmission rate of 100 Mbps, the letter "T" - twisted pair, the letter "F" - fiber optic cable. The 100BASE-TX and 100BASE-FX types are sometimes lumped together under the name 100BASE-X, and 100BASE-T4 and 100BASE-TX under the name 100BASE-T.
Token ring network
The Token-Ring network (marker ring) was proposed by IBM in 1985 (the first version appeared in 1980). It was intended to network all types of computers manufactured by IBM. The very fact that it is backed by IBM, the largest computer technology, suggests that it needs special attention. But just as importantly, Token-Ring is currently the IEEE 802.5 international standard (although there are minor differences between Token-Ring and IEEE 802.5). This puts the network on par with Ethernet in status.
Token-Ring was developed as a reliable alternative to Ethernet. And although Ethernet is now replacing all other networks, Token-Ring cannot be considered hopelessly outdated. More than 10 million computers around the world are connected by this network.
The Token-Ring network has a ring topology, although outwardly it looks more like a star. This is due to the fact that individual subscribers (computers) are connected to the network not directly, but through special hubs or multiple access devices (MSAU or MAU - Multistation Access Unit). Physically, the network forms a star-ring topology (Fig. 7.3). In reality, the subscribers are still united in a ring, that is, each of them transmits information to one neighboring subscriber, and receives information from another.
Rice. 7.3. Star-ring topology of the Token-Ring network.
As a transmission medium in the IBM Token-Ring network, twisted pair was first used, both unshielded (UTP) and shielded (STP), but then equipment options appeared for coaxial cable, as well as for fiber optic cable in the FDDI standard.
Main specifications classic version of the Token-Ring network:
· the maximum number of hubs type IBM 8228 MAU - 12;
· the maximum number of subscribers in the network - 96;
The maximum length of the cable between the subscriber and the hub is 45 meters;
maximum cable length between hubs - 45 meters;
The maximum length of the cable connecting all hubs is 120 meters;
· Data transfer rate – 4 Mbps and 16 Mbps.
All specifications given apply to the use of unshielded twisted pair. If a different transmission medium is used, the network characteristics may differ. For example, when using shielded twisted pair (STP), the number of subscribers can be increased to 260 (instead of 96), the cable length - up to 100 meters (instead of 45), the number of hubs - up to 33, and the total length of the ring connecting the hubs - up to 200 meters . The fiber optic cable allows you to increase the length of the cable up to two kilometers.
To transfer information in Token-Ring, a bi-phase code is used (more precisely, its variant with a mandatory transition in the center of the bit interval). As with any star topology, no additional electrical termination or external grounding is required. Negotiation is performed by the network adapter hardware and hubs.
RJ-45 connectors (for unshielded twisted pair), as well as MIC and DB9P connectors are used to connect cables in Token-Ring. The wires in the cable connect the pins of the connectors of the same name (that is, the so-called "straight" cables are used).
The classic Token-Ring network is inferior to the Ethernet network both in terms of the allowable size and the maximum number of subscribers. In terms of transmission speed, there are currently 100 Mbps (High Speed Token-Ring, HSTR) and 1000 Mbps (Gigabit Token-Ring) versions of Token-Ring. Companies that support Token-Ring (including IBM, Olicom, Madge) do not intend to abandon their network, considering it as a worthy competitor to Ethernet.
Compared to Ethernet equipment, Token-Ring equipment is noticeably more expensive, since it uses a more complex exchange control method, so the Token-Ring network has not become so widespread.
However, unlike Ethernet, the Token-Ring network is much better at keeping a high load level (more than 30-40%) and provides guaranteed access time. This is necessary, for example, in industrial networks, where a delay in response to an external event can lead to serious accidents.
The Token-Ring network uses the classic token access method, that is, a token constantly circulates around the ring, to which subscribers can attach their data packets (see Fig. 4.15). This implies such an important advantage of this network as the absence of conflicts, but there are also disadvantages, in particular, the need to control the integrity of the marker and the dependence of the network on each subscriber (in the event of a malfunction, the subscriber must be excluded from the ring).
The time limit for transmitting a packet in Token-Ring is 10 ms. With a maximum number of subscribers of 260, the full cycle of the ring will be 260 x 10 ms = 2.6 s. During this time, all 260 subscribers will be able to transfer their packages (if, of course, they have something to transfer). During the same time, a free token will definitely reach each subscriber. The same interval is the upper limit of the Token-Ring access time.
Arcnet network
Arcnet network (or ARCnet from the English Attached Resource Computer Net, computer network connected resources) is one of the oldest networks. It was developed by Datapoint Corporation back in 1977. There are no international standards for this network, although it is considered to be the ancestor of the token access method. Despite the lack of standards, the Arcnet network until recently (in 1980 - 1990) was popular, even seriously competing with Ethernet. A large number of companies produced equipment for this type of network. But now the production of Arcnet equipment is practically stopped.
Among the main advantages of the Arcnet network compared to Ethernet are the limited access time, high communication reliability, ease of diagnostics, and the relatively low cost of adapters. The most significant disadvantages of the network include low information transfer rate (2.5 Mbps), addressing system and packet format.
To transmit information in the Arcnet network, a rather rare code is used, in which two pulses correspond to a logical unit during a bit interval, and one pulse corresponds to a logical zero. Obviously, this is a self-synchronizing code that requires even more cable bandwidth than even Manchester.
As a transmission medium in the network, a coaxial cable with a characteristic impedance of 93 ohms, for example, brand RG-62A/U, is used. Twisted-pair versions (shielded and unshielded) are not widely used. Fiber-optic options have also been proposed, but they also did not save Arcnet.
The Arcnet network uses a classic bus (Arcnet-BUS) as well as a passive star (Arcnet-STAR) as its topology. Hubs are used in the star. It is possible to combine bus and star segments into a tree topology using hubs (as in Ethernet). The main limitation is that there should not be closed paths (loops) in the topology. Another limitation: the number of segments connected in a daisy chain using hubs should not exceed three.
Thus, the topology of the Arcnet network is as follows (Fig. 7.15).
Rice. 7.15. Topology of the Arcnet bus type network (B - adapters for bus operation, S - adapters for operation in a star).
The main technical characteristics of the Arcnet network are as follows.
· Transmission medium – coaxial cable, twisted pair.
· The maximum length of the network is 6 kilometers.
· The maximum cable length from the subscriber to the passive hub is 30 meters.
· The maximum cable length from the subscriber to the active hub is 600 meters.
· The maximum cable length between active and passive hubs is 30 meters.
· The maximum cable length between active hubs is 600 meters.
The maximum number of subscribers in the network is 255.
The maximum number of subscribers on the bus segment is 8.
· The minimum distance between subscribers in the bus is 1 meter.
· The maximum length of the tire segment is 300 meters.
· Data transfer rate - 2.5 Mbps.
When creating complex topologies, it is necessary to ensure that the signal propagation delay in the network between subscribers does not exceed 30 μs. The maximum attenuation of the signal in the cable at a frequency of 5 MHz should not exceed 11 dB.
The Arcnet network uses a token access method (transfer of right), but it is somewhat different from that of the Token-Ring network. This method is closest to the one provided in the IEEE 802.4 standard.
Just like in the case of Token-Ring, conflicts in Arcnet are completely excluded. Like any token network, Arcnet holds the load well and guarantees the amount of network access time (unlike Ethernet). The total time for the marker to bypass all subscribers is 840 ms. Accordingly, the same interval determines the upper limit of network access time.
The marker is formed by a special subscriber - the network controller. It is the subscriber with the minimum (zero) address.
FDDI network
The FDDI network (from the English Fiber Distributed Data Interface, fiber optic distributed data interface) is one of the latest developments in local area network standards. The FDDI standard was proposed by the American National Standards Institute ANSI (ANSI specification X3T9.5). Then the ISO 9314 standard was adopted, corresponding to the ANSI specifications. The level of standardization of the network is quite high.
Unlike other standard local area networks, the FDDI standard was initially focused on high transmission speed (100 Mbps) and on the use of the most advanced fiber optic cable. Therefore, in this case, the developers were not constrained by the framework of the old standards, which focused on low speeds and electric cable.
The choice of fiber as a transmission medium has determined such advantages new network, as high noise immunity, maximum secrecy of information transmission and excellent galvanic isolation of subscribers. The high transmission speed, which is much easier to achieve with fiber optic cable, allows many tasks that are not possible with slower networks, such as real-time image transmission. In addition, fiber optic cable easily solves the problem of transmitting data over a distance of several kilometers without retransmission, which makes it possible to build large networks, covering even entire cities, while having all the advantages of local networks (in particular, low error rate). All this determined the popularity of the FDDI network, although it is not yet as widespread as Ethernet and Token-Ring.
The FDDI standard was based on the token access method provided for by the international standard IEEE 802.5 (Token-Ring). Insignificant differences from this standard are determined by the need to ensure a high speed of information transmission over long distances. Network topology FDDI is a ring, the most suitable topology for fiber optic cable. The network uses two multi-directional fiber optic cables, one of which is usually in reserve, however, this solution also allows the use of full-duplex information transmission (simultaneously in two directions) with an effective double speed of 200 Mbps (each of the two channels operates at a speed of 100 Mbps). A star-ring topology is also used with hubs included in the ring (as in Token-Ring).
Basic technical characteristics of the FDDI network.
The maximum number of network subscribers is 1000.
· The maximum length of the network ring is 20 kilometers.
· The maximum distance between network subscribers is 2 kilometers.
· Transmission medium – multimode fiber optic cable (it is possible to use electric twisted pair cable).
· Access method – marker.
· Information transfer rate – 100 Mbit/s (200 Mbit/s for duplex transfer mode).
The FDDI standard has significant advantages over all previously discussed networks. For example, a Fast Ethernet network with the same bandwidth of 100 Mbps cannot match FDDI in terms of allowable network sizes. In addition, the FDDI marker access method, unlike CSMA / CD, provides guaranteed access time and the absence of conflicts at any load level.
The limitation on the total network length of 20 km is not due to the attenuation of signals in the cable, but to the need to limit the time of complete signal propagation around the ring in order to ensure the maximum allowable access time. But the maximum distance between subscribers (2 km with a multimode cable) is determined precisely by the attenuation of signals in the cable (it should not exceed 11 dB). It is also possible to use a single-mode cable, in which case the distance between subscribers can reach 45 kilometers, and the total length of the ring is 200 kilometers.
There is also an implementation of FDDI on an electrical cable (CDDI - Copper Distributed Data Interface or TPDDI - Twisted Pair Distributed Data Interface). This uses Category 5 cable with RJ-45 connectors. The maximum distance between subscribers in this case should be no more than 100 meters. The cost of network equipment on an electric cable is several times less. But this version of the network no longer has such obvious advantages over competitors as the original fiber optic FDDI. Electrical versions of FDDI are much less standardized than fiber optics, so interoperability between equipment from different manufacturers is not guaranteed.
For data transmission in FDDI, a 4V / 5V code is used, specially developed for this standard.
The FDDI standard, in order to achieve high network flexibility, provides for the inclusion of two types of subscribers in the ring:
· Subscribers (stations) of class A (dual connection subscribers, DAS - Dual-Attachment Stations) are connected to both (inner and outer) rings of the network. In this case, the possibility of exchanging at speeds up to 200 Mbps or redundant network cable is realized (if the main cable is damaged, a backup cable is used). The equipment of this class is used in the most critical parts of the network in terms of performance.
· Subscribers (stations) of class B (single connection subscribers, SAS - Single-Attachment Stations) are connected to only one (outer) ring of the network. They are simpler and cheaper than class A adapters, but do not have their capabilities. They can only be connected to the network through a hub or a bypass switch that turns them off in case of an accident.
In addition to the actual subscribers (computers, terminals, etc.), the network uses Wiring Concentrators, the inclusion of which allows you to collect all connection points in one place in order to monitor network operation, diagnose faults and simplify reconfiguration. When using different types of cables (for example, fiber optic cable and twisted pair), the hub also performs the function of converting electrical signals to optical signals and vice versa. Hubs also come in dual connection (DAC - Dual-Attachment Concentrator) and single connection (SAC - Single-Attachment Concentrator).
An example of an FDDI network configuration is shown in fig. 8.1. The principle of combining network devices is illustrated in Figure 8.2.
Rice. 8.1. FDDI network configuration example.
Unlike the access method offered by the IEEE 802.5 standard, FDDI uses what is known as multiple token passing. If in the case of the Token-Ring network a new (free) token is transmitted by the subscriber only after his packet has returned to him, then in FDDI a new token is transmitted by the subscriber immediately after the end of the transmission of the packet by him (similar to how this is done with the ETR method in the Token-Ring network). ring).
In conclusion, it should be noted that despite the obvious advantages of FDDI this network not widely used, which is mainly due to the high cost of its equipment (on the order of several hundred and even thousands of dollars). The main scope of FDDI now is the basic, backbone (Backbone) networks that combine several networks. FDDI is also used to connect powerful workstations or servers that require high-speed exchange. Fast Ethernet is supposed to replace FDDI, but the advantages of fiber optic cable, token control, and record network size allow FDDI to stand out today. And in cases where hardware cost is critical, a twisted-pair version of FDDI (TPDDI) can be used in non-critical areas. In addition, the cost of FDDI hardware can greatly decrease as the volume of its production increases.
Network 100VG-AnyLAN
The 100VG-AnyLAN is one of the latest high-speed LANs to hit the market recently. It complies with the international standard IEEE 802.12, so the level of its standardization is quite high.
Its main advantages are a high exchange rate, a relatively low cost of equipment (about twice as expensive as the equipment of the most popular 10BASE-T Ethernet network), a centralized exchange control method without conflicts, and packet format compatibility with Ethernet and Token-Ring networks.
In the name of the 100VG-AnyLAN network, the number 100 corresponds to a speed of 100 Mbps, the letters VG indicate a cheap unshielded twisted pair of category 3 (Voice Grade), and AnyLAN (any network) indicates that the network is compatible with the two most common networks.
Main technical characteristics of the 100VG-AnyLAN network:
· Transfer rate - 100 Mbps.
Topology - a star with the possibility of building (tree). The number of cascading levels of concentrators (hubs) is up to 5.
· Access method - centralized, conflict-free (Demand Priority - with priority request).
· The transmission medium is quad unshielded twisted pair (UTP category 3, 4, or 5 cables), double twisted pair (UTP category 5 cable), double shielded twisted pair (STP), and fiber optic cable. Now the quad twisted pair is mostly common.
· The maximum cable length between a hub and a subscriber and between hubs is 100 meters (for UTP category 3 cable), 200 meters (for UTP category 5 cable and shielded cable), 2 kilometers (for fiber optic cable). The maximum possible network size is 2 kilometers (determined by allowable delays).
The maximum number of subscribers is 1024, the recommended number is up to 250.
Thus, the parameters of the 100VG-AnyLAN network are quite close to those of the Fast Ethernet network. However, the main advantage of Fast Ethernet is its full compatibility with the most common Ethernet network (in the case of 100VG-AnyLAN, this requires a bridge). At the same time, the centralized management of 100VG-AnyLAN, which eliminates conflicts and guarantees the maximum value of access time (which is not provided in the Ethernet network), cannot be discounted either.
An example of the structure of a 100VG-AnyLAN network is shown in Fig. 8.8.
The 100VG-AnyLAN network consists of a central (main, root) level 1 hub, to which both individual subscribers and level 2 hubs can connect, which in turn are connected to subscribers and level 3 hubs, etc. In this case, the network can have no more than five such levels (in the original version there were no more than three). The maximum network size can be 1000 meters for unshielded twisted pair.
Rice. 8.8. 100VG-AnyLAN network structure.
Unlike non-intelligent hubs of other networks (eg Ethernet, Token-Ring, FDDI), 100VG-AnyLAN network hubs are intelligent controllers that control access to the network. To do this, they continuously monitor requests on all ports. Concentrators receive incoming packets and send them only to those subscribers to whom they are addressed. However, they do not perform any information processing, that is, in this case, it turns out that it is still not an active, but not a passive star either. Hubs cannot be called full-fledged subscribers.
Each of the hubs can be configured to work with Ethernet or Token-Ring packet formats. In this case, the hubs of the entire network should work with packets of only one format. Bridges are required to communicate with Ethernet and Token-Ring networks, but bridges are fairly simple.
Hubs have one upper level port (for connecting it to a higher level hub) and several lower level ports (for connecting subscribers). A computer (workstation), server, bridge, router, switch can act as a subscriber. Another hub can also be attached to the lower level port.
Each hub port can be set to one of two possible modes of operation:
· Normal mode involves forwarding to the subscriber attached to the port, only packets addressed to him personally.
· The monitor mode assumes forwarding to the subscriber attached to the port, all packets coming to the concentrator. This mode allows one of the subscribers to control the operation of the entire network as a whole (to perform the monitoring function).
The 100VG-AnyLAN network access method is typical for star networks.
When using quad twisted pair, each of the four twisted pairs is transmitted at 30 Mbps. The total transfer rate is 120 Mbps. However, the payload due to the use of the 5B/6B code is transmitted at only 100 Mbps. Thus, the bandwidth of the cable must be at least 15 MHz. Category 3 twisted-pair cable (16 MHz bandwidth) satisfies this requirement.
Thus, the 100VG-AnyLAN network is an affordable solution for increasing the transmission rate to 100 Mbps. However, it does not have full compatibility with any of the standard networks, so its future fate is problematic. In addition, unlike the FDDI network, it does not have any record parameters. Most likely, 100VG-AnyLAN, despite the support of reputable companies and a high level of standardization, will remain just an example of interesting technical solutions.
In the most common 100 Mbps Fast Ethernet network, 100VG-AnyLAN provides twice the length of Category 5 UTP cable (up to 200 meters) as well as a contention-free method of traffic control.
Ethernet, but also to the equipment of other, less popular networks.Ethernet and Fast Ethernet adapters
Adapter Specifications
Network adapters(NIC, Network Interface Card) Ethernet and Fast Ethernet can be interfaced with a computer through one of the standard interfaces:
- bus ISA (Industry Standard Architecture);
- PCI bus (Peripheral Component Interconnect);
- PC Card bus (aka PCMCIA);
Adapters designed for the system bus (backbone) ISA, not so long ago were the main type of adapters. The number of companies producing such adapters was large, which is why devices of this type were the cheapest. ISA adapters are available in 8-bit and 16-bit versions. 8-bit adapters are cheaper, while 16-bit adapters are faster. True, the exchange of information over the ISA bus cannot be too fast (in the limit - 16 MB / s, in reality - no more than 8 MB / s, and for 8-bit adapters - up to 2 MB / s). Therefore, Fast Ethernet adapters, which require high exchange rates for efficient operation, are practically not produced for this system bus. The ISA bus is a thing of the past.
The PCI bus has now practically supplanted the ISA bus and is becoming the main expansion bus for computers. It provides 32-bit and 64-bit data exchange and has a high throughput (theoretically up to 264 MB / s), which fully meets the requirements of not only Fast Ethernet, but also faster Gigabit Ethernet. It is also important that the PCI bus is used not only in IBM PC computers, but also in PowerMac computers. In addition, it supports Plug-and-Play hardware auto-configuration mode. Apparently, in the near future, the majority of network adapters. The disadvantage of PCI compared to the ISA bus is that the number of expansion slots in a computer is usually small (usually 3 slots). But precisely network adapters connect to PCI first.
Bus PC Card (old name PCMCIA) is used so far only in portable computers class Notebook. In these computers, the internal PCI bus is usually not exposed. The PC Card interface provides for a simple connection to a computer of miniature expansion cards, and the exchange rate with these cards is quite high. However, more and more portable computers are equipped with built-in network adapters, as the ability to access the network becomes an integral part of standard set functions. These built-in adapters are again connected to the internal PCI bus computer.
When choosing network adapter oriented to one or another bus, you must first of all make sure that there are free expansion slots for this bus in the computer connected to the network. You should also evaluate the complexity of installing the purchased adapter and the prospects for the production of boards of this type. The latter may be needed in the event of an adapter failure.
Finally meet again network adapters, connecting to a computer through a parallel (printer) LPT port. The main advantage of this approach is that you do not need to open the computer case to connect adapters. In addition, in this case, the adapters do not occupy the computer's system resources, such as interrupt and DMA channels, as well as memory and I / O device addresses. However, the speed of information exchange between them and the computer in this case is much lower than when using the system bus. In addition, they require more processor time to exchange with the network, thereby slowing down the computer.
Recently, there are more and more computers in which network adapters built into system board. The advantages of this approach are obvious: the user does not have to buy a network adapter and install it in the computer. You just need to connect the network cable to the external connector of the computer. However, the disadvantage is that the user cannot select the adapter with the best performance.
To other important features network adapters can be attributed:
- adapter configuration method ;
- the size of the buffer memory installed on the board and the modes of exchange with it;
- the ability to install a permanent memory chip on the board for remote boot ( BootROM ).
- the ability to connect the adapter to different types of transmission media (twisted pair, thin and thick coaxial cable, fiber optic cable);
- the network transmission speed used by the adapter and the availability of its switching function;
- the ability to use the adapter full duplex exchange mode;
- adapter compatibility ( more precisely, adapter driver) with the network software used.
Adapter configuration by the user was used mainly for adapters designed for the ISA bus. Configuration involves setting up the use of computer system resources (input/output addresses, interrupt channels and direct memory access, buffer memory addresses and remote boot memory). Configuration can be carried out by setting the switches (jumpers) to the desired position or using the DOS configuration program supplied with the adapter ( Jumperless , Software configuration). When starting such a program, the user is prompted to set the hardware configuration using a simple menu: select adapter parameters. The same program allows you to self-test adapter . The selected parameters are stored in the non - volatile memory of the adapter . In any case, when choosing parameters, it is necessary to avoid conflicts with system devices computer and other expansion cards.
The adapter can also be configured automatically in Plug-and-Play mode when the computer is powered on. Modern adapters usually support this mode, so they can be easily installed by the user.
In the simplest adapters, exchange with the adapter's internal buffer memory (Adapter RAM) is carried out through the address space of I/O devices. In this case, no additional memory address configuration is required. The base address of the buffer memory operating in shared memory mode must be specified. It is assigned to the upper memory area of the computer (
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