What is gigabit ethernet. Gigabit Ethernet network. Fig.5. Gigabit Ethernet frame with media extension field

I was in no rush to upgrade my home network from 100 Mbps to 1 Gbps, which is rather strange for me, since I transfer a large number of files over the network. However, when I spend money on upgrading my computer or infrastructure, I find myself getting an immediate performance boost in the applications and games I run. Many users like to amuse themselves new video card, central processing unit and some gadget. However, for some reason, network equipment does not attract such enthusiasm. Indeed, it is difficult to invest earned money in network infrastructure instead of another technological birthday present.

However, my bandwidth requirements are very high, and at one point I realized that the infrastructure for 100 Mbps was no longer enough. All my home computers already have integrated 1 Gb/s adapters (on motherboards), so I decided to take the price list of the nearest computer company and see what I need to convert the entire network infrastructure to 1 Gb/s.

No, a gigabit home network is not that complicated at all.

I bought and installed all the hardware. I remember that it used to take about a minute and a half to copy a large file over a 100Mbps network. After upgrading to 1 Gb / s, the same file began to be copied in 40 seconds. The performance boost was nice, but still I didn't get the 10x improvement I'd expect from comparing 100Mbps to 1Gbps throughput of the old and new networks.

What is the reason?

For a gigabit network, all its parts must support 1 Gb / s. For example, if you have gigabit network cards and appropriate cables installed, but the hub / switch only supports 100 Mbps, then the entire network will operate at 100 Mbps.

The first requirement is a network controller. It is best if each computer on the network is equipped with a gigabit network adapter (separate or integrated on the motherboard). This requirement is the easiest to meet, since most motherboard manufacturers have been integrating gigabit network controllers for the past couple of years.

The second requirement is that the network card must also support 1 Gb / s. There is a common misconception that Gigabit networks require Category 5e cable, but in fact, even older Cat 5 cable supports 1 Gbps. However, Cat 5e cables have better performance, so they will be more optimal solution for gigabit networks, especially if the length of the cables is decent. However, Cat 5e cables are still the cheapest today, since the old Cat 5 standard is already outdated. The newer and more expensive Cat 6 cables offer even better gigabit performance. We will compare the performance of Cat 5e vs Cat 6 cables a bit later in our article.

The third and probably the most expensive component in a gigabit network is the 1 Gbps hub/switch. Of course, it is better to use a switch (perhaps paired with a router), since a hub or hub is not the most intelligent device, it simply broadcasts all network data on all available ports, which leads to a lot of collisions and slows down network performance. If you need high performance, then a gigabit switch is indispensable, as it forwards network data only to the desired port, which effectively increases the speed of the network compared to a hub. The router usually contains a built-in switch (with multiple LAN ports) and also allows you to connect your home network to the Internet. Most home users understand the benefits of a router, so a gigabit router is an attractive option.

How fast should a gigabit be? If you hear the prefix "giga", then you probably mean 1000 megabytes, while a gigabit network should provide 1000 megabytes per second. If you think so, then you are not alone. But alas, the reality is different.

What is gigabit? That's 1000 megabits, not 1000 megabytes. There are 8 bits in one byte, so let's just calculate: 1,000,000,000 bits divided by 8 bits = 125,000,000 bytes. There are about a million bytes in a megabyte, so a gigabit network should provide a theoretical maximum data transfer rate of about 125 MB / s.

Sure, 125 MB/s doesn't sound as impressive as a gigabit, but think about it: a network at that speed should theoretically transfer a gigabyte of data in just eight seconds. A 10 GB archive should be transferred in just a minute and 20 seconds. The speed is incredible: just remember how long it took to transfer a gigabyte of data before USB sticks became as fast as they are today.

Expectations were high, so we decided to transfer the file over a gigabit network and enjoy speeds close to 125 MB / s. We don't have any specialized miraculous equipment: a simple home network with some old but decent technology.

Copying a 4.3 GB file from one home computer the other ran at an average speed of 35.8 MB/s (we ran the test five times). This is only 30% of the theoretical 125 MB/s gigabit network ceiling.

What are the causes of the problem?

Picking up components for installing a gigabit network is quite simple, but getting the network to work at maximum speed is much more difficult. The factors that can cause a network to slow down are quite numerous, but as we have found, it all comes down to how quickly hard disks capable of transmitting data to the network controller.

The first limitation to consider is the gigabit network controller interface with the system. If your controller is connected via an old PCI bus, the amount of data that it can theoretically transfer is 133 MB / s. For Gigabit Ethernet's 125 MB/s bandwidth, this seems to be sufficient, but remember that PCI bus bandwidth is distributed throughout the system. Each additional PCI card and many system components will use the same bandwidth, reducing the resources available to the network card. Controllers with the new PCI Express (PCIe) interface do not have these problems, as each PCIe lane provides at least 250 MB/s of bandwidth, and is exclusive to the device.

The next important factor that affects network speed is cables. Many experts point out that in the case of laying network cables near power cables that are sources of interference, low speeds are guaranteed. Long cable lengths are also a problem, as Cat 5e copper cables are certified for a maximum length of 100 meters.

Some experts recommend running the new Cat 6 cable instead of Cat 5e. It is often difficult to justify such recommendations, but we will try to test the impact of the cable category on a small gigabit home network.

Let's not forget about the operating system. Of course, this system is rarely used in a gigabit environment, but it should be mentioned that Windows 98 SE (and older operating systems) will not be able to take advantage of gigabit Ethernet, since the operating system's TCP / IP stack can hardly load a 100-Mbps connection in to the fullest. Windows 2000 and later versions of Windows will work, although older operating systems will need to be tweaked to get the most out of the network. We'll be using Windows Vista 32-bit for our tests, and while Vista doesn't have the best reputation for some tasks, it's a gigabit networking system from the get-go.

Now let's move on to hard drives. even old IDE interface with the ATA/133 specification should be enough to support a theoretical file transfer rate of 133 MB/s, and the newer SATA specification fits the bill as it provides at least 1.5 Gb/s (150 MB/s) throughput. However, while cables and controllers can handle transferring data at that speed, hard drives themselves can't.

Take for example a typical modern 500 GB hard drive, which should provide a constant throughput of about 65 MB / s. At the beginning of the platters (outer lanes) the speed can be higher, but as you move to the inner lanes, the throughput drops. Data on the internal tracks is read slower, at about 45 MB/s.

It seemed to us that we considered all possible "bottlenecks". What was left to do? It was necessary to conduct several tests and see if we could get the network performance to the theoretical limit of 125 MB / s.

Test configuration

Tests and settings

Before we get into any tests, we decided to test the hard drives offline to see how much throughput we can expect in an ideal scenario.

We have two PCs running on our gigabit home network. The first one, which we will call the server, is equipped with two disk subsystems. The main hard drive is a 320 GB Seagate Barracuda ST3320620AS a couple of years old. The server acts as a NAS with a RAID array of two 1TB Hitachi Deskstar 0A-38016 hard drives mirrored for redundancy.

We called the second PC on the network a client, it has two hard drives: both 500 GB Western Digital Caviar 00AAJS-00YFA, about six months old.

We first tested the speed of the server and client system hard drives to see what performance we can expect from them. We used the hard disk test in SiSoftware Sandra 2009.

Our dreams of achieving gigabit file transfer speeds immediately dissipated. Both of the single hard drives reached a maximum read speed of around 75 MB/s under ideal conditions. Since this test is conducted in real conditions, and the drives are 60% full, we can expect read speeds closer to the 65 MB / s index that we got for both hard drives.

But let's look at the performance of RAID 1 - the best thing about this array is that the hardware RAID controller can increase read performance by acquiring data from both hard drives at the same time, similar to RAID 0 arrays; but this effect is obtained (as far as we know) only with hardware RAID controllers, but not with software solutions RAID. In our tests, the RAID array provided much better read performance than a single hard drive, so chances are good that we'll get high network file transfer speeds from a RAID 1 array. The RAID array delivered an impressive peak throughput of 108MB/s, In reality, performance should be close to the 88 MB/s index since the array is 55% full.

Therefore, we should get about 88 MB/s over a gigabit network, right? It's not that close to the 125Mb/s Gigabit network ceiling, but much faster 100Mb/s networks have a 12.5Mb/s ceiling, so getting 88Mb/s in practice wouldn't be bad at all.

But not everything is so simple. The fact that the read speed from hard drives is quite high does not mean at all that they will write information quickly in real conditions. Let's run some disk write tests before using the network. We will start from our server and copy a 4.3 GB image from a fast RAID array to the 320 GB system hard drive and back. We will then copy the file from the client's D: drive to its C: drive.

As you can see, copying from a fast RAID array to drive C: gave an average speed of only 41 MB / s. And copying from drive C: to a RAID 1 array brought it down to just 25 MB/s. What's happening?

This is exactly what happens in reality: hard drive C: was released a little over a year ago, but it is 60% full, probably a little fragmented, so it does not break records. There are other factors, namely how fast the system and memory in general are. RAID 1 is made up of relatively new hardware, but due to redundancy, information must be written to two hard drives at the same time, which reduces performance. While a RAID 1 array can give you high read performance, write speed comes at a sacrifice. Of course, we could use a striped RAID 0 array, which gives high write and read speeds, but if one hard drive dies, then all the information will be corrupted. In general, RAID 1 is the better option if you value the data stored on the NAS.

However, not all is lost. The new 500 GB Digital Caviar is capable of writing our file at 70.3 MB/s (average over five test runs) and also tops out at 73.2 MB/s.

With all that said, we were expecting a maximum Gigabit transfer rate of 73MB/s from a NAS RAID 1 array to the client's C: drive in real-world conditions. We will also test transferring files from the client C: drive to the server C: drive to see if we can realistically expect 40 MB/s in that direction.

Let's start with the first test, where we sent a file from the client's C: drive to the server's C: drive.

As you can see, the results are in line with our expectations. A gigabit network, theoretically capable of 125 MB/s, sends data from the client drive C: at the maximum possible speed, probably around 65 MB/s. But, as we showed above, the server drive C: can only write at a speed of about 40 MB / s.

Now let's copy the file from the server's high-speed RAID array to drive C: client computer.

Everything turned out just as we expected. From our tests, we know that the C: drive of the client computer is capable of writing data at about 70 MB/s, and gigabit network performance was very close to this speed.

Unfortunately, our results don't even come close to the theoretical maximum throughput of 125 MB/s. Can we test the maximum speed of the network? Sure, but not in a realistic scenario. We will try to transfer information over the network from memory to memory in order to bypass any bandwidth limitations of hard drives.

To do this, we will create a 1 GB RAM disk on the server and client PCs, and then transfer the 1 GB file between these disks over the network. Since even slower DDR2 memory can transfer data at over 3000 MB/s, network bandwidth will be the limiting factor.

We got a maximum speed of 111.4 MB/s for our gigabit network, which is very close to the theoretical limit of 125 MB/s. An excellent result, there is no reason to complain about it, since the real throughput will still not reach the theoretical maximum due to the transfer of additional information, errors, retransmissions, etc.

The conclusion will be as follows: today, the performance of information transfer over a gigabit network rests on hard drives, that is, the transfer speed will be limited by the slowest hard drive involved in the process. Having answered the most important question, we can move on to speed tests depending on the cable configuration, so that our article is complete. Could optimizing cabling bring network speeds even closer to the theoretical limit?

Since the performance in our tests was close to what we expected, we are unlikely to see any improvement when changing the cabling configuration. But we still wanted to run tests to get closer to the theoretical speed limit.

We ran four tests.

Test 1: default.

In this test, we used two cables about 8 meters long, each connected to a computer on one end and to a gigabit switch on the other. We left the cables where they were laid, that is, next to the power cables and sockets.

This time we used the same 8m cables as in the first test, but moved the mains cable as far away from the power and extension cables as possible.

In this test, we removed one of the 8 cables and replaced it with a meter long Cat 5e cable.

In the last test, we replaced the 8th Cat 5e cables with the 8th Cat 6 cables.

In general, our testing of different cable configurations did not show a serious difference, but conclusions can be drawn.

Test 2: Reduce interference from power cables.

On smaller networks, such as our home network, tests show that you don't have to worry about running LAN cables near power cables, outlets, and extension cords. Of course, the pickups will be higher, but this will not give a serious effect on the network speed. However, with all that said, it is best to avoid laying near power cables, and you should remember that in your network the situation may be different.

Test 3: we reduce the length of the cables.

This is not a completely correct test, but we tried to find the difference. It should be remembered that replacing an eight-meter cable with a one-meter cable may cause the result to be influenced by just different cables than differences in distance. In any case, in most tests, we do not see a significant difference, with the exception of an anomalous increase in throughput during copying from the client drive C: to the server C:.

Test 4: Replace Cat 5e cables with Cat 6.

Again, we did not find a significant difference. Since the cables are about 8 meters long, longer cables can make a big difference. But if you do not have the maximum length, then Cat 5e cables will work quite well in a gigabit home network with a distance between two computers of 16 meters.

It is interesting to note that cable manipulation had no effect on data transfer between computer RAM disks. It's pretty obvious that some other component on the network was limiting performance to the 111 MB/s magic number. However, such a result is still acceptable.

Do gigabit networks provide gigabit speeds? As it turns out, they almost do.

However, in real conditions, network speed will be severely limited by hard drives. In a synthetic memory-to-memory scenario, our gigabit network delivered performance very close to the theoretical limit of 125 MB/s. Normal network speeds, taking into account the performance of hard drives, will be limited to 20 to 85 MB / s, depending on the hard drives used.

We also tested the effects of power cables, cable length, and Cat 5e to Cat 6 upgrades. In our small home network none of the factors mentioned had a significant effect on performance, although we want to note that in a larger and more complex network with longer lengths, these factors can affect much more.

In general, if you transfer a large number of files on your home network, then we recommend installing a gigabit network. Switching from a network to 100 Mbps will give a nice performance boost, at least you will get a twofold increase in file transfer speed.

Gigabit Ethernet on a home network can give you a bigger performance boost if you read files from a fast NAS that uses a hardware RAID array. On our test network, we transferred a 4.3 GB file in just one minute. On a 100 Mbps connection, the same file was copied for about six minutes.

Gigabit networks are becoming more and more affordable. Now it remains only to wait for the speed of hard drives to rise to the same level. In the meantime, we recommend building arrays that can bypass the limitations of current HDD technology. Then you can squeeze more performance out of a gigabit network.

No sooner had the milk dried on the lips of the newly born fast Ethernet standard, as the 802 committee set to work on new version(1995). It was almost immediately dubbed the Gigabit Ethernet network, and in 1998 the new standard was already ratified by the IEEE under the official name 802.3z. Thus, the developers emphasized that this is the latest development in the 802.3 line (unless someone urgently comes up with the idea of ​​calling the standards, say, 802.3s. At one time, Bernard Shaw proposed expanding the English alphabet and including, in particular, the letter "s", but was not convincing.).

The main prerequisites for creating 802.3z were the same as when creating 802.3u - 10 times faster speed while maintaining backward compatibility with older Ethernet networks. In particular, gigabit Ethernet had to provide datagram service without acknowledgment in both one-way and multicast transmissions. At the same time, it was necessary to keep the 48-bit addressing scheme and frame format unchanged, including the lower and upper limits on its size. The new standard met all these requirements.

Gigabit Ethernet networks are built on a point-to-point basis, they do not use a monochannel, as in the original 10-Mbit Ethernet, which, by the way, is now called classic Ethernet. The simplest gigabit network, shown in diagram "a", consists of two computers directly connected to each other. In a more general case, however, there is a switch or hub to which many computers are connected, it is also possible to install additional switches or hubs (diagram "b"). But in any case, two devices are always connected to one gigabit Ethernet cable, no more, no less.

Gigabit Ethernet can operate in two modes: full duplex and half duplex. "Normal" is considered full duplex, while traffic can go in both directions at the same time. This mode is used when there is a central switch connected to peripheral computers or switches. In this configuration, the signals of all lines are buffered, so subscribers can send data when they want. The sender does not listen to the channel because he has no one to compete with. On the line between the computer and the switch, the computer is the only potential sender; the transfer will succeed even if there is a transfer from the switch side at the same time (full duplex line). Since there is no competition in this case, the protocol CSMA/CD does not apply, so the maximum cable length is determined solely by the signal strength, and the questions of the propagation time of the noise burst do not arise here. Switches can operate at mixed speeds; moreover, they automatically select the optimum speed. Self-tuning is supported in the same way as in fast ethernet.

Half-duplex mode of operation is used when computers are connected not to a switch, but to a hub. The hub does not buffer incoming frames. Instead, it electrically connects all the lines, simulating a mono link on a normal Ethernet. In this mode, collisions are possible, so it is applied CSMA/CD. Since the minimum size frame (that is, 64 bytes) can be transmitted 100 times faster than in a classic Ethernet network, the maximum segment length must be reduced by a factor of 100 accordingly. It is 25 m - it is at this distance between stations that the noise burst is guaranteed to reach the sender before the end of its transmission. If the cable had a length of 2500 m, then the sender of a 64-byte frame at 1 Gb / s would have time to do a lot even while his frame traveled only a tenth of the way in one direction, not to mention that the signal should again and go back.

The 802.3z drafting committee rightly pointed out that 25 m is an unacceptably short length, and introduced two new properties that made it possible to increase the radius of the segments. The first is called media extension. This extension consists only in the fact that the equipment inserts its own padding field, which stretches the normal frame to 512 bytes. Because this field is added by the sender and removed by the receiver, the software doesn't care about it. Of course, wasting 512 bytes to transfer 46 bytes is somewhat wasteful in terms of bandwidth efficiency. The transmission efficiency is only 9%.

The second feature that allows you to increase the allowable segment length is frame bursting. This means that the sender can send not a single frame, but a packet that combines many frames at once. If the total packet length is less than 512 bytes, then, as in the previous case, hardware filling with dummy data is performed. If there are enough frames waiting for transmission to fill such a large packet, then the operation of the system is very efficient. Such a scheme is, of course, preferable to media expansion. These methods made it possible to increase the maximum segment length to 200 m, which is probably already quite acceptable for organizations.

It is hard to imagine an organization that would spend a lot of effort and money installing boards for a high-performance gigabit Ethernet network, and then connect computers with hubs that simulate the operation of classic Ethernet with all its conflicts and other problems. Hubs are, of course, cheaper than switches, but Gigabit Ethernet interface cards are still relatively expensive, so saving on buying a hub instead of a switch is not worth it. In addition, this drastically reduces performance, and it becomes completely incomprehensible why it was necessary to spend money on gigabit boards. However, backward compatibility is something sacred in the computer industry, so, no matter what, 802.3z provides for such a possibility.

Gigabit Ethernet supports both copper and fiber optic cables. Running at 1 Gbps means that the light source must turn on and off about once every nanosecond. LEDs just can't run that fast, so lasers have to be used here. The standard provides for two operating wavelengths: 0.85 µm (short waves) and 1.3 µm (long). Lasers rated at 0.85 µm are cheaper, but do not work with single-mode cables.

Three fiber diameters are officially allowed: 10, 50 and 62.5 microns. The first is for single-mode transmission, the other two are for multi-mode. Not all of the six combinations are allowed, and the maximum segment length depends on the selected combination. The numbers given in the table are the best case. In particular, a 5 km cable can only be used with a 1.3 µm laser operating on 10 µm single mode fiber. This option, apparently, is the best for highways of various kinds of campuses and production areas. It is expected to be the most popular despite being the most expensive.

1000Base-CX uses a short shielded copper cable. The problem is that competitors are pushing it both from above (1000Base-LX) and from below (1000Base-T). As a result, it is doubtful that he will win wide public recognition.

Finally, another cable option is a bundle of four unshielded twisted pairs. Since such wiring exists almost everywhere, it looks like this will be the most popular gigabit Ethernet.

The new standard uses new rules for encoding signals transmitted over fiber optics. Manchester code at a data rate of 1 Gb/s would require a signal change rate of 2 Gbaud. It's too complex and takes up too much bandwidth. Instead of Manchester encoding, a scheme called 8V / 10V is used. As you might guess from the name, each 8-bit byte is encoded for transmission over the fiber with ten bits. Since there are 1024 possible resulting codewords for each input byte, this method allows some freedom in the choice of codewords. The following rules are taken into account:

No codeword shall have more than four identical bits in a row;

No code word should contain more than six zeros or six ones.

Why exactly these rules?

First, they provide enough state changes in the data stream to keep the receiver in sync with the transmitter.

Secondly, they try to roughly equalize the number of zeros and ones. In addition, many incoming bytes have two possible codewords associated with them. When an encoder has a choice of codewords, it is likely to choose one that matches the number of 0s and 1s.

The balanced number of zeros and ones is therefore given such importance that it is necessary to keep the DC component of the signal as low as possible. Then it will be able to pass through the transducers unchanged. People involved in computer science are not enthusiastic about the fact that converter devices dictate certain rules for encoding signals, but life is life.

Gigabit Ethernet, built on 1000Base-T, uses a different coding scheme, since it is difficult to change the signal state within 1 ns for a copper cable. It uses 4 twisted pairs of category 5, which makes it possible to transmit 4 characters in parallel. Each character is encoded with one of five voltage levels. Thus, one signal can mean 00, 01.10 or 11. There is also a special, service voltage value. There are 2 data bits per twisted pair, respectively, for one time interval, the system transmits 8 bits over 4 twisted pairs. The clock frequency is 125 MHz, which allows you to work at a speed of 1 Gb / s. A fifth voltage level has been added for special purposes - framing and control.

1 Gbps is quite a lot. For example, if the receiver is distracted by some business within 1 ms and at the same time forgets or does not have time to free the buffer, this means that it will “sleep” for about 1953 frames. There may be another situation: one computer issues data over a gigabit network, and the other receives them over classic Ethernet. Probably, the first will quickly overwhelm the second with data. The clipboard will overflow first. Based on this, it was decided to introduce a flow control system into the system (this was also the case in fast ethernet, although these systems are quite different).

To implement flow control, one of the parties sends a service frame indicating that the other party needs to pause for a while. Service frames are, in fact, regular Ethernet frames with 0x8808 written in the Type field. The first two bytes of the data field are command, and the next, if necessary, contain command parameters. For flow control, PAUSE type frames are used, and the duration of the pause is specified as a parameter in units of the minimum frame transmission time. For Gigabit Ethernet, this unit is 512 ns, and pauses can last up to 33.6 ms.

Gigabit Ethernet was standardized and the 802 committee got bored. Then the IEEE suggested that he start working on 10-gigabit Ethernet. Long attempts began to find in the English alphabet some letter after z. When it became obvious that such a letter does not exist in nature, it was decided to abandon the old approach and switch to two-letter indices. So in 2002, the 802.3ae standard appeared. Apparently, the emergence of 100-gigabit Ethernet is also not far off.

Decide if you need to upgrade your network.

• If you and your family members regularly download large files, stream media on the Internet, or perform other tasks that heavily load your network, such as a file hosting server or playing online games, you would be happy to invest in improving up to gigabit ethernet.
• Medium and large enterprises require many users to be connected over a network and simultaneously be able to increase their productivity.
• Individuals who use the internet alone for non-resource-intensive networking tasks like Email, instant messaging, or web surfing may not see the benefit of upgrading network access to Gigabit Ethernet.

Introduction

A network based on 10/100 Mbps Ethernet will be more than enough for any task in small networks. But what about the future? Have you thought about the video streams that will flow through your home network? Will 10/100 Ethernet handle them?

In our first Gigabit Ethernet article, we'll take a closer look at it and determine if you need it. We will also try to find out what you need to create a "gigabit ready" network and take a quick tour of gigabit equipment for small networks.

What is gigabit ethernet?

Gigabit Ethernet is also known as "gigabit over copper" or 1000BaseT. It is a regular version of Ethernet, operating at speeds up to 1.000 megabits per second, i.e. ten times faster than 100BaseT.

Gigabit Ethernet is based on the IEEE standard 802.3z which was approved in 1998. However, in June 1999, an addition was released to it - the gigabit Ethernet standard over copper twisted pair. 1000BaseT. It was this standard that was able to bring gigabit Ethernet out of server rooms and backbone channels, ensuring its use in the same conditions as 10/100 Ethernet.

Prior to 1000BaseT, Gigabit Ethernet required the use of fiber optic or shielded copper cables, which are hardly suitable for conventional cabling. local networks. These cables (1000BaseSX, 1000BaseLX and 1000BaseCX) are still used in special applications today, so we won't cover them here.

The 802.3z Gigabit Ethernet group has done a great job of releasing a universal standard that is ten times faster than 100BaseT. 1000BaseT is also backward compatible with 10/100 hardware, he uses CAT-5 cable (or higher category). By the way, today a typical network is built on the basis of a cable of the fifth category.

Do we need it?

The first Gigabit Ethernet literature cited the enterprise market as the application area for the new standard, and most commonly data warehouse communications. Because Gigabit Ethernet provides ten times the bandwidth of conventional 100BaseT, the standard's natural application is to connect high-bandwidth sites. This is the connection between servers, switches and backbone nodes. This is where Gigabit Ethernet is needed, needed and useful.

As the price of gigabit hardware has declined, 1000BaseT's scope has expanded to "power user" computers and workgroups running "bandwidth-intensive applications."

Since most small networks have modest data transfer requirements, they are unlikely to ever need 1000BaseT network bandwidth. Let's take a look at some typical small network applications and evaluate their need for Gigabit Ethernet.

Do we need it, continued

• Transferring large files over the network

  Such an application is rather typical for small offices, especially in companies involved in graphic design, architecture or other business related to processing files of tens to hundreds of megabytes. You can easily calculate that a 100MB file will be transferred over a 100BaseT network in just eight seconds [(100MB x 8bps)/ 100Mbps]. In reality, many factors degrade the transfer speed, so your file will take a little longer to transfer. Some of these factors are related to operating system, running applications, the amount of memory on your computers, processor speed and age. (The age of the system affects the speed of the buses on the motherboard).

  Another important factor is the speed of network equipment, and moving to gigabit equipment eliminates a potential bottleneck and speeds up the transfer of large amounts of files. Many will confirm that getting speeds above 50 Mbps on a 100BaseT network is by no means a trivial matter. Gigabit Ethernet, on the other hand, will be able to provide throughput in excess of 100 Mbps.

• Network Redundancy Devices

  You can consider this case as a variant of "large files". If your network is configured to back up all computers to a single file server, then Gigabit Ethernet will allow you to speed up this process. However, there is also a pitfall here - increasing the “pipe” of transmission to the server may not lead to a positive effect if the server does not have time to process the incoming data stream (this also applies to the backup media).

  To take advantage of a high speed network, you should equip your server with more memory and back up to a fast hard disk rather than tape or CDROM. As you can see, you should thoroughly prepare for the transition to gigabit Ethernet.

• Client-Server Applications

  This area of ​​application is again more common in small business networks than in home networks. A large amount of data can be transferred between the client and server in such applications. The approach is the same: you need to analyze the amount of network data being transferred to see if the application can “keep up” with the increase in network bandwidth and whether this data is enough for the gigabit Ethernet load.

To be honest, we don't think most home network builders will find enough reason to buy gigabit hardware. In small business networks, switching to gigabit can help, but we recommend that you first analyze the amount of data transferred. With the current state, everything is clear. But what if you want to take into account the possibility of future modernization. What do you need to do today to be ready for it? In the next part of our article, we will look at the changes that need to be made to the most expensive, most often and most time-consuming, part of the network - cable.

Gigabit Ethernet Cable

As we mentioned in the introduction, one of the key requirements of the 1000BaseT standard is the use of Category 5 (CAT 5) or higher cable. That is gigabit ethernet can work on existing Category 5 cable structure. Agree, such an opportunity is very convenient. Generally, all modern networks use Category 5 cable, unless your network was installed in 1996 or earlier (the standard was approved in 1995). However, here exist several pitfalls.

• Requires four pairs

  As seen from this article, 1000BaseT uses all four pairs of Category 5 (or higher) cable to create four 250 Mbps links. (Another coding scheme, five-level pulse-amplitude modulation, is also applied to stay within the 100 MHz CAT5 frequency band.) As a result, we can use the existing CAT 5 cabling structure for Gigabit Ethernet.

  Because 10/100BaseT only uses two of the four CAT 5 pairs, some people didn't connect the extra pairs when they laid their networks. Pairs were used, for example, for a telephone or for Power over Ethernet (POE). Fortunately gigabit NICs and switches are smart enough to fall back to 100BaseT if all four pairs are unavailable. Therefore, in any case, your network will work with gigabit switches and network cards, but you will not get high speed for the money you paid.

• Don't use cheap connectors

  Another problem for amateur networkers is poor crimping and cheap wall sockets. They lead to impedance mismatches, resulting in return loss and consequently reduced bandwidth. Of course, you can try to look for the cause "head on", but you'd still be better off getting a network tester that can detect return loss and crosstalk. Or just put up with the low speed.

• Length and topology restrictions

  1000BaseT is limited to the same maximum segment length as 10/100BaseT. Thus, the maximum network diameter is 200 meters (from one computer to another through one switch). As for the 1000BaseT topology, the same rules apply as for 100BaseT, except that only one repeater per network segment (or, to be more precise, one "half-duplex collision domain") is allowed. But since gigabit ethernet doesn't support half duplex, you can forget about the last requirement. In general, if your network was fine under 100BaseT, you should have no problems moving to gigabit.

Gigabit Ethernet cable, continued

For laying new networks, it is best to use cable CAT 5e. And although CAT 5 and CAT 5e both pass 100 MHz, CAT5e cable is manufactured with additional parameters important for better transmission of high frequency signals.

View the following Belden documents to learn more about CAT 5e cable specifications (in English):

While a modern CAT 5 cable will work just fine with 1000BaseT, you'd be better off choosing CAT 5e if you want to guarantee high throughput. If you hesitate, estimate the cost of CAT 5 and CAT 5e cable and proceed within your means.

The Only Thing You Should Avoid Are Buying Recommendations CAT 6 cable for gigabit ethernet. CAT 6 was added to TIA-568 in June 2002 and it skips frequencies up to 200 MHz. Sellers will certainly persuade you to buy the more expensive sixth category, but you will need it only if you plan to build a network 10 Gbps Ethernet over copper wiring, which is hardly realistic at the moment. What about CAT 7 cable? Forget about him!

If you have a good amount of money, then it is better to spend it on network specialist, which has sufficient experience in laying gigabit networks. A specialist can competently lay cables or test your existing network to work with gigabit Ethernet. When installing a CAT 6 cable, we highly recommend that you seek the help of professionals, as this cable stipulates a bending radius and special quality connectors.

Gigabit equipment

In some ways, the question of "gigabit or not" could have been a point of contention a year or a couple of years ago. From the point of view of the SOHO buyer, the transition from 10 to 10/100 Mbps has already happened. Newer computers are equipped with 10/100 Ethernet ports, routers already use built-in 10/100 switches rather than 10BaseT hubs. However, such a change is not a consequence of the requirements and wishes of home "networkers". They are content with existing equipment.

For these changes, we have to thank the corporate users, who today buy only 10/100 equipment in bulk quantities, which allows them to lower their prices. Once consumer equipment manufacturers found that using 10BaseT chips versus 10/100 options expensive They didn't hesitate for a long time.

Thus, yesterday's architecture based on 10BaseT hubs has quietly moved into today's 10/100 switched networks. We will experience exactly the same transition from 10/100 to 10/100/1000 Mbps. And although the tipping point is still a year or two away, the transition already started and prices continue to fall steadily.

All you need is to buy a gigabit network card and a gigabit switch. Let's look at them in a little more detail.

• network cards

  Branded 32-bit PCI 10/100/1000BaseT network cards like Intel PRO1000 MT, Netgear GA302T and SMC SMC9552TX cost $40 to $70 on the Internet. Products from second-tier manufacturers are about $5 cheaper. And although gigabit NICs are about two and a half times more expensive than average 10/100 cards, it's unlikely your wallet will notice any difference at all unless you buy them in bulk.

  You can find network cards that support not only the 32-bit PCI bus, but also the 64-bit one, but they are also more expensive. What you won't see are CardBus adapters for your laptops. For some reason, manufacturers believe that laptops do not need gigabit networks at all.

• Switches

  But the price of 10/100/1000 switches makes you think ten times about the advisability of switching to gigabit Ethernet. The good news is that transparent gigabit switches have already appeared today, which are much cheaper than their managed counterparts for the corporate market.

  A simple four-port 10/100/1000 Netgear GS104 switch can be purchased for less than $225. If you opt for lesser-known brands like TRENDnet's TEG-S40TXE, you'll get the price down to $150. Not enough four ports - please. The eight-port version of the Netgear GS108 will cost you about $450, while the TRENDnet TEG-S80TXD will cost you about $280.

  Considering that a five-port 10/100 switch costs only $20 today, the price per gigabit will seem too high to some. But remember: until recently, you could only buy $100+ managed gigabit switches per port. Prices are going in the right direction!

Will computers need to be changed?

Let's open a little secret of gigabit Ethernet: under Win98 or 98SE, you most likely will not get any advantage from gigabit speed. And while editing the registry can try to improve throughput, you still won't get a significant performance boost over current 10/100 hardware.

The problem lies in the Win98 TCP/IP stack, which was not designed with high speed networks in mind. The stack has problems even using 100BaseT network, then why talk about gigabit communication! We will return to this issue in the second article, but for now you should only consider Win2000 and WinXP to work with gigabit Ethernet.

With the last sentence, we not we assume that only Windows 2000 and XP support gigabit network cards. We just haven't tested performance under other operating systems, so please refrain from stinging remarks!

If you're wondering if you'll have to throw away your good old computer and buy a new one to use Gigabit Ethernet, then our answer is "probably". According to our practical experience, one hertz of "modern" processors equals one bit per second of network bandwidth. One of the manufacturers of gigabit network equipment agreed with us: any machine with clock frequency 700 MHz or below will not be able to fully utilize the bandwidth of gigabit Ethernet. So even with the right operating system, gigabit ethernet is like a dead poultice to old computers. You'd rather see speeds 100-500 Mbps