Fast ethernet 100 mbps. Ethernet and Fast Ethernet equipment

The ComputerPress test laboratory tested 10/100 Mbit / s network cards for the PCI bus, designed for use in 10/100 Mbit / s workstations. The most common currently used cards with a throughput of 10/100 Mbit / s were selected, since, firstly, they can be used in Ethernet, Fast Ethernet and mixed networks, and, secondly, the promising Gigabit Ethernet technology ( bandwidth up to 1000 Mbit / s) is still used most often 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 on the network. It is well known that if Category 3 twisted pair cable is sufficient for Ethernet networks, Category 5 is required for Fast Ethernet. Signal scattering, poor noise immunity can significantly reduce network bandwidth.

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 the throughput. The P / E index is calculated as the ratio of the bandwidth of the network card in Mbps to the percentage of the CPU utilization. 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 network cards of CPU resources. This is because some manufacturers of network adapters try to get the best performance by using more computer processor cycles to perform network operations. Low CPU usage and relatively high bandwidth are essential for running mission-critical business and multimedia applications, as well as real-time tasks.

We tested the cards that are currently most often used for workstations in corporate and local networks:

1. D-Link DFE-538TX
2. SMC EtherPower II 10/100 9432TX / MP
3. 3Com Fast EtherLink XL 3C905B-TX-NM
4. Compex RL 100ATX
5. Intel EtherExpress PRO / 100 + Management
6. CNet PRO-120
7. NetGear FA 310TX
8. Allied Telesyn AT 2500TX
9. Surecom EP-320X-R

The main characteristics of the tested network adapters are shown in table. 1 . Let us explain some of the terms used in the table. Automatic detection of the connection speed means that the adapter itself determines the maximum possible speed of operation. In addition, if autosensing 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 the drivers.

Support for Bus Master mode allows data to be transferred directly between the network card and the computer's memory. This frees up the central processor to perform other operations. This property has become the de facto standard. No wonder all known network cards support the Bus Master mode.

Remote wake-on (Wake on LAN) allows you to turn on the PC over the network. That is, it becomes possible to service the PC outside of working hours. For this purpose, three-pin connectors on the motherboard and network adapter are used, which are connected with a special cable (included in the delivery set). In addition, special control software is required. Wake on LAN technology is developed by the Intel-IBM alliance.

Full duplex mode allows data to be transmitted simultaneously in both directions, half duplex - in only one. Thus, the maximum possible throughput in full duplex mode is 200 Mbps.

DMI (Desktop Management Interface) provides the ability to obtain information about the configuration and resources of the PC using network management software.

Support for the WfM (Wired for Management) specification enables a network adapter to interact with network management and administration software.

To remotely boot a computer's OS over a network, network adapters are supplied with a special BootROM memory. This allows for efficient use of diskless workstations on the network. Most of the tested cards only had a BootROM slot; the BootROM itself is usually a separately ordered option.

ACPI (Advanced Configuration Power Interface) support helps reduce power consumption. ACPI is a new technology for power management. It is based on the use of both hardware and software. Basically, Wake on LAN is an integral part of ACPI.

Proprietary means of increasing productivity can increase the efficiency of the network card. The most famous of these are Parallel Tasking II from 3Com and Adaptive Technology from Intel. These funds 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, a diskette with drivers and the ability to download the latest drivers from the company's website. 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 was satisfactory for all cards.

Typically, the warranty covers the entire life of the power adapter (lifetime warranty). Sometimes it is limited to 1-3 years.

Testing technique

All tests used the latest NIC drivers downloaded from the respective vendors' Internet servers. In the case when the driver of the network card allowed any adjustments and optimizations, the default settings were used (except for the Intel network adapter). Note that the cards and corresponding drivers from 3Com and Intel have the richest additional capabilities and functions.

Performance was measured using Novell's Perform3 utility. The principle of operation of the utility is that a small file is copied from a workstation to a shared network drive on the server, after which it remains in the server's file cache and is read from there many times over a specified period of time. This allows for memory-network-memory interactions and eliminates the impact of disk latency. The utility parameters include initial file size, final file size, resizing step, and test time. 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 test time with each file was set to twenty seconds.

Each experiment used a pair of identical network cards, one running on a server and the other on a workstation. This does not seem to be in line with common practice, as servers usually use specialized network adapters with a number of additional features. But this is exactly how - the same network cards are installed on the server and on workstations - testing is carried out by all well-known test laboratories in the world (KeyLabs, Tolly Group, etc.). The results are slightly lower, but the experiment turns out to be clean, since only the analyzed network cards work on all computers.

Compaq DeskPro EN client configuration:

• Pentium II 450 MHz processor
• cache 512 KB
• RAM 128 MB
• hard drive 10 GB
• operating system Microsoft Windows NT Server 4.0 c 6 a SP
• TCP / IP protocol.

Compaq DeskPro EP server configuration:

• Celeron 400 MHz processor
• 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 conducted with computers connected directly with a UTP Category 5 crossover cable. During these tests, the cards were operating in 100Base-TX Full Duplex mode. In this mode, the throughput is slightly higher due to the fact that part of the service information (for example, acknowledgment of receipt) is transmitted simultaneously with the useful information, the amount of which is estimated. In these conditions, it was possible to record rather high values ​​of the throughput; for example, 3Com Fast EtherLink XL 3C905B-TX-NM adapter averages 79.23 Mbps.

The processor load was measured on the server using the Windows NT Performance Monitor utility; the data was written to a log file. Perform3 was run on the client so as not to affect the server processor load. Intel Celeron was used as the processor of the server computer, the performance of which is significantly lower than the performance of Pentium II and III processors. Intel Celeron was used deliberately: the fact is that, since the processor load is determined with a sufficiently large absolute error, in the case of large absolute values, the relative error turns out to be smaller.

After each test, Perform3 utility places the results of its work into a text file as a dataset 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 for the entire test. The resulting average values ​​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 the throughput to the processor load as a percentage. Subsequently, the average value of the P / E index was calculated based on the results of three measurements.

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, as there was no data transfer per se over the network. In order for applications to treat shared network drives as ordinary local drives, the operating system uses a special network component called a redirector that redirects I / O requests over the network. Under normal operating conditions, when executing the procedure for 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, the parameter values ​​in the Windows NT registry were changed, which made it possible to disable the caching performed by the redirector. Here's how it was done:

1. Registry path:

   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)

2. Registry path:

   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 content.

   Type: REG_DWORD Value: 0 (default: 1)

Intel EtherExpress PRO / 100 + Management Network Adapter

The card's throughput and processor utilization are nearly the same as that of 3Com. The windows for setting the parameters of this map are shown below.

The new Intel 82559 controller in this card provides very high performance, especially in 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 congestion increases, the distance between individual Ethernet packets dynamically increases, which reduces collisions and increases throughput. With a low network load, when the probability of collisions is low, the time intervals between packets are reduced, which also leads to increased performance. The benefits of this method should be greatest in large collisional Ethernet segments, that is, in cases where hubs rather than switches dominate the network topology.

Intel's new technology, called Priority Packet, allows traffic through the NIC to be tuned according to the priorities of individual packets. This provides the ability to increase data transfer rates for mission-critical applications.

VLAN support is provided (IEEE 802.1Q standard).

There are only two indicators on the board - work / connection, speed 100.

www.intel.com

SMC EtherPower II 10/100 SMC9432TX / MP Network Adapter

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 about the degree of efficiency of the implementation of these technologies. Note also that this network card showed the third result in terms of performance and P / E index, outperforming all cards except 3Com and Intel.

There are four LED indicators on the card: speed 100, transmission, connection, duplex.

The company's main Web site is www.smc.com

Ethernet is the most widely used standard for local area networks today. Total number of networks currently in use

Fast Ethernet

Fast Ethernet technology is much the same as traditional Ethernet technology, but it is 10 times faster. Fast Ethernet or 100BASE-T operates at 100 megabits per second (Mbps) instead of 10 for traditional Ethernet. 100BASE-T technology uses frames of the same format and length as Ethernet and does not require changes in higher 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 the associated delays. Fast Ethernet technology uses the CSMA / CD protocol of the MAC sublayer to provide access to the transmission medium. Most modern Ethernet networks are based on a star topology, with a hub at the center of the network and cables from the hub to each computer. The same topology is used in Fast Ethernet networks, although the network diameter is slightly smaller due to the higher speed. Fast Ethernet uses an 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 conductors enclosed in a plastic sheath. Category 5 cables are certified for 100 MHz bandwidth. In 100BASE-TX, one pair is used for data transmission, the other for collision detection and reception.

The Fast Ethernet standard defines three modifications to work with different types of cables: 100Base TX, 100Base T4 and 100Base FX. The 100Base TX and 100Base T4 versions are designed for twisted pair cables, while 100Base FX was designed for optical cable.

The 100Base TX standard requires the use of two shielded or unshielded twisted pairs. One pair is for transmission, the other for reception. Two main 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-wire cable: one pair for transmitting, the other for receiving, and the remaining two pairs work for both transmit and receive. As a result, in the 100Base T4 standard both reception and transmission of data can be carried out in three pairs. For the implementation of 100Base T4 networks, cables with an unshielded twisted pair of category 3-5 and shielded type 1 are suitable.

The succession of Fast Ethernet and Ethernet technologies makes it easy to develop recommendations for use: Fast Ethernet is advisable to use in those organizations that have widely used classic Ethernet, but today are experiencing a need to increase bandwidth. At the same time, all the accumulated experience with Ethernet and, in part, the network infrastructure is retained.

For classic Ethernet, 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 that frame at the workstation. For an Ethernet network, this distance is 2500 meters. In a Fast Ethernet network, the same 512-bit frame will only travel 250 meters in the time it takes to process it on a workstation.

The main area of ​​Fast Ethernet today is workgroup and departmental networking. It is wise to make the transition to Fast Ethernet gradually, leaving Ethernet where it does the job well. One of the obvious cases where Ethernet should not be replaced with Fast Ethernet is when connecting older personal computers with ISA to the network.

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 differs from Fast Ethernet more than Fast Ethernet from Ethernet. In particular, if Ethernet was characterized by a variety of supported transmission media, which gave reason to say that it can work even over barbed wire, then in Gigabit Ethernet, fiber-optic cables are becoming the dominant transmission medium (this, of course, is not the only difference , but we'll get to know the rest in more detail below). In addition, Gigabit Ethernet poses incomparably more complex technical challenges and demands much higher quality wiring. In other words, it is much less versatile than its predecessors.

GIGABIT ETHERNET STANDARDS

The main effort of the IEEE 802.3z working group is focused on defining physical standards for Gigabit Ethernet. As a basis, she took the ANSI X3T11 Fiber Channel standard, more precisely, its two lower sublayers: FC-0 (interface and transmission medium) and FC-1 (encoding and decoding). The physical media-specific Fiber Channel specification currently specifies 1.062 Gbps. In Gigabit Ethernet, it has been increased to 1.25 Gbps. Considering 8B / 10B encoding, we get a data transfer rate of 1 Gbps.

TechnologyEthernet

Ethernet is the most widely used standard for local area networks 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 version II standard for a coaxial cable network, which was 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.

On the basis of the Ethernet standard, additional standards were adopted: in 1995 Fast Ethernet (an addition to IEEE 802.3), in 1998 Gigabit Ethernet (IEEE 802.3z section of the main document), which are in many ways not independent standards.

For transmission of binary information via cable for all variants of the physical layer of Ethernet technology, providing a throughput of 10 Mbit / s, the Manchester code is used (Fig. 3.9).

The Manchester code uses the potential drop, that is, the pulse front, to encode ones and zeros. In Manchester encoding, each bar is divided into two parts. Information is encoded by potential drops that occur in the middle of each clock cycle. One is encoded by the slope from low to high signal level (the leading edge of the pulse), and zero is coded by the falling edge (trailing edge).

Rice. 3.9. Differential Manchester Coding

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 generate a jamming signal that does not look like a valid message. Ethernet can recognize interference and forces the sender to pause transmission and wait a while before re-sending the message.

The reasons for the widespread use and popularity of Ethernet (advantages):

1. Cheapness.

2. Extensive experience of use.

3. Continuing innovations.

4. A wealth of equipment selection. Many manufacturers offer Ethernet-based networking equipment.

Disadvantages of Ethernet:

1. Possibility of message collisions (collisions, interference).

2. In the case of a large network load, the transmission time of messages is unpredictable.

TechnologyTokenRing

Token Ring networks, like Ethernet networks, are characterized by a shared data transmission medium, which consists of lengths of cable connecting all stations on the network in a ring. The ring is considered as a shared resource, and access to it requires not a random algorithm, as in Ethernet networks, but a deterministic one, based on the transfer of the right to use the ring to stations in a certain order. This right is conveyed using a special format frame 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 adopted the 802.5 standard on its basis in 1985.

Each PC operates in Token Ring according to the principle “Wait for a token, if you need to send a message, attach it to a token 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 stations operating at different speeds in one ring is not allowed.

Token Ring technology is more complex than Ethernet. It has the properties of fault tolerance. The Token Ring network defines network control procedures that use a ring-shaped feedback structure - a sent frame is always returned to the sending station.

Rice. 3.10. TOKEN RING technology principle

In some cases, detected errors in the network operation are eliminated automatically, for example, a lost token can be restored. In other cases, errors are only recorded, and their elimination is performed manually by the service personnel.

To monitor 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 maximum MAC address. If the active monitor fails, the ring initialization procedure is repeated and a new active monitor is selected. Token Ring can have up to 260 nodes.

A Token Ring hub can be active or passive. A passive hub simply interconnects the ports with interconnects so that the 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, a Token Ring network has a combined star-ring configuration. End nodes are connected to MSAUs in a star topology, and the MSAUs themselves are combined through special Ring In (RI) and Ring Out (RO) ports to form a physical backbone ring.

All stations in the ring must operate at the same speed, either 4 Mbps or 16 Mbps. The cables connecting the station to the hub are called lobe cables, and the cables connecting the hubs are called trunk cables.

Token Ring technology allows the use of various types of cable to connect endpoints and hubs:

- STP Type 1 - shielded twisted pair (Shielded Twistedpair).
It is allowed to combine up to 260 stations into a ring with a branch cable length of 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 a drop cable length of up to 45 meters;

- 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. Between active MSAUs, the maximum distance increases to 730 m or 365 m, respectively, depending on the type of cable.

The maximum ring length of Token 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 stringent as in Ethernet technology. Here, these limitations are mainly related to the turnover time of the marker around the ring.

All of the timeout values ​​on the network adapters of the Token Ring hosts are configurable, so you can build a Token Ring network with more stations and longer ring lengths.

Token Ring Technology Advantages:

· Guaranteed message delivery;

· High speed of data transfer (up to 160% Ethernet).

Disadvantages of Token Ring technology:

· Expensive devices for access to the environment are required;

· The technology is more difficult to implement;

· 2 cables are required (to improve reliability): one incoming, the other outgoing from the computer to the hub;

· High cost (160-200% of Ethernet).

TechnologyFDDI

Fiber Distributed Data Interface (FDDI) technology is the first local area network technology to use fiber as the transmission medium. The technology appeared in the mid-80s.

FDDI technology relies heavily on Token Ring technology, supporting the 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 the network nodes. Having two rings is the primary way to improve resiliency in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings.

In normal network operation, data passes through all nodes and all cable sections of only the Primary ring, this mode is called Thru mode - "through", or "transit". Secondary ring is not used in this mode.

In the event of some type of failure, where part of the primary ring cannot transmit data (for example, a cable break or node failure), the primary ring is combined with the secondary ring, again forming a single ring. This mode of operation of the network is called Wrap, that is, "folding" or "folding" the rings. The folding operation is performed by means of hubs and / or FDDI network adapters.

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 along the secondary - in the opposite direction (shown clockwise). Therefore, when a common ring of two rings is formed, 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 splits into several unconnected networks.

Rings in FDDI networks are considered as a common shared data transmission medium, therefore a special access method is defined for it. This method is very close to the Token Ring access method and is also called the token ring method.

The differences in the access method are that the retention time of the token in the FDDI network is not constant. 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 changes in the access method apply only to asynchronous traffic, which is not critical to small frame transmission delays. For synchronous traffic, the token retention time is still a fixed value.

FDDI technology currently supports cable types:

- fiber optic cable;

- unshielded twisted pair of category 5. The last standard appeared later than optical and is called TP-PMD (Physical Media Dependent).

Fiber optic technology provides the necessary means for transmitting data from one station to another via optical fiber and determines:

Use of 62.5 / 125 µm multimode fiber optic cable as the main physical medium;

Requirements for the power of optical signals and the maximum attenuation between network nodes. For standard multimode cable, these requirements lead to a maximum distance 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 for transmitting light with a wavelength of 1.3 nm;

The maximum total length of the FDDI ring is 100 kilometers, and the maximum number of double-connected stations in the ring is 500.

FDDI technology was developed for use in critical areas of networks - on backbones between large networks, such as building networks, as well as for connecting high-performance servers to the network. Therefore, the main requirements for the developers were ( dignity):

- ensuring high speed of data transfer,

- fault tolerance at the protocol level;

- long distances between network nodes and a large number of connected stations.

All these goals have been achieved. As a result, the FDDI technology turned out to be of high quality, but very expensive ( flaw). Even the appearance of a cheaper twisted pair option did not significantly reduce the cost of connecting one node to the 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 a network of the scale of a large city, that is, of the MAN class.

TechnologyFastEthernet

The need for high-speed yet inexpensive technology to connect powerful workstations to a network of powerful workstations led in the early 90s to the creation of an initiative group that began to look for a new Ethernet, the same simple and effective technology, but operating at a speed of 100 Mbps. ...

The specialists split 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 the 10 Mbps Ethernet technology.

Fast Ethernet technology has kept the CSMA / CD access method intact, keeping the same algorithm and the same time parameters in bit intervals (the bit interval itself has decreased 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 (coding method 4V / 5V);

- l00Base-FX for multimode fiber optic cable with two optical fibers (coding method 4V / 5V);

- 100Base-T4, operating on 4 pairs of UTP category 3, but using only three pairs simultaneously for transmission, and the rest - for collision detection (8B / 6T coding method).

The l00Base-TX / FX standards can operate in full duplex mode.

The maximum diameter of a Fast Ethernet network is approximately 200 m, and the exact value depends on the specification of the physical medium. In the Fast Ethernet collision domain, no more than one class I repeater is allowed (allowing to translate 4B / 5B codes into 8B / 6T codes and vice versa) and no more than two class II repeaters (not allowing codes translation).

Fast Ethernet technology when working on twisted pair allows two ports to choose the most efficient mode of operation through the auto-negotiation procedure - 10 Mbps or 100 Mbps, as well as half-duplex or full-duplex mode.

Gigabit Ethernet technology

Gigabit Ethernet technology adds a new 1000 Mbps step in the speed hierarchy of the Ethernet family. This stage makes it possible to effectively build large local networks, in which powerful servers and backbones of the lower network levels operate at a speed of 100 Mbit / s, and the Gigabit Ethernet backbone unites them, providing a sufficiently large margin of bandwidth.

The developers of Gigabit Ethernet technology have retained a great deal of continuity with Ethernet and Fast Ethernet technologies. Gigabit Ethernet uses the same frame formats as previous Ethernet versions, operates in full and half duplex modes, supporting the same CSMA / CD access method on shared media with minimal changes.

To ensure an acceptable maximum network diameter of 200 m in half-duplex mode, the technology developers decided to increase 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 up the medium, on an interval of 8096 bytes, then the frames do not have to be padded to 512 bytes. The rest of the access method and maximum frame size parameters remained unchanged.

In the summer of 1998, the 802.3z standard was adopted, which defines the use of three types of cable as the 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.

To develop a variant of Gigabit Ethernet on UTP category 5, a special group 802.3ab was created, which has already developed a draft standard for working on 4 pairs of UTP category 5. Adoption of this standard is expected in the near future.

Easy to install.

Well known and most widely used networking technology.

Low cost of network cards.

The possibility of implementation using various types of cables and cabling schemes.

Disadvantages of Ethernet

A decrease in the real data transfer rate in a heavily loaded network, up to its complete stop, due to conflicts in the data transmission medium.

Difficulties in troubleshooting: if the cable breaks, the entire LAN segment fails, and it is quite difficult to localize a faulty node or section of the network.

Brief characteristics 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 Mbit / s, retaining to the maximum extent the features of 10 Mbit Ethernet (Ethernet-10) and implemented in the form of the 802.3u standard (more precisely, an addition to the standard 802.3 as chapters 21 to 30). The access method is the same as in Ethernet-10 - CSMA / CD of the MAC level, which allows you to use the old software and management tools for Ethernet networks.

All the differences between Fast Ethernet and Ethernet-10 are focused on the physical layer. 3 types of cable systems are used:

multimode FOC (2 fibers are used);

Network structure- a hierarchical tree structure based on hubs (like 10Base-T and 10Base-F), since no coaxial cable is used.

Net diameter Fast Ethernet has been reduced to 200 meters, which is explained by a 10-fold reduction in the transmission time of a minimum frame length due to a 10-fold increase in transmission speed compared to Ethernet-10. Nevertheless, it is possible to build large networks based on Fast Ethernet technology, due to the widespread use of inexpensive high-speed technologies, as well as the rapid development of LAN based on switches. 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, and only restrictions on the length of the physical segments connecting neighboring devices (adapter - switch or switch - 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 categories 3, 4 or 5);

100Base-FX- data transmission over two fibers of a multimode FOC.

What is the transmission time of the minimum (maximum) frame length (including the preamble) in bit intervals for a 10Mbps Ethernet network?

? 84 / 1538

What is PDV (PVV)?

PDV - the time it takes for the collision signal to propagate from the farthest node in the network - the time of the double turnover (Path Delay Value)

PVV - reduction of interframe interval (Path Variability Value)

What is the PDV Limit (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 slots is there a sufficient safety margin for PDV? 4

When is it necessary to calculate the maximum number of repeaters and the maximum network length? Why can't we just apply the “5-4-3” or “4-hubs” rules?

When different types of transmission media

List the basic conditions for the correct operation of an Ethernet network consisting of segments of different physical nature.

number of stations no more than 1024

the length of all branches is not more than the standard

PDV not more than 575

PVV- when passing a sequence of frames through all repeaters, there should be no more than 49 bit intervals

What is the segment base when calculating PDV?

Repeater delays

Where in the worst case does the collision take place: in the right, left, or intermediate segment?

In the right - the host

When do you need to calculate PDV twice? Why?

If there are different segment lengths at the far ends of the network, because they have different base latency values.

Brief description of the Token Ring LAN.

Token Ring (token ring) - a network technology in which stations can transmit data only when they own a token that continuously circulates 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 Token Ring network technology.

The Token Ring network was proposed by IBM in 1985 (the first option appeared in 1980). The purpose of Token Ring was to network all types of computers manufactured by the company (from PCs to mainframes).

What is the international standard for Token Ring networking?

Token Ring is currently an international IEEE 802.5 standard.

What 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 the MSAU Multiple Access Device?

The MSAU hub is a self-contained unit with 8 connectors for connecting computers using adapter cables and two outer connectors for connecting to other hubs using trunk cables.

Several MSAUs can be constructively 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 bi-directional links.

Draw the structure and 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 connect the MSAU in a ring (Figure 3.3), in contrast to the unidirectional trunk cable, as shown in Figure 3.2.

Each LAN node receives a frame from a neighboring node, restores signal levels to nominal, and transmits the frame to the next node.

The transmitted frame can contain data or be a marker, which is a special service 3-byte frame. The node that owns the token has the right to transfer data.

When the PC needs to transmit a frame, its adapter waits for the token to arrive, and then converts it into a frame containing data generated according to the protocol of the corresponding layer and transmits it to the network. The packet is transmitted over the network from adapter to adapter until it reaches the destination, which sets certain bits in it to confirm that the frame was received by the destination, and relays it further to the network. The packet continues to travel through the network until it returns to the sending node, where the correct transmission is verified. 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 and logical topology of a Token Ring LAN?

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 along the ring until it returns to the node where it was originated.

Draw possible options for the structure of a Token Ring LAN.

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 a marker;

formation of a new marker after detecting the loss of a marker;

the formation of diagnostic personnel under certain circumstances.

When an active monitor fails, a new active monitor is assigned from many other PCs.

What mode (method) of token transfer is used on a 16 Mbps Token Ring LAN?

To increase network performance, Token Ring with a speed of 16 Mbps uses the so-called early token transfer mode (Early Token Release - ETR), in which the PC transmits the token to the next PC immediately after transmitting 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 frame types used on a Token Ring LAN.

marker; data frame; completion sequence.

Draw and explain the format of the token (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 - start sequence of the frame

BUT - initial delimiter - [J | K | 0 | J | K | 0 | 0 | 0]

UD - access control - [P | P | P | T | M | R | R | R]

UK - personnel management

AN - destination address

AI - source address

Data - data field

KS - checksum

PKK - sign of the end of the frame

KO - final limiter

SC - frame status

Completion sequence format

The structure of the Access Control field in a Token Ring LAN frame.

UD- access control(Access Control) - has the following structure: [ P | P | P | T | M | R | R | R ] where PPP is the priority bits;

the network adapter has the ability to assign priorities to the marker and data frames by writing in the priority bits 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 that 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 equal to 1, it means that the message or marker bypassed the LAN without finding the addressee; RRR- Reservation bits are used in conjunction with priority bits; The PC 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 frames and LLC frames?

Of the Criminal Code- frame control(Frame Control - FC) defines the frame type (MAC or LLC) and MAC control code; a single byte field contains two areas:

Where FF- frame format (type): 00 - for a MAC-type frame; 01 - for LLC level frame; (values ​​10 and 11 are reserved); 00 - unused reserve digits; CCCC- MAC-frame code MAC (physical control field), defining to what type (defined by the IEEE 802.5 standard) MAC layer control frames it belongs to;

Which field of the data frame indicates the MAC (LLC) type? In the UK field (see above)

The length of the data field in Token Ring LAN frames.

There is no special limitation on the length of the data field, although in practice it arises due to limitations on the permissible time for a network to be occupied by a separate workstation and is 4096 bytes and can reach 18 Kbytes for a network with a transmission rate of 16 Mbit / s.

What additional information and why does the Token Ring LAN frame end delimiter contain?

KO is an end limiter containing, in addition to a unique sequence of electrical impulses, two more areas 1 bit long each:

tween bit (Intermediate Frame), which takes values:

1 if the frame is part of a multi-burst transmission,

0 if the frame is the last or the only one;

error detected bit (Error-detected), which is set to 0 at the moment of creating a frame in the source and can be changed to 1 in case of an error detected while passing through the network nodes; thereafter, the frame is retransmitted without error control in subsequent nodes until it reaches the source node, which in this case will try to transmit the frame again;

How does Token Ring function when the error detected bit in the frame trailing separator is set to 1?

thereafter, the frame is retransmitted without error control in subsequent nodes until it reaches the source node, which in this case will try to transmit the frame again;

The structure of the packet status field of the Token Ring LAN data frame.

SC- (condition) frame status(Frame Status - FS) is a one-byte field containing 4 reserved bits (R) and two internal fields:

bit (indicator) address recognition (A);

bit (indicator) copy packet (C): [ ACRRACRR]

Since the checksum does not cover the SP field, each one-bit field in the byte is duplicated to ensure the reliability of the data.

The transmitting node sets bits to 0 A and WITH.

The receiving node after receiving the frame sets the bit A in 1.

If, after copying the frame to the buffer of the receiving node, no frame errors are detected, then the bit WITH also set to 1.

Thus, a sign of a successful frame transmission is the return of the frame to the source with bits: A= 1 and WITH=1.

A = 0 means that the destination station is no longer in the network or the PC is out of order (turned off).

A = 1 and C = 0 means that an error has occurred on the path of the frame from the source to the destination (this will also set the error detection bit in the trailing separator to 1).

A = 1, C = 1 and the 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 value of the "address recognition bit" ("packet copying bit to buffer"), equal to 1 (0), indicate?- See above

Is the maximum number of stations in one Token Ring LAN equal to ...?-256

What is the maximum distance between stations on 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.

Token Ring pros and cons.

Token Ring Advantages:

no conflicts in the data transmission medium;

guaranteed access time for all network users;

Token Ring network functions well even under heavy loads, up to 100% load, in contrast to Ethernet, in which access time increases significantly even at 30% load or more; this is extremely important for real-time networks;

the larger allowable size of the transmitted data in one frame (up to 18 Kbytes), in comparison with Ethernet, provides a more efficient network operation when transferring large amounts of data;

the real data transfer rate in the Token Ring network may turn out to be higher than in the ordinary Ethernet (the real speed depends on the characteristics of the hardware of the adapters used and on the speed of the network computers).

Disadvantages of Token Ring:

the higher cost of the Token Ring network compared to Ethernet, because:

more expensive adapters due to the more complex Token Ring protocol;

additional costs for the purchase 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 are there no conflicts in the data transmission medium (guaranteed access time for all network users)?

On a LAN with token access

Brief description of LAN FDDI.

The maximum number of stations in a ring is 500.

The maximum length of the network is 100 km.

Transmission medium - fiber-optic cable (twisted pair can be used).

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 single-mode fiber optic cable;

100 m - for twisted pair (UTP category 5);

100 m - for twisted pair (IBM type 1).

The access method is marker.

The data transfer rate is 100 Mbps (200 Mbps for full duplex transmission).

The limitation on the total length of the network is due to the limitation of the time for the complete passage of the signal along the ring to ensure the maximum allowable access time. The maximum distance between subscribers is determined by the attenuation of the 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 FDDI network technology.

The FDDI standard is focused on high data transfer rates - 100 Mbit / s. 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 provides for the use of optical fiber as a transmission medium, which provides:

high reliability;

flexibility of reconfiguration;

high data transfer rate - 100 Mbit / s;

long distances between stations (for multimode fiber - 2 km; for single-mode when using laser diodes - up to 40 km; maximum length of the entire network - 200 km).

What bandwidth is provided on the FDDI LAN?

Ethernet, consisting of segments of various types, many questions arise, primarily related to the maximum allowable size (diameter) of the network and the maximum possible number of different elements. The network will be operational only if propagation delay the signal in it will not exceed the limit value. It is determined by the chosen exchange control method CSMA / CD based collision detection and resolution.

First of all, it should be noted that to obtain complex Ethernet configurations from individual segments, intermediate devices of two main types are used:

• Repeater hubs (hubs) are a set of repeaters and do not logically separate the segments connected to them;
• 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 concentrator 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 operability 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 focus on them.

There are two basic models used when choosing and evaluating an Ethernet configuration.

Model 1 rules

The first model formulates a set of rules that must be followed by the network designer when connecting individual computers and segments:

1. A repeater or hub connected to a segment reduces by one the maximum number of subscribers connected to the segment.
2. A complete path between any two subscribers should include no more than five segments, four hubs (repeaters) and two transceivers (MAUs).
3. If the path between the subscribers consists of five segments and four concentrators (repeaters), then the number of segments to which the subscribers are connected should not exceed three, and the remaining segments should simply connect the concentrators (repeaters). This is the already mentioned "5-4-3 rule".
4. If the path between subscribers consists of four segments and three concentrators (repeaters), then the following conditions must be met:
   • the maximum length of a 10BASE-FL segment fiber-optic cable connecting hubs (repeaters) should not exceed 1000 meters;
   • the maximum length of a 10BASE-FL segment fiber-optic cable connecting hubs (repeaters) with computers should not exceed 400 meters;
   • computers can connect 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. Compliance with these rules is believed to guarantee acceptable network latency.

When organizing the interaction of nodes in local networks, the main role is assigned to the link layer protocol. However, in order for the data link layer to cope with this task, the structure of local networks must be quite definite, for example, the most popular data 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 of using simple structures of cable connections between computers in a local area network was in line with the main goal set by the developers of the first local area networks in the second half of the 70s. This goal was to find a simple and cheap solution for combining 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 the classic Ethernet technology. Its main advantages are:

1) increasing the bandwidth of network segments up to 100 Mb / s;

2) saving the Ethernet random access method;

3) maintaining a star-shaped network topology 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 today - to high-speed networks that maintain a significant continuity with a well-known technology: Fast Ethernet does not require a radical retraining of personnel and replacement of equipment at 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 systems:

1) 100Base-TX for two-pair cable on unshielded twisted pair UTP Category 5, or shielded twisted pair STP Type 1;

2) 100Base-T4 for a four-pair cable on an unshielded twisted pair UTP Category 3, 4 or 5;

3) 100Base-FX for multimode fiber optic cable.

Gigabit Ethernet 1000Base-T is based on twisted pair and fiber optic cable. Since Gigabit Ethernet is compatible with 10 Mbps and 100Mbps Ethernet, it is easy to migrate to this technology without investing heavily in software, cabling, and training.

Gigabit Ethernet is an extension of IEEE 802.3 Ethernet that uses the same packet structure, format and support for CSMA / CD, full duplex, flow control, and more, while delivering a theoretical 10x performance improvement. CSMA / CD (Carrier-Sense Multiple Access with 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 the 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 1000 Mbps transfer rates. The following modifications of the standard exist:

1) 1000BASE-SX - a fiber optic cable with a light wavelength of 850 nm is used.

2) 1000BASE-LX - a fiber optic cable with a light wavelength of 1300 nm is used.

Objectives of the work

The purpose of this work is to study the principles of Ethernet and Fast Ethernet technologies and the practical development of methods for assessing the performance of a network built on the basis of Fast Ethernet technology.

Theoretical information

Ethernet technology. The Ethernet specification was proposed by DEC, Intel and Xerox (DIX) in 1980, and a little later on it was based on the IEEE 802.3 standard.

The first versions of Ethernet vl.O and Ethernet v2.0 used only coaxial cable as the transmission medium. The IEEE 802.3 standard also allows the use of twisted pair and fiber optics as a transmission medium. In 1995, the IEEE 802.3u (Fast Ethernet) standard was adopted with a speed of 100 Mbit / s, and in 1997, IEEE 802.3z (Gigabit Ethernet - 1000 Mbit / s). In the fall of 1999 the standard IEEE 802.3ab - Gigabit Ethernet on twisted pair of category 5 was adopted.

In Ethernet notation (10BASE2, 100BASE-TX, etc.), the first element denotes the data transfer rate in Mbps; the second BASEB means that direct (unmodulated) transmission is used; the third B element denotes the rounded value of the cable length in hundreds of meters B (10BASE2 - 185 m, 10BASE5 - 500 m) or the type of transmission medium (T, TX, T2, B T4 - twisted pair; FX, FL, FB, SX and LX - fiber optic; CX - twinax cable for Gigabit Ethernet).

At the heart of Ethernet is Carrier Listening and Collision Detection Multiple Media Access - CSMA / CD

• (Carrier Sense with Multiple Access and Collision Detection), implemented by the adapters of each network node at the hardware or firmware level:
• all adapters have a medium access unit (MAU) - a transceiver connected to a common (shared) data transmission medium;
• each adapter of the node, before transmitting information, listens to the line until there is no signal (carrier);
• the adapter then generates a frame starting with a sync preamble followed by a self-sync (Manchester) binary stream;
• other nodes receive the sent signal, synchronize with the preamble and decode it into a sequence of bits;
• the end of the frame transmission is determined by the receiver B detecting that there is no carrier;
• in case of detection collisions(collision of two signals from different nodes) the transmitting nodes stop transmitting the frame, after which, at a random time interval (each through its own), they carry out a repeated transmission attempt after the line is released; at the nextB failure, the next attempt is made (and so on up to 16 times), and the delay interval B increases;
• the collision is detected by the receiver at a non-standard frame length B, which cannot be less than 64 bytes, excluding the preamble;
• a time gap must be provided between frames ( interframe or inter-packet gap, IPG - inter-packet gap) duration B 9.6 μs - the node does not have the right to start transmission earlier than after the interval B IPG, after determining the moment of loss of the carrier.

Definition 1. Collision domain- a group of nodes connected by a common transmission medium (cables and repeaters).

The length of the collision domain is limited by the propagation time of the signal between the nodes most distant from each other.

Definition 2. Collision domain diameter- the distance between the two terminal devices farthest from each other.

Definition 3. Bit interval- the time required to transmit one bit.

The bit interval on Ethernet (at 10 Mbps) is 0.1 µs.

Fast Ethernet technology. In Fast Ethernet technology, the bit interval is 0.01 µs, which gives a tenfold increase in the data transfer rate. At the same time, the frame format, the amount of data carried by the frame and the mechanism for accessing the data transmission channel remained unchanged in comparison with Ethernet.

Fast Ethernet uses a data transmission medium for operation at a speed of 100 Mbit / s, which in the IEEE 802.3u specification is designated "100BASE-T4" and "100BASE-TX" (twisted pair); "100BASE-FX" and "100BASE-SX" (fiber optic).

Networking rules

First model of Fast Ethernet network. The model is, in fact, a set of rules for building a network (Table L.1):

• - the length of each twisted pair segment must be less than 100 m;
• - the length of each fiber-optic segment must be less than 412 m;
• - if MP (Media Independent Interface) cables are used, then each of them must be less than 0.5 m;
• - delays introduced by the MP cable are not taken into account when assessing the temporal parameters of the network, since they are an integral part of the delays introduced by terminal devices (terminals) and repeaters.

Table L. 1

Maximum permissible collision domain diameter in Fast Ethernet

The standard defines two classes of repeaters:

• class I repeaters convert the input signals B to digital form, and upon transmission, re-encode the digital data B into physical signals; signal conversion in the repeater requires some time, so only one class I repeater is allowed in the collision domain;
• class II repeaters immediately transmit the received signals without any conversion, therefore, only segments can be connected to them using the same data coding methods; no more than two class II repeaters can be used in one collision domain.

The second model of the Fast Ethernet network. The second model contains a sequence of calculations of the network time parameters in the half-duplex mode of data exchange. The diameter of the collision domain and the number of segments in it are limited by the double turnover time required for the correct operation of the collision detection and resolution mechanism (Table L.2).

Table L2

Time delays of Fast Ethernet network components

The double-turnover time is calculated for the worst (in terms of signal propagation) path between two nodes in the collision domain. The calculation is performed by summing the time delays in segments, repeaters and terminals.

To calculate the double turnover time, multiply the segment length by the specific double turnover time of the corresponding segment. After determining the round-trip times for all segments of the worst-case path, add the latency introduced by the pair of end-nodes and repeaters. To take into account unforeseen delays, it is recommended to add 4 more bit intervals (bi) V to the result obtained and compare the result with 512. If the result does not exceed 512 bi, then the network is considered healthy.

An example of calculating the configuration of a Fast Ethernet network. In fig. L.28 is an example of one of the maximum permissible configurations of the Fast Ethernet network.

Rice. L.28. Example of a valid Fast Ethernet network configuration

The collision domain diameter is calculated as the sum of the lengths of the A (100 m), B (5 m) and C (100 m) segments and is equal to 205 m.The length of the segment connecting B repeaters can be more than 5 m, if the collision domain diameter does not exceed the allowed limit for this configuration. The switch (switching hub), which is part of the network (see Fig. L.28), is considered a terminal device, since collisions do not propagate through it. Therefore, a 2-kilometer segment of fiber-optic cable connecting this switch with a router (router), is not taken into account when calculating the diameter of the collision domain of the Fast Ethernet network. The network satisfies the rules of the first model.

Let us now check it using the second model. The worst paths in the collision domain are from DTE1 to DTE2 and from DTE1 to the switching hub. Both paths consist of three twisted-pair segments connected by two class II repeaters. Two segments have a maximum permissible length of 100 m. The length of the segment connecting the repeaters is 5 m.

Suppose that all three segments under consideration are 100BASE-TX segments and use Category 5 twisted pair cable. LZ shows the values ​​of the double turnover time for the paths consideredB (see Fig. L.28). Adding the numbers from the second column of this table, we get 511.96 bi - this will be the double turnover time for the worst path.

Table L.Z

Network double turnover time Fast Ethernet

It should be noted that in this case there is no safety stock of 4 bi, since in this example the worst values ​​of delays B are used (see Table L.2). Actual timing of FastB Ethernet components may vary for the better.

Task to complete

It is required to evaluate the performance of a 100-megabit Fast Ethernet network in accordance with the first and second models. Network configurations are given in table. L.4. The network topology is shown in Fig. L. 29-L.ZO.

Table L.4

Job options

	Segment 1	Segment 2	Segment 3	Segment 4	Segment 5	Segment 6
	100BASETX, 100 m	100BASETX, 95 m	100BASETX, 80 m		100BASETX, 100 m	100BASETX, 100 m

	Segment 1	Segment 2	Segment 3	Segment 4	Segment 5	Segment 6
	YUOVABE-TX, 15 m	YUOVABE-TX, 5 m	YUOVAEE-TX, 5 m	100V ABE-EX, 400 m	YUOVABE-TX, 10 m	YUOVABE-TX, 4 m
	YUOVABE-TX, 60 m	YUOVABE-TX, 95 m	YUOVABE-TX, 10 m	YUOVABE-TX, 10 m	YUOVABE-TX, 90 m	YUOVABE-TX, 95 m

Rice. L.29. Network topology 1

Rice. L. 30. Network topology 2

Let's note the main features of the development of Ethernet networks and the transition to Fast Ethernet networks (IEEE 802.3u standard):

• - tenfold increase in throughput;
• - preservation of the random access method CSMA / CD;
• - preservation of the frame format;
• - support for traditional data transmission media.

These properties, as well as support for two speeds and auto-sensing 10/100 Mbps, built into NICs and Fast Ethernet switches, allow for a smooth transition from Ethernet to faster Fast Ethernet networks, providing an advantageous succession compared to other technologies. Another additional factor for successful market penetration is the low cost of Fast Ethernet equipment.

Fast Ethernet architecture

Fast Ethernet layer structure (including MII interface and Fast Ethernet transceiver) is shown in Fig. 13. At the stage of development 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). Compared to the Ethernet standard, the encoding function (Manchester code) is performed by the physical signaling layer PLS (Fig. 5), which is located above the medium-independent interface AUI. In the Fast Ethernet standard, the encoding functions are performed by the PCS encoding 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. MII (medium independent interface) in Fast Ethernet is analogous to AUI in Ethernet. The MII interface provides communication between the negotiation and physical coding sublayers. Its main purpose is to simplify the use of different types of environments. MII interface assumes further connection of Fast Ethernet transceiver. A 40-pin connector is used for communication. The maximum distance over the MII interface cable should not exceed 0.5 m.

If the device has standard physical interfaces (for example, RJ-45), then the structure of the physical layer sublayers can be hidden inside the microcircuit with a large logic integration. In addition, deviations in the protocols of intermediate sublevels in a single device are permissible, with the main goal of increasing performance.

Physical interfaces Fast Ethernet

The Fast Ethernet IEEE 802.3u standard establishes three types of physical interface (Fig. 14, Table 6 Main characteristics of physical interfaces of the IEEE 802.3u Fast Ethernet standard): 100Base-FX, 100Base-TX and 100Base-T4.

100Base-FX. The standard for 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 full duplex communication channel.

• * - the distance is reached only in duplex communication mode.
• 100Base-TX. The standard for this physical interface assumes the use of an 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 present on a Fast Ethernet repeater.

Pairs 1 and 3 are used for transmission over copper cable. Pairs 2 and 4 are free. The RJ-45 port on the network card and on the switch can support, in addition to the 100Base-TX mode, the 10Base-T mode, or the auto-sensing function. Most modern network cards and switches support this function over RJ-45 ports and, in addition, can operate in full duplex mode.

100Base-T4. This type of interface allows providing a half-duplex communication channel over a twisted pair UTP сat. 3 and higher. It is the ability of an enterprise to migrate from Ethernet to Fast Ethernet without radical replacement of the existing cabling 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 a workstation and a 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 - along 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 direction or in the other direction. Transmitting a signal in parallel over three twisted pairs is equivalent to inverse multiplexing discussed in Chapter 5. The bit rate per channel is 33.33 Mbps.

Character coding 8B / 6T... If Manchester coding were used, the bit rate per twisted pair would be 33.33 Mbit / s, which would exceed the established 30 MHz limit for such cables. An effective reduction in the modulation frequency is achieved by using a ternary code instead of a direct (two-level) binary code. This code is known as 8B / 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 during the construction of small Fast Ethernet networks using 100Base-TX repeaters it has no advantages over 100Base-T4 (there is a collision domain, the bandwidth of which is not more than 100 Mbit / s), then during the construction of networks using switches, the disadvantage of the 100Base-T4 interface becomes obvious and very serious. Therefore, this interface is not as widespread as 100Base-TX and 100Base-FX.

Fast Ethernet device types

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, PMD, PMD and AUTONEG sublevels, and having, on the one hand, an MII interface, on the other, one of the environment-dependent physical interfaces (100Base-FX, 100Base-TX or 100Base-T4). Transceivers are used relatively rarely, as well as network cards, repeaters, switches with an MII interface are rarely used.

Network Card. The most widespread are network cards with a 100Base-TX interface to the PCI bus. Optional, but highly desirable, RJ-45 port features include 100/10 Mbps autoconfiguration and full duplex support. Most of the current cards being released support these functions. There are also network cards with 100Base-FX optical interface (manufacturers IMC, Adaptec, Transition Networks, etc.) - the main standard optical connector is SC (ST allowed) for multimode 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 for the case when there is a 100Base-T4 port. 100Base-TX / 100Base-FX converters are widespread. Due to the general trends in the growth of long-range broadband networks with the use of single-mode FOCs, the consumption of optical transceivers based on single-mode fiber has increased sharply in the last decade. Converter chassis that combine multiple individual 100Base-TX / 100Base-FX modules allow multiple converging fiber segments 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 retransmission, Fast Ethernet repeaters are divided into two classes:

• - Class I. Delay on double run RTD should not exceed 130W. 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 have more stringent double run delay requirements: RTD

Switch- an important device of corporate networks. Most modern Fast Ethernet switches support 100/10 Mbit / s autoconfiguration over RJ-45 ports and can provide full duplex communication on all ports (with the exception of 100Base-T4). Switches can have special additional slots for installing an up-link module. Optical ports such as Fast Ethernet 100Base-FX, FDDI, ATM (155 Mbit / s), Gigabit Ethernet, etc. can act as interfaces for such modules.

Large switch manufacturers Fast Ethernet companies are: 3Com, Bay Networks, Cabletron, DEC, Intel, NBase, Cisco, etc.

Ethernet, but also to the equipment of other, less popular networks.

Ethernet and Fast Ethernet Adapters

Adapter characteristics

Network adapters (NIC, Network Interface Card) Ethernet and Fast Ethernet can interface with a computer through one of the standard interfaces:

• ISA bus (Industry Standard Architecture);
• PCI bus (Peripheral Component Interconnect);
• PC Card bus (aka PCMCIA);

Adapters designed for the ISA system bus (backbone) were not so long ago the main type of adapters. The number of companies producing such adapters was great, which is why devices of this type were the cheapest. ISA adapters are available in 8-bit and 16-bit. 8-bit adapters are cheaper, while 16-bit adapters are faster. True, the exchange of information via 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 baud rates for efficient operation, are practically not available 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- 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 PCs, but also in PowerMac computers. In addition, it supports Plug-and-Play automatic hardware configuration. Apparently, in the near future, the majority of network adapters... The disadvantage of PCI in comparison with the ISA bus is that the number of its expansion slots in a computer is usually small (usually 3 slots). But it is precisely network adapters connect to PCI first.

The PC Card bus (formerly PCMCIA) is currently only used in notebook computers. In these computers, the internal PCI bus is usually not routed out. The PC Card interface provides a simple connection to a computer of miniature expansion cards, and the exchange rate with these cards is quite high. However, more and more laptops are equipped with built-in network adapters, as the ability to access the network becomes an integral part of the standard set of functions. These on-board adapters are again connected to the internal PCI bus of the computer.

When choosing network adapter oriented to a particular bus, you must first of all make sure that there are free expansion slots for this bus in the computer connected to the network. It is also necessary to evaluate the laboriousness of installing the purchased adapter and the prospects for the release of boards of this type. The latter may be needed in the event of an adapter failure.

Finally, there are more network adapters connecting to the computer via the parallel (printer) LPT port. The main advantage of this approach is that you do not need to open the computer case to connect the adapters. In addition, in this case, the adapters do not occupy the system resources of the computer, such as interrupt channels and DMAs, as well as the addresses of memory and I / O devices. 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 communicate with the network, thereby slowing down the computer.

Recently, more and more computers are found in which network adapters built into the system board. The advantages of this approach are obvious: the user does not have to buy a network adapter and install it in a computer. All you need to do is connect the network cable to an external connector on your computer. However, the disadvantage is that the user cannot select the adapter with the best performance.

To other important characteristics network adapters can be attributed:

• way to configure the adapter;
• the size of the buffer memory installed on the board and the modes of exchange with it;
• the ability to install a read-only 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);
• used by the adapter transmission speed over the network and the presence of the function of its switching;
• the possibility of using the adapter of the full-duplex exchange mode;
• compatibility of the adapter (more precisely, the adapter driver) with the network software used.

User configuration of the adapter was mainly used for adapters designed for the ISA bus. Configuration implies tuning to the use of computer system resources (I / O addresses, interrupt channels and direct memory access, buffer memory 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 launching 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 make self-test adapter. The selected parameters are stored in the adapter's non-volatile memory. In any case, when choosing parameters, you must avoid conflicts with system devices computer and with 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 very 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 the I / O devices. In this case, no additional configuration of memory addresses is required. The base address of the shared memory buffer must be specified. It is assigned to the area of ​​the computer's upper memory (