The HARDWARE 2 course: server, network and communication

4.1. Introduction - 4.2. Ethernet, IEEE 803.3 10 base 5 - 4.3. Ethernet, IEEE 802.3 10 base 2 - 4.4. Ethernet, IEEE 802.3 10 Base T RJ45 - 4.5. Ethernet 100 bases T RJ45, fast Ethernet - 4.6. Giga Ethernet - 4.7. 10 Gigabit - 4.8. Network card - 4.9.Duplex Half and Duplex Full - 4.10. Connection RJ45 - 4.11. Networks RJ45, problems of connection, tests equipments - 4.11. Mac address

4.1. Introduction

Connection between computers requires a network interface card (NIC) established in each PC witch are connected with twisted pair or fiber optic cable. The most current local area networks boards are Ethernet type. This chapter gathers all types of Ethernet connection and wiring (manufacture, precaution...).

The Ethernet network appeared at the end of the Seventies in the United States. This network, most widespread from the local area networks, was born from the complementary experiments of DEC, INTEL and Xerox, well before standardization. This implies that the main part of the road bases of OSI model is not specified.

All the PC can communicate on the cable network at the same time. It is necessary thus a rule if two stations would start to communicate at the same time. The method used is the contention. The principal method of application in local area networks is the CSMA/CD (Carrier Sense Multiple Access), with collision detection (CD). It is that of the Ethernet networks. It consists for a station, at the moment when it emits, to listen if another station is not also emitting. If it is the case, the station ceases emitting and re-emits its message at the end of a fixed time. This method is random, in the sense that one cannot envisage time necessary to a message to be emitted, transmitted and received.

4.2. Ethernet, IEEE 803.3 10 Base 5

10 Base 5 version (10Mbps on coaxial cable with a maximum length by segment of 500 meters) is the version of origin of Ethernet, it is represented below:

Each station is equipped with an network "Ethernet" adapter (NIC, Network Interface Card). This equipment ensures the physical adaptation and manages algorithm CSMA/CD. As in all connections coaxial, the 2 ends of the cable are connected to a stopper (it is also called resistance of termination), a specific resistance which attenuates the reverberation of the signal on the cable.

The drop cable consists of twisted pairs and can have a maximum length of 50 meters. The coaxial cable is a thick cable of yellow color an half-inch in diameter of the type BELDEN 9580. The overall length of the network can reach 2,5 kilometers with 100 points of connection.

The 10 base 5 is used practically more only in the disturbed environments (electromagnetic radiation) or when one wants to guarantee the confidentiality of the exchanges (non radiation for coaxial cable).

4.3. Ethernet, IEEE 802.3 10 Base 2

A cut-rate version of wiring IEEE 802.3 10 base 5 was carried out with fine coaxial cable (Thin Ethernet). This type is represented below:

This physical architecture of network is recommended for the realization of small networks 2 or 3 PC. Each network adapter is connected to the cable via a connector in T of the type BNC. The 2 ends of the network are closed by a resistance of termination (stopper) of 50 ohms. This termination is not obligatory, but the speed transmission is definitely reduced since this resistance eliminates the "reverberations on the cable": the transmitted signal returns on the cable and the stations believing in a true signal wait until the line is free.

The connection is easy to start, nevertheless, as soon as one installs 3 PC or more, the speed transmission strongly decreases. This solution is thus to used only in specific cases.

The maximum length of the network is 185 meters, with a maximum of 30 equipments connected. The minimal distance between 2 connections is 50 centimeters. This wiring is often used to connect "the small station in bottom of factory". This solution does not function badly but it is absolutely necessary to separate this part of the others with for example a HUB. The reason is not data-processing but related to the electromagnetic disturbances, storms... If the cable takes these disturbances, all the network disturbed or is broken down.

4.4. Network Ethernet, IEEE 802.3 10 Base T

With the problems of wiring, AT&T imagined to re-use preexistent telephone wiring in the office buildings for the realization of the network. That imposed two constraints: one of flow, the other of distance. The network thus carried out functioned with 1Mbps, the stations were connected on star concentrators via repeaters (hub) and outdistances it between the hub and a station was limited to 250 meters. This architecture (802.3 1 base 5 or Starlan) completely obsolete evolved to a version 10MBps (802.3 10 base T). The following figure presents network 10 bases T.

    Ethernet 10 bases T uses a wiring per telephone pair (8 pairs is 4 wire). Its maximum speed is 10 Mbps (méga bit a second). Wiring is of star type. The nodes consist of concentrators. This solution is currently most widespread, but if the standard evolved/moved of speed.

Wiring under RJ45 in 10BaseT requires 4 wires (for 8 accessible in the connector). The wire are sold done everything in the trade, but one can easily manufacture cables RJ45. Generally, 8 wire are inserted but it is not obligatory, in particular if you wish to use a cable for 2 stations (attention with the disturbances).

If one does not use a concentrator (connection of 2 stations) or to connect 2 concentrators between-them, the wire must be of type cables cross like below. You must respect the polarities and the pairs must be paired.

Why respect wiring per pairs.

The signal at the beginning of the board network is sent on the T+ form and the form T (reversed signal). Let us suppose a parasite which appears on the cable during the transmission of the signal. It is of the same direction on 2 wire. As a pair is twisted, the electric disturbances related to induced currents will be generally different from one pair to another. For recall, the passage of an electrical current in a son produces fields electromagnetic in its entourage and of this fact a current in close electric wire induces.

Let us reverse T(-). the signal and the parasite are reversed. While adding T(+) and T(-) reversed, the double signal but the parasite is removed.

Material necessary for a cable RJ45:

• Cable 4 twisted pairs category 5
• Connectors RJ45 to crimp category 5
• Sleeves rubber, to avoid dividing the cable.
• A grip to be crimped and if the grip does not include it: cutting pliers and a grip to be stripped.

Procedure to be followed:

• To thread the sleeve on the cable.
• To strip the external sheath on approximately 15 mm.
• For the cord crossed, Trier wire according to the diagram below.

Cable cross connection RJ45 (10 base T and 100 base T)

• To maintain wire in place by respecting the pairs and to cut them well on line. There must remain approximately 13mm, the end should not form an arc of circle.
• To place wire in the connector while supporting on the whole of the wire so that the pairs return until the bottom of the connector.
• To crimp the connector.
• To plug in the sleeve.

Check, by transparency, the good state of your assembly, if the wire arrive well in end of connector.

4.5. 100 Bases TX and 100 Base T4, Fast Ethernet

Since 1992, one uses the 100 base T. The theoretical flow is 100 Mbps. The fast Ethernet also obliges to use concentrators of the hub type or switch.

One finds 2 category of 100 Base T: 100 Base T4 and 100 Base TX. The 100 Base TX (most widespread) uses same the 2 pairs that the 10 Base T On the other hand, the 100 T4 Base uses the 4 pairs. Nevertheless, the 100 T4 base (almost more used) simultaneously uses 3 pairs for the emission and the reception. This mode cannot thus use Full Duplex (simultaneous bidirectional communication). It can be used on cable of category 3, 4 or 5.

In 100 base TX, wiring is the same one as in Ethernet bases 10, only the cable must be of better quality (category 5) and the 4 others wire must be connected according to the colors below. Attention which each "cabler" often uses his own code of colors. The cross cables use the two same crossings that into 10 base T.

Normal and cross cable RJ45 100 Base TX diagram	Normal and cross cable RJ45 100 T4 Base diagram

4.6. Ethernet gigabit.

If at the beginning, the gigabit used an optical fibre connection, it is replaced by a connection of the type RJ45 of class 5e (with a limitation of distance limited to 100 meters). The gigabit uses the same format of screens of data that the 10 Base - T and the 100 Base TX and the same anti-collision protocol, namely the CSMA-CD (Carrier Sense Multiple Access with Collision Avoidance). This standard makes it possible each computer to announce that it will transmit a message before transmitting the data on the network (what avoids the collisions).

Network adapter INTEL PCI-X 64 bits - 133 MHz

1000 Base SX

(1 Gbit/s on multimode optical fibre (MMF): 500 m)

1000 Base LX
(1 Gbit/s on monomode optical fibre (SMF): 3000 m)

1000 Base C
(1 Gbit/s out of 4 pairs UTP5: 25 m)

1000 Base T - 1000 Base TX IEEE 802.3 ab ratified on June 26, 1999

1 Gbit/s on cable category 5, transmission out of 4 pairs (250 Mbits/paire) over a 100 meters length)

    Wiring on twisted pairs of 1000 C and 1000 TX is identical to that of the 100 T4 Base, including for the Ethernet cables cross RJ45.

4.7. Network 10 Giga hertz

    Currently in court of development, it should compete with on the lines at high speeds, connections ATM. 

4.8. Ethernet Network adapter

One finds in the PC three types of boards networks: 10, 100 and Giga Ethernet. The first boards bases 10 of 3Com used only the connectors coaxial and a specific connector. Currently, the network adapters 10 MB are connected into coaxial and RJ45. On the other hand, the boards does not base 100 do not use any more but the RJ45.

Consequently, the use of a network into coaxial obliges the use of a board bases 10. As the use of a cable RJ45 requires the use of a concentrator, this one and the boards connected must use the same parameters is of the 10 MBb/s. Concentrators 10 generally include (but not each time) a coaxial connector and the number specific to the concentrator of wiring RJ45. Concentrators 100 allow the connections with 100 Mb, on some, they also detect boards 10 Mb.

The networks boards are also characterized by the internal bus used: ISA and PCI. As a recall, there have sometimes incompatibilities between the boards PCI 3.3V and mother board in 5V (old Pentium). Like all boards PC, they are characterized by an address and an interruption for which are recognized by the PC. Certain adapter include a socket making it possible to insert Eprom to start the PC via the network (without hard disk). This solution is used little.

Each Ethernet network adapter in RJ45 includes 2 LED. The first, generally green, announces that the lan is connected on a concentrator via a cable. The second, orange or green, announce the transmission/reception of data.

The current network adapter make it possible to commutate on each Ethernet speed automatically (10 or 100).

    With very rare exceptions (hub and switch the bottom-of-the-range one), with a board in connected in RJ45 on a concentrator, it (them) LED must ignite on the board and the HUB, Switch, Routeur. As a technician hardware, that means that the access network is badly parameterized, it is spring of the administrators networks, except if the speed of connection is low.

4.9. Duplex Half and Duplex Full.

A Ethernet network adapter can be of type Half Duplex and Full duplex. The boards Half Duplex (normal) cannot emit and receive at the same time. By counter the boards Full Duplex (and the switch associated) can emit and receive at the same time on channels (cables) different. This solution makes it possible to double the rate of transfer on the Ethernet network. For example, a board 100 bases TX (100 T4 base does not authorize duplex Full) goes authorized a rate of transfer of 200 Mbps for 100 in the duplex case half.

It is necessary to slow down the network (to pass into 100 Half mode or even in the event of disturbances network to oblige the board 100 Base TX to work into 10 base T). The parameter setting is done in the parameters networks by using the properties of the network adapter. Here for example the case of a Ethernet adapter at base of the circuit Realtec RTL8139D (10base T and 100 automatic base TX).

4.10. Wiring RJ45 Ethernet, rules, problems of connections and tests equipments

Cables RJ45 can be bought done everything. Nevertheless, in professional wiring, they are integrated in chutes, pass through walls... The solution consists in buying a grip, the connectors (with protections), the cable and to respect strictly the colors of wiring RJ45 above.

To connect two structures between them by cables brings always various types of problems.

The first remains the maximum conditions of operating. It is trying to put a wire longer than that envisaged by the standard between Hub (or a switch) and computer (100 meters for one T bases 10 or 100). First error.

If the cable is bought done everything, connection is generally good. This is valid for the small internal networks but is seldom the case for the industrial networks. As a tester of wiring network is worth easily the price of a small sporting car, better is worth to cable correctly in advance.

Each connection is limited by the number of HUBS in cascade. For a connection 10 bases T, the maximum number between 2 stations east of 4. On the other hand, it is 2 into 100 base T

In the last, cable RJ45 must be correctly posed. Among the encountered problems, one finds:

• cable network cut or scratched or folded.
• more underhand: the cable passes to with dimensions from electric cables which disturb the signal, beside fluorescent tubes or neon (minimum 50 cm). Proximity of electric motors of strong powers. The table below shows the distances minimum between the cables networks and the electric cables according to the distance.

Spacing enters the cables current strong (electrical supply network, neon) and low current (Ethernet network)

For a cable RJ45 low length, one could put the electric cables and networks in the same chutes. This would be to forget the electric safety requirements which prohibit to insert electric cables and telephone (low voltage) in the same chutes, even if it is common in the suspended ceilings in industries.

One finds on the market various types of apparatuses of tests of the cables networks.

The first network tests equipment type functions like an ohmmeter on 8 lines. It is important that the apparatus can be divided into two part (a part of control and a case of termination) to allow the tests of cables posed. These equipments generally make it possible to detect the right cables and the cross cables as well as other connectors (RJ11, RJ45, USB...). These apparatuses are reliable only up to one certain points. It check only if connection is correct, not if the connection is correct. If the apparatus detects an error of wiring, the son is to be started again. If it does not detect an error, that does not mean inevitably that the cable is good. A bad contact will be often regarded as good by the tester, but not of connection network.

Here, a test of cross cable. The left part takes again the module of order, the right part, the detachable termination. The 8 Led above indicates if the wire individually are correct. In the left part gives indications on connections. Shorts (cable cut or bad connection on at least a son). CONNECTED which the cable is right or cross connection. NO CONNECTION which the cable is not inserted. The price varies from 100 to 150€.

The second type functions with the manner of a network card. These equipment test the line (and not only the wire the apparatus is connected at the end of a cable and tests the connection on a HUB or a switch. In this direction, they are more effective. They are a little more expensive.

The third type of tester network resembles a minicomputer. Does the price return easily to 10.000 € and is thus not with the range of everyone. The method of test is identical to that of the first apparatuses. They offer the same possibilities that the apparatuses of the first group but allow moreover:

• effective tests of the poor contacts or the cuts on each cable.

• cable length

• in the event of cut of a son (or of several), the distance to which it is cut.

• various disturbances which forward on the cable (electric disturbances).

4.11. MAC address

    Each network adapter is characterized by a MAC address. This address is single for all the boards networks in the world. It consists of 6 bytes of the type XX.XX.XX.XX.XX.XX or each XX vary from 0 to 255. The address is often given in form hexadecimal. For example 4D.FF.56.D2.AF.26.

    In Starts - > to carry out, type order WINIPCFG (present in the Windows repertory under Windows 98) or ipconfig/all in a window DOS (Windows 2000 and XP) for given the following your board network.

    The address Mac FF.FF.FF.FF.FF.FF is particular, the data are sent to the whole of the network. It is the address of Broadcast.

    The Ethernet protocol uses this MAC address to make communicate equipment between them via network. When a machine wants to speak with another, it sends a package on the network, containing the address MAC destination, the address MAC source, the length of the packet, the data and the CRC (Cyclic Redundancy Checking), an error control, ...

    The MAC address has priority on address IP. When a communication network was established under Ethernet, order DOS arp - A makes it possible to find the MAC address of the other PC of the network.

1. Network hardware course - 2. Network hardware Introduction - 3. Base of transmission -  4. Ethernet - 5. Switch, router, ... Ethernet - 6. Internet connections - 7. Networks servers - 8. SCSI, SAS, RAID - 9. Backup Tape drives, NAS, ... - 10. Hardware Security - 11. Wireless and Wifi - 12. UPS, Inverter, Power Supply - 13 . Corporate network - 14. Alternative technologies - 15. Touch Screen, video projector 17. Exercise: hardware firewall

The Hardware 1 course: computers and peripherals, Complete technical training

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