Wednesday, December 9, 2015
NETWORKING ACTIVITIES FOR COMPUTER SCIENCE/ENGINEERING - SIWES
CHAPTER FIVE
NETWORKING WITH EMPHASIS ON ETHERNET CABLING
The basic ideas in all types of communication are that there must be three ingredients for the communication to be effective. First, there must be two entities, dubbed as a sender and a receiver. These two must have something they need to share. Second, there must be a medium through which the sharable item is channeled. This is the transmission medium. When you link computers to share files and communicate and do all the things we like to do, you create a network. Networks range in size from the smallest and simplest network- two computers connected together- to the largest and most complex network of all- the Internet.
A network can be defined as a group of computers and other devices connected in some ways so as to be able to exchange data. Each of the devices on the network can be thought of as a node.
5.1 TYPES OF NETWORKS
· Local area networks
· Metropolitan area networks
· Wide area networks
5.1.1 LOCAL AREA NETWORKS
As its name implies, a local area network is a data communication network, typically a packet communication network, limited in geographic scope. Alocal area network generally provides high-bandwidth communication over inexpensive transmission media. A local area network (LAN) typically is confined to a single building, such as an office building, your home network, or a college campus.
Fig.5.1 LAN Architecture
5.1.2 METROPOLITAN AREA NETWORKS (MAN)
Between the LAN and WAN, there is also a middle network called the metropolitan area network (MAN) because it covers a slightly wider area than the LAN but not so wide as to be considered a WAN. Civic networks that cover a city or part of a city are a good example of a MAN. MANs are rarely talked about because they are quiet often overshadowed by cousin LAN to the left and cousin WAN to the right. Sites on a MAN are usually interconnected using fibre-optic cable and may carry voice as well as data traffic.
Fig.5.2 Metropolitan Area Network
5.1.3 WIDE AREA NETWORKS (WAN)
A wide area network (WAN) covers a large area and can have a substantial number of computers. It is a network that spans large geographical locations, usually to interconnect multiple Local Area Networks (LANs).
Fig.5.3 Wide Area Network
5.2 HOW ETHERNET CABLES ARE CONFIGURED
The cable used on an Ethernet network is described as UTP cable, which stands for unshielded twisted pair. Inside, the cable has eight cable cores arranged as four twisted pairs, but unlike the audio and video cables, there is no foil shielding around the inner cores. It is the twisting alone that provides a degree of isolationfrom interference from outside the cable and, allows the cable to carry data at very high rates up to a distance of 100 meters (300 feet). Often, the cable is named by its specification schedule of Category-5 (think of the worse hurricane level), which is abbreviated to Cat-5 or Cat-5E. Network cable is terminated with an RJ45 module (wall socket) or, an RJ45 plug. Cat-6 cable is very similar, but will allow even faster data transmission rates.
In the Ethernet cabling schemes, the Unshielded Twisted Pair cable is most certainly by far the most popular cable around the world. UTP cable is used not only for networking but also for the traditional telephone (UTP-Cat 1). There are 6+ different types of UTP categories and, depending on what you want to achieve, you would need the appropriate type of cable. UTP-CAT5e is the most popular UTP cable; it came to replace the well-known coaxial cable which was not able to keep up with the continuous growth for faster and more reliable networks. They are very good and make it easy to work with, install, expand and troubleshoot. Unlike the twisted pair cable, the coaxial cable is not as popular today as it was a few years ago; today the popularity contest has been dominated by twisted-pair cabling. Twisted-pair cabling gets its name by having four pairs of wires that are twisted to help reduce crosstalk or interference from outside electrical devices (Crosstalk is interference from adjacent wires). UTP cable uses small plastic connectors designated as registered jack 45, or most often referred to as RJ-45.
The RJ-45 connector is similar to the phone connectors, except that instead of four wires, as found in the home system, the network RJ-45 connector contains eight contacts, one for each wire in a UTP cable.
Fig.5.4 Unshielded twisted pair cable
5.2.1 DIFFERENT CATEGORIES OF UTP CABLING
Each category of UTP cabling was designed for a specific type of communication or transfer rate. The most popular today being CAT 5e, which can reach transfer rates of over 1000 Mbps or 1 gigabit per second (Gbps).
Fig.5.5 Table showing the UTP cable categories
Category 1/2/3/4/5/6 – a specification for the type of copper wire (most telephone and network wire is copper) and jacks. The number (1, 3, 5, etc) refers to the revision of the specification and in practical terms refers to the number of twists inside the wire (or the quality of connection in a jack).
CAT1 is typically telephone wire. This type of wire is not capable of supporting computer network traffic and is not twisted. It is also used by phone companies who provide ISDN, where the wiring between the customer's site and the phone company's network uses CAT 1 cable.
CAT2, CAT3, CAT4, CAT5 and CAT6 are network wire specifications. This type of wire can support computer network and telephone traffic. CAT2 is used mostly for token ring networks, supporting speeds up to 4 Mbps. For higher network speeds (100Mbps plus) you must use CAT5 wire, but for 10Mbps CAT3 will suffice. CAT3, CAT4 and CAT5 cable are actually 4 pairs of twisted copper wires and CAT5 has more twists per inch than CAT3 therefore can run at higher speeds and greater lengths. The "twist" effect of each pair in the cables will cause any interference presented/picked up on one cable to be cancelled out by the cable's partner which twists around the initial cable. CAT3 and CAT4 are both used for Token Ring and have a maximum length of 100 meters.
CAT6 wire was originally designed to support gigabit Ethernet (although there are standards that will allow gigabit transmission over CAT5 wire, that's CAT 5e). It is similar to CAT5 wire, but contains a physical separator between the 4 pairs to further reduce electromagnetic interference. Cat 7– Also called Class F, this is a fully-shielded cabling and supports up to 600 MHz. This is a relatively new type of cabling and isn’t used much.
5.2.2 NETWORKING TOOLS USED FOR ETHERNET CABLING
Apart from the UTP cable, in order to carrying out a successful Ethernet cabling configuration, there are certain tools the network engineer must have in place, These include:
· A crimping tool: A tool designed to crimpor connect a connector to the end of a cable. For example, network cables and phone cables are created using a crimping tool to connect the RJ-45 and RJ-11 connectors to the end of the cable.
Fig.5.6 A crimping tool
· RJ-45 connectors: An eight-wire connector used commonly to connect computers onto a local-area network (LAN). RJ-45 connectors look similar to the ubiquitous RJ-11 connectors used for connecting telephone equipment, but they are somewhat wider.
Fig.5.7 RJ-45 connector
· Ethernet cable tester: An Ethernet cable tester is a device that is designed to verify whether or not an Ethernet computer network cable is capable of successfully transferring data from "point A" to "point B." If you want to use your cable tester, you need only to make sure that the actual cable you want to test is hooked up correctly.
Fig.5.8a Ethernet cable tester Fig.5.8b Some networking tools and UTP cable
· Switch:
5.2.3 TYPES OF ETHERNET CABLES AND THE WIRING STANDARDS USED
There are two wiring standards for RJ-45 wiring: T-568A and T-568B. The two wiring standards are used to create a cross-over cable (T-568A on one end, and T-568B on the other end), or a straight-through cable (T-568B or T-568A on both ends). The RJ45 cable uses only 2-pairs of wires: Orange (pins 1 & 2) and Green (pins 3 & 6). Pins 4, 5 (Blue) and 7, 8 (Brown) are NOT used. For Straight-through cable, as its name suggests, connects pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3, and pin 6 to pin 6, while Cross-over cables are used to connect TX+ to RX+, and TX- to RX-, which connects pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin 1 and pin 6 to pin 2. The unused pins are generally connected straight-through in both straight-through and cross-over cables.
T-568B T-568A
-------------------------- ------------------------
Pin Color Pin Name Color Pin Name
--- ------------- -------- ------------- --------
1 Orange Stripe Tx+ Green Stripe Rx+
2 Orange Tx- Green Rx-
3 Green Stripe Rx+ Orange Stripe Tx+
4 Blue Not Used Blue Not Used
5 Blue Stripe Not Used Blue Stripe Not Used
6 Green Rx- Orange Tx-
7 Brown Stripe Not Used Brown Stripe Not Used
8 Brown Not Used Brown Not Used
Fig.5.9 T568A and T568B Wiring Standards for a Straight-through cable
Based on my SIWES programme, I carried out the Ethernet cabling configuration for straight-through cable and cross-over cable for similar devices. In a nutshell, there are three types of Ethernet cables, these include:
· Straight-through cable: A Straight-through cable is a type of twisted pair copper wire cable for local area network (LAN) use for which the RJ-45 connectors at each end which have the same pin out (i.e., arrangement of conductors). It is identical to crossover cable, except that in the latter the wires on the cable are crossed over so that the receive signal pins on the connector on one end are connected to the transmit signal pins on the connector on the other end. Straight-through cable is also commonly referred to as patch cable. Straight-through cable is used to connect computers and other end-user devices (e.g., printers) to networking devices such as hubs and switches. It can also be used to directly connect like devices (e.g., two hubs or two switches) if the cable is plugged into an uplink port on one (but not both) of the devices. Four wires are used in straight-through cable to connect Ethernet devices. Ethernet cabling for straight-through cable usually uses only four wires when sending and receiving information on the network. The four wires of the eight that are used are wires 1, 2, 3, and 6. When you configure the wire for the same pin at either end of the cable, this is known as a straight-through cable. Wires 1 and 2 are used to transmit data (TX) from the computer, while wires 3 and 6 are used to receive information (RX) on the computer. The transmit pin on the computer is connected to the receive pin (RX) on the hub via wires 1 and 2. This is important because we want to make sure that data that is sent from the computer is received at the network hub. We also want to make sure that data sent from the hub is received at the computer, so the transmit pins (TX) on the hub are connected to the receive pins (RX) on the computer through wires 3 and 6. This will allow the computer to receive information from the hub.
The straight-through cable is used to connect
· Host to switch or hub
· Router to switch or hub
Straight-through Ethernet cable
Hub/Switch Host
1 1
2 2
3 3
6 6
Fig.5.9 Drilling holes to trunk crimped Ethernet cables
· Cross-over cable: A crossover cable is a cable that is used to interconnect two computers by "crossing over" (reversing) their respective pin contacts. At some point, you may need to connect two computer systems directly together without the use of a hub, from network card to network card. To do this, you would not be able to use a straight-through cable because the transmit pin on one computer would be connected to the transmit pin on another computer. In order to connect two systems directly together without the use of a hub, you will need to create a crossover cable by switching wires 1 and 2 with wires 3 and 6 at one end of the cable. The transmit pins on Computer A are connected to the receive pins on Computer B, thus allowing Computer A to send data to Computer B. The same applies for Computer B to send to Computer A—pins A and B on Computer B are wired to pins 3 and 6 on Computer A so that Computer A can receive data from Computer B, i.e you connect pins 1 to 3 and 2 to 6 on each side of the cable.
The crossover cable can be used to connect
· Switch to switch
· Hub to hub
· Host to host
· Hub to switch
· Router direct to host
Fig.5.92 T568B Wiring Standards for Crossover and Straight-through cables
· Rollover Cable: A rollover cable uses 8 pins but is different from a straight-through cable or crossover cable that you may build. With a rollover cable, pin 1 on one end connects to pin 8 on the other end. Pin 2 connects to pin 7, pin 3 connects to pin 6, and so on. This is why it is referred to as a rollover, because the pins on one end are all reversed on the other end as though one end of the cable was just rotated or rolled over. Yost cables (also known as Cisco console cable) as it is sometimes called isn’t used to connect any Ethernet connections together; you can use a rolled Ethernet cable to connect a host to a router console serial communication (com) port mostly when carrying out a router configuration, thus they are most commonly used to connect to a device to a router or switch’s console port to make programming changes to the device. This allows a programmer to make a connection to the router or switch, and program it as needed. Unlike crossover and straight-wired cables, rollover cables are not intended to carry data but instead create an interface with the device.
