Thick Ethernet Cabling example essay topic

Bob Metcalfe of the Xerox Corporation developed the first experimental Ethernet system in late 1972. The goal of the Ethernet was to interconnect the Xerox Alto Aloha Network. The experimental Ethernet was used to link Altos workstations, servers, and laser printers. Data transmission of the Ethernet was 2.94 Mbps. In 1973, Metcalfe changed the name to 'Ethernet,' to make it clear that the system could support any computer, and not just Altos, and to point out that his new network mechanisms had evolved well beyond the Aloha system.

He chose to base the name on the word 'ether' as a way of describing an essential feature of the system. The physical medium (cable) carries bits to all stations, much the same way that the old 'luminiferous ether' was once thought to propagate electromagnetic waves through space. The Ethernet is a LAN (Local Area Network) technology that uses a shared bus topology, and Carrier Sense Multiple Access / Collision Detection access. It consists of a single, long cable, named the bus, to which computers, or sometimes referred to as workstations, are attached. Ethernet signals are transmitted serially, one bit at a time, over the bus and are received by every attached station. Data in the Ethernet is transmitted in the form of a frame, or packet.

The frame consists of a set of bits organized into several fields. These fields include address fields, a variable size data field that carries from 46 to 1,500 bytes of data, and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact. The first two fields in the frame carry 48-bit addresses, called the destination and source addresses. The Destination Address contains the physical address of the station to which the frame is being sent. Any signal sent across the shared network reaches all attached workstations. However, communication doesn't usually involve all workstations.

To allow direct communication between stations the addressing scheme is used. Each workstation is assigned a unique numeric value, called a physical address or media access control address (MAC address). Although sharing allows all workstations to receive a copy of a frame, the hardware of each workstation checks the address of each incoming frame to determine whether it should accept the frame. The Source Address contains the physical address of the workstation that sent the frame. Including the sender's address in each frame makes it easy for the recipient to generate a reply. The I controls the assignment of these addresses by administering a portion of the address field.

The I does this by providing 24-bit identifiers called 'Organizationally Unique Identifiers' (OU Is). The organization, in turn, creates 48-bit addresses using the assigned OUI as the first 24 bits of the address. A unique 48-bit address is commonly pre-assigned to each Ethernet network interface card when it is manufactured. As each Ethernet frame is sent onto the shared signal channel, all Ethernet workstations look at the first 48-bit field of the frame, which contains the destination address.

The workstations compare the destination address of the frame with their own address. The Ethernet workstation with the same address, as the destination address in the frame will read in the entire frame and deliver it to the networking software running on that computer. All other network workstations will stop reading the frame when they discover that the destination address does not match their own address. After each frame transmission, all workstations on the network must contend equally for the next frame transmission opportunity.

This ensures that access to the network cable is fair, and that no single workstation can lock out the other workstations. Access to the shared cable is determined by the medium access control (MAC) mechanism embedded in the Ethernet network interface card located in each station. The medium access control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMA / CD). Computers attached to a bus network must coordinate to ensure that only one computer sends a signal at any time or the signals will collide. The workstations are notified of the collision, and instantly reschedule the signal transmission using a specially designed algorithm. As part of this algorithm, the workstations involved each choose a random time interval to schedule the retransmission of the frame, which keeps the stations from making transmission attempts at the same time.

The CSMA / CD protocol ensures that each workstation must wait until there is no signal on the cable, before it can begin transmitting. If another workstation is transmitting, there will be a signal on the cable, which is called carrier. All other interfaces must wait until the carrier ceases before trying to transmit, and this process is called Carrier Sense. However, if both workstations begin to retransmit the moment the bus becomes free, there will be another collision. To avoid this situation the Ethernet uses the binary exponential back-off algorithm. The Back-off Algorithm ensures after a collision each workstation will delay a random amount of time between 0 and d (d is some standard delay value) before attempting to retransmit.

If another collision occurs, each workstation doubles the range from which the delay is chosen. The random delay will now be between 0 and 2d. This will repeat if another collision occurs. After each collision the range of the random delay increases exponentially, therefore the probability of collision rapidly decreases and after little iteration becomes negligible. All Ethernet workstations are equal in their ability to send frames onto the network.

No workstation has higher priority. This is known as Multiple Access. Since signals take a finite time to travel from one end of an Ethernet system to the other, the first bits of a transmitted frame do not reach all parts of the network simultaneously. Therefore, it's possible for two workstations to sense that the network is free and to start transmitting their frames simultaneously. When this happens, the Ethernet system has a way to sense the 'collision' of signals, stop the transmission, and resend the frames. This is called Collision Detect.

The CSMA / CD protocol is designed to provide fair access to the shared cable so that all stations get a chance to use the network. After every packet transmission, all workstations use the CSMA / CD protocol to determine which workstation gets to use the Ethernet channel next. The Ethernet uses "a best effort" data delivery system. The workstation doesn't need to establish a connection before sending a packet. To keep the complexity and cost of a LAN to a reasonable level, no guarantee of reliable data delivery is made. While the bit error rate of a LAN is carefully engineered to produce a system that normally delivers data extremely well, errors can still occur.

A burst of electrical noise may occur somewhere in a cabling system, for example, corrupting the data in a frame and causing it to be dropped. Or a LAN cable may become overloaded for some period of time, which in the case of Ethernet can cause 16 collisions to occur on a transmission attempt, leading to a dropped frame. It is up to the high-level protocol that is sending data over the network to make sure that the data is correctly received at the destination computer. High-level network protocols can do this by establishing a reliable data transport service using sequence numbers and acknowledgment mechanisms in the packets that they send over the LAN. The Ethernet supports four different cabling or media types to connect between the NIC and the network. These types are Thick Ethernet Cabling, Thin Ethernet Cabling, Twisted Pair Cabling, and Fiber Optics Cabling.

Thick Ethernet Cabling, the original Ethernet cabling type, is also known as Thicknet, because the communication medium consists of a thick coaxial cable. The cable is about. 5 inches thick and can carry a signal a maximum length of about 1640 feet attenuation occurs. Insulation, a braided metal shield, and an outside shield that consists of rubber, plastic, or Teflon surround the conductive core wire. The formal name of this type is 10 Base 5. The transceiver is an analog electronic device, which handles analog signals.

It is attached directly to the Ethernet cable, and a separate cable, known as Attachment Unit Interface (AUI) cable, connects the transceiver to the NIC in the computer, which handles the digital aspects of communication. Each end of the Ethernet coaxial cable must have a termination device, called terminator, installed. When the signal reaches the terminator, the signal is discarded. Termination is essential to correct operation of the network, because the end of a non-terminated cable reflects signals back along the cable. When the reflected signal reaches the sending station, the sender will assume that it was caused by another station and will invoke the back-off algorithm to handle the collision. This makes the transmission along the non-terminated cable virtually impossible.

ThickNet cabling can be inconvenient, for instance, in case of multiple computers in a single room. Each computer needs an individual transceiver, which must be spaced along the Ethernet cable. To solve this problem engineers have developed an electronic device called a connection multiplex or that allows multiple computers to attach to a network through a single transceiver. Instead of attaching the AUI cable of each computer to an individual transceiver, it connects to a port of the multiplex or. The multiplex or is connected to the Ethernet by a single AUI cable. Since the multiplex or delivers exactly the same electrical signals as a transceiver, a computer doesn't know whether it's attached to a transceiver or a multiplex or.

Thin Ethernet cabling, uses an easier to install thinner, more flexible coaxial cable than the original thick cabling. This cabling is about. 25 inch thick and can carry a signal up to about 607 feet before attenuation occurs. Its' formal name is 10 Base 2 and it's also known as Thinnet. Thinnet generally costs less than Thicknet. In Thinnet the hardware that performs the transceiver function is built into the NIC, so no external transceivers are needed.

Also Thinnet doesn't use an AUI cable to attach the NIC to the communication medium. Instead, Thinnet attaches directly to the back of each computer using a BNC connector. The medium is a flexible cable than connects from the NIC on one computer directly to the NIC on another computer. Although they differ physically, the thick and thin Ethernet cables have similar electrical characteristics. Twisted Pair cabling differs dramatically from both thick and thin Ethernet.

It's also known as, 10 Base. Twisted Pair cabling consists of two copper-insulated strands twisted around each other in order to cancel electrical noise from adjacent pairs. If a pair has a shield then it is referred to as a shielded twisted pair. If it does not have a shield then it is referred to as an unshielded twisted pair. Twisted pair cabling has a maximum length of 100 meters before attenuation occurs.

Twisted Pair cabling doesn't have a shared physical medium like the other cabling schemes. Instead, it has an electronic device, called an Ethernet hub, which serves as the center of the network. Twisted pair cabling using RJ-45 connectors connects each computer to the hub. Electronic components in the hub simulate a physical cable, making the entire system operate like a conventional Ethernet. Fiber Optics cabling is also known as 10 Base.

This cabling consists of a thin cylinder of glass cladding. Each strand passes signal as pulses of light in one direction. So the cable must have two strands in two Kevlar fiber reinforced jackets. Fiber optic cabling is very secure and can carry a signal for up to 62 miles. This alternative is the most expensive, but it has excellent noise immunity and is used when running between buildings or widely separated hubs. Fiber optic cable is used to connect segments separated by long distances.

Though each form of media has a maximum length before attenuation occurs the Ethernet was designed to be easily expandable to meet networking needs. Devices such as repeaters and hubs link individual Ethernet media segments together in order to extend, split and / or regenerate the signal to create a larger Ethernet network. The Ethernet's physical layout of connected devices or topology can be categorized into the following basic types: bus, star, tree, or mesh. A bus topology uses a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium, that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

A bus topology works best with a limited number of devices. If more than a few dozen computers are added to a bus, performance problems will likely result. In addition, if the backbone cable fails, computers can still function as stand alone computers, but they cannot communicate with each other. The advantages to using a bus topology are inexpensive media, simple setup, and it's easy to extend.

A star topology features a central connection point called a 'hub' that may be an actual hub or a switch. Devices typically connect to the hub with unshielded twisted pair cabling. A star topology generally requires more cable than a bus, but there are advantages to using this topology. The advantages are that it's easy to add new computers, centralized monitoring and management are possible, and a failure in any cable will only take down one computer's network access and not the entire LAN. However, if the hub fails, the entire network fails.

A tree topology integrates multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the 'root' of a tree of devices. This bus / star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub ports) alone. In a mesh topology each computer is connected to every other computer by separate cabling. This allows for superior redundancy and reliability, as well as ease of troubleshooting. This type of topology is expensive and difficult to install because of the amount of cabling required.

The original Ethernet operated at 10 Mbps, a later version Fast Ethernet operates at 100 Mbps and the newest version Gigabit Ethernet operates at 1 Gbps. The Ethernet is the most popular physical layer LAN technology in use today. It is popular because it strikes a good balance between speed, cost and ease of installation. These benefits combined with wide acceptance in the computer marketplace and the ability to support virtually all-popular network protocols, make the Ethernet an ideal networking technology for most computer users today.