Ethernet Term Paper Introduced by: Almarshood, Yosef Bahaitham, Ahmed Alrashudi, Ahmed

Outline Introduction to LANs What is Ethernet? Network topology Ethernet communications & collisions Ethernet frame format Ethernet products

Introductions to LANs In 1970s, many commercial atmospheres of production and business recognized the need of sharing data and works. It was not practical or cost-effective for businesses to use floppy disks to share data, hence, the Local Area Network (LAN) was introduced. LAN is a collection of independent computers that communicate with one another over a shared network medium.

Introductions to LANs (cont.) LAN technologies: Ethernet : a local area network, using a bus topology, which provides reliable high-speed communications in a limited geographic area. Token Ring: A local area network in which all computers are connected in a ring or star with a token passing schem. FDDI ( Fiber Distributed Data Interface ) : A very high speed network protocol uses fiber optic cable.

Closer look A Network Interface Card, or LAN adapter, is your gateway of network communication to and from a PC. It provides a physical connection between the networking cable and the computer's internal bus. NIC is an important icon for LANs because it is the interface for each host. Most NICs in the market are found to support Ethernet.

What is Ethernet? The name comes from the word "the Ether" ; a medium, or the air, through which radio, or electromagnetic, waves travel. It was introduced in 1970s. Ethernet is a family of networking technologies. Generally speaking, these are common families of Ethernet:

What is Ethernet? (cont.) The 10-Mbps bandwidth was enough in the 1980s. In 1995, IEEE announced a standard for a 100-Mbps Ethernet. This was followed by standards for Gigabit Ethernet in 1998 and The IEEE defines the Ethernet standard as IEEE Standard

Ethernet naming standards The new supplements are given a one or two letters label such as 802.3x. An abbreviated description, called an identifier. The identifier consists of the following elements: ( Number, Word, Number or Letter ) 10Base2 Data rate 10 Mbps Baseband or broadband Max. segment link 200 m 10BaseT Twisted pair

Network topology Physical topology Defines the actual layout of the media. Logical topology Defines how hosts access media to send data. Two most common logical topologies: Broadcast: Sending data to all hosts on the network medium. First come, first serve. Token passing: an electronic token is passed sequentially to each host. Ethernet adopts, commonly, Bus and Broadcast topologies.

Ethernet signaling technique Baseband The entire bandwidth is used. Data signal is transmitted directly over the medium. Broadband Uses modulated carrier signal to transmit data. Ethernet relies on Baseband signaling technique. It used to use broadband signaling in the 10BROAD36 standard but now it is not considered anymore. e.g.

Ethernet communications & collisions Communication & Media Access Control Address Elements (send/receive) data in terms of Frames. Unique MAC (Media Access Control) address as an identifier for each element. NIC within every element uses MAC addresses as an address of a house, determining if a frame carries its own address in the sake of passing it on to upper layers (accepted) or take no action because it is directed to another element. The NIC does not use CPU processing time to make this assessment, enabling better communication times on Ethernet network. All devices that are connected to the Ethernet LAN have MAC addressed interfaces. This includes workstations, printers, routers, and switches …etc.

Collisions Ethernet is a shared media with broadcast and bus topology. P ossible: T wo or more Ethernet stations are transferring a frame to the network at the same time, results a collision. CSMA/CD ( Carrier Sense Multiple Access/Collision Detection ) Probabilistic protocol ( Listen-before-transmit-mode ). Physically monitoring traffic on the network line. Exponential back off algorithm is applied to resend data and back to normal after a collision has occurred. The CSMA/CD access method is internationally standardized in Ethernet.

From signal point of view, networking devices detects a collision when the amplitude of the signal on the media gets increased significantly (doubled). When a collision occurs, the sending stations transmit a 32-bit “jam” signal that will enforce the collision.

Ethernet Auto-negotiation Ethernet stations transmit a link pulse about every dozens of milliseconds, whenever the station is not engaged in transmitting a message. This pulse known as Normal Link Pulse (NLP). Auto-negotiation can be used by devices that are capable of different transmission. These devices then choose the best possible mode of operation that is shared by them.

The Basic Ethernet Frame Format: IEEE defines a basic data frame format required for all MAC implementations. Preamble (PRE): alternating pattern of ones and zeros, provides a means of synchronization. Start-of-frame delimiter (SOF): alternating pattern of ones and zeros, two consecutive 1-bits indicating that the next is the destination address. Ethernet Frame Format Destination address (DA): indicates the receiving station(s). Individual/group address. Globally/locally administered.

Source addresses (SA). Identifies the sending station. The SA is always an individual address. Ethernet Frame Format (cont.) Length/Type: Indicates either the number of MAC-client data bytes, or the frame type ID. Data: sequence of n bytes of any value less than or equal to If it is less than 46, the Data field is extended by adding a filler (pad) to bring the Data field length to 46 bytes. Frame check sequence (FCS): This contains a 32-bit cyclic redundancy check (CRC) value created by the sending MAC station, used to check damaged frames

Network Interface Card (NIC), connect pc to a network. 3 types. Transceiver, connect stations and nodes to different Ethernet media. Most NICs contain a built-in transceiver. Hubs/Repeater, interconnect clients and servers, repeating/amplifying signals. Wiring concentrators. Routers, determine the next network point (destination). network layer of OSI. Bridges, connect two networks usually with the same type. 2 layer. Smarter than repeater. Switch, filter and forward packets between LAN segment. data link layer. So, support any packet protocol. Ethernet Products

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