Enterprise network 8.1:Introduction 8.2:LANs 8.3:Ethernet / IEEE :Token ring 8.5:Bridges 8.6:FDDI 8.7:High-speed LANs 8.8:LAN protocol 8.9:Multicast LAN interconnect technologies

8.1:Introduction PSTN ISDN PBX (private branch exchange)

8.2:LANs LANs are used to interconnect distributed communities of end systems To ensure the transmission bandwidth is shared fairly between all of the attached stations, a number of different medium access control (MAC) methods are used. These include (CSMA/CD) and Token ring

8.3:Ethernet / IEEE802.3 Ethernet networks – and the more recent derivative IEEE802.3 – are used extensively in technical and office environment CSMA/CD –All the stations are attached directly to the same cable/bus,it is said to operate in a multiple access mode –The bus operates in the broadcast mode which means that every frames transmitted is received by all the other stations that are attached to the bus –Because of the broadcast mode,this will result in the contents of the two frames being corrupted and a collision is said to have occurred

CSMA/CD Protocol Carrier Sense before transmission Carrier Sense while transmission Collision: Two or more stations transmitting simultaneously Backoff: Random delay after collision Deference: Defers transmission if channel is sensed busy Collision Window (Slot time): Round-trip propagation delay time plus some carrier sense time. In IEEE 802.3, this value is defined to be 51.2 us.

CSMA/CD Collision Handling Collision Signal is generated by Physical layer. Jam signal (collision enforcement): To make sure that all stations involved in the collision will detect collision. A pattern of 32 bits. Collision backoff and retransmission method (Truncated Binary Exponential Backoff Algorithm, BEBA): – n : number of collisions experienced (n <= 16) – k : Min (n,10) -- Truncation – r : Random delay time (unit: slot time) between 0 <= r < 2 k

CSMA/CD worse-case collision detection

Hub configuration principles

IEEE Frame Format

8.4:Token ring All the stations are connected together by a set of unidirectional links in the form of a ring and all frame transmissions between any of the stations take place over it by circulating the frame around the ring Only one frame transfer can be in progress over the ring at a time Fig 8.5

Token ring network operation

Token ring wiring configuration

Token ring Frame Format

8.5:Bridges There are two types of bridges, the one are used with Ethernet LANs, knows as transparent bridges, and the others with token ring LANs, known as source routing bridges.

Bridge vs Repeater

8.5.1:Transparent bridges With a transparent bridge, as with a repeater,the presence of one (or more) bridges in a route between two communicating stations is transparent to the two stations. All routing decisions are made exclusively by the bridge(s) Fig 8.12 A bridge maintains a forwarding database Bridge learning –Forwarding database to be created in advanced

Transparent bridges(cont.)

8.5.2:Source routing bridges The major difference between a LAN base on source routing bridges and one base on spanning tree bridges is that with the latter the bridges collectively perform the routing operation in a way that is transparent to the end stations. Conversely, with source routing, the end stations perform the routing function. Fig 8.15

Token ring Frame Format

Example

8.6:FDDI FDDI is an optical fiber-based ring network that supports a bit rate of 100 Mbps. It can used for the interconnection of segments spread over a wider geographical area than a single building, such as a university campus or manufacturing plant. Fig 8.18 Use two counter-rotating rings to enhance reliability:primary ring and secondary ring Two type of station: DAS and SAS Fig 8.19

Physical interface

FDDI Frame Format

8.7:High-speed LANs 8.7.1:Fast Ethernet 8.7.2:Switched Fast Ethernet 8.7.3:Gigabit Ethernet

8.7.1:Fast Ethernet Fast Ethernet was to use the same shared, half- duplex transmission mode as Ethernet but to obtain a*10 increase in operational bit rate over 10BaseT while at the same time retaining the same wiring systems, MAC method, and frame format. The major technological hurdle to overcome with Fast Ethernet was how to achieve a bit rate of 100Mbps over 100m of UTP cable. Fig 8.26

Collision detection Fig 8.28 Detect a collision by detecting a signal on pair 2 while it is transmitting and, the hub detects a collision by the presence of a signal on pair 1

8.7.2:Switched Fast Ethernet In order to allow multiple access/transfers to be in progress concurrently, two developments have been made: –Switch hub architecture –Duplex working over the circuits that connect the stations to the hub. Fig 8.29

8.8:LAN protocol

8.8.1:Physical layer

8.8.2:MAC sublayer

8.8.3:LLC sublayer

8.8.4:Network layer IPX –connectionless TCP/IP

8.9:Multicast LAN interconnect technologies 8.9.1:Intersite gateways 8.9.2:ISDN switched connection 8.9.3:Frame relay 8.9.4:High bit rate leased lines

8.9.1:Intersite gateways

8.9.2:ISDN switched connection

8.9.3:Frame relay

8.9.4:High bit rate leased lines

Summary