Enterprise network • 8.1:Introduction • 8.2:LANs • 8.3:Ethernet / IEEE802.3

• 8.4: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 802.3 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