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 simul
taneously• Backoff: Random delay after collision• Deference: Defers transmission if channel is sense
d busy• Collision Window (Slot time): Round-trip propaga
tion 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 < 2k
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
