Enterprise network
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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 < 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, halfduplex 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
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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