Download Token-Ring Networks

Token-Ring Networks
Chapter 4a
Panko’s
Business Data Networks and Telecommunications,
6th edition
Copyright 2007 Prentice-Hall
May only be used by adopters of the book
Figure 4a-1: Ring Network
Wrapped Ring
Access Unit
Main Ring
Backup Ring
Token
Break
STP
1. Frames travel around the ring.
The ring is a dual ring.
Normally, the backup ring is not used.
Computer
A
Computer
B
Computer C
STP or UTP
2. If a trunk line between
access units breaks,
The ring is wrapped,
Computer
so the loop is restored
Computer E
D
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802.5 Token-Ring Network
• Created about the Same Time as Ethernet
– Standardized as 802.5
– 16 Mbps maximum speed
• Token Passing Media Access Control
– Special token frame circulates around the ring when
no station is transmitting
– When a station gets the token, it may transmit a frame
– When a station finishes sending the frame, it releases
the token
• Token Passing is Complex and Expensive
– 802.5 quickly lost out to Ethernet
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Figure 4a-2: Early Ethernet Bus Topology
NIC
NIC
(1) Transmitted
Signal
(3) Received
Signal
Trunk Cable
(2) Transceiver Broadcasts Signal in Both Directions (Bus Transmission)
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Figure 4a-3: FDDI Backbone Network
16 Mbps
802.5 Netw ork
10 Mbps
802.3 Netw ork
100 Mbps
FDDI Backbone Netw ork
16 Mbps
802.5 Netw ork
10Mbps
802.3 Netw ork
Fiber Distributed Data Interface (FDDI) was a 100 Mbps token ring network
technology that could spans tens of kilometers
This made it an ideal backbone network to connect 10 Mbps Ethernet networks
and 16 Mbps 802.5 Token-Ring networks
As Ethernet grew to 100 Mbps and faster, FDDI became obsolete and was
discarded
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Perspective
• Ring Topologies are Desirable
– The ability to be wrapped is vital where high reliability
is important
– The SONET/SDH carrier technology discussed in
Chapter 7 and Module C uses a ring topology
• However, Token Passing is Not Necessary with
Switched Networks
– Just as CSMA/CD is not necessary in switched
Ethernet networks
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