Ethernet
5-2
Description
If the technology was left at that, it is easy to see that it would not function with
more than one station on the network not a very efficient networking solution. If
two stations, which can transmit without requiring permission, both transmitted
different packets at the same time, the electrical impulses that make up their
signals would get combined into a long string of gibberish. The more stations you
added, and the more they needed to communicate, the less the number of
non-mangled packets on the network.
Rather than having each station take a pre-determined turn transmitting, the first
part of CSMA/CD, Carrier Sense, was incorporated. Carrier Sense is the method
by which a station takes a look at the cable to which it is attached. If the cable is
being used, the station will wait and try again later. If the cable is without signals,
the station will transmit. By using Carrier Sense, Ethernet stations greatly reduce
the number of collisions a network experiences.
Figure 5-1. CSMA/CD Operation
NOTE
In Figure 5-1, above, stations B and D receive the transmission
before station A. This is due to the fact that signals in a cable or
media travel through that media at an appreciable fraction of
the speed of light. The differences in reception time are called
propagation delay.
Station C examines network for
availability. No signals noted.
Station C transmits. Stations B and
D receive transmission.
Station C monitors network for
error signals. Stations B and D
discard transmission. Station A
receives transmission.
1706n21
A
C
D
B
A
C
D
B
A
C
D
B
Summary of Contents for MMAC-5FNB
Page 1: ...Cabletron Systems Networking Guide MMAC FNB Solutions ...
Page 2: ......
Page 4: ...ii ...
Page 10: ...viii ...
Page 188: ...Expansion Ethernet 8 12 Port Assignment and Virtual LANs ...
Page 194: ...Expansion Token Ring 9 6 Port Assignment ...