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What is a CSU/DSU?
A CSU/DSU (Channel Service Unit/Data Service Unit) is a piece of equipment that connects a leased line from the telephone company to a customer's equipment (e.x. router). It performs line encoding and conditioning functions and often has a loop-back function for testing.
CSU/DSU's look similar to modems, they are not modems, and they don't modulate or demodulate between analog and digital. All they really do is interface between a 56K, T1, or T3 line and serial interface (typically a V.35 connector) that connects to the router. Newer routers have 56K or T1 CSU/DSUs built into them. CSU/DSU's for 56K, T1, and T3 lines are NOT the same and not inter-changeable.
What is Ethernet?
Ethernet is a type of network cabling and signaling specification originally developed by Xerox in the late 1970s. In 1980, Digital Equipment Corp.
What is a segment?
A piece of network wire bounded by bridges, routers, repeaters, or terminators.
What is a subnet?
Another overloaded term. It can mean, depending on the usage, a segment, a set of machines grouped together by a specific protocol feature (these machines do not have to be on the same segment, but they could be).
What is a transceiver?
Allows a station to transmit and receive to/from the common medium. In addition, Ethernet transceivers detect collisions on the medium and provide electrical isolation between stations.
What is a hub?
A common synonym for concentrator. Connect multiple cable runs in a network topology into a single network.
What is a bridge?
Connect two distinct segments and transmit traffic between them. This allows you to extend the maximum size of the network while still not breaking the maximum wire length, attached device count, or number of repeaters for a network segment.
What is a collision?
Where two devices detect the network is idle and end up trying to send packets at exactly the same time. Since only one device can transmit at a time, both devices must back off and attempt to retransmit again.
What causes a collision?
It is possible to not sense carrier from a previous device and attempt to transmit anyway, or to have two devices attempt to transmit at the same time, in either case a collision results. Ethernet is particularly susceptible to performance loss from such problems when people ignore the "rules" of wiring Ethernet.
What is a jam?
When a workstation receives a collision, and it is transmitting, it puts out a jam so all other stations will see the collision also. When a repeater detects a collision on one port, it puts out a jam on all other ports, causing a collision and any non-transmitting stations to wait to transmit.
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