Repeaters

• Repeaters
• EXTEND the network segment by REGENERATING the signal from one segment to the next
• Repeaters regenerate BASEBAND, digital signals
• don't translate or filter anything
• is the least expensive alternative
• work at the Physical layer of OSI
• Both segments being connected must use the same access method e.g. an 802.3 CSMA/CD  (Ethernet) LAN segment can't be joined to a 802.5 (Token Ring) LAN segment. Another way of saying this is the Logical Link Protocols must be the same in order to send a signal.
• BUT repeaters CAN move packets from one physical medium to another: for example can take an Ethernet packet from a thinnet coax and pass it on to a fiber-optic segment. Same access method is being used on both segments, just a different medium to deliver the signal
• They send every bit  of data on => NO FILTERING, so they can pass a broadcast storm along from on segment to the next and back. So you want to use a repeater when there isn't much traffic on either segment you are connecting.
• There are limits on the number of repeaters which can be used. The repeater counts as a single node in the maximum node count associated with the Ethernet standard [30 for thin coax].
• Repeaters also allow isolation of segments in the event of failures or fault conditions. Disconnecting one side of a repeater effectively isolates the associated segments from the network.
• Using repeaters simply allows you to extend your network distance limitations. It does not give you any more bandwidth or allow you to transmit data faster.
• Why only so many repeaters are allowed on a single network: "propagation delay". In cases where there are multiple repeaters on the same network, the brief time each repeater takes to clean up  and amplify the signal, multiplied by the number of repeaters can cause a noticeable delay in network transmissions.
• It should be noted that in the above diagram, the network number assigned to the main network segment and the network number assigned to the other side of the repeater are the same.
• In addition, the traffic generated on one segment is propagated onto the other segment. This causes a rise in the total amount of traffic, so if the network segments are already heavily loaded, it's not a good idea to use a repeater.
• A repeater works at the Physical Layer by simply repeating all data from one segment to another.

Summary of Repeater features

• increase traffic on segments
• limitations on the number that can be used
• propagate errors in the network
• cannot be administered or controlled via remote access
• no traffic isolation or filtering

Summary:

A repeater

• Connects two segments of similar or dissimilar media
• Regenerates the signal to increase the distance transmitted
• Functions in the Physical Layer of the OSI model
• Passes ALL TRAFFIC in both directions
• Use a repeater to improve performance by dividing the network segments, thus reducing the number of computers per segment (This is what it says in the book, but it doesn't make sense to me)
• Do NOT use a repeater when:
• There is heavy network traffic
• Segments are using different access methods
• You need any kind of data filtering.

Amplifiers are just like repeaters, but generate a BROADBAND, analog signal. That analog signal can have different frequencies and carry both voice and data.