•sharing a single link among multiple transmissions
•3 basic possibilities:
* Frequency division multiplexing (FDM)
* Time division multiplexing (TDM)
* Statistical multiplexing
Frequency Division Multiplexing (FDM)
Time DivisionMultiplexing (TDM)
Statistical Multiplexing
•both FDM and TDM divide the link into independentchannels
•inefficient if traffic is bursty, since no sharing allowed
•in statistical multiplexing, the idea is that the link should never be idle when there is data to be transferred
transferred Frames have an additional overhead (compared to FDM or TDM) to indicate which input stream they belong to; the packet queuing delay is now variable;and a (possibly complex) method is needed to decide which packets to multiplex
Network Performance Measures
l= length of signal path in communication medium (metres)
v= signal propagation speed in the medium (metres/second)
L= average length of frame or packet (bits)
C= transmission rate (bits/second)
•Propagation delay= l/ v, in seconds
•shows how long a bit takes to propagate along the path
•Transmission time= L/ C, in seconds
•shows how long it takes to get packet onto the medium
•Throughput:how fast data can pass a certain point
•can be measured in bits/second, packets/second, …
•Efficiency's related to throughput, e.g.
efficiency = throughput (in packets/sec) * packet transmission time
•3 basic possibilities:
* Frequency division multiplexing (FDM)
* Time division multiplexing (TDM)
* Statistical multiplexing
Frequency Division Multiplexing (FDM)
Time DivisionMultiplexing (TDM)
Statistical Multiplexing
•both FDM and TDM divide the link into independentchannels
•inefficient if traffic is bursty, since no sharing allowed
•in statistical multiplexing, the idea is that the link should never be idle when there is data to be transferred
transferred Frames have an additional overhead (compared to FDM or TDM) to indicate which input stream they belong to; the packet queuing delay is now variable;and a (possibly complex) method is needed to decide which packets to multiplex
Network Performance Measures
l= length of signal path in communication medium (metres)
v= signal propagation speed in the medium (metres/second)
L= average length of frame or packet (bits)
C= transmission rate (bits/second)
•Propagation delay= l/ v, in seconds
•shows how long a bit takes to propagate along the path
•Transmission time= L/ C, in seconds
•shows how long it takes to get packet onto the medium
•Throughput:how fast data can pass a certain point
•can be measured in bits/second, packets/second, …
•Efficiency's related to throughput, e.g.
efficiency = throughput (in packets/sec) * packet transmission time
