Delay
Serialization Delay
#bits sent / linkspeed
For example : 125 bytes to send over a fastethernet
line :
125 byte =
1000 bit
1.000 bit /
100.000.000 bit/s =
0,000.01 s = 0,01 ms
For example : 125 bytes to send over a 56 kbit
modem line :
125 byte =
1000 bit
1.000 bit /
56.000 bit/s = 0,01785 s = 17,85 ms
Propagation Delay
Length of
meters / (3.0 * 108 meter/second)
is the speed of light in vacuum.
Length of
meters / (2.1 * 108 meter/second)
is for most exact measurement for copper and optical media.
For example : Send data over a distance of 1.000 km = 1.000.000
meter
1.000.000
meter / (2.1 * 108 meter/second) = 0,00048 s = 4,8 ms
Propagation
delay is not affected by clock rate !
Queuing Delay
It depends
on serialization delay and number/size of packets to send.
For example : 4 packtes á 1500 byte to send over 56 kbit
modem line
1500 * 8 bits / 56.000 bits/second = 214 ms for each packet. Packets 2, 3, and 4 have to queued and have to wait 214 ms for the first packet is
transmitted. Packets 3 and 4 have to wait another 214 ms for packet 2 is
transmitted. Packet 4 has to wait another 214 ms. So
the queuing delay is a total of 642 ms.
Forwarding Delay
The term
forwarding delay describes the time between a frame is fully-received and when
the packet has been placed in an output queue. This means the time the router
or switch needs to find a next-hop or forwarding port. Forwarding delay depends
on chosen switching methods (for example CEF, process-switching etc.).