Computer Networking chapt 1
Traceroute
command to check the path that a packet takes to reach a destination details ...
queueing delay
the time the packet waits to be transmitted out of the link. the time depends on the number of earlier arrivals to the queue. queueing delays can be on the order of microseconds to milliseconds.
Nodal Delay
(Nodal Delay) = (Processing Delay) + (Queuing delay) + (Transmission Delay) + (Propagation Delay)
traffic intensit
La/R L = length of packets a = average rate at which packets arrive at the queue R = transmission rate if La/R > 1 then the average rate at which bits arrive at the queue exceeds the rate at which they can be transmitted from the queue. the queue will increase without bound and tend toward infinity, so design the queue so traffic delay is no greater than 1. if one packet arrives every L/R seconds then every packet arrives at an empty queue so no queueing delay. if packets arrive in bursts of N packets, the. the first packet has no queueing delay, while the nth packet has a delay of (n - 1)L/R seconds. (what is the formula for average here?)
end to end delay
N(d_proc + d_trans + d_prop) where there are N - 1 routers between the source host and the destination host.
Bandwidth Delay Product
defines the number of bits that can fill the link = R × d_prop
Transmission Delay
if transmitted in first come first serve manner, packets can be transmitted only after the packets that have arrived before it have been transmitted. L = length of packet R = transmission rate = bits/sec (ex: for a 10 Mbps link, R = 10 Mbps) transmission delay = L/R (the time to push, or transmit, all the packet's bits onto the link) typically on the order of microseconds to milliseconds.
processing delay
includes: -The time required to examine the packet's header and determine where to direct the packet -the time needed to check for but level errors in the packed that occurred in transmission from the upstream node. usually on the order of microseconds or less in high speed routers. after processing, the router directs the packet to the queue.
throughput
instantaneous throughput: the rate in bits/sec at which host B receives a file from host A at any given moment in time. average throughput: F/T where F = num bits T = time in seconds it is desirable to keep the instantaneous throughput above a predetermined threshold overall throughput is only as fast as the slowest link (or the bottleneck link) in the network so throughput = min(R1, R2 ...)
propagation delay
the time for a bit to propagate through the link to the next node. the bit propagates at the speed of the link, so it depends on the material, usually ranging from: 2×10^8 meters/sec to 3×10^8 meters/sec or, equal to or a little less than the speed of light. the propagation delay = d/s d = the distance between the two nodes s = the propogation speed once all bits of the packet are at the next node, the whole process is started again beginning with processing. propogation delays are on the magnitude of milliseconds
