|
A 1 Mbps audio application shares the 1.5 Mbps link between R1 and R2 with an FTP application that is transferring a
file from H2 to H4. In the best-effort Internet, the sudio and FTP packets are mixed in the output queue at R1 and transmitted
in a first-in-first-out (FIFO) order. In this scenario, a burst of packets from the FTP sources could potentially fill
up the queue, causing IP audio packets to be excessively delayed or lost due to buffer overflow at R1.
U:nder a strict priority scheduling discipline, an audio packet in the R1 output buffer would always be transmitted before
any FTP packet in the R1 output buffer. The link from R1 to R2 would look like a dedicated link of 1.5 Mbps to the audio
traffic, with FTP traffice using the R1-to-R2 link only when no audio traffic is queued.
In order for R1 to distinguish between the audio and FTP packets in its queue, each packet must be marked as belonging
to one fo these two classes of traffic.
Principle 1: Packet marking allows a router to distinguish among packets belonging to differnet classes of
traffic.
|
