Delay and Jitter
Network traffic experiences four types of delay:
■ Processing delay—The time it takes a packet to move from the input
interface of a router or Layer 3 switch, to the output interface.
Processing delay depends on switching mode, CPU speed and utilization,
the router’s architecture, and interface configuration. This is a
variable delay.
■ Queuing delay—The length of time a packet waits in the interface
queue before being sent to the transmit ring. Queuing delay depends
on the number and size of packets in the queue, and the queuing
methods in place. This is a variable delay.
■ Serialization delay—The length of time it take to place the bits from
the interface transmit ring onto the wire. Serialization delay depends
on the bandwidth of the interface—higher bandwidth equals smaller
serialization delay. This is a fixed delay.
■ Propagation delay—The length of time it takes the packet to move
from one end of the link to the other. Propagation delay depends on the
type of media, such as fiber or satellite links. This is a fixed delay.
The total delay is the sum of all four delays on every link along the path.
Because processing and queuing delay times can vary, end-to-end delay can
vary from packet to packet. This variation is called jitter.
To decrease delay, you can increase the link bandwidth, prioritize important
packets (note that this increases the delay for non-priority traffic), or
compress the packet headers or the payloads. On links under T1 speed, you
can fragment large packets and interleave smaller, interactive, packets
between them—this is called Link Fragmentation and Interleave (LFI).
When your traffic traverses an ISP network, you might need to reprioritize it
to match the provider’s standards.