There are 4 types of network delay which are summarized to form end to end delay they are;
Processing Delay, which is the time it takes a network device to make a decision on what to action to perform to a packet
Queuing Delay, is the time a packet spends in the outbound queue
Serialization Delay, how long it takes to put the bits onto the physical link
Prorogation Delay, this is the time a packet takes to travel down a physical link

Delays generally occur at the points where multiple downstream links aggregate into an upstream link or when there is a speed mismatch, eg your high speed LAN access the lower speed ISP connection.

But its not just delay which can cause problems, other network nasties include Packet Loss, Jitter, and lack of available bandwidth.

When the network was only being used for web, email, and file sharing it didn’t matter so much if there was jitter, a moderate packet loss or bad delays. Now with applications such as VOIP and video conferencing it has shifted engineers focus onto providing Quality of Service for the network, delays of greater than 150-200ms and packet losses higher than 1% can cause a significant degradation in quality.

The recognised methods of reducing delay are;
Increasing link speed – this can be an expensive approach and rarely solves the issue
Prioritise packets – by implementing queuing methods
Compress the packet payload – this is CPU Intensive
Compress the headers - this uses cRTP and is exceptionally handy for small VOIP packets where the header is a large percentage of the packet size
Avoid Congestion – using Congestion Avoidance techniques

In my next few posts I will go through the various stages for implementing Quality of Service, starting with classification & marking, congestion management & queuing, and policing & shaping.