Packet Delivery Parameters and Reliability in Network Design

There are 3 packet delivery parameters.

1. Delay / Latency

Time which a legitimate packet takes to travel from source to destination. 

2. Jitter

Consistency of delay / latency

3. Packet Loss / Drop Ratio

Fraction of packets sent by the source but not received by the destination.

General accepted best practices for the Delay, Jitter and Packet Loss ratio has been defined per type of applications. For example, one way Delay for VoIP (mouth to ear delay) should be less than 150ms, Jitter should be less than 30ms and PLR should be below 1%.

Reliability

Delivering the legitimate packets from source to destination within a reasonable delay / latency which is defined based on the application type and architecture.

Reliability is often mentioned in choosing links. As an example, if you have to utilize a mix of reliable and unreliable links, best practice is to carry VoIP traffic over the reliable links which don’t have packet loss and latency, and use the cheaper unreliable links such as internet to transport packet loss tolerant application traffic.

But reliability should be considered for everything in the path, including links, devices such as switches, routers, firewalls, application delivery controllers, servers, storage systems etc. Even the hardware onboards should be reliable too. That’s why vendors bother with ASICs, Quantum Flow processors etc in their marketing propagandas.