CAUSES:

The latency is also known as delay. It is not a specific problem of the connectionless networks and therefore a VoIP problem. It is a general problem of telecommunication networks. For example, the latency in satellite connections is very high because the distances are big.

Latency is technically the amount of time it takes a packet to travel from source to destination. Together, latency and bandwidth define the speed and capacity of a network.

Real time communications (for instance VoIP) and full-duplex communications are aware of this problem. Like jitter, it is a common problem in slow-speed or congested connections.

RECOMMENDED VALUES:

Callers usually notice roundtrip voice delays of 150 ms or more. The human ear is able to detect about 250 ms latencies, 200 ms in sensitive people. If that threshold is passed the communication returns annoying.

SOLUTIONS:

There is not a simple solution for this problem. It often depends on the devices that route the packets, in other words, in the same network. One solution could be to reserve a bandwidth from the origin to the final end or to mark the packets with TOS values. This way, routers can know that the traffic is in real time. Nowadays this is not very useful because we can control the network itself.

If the latency problem is in our own LAN or private network we can increase the bandwidth or give priority to those packages.