One major issue with Ethernet connectivity is proper configuration of the speed and duplex settings. The speed and duplex settings must be configured properly and must match.

A duplex mismatch condition results in a state where one side perceives a high number of collisions, while the other side does not. This results in packet loss. Although it degrades performance in all cases, this level of packet loss might go unnoticed in a data network because protocols such as TCP retransmit lost packets. In voice networks, however, this level of packet loss is unacceptable. Voice quality rapidly degrades in one direction. When voice quality problems are experienced, you must first check the duplex mismatches.

The best practice is to use autonegotiation on both sides of an IP connection. You can also lock down interfaces on both sides of a link. However, many a times, this practice requires a coordination between the Ethernet switch data team and the voice team. Gigabit links should always use Auto-Negotiation. For details of all aspects of Auto-Negotiation and lockdown, see the Ethernet Link Guidelines for Avaya Aura Unified Communications Products whitepaper at http://support.avaya.com/.

Whether you choose the autonegotiation mode or the lock down mode, make sure that both the ends of the link use the same mode which results in 100 Mbps and full duplex for 10/100 Mbps links. Also, ensure that Gigabit links result in 1 Gbps and full duplex in autonegotiation mode.