Avaya Application Solutions Deployment Manual Download

Page: 293 / 420

IP terminals deployment

Issue 3.4.1 June 2005

293

Speed and duplex

Newer Avaya IP Telephones such as the 4620 and the 4602SW contain a 10/100 Ethernet
switch. This switch is set to autonegotiate speed and duplex by default. As was stated above,
the closet Ethernet switch to which the IP Telephone is attached should be set to autonegotiate,
as well. Locking down the closet switch to full duplex will lead to packet loss, and thus result in
problems with voice quality.

Older Avaya IP Telephones such as the 4606, 4612, 4624, and 4630 contain a 10/100 hub. The
integrated hub in the IP Telephone operates at 10 mbps, or 100 mbps half duplex. There are
generally no speed or duplex issues with the IP Telephone. When connected to an Ethernet
switch port that is configured to autonegotiate, the Ethernet switch port stabilizes at 100/half.
The exception to this is if a personal computer is attached to the telephone that is capable of
only 10 mbps. In this case, case all three devices stabilize at 10/half. If no personal computer is
to be attached to the telephone, or if the attached computer will always be capable of 100 mbps
operation, it is good practice to lock down the Ethernet switch to 100/half. If a personal
computer might be attached to the telephone, and there is a chance that the computer might
have a 10-mbps NIC, leave the Ethernet switch port in autonegotiate mode.

Note about Single-Speed Bus: Dual-speed hubs and switches must inherently buffer and
discard traffic because of the inconsistent flows (one port receives at 100 mbps, but the other
can only send at 10 mbps). The Avaya IP Telephone is designed with a single-speed bus in the
hub, and does not perform these functions. Instead, these functions are transferred to the
enterprise Ethernet switch, where they really belong. Although the IP Telephone can
accommodate a second user device (the telephone itself being the first), its primary function is
not that of an enterprise network device.

30A base switch

The 30A base switch is a three-port switch that is integrated into the base stand of 4612 and
4624 sets. The pigtail cable attaches to the uplink port of the IP Telephone. The other two ports
are an uplink port to connect to the enterprise Ethernet switch, and a user port to connect to a
personal computer, just like the IP Telephone. Both ports to require standard Ethernet cables,
just like the IP Telephone. Each port supports 10/100 capability at full duplex or half duplex. The
ports are in autonegotiate mode, and cannot be configured. Therefore, the attached devices
must also be in autonegotiate mode, or they must be fixed to 100/half or 10/half. Limited
experience has shown that the 30A base switch functions adequately with the attached devices
in autonegotiate mode. Because the 30A base switch is not an enterprise-class switch, it is best
to have the speed and duplex on both ports be the same. Otherwise, the 30A base switch is
required to buffer and discard frames, which it can do but not as well as an enterprise Ethernet
switch.

The 30A base switch has built-in QoS, and gives strict priority to the traffic of the IP Telephone
traffic on the uplink port. That is, when the IP Telephone and the personal computer are both
transmitting, the telephone traffic is given strict priority out the uplink port to the enterprise
Ethernet switch. This is not an issue for the computer, because under normal conditions the IP
Telephone transmits less than 100 Kbps of audio traffic. Prioritization of traffic downstream from
the enterprise Ethernet switch to the 30A base switch must be handled by the enterprise
Ethernet switch.

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