Description; Ip Phone Support - Nortel 2001 Installation And Operation Manual

Page 258 of 302

Description

IP Phone support

553-3001-368 Standard 4.00
Appendix A: 802.1Q VLAN description
Note: 802.1Q functionality is supported only on the IP Phone. The IP
Line application's IP stack does not provide 802.1Q support for the
ITG-P or SMC.
The p bits within the 802.1Q standard allow packet prioritization at Layer 2
improving network throughput for VoIP data.
The 802.1Q standard specifies a new format of Ethernet frame. A standard
Ethernet frame contains:
• a header consisting of a six-byte destination MAC address (following the
header is a data area)
• a six-byte source MAC address
• a two-byte protocol identifier
The 802.1Q formatted frame is identical to a standard Ethernet frame, with
the exception of the 4-byte 802.1Q tag that is inserted between the source
MAC address and the protocol identifier. The first 16 bits of the 802.1Q tag
field is the Tag Protocol Identifier containing 8100 (hex), allowing the
Ethernet interface to distinguish it from standard Ethernet frames. The last 16
bits of the 802.1Q tag contain the following information:
• a 3-bit Priority field (the 802.1p defined bits)
• a 1-bit Canonical Field Identifier (CFI)
• a 12-bit VLAN ID field
The IP Phone 2001, IP Phone 2002 and IP Phone 2004 support 802.1Q as
follows:
• 802.1Q can be enabled or disabled at boot time using manual
configuration or control downloaded from the TPS.
• If 802.1Q is disabled, standard Ethernet frames are transmitted.
February 2005