Diffserv; Udp Port Selection - Avaya 4600 Series Administrator's Manual

DIFFSERV

As defined in IETF RFCs 2474 and 2475, "services" are basically ways of treating different subsets of a
network's traffic in different ways at the Internet Protocol (IP) layer, Layer 3. For example, some packets
might be routed in such a way as to expedite delivery (minimize delay), while others are routed to
minimize loss, minimize cost, etc. The differentiation between these services (that is, Differentiated
Services) is provided by a redefinition of an octet in the Layer 3 headers for IP versions 4 and 6, also
termed IPv4 and IPv6, respectively. This octet is called a Type of Service (TOS) octet in IPv4 and a
Traffic Class octet in IPv6, but in both cases the octet is interpreted differently than it was originally
defined. With Differentiated Services, bits 0 through 5 of the octet identify a Differentiated Services Code
Point (DSCP) that identifies a procedure to be used to handle that packet on a per-hop basis. Bits 6 and 7
of the octet are currently unused, and are ignored by DSCP-compliant routers.
With DiffServ, the default DSCP is all zeroes, and represents "no special handling." RFC 2474 also
defines eight "Class Selector Codepoints," which are the eight DSCP encodings that can be represented
by xxx000 (where "x" represents one bit). These Code Selector Codepoints are considered prioritized,
with the larger numerical values having a higher relative order. DSCP-compliant routers should treat
larger-valued DSCPs in such a way as to give the associated packets a "probability of timely forwarding"
greater than a packet with a lower-valued DSCP. In addition to the eight Class Selector Codepoints, a
network may define its own DSCPs by defining encodings that do not terminate in 000. The specific
treatment intended by these custom DSCPs will not necessarily be carried out by routers outside the
customer's own network.
In the 4600 Series IP Telephone Installation Guide, the Local Administrative Option for QoS allows you
to specify Diffserv values for Layer 3 audio ("L3QAUD") and signaling traffic ("L3QSIG") on a phone-
by-phone basis if necessary.
The Avaya IP Telephones' DiffServ values will be changed to the values administered on the media
server as soon as the phone is registered. For more information, see the document titled Administration
for Network Connectivity (555-233-504). Unless there is a specific need in your enterprise LAN, we do
not recommend you change the default values.

UDP Port Selection

Some data networks include equipment that can perform UDP port selection. This is a mechanism by
which packets with port numbers in a given range are given priority over packets with port numbers
outside that range.
To support UDP port selection, the 4600 Series IP Telephones can be administered either from the Avaya
Communication Manager Network Region form, or at the telephone itself via dialpad input. Specific
implementation details for local administration of MCPORT are in the 4600 Series IP Telephone
Installation Guide, and, for Avaya Communication Manager administration, are in Administration for
Network Connectivity for Avaya Communication Manager Software. In summary, the system value
MCPORT represents the port on the TN2302AP board. This port number can be used to administer
routers, etc. that support UDP port selection, to maximize the priority given to the voice packets being
exchanged between the PBX and the telephone.
The default value for MCPORT is 1719. The switch must be administered to use a port within the proper
range for the specific LAN, and the IP Telephone(s) will copy that port. A related parameter is
PORTAUD, which is the RTP port used by the switch. In accordance with standards RFC 1889 and 1890,
the IP Telephone uses a default value for PORTAUD of 5004.
4600 Series IP Telephone Release 2.1 LAN Administrator's Guide
July 2004
Server Administration
QoS
63