User's Manual
45
February 2007
MP-202 Telephone Adapter
5. Configuring VoIP Parameters
Table
5-9: VoIP - Advanced - Media Streaming Parameters
Parameter
Description
RTP Port Range -
Contiguous Series of 8
Ports Starting From:
Defines the port range for Real Time Protocol (RTP) voice transport.
DTMF Relay RFC 2833
Payload Type
The RTP payload type used for RFC 2833 DTMF relay packets. Range = 0-
255. Default = 101.
G.726/16 Payload Type
The RTP payload type used for 16 kbps G.726 packets. Range = 0-255.
Default = 98.
Table
5-10: VoIP - Advanced - Quality of Service Parameters
Parameter
Description
Type of Service (Hex)
This is a part of the IP header that defines the type of routing service to be
used to tag outgoing voice packets, originated from the MP-202. It is used
to tell routers along the way that this packet should get specific QoS. Leave
this value as 0xb8 (default) if you are unfamiliar with the Differentiated
Services IP protocol parameter.
Use MSS Clamping to
Reduce Voice Delay
When using Maximum Segment Size (MSS) Clamping, TCP streams routed
via the MP-202 when a voice call is active, will have a smaller segment
size. This will cause RTP to receive a better priority and will help prevent
high voice jitter that results of slow upstream transmission rate, as common
with most WAN connections (DSL, DOCSIS, etc.).
5.1.3.1 Configuring
Codecs
Codecs define the method of relaying voice data. Different codecs have different
characteristics, such as data compression and voice quality. For example, G.723 is a
codec that uses compression, so it is good for use where bandwidth is limited but its voice
quality is not as good compared to other codecs such as the G.711.
5.1.3.2 Supported
Codecs
To make a call, at least one codec must be enabled. Moreover, all codecs may be enabled
for best performance. When you start a call to a remote party, your available codecs are
compared against the remote party's, to determine which codec will be used. The priority
by which the codecs are compared is according to the descending order of their list,
depicted in the figure above. To change the priorities, rearrange the codecs in the required
order.
If there is no codec that both parties have made available, the call attempt will fail. Note
that if more than one codec is common to both parties, you cannot force which of the
common codecs that were found will be used by the remote party's client. If you do wish to
force the use of a specific codec, leave only that codec checked.