Linksys SPA 900 manual SDP Payload Types

Chapter 5 Linksys IP Phone Field Reference

SIP Tab

Field	Description
RTCP Tx Interval	Interval for sending out RTCP sender reports on an active connection. It can range from
(not applicable to SPA901)	0 to 255 seconds. During an active connection, the Linksys IP phone can be programmed
	to send out compound RTCP packet on the connection. Each compound RTP packet
	except the last one contains a SR (Sender Report) and a SDES (Source Description). The
	last RTCP packet contains an additional BYE packet. Each SR except the last one contains
	exactly 1 RR (Receiver Report); the last SR carries no RR. The SDES contains CNAME,
	NAME, and TOOL identifiers. The CNAME is set to <User ID>@<Proxy>, NAME is set
	to <Display Name> (or Anonymous if user blocks caller ID), and TOOL is set to the
	Vendor/Hardware-platform-software-version (such as Linksys/Linksys IP
	phone-1.0.31(b)). The NTP timestamp used in the SR is a snapshot of the Linksys IP
	phone’s local time, not the time reported by an NTP server. If the Linksys IP phone
	receives a RR from the peer, it attempts to compute the round trip delay and show it as the
	<Call Round Trip Delay> value (ms) in the Info section of Linksys IP phone web page.
	Defaults to 0.
No UDP Checksum	Select yes if you want the Linksys IP phone to calculate the UDP header checksum for
(not applicable to SPA901)	SIP messages. Otherwise, select no.
	Defaults to no.
Symmetric RTP	Enable symmetric RTP operation. If enabled, sends RTP packets to the source address and
(not applicable to SPA901)	port of the last received valid inbound RTP packet. If disabled (or before the first RTP
	packet arrives) sends RTP to the destination as indicated in the inbound SDP.
	Defaults to yes.
Stats In BYE	Determines whether the Linksys IP phone includes the P-RTP-Stat header or response to
(not applicable to SPA901)	a BYE message. The header contains the RTP statistics of the current call. Select yes or
	no from the drop-down menu. The format of the P-RTP-Stat header is:
	P-RTP-State: PS=<packets sent>,OS=<octets sent>,PR=<packets received>,OR=<octets
	received>,PL=<packets lost>,JI=<jitter in ms>,LA=<delay in ms>,DU=<call duration in
	s>,EN=<encoder>,DE=<decoder>.
	Defaults to no.

SDP Payload Types

The configured dynamic payloads are used for outbound calls only where the Linksys IP phone presents the SDP offer. For inbound calls with a SDP offer, the Linksys IP phone follow the caller dynamic payload type assignments.

The Linksys IP phone uses the configured codec names in its outbound SDP. The Linksys IP phone ignores the codec names in incoming SDP for standard payload types (0 – 95). For dynamic payload types, the Linksys IP phone identifies the codec by the configured codec names. Comparison is case-insensitive.

Field		Description
AVT Dynamic Payload		AVT dynamic payload type. Ranges from 96-127.
		Defaults to 101.
	Linksys IP Phone Administrator Guide
5-14		Firmware Version 5.1