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5-14
Linksys IP Phone Administrator Guide
Firmware Version 5.1
Chapter 5 Linksys IP Phone Field Reference
SIP Tab
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.
RTCP Tx Interval
(not applicable to SPA901)
Interval for sending out RTCP sender reports on an active connection. It can range from
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
(not applicable to SPA901)
Select yes if you want the Linksys IP phone to calculate the UDP header checksum for
SIP messages. Otherwise, select no.
Defaults to no.
Symmetric RTP
(not applicable to SPA901)
Enable symmetric RTP operation. If enabled, sends RTP packets to the source address and
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
(not applicable to SPA901)
Determines whether the Linksys IP phone includes the P-RTP-Stat header or response to
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.
Field Description
Field Description
AVT Dynamic Payload AVT dynamic payload type. Ranges from 96-127.
Defaults to 101.