Cisco SPA IP Phone Field Reference
SIP Tab
Cisco Small Business SPA 300 Series, SPA 500 Series, and WIP310 IP Phone Administration Guide 226
B
 
RTCP Tx Interval  Interval for sending out RTCP sender reports on an 
active connection. It can range from 0 to 255 seconds. 
During an active connection, the 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 Cisco/IP phone-1.0.31(b)). The NTP timestamp used 
in the SR is a snapshot of the IP phone’s local time, not 
the time reported by an NTP server. If the 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 IP phone web 
page.
Defaults to 0.
No UDP Checksum  Select yes if you want the IP phone to calculate the 
UDP header checksum for SIP messages. Otherwise, 
select no.
Defaults to no.
Symmetric RTP 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 no.
Parameter Description