Cisco 521SG Administration Guide - Page 241

Cisco SPA IP Phone Field Reference SIP Tab Parameter RTCP Tx Interval A Description Interval for sending out RTCP sender reports on an active connection. It can range from 0 to 255 seconds. During an active connection, the SPA9000 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 @, NAME is set to (or Anonymous if user blocks caller ID), and TOOL is set to the Vendor/Hardware-platform-softwareversion (such as Cisco/SPA9000-1.0.31(b)). The NTP timestamp used in the SR is a snapshot of the SPA9000 local time, not the time reported by an NTP server. If the SPA9000 receives a RR from the peer, it attempts to compute the round trip delay and show it as the value (ms) in the Info section of SPA9000 web page. Defaults to 0. Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 240