Linksys RTP300 User Guide - Page 26

Introducing Linksys Analog Telephone Adapters ATA Software Features Feature SIP Over TCP SIP Over TLS Media Loopback Register Retry Enhancements Description To guarantee state-oriented communications, Linksys SPA2102 and SPA3102 devices allow you to choose TCP as the transport protocol for SIP. This protocol is "guaranteed delivery", which assures that lost packets are retransmitted. TCP also guarantees that the SIP packages are received in the same order that they were sent. As a result, TCP overcomes the main disadvantages of UDP. In addition, for security reasons, most corporate firewalls block UDP ports. With TCP, new ports do not need to be opened or packets dropped, because TCP is already in use for basic activities such as Internet browsing or e-commerce. SIP over TCP is configured in the Line tabs. See "Linksys ATA Voice Field Reference," on page 94. Linksys SPA2102 and SPA3102 devices allow the use of SIP over Transport Layer Security (TLS). SIP over TLS is designed to eliminate the possibility of malicious activity by encrypting the SIP messages of the service provider and the end user. SIP over TLS relies on the widely-deployed and standardized TLS protocol. SIP Over TLS encrypts only the signaling messages and not the media. A separate secure protocol such as Secure Real-Time Transport Protocol (SRTP) can be used to encrypt voice packets. SIP over TLS is configured in the SIP Transport parameter configured in the Line tab(s). See "Linksys ATA Voice Field Reference," on page 94. Linksys SPA2102, SPA3102, and PAP2T devices allow service providers to use media loopback to quantitatively and qualitatively measure the voice quality experienced by the end user. One device acts as the audio transmitter and receiver while the other device acts as the audio mirror. The audio mirror transmits the audio packets that it receives back to the transmitter/receiver instead of transmitting the data sampled on its local microphone (IP phone) or attached analog telephone (ATA-type device). Media loopback is configured in the User tab. See "Linksys ATA Voice Field Reference," on page 94. The Register Retry Enhancements feature for Linksys SPA2102, SPA3102, and PAP2T devices adds flexibility to the delay timers that are activated when the SIP REGISTER of a device fails. Once a SIP REGISTER failure response code is sent, a delay timer is selected depending on the type of registration failure response code. The delay timers can be one of the following: • Reg Retry Random Delay-Random delay range (in seconds) to add to the Register Retry Intvl parameter when retrying a SIP REGISTER after a failure. The default is 0, which disables this feature. • Reg Retry Long Random Delay-Random delay range (in seconds) to add to the Register Retry Long Intvl parameter when retrying a SIP REGISTER after a failure. The default is 0, which disables this feature. • Reg Retry Intvl Cap-The maximum value to cap the exponential backoff retry delay. The exponential back-off retry delay starts with the setting found in the Register Retry Intvl parameter and doubles it on every REGISTER retry after a failure. In other words, the retry interval after a failure is always set to the seconds configured in the Register Retry Intvl parameter. If this feature is enabled, the Reg Retry Random Delay setting is added on top of the exponential back-off adjusted delay value. The default value is 0, which disables the exponential back-off feature. Register Retry is configured in the SIP tab. See "Linksys ATA Voice Field Reference," on page 94. Linksys ATA Administration Guide 26