Difference Between SIP I and SIP T

The existing communication system is the PSTN network. However the Global voice network plans to change it to IP. But the present system is expected to stay for a few more years. The interrelated function plays a main role between Voice over IP and PSTN. By interrelated function we mean the mapping of two systems like translation of two languages.

Both SIP-I and SIP-T help in mapping of messages, parameters and error codes amongst SIP and ISUP networks. With SIP network both of them are interconnected. The information is kept intact when calls that start and end on ISUP network are transferred through SIP network. Both of these have the same tactics in interworking amongst ISUP and SIP networks which is the same as PSTN and VoIP. The process of transferring ISUP parameters with SIP network is done by putting together a factual copy of the real ISUP message to the SIP message towards the doorway of PSTN gateway. It appears as a different body on the SIP message.

The ITU in 2004established the SIP-I and the IETF established SIP-T. In terms of accuracy and clearly expressing parameters between ISUP and SIP, SIP-I is better. It identifies the additional services for telecommunication interconnection briefly unlike SIP-T. Interoperation with SIP terminals is supported by SIP-T only.  Manufacturers and carriers like soft switch and SBC vendors prefer SIP-I more than SIP-T.


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