Adrian Georgescu wrote: > Why should SIP-T still exist? Is it cheaper than having a gateway? What > is the practical use case for investing in such technology? > > I am eager to learn
We've used it extensively in work with CLECs that operate TDM switches such as the Metaswitch, Lucent LCS/Telica, etc. When a carrier operates more than one switch, SS7 interconnection between them is generally required so, for the same basic reasons an internal iBGP mesh or partial mesh (confederation) between two border routers is required for IP. One switch must be aware of numbers routed or ported into the other switch, and so on. The reason for its existence is that if both network elements support SIP-T, it allows you to replace an SS7 IMT (inter-machine trunk) with an IP-based mechanism for this interconnection. This allows you to move the traffic over a data network and get all the benefits that this brings; economies of scale through decreased facilities, oversubscription, etc. The main benefit is the elimination of TDM trunk exhaust; SS7 IMTs are physically bundles (trunk groups/TCICs) of DS0s, usually consisting of one or more T1s, and sometimes DS3s or more. That means that when a large volume of calls is running between the two switches, you could burn up all your SS7 trunks. Running the calls as SIP-T allows you to use something like a gigabit network core to make that problem go away somewhat -- a key benefit of VoIP in most other scenarios with which you are familiar with. At the same time, the switches still need ISUP attributes carried in SS7 IAMs and ACMs for billing, because that's just the information they operate on internally. SIP-T provides an IP-based way to encapsulate that information. SIGTRAN (essentially, SS7-over-IP) is another way to do this. However, SIP-T is lightweight and easier to deploy. It also allows you to use existing SIP network elements (proxies, session border controllers, etc.) to route and manage the traffic. For example, if you were using OpenSIPS + ACC + FreeRADIUS as a CDR catcher, you could run the "SS7" calls between two switches and log the appropriate information as custom attributes. There are no good open-source implementations for SIGTRAN - nothing as turn-key as Kamailio or OpenSIPS. SIP is high-level and much easier to deal with and manipulate using a far wider range of tools. SIP-T is also becoming an attractive external interconnect option. -- Alex Balashov Evariste Systems Web : http://www.evaristesys.com/ Tel : (+1) (678) 954-0670 Direct : (+1) (678) 954-0671 Mobile : (+1) (678) 237-1775 _______________________________________________ Users mailing list [email protected] http://lists.opensips.org/cgi-bin/mailman/listinfo/users
