Summary of the types of softswitch protocols

In terms of routes and switches, we have learned a lot about them. Now, let's take a look at the content about the softswitch protocol. Currently, 3GPP uses SIP as the core protocol of the third-generation mobile communication network. In Windows XP, NetMeeting's Softswitch protocol is also changed from H.323 to the SIP protocol. Considering its business flexibility, the SIP protocol will become the future development direction.

Comparison Between SIP and BICC

BICC is directly oriented to telephone applications. It comes from the traditional telecom camp and has a more rigorous system architecture, therefore, it can provide good transparency for implementing services in existing circuit switched telephone networks in Softswitch. In contrast, the SIP architecture is not as complete as BICC defines. SIP is mainly used to support multimedia and other new services, and has more flexible and convenient features in multiple service applications based on IP networks. BICC is developed on the basis of ISUP. It is mature in terms of voice service support and can support all previously narrowband voice services, supplementary services and data services. However, the BICC Softswitch protocol is complex, poor scalability. In wireless 3G applications, the BICC Softswitch protocol is in the Nc Interface of the core network of the 3GPPR4 circuit domain, and supports call connection between (G) mscservers.

In a fixed network Softswitch application, BICC is in the call control layer of the layered architecture, providing support for call connection between different SoftSwitch. When the BICC architecture is adopted, all current functions can be kept unchanged, such as number and route analysis. The routing concept is still used. This means that the network management method is very similar to the existing circuit switching network. SIP is not yet mature in terms of voice services, but it supports strong multimedia services with good scalability. It can be expanded based on different applications. In fixed network Softswitch applications, the SIP protocol is in the call control layer in a flat architecture and supports call connection between different SoftSwitch. When using the SIP architecture, there are two situations from the routing perspective:

In the first case, some information is added to a normal ISUP message and encapsulated in the SIP Message for transmission. functions such as the call server, number, route analysis, and communication between services remain unchanged, route analysis guides you to the addressing of the target IP address.

The second case is based on the ENUM (IETF's telephone number ing workgroup) database. In this way, the call control of the call server is completely different from the call control in the existing circuit exchange network. There will be no number and route analysis in the call control, but business ing and intercommunication are still required. Because the circuit identification code CIC, ISUP management process, and message transmission Softswitch protocol MTP are not used, the standard ISUP protocol must be modified accordingly. Network management is simplified to some extent (for example, there is no need to build a signaling network and no routing definition ). In addition, compared with the existing network, the operator's control over the network is reduced, and the control mode has undergone great changes.

Through the above analysis, using the SIP Softswitch protocol will lose some existing functions in the telephone network to some extent. To introduce these functions, you need to expand the SIP Softswitch protocol. BICC provides basically all existing telephone network functions. We believe that the modified and standardized SIP can provide BICC with support for traditional services.

Comparison of SIP-T and SIP-I

There are two standard systems about intercommunication between Softswitch SIP domain and traditional PSTN, that is, SIP-T protocol family of IETF and ITU-T protocol family of SIP-I.

1. IETF SIP-T Protocol

SIP-T (SIPforTelephones) is defined by RFC3372 of IETFMMUSIC workgroup. The entire protocol family includes RFC3372, RFC2976, RFC3204, RFC3398, etc. It uses an end-to-end research method to establish three intercommunication models for intercommunication between SIP and ISUP, that is, the call initiated by the PSTN user through the SIP network is terminated by the PSTN user; A call is initiated by a SIP user and terminated by a PSTN user. A call is initiated by a PSTN user and terminated by a SIP user. SIP-T provides two methods for intercommunication between SIP and ISUP, namely encapsulation and ing, which are defined by RFC3204 and RFC3398 respectively. However, the SIP-T only focuses on the intercommunication of basic calls, while the supplementary business is basically not involved.

2. ITU-T protocols for SIP-I

SIP-I (SIPwithEncapsulatedISUP) Softswitch protocol families include ITU-TSG11 workgroup TRQ.2815 and Q.1912.5. The former defines the technical requirements for intercommunication between SIP and BICC/ISUP, including the intercommunication interface model, the Protocol capability set that the intercommunication unit IWU should support, and the security model of intercommunication interfaces. The latter is based on the capacity configuration set of different Softswitch protocols supported by IWU on the NNI on the SIP side, the Intercommunication between ppsip and BICC/ISUP is defined in detail. Generally, the intercommunication between SIP and BICC/ISUP is defined, and the intercommunication between SIP and BICC/ISUP when there is an ISUP message encapsulation (SIP-I. The SIP-I protocol family reuses many IETF standards and drafts that cover not only basic call interworking, but also BICC/ISUP complementary business interworking.

3. Comparison of SIP-T and SIP-I

Obviously, the SIP-I protocol family is much richer than the SIP-T content. The SIP-I protocol family not only includes the basic call intercommunication, but also includes the CLIP, CLIR and other supplementary business intercommunication; in addition to the call signaling intercommunication, resource Reservation and media information conversion are also taken into account. In the fixed-network Softswitch environment, the intercommunication between SIP and BICC/ISUP, And the intercommunication between mobile protocol ppsip and BICC/ISUP.

It is particularly important that the SIP-I protocol family has the ITU-T standard inherent clear accurate and detailed specific, operability is very strong. In addition, 3GPP has adopted Q.1912.5 as the final standard for intercommunication between IMS and PSTN/PLMN. Therefore, the intercommunication between Softswitch SIP domain and PSTN should follow the ITU-T protocol family of SIP-I. In fact, many telecom operators have finally chosen SIP-I and abandoned the SIP-T. Based on the comparison and analysis above, we can draw the following conclusions:

In terms of intercommunication among Softswitch protocols, SIP-T and BICC are widely used in fixed network, and SIP-I is the future development direction; MGCP is mature in controlling the softswitch protocol between SoftSwitch and media gateway, but H.248 inherits all the advantages of MGCP and has a tendency to replace MGCP; MGCP is mature in terms of control protocols between SoftSwitch and IAD, but H.248 inherits all the advantages of MGCP and has the tendency to replace MGCP. In terms of control protocols between SoftSwitch and terminals, SIP is the trend; SIP is the mainstream between SoftSwitch and application servers. Currently, this service interface is basically mature; Parlay is the direction for application servers and third-party services, but it is not mature for commercial use.