BICC (Bearer Independent Call Control) and SIP-I (Session Initiation Protocol – ISUP) are session control protocols, which are used to create, modify and terminate IP based communications such as voice and multimedia services. Both methods are developed to carry ISUP signalling messages over IP based networks. Different releases of 3GPP adapted both these protocols in order to cater the evolving networks and their interworking.
BICC
BICC was defined to cater ISUP signalling based services over broadband backbone network. Since ISUP was designed to cater narrowband signalling requirements over TDM networks, BICC specification was defined and standardized by ITU-T as per the recommendation Q.1902 in year 2000 to create, modify and terminate voice calls between MSC servers (Mobile Switching Center). BICC handles the signalling part of the voice calls, which ultimately controls the bearer setup and disconnection. BICC inherits the message and parameter set of ISUP, which leads to compatibility and support of ISUP services. 3GPP (3rd Generation Partnership Project) adopted BICC in the UMTS Release 4 standard, which was published in year 2001. BICC addresses most of the requirements of GSM and UMTS domains, but failed to address the future flexibility requirements with the evolution of networks. BICC CS2 (Capability Set 2) comprised of the ability to control the IP bearer network, codec negotiation, and modification using the BCP (Bearer Control Protocol). This leads to separation of call control and bearer connection control into two independent networks within the UMTS architecture.
SIP-I
SIP-I is an extension to existing SIP protocol with encapsulated ISUP messages to transport narrowband signalling over SIP based networks. Both ITU-T and ANSI standardised the SIP-I specification to cater the interworking with ISUP and BICC networks. As per the SIP specifications, 3 profiles are defined to cater major interworking scenarios. For an example, Profile A support only ISUP services by mapping the ISUP information into SIP headers, Profile B provides generalized SIP solution with the ability to cover interworking between range of ISUP networks and Profile C covers regulatory requirements with encapsulated ISUP. SIP-I facilitates the interconnection with ISUP islands into the SIP backbone. Another advantage of SIP-I is the possibility to create trust domains, so that, any message received from that trust domain is assumed to be treated as valid network node, which is essential to cater the interworking with legacy ISUP networks.
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What is the difference between BICC and SIP-I? – Both BICC and SIP-I signalling can be used in Nc interface of NGN (ie. Between MSC server communications), and for the interconnection of IMS and NGN domains (ie. Between MSC server and MGCF). – Initially BICC was developed to cater the ISUP interworking in the GSM and UMTS domains, but due to the limited flexibility and evolution of the standard, SIP-I was introduced to UMTS domain to cater the ISUP and SIP interworking requirements, which evolved with the networks. – Unlike SIP-I, there are some concerns about BICC for the interoperability across domains other than UMTS and GSM, therefore, later releases of 3GPP chose SIP-I over BICC. – 3GPP version of BICC is generally used by wireless operators, and leads to difficulties in interoperability with wired operators. This can be avoided by using SIP encapsulated ISUP, as standards for both wireless and wired operators are available. – BICC specification was initially used by 3GPP to facilitate the services such as packetized voice between UMTS call servers, while SIP-I was more focused on evolution of networks and facilitation of interworking. – BICC uses IuFP media packet framing protocol specified by 3GPP, while SIP-I uses packet framing based on IETF specifications, which is widely used between operators. – Further the media packet framing protocol used by BICC is less efficient when compared with SIP due to the duplication of some RTP layer functions on the BICC. – SIP-I was developed with the concept of trust domains, so that it will be better suited for UMTS networks as same as the BICC. BICC and SIP-I are mechanism to interworking and encapsulation of ISUP messages to transport over the IP based networks. In general BICC is limited to operation within GSM and UMTS context, while SIP-I provides interworking with most of the networks.
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