Interworking Between Session Initiation Protocal (SIP) And ISDN User Part
|Publication Date:||1 April 2015|
This Standard defines the signaling interworking between SIP, with its associated Session Description Protocol (SDP), and the ISDN User Part (ISUP) protocol at an Interworking Unit (IWU). The capabilities of SIP and SDP that are needed to interwork with ISUP are defined in Annex C of this Standard. SIP and SDP are defined by the IETF. ISUP is defined in accordance with ATIS-1000113.2005.
An IWU may be stand-alone or may be combined with an ISUP exchange. It is assumed in this Standard that the initial service requests must be forwarded and/or delivered via a trusted Adjacent SIP Node (ASN) within a SIP network domain. The ASN is viewed as a trusted network entity rather than untrusted user entity, and thus the interface between the IWU and the ASN is a Network-to-Network interface (NNI). Where SIP with Encapsulated ISUP (SIP-I) is used, it is assumed that the remote SIP User Agent can be trusted to receive the ISUP information and is able to process ISUP. Similarly, it is assumed that the ISUP information received from the remote UA can be trusted. Support for SIP interworking at a User-Network Interface (UNI) is not within the scope of this standard. Many security concerns arise if a PSTN/ISDN interconnects with a SIP network (via an IWU) where either some of these assumptions are not valid or the validity of these assumptions cannot be ascertained. In addition, because of the inherently open and distributed nature of IP networks, it should be assumed that PSTN/ISDNs could be susceptible to increased security risks through the interconnection with such networks. Therefore, to reduce such risk, it is highly desirable to follow strong security requirements and guidelines when PSTN/ISDNs are interconnected with SIP networks. RFC 3398 identifies some security issues for SIP-PSTN/ISDN interconnection. This standard takes into account some security aspects including some identified in RFC 3398. RFC 3261 describes various aspects of security for SIP headers and message bodies and various mechanisms to reduce security risks within the SIP network itself. This material should be used as the basis for developing detailed security requirements applicable to an IWU. Such requirements are outside the scope of this standard. The services that can be supported through the use of the signaling interworking are limited to the services that are supported by SIP and ISUP based network domains. Services that are common to the SIP and ISUP network domains will interwork by using the function of an IWU. The IWU will also handle (through default origination or graceful termination) services or capabilities that do not interwork across domains.
The scope of this Standard is shown in Figure 1.1