e session that the user is being invited to. The SIP message is not sent directly to the called party but rather through a proxy server. Since SIP is based on a request/response paradigm, it conveys the response to the session initiator upon delivery of the session description. Once the session is setup, SIP can be used to modify the session as well by adding/removing audio and video streams or changing codecs, holding and muting, for example. SIP Capable Devices Proxy Media Server Proxy Server Proxy Server Proxy Location Server Server SIP Capable Call Control Devices Path Using Server Figure 36. SIP-Based Signaling Chapter 8 - Next-Generation OSS A wide range of products incorporate SIP at different levels in the network. For example, the softswitch community has embraced the SIP concept as a way of facilitating communication network softswitches and feature/media servers in the next-generation networks. Other companies are basing software VoIP clients on SIP and providing technology for use by anyone with a multimedia PC and browser. We are also seeing the emergence of intelligent SIP phones for use in VoIP services. 3GPP, an effort that describes the 3G wireless network architectures and signaling, has also included SIP in its specifications. 2.7 DOCSIS and PacketCable Besides wireline companies and service providers, the cable companies will also be deploying next-generation networks. In fact, the cable companies only have a very small, embedded base of Class 5 switches and hence are much like greenfields. This could very well be a big opportunity for softswitches if the cable companies seriously focus on voice services. The cable MSOs are steadily moving towards the next-generation service opportunity through a standards-based, well-organized process. CableLabs, a consortium of cable MSOs, initially defined DOCSIS 1.0 a specification for carrying data over cable. This standard specified the mechanism for transporting IP-based data packets over the HFC cable network. The standards led to development of DOCSIS