The future of PacketCable: PacketCable Release 2 and IMS

In the earlier phases of PacketCable, PacketCable 1.x, the aim was defining a complete architecture for providing primary line telephony in a cable environment. This architecture includes security requirements, QoS requirements, call signaling requirements, resource accounting requirements, and network management requirements. Partly due to time to market needs well established protocols, such as MGCP, and concepts, such as the softswitch, were used as the basis to provide the required functionality. The initial PacketCable charter was to provide a telephony service that offers voice quality as good as or better than that of the legacy PSTN and with the same suite of call features. The next phase of PacketCable, PacketCable Release 2, makes use of the capabilities of an advanced multimedia IP network to provide feature functionality far beyond that of the PSTN. PacketCable Release 2, hereon referred to as PacketCable 2.0, is based on Release 6 of the IP Multimedia Subsystem (IMS) developed by the 3rd Generation Partnership Project (3GPP). The scope of 3GPP is the development of a SIP based IP communication architecture for mobile networks. PacketCable 2.0 tries to align with IMS as much as possible. Compared to IMS, PacketCable 2.0 is simplified in some areas and enhanced in others in order to address cable specific requirements. One of the differences is for providing QoS over the DOCSIS cable network using PacketCable Multimedia. With PCMM dynamic QoS, security, and resource accounting can be created for any arbitrary application. Other differences include the support of NAT and firewall devices for the transport of signaling and media by using IETF STUN, a complete lawful intercept solution, and the provisioning, configuration, activation, and management (PACM) of user equipment (UE). PC 2.0 supports a diverse set of user equipment; some examples include software based applications like a soft phone or instant messager client and hardware based devices such as a video phone or a client embedded in a cable modem or set-top box. These UEs all use the same basic SIP infrastructure to obtain real-time multimedia services.

In my initial blog entry I mentioned cross-platform integration as one of the advanced capabilities possible with PacketCable 2.0. An example is alerting customers of incoming telephone calls via a message with the caller identity popping up on the television at the same time their phone rings. This is an example of an enhanced voice and video service possible with PC 2.0. Other examples include "click-to-dial" where a customer can click on a WEB page automatically triggering a telephone call to a particular person or company. Yet another example is video telephony. Another aspect of PC 2.0 is cellular integration enabling a customer to have telephony service over a cellular network when not at home and over a lower cost cable network when at home. The customer has a single telephone number and his or her service moves seamlessly between these two networks. Other services enabled with PC 2.0 include business telephony with IP Centrex services, VoIP trunking for enterprise PBXs, and residential SIP telephony.

The PC 2.0 architecture is divided into local, access, edge, core, interconnect, and OSS networks. The local network is where user equipment is connected to the access network; for example it could be a software based application on a personal computer connected to a router via wireless which in turn is connected to a cable modem via Ethernet. The access network could be DOCSIS based consisting of the CMTS, CM, and HFC network in between or it could be a cellular network. The edge network consists of the Proxy-Call Session Control Function (P-CSCF) and optionally a STUN server. The P-CSCF is the UE entry point into the SIP network and it maintains security associations with UEs. If the access network is DOCSIS the P-CSCF also communicates with a PacketCable Application Manager in order to establish dynamic QoS on the DOCSIS network. The STUN server is used to provide NAT functionality in the event a NAT device or firewall exists between the UE and access network. The core consists of components used to provide SIP services. Among these are the Serving-Call Session Control Function (S-CSCF) responsible for SIP session processing and the Interrogating-Call Session Control Function (I-CSCF) which works with the Home Subscriber Server (HSS) to determine the S-CSCF assigned to users. Interconnect devices consist of the Breakout Gateway Control Function (BGCF) which interfaces with other networks. For example in the case of telephony where a call needs to reach the PSTN, the BGCF routes the call to an appropriate PacketCable Media Gateway Controller (MGC). Note, a PacketCable Call Management Server (CMS) is also classified as an interconnect device. Operation Support System (OSS) devices consist of backend servers such DHCP and DNS servers. At first glance the number of components in the PC 2.0 architecture may seem intimidating, but keep in mind these are logical functions and can be combined into common physical components.

If you already have a PC 1.x network keep in mind you can transition to a PC 2.0 network in stages. For example one of the first things you might want to do is separate CMS and MGC functionality into different devices allowing them to scale independently. Thus as you increase your cable voice customer base you can add CMS devices accordingly without having to worry about costly PSTN inter-connectivity. You can then route calls between CMS and MGC devices using SIP. Initially you could manually configure these SIP trunks or you could implement the S-CSCF, I-CSCF, and HSS components to do this routing. Note, the ability to route between CMS devices using SIP and the IP network allows you to bypass the PSTN which would be needed otherwise. This is known as PSTN bypass and should help reduce the operation expenses of the cable operator dramatically. Also, you could support residential telephony on embedded MTAs via SIP as in PC 2.0 and via NCS as in PC 1.x simultaneously. For the SIP based MTAs you would need to add the P-CSCF component as well as the PacketCable Multimedia components in order to provide DOCSIS network QoS and security.

As always if you have any comments or questions I would like to hear them.

- Jeff