Since its inception the PacketCable initiative has been positioned as an IP-based Multimedia service deployment infrastructure, exploiting and enhancing the underlying QoS capabilities of the DOCSIS access network.
Based on market demand and technology readiness, VoIP was chosen as the first IP-based service to leverage these unique broadband access network capabilities, as the PacketCable 1.x suite of specifications simultaneously defines both a general QoS-based service delivery framework and a number of telephony-specific functional elements and mechanisms.
Specifically, the PacketCable 1.x VoIP architecture provides specifications promoting multi-vendor interoperability and CableLabs certification and qualification in the following key telephony areas:
- Network-based call signaling (NCS)
- Inter-domain call signaling (CMSS)
- PSTN gateway and interop functionality (TGCP, ISTP)
- Access-network and backbone QoS capabilities (DQoS, IQoS)
- Event messaging with telephony-specific extensions (EM)
- CPE endpoint provisioning and monitoring (Provisioning and SNMP MIBs)
- Comprehensive suite of interface security mechanisms (Security)
- Primary-line telephony characteristics
- Electronic surveillance
Since the intent of this specification is to extract the functional core of this architecture in support of the enhancement and deployment of other Multimedia services, support for these telephony-specific features is not required, while the core QoS, event messaging and security mechanisms are emphasized and generalized.
The result is a framework that provides IP-based access to DOCSIS access-network QoS mechanisms complemented by secure and robust authorization and audit mechanisms.
In keeping with the PacketCable 1.x Dynamic Quality of Service (DQoS) model, the primary logical construct in support of QoS-based service delivery is a Gate (along with its accompanying authorization token).
A PacketCable Gate represents a policy-based authorization for a specific envelope of network resources characterized by a suite of QoS parameters, as well as classifiers for originating and terminating IP addresses and ports, which define and limit the scope of the associated QoS-enhanced flow.
PacketCable 1.x defines a pre-authorization model in which Gates are created and installed at policy enforcement points (e.g., a CMTS) prior to actual network resource reservation or activation requests. This process, termed Gate Control, is managed through a COPS-based policy interface on the CMTS.
In this specification, this interface is generalized and enhanced to allow for full lifecycle management of QoS-based service flows through this policy interface. That is, Gate installation and management is supplemented with service flow creation, modification and deletion functions to provide for network-based QoS service delivery.
To complement these enhanced QoS policy and signaling capabilities, the RADIUS-based event messaging infrastructure of PacketCable 1.x is carried over, but with telephony-specific primitives tagged as optional.
Since the EM protocol was designed with a considerable amount of generality and abstraction, this approach provides continuity with existing protocol and Record Keeping Server (RKS) implementation while still allowing Multimedia vendors to select from a set of supplementary protocol primitives on an as-needed basis.
For example, if a QoSbased video conferencing service were being developed based on this specification, a number of telephony-specific EM message types (e.g., Call_Answer and Call_Disconnect) may map directly to the service’s audit requirements.
Finally, in order to provide robust security for this Multimedia framework, IPsec will be applied to the COPS and RADIUS interfaces in a manner analogous to the corresponding interfaces in the PacketCable 1.x architecture.
