Excerpt from PacketCable Implementation.
Published by Cisco Press, 02/09/07 ISBN-10: 1-58705-181-8 ISBN-13: 978-1-58705-181-4

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Now that you know how distributed quality of service (DQoS) provides premium service for telephone calls, the focus shifts to other applications for DQoS and PacketCable. Back in the very first chapter you learned that cable providers are expanding their service offerings to include applications such as videoconferencing, streaming media, interactive gaming, and telephony. Telephony is just the beginning; PacketCable can be used to provide a guaranteed and reliable network for any of these service offerings.

The architecture and protocols used to provide these services are defined under the PacketCable Multimedia (PCMM) specifications. PCMM provides the ability to provide quality of service (QoS) over a Data-Over-Cable Service Interface Specification (DOCSIS) network for different types of multimedia applications. PCMM is unaware of the application specifics requiring QoS. Thus, it does not specify the details of other aspects of the multimedia application, such as signaling and provisioning. This is different from PacketCable 1.x, where these application details are defined. PacketCable 2.0 addresses these additional architecture mechanisms for offering multimedia applications. Technologies such as Session Initiation Protocol (SIP) and IP Multimedia Subsystem (IMS), as well as PCMM for providing QoS over the DOCSIS network, are all used in PacketCable 2.0.

This chapter begins with an overview of how PacketCable multimedia works. This includes an in-depth look at how PacketCable Multimedia varies from PacketCable telephony. Differences in the Common Open Policy Service (COPS) and DOCSIS protocols and their messaging are compared to what you learned previously. Also call flows are examined to help illustrate PCMM functionality. The use of security and event messaging in PCMM is also discussed. Finally, the chapter addresses relevant configuration and troubleshooting of PCMM on a Cisco cable modem termination system (CMTS).

PCMM Overview

PacketCable Multimedia defines a framework for providing QoS, security, and resource accounting for any type of service in a DOCSIS network requiring this functionality. The methods of providing these mechanisms in PCMM are based on mechanisms defined in PacketCable 1.x. As you will see, PacketCable 1.x components, such as the multimedia terminal adapter (MTA) and call management server (CMS), are similar to a PCMM client and application server.

The main goal of PCMM is to provide a framework where reliable DOCSIS resources can be reserved for a variety of applications, which include videoconferencing, interactive gaming, streaming media, and so on. Voice and video applications tend to be very sensitive to network delay and interpacket delay (jitter); therefore, they can greatly benefit from the reliable resources provided by PCMM. Applications that are not real-time in nature can benefit from PCMM as well. For example, high-speed data users can be given boosts to their Best Effort service to allow for faster file transfers. PCMM can be used to give subscribers temporary speed increases in their high-speed data (HSD) service to entice them to move to one of these higher-speed service offerings. Another anticipated use of PCMM is with Deep Packet Inspection (DPI) devices. Either these devices can sit inline in the PacketCable network so they can inspect all network traffic, or traffic can be replicated to these devices. A DPI device can then recognize certain type of traffic and initiate a request for QoS to the PCMM devices in the network. For example, they could identify Real-time Transport Protocol (RTP) voice streams, and then initiate the request for DOCSIS Unsolicited Grant Service (UGS) service flows. Also a DPI device can be used to identify misbehaving subscribers or viruses and initiate requests to limit or cut off the QoS assigned to these subscribers.

The PCMM framework allows for client devices to use PCMM resources without having to be tightly integrated in the resource reservation and commitment processes. This is different from PacketCable 1.x, where embedded MTAs are required to fully understand and implement DQoS resource manipulation. PCMM also separates resource policy decisions from application-specific decisions, which increases flexibility in providing services. Finally, the PCMM architecture is such that a third-party service provider can manipulate QoS on the Multiple Systems Operator (MSO) network.