VoIP SERVICES:PacketCableTM DELIVERS A COMPREHENSIVE SYSTEM David McIntosh Maria Stachelek CableLabs

Abstract voice services include multi-player gaming, videoconferencing, and unified messaging. This paper provides a high-level overview of the PacketCable IP-based The PacketCable Event Messages services delivery architecture as well as a framework supports collection of more detailed discussion of the PacketCable information necessary to create a PSTN- Event Messages framework used to track style call detail record (CDR) that may be access network resources used by those used for purposes of customer billing, services. settlements, traffic analysis, and other back office functions. The cable plant has experienced significant upgrades in the past several years allowing for the delivery of advanced broadband services. The DOCSISTM 1.1 ARCHITECTURAL OVERVIEW specification defines the robust, highly- reliable, and highly-efficient broadband One of the fundamental PacketCable transport mechanism necessary to support objectives is to define a QoS-enabled, IP- time-critical services such as voice. based services delivery platform that extends the capabilities of the highly The PacketCable architecture is a efficient DOCSIS 1.1 access network so as multimedia services delivery platform, to allow cable operators to deploy a variety layered over the DOCSIS 1.1 access of IP-based services. network, designed to support a wide variety of quality-of-service (QoS) enabled IP-based The initial service offering identified for services. The end-to-end architecture as the PacketCable architecture is residential designed[1][6], offers a complete system Voice Over IP (VoIP). While the that includes: device provisioning, PacketCable architecture doesn’t preclude signaling, event messaging, configuration the delivery of small-office-home-office management, QoS, and security. These (SOHO) and business VoIP services, the services are managed by specific servers focus has been on residential services and network endpoints that collectively allowing cable operators to provide value create a PacketCable network. and to leverage relationships with their residential cable subscribers. Voice over IP (VoIP) is the first service identified for delivery over the PacketCable Several factors differentiate Packet- architecture. Additional non-voice services Cable VoIP services from traditional “IP are also being analyzed as candidate telephony” services. For example: services for delivery over the PacketCable architecture. Examples of these beyond-

§ PacketCable VoIP is a phone-to-phone the PacketCable architecture requires several service rather than a personal computer- network elements with well-defined based telephony service. interfaces between those elements. This § PacketCable services are guaranteed section describes several key functional priority delivery on the DOCSIS access components in the PacketCable architecture. network ensuring a consistent, high- quality service. Multimedia Terminal Adapter § PacketCable services are not delivered over the public Internet. PacketCable In the home, a standard phone plugs into mandates the use of a managed IP the multimedia terminal adapter (MTA) backbone that provides service delivery allowing voice to be converted into IP consistent with that of the DOCSIS packets. An MTA may be designed to be access network. either a separate standalone device or to be embedded within the . The PacketCable architecture, pictured in Figure 1, provides the comprehensive system necessary to deliver VoIP services. Cable Modem Termination System When describing the architecture, we often talk about the three networks involved in the The CMTS is responsible for managing delivery of VoIP services: the access access network resources for PacketCable network, the managed IP backbone, and the services. Access network resources are first public switched telephone network (PSTN). reserved when service is requested, then committed when service is delivered, and Access Network - the HFC network finally released when the service has connecting the subscriber to the MSO. The completed. MTA and CM reside on the access network. The CMTS connects the access network to Call Management Server the managed IP network. The CMS manages and maintains call Managed IP Network - a high bandwidth state for VoIP services. The CMS is IP network used to connect the MSOs composed of a call agent (CA) and a gate headend servers. This network is often controller (GC). The CA manages the call called the “Managed IP backbone” when it state and controls the MTA. The GC is used to interconnect several managed IP performs QoS admission control and networks, DOCSIS HFC networks, or communicates with the CMTS to allow connect PSTN gateways to the PSTN. services to obtain access network resources.

PSTN - interconnects with the PacketCable Managed IP Network via a PSTN gateway.

FUNCTIONAL COMPONENTS

As part of the comprehensive end-to-end system necessary to deliver VoIP services,

Router Cable Modem Termination System Managed IP Embedded Backbone CMTS MTA Router Router CMTS

MTA/ CM MTA/ CM

PSTN OSS Call Management Media Servers Gateways Servers Server RKS Media Call Agent Gateway DNS Controller Media DHCP Player Gate Media SNMP Controller Gateway TFTP PSTN Media Player SYSLOG Controller Signaling Gateway KDC

Figure 1: PacketCable 1.0 Network Component Reference Model

Record Keeping Server The OSS back office contains service and network management components The RKS is the short-term repository for supporting the core business processes. PacketCable Event Messages. It receives messages from the CMS, CMTS and MGC Media Server then collates them into coherent sets for designated back office systems for The media server provides network additional applications processing. It serves announcements and information, e.g. “The as the interface between the PacketCable number you have called is no longer in network and relevant back office servers. service…” . There are two logical pieces to the Media Server, the Media Player Operational Support Systems Controller (MPC) and the Media Player (MP). The MPC requests the MP to play Operational support systems (OSS) announcements based on call state as contain a variety of supporting servers and determined by the CMS. The MP is infrastructure functions for such activities as responsible for delivering the appropriate provisioning, record keeping for billing, key announcement to the MTA or to the MG. distribution for security, domain name service (DNS) for name resolution, etc.

PSTN Gateway PacketCable splits the management of QoS resources into access network segments A PacketCable PSTN Gateway can be and backbone network segments. This decomposed into a Media Gateway approach allows for different bandwidth Controller (MGC), Media Gateway (MG), provisioning and signaling mechanisms for and Signaling Gateway (SG). The MGC different network segments: the origination manages the interconnection with the PSTN side, the far end, and the backbone network. by controlling the MG and SG. The MGC is Additionally it allows for resource- responsible for maintaining the call state for constrained segments to manage resource calls requiring PSTN interconnection. usage and maintain per-flow reservations carefully. The PacketCable DQoS The PacketCable architecture also Specification details this design [3]. supports a hybrid gateway solution that takes advantage of legacy PSTN switches Security already owned by cable operators while providing a migration path to the fully IP- PacketCable security spans all interfaces based PacketCable solution. This hybrid in the PacketCable architecture [5]. It architecture uses PacketCable IP-based provides confidentiality for media packets components on the access network and and for signaling communication across the circuit switch call control derived from a network via authentication, encryption, and PSTN local digital switch location. key management. It ensures that unauthorized message modification, insertion, deletion and replays anywhere in ARCHITECTURAL CAPABILITIES the network are easily detectable without affecting network operation. Security is Several core capabilities are fundamental interface specific, but the majority of to the delivery of VoIP services on the signaling interfaces are secured using IP PacketCable architecture. This section security (IPSec). The media stream is provides a high-level discussion of Dynamic secured by encrypting and authenticating the QoS and Security. Event Messaging is also payload directly. a core capability that is discussed in more detail in a later section. In addition to defining the security protocol that will be applied to each Dynamic QoS interface, PacketCable also defines a corresponding key management mechanism. An IP-based network, by definition of There are three basic key management the underlying TCP and UDP transport mechanisms defined for use in PacketCable: mechanisms, delivers packets in a best-effort Kerberized Key Management, internet key manner. Dropped or delayed packets result exchange (IKE) with either pre-shared keys in unpredictable end-to-end throughput. or X.509 digital certificates, and randomly PacketCable and DOCSIS 1.1 provide a generated keys exchanged within secured comprehensive, integrated QoS delivery signaling messages. mechanism [4] that ensures PacketCable packets are delivered in a guaranteed manner, not a best-effort manner.

OPERATOR OBSERVATIONS The multiple vendor and service The PacketCable Event Messages provider environment into which a cable framework has been designed to be flexible operator enters with the delivery of VoIP and extensible enough to support the initial services through a distributed architecture suite of PacketCable voice services, as well requires on-going attention. It has been as accommodate beyond-voice services in observed that this is not necessarily one-stop the future. shopping and each cable operator will be required to develop their own management A single PacketCable Event Messages strategies to navigate the variety of vendor, framework has been defined to support a network provider, and service provider variety of service-delivery scenarios and relationships. Take for example, resolving a network topologies. For example, tracking fault management issue. These can arise information for services that either originate within any number of scenarios, each with or terminate on the PSTN, as well as their own respective source and solution. services that stay on the MSOs network are Having the expertise in place, whether in- supported by the framework. house, or supported by a third party, to deal with such an issue will be important. Event Message Information

Another example of managing the multi- An Event Message is a data record service provider environment can be found containing information about usage and in the issue of local number portability service activities. Telephone number is an (LNP). In those instances where a PSTN example of the type of information carried customer would like to keep their existing in an Event Message. An event-based telephone number as part of their cable VoIP format is necessary to accommodate the service, LNP comes into play. The interval distributed architecture where complete of porting a subscriber’s telephone number “session state” no longer resides in one or has to be managed closely in order for the two network elements, but is instead spread subscriber to experience a seamless service across any of these, i.e. CMS, CMTS, and transition. MGC.

A single event message may contain a PACKETCABLE EVENT MESSAGES complete set of data regarding usage or it may only contain part of the total usage The PacketCable architecture provides a information. When correlated by the RKS, QoS-enabled IP-based service delivery information contained in multiple event platform for voice and other multimedia messages provides a complete record of the services. The PacketCable Event Messages service. Event messages are collected and framework provides a mechanism for are sent to one or more back office tracking access network resources that have applications such as a billing system, a fraud been requested and consumed by these detection system, or a pre-paid services services. This information can be used by processor. back office systems for many purposes including billing, settlements, network usage monitoring, and fraud management [2]. Originating/Terminating Model - generated, Event Messages may be stored on PacketCable makes use of an the CMS/CMTS/MGC and sent to the RKS “originating/terminating model” based on in a single file. the PSTN “half-call model.” In this model, the originating party’s service provider is Call Detail Records - Using the unique responsible for tracking information billing correlation ID (BCID) assigned to a sufficient to bill the originating party for given call, the RKS collects all the service, and to settle with the terminating individual Event Messages for that call, and provider. The terminating party’s service assembles them into a single call detail provider has the same responsibility for the record. The format of the CDR may be terminating party. This “originating/ AMA, BAF, IPDR, or any format terminating model” supports the various appropriate for the billing and other back- PacketCable network topologies. office servers that will make use of the information. Batch vs. real time - PacketCable allows Event Messages to be sent to the RKS as they are generated. Alternatively, once

PacketCable™ Event Messages Model

PacketCable Not specified Defined in PacketCable •Inter-Carrier Network Element Event CMTS Messages •Batch Billing Systems

•Pre-Paid Services Network Element Event RKS CMS Messages •Real-Time Event Billing Systems Messages Network Element •Fraud Detection MGC

Figure 2: PacketCable Event Message Model

Figure 2 depicts the PacketCable Event billing, settlement, reconciliation, and other Message architecture. By standardizing the systems. transport, syntax, and collection of appropriate Event Message attributes from a The CMS, MGC, and CMTS generate distributed set of network elements (CMS, Event Messages for the portion of the CMTS, MGC), this architecture provides a communication pertaining to them. For single repository (RKS) to interface with example, the CMTS generates a “start of QoS” message, when the CMTS commits The PacketCable Event Messages access network resources to a PacketCable framework is a flexible and extensible service. model that supports subscriber billing, settlements, and other back office functions. Going forward, the PacketCable Event SPECIFICATIONS AND STANDARDS Messages framework will be expanded to keep pace with a wide variety of IP-based The comprehensive nature of the services beyond voice that will be delivered PacketCable architecture is the result of a over the PacketCable service delivery suite of Technical Reports and platform. Specifications that delineate the end-to-end architecture and associated interfaces for a complete IP-based services delivery REFERENCES platform. These Technical Reports and Specifications (available at [1] “PacketCable 1.0 Architecture www.PacketCable.com) have been accepted Framework Technical Report”, PKT- as standards by several North American and TR-ARCH-V01-991201, December 1, International standards organizations 1999, CableLabs, including the Society of Cable www.packetcable.com Telecommunications Engineers (SCTE), [2] “PacketCable Event Messages American National Standards Institute Specification,” PKT-SP-EM-I03- (ANSI), and the International 011221, December 21, 2001, Telecommunications Union (ITU). CableLabs, www.packetcable.com

[3] “PacketCable Dynamic Quality-of- CONCLUSION Service Specification,”PKT-SP-DQOS- I03-020116, January 16, 2002, The PacketCable architecture described CableLabs, www.packetcable.com in this paper is a comprehensive end-to-end [4] “Quality-of-Service: A system necessary to deliver VoIP and other DOCSIS/PacketCable™ Perspective”, IP-based multimedia services. Venkatesh Sunkad and Majid For the delivery of VoIP, the Chelehmal, Proceedings of SPIE PacketCable architecture can be thought of Volume: 4522, pgs. 87-98, July 2001. as three networks coordinated through a www.spie.org collection of functional components and servers. The PacketCable architecture [5] “PacketCable Security Specification,” supports several core capabilities, such as PKT-SP-SEC-I05-020116 January 16, dynamic QoS and security, that are 2002, CableLabs, fundamental to the efficient, reliable deliver www.packetcable.com of IP-based services. [6] “The PacketCable Architecture”, Ed Efforts are underway to develop Miller, Flemming Andreasen, and extensions to the PacketCable architecture to Glenn Russell, IEEE Communications support a wide range of IP-based multimedia Interactive, June 2001, www.ieee.org services.