August 2002
PacketCable And The Road To Cable
Telephony
BY DON STANWYCK
CableLabs� PacketCable project began in late 1997, and in December of
1999 released the first set of technical specifications for an IP-based
services delivery platform capable of providing residential telephony
service. PacketCable services require the managed Quality of Service (QoS)
and other advanced capabilities provided by the DOCSIS 1.1 Cable Modem
specifications. CableLabs members were eager to have industry specifications
that allowed vendors to build products that meet the needs of the cable
industry and assurance of multi-vendor systems that interoperate.
The PacketCable specifications were released in phases. The initial
phase, PacketCable 1.0, is the foundation of the IP-services delivery
platform and provides sufficient functionality necessary for an MSO to
deliver residential telephony service. PacketCable 1.1 adds additional
functionality necessary to provide a primary line telephony service, and
PacketCable 1.2 defines how to connect multiple PacketCable networks.
One goal of PacketCable 1.0 was to provide sufficient detail to allow
vendor interoperability and capabilities as needed for simple telephone
calls within a single cable operator (MSO) network. The 1.0 release included
specifications covering:
- The required and recommended codecs;
- Dynamic quality of service control on the cable plant;
- Signaling based on MGCP (NCS) for use between the softswitch (call
management server, CMS, in PacketCable parlance) and the residential
gateway (multimedia terminal adapter, MTA);
- Signaling based on MGCP (TGCP) for use between the softswitch (media
gateway controller, MGC, in PacketCable parlance) and the PSTN media
gateway (MG);
- A specification of event messages used by a record keeping server (RKS)
to correlate events to create billing records;
- A protocol for transporting SS7 ISUP and TCAP messages between
signaling gateways and softswitches;
- MIBs and MIB framework documents for the MTAs;
- Provisioning protocols and techniques for the MTAs; and
- A security specification addressing the PacketCable defined
interfaces.
In addition to these PacketCable 1.0 specifications a number of 1.0
related technical reports have been published. These include:
- The PacketCable Architecture;
- Call flows for various scenarios including both cable network devices
and PSTN devices; and
- An overview of the operation support systems (OSS) for cable telephony
networks.
Between December 1999 and November 2000 the PacketCable project released
the PacketCable 1.1 specifications. The goal of the 1.1 specifications was
to add the necessary components to enable primary line support in the cable
network. PacketCable 1.1 was still targeted at a single MSO implementation.
The additional specifications issued included:
- Primary line support requirements;
- Management event reporting and control mechanisms;
- CALEA requirements and processes for communications service providers
(known in PacketCable as the Electronic Surveillance Protocol
Specification, ESP); and
- An MGCP package for the control of media servers (audio players).
In addition to the PacketCable 1.1 specifications, four new technical
reports were generated:
- The line control signaling system architecture;
- More management event clarification (the identifiers);
- A VoIP availability and reliability model; and
- Call flows to go along with the ESP specification.
PacketCable 1.2 addresses how telephony networks operated by different
MSOs can work together to provide end-to-end services. The specifications
include a SIP-based signaling specification (CMSS) for inter-CMS operation,
and an interdomain quality-of-service specification. An architecture
technical report was also issued that included the interdomain aspects of
PacketCable 1.2.
The specifications for all three releases continue to be updated and
reissued as necessary to reflect clarifications and corrections based on
experience gained from vendor product implementation and multi-vendor
interoperability testing.
CableLabs has been engaged in PacketCable interoperability testing for
the last three years. In line with the testing strategy used for DOCSIS,
PacketCable has built a certification program. Customer-premise equipment (MTA)
is �certified� against requirements in the specifications, while network
elements that are under the care of operators are �qualified� against
the specifications.
PacketCable has been operating a test network with those products that
contain the most advanced PacketCable features. This Advanced
Interoperability Test Network (AITN) gives the industry a fully operational
PacketCable network model using PacketCable protocols. The AITN demonstrates
that the architecture works and provides an operational forum for
interpreting the specifications and evaluating interoperability. In order to
ensure the AITN contains products with the most advanced PacketCable
features, product acceptance into the AITN is based on the results of
PacketCable interoperability test events in accordance with criteria
established by CableLabs. The AITN is reviewed and modified as appropriate
to ensure that the most advanced products with the most advanced PacketCable
capabilities are available for interoperability testing.
In addition to the continued work on the telephony specifications,
CableLabs has also chartered a new group to look at multimedia applications
over the broadband cable. The new DOCSIS 2.0 specification was released at
the end of 2001. DOCSIS 2.0 increases the data rate on the cable upstream
plant to significantly greater rates.
WHEN WILL THIS BE REAL?
Cable companies have been trialing VoIP solutions for at least five years. A
lot has been learned, and there is more yet to learn. Nearly every one of
the larger MSOs has trials in progress: Lab trials, field trials, or both.
The early trials predated and led to the PacketCable work; most of the
trials now in progress reflect the latest PacketCable architecture and
specifications.
Indications are that the first revenue trials based on PacketCable
specifications will begin later this year. There are still some issues to be
resolved. The work continues as the specifications are subjected to more
vendor implementations and more scrutiny from network operators, but the
present work provides an adequate basis for initial deployments.
WHAT�S HOLDING UP DEPLOYMENT?
There are a number of factors that jointly impact the deployment rate. Among
these factors are:
The need to upgrade or rebuild plant: To deploy DOCSIS-based
PacketCable solutions requires high-quality two-way plant. Customers are
demanding cable modem services, and most MSOs are moving as quickly as
economics allow to rebuild their plants to support high-speed data services;
the same rebuild will support the two-way voice services and the multimedia
service interfaces now being standardized. The rebuild is nearing completion
in most of the larger MSO networks and has been completed in many of the
smaller ones. A few networks still have not completed the necessary
upgrades.
The need for trained technicians: The Society of Cable
Telecommunication Engineers (SCTE) now provides technician certification in
the area of cable telephony; many of the younger engineers coming into the
MSOs today are Cisco-certified network engineers or have received similar
training as part of their education. The workforce is available and rapidly
evolving to meet the needs of the MSO operated next-generation multiservice,
multimedia network.
Capital available for new network equipment: The economic impact
of the 2001 and early 2002 market retraction has limited the amount of
capital available to the MSOs for new equipment purchases. As the recovery
occurs through the end of 2002 and into 2003 the rate of deployment should
pick up.
Final availability of PacketCable compliant product: Since the
PacketCable specifications are only recently stable, the number of vendors
that have mature product in each area of the network is less than some of
the MSOs are comfortable with. The vendors are rolling out product as
rapidly as the current economics allow, and the number of available products
is growing each month.
SUMMARY
The broadband access network is a reality. The specifications are in place,
and vendors are delivering products today that comply with these
specifications. Deployments are beginning to occur, and the rate of
deployment will increase as the network operators get more comfortable with
the equipment and the CapEx budgets recover.
I wish to express my sincere appreciation to
the staff at the CableLabs PacketCable project who reviewed this article and
made excellent suggestions. Their suggestions have, I believe, ensured that
the article portrays an accurate picture of the process and progress of the
PacketCable project.
-- Don Stanwyck
Don Stanwyck is VP, Technology and Standards at IP Unity. IP Unity is
an emerging technology leader offering a carrier grade services platform for
enhanced voice and telephony applications over ATM, TDM, and VoIP networks.
The company�s offerings include media servers, applications servers, and
prepackaged enhanced services. For more information visit their Web site at www.ip-unity.com.
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