DELIVERY OF NEW PACKET-BASED SERVICES OVER CABLE: THE PACKETCABLE™ CONCEPT Steven C. Craddock, Comcast Corporation David Reed, Cable Television Laboratories, Inc.

Extended Abstract features of circuit-switched telecommunications systems. Consumers will originate and receive CableLabs, and its member companies, are voice calls using either their existing telephones developing a packet network to overlay on cable, or a multimedia personal computer (PC). Using which will deliver a new family of services. Ge- the service, consumers will encounter normal nerically called “PacketCable™,” these services PSTN-like audible tones, such as a dial-tone when could be any useful features capable of being going off-hook, a busy signal if the receiving sta- transported by a packet network. The technical tion is off-line or engaged in another call, or ring- underpinning of this overlay network is the Inter- ing. In addition, consumers will receive the net protocol (IP) running over standard cable equivalent of today’s CLASS Services (e.g., call modems. The following extended abstract dis- waiting, call forwarding, and 3-way calling). cusses the conceptual framework and focus of the PacketCable development effort.1 Packet Video is an audio and video confer- encing service that will enable consumers to PACKETCABLE SERVICES place and receive video calls. At the customer premises, we envision delivering a symmetrical Any data or information service that lends it- service through a cable modem, and terminating self to packet-based transport is a potential Pack- in one of three premises device options: etCable service candidate. We anticipate that the initial PacketCable service set will be Packet Voice and Packet Video for business and residen- 1. a special adapter we call a Multimedia Ter- tial markets. Our approach to providing these ser- minal Adapter (MTA), interconnecting a vices is described below. Over time, it is likely television set, video camera, and a standard that other IP-based business and residential ser- telephone; vices will be added to the product line. Key fac- tors differentiating the PacketCable concept from ™ the market are: the North American footprint rep- 2. a cable television OpenCable digital set- resented by CableLabs’ member companies; ca- top, equipped with a PacketCable client, ble networks’ ample bandwidth, enabling interconnecting a television set, video cam- broadband packet-based services such as video; era, and a standard telephone; or and the capability of packaging a unique set of packet-based services customized to users’ needs. 3. multimedia PCs equipped for video confer- encing (plus any required peripherals). As envisioned, Packet Voice will provide a PSTN-like (Public Switched Telephone Network) We also envision some asymmetrical appli- experience to users by providing all the enhanced cations using one-way Packet Video with two- way audio. For example, live video conferencing 1. The authors note the contributions of many other with a call center representative where the cus- individuals, collectively representing the membership of the PacketCable product definition group, for their tomer sees and hears the Customer Service Rep- contributions to the production definition concept. resentative (CSR), and the CSR only hears the customer. PACKETCABLE NETWORK SUPPORT PACKETCABLE INFRASTRUCTURE

Conceptually, the PacketCable develop- The infrastructure required to deploy Packet- ment effort focuses upon the higher application Cable services in a local geographic area, consists layer, with the presumption that network-layer of three categories of equipment: services, and those below, will be provided by the DOCSIS modem or the OpenCable set-top • a logical gatekeeper, consisting of a set box delivered through a hybrid fiber/coax of servers, to manage most aspects of (HFC) cable network. The exception is the re- the service connections; quirement for quality of service created by the isochronous2 PacketCable services. • clients homed on the Packetcable server group; and Within this context, our development effort assumes PacketCable services will utilize a “ca- • local gateways used to enter or exit the ble intranet,” or private IP network, that uses IP network to the PSTN. edge devices, known as clients, to perform pro- tocol conversions that permit communications This architecture can be expanded to cover between subscribers directly connected to those a larger “On-Net” footprint by interconnecting devices. It also allows PacketCable subscribers local PacketCable networks using a hierarchy of to originate and terminate calls to stations con- directory servers and IP gateways. The actual nected to the PSTN through other edge devices, media connections between local IP networks, known as PSTN gateways. over which the voice and video packets are transmitted, are made through a series of IP gateways, which function as private network ac- A “cable intranet” consists of interconnect- cess points called C-NAPs (Cable - Network ed IP networks operated locally by the individu- Access Points). The PacketCable directory- al cable companies and interconnected, server hierarchy and C-NAP gateways permit managed-IP backbones (such as @Home and calls to be originated by a PacketCable client in RoadRunner/MediaOne Express). Such inter- one gatekeeper zone. The calls are terminated to connect capabilities will give the PacketCable a PacketCable client in any other gatekeeper service a North American footprint (i.e., allow- zone served by PacketCable, regardless of who ing PacketCable subscribers to make calls operates the system. throughout North America to other subscribers without having to interface with the PSTN). In instances where connectivity with the PSTN is SPECIFICATION EFFORT desired, such connections may be accomplished through conventional interconnect means. This Whenever possible, our preference in creat- may include leveraging the existing presence of ing a PacketCable specification is to utilize ex- some MSOs and their affiliates in the CLEC isting technical standards or known service- (Competitive Local Exchange Carrier) and CAP quality parameters where they exist. For exam- (Competitive Access Provider) markets to pro- ple, Packet Voice is an isochronous service, the vide these interfaces. quality of which is very sensitive to packet loss, “jitter,”3 and overall network latencies (delay). The PacketCable development effort will speci- 2. A descriptive terminology to describe a datastream that has a guaranteed, constant time relationship, or a fy an acceptable range of values for these pa- signal in which the time intervals between rameters. Moreover, we require Packet Voice be consecutive bits have the same duration. compatible with the basic functions of ITU rec- ommendation H.323. Similarly, Packet Video is also an isochronous service, the quality of which primarily on ITU H.263, supporting different is very sensitive to packet loss, “jitter,” video/ grades of video quality. audio “skew,”4 and overall network latencies. This two-way symmetrical service will be based Our investigation of these relevant techni- cal standards, however, reveals that they are in- 3. The time elapsing between the emission of the first complete to specify and to support fully the bit of a data block or packet by the transmission deployment of interoperable IP voice and video client, and its reception by the receiving client, is known as the network transit delay. The variation of services over cable networks. Consequently, the this delay over time, or the extent to which it varies PacketCable committee is currently in the pro- from packet to packet, is known as “jitter.” cess of developing a functional specification to deliver the services noted above that “fills in the 4. Video/audio “skew” refers to the stringent type of gaps” of these technical standards. The Packet- synchronization that occurs when speech is played Cable committee hopes to complete this specifi- out at the same time the image of the speaker is displayed. In the case of video conferencing, this is cation with the goal of delivering commercial also known as “lip-synchronization.” products for consumer and business applications within the next 9–12 months.