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Putting the pieces together for VoIP

Mon, 11/30/1998 - 7:00pm
Jim Albrycht, Technical Consultant, Nortel Networks

With the implementation of broadband networks, subscribers can utilize simultaneous video, voice and data services over a two-way connection. Taking advantage of this technology, cable operators are beginning to offer subscribers a two-way broadband service, both in real-time and store-and-forward modes. This new technology, with additional programming improvements, is just the beginning of the types of improved broadband services that will revolutionize the way people work, learn and play.

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Figure 1: Broadband reference model. Live, real-time voice and video telephony conferencing services are positioned as a cable modem Internet protocol service, close to and related with their higher quality television counterparts.

Among the daily rituals that will change with the implementation of broadband is the use of the telephone. Broadband will enable the addition of new and improved telephony voice services that exceed the performance of traditional telephone service in many ways. Broadband will allow cable operators and consumers to take advantage of real-time audio and videoconferencing, purchasing power via audio and video storefronts, and a la carte cable/voice capabilities. Unlike the traditional telephone, broadband technology has infinite possibilities based on its ability to grow geometrically and spawn new and affordable multimedia applications.

Typical telephony services can be viewed as having a range of subscriber values. These include:

  • Higher quality sound
  • Low subscription and service costs
  • The ability to add new lines or phone numbers
  • Interoperability and ubiquity over the entire public telephone network
  • Ease-of-use.

Furthermore, broadband enables subscribers to utilize voice-over-IP services only when they are needed. The cable operator can provide this service at a customer's request, provided it is available in their area. The DOCSIS standard will help solve the problem of interoperability and ubiquity over the cable line. As PCs add more bandwidth, telephony communications will improve. To entice customers to implement voice communication via a cable line, cable operators must offer reliable cost savings, increased voice quality and substantial customer support.

The distinct advantages of voice-over-IP (VoIP) via a DOCSIS cable modem include:

  • Channel bandwidth availability
  • Data processing power
  • Storage capacity
  • Integrated bundling and billing.

Processing power, storage capacity and bandwidth availability all work in concert to deliver a high performance communications experience, while providing cost savings for both the operator and subscriber.

Cable modems are designed to carry data at high speeds over Ethernet interfaces. They are also designed to cover long distances from subscriber to headend controller across communities and regions, while supporting a wide range of multimedia applications. These requirements forced the data traffic packaging into streams that were similar to the voice and video patterns that existed in traditional stand-alone legacy networks (see Figure 1). The DOCSIS standard will reinforce the multiple data traffic patterns with extensions to support integrated data, voice and video services concurrently over the same channel and data streams.

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Figure 2: IP voice network interfaces. Cable modems provide links to the local community, while privately-managed cable backbones act as a gateway inot traditional networks for global connectivity.

However, while PCs plug into high-speed cable modems and integrate voice, video and data, the PC is used for many applications at the same time, which can drastically impact the sound quality of the telephone call. Dedicated telephony in the form of voice cards with digital signal processors (DSP) are designed to carry the smoothest and highest voice quality over Internet protocol. Enabling voice communications over DOCSIS standard cable modems is only one goal in the standard broadband integrated service. CableLabs is pursuing three initiatives involving the DOCSIS cable modem, which include:

DOCSIS for data PacketCable for real-time interactive services that involve both voice and video OpenCable for IP broadcasting and linking all other services.

The PacketCable initiative will provide an open architecture with real-time interactive broadband applications primarily for integrated voice and video communications. A wide variety of products and implementation scenarios, including the convergence of traditional legacy consumer appliances with advanced digital appliances, will result for the broadband subscriber. Traditional telephony services will be among the first offerings to converge with advanced telephone applications under PacketCable compliant solutions.

The traditional telephone is inexpensive because it relies on the processing power and switching at the telephone central office. In broadband, the intelligent processing power and switching is not centralized, but distributed at the network periphery in the cable modem, reducing the overall costs of entry and operations.

When a subscriber decides to change telephone service carriers and move to broadband, the standard RJ-11 connection is unplugged from the twisted-pair terminal block and plugged directly into a standard PacketCable-compliant DOCSIS cable modem. The telephony enhanced modem creates the same dial-tone, ring, busy and other call management features associated with traditional telephones. The cable modem begins to pick up some of the sound processing features of the PC at a fraction of the cost. All call management is done by the same touch-tone keypad, and there is nothing new to learn in the call set-up or operation.

Today's home phone wiring supports multiple lines for fax machines, answering machines, dial-up modems, cordless phones, security systems, etc. When a new traditional dial-up service is deployed in the home or office, a minimum of a six-pair cable is brought to the demarcation point on the side of the house. Dial-tone and billing are activated from the central office on each local pair, as needed. PacketCable modems will allow communications wiring to converge within the establishment. This new centralized broadband communications processor that includes all network peripherals is referred to as a "digital furnace."

The basic broadband IP telephone client terminal may come in the form of a:

  • Multimedia PC
  • Cable modem with an external telephone adapter
  • Cable modem with an embedded telephone adapter
  • Cable modem with a telephone adapter embedded in a set-top box.

The basic broadband IP telephone server system comes in the form of:

  • IP-to-PSTN (public switched telephone network) gateway
  • Directory servers
  • Back office traffic and billing server
  • IP-to-IP policy router.

The use of common servers across voice, video and data lines supports independent and integrated revenue streams, thus reducing implementation costs and operational complexity. The integration of server technology, supporting both software and hardware applications, further reduces cost and complexity and offers higher performance while increasing penetration and subscriber take rates.

These servers work in concert with the DOCSIS cable modem termination system (CMTS) at the headend, which in turn works with the IP telephone client and consumer communication terminals. A PacketCable/DOCSIS standards-based client and server system, deployed on the cable operator's privately-managed local and wide area broadband Intranet, enables interfacing and interoperability with other private, public or PSTN networks.

Business experience

The key benefit to broadband PacketCable is its low cost of entry and operator ownership. PacketCable provides operators the ability to implement PacketCable modems in bulk to any residential or business establishment. Broadband IP telephony is a service that is riding on top of an existing network platform, similar to an application operating on a PC. Operators benefit from the new service offering, and subscribers receive an improved telephony service with the same or less expensive monthly billing.

A PacketCable modem can also be installed without reconfiguring the infrastructure in the home or office. Headend servers can be either dedicated or shared with other broadband services at incremental costs. This "pull" technology is expected to grow as new subscribers are added and the service expands.

With additional managed bandwidth and coupled processing power at his disposal, the operator can offer a quality audio experience for the subscriber. IP telephony does not require a dedicated line or channel with an associated number. During a calling session, a private virtual circuit is established only when a ring or dial-tone command is issued, and only for the duration of the call. If a session is in progress from a home or office and another party wishes to make a call, another virtual circuit is established without blockage or a busy signal.

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Figure 3: Broadband IP voice data interfaces. As subscriber technology converges, cable modem high-speed ports are joined by telephony dial-tone service ports, all from the same common interactive digital cable channels.

The same principal holds true if another party is calling in from another location; another virtual circuit will take the call. This process is scaled across the cable modem channel throughout the home and across the community. If there are data traffic bursts on the channel, voice services have priority without interruption or degradation, as per the DOCSIS Quality of Service protocols. Traditional features, such as voice mail, call forwarding, call waiting and camp-on, are all part of the IP telephone package. All other communications appliances in the telephone category that require a dial-tone, including fax machines, answering machines, and even dial-up modems, can be serviced via IP telephony over broadband as well.

While the subscriber is enjoying a new experience and using a familiar legacy appliance, the operator is sharing resources, both in systems and servers as well as trained human resources. In a network operations center, employees need little incremental training when managing or deploying IP telephony via a cable modem. It becomes an extension of the broadband network management features. Furthermore, installers will be able to use a standard phone when deploying IP telephony over a cable modem.

The future migration of the PacketCable real-time interactive broadband initiative is to take the IP telephone service to full audio and videoconferencing. This strategy calls for servers that will conference a large number of calls together. The home TV set and camcorder can be brought into a voice session that will provide full duplex or simplex videoconferencing links to all managed broadband telephones. A range of sound and video quality sessions can be created to join the in-progress voice session. This can be done both across the cable Intranet as well as across other television networks depending on resource availability and network traffic. Both live and stored information can be brought to the conference as needed.

Conclusion

It is clear that DOCSIS cable modems with PacketCable and IP telephony are moving closer to OpenCable and broadband integration. As telephone numbers and IP addresses are cross referenced, media identification and location can become commonplace. Video-on-demand can be ordered from the telephone keypad with confirmation from voice prompts for retrieval from common voice and video mailboxes around the world. There is no end to where the broadband experience can lead.

The ultimate goal is to provide the consumer a la carte voice, video and data broadband services, enabling every consumer to pick and choose any and all communication mediums. To accomplish this goal, both the service provider and the consumer must be able to afford and understand the technology and business relationships to enjoy the full communications experience.

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