January 1999

The Introduction Of H.323-Compliant VoIP Solutions

BY TOM FLANAGAN AND DR. MICHELLE BLANK

For enterprise users, manufacturers, service providers, and industry watchers interested in Voice over IP (VoIP), 1998 will be remembered as a year of high-speed racing just to keep up with an industry evolving at an astonishing rate. While standards have been in development, the frenetic pace has meant that few can invest the time and resources necessary to keep up with the changes. However, without widely accepted, stable standards, enterprise users cannot be assured of interoperability between business applications. A race is on to create the systems that will enable the migration of voice, fax, and data traffic from the PSTN to carrier-grade IP networks. Perhaps, when viewed with the clarity of 20/20 hindsight, the issuance and acceptance of the H.323 recommendation will be remembered as the breakthrough that gave visionary manufacturers and service providers the confidence to move forward. This is not meant to disparage alternative signaling protocols like Session Initiated Protocol (SIP) or Media Gateway Control Protocol (MGCP, formerly known as Simple Gateway Control Protocol, or SGCP). It's just that H.323's early arrival and implementation has provided the industry a critical stepping stone from which to move forward.

H.323 directly benefits end user organizations deploying VoIP by offering a stable and backward compatible protocol upon which future generations of products can rely. The standard's adoption by hundreds of manufacturers has an additional benefit: it means that businesses deploying VoIP have multiple sources for any given solution. Competitive pressure in technology guarantees continued innovation and, eventually, lowers prices for goods and services, spurring further growth in the industry. Consumers, manufacturers, software designers, and service providers all benefit.

H.323 is the International Telecommunication Union (ITU) "series H" recommendation for "Packet-based multimedia communications systems." Issued in February 1998, H.323 resides comfortably between H.322 - "Visual telephone systems and terminal equipment for local area networks which provide a guaranteed quality of service" - and H.324 - "Terminal for low bit rate Multimedia Communication." H.323 has become the globally accepted standard for audio/video/data communications between user terminals, network equipment, and assorted services on Local and Wide Area Internet Protocol (IP) networks.

The H.323 recommendation is an "umbrella" specification, meaning it contains references to other recommendations, including H.225.0 packet and synchronization, H.245 control, H.261 and H.263 video codecs, G.711, G.722, G.728, G.729, and G.723 audio codecs, and the T.120 series of multimedia communications protocols. Together, these specifications define a number of new network components - H.323 terminal, H.323 multipoint controller, H.323 multipoint processor, H.323 gatekeeper, and H.323 gateway - which interoperate with other standards-compliant end points and networks.

H.323 is particularly noteworthy due to the support that has coalesced around it. A global coalition of companies, including personal computer and communications systems manufacturers, as well as operating systems makers, have come together in support of H.323. In other words, H.323-compliance has been accepted by computer telephony and VoIP manufacturers as the standard for interoperability. Today, more and more VoIP networks rely on H.323 gateways to adapt traditional telephony to IP and gatekeepers to provide services like address translation and accounting.

INTEROPERABILITY: THE FUNDAMENTAL ADVANTAGE
The bottom line benefit of the acceptance of the H.323 recommendation is the resulting interoperability of Internet telephony network components. Though the computer telephony industry still suffers from lack of standards in certain areas (quality of service and billing in particular), H.323 has blown wind into the sails of manufacturers eager to bring products to market quickly that will perform effectively when implemented across disparate networks.

The interoperability of Internet telephony networks was given a boost in September, when three of the industry's biggest players - Lucent Technologies, VocalTec, and ITXC - demonstrated the interoperability of Lucent's PacketStar Internet telephony system and the VocalTec Ensemble Architecture System over ITXC's WWexchange Service. This event was noteworthy in that two gateway systems (Lucent's and VocalTec's), were able to interconnect calls using independent gatekeeper services provided by the third (ITXC). H.323 was the common denominator that allowed this to happen. Also in September, Telogy Networks and RADVision demonstrated the industry's first embedded VoIP software integrated with H.323.

Ironically, the lightning fast pace of development is responsible for both the confusion surrounding VoIP and H.323's concurrent acceptance. The computer industry is renowned for releasing test versions of products, and customers traditionally have tolerated low levels of both reliability and interoperability. In too many instances economic considerations or competitive instincts have had more to do with driving standards than standards bodies such as the ITU or W3C.

End user acceptance of proprietary VoIP systems has been high because the payback periods are so short. Even while this industry is in its infancy it is economically justifiable to install a proprietary system on an enterprise-wide basis, knowing that within a year to 18 months it will be obsolete. This is the reason that VoIP manufacturers like Cisco Systems report per port shipments doubling quarter over quarter. Many of these systems are running on intranets rather than on the public Internet. However, collaboration between telecommunications and computer industry leaders rose dramatically during H.323's development. As a result the specification progressed rapidly, incorporating experience and innovations from both industries.

FUNDAMENTALS OF AN H.323 VoIP SOLUTION
The fact that we can purchase a device for a few dollars that will enable us to speak real-time with someone in Fiji should be astounding. This sophisticated, multi-stepped process is taken for granted. At least eight signaling-related steps are involved in the "simple" act of picking up the telephone, hearing a dial tone, dialing a number, and connecting to another telephone.

These steps are signaling events: signals are exchanged between a telephone, an originating PSTN Central Office switch, a terminating switch, and the terminating phone. These signals are functional: they connect and disconnect calls as well as inform the caller of the progress of the call.

VoIP calls fall into three categories: PC-to-PC, PC-to-phone, and phone-to-phone. All three types can use H.323 to set up the Internet portion of the call. In order for these calls to be transmitted over the Internet, VoIP gateways must perform advanced telephony signaling techniques. All of the PSTN's signaling steps must be received by the gateway, interpreted, converted into a specific message such as "call request" or "disconnect," transmitted, received at the destination gateway, and reconverted to analog form before transmission to the receiving telephone.

This complex conversion process (which includes the translation of analog telephone numbers to digital Internet addresses) applies to all of the telephony signaling events that occur when someone picks up the phone to make a call, and must occur within today's strict tolerances. As these telephony signals are interpreted by the gateway, they are mapped to the H.323 protocol, which ensures the proper transmission of set-up, maintenance, billing, and tear-down messages.

AN EMBEDDED SOFTWARE APPROACH TO AN H.323 VoIP GATEWAY
Scalable gateways are further evidence of VoIP's evolution from hobbyist to carrier-class, next-generation network technology. In addition to being able to handle multiple ports with telco-style reliability, these sophisticated systems must simultaneously support multiple voice codecs, as well as fax and data transmission.

The first VoIP gateways were PC plug-in boards often running in NT servers. As demands placed upon the systems grew in scale and functionality, and as Digital Signal Processor (DSP) and microprocessor technology improved, developers began to examine other approaches to gateways. The favored approaches have become building dedicated standalone hardware (i.e., not PC or NT-server based) or creating Internet telephony replacement or expansion cards for existing products like routers, switches, and PBXs. Designers of these second-generation systems are increasingly turning to off-the-shelf software solutions for core voice processing and signaling software. An advantage of an embedded software gateway is that its DSP components can be designed to accommodate dynamic processor configuration, which provides a more cost-effective approach than periodic hardware upgrades necessitated by rapidly changing specifications.

Initially, H.323 was only available for use in PC client devices such as Microsoft's NetMeeting. With the extension of H.323 into embedded software, the range of interoperable platforms will extend to include all manner of networked devices, including large-scale VoIP gateways, IP-PBXs, Central Office switches, and routers.

ANATOMY OF A VoIP EMBEDDED SOFTWARE GATEWAY
In a carrier-class VoIP embedded software gateway, a series of DSPs and microprocessors manage the advanced telephony signaling functions:

DSPs manage:

• Tone Generation.
• Tone Detection.
• Voice Processing.
• Echo Cancellation.
• RTP (Real-Time Protocol).

Microprocessors manage:

• Telephony Protocols.
• H.323.
• Network Protocols.
• Management.
• Routing.
• Billing.

Complete embedded VoIP solutions provide telephony signaling protocols such as Channel Associated Signaling (CAS) and Common Channel Signaling (CCS) in Switched mode, where data calls are dynamically set up to accommodate signaling messages, and in Transparent Mode, where a dedicated signaling channel is deployed. Emulation of FXS and FXO (Foreign Exchange Station and Office, respectively) are also provided. They also feature complete signal processing software codecs, echo cancellation, tone detection and generation VAD, silence suppression, jitter removal, multi-channel/multi-function and real-time fax transmission capabilities.

SUMMARY OF BENEFITS TO ENTERPRISE USERS
What does the emergence of embedded H.323-compliant VoIP equipment mean to enterprise users? Here are four key benefits:

Improvements In Call Signaling For More Collaborative Applications
Prior to the advent of embedded H.323 solutions, H.323-compliant VoIP was limited to PC-to-PC communication. Now, enterprise users utilizing H.323 devices can also communicate between PCs and phones and from phone to phone. Serious business applications require the option to use all three forms of communication.

Reduced Risk Of Incompatibility Among Systems
The merger mania that swept the globe in the past decade resulted in difficulties for the communications professionals responsible for assimilating widely dispersed office locations into one cohesive corporate network. The advent of embedded H.323 solutions allows interoperable VoIP equipment, reducing the risk of acquiring incompatible VoIP equipment.

Better Utilization Of Assets
VoIP enables network managers to "fully load" IP networks that were previously designated only for data, sending excess voice traffic across the IP network. New advances in voice compression, such as the G.723.1 standard, allow IP voice to be transmitted using only 5.3 Kbps, compared to the 64 Kbps of a standard phone call.

Cost Savings
Many businesses around the world are taking advantage of the cost savings inherent in using private or public IP networks to send voice traffic. The regulatory issues surrounding this phenomenon are still being battled out, but for now, many are taking advantage of the opportunity to avoid international settlement fees.

Tom Flanagan is director of business development for Telogy Networks, a leading provider of embedded communications software for VoIP applications, and developer of the Golden Gateway Voice and Fax over IP product suite. Dr. Michelle Blank is president of RADVision, a leading provider of standards-based internetworking gateways for video conferencing and telephony. For more information, call Telogy Networks at 301-515-6690 or RADVision at 201-529-4300. Information about both companies is available on the Web at www.telogy.com and www.radvision.com.