October 1998

BY BRUCE KRAVITZ

Many of today's packet networks lack the bandwidth and quality of service capabilities to handle multimedia traffic. Nevertheless, these networks are improving, and they are improving in conformance with H.323 -- a standard that promises to unify voice, video, and data across a single network. Thus, if we think of an emerging multimedia network as a road, and the network manager's multimedia deployment plan as a map, we can see that each -- the road and the map - must account for the same underlying reality (or landscape, if you will). And that reality is H.323.

H.323 allows high-quality voice, video, and data to be transmitted over local, metropolitan, regional, and wide area networks. (As first specified by the International Telecommunications Union in 1996, H.323 is an umbrella recommendation that enables packet-based videoconferencing. In this respect, H.323 is analogous to H.320, which enables ISDN-based videoconferencing.) Since H.323's contours will define many of the curves in the road ahead, network managers will need to keep H.323 in mind as they draw their plans for unified networks, that is, networks that can accommodate voice, video, and data. These plans will include familiar challenges - assessing needs and upgrading facilities (albeit with an H.323 twist) - as well as the additional task of keeping up to date on H.323 developments.

ASSESSING NEEDS
The first step toward building a unified network is to forecast future network usage. This challenge can be broken into more manageable sub-challenges. We will discuss each of these in turn.

• Evaluate Users' Needs: Consider the fact that H.323 is a complete system with a combination of telephony-like and data network-like services. Since users will not immediately utilize the full assortment of new services, application and network designers must collaborate in forecasting the most likely behavior or common-use scenarios for potential applications.
• Constrain Applications At The Outset: Understand and constrain the most likely applications during an introductory period. For instance, a video help desk shares some requirements with a PBX-based automatic call center application. However, H.323 video capability may add new elements to this process, such as being able to see a broken part in an order-desk application directly. Business processes and behaviors will need to change to take full advantage of these new potentials, and to insure that the technology remains comfortable and efficient for all users. Such changes are best taken in incremental steps.
• Predict Bandwidth Requirements: Based on the projected behavior of the different application users, predict the bandwidth needed on a particular network segment and across the WAN. Whether using a gatekeeper or manually configuring a terminal, the appropriate application bandwidth and usage patterns will depend on the total bandwidth available on the subnets, in the backbone, and across the WAN.
• Estimate Video Call Volume: Estimating video call volume will help you calculate the required network bandwidth. Most companies have telecommunications management tools that track and report call activity. A conservative scenario of call volume in the first four months of H.323 deployment predicts one-third of intra-company video calls will transfer to the IP network, leaving two-thirds on the existing ISDN video network. As time passes, successful H.323 deployments will see an increase in the percentage of video calls traveling over the IP network.

HARDWARE IMPROVEMENTS
In addition to forecasting future network usage, the roadmap for H.323 should include periodic upgrades of existing networking equipment.

Upgrading Existing Clients
The quality of the conferencing experience depends on the network bandwidth and the processor power at each terminal. If a processor is not sufficiently powerful to encode video at 15 to 30 frames per second, it will drop frames. In a circuit-switched network, the receiving decoder can optionally repeat frames to provide the illusion of a higher frame rate. But in an IP network, network components and the destination terminal may be expecting packets at a certain frequency and may be disrupted by network latency and jitter. Therefore, upgrading existing clients is a must.

In desktop systems, faster processors are more likely to deliver satisfactory H.323 performance. Products with hardware-assist will deliver even better performance. Similar concepts can be applied to group videoconferencing systems. The application will drive the requirements in terms of audio and video quality.

Upgrading Existing Network
Network improvements span both the physical network and the software. Network managers should follow these general steps in sequence:

• Upgrade Wiring: Replace all Category 3 wiring with Category 5 wiring.
• Comply With RSVP: Be sure all the new routers you install are RSVP-ready. If you can upgrade existing routers to RSVP, do so. If not, replace them. (RSVP is the preferred signaling protocol designated in H.323 for satisfying application QoS requirements, combined with the appropriate QoS services, scheduling mechanisms, and policy-based admission control modules.)
• Install LAN Switches: LAN switching can cost-effectively segment an overcrowded, shared-bandwidth workgroup into numerous "private" LANs, giving workgroup users, or even individual power users, access to a greater percentage of the full LAN bandwidth.
• Increase LAN Speeds: Replace 10 Mbps Ethernet with Fast (100 Mbps) Ethernet segments.
• Increase Backbone Bandwidth: Use Gigabit Ethernet or ATM products and services. Replace/upgrade current firewalls with H.323-ready products and proxy servers.

Putting H.323 Hardware And Software In Place
A third aspect in implementing an H.323 network is to add products that are H.323 compliant. A full-featured application will require H.323-compliant terminals, gatekeepers, gateways, multipoint conferencing servers, and proxy servers accessible from any point in the network.

• Gatekeepers And Zones: Most H.323 deployments will include a gatekeeper to manage address resolution (directory services), allocate bandwidth, and enforce an array of policies. Today's gatekeepers control special supplementary services such as forwarding, zone prefix, out of zone prefix, and access to WAN services via a gateway. An H.323 zone is the set of devices controlled by a single gatekeeper.
  
  H.323 network builders will encounter many addressing issues when setting up gatekeeper zones, including inbound dialing, inter-zone naming, and gateway selection. Gatekeepers must contain a core set of features as specified by the standard, but the market will see a variety of products with "extended" feature sets that will represent value-added services not defined in the current version of the H.323 standard. Once again, the application will determine the most appropriate feature set for a given implementation, combined with current infrastructure, network policy, and the organization's IT/Telecom strategy.
• Gateways: At the most basic level, the gateway provides the necessary conversion between different terminal types. For example, a gateway will allow LAN-based H.323 terminals to communicate with ISDN-based H.320 videoconferencing terminals. On like networks, gateways operate as a destination terminal. Thus, gatekeepers must be aware of which terminals are gateways. Another issue involves supporting interworking with speech-only terminals on POTS or ISDN by generating and detecting DTMF signals. The specification at this time does not define assigning extensions or addresses, so there remains some ambiguity about its implementation.
• Multipoint Control Units (MCUs): Many applications will require H.323 products to engage in multipoint, multiparty conferences. H.323-compliant multipoint control products are just becoming available. For those companies that already have H.320-compliant MCUs or use an established conferencing service bureau, it is possible for an H.323 endpoint to go through an H.323-H.320 gateway and participate in multipoint sessions hosted by an H.320 MCU. Multicasting and multipoint conferencing software for IP networks will continue to mature, giving H.323 users access to streaming (one-way) video and "native" multipoint capabilities.
• Proxies And Firewalls: Most firewalls are capable of primary and secondary TCP and UDP connections. Some firewalls only can pass through primary TCP connections on assigned ports. To enable H.323 conferencing across a firewall, the firewall must be able to pass through secondary TCP and UDP connections on dynamically assigned ports. A proxy can solve some security issues because it can be used to hide H.323 addresses in one zone from view by devices in another zone. Proxies can also be used to perform application-specific routing, which can direct H.323 traffic over various network segments with the appropriate quality of service.

STAYING CURRENT WITH H.323 DEVELOPMENTS
Current H.323 products are still in their infancy. Vendors continue investing heavily in research and product development, but a great deal of work remains. In fact, most products being tested for interoperability are first-generation H.323 products. Nonetheless, user feedback from these tests, along with the deployment of better technology, is hastening the rollout of second-generation products. H.323 products with greatly improved functionality will emerge over the next 12 months.

First Generation
First-generation H.323 products are becoming popular for certain types of distributed workgroup communication and project collaboration. Some customers are implementing trials, running H.323 over their private intranets. Although global network service providers are eagerly testing first-generation H.323 products, commercial IP transport services offering a guaranteed level of end-to-end quality of service are just starting to become available.

Interoperability issues remain. Today's H.323 solutions will be the most reliable when selecting a set of products from a single vendor or a tested set of compatible products. The fixed menu proposition (selecting from a subset of all the possible H.323 solutions and sticking only with known components from a single vendor) is receiving a great deal of support. In the near term, homogeneous network environments will be much easier to implement and manage.

Second Generation
By the end of 1998, a second generation of H.323 products will start to become available. Interoperability of these products is likely to be higher, although there may be some compatibility issues between first- and second-generation products developed by different vendors.

In preparation for future products and the anticipated rapid adoption of H.323 solutions, service providers are planning pilots and identifying the appropriate types of WAN services to offer. Network management, conference reservation, and security are among the likely services to emerge.

CONCLUSION
Even though this technology is still in its developing stages, the time is rapidly approaching when H.323 voice, video, and data will merge into one consolidated backbone network. By developing a roadmap and laying the groundwork today, network managers and their organizations will be able to make the transition smoothly and efficiently toward a single multimedia communications network in the months and years to come.

Bruce Kravitz is the Product Marketing Manager, Networking Technologies, for VTEL Corporation. VTEL Corporation is one of the world's largest developers and manufacturers of Digital Visual Communications technology. VTEL's products provide video, data, and voice quality and are simple to use. Because they are microcomputer-based, VTEL systems are scaleable, easily upgradeable, and highly networkable. For more information, contact the company at 512-437-2700 or visit their Web site, located at www.vtel.com.