Content

| 7.1 |  | Introduction to Cisco AVVID |
| 7.1.7 |  | Legacy migration |

Although building a converged network with Cisco AVVID has obvious advantages, some existing legacy voice and video systems require a seamless migration into the New World. One example might be a scenario where an existing PBX has reached capacity and its growth is dependent on IP telephony. In some cases the existing voice-mail system still has the capacity to sustain the additional users and it is desired maintain the existing system in production.

Here, a voice-mail system is connected to the PBX using multiple analog voice ports to carry voice traffic and a signaling line called a Simple Messaging Desktop Interface (SMDI) that passes information, such as whose mailbox greeting to play on which particular voice port, to the voice-mail system. This is one of many ways to network voice mail to a PBX.

The first part of the migration to consider is establishing uniform dialing plans that are the same on both the legacy and Cisco AVVID networks. This is easily achieved using either a standalone gateway or one of the many router/gateway combinations available from Cisco. Regardless of which side of the network the user is on, the incoming and outgoing calls from the outside world appear exactly the same (whether using direct inward dial or using an operator and extensions). Internal dialing using a shorter dial plan (perhaps four or five digits) can also be maintained.

From a voice-mail perspective, Cisco CallManager also supports SMDI for control of a voice-mail system. Coupled with analog gateways connecting to the same voice mail, calls on either side of the network appear exactly the same to voice mail.

In the video world, it is common to have H.320 based videoconferencing systems, each with their own PSTN network connections. LAN-based H.323 video systems also are commonly deployed in many companies, such as Microsoft NetMeeting, which utilizes H.323 for videoconferencing and shared collaboration. Again, the Cisco AVVID solution provides several different ways to preserve investment in legacy systems while investing in converged network solutions.

Two different scenarios are shown in Figure .

On the left side, there may be a whole network of H.320 systems deployed by the corporation or customers. Using a Cisco video gateway enables communication between the converged H.323 network and the legacy video network. It would also allow customers or vendors who have only H.320 systems to communicate with a new network of H.323-only systems. Additionally, on the right side, individual H.320 endpoints can be networked seamlessly in an H.323 network with the use of a Cisco video terminal adapter.

Conclusions
The fact that every major networking vendor has announced plans for IP telephony solutions leads to the conclusion that the convergence of data, voice, and video networks is inevitable. The only possible convergence solution is to merge the existing voice and video networks onto the IP data network. For this to succeed, many aspects of the intelligence of the IP data network need to be exercised.

Lastly, tools that aid in migration from legacy voice and video networks toward networks converged on IP make it possible for mass deployment of networks based on the Cisco AVVID architecture.

The next section introduces IP multicast technology.