34.2 ARCHITECTURE FOR MULTIMEDIA COMMUNICATIONS OVER IP NETWORKS

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34.2 ARCHITECTURE FOR MULTIMEDIA COMMUNICATIONS OVER IP NETWORKS

The architecture for multimedia communications over the IP network is shown in Figure 34.1. Corporate LANs can be connected to an IP-based intranet or the Internet through routers/gateways. The corporate LAN will consist of nodes with multimedia capability. The multimedia PC can make voice calls, carry out video conferencing, or exchange fax messages with users on the Internet/intranet or with users on the PSTN. If a multimedia PC has to make a call to a telephone on the PSTN, there is a need for a special gateway (also called interworking function or IWF), which does protocol conversion between the IP-based protocols and PSTN protocols for call processing. Note the special IP Phone device connected to the corporate LAN-this is a telephone with an Ethernet interface that can be connected to the hub/switch of the LAN. Persons who do not need a PC can be provided with an IP phone for making voice calls. Like any PC on the LAN, an IP phone will have an IP address. This IP phone can be used to make calls to a local PC, an external IP phone, or a fixed telephone on the PSTN. Of course, for all this to happen, we need special protocols to overcome the deficiencies of TCP/IP protocols for real-time transmission of voice. Similarly, a fax machine on the LAN or a PC-based fax system can interchange fax messages with fax machines connected over the PSTN.

Figure 34.1: Multimedia communication over IP network.

For transmission of voice over IP networks, PCM coding will result in very high data rate-the number of packets to be transmitted will be very high, resulting in high delays. To reduce the delay and also the processing requirements, low bit rate speech coding techniques are used. The same is the case for video communication.

An IP network can be interworked with the PSTN through a gateway or interworking function (IWF), which does the necessary protocol conversions. Note that the signaling used in the PSTN and IP networks is different to establish voice calls.

Note 

The IP phone is a gadget that functions as a normal telephone. However, it can be connected to an IP network through an Ethernet interface. An IP phone will have an IP address that can be mapped to a telephone number.

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