audio and video, sometimes called lip sync. This is nothing more than maintaining an accurate timing rela- tionship between audio and video. What is important from a communications network perspective is the bit rate and signal interface. The output of the audio console or mixer PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS will get connected to a wire or fiber conductor or some type of network interface. A good example is AES3 serial digital interface used in television audio. The physical connector is a BNC coaxial connector and the encoded bit rate ranges from 192 to 756 Kbs for dual channel audio, scaling linearly upward for multi-channel sound payloads. The second of our three basic models is the network interface device (NID). The basic function of the NID is as its name implies, interface the broadcast facility with the communications network. Figure 1-6 is a functional block diagram of a generic NID. In simple terms, the NID enables content to be moved from the televi- sion world to the network transport world and back to the television environment, safely and securely, one bit, byte, cell, or packet at a time. Couple a well-designed NID with proper communications facilities and you have capability to interface and manage all the supporting voice and data communications, as well as managing end-to-end service for a simple point-point connection supporting content cre- ation, or a multi-point network distributing and delivering content. SMPTE 259 L4 (ATM VBR nrt, TCP, UDP) SMPTE 292 Compression & Decompression L3 (ATM VBR rt, IP) AES-EBU Audio L2 (ATM CBR, Ethernet, ISDN) DVB-ASI Wired Direct Mapping & L1 Channel Interface (PDH, E1/T1 Adaptation SONET, SDH) Wireless E3/DS3 Internet Broadcast Interface Telecom Interface RS 232 10/100BT FIGURE 1-6 Functional Block Diagram Network Interface Device The last model to be used is shown in Figure 1-7. The purpose of this model is to provide the broadcaster with a tool to specify, quantify, and contract for equipment and services. With invo- cat