nment. Multimedia applications and as traffic load increases and congestion builds. For audio convergence changed the situation-usage and users traffic, three main approaches are available to minimize must now be distinguishable and network processing bandwidth usage, as follows: needs to be tailored to each class of traffic. For example, 1. choose a low-bit-rate audio codec; a real-time telephone call should not be handled the same way as a large file transfer if they share a link. Differen- 2. combine multiple audio frames into one packet; tiating among QoS requirements can be done by classi- 3. suppress transmission of silence. fying each packet and using this information in switching decisions. The IETF (in a working group called DiffServ) The first method can reduce the audio data rate from is completing a series of standards that re-define the type 64 kbps (PCM) to 8 kbps (G.729), or even as low as 5.6 of service (ToS) byte and re-name it as the Differentiated kbps (G.723.1). (Note that addition of RTP/IP overhead Services Control Byte (DSCP). RFCs 2474 and 2475 makes the net traffic differences smaller than the data provide the details. Figure 3.2-11 illustrates the DSCP rate differences, though the use of header compression within the context of the IP protocol header. can mitigate this effect.) Two sacrifices must be made to DiffServ [RFC2474] makes use of the existing Type- obtain this reduction: Processing must be expended to of-Service (ToS) octet in the existing IP Version 4 header perform the encoding and decoding; and, the audio [RFC791]. As such, it may be set by information senders quality is degraded to an extent dependent on the codec and used by IP (Layer 3) routers within the enterprise used. The second method reduces packet overhead, does network. Effectively, the ToS octet is really just 6 bits not affect audio reproduction, but does increase the la- wide because neither DiffServ nor IP ToS use the least- tency by the time represented by the number of addi- significant 2 bits; they are rese