rs may latency jittering, and packet loss, and requires much elect to tolerate it, just as many people accept sub- more attention than a data packet. Figure 3.2-9 shows standard quality when using cell phones. a typical VoIP converged network with different type media and signaling gateway. Packet loss Implementing VoIP requires attention to many fac- Typically occurs either in bursts or periodically due to tors, including a consistently congested network. Periodic loss in excess Delay of 5-10 percent of all voice packets transmitted can Packet loss degrade voice quality significantly. Occasional bursts of Available bandwidth packet loss can also make conversation difficult. In a VoIP network, there are several factors influencing packet loss. Manageability Jitter Packet loss requirements are tighter for tones (other Packet prioritization than DTMF) than for voice. The ear is less able to Latency detect packet loss during speech (variable pitch) than it is during a tone (consistent pitch). Media Media gateway controller gateway controller Signalling Signalling Signalling Signalling conversion conversion Signalling gateway H-323 gateway Sigtran ISUP/TCP Sigtran Media IP Network signalling Media gateway gateway control control signalling H.GCP H.GCP Q.Sig Q.Sig Media RTP,RTCP Media Media gateway gateway Figure 3.2-9 Converged architecture. CHAPTER 3.2 Network infrastructure success of this effort depends on the statistical averaging Table 3.2-6 Sample delay budget table. effects of many calls. Another approach to bandwidth Parameter Fixed delay Variable delay management is through prioritization: Give audio pre- ferred access to the limited facilities and let other types CODEC (G.729) 25 msec of data streams contend for what's left. This approach Packetization Included in CODEC may be invoked by choice of an 802. 1p priority (at layer 2), or a DiffServ service tag (at layer 3). Queuing delay Depends on uplink. In Despite the high speeds available in today's LANs, the order of a few mSec. they are not immune to QoS 