DOWNLOAD MY Ph.D Thesis - UNAM

Chapter 5Upstream channel capacity and characterisation pAnother novel and topical VoIP stream that will be analysed is that of 12.4 kbps, whereevery 30 ms a voice frame is generated and encoded using header compression, asillustrated also in Table 5.2.In order to support VoIP traffic, according to [118], there is a need for an overall end-toendpacket delay of less than 150 ms for a high-quality call and up to 400 ms for a lowservicequality call. In our experiments we consider delays under 50 ms from the NIU tothe headend for the support of VoIP streams, leaving an extra 100 or 350 ms delay forthe final destination according to the expected quality of the call.5.3.3 Mixed traffic (Internet +VoIP)This traffic type emulates a combined traffic situation, where each station is generatinga VoIP data stream of 9.7 kbps, as introduced in Section 5.3.2. Additionally, someInternet traffic, as presented in Section 5.3.1, is multiplexed into the data stream and istransmitted via the upstream channel. The mean data rate per active station is set to32 kbps (consisting of 9.7 kbps of VoIP traffic and 22.3 kbps of Internet traffic) or 41.7kbps (consisting of 9.7 kbps of VoIP traffic and 32 kbps of Internet traffic) according tothe case study analysed.5.3.4 Isochronous streamsIsochronous streams are time-dependent and exist with processes where data must bedelivered within certain time constraints. For example, most multimedia streams requirean isochronous transport mechanism to ensure that data is delivered as fast as it isdisplayed and that the audio is synchronised with the video. This traffic type emulatesisochronous streams with data rates of 12 kbps, 32 kbps, 64 kbps and 128 kbps, suitablefor timing-critical interactive services (e.g. low quality video,compressed/uncompressed voice telephony and audio). Different packet sizes (64, 128,256, 512, 1024 and 1518 bytes) were considered for the delivery.All isochronous streams used in the simulations included the higher layer protocoloverhead. For example, the most likely protocol for isochronous streams is TCP/IP witha Direct IP or Ethernet bridge solution. The latter has (at the MAC layer) a 61-byteoverhead comprising of 20-bytes (TCP header) + 20-bytes (IP header) + 3-bytes (LLC5-6