Will Your Structured Cabling be Suitable for IP Telephony?

Will Your Structured Cabling be Suitable for IP Telephony?Discussions on the impact that a networks structured cabling system has on VoIP operation.Introduction IP Telephony, which includes the commonly known Voice over Internet Protocol (VoIP), is usually introduced into an enterprise as a cost saving measure. This is part of the convergence of data and voice (and video) on the local network so that it is under the control of the enterprise rather than relying on outside specialists. To implement this successfully all components including the network cabling infrastructure, need to be evaluated to ensure the voice quality of the telephone...
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Will Your Structured Cabling be Suitable for IP Telephony? KRONE factsWill Your Structured Cabling beSuitable for IP Telephony?Discussions on the impact that a networks structuredcabling system has on VoIP operation.Introduction IP Telephony, which includes the commonlyknown Voice over Internet Protocol (VoIP), is usuallyintroduced into an enterprise as a cost savingmeasure. This is part of the convergence of dataand voice (and video) on the local network so thatit is under the control of the enterprise rather thanrelying on outside specialists. To implement thissuccessfully all components including the networkcabling infrastructure, need to be evaluated toensure the voice quality of the telephone systemwill not suffer.How does VoIP work? There are three stages in making VoIP work. Speech requires a constant stream of packets, unlike data that can accumulate packets and send them in bursts. To maintain reasonable quality of the conversation, the IP voice packets cannot take too long to arrive at their destination and they must arrive in the correct order. Transmission Delays There are four main delays that could affect a VoIP signal; Propagation Delay is the time taken for the signal to travel from the transmitter to the receiver. If the First is the conversion of the analogue audio signal takes too long to arrive conversation clashessignal into a digital signal by an A/D converter (or will occur.codec) at the transmitter end. Transport Delay is the time taken to pass through Second is the breaking up of the digital signal each networking device. Every switch, router, trafficinto packets of data then sending these IP packets shaper, firewall, and hub adds a small delay. Forto the receiving IP telephone via the network. unintelligent devices like hubs the delay is constant,Third is the conversion of the digital signal at the but for intelligent switches the delays increase orreceiver using another codec back to analogue decrease as the levels of other traffic on theaudio for the listener. network increase or decrease.KRONE (Australia) Holdings Pty Limited2 Hereford Street Berkeley Vale NSW 2261PO Box 335 Wyong NSW 2259Phone: 02 4389 5000Fax: 02 4388 4499Tech Support: 1800 801 298Email: kronehlp@krone.com.auWeb: krone.com.auCopyright © 2004 KRONE (Australia) Holdings Pty. LimitedJob No.: 6169 02/04 Packetisation Delay is the time taken to convert However, there has been considerable progressthe analogue signal into a digital signal and vice towards objective measurement systems. For example:versa through the coder/decoder (codec). Different PSQM - Perceptual Speech Quality Measurecodecs have different data transfer rates and (ITU P.861)packetisation delays MNB - Measuring Normalised Blocks Jitter Buffer Delay is the time taken to queue (ITU P.861)inside a jitter buffer. Rather than converting VoIP PESQ - Perceptual Evaluation of Speed Quality (ITU P.862) Table 1 Packetisation Delay Code Date Rate Packetisation PAMS - Perceptual Analyses Measurement kbps Delay mS System (British Telecom) G.711 64.0 1.0 G.729 8.0 25.0 E-Model - A computational model for use in G.723.1m 6.3 67.5 transmission planning (ITU-T G.107) Most of these measurements are good in test labspackets directly back to analogue when they arrive, ...