tailieunhanh - Will Your Structured Cabling be Suitable for IP Telephony?

Will Your Structured Cabling be Suitable for IP Telephony? Discussions on the impact that a network's 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'. | KRONEfaCtS Will Your Structured Cabling be Suitable for IP Telephony Discussions on the impact that a network s 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 system will not suffer. How does VoIP work There are three stages in making VoIP work. Analogue Voice Signal sampled for digitising 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 Resultant digital telephone signal First is the conversion of the analogue audio signal into a digital signal by an A D converter or codec at the transmitter end. Second is the breaking up of the digital signal into packets of data then sending these IP packets to the receiving IP telephone via the network. Third is the conversion of the digital signal at the receiver using another codec back to analogue audio for the listener. 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 signal takes too long to arrive conversation clashes will occur. Transport Delay is the time taken to pass through each networking device. Every switch router traffic shaper firewall and hub adds a small delay. For unintelligent devices like hubs the delay is constant but for intelligent switches the delays increase .