nology for VoIP does not yet provide voice quality that is as good as a circuit-switched telephone network, but a lot of activity is being aimed at developing protocols for the implementation of high-quality voice service. The problem is that IP was designed for data communications and the pack- ets suffer a long and variable delay, which decreases voice quality. In princi- ple, samples of speech are transmitted in an IP packet payload and they do not arrive in regular intervals as they do in the case of circuit-switched serv- ice. To overcome this problem, the protocols of the Internet are being devel- oped to provide a fixed share of network resources for each voice call through the network. Figure 6.58 shows three possible ways to make telephone call over the Internet. In the first application example, a telephone subscriber dials the telephone number of the local gateway for an IP telephone service provider. The call travels over the PSTN to the nearest gateway that acts as an access point to the Internet. The service providers have their own telephone number prefix that connects a customer to the right gateway. Then the caller enters the destination telephone number and the gateway in the local office IP telephone service provider's local office Remote office Internet Gateway Gateway Web server Call center Internet or ISDN, PSTN, or cable modem To PSTN Gateway Router Internet or intranet Office A Office B Figure 6.58 Voice over Internet applications. Introduction to Telecommunications Network Engineering establishes a connection over the Internet to the gateway in his remote office closest to the destination. Then the gateway in the remote office calls the des- tination subscriber via the local PSTN. Internet routing and speech process- ing is performed by the gateways and ordinary telephones can be used for the call. Now the Internet, instead of PSTN, carries a long-distance section of the call. In this way, international calls in particular can be provided at very attractive fees because only the local par