Neither the ISDN nor the subsequent broadband-ISDN (B-ISDN) delivered on the promise of being a network for all services. Now that mantle has been passed to IP networks born out of computer-to-computer communications. But their benefits, such as great flexibility of bit rate and resilience, are accompanied by other characteristics which are alien not only to traditional telephony but also to many of the multimedia services which telcos are now seeking to offer their customers. As part of the adaptation of IP networks to carry the widest range of services and applications, the concept of quality of service has been invoked. This paper looks at the performance characteristics which various applications require. It also describes techniques they can incorporate to reach a satisfactory overall result in combination with the network.