fness' If you use a certain data communication (for example an e-mail program), you do not want to lose information when you upgrade to a newer version (for example, have to rewrite your address book). This has more to do with the terminal software than the Understanding Changing Telecommunications - Building a Successful Telecom Business actual communication network. For the operator, the choice of technology for imple- menting a service should be future-proof, which means it must be scalable and possible to upgrade to new versions. Otherwise the operator might be in a situation where the original investments have to be totally replaced by new investments. Compare ROCE. Reliability In telecommunications we have been used very reliable networks that are up and running almost all the time. This is in contrast to the local enterprise networks, where stop-time during maintenance or upgrades have been common. 7.3.4 MOVING IMAGE (VIDEO) There are a few quality areas specific to video: Delay variation Video is an isochronous service, just as telephony. The information is sent in a stream (streaming video) that has to be consistent and steady, not jumpy and jittery. Otherwise the picture will freeze and jump forward. Total delay There is a difference between one-way broadcast services and two-way interactive services. When broadcasting rental films over a network, the delay will not affect the quality. In a video conference, or when using net-meeting on a PC, the delay is as important for the quality as it is for telephony. Bit error rate Depending on the compression technique that is used, bit errors might cause problems. The more the information is compressed (to save bandwidth), the more is lost if a packet is lost, or the more is misinterpreted if a bit error occurs in a packet that arrives. So normal TV broadcasting is not sensitive to bit errors, whereas net-meeting on the PC is. 7.3.5 MULTIMEDIA (VIDEO + AUDIO) The same quality aspects as for moving image apply to multimedia communication, with one addition: The 