High Speed Circuit Switched Data (HSCSD) Cont..

Although HSCSD delivers major advantages in data transmission over GSM CS it does have several major disadvantages, it still uses a connection-orientated mechanisms of GSM, these mechanisms are not very efficient when it comes to computer data traffic, which typically uses bursts of data. If a large file is being downloaded HSCSD may require all channels to be reserved, where as typical web browsing would leave the channels idle most of the time. The allocation of channels is reflected directly in the service cost, as once the channels have been reserved by one HSCSD user other users can not use them, even if they are idle.

HSCSD was not used by any of the UK operators, this was because of the disadvantages stated above and the fact that GPRS came along so fast.


Figure 19 Areas of Bursty and/or bandwidth consuming communications
(Adapted from Ericsson Document EN/LZT 123 5374 R1B)

There are two main ways of transmitting data, Circuit-Switched (CS) and Packet-Switched (PS) communication, this is sometimes referred to packet data communication).
Figure 19 illustrates areas of bursty and/or bandwidth consuming communications. Burstiness and bandwidth requirements affect the type of communication chosen - circuit-switched, packet-switched, or e.g. SMS (Short Message Service) communication. However it should be noted that when choosing the manner of communication for an application the cost should be considered.