UMTS Services

Of course, the most notable capability promised by UMTS is a high data
rate—up to 2 Mbps. There is, however, more to a given service than just the
data rate that the service demands. Depending on what the end user is trying
to do, various considerations must be made, of which data rate is only
one.

UMTS specifications define four service classes, where the services
within a given class have a common set of characteristics. The service
classes are as follows:

■ Conversational This is characterized by low delay tolerance, low
jitter (delay variation) and low error tolerance. The data rate
requirement may be high or low, but is generally symmetrical. In other
words, the data rate in one direction will be similar to that in the other
direction. Voice, which is highly delay-sensitive, is a typical
conversational application, one that does not require very high data
rates. Video conferencing is also a conversational application. It has
similar delay requirements to voice, but is less error-tolerant and
generally requires a higher data rate.

■ Interactive This consists of typically request/response-type
transactions. Interactive traffic is characterized by low tolerance for
errors, but with a larger tolerance for delays than conversational
services. Jitter (delay variation) is not a major impediment to
interactive services, provided that the overall delay does not become
excessive. Interactive services may require low or high data rates
depending on the service in question, but the data rate is generally
significant only in one direction at a time.
■ Streaming This concerns one-way services, using low- to high-bit
rates. Streaming services have a low-error tolerance, but generally
have a high tolerance for delay and jitter. That is because the receiving
application usually buffers data so that it can be played to the user in a
synchronized manner. Streaming audio and streaming video are typical
streaming applications.

■ Background This is characterized by little, if any, delay constraint.
Examples include server-to-server e-mail delivery (as opposed to user
retrieval of e-mail), SMS, and performance/measurement reporting.
Background applications require error-free delivery.