Sources of Delay, Error, and Jitter Sensitivity

Sources of Delay, Error, and Jitter Sensitivity
We can qualify and quantify sources of end-to-end delay as follows:
 Source encoding introduces delay—typically 20 or 30 ms to source encode an
audio or video bit stream. The more complex the encoding process, the greater
the delay. Also, as we increase compression ratios, jitter sensitivity increases.
 Encryption may add additional processing delay.
 Channel multiplexing introduces additional delay and is largely determined by
interleaving depth (which can vary between 10 and 80 ms in IMT2000DS) and
the convolutional or turbo encoder delay.

 Radio path delay in comparison is relatively insignificant—typically a few
microseconds. The radio path may, however, be discontinuous. If a user, for
example, goes into a tunnel without radio coverage, the session will hang—
delay and delay variability will be introduced. Discontinuous radio coverage
will cause packet loss and trigger retry requests.
In a receiver the delay budget overhead is a product of demodulation and multiplexing,
de-interleaving, channel decoding, and source decoding, including display
driver or display delay, which means our conversational delay budget (80-ms end-toend
delay) is already accounted for by the delay introduced by the handset
encoder/decoder delay. There is no additional delay budget available for network
delay. This is why wireless IP doesn’t work as well as wireline IP. Because wireless uses
a variable-quality transmission medium (the fading radio channel), we need to add in
processing overhead and processing delay to hide the channel variability and provide
adequate channel consistency. In addition, we need to manage the gaps in radio transmission,
making sure we can restart a session after it has been interrupted.
Table 14.2 characterizes traffic types in terms of their error, delay, and jitter sensitivity.
Video, image transfer, file transfer, and transaction processing are all errorsensitive.
Voice is error-tolerant. Conversational voice and interactive video are delaysensitive.
Transaction processing can be delay-sensitive if timeout challenge and
response authentication algorithms are used. Voice messaging, file transfer, and image
transfer are delay-tolerant. Error, delay, and jitter sensitivity are all properties that need
to be preserved by the radio and network layer. The problem is that we are adding the
delay and delay variability overhead introduced by the radio layer to the delay and
delay variability introduced by the network. 341