The Four Classes of Traffic

The four classes of traffic in IMT2000 are conversational, streaming, interactive, and
background:
 Conversational implies a delay of not more than 80 ms.
 Streaming implies a delay of not more than 500 ms.
 Interactive implies a delay of not more than 1 second.
 For background, delay is not specified.
Conversational traffic is historically constant bit rate. This means most conversational
traffic to date has been voice, and voice has used constant-rate encoding. You can
also have a conversational exchange of complex content, that is, a conversational rich
media exchange. It would be more bandwidth-, power-, and quality-efficient for this to
be variable rate.
Streamed content is also likely to be complex content—audio, image, video, data—
and is therefore best supported as a variable bit rate service. Interactive uses available
bit rate. This is variable bit rate, but with the network deciding on bit rate availability
on the basis of congestion measurements from the network and interference measurements
from the radio physical layer. Background uses unspecified bit rate, which
means it’s a best-effort service.