Mode is a Set of Streams (Q61)

The information in this article applies to:

There has been some confusion about what "mode" refers to in the Mode Request Signaling Entity. Section 3/H.245v2 states, "A mode is a set of elementary streams that a terminal is transmitting, intends to transmit, or would like to receive." Note that it says that a mode is a set of streams, not a single stream. Further, the Introduction to the Mode Request procedures, section 8.9.1/H.245v2, makes this point clear in paragraphs 6 and 7. IMO, the reason that people misunderstand this point is that "mode" is used incorrectly elsewhere in H.245 as a synonym for "stream." (To make matters worse, it also appears that "stream" and "signal" are used interchangeably but are not defined.) According to the definition in section 3, "mode" is a set of streams; the Mode Request procedures use and clarify this definition. However, passages such as the following from section 5.2/H.245v2 erroneously use "mode" as a synonym for "stream."

Capability messages have been defined to allow a terminal to indicate that it does not have fixed capabilities, but that they depend on which other modes are being used simultaneously.

Note that only one mode can be transmitted at a time but that any number of streams/signals may be.