A.10 H.223
26.1103GPPCodec for circuit switched multimedia telephony serviceGeneral descriptionRelease 17TS
H.223 describes the multiplexing protocol used between H.324 terminals. It is packet oriented and each packet can contain a subset of a maximum of 65536 LCs. Each LC represents a single media, information, or control channel. The H.223 protocol is split into two layers, the lowest being the Multiplex Layer.
The Multiplex Layer exchanges data with the end terminal via MUX-PDUs. Multiplex table entries, of which there are 16 (and can be changed during a session), describe which octets from within the PDU are allocated to which logical channels. The multiplex table entry employed for a particular PDU is indicated by the 4 bit MC field in the MUX-PDU header. MUX-PDUs contain an integer number of octets. Errors within the MUX-PDU header are controlled using the HEC field in the MUX-PDU header. H.324 terminals utilising the V.34 transmission protocol frame MUX-PDUs with HDLC. Bit stuffing is used for data transparency in this case.
Above the Multiplex Layer is the Adaptation Layer, of which there are three different types.
1) AL1 is designed primarily for control information and data protocols. It can be either framed or unframed and does not provide any error control.
2) AL2 is designed primarily for the transfer of digital audio. AL2 PDUs contain 1 octet for an 8-bit CRC and an optional octet for a sequence number.
3) AL3 is designed primarily for the transfer of digital video. AL3 PDUs contain 2 octets for a 16-bit CRC. There is also optionally 1 or 2 octets for control. AL3 also allows limited retransmission.
For purposes of video telecommunications over wireless networks, four annexes to H.223 have been created. These create four levels of error detection and error correction.
A.10.1 Level 0
Level 0 applies to H.223 as described above.
A.10.2 Level 1
Level 1, described in Annex A, replaces HDLC framing with 1 or 2 16 bit flags. Unlike HDLC, Level 1 does not guarantee data transparency. However, if the MUX-PDU header is constructed in such a way as to make emulating the Level 1 framing flags impossible, data transparency can be achieved by correctly decoding the MUX-PDU. Should there be and error in the MUX-PDU header, resynchronization techniques will have to be applied.
A.10.3 Level 2
Level 2, described in Annex B, uses the same framing as Level 1, but utilises a 3 octet header. This header starts with a 4 bit MC, which is the same as in Level 0. This is followed by an 8-bit MPL-field, with a range of values 0 – 254. Lastly, a 12 bit extended Golay code is used for parity bits. The PM in Level 2 is signalled through the polarity of the MUX-PDU flag. If the output of the correlator is greater than or equal to CT, the PM is 0. If it is less than or equal to -CT, the PM equals 1. After the parity bits, there can be an optional MUX-PDU header for the previous (corrupted) MUX-PDU. This 1 octet field uses the format described in Level 0. Level 2 also offers enhanced packet resynchronization.
A.10.4 Level 3
Level 3, described in Annexes C and D, provides error correction capabilities at the mux level.
Annex B (informative):
Bibliography
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Annex C (informative):
Change history
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Change history |
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Date |
TSG # |
TSG Doc. |
CR |
Rev |
Subject/Comment |
Old |
New |
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06-1999 |
04 |
Approved at TSG-SA#4 |
3.0.0 |
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09-2000 |
09 |
SP-000395 |
001 |
CS Multimedia Codec specification for real time text conversation |
3.0.1 |
4.0.0 |
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03-2001 |
011 |
SP-010105 |
002 |
1 |
Support of mobile multi-link operation in 3G-324M |
4.0.0 |
4.1.0 |
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03-2001 |
011 |
SP-010105 |
004 |
1 |
Correction of incorrect reference |
4.0.0 |
4.1.0 |
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06-2002 |
016 |
Version for Release 5 |
4.1.0 |
5.0.0 |
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12-2004 |
026 |
Version for Release 6 |
5.0.0 |
6.0.0 |
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06-2007 |
036 |
Version for Release 7 |
6.0.0 |
7.0.0 |
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12-2008 |
042 |
Version for Release 8 |
7.0.0 |
8.0.0 |
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12-2009 |
046 |
Version for Release 9 |
8.0.0 |
9.0.0 |
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03-2011 |
051 |
Version for Release 10 |
9.0.0 |
10.0.0 |
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09-2012 |
057 |
Version for Release 11 |
10.0.0 |
11.0.0 |
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09-2014 |
065 |
Version for Release 12 |
11.0.0 |
12.0.0 |
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12-2015 |
070 |
Version for Release 13 |
12.0.0 |
13.0.0 |
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Change history |
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Date |
Meeting |
TDoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
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2017-03 |
75 |
Version for Release 14 |
14.0.0 |
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2018-06 |
80 |
Version for Release 15 |
15.0.0 |
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2020-07 |
– |
– |
– |
– |
– |
Update to Rel-16 version (MCC) |
16.0.0 |
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2022-04 |
– |
– |
– |
– |
– |
Update to Rel-17 version (MCC) |
17.0.0 |
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Note that ITU-R 601 represents 16 bit precision colour, whereas true colour is usually considered to require 24 bit precision. Also, the spatial resolution of ITU-R 601 is substantially less than can be achieved with normal human vision. ↑