1、SMPTE STANDARD SMPTE 345M-2002 for Television - Mapping of SYNC Stream Block in ATM Common Layer to ATM Adaptation Layer Type 1 Page 1 of 3 pages 1 Scope This standard defines the mapping format of the SYNC stream block (SSB), defined in SMPTE 354M, to ATM adaptation layer type 1 (AAL1). 2 Normative
2、 references The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged
3、to investigate the possibility of applying the most recent edition of the standards indicated below. SMPTE 354M, Television -ATM Common Layer for Transport of Packetized Audio, Video and Data over Asynchronous Transfer Mode using ATM Adaptation Layer Type 1 ITU-T 1.363.1 (08/96), B-ISDN ATM Adaptati
4、on Layer (AAL) Specification: Type 1 (AAL) 3 Specification of AAL type 1 The ATM adaptation layer (AAL) supports the map- ping between the ATM layer and the next higher layer and functions required by the next higher layer. 3.1 Functions of AAL type 1 for packetized audio, video and data transport F
5、unctions and protocols of AAL type 1 (AAL1) to be used are those described in ITU-T 1.363.1. The layer services at the AAL service access point (AAL-SAP) provided by AAL1 to the AAL user are: - transfer of AAL-service data units (AAL-SDU) with a constant source bit rate and the delivery of them with
6、 the same bit rate; - transfer of timing information between source and destination; - cell loss and cell error correction capability. AAL1 is composed of two sublayers. The lower layer is the segmentation and reassembly (SAR) sublayer andthe upper layer is the convergence sublayer (CS). SAR is in c
7、onformity with ITU-T 1.363.1. CS for video signal transport defined in ITU-T 1.363.l/clause 2.5.1 -2 shall be used for AALapplication. These func- tions are listed in detail below. 3.1.1 Handling of AAL user information The length of the AAL-SDU is one byte and the time interval between two consecut
8、ive AAL-SDU should be constant, when utilizing the correction methods described in ITU-T 1.363.l/clause 2.5.2.4. 3.1.2 Handling of cell delay variation (CDV) It is mandatory to perform this function to reduce CDV values. A buffer is used to perform this function. In the event of buffer underflow, it
9、 may be necessaiy for the CS to maintain bit counter integrity by inserting the appropriate number of dummy bits. In the event of buffer overflow, it may be necessary for the CS to maintain bit counter integrity by dropping the appro- priate number of bits. Copyright 8 2002 by THE COCIEW OF MOTION P
10、ICNRE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914) 761-1100 Approved January 31,2002 SMPTE 345M-2002 ? I i j 3.1.3 Handling of lost and misinserted cells The sequence count values (SC) are further proc- essed to detect lost and misinserted cells. Detected misinserted
11、cells are discarded. 3.1.4 Handling of the timing relationship In order to provide a timing relationship between the source and destination, end-to-end synchronization is required. The adaptive clock method described in ITU-T 1.363.l/clause 2.5.2.2.1 shall be used. The receiver recovers the source c
12、lock frequency by averaging the amount of received data. 3.1.5 Correction of bit errors and lost cells To transmit packetized audio, video, and data stream, a long interleaver matrix which combines forward error correction (FEC) and byte interleaving shall be used to correct bit errors and cell loss
13、es (see figure 1). FEC usesthe Reed-Solomon (128,124) code. This interleaver matrix is defined in ITU-T 1.363.l/clause 2.5.2.4. The byte interleaver is organized as a matrix of 128 columns and 47 rows. The interleaver is used as follows: - at the input, incoming 128-by .-long blocks are stored row b
14、y row (one block corresponding to one row); - at the output, bytes are read out column by column. 4 SYNC stream block (SSB) mapping format to AAL1 The common layer, which is defined in SMPTE 354M, is the next higher layer of the AAL1 and provides transmission packets of applications. The common laye
15、r consists of two layers: The lower layer is the SYNC layer and the higher layer is the container layer. The SYNC layer defines the SYNC stream block (SSB) which is defined in SMPTE 354M. SSB is mapped to the AAL1 long interleaver matrix payload as described in 3.1 5. The size of the SSB depends on
16、the application. The position of the SSB byte data is not synchronized with the interleaver matrix (see annex A). Writing order 124 bytes 4 bytes Data I FEc I I I Figure 1 - Structure and format of the long interleaver matrix Page 2 of 3 pages SMPTE 345M-2002 Annex A (informative) Long interleaver m
17、atrix The size of the AAL1 long interleaver matrix payload is 5828 bytes (124*47). As defined in SMPTE 352M, one unit of SSB is transferred in one video frame period. In figure A.1, the size of the nth SSB, SSB(n), is set to X bytes, so the size of X becomes as follows: X = P + 5828 * M + Q bytes. T
18、ransmission order SSB (n-i) SsB (n) Gbytes) SSB (n+l) 11- SSB Header SSB Header M pieces of long interleave1 .+:.:.:.:,:.; . . . . . . . ., . . , . . , the position of SSB is not synchronized with the interleaver matrix Figure A.l - SSB asynchronous mapping to AAL1 long interleaver matrix Annex B (informative) B i bliog rap hy SMPTE 352M-2001 , Television - Video Payload Identi- fication for Digital Television Interfaces ITU-T 1.361 (02/99), B-ISDN ATM Layer Specification ITU-T 1.356 (03/00), B-ISDN ATM Layer Cell Transfer Per- formance Page 3 of 3 pages
