diff options
| -rw-r--r-- | epan/dissectors/packet-mp2t.c | 64 |
1 files changed, 46 insertions, 18 deletions
diff --git a/epan/dissectors/packet-mp2t.c b/epan/dissectors/packet-mp2t.c index 413cda347d..08865d1ea9 100644 --- a/epan/dissectors/packet-mp2t.c +++ b/epan/dissectors/packet-mp2t.c @@ -553,24 +553,52 @@ mp2t_fragment_handle(tvbuff_t *tvb, guint offset, packet_info *pinfo, } -/* Decoding of DOCSIS MAC frames within MPEG packets. MAC frames may begin anywhere - * within an MPEG packet or span multiple MPEG packets. - * payload_unit_start_indicator bit in MPEG header, and pointer field are used to - * decode fragmented DOCSIS frames within MPEG packet. - *------------------------------------------------------------------------------- - *MPEG Header | pointer_field | stuff_bytes | Start of MAC Frame #1 | - *(PUSI = 1) | (= 0) | (0 or more) |(up to 183 bytes) | - *------------------------------------------------------------------------------- - *------------------------------------------------------------------------------- - *MPEG Header | Continuation of MAC Frame #1 | - *(PUSI = 0) | (up to 183 bytes) | - *------------------------------------------------------------------------------- - *------------------------------------------------------------------------------- - *MPEG Header | pointer_field |Tail of MAC Frame| stuff_bytes |Start of MAC Frame| - *(PUSI = 1) | (= M) | #1 (M bytes) | (0 or more) |# 2 (N bytes) | - *------------------------------------------------------------------------------- - * Source - Data-Over-Cable Service Interface Specifications - * CM-SP-DRFI-I07-081209 +/* + * Reassembly of various payload types. + * + * DOCSIS MAC frames, PES packets, etc. may begin anywhere within an MPEG-TS + * packet or span multiple MPEG packets. + * + * The payload_unit_start_indicator bit in the MPEG-TS header, and the pointer + * field, are used to reassemble fragmented frames from MPEG-TS packets. + * + * If that bit is set, a higher-level packet begins in this MPEG-TS + * packet, and the MPEG-TS header is followed by a 1-octet pointer field. + * The value of the pointer field indicates at which byte the higher- + * level packet begins. If that bit is not set, the packet begun in + * an earlier MPEG-TS packet continues in this packet, with the data + * in the payload going after the data in the previous MPEG-TS packet + * (there can be more than one continuing packet). + * + * If the pointer field is non-zero, this MPEG-TS packet contains + * the conclusion of one higher-level packet and the beginning of + * the next packet. + * + * As the MPEG-TS packets are of a fixed size, stuff bytes are used + * as padding before the first byte of a higher-level packet as + * necessary. + * + * This diagram is from Data-Over-Cable Service Interface Specifications, + * Downstream RF Interface Specification, CM-SP-DRFI-I16-170111, section 7 + * "DOWNSTREAM TRANSMISSION CONVERGENCE SUBLAYER", and shows how the + * higher-level packets are transported over the MPEG Transport Stream: + * + *+--------------------------------------------------------------------------------+ + *|MPEG Header | pointer_field | stuff_bytes | Start of Packet #1 | + *|(PUSI = 1) | (= 0) | (0 or more) | (up to 183 bytes) | + *+--------------------------------------------------------------------------------+ + *+--------------------------------------------------------------------------------+ + *|MPEG Header | Continuation of Packet #1 | + *|(PUSI = 0) | (up to 183 bytes) | + *+--------------------------------------------------------------------------------+ + *+---------------------------------------------------------------------------------+ + *|MPEG Header | pointer_field |Tail of Packet #1 | stuff_bytes |Start of Packet #2 | + *|(PUSI = 1) | (= M) |(M bytes) | (0 or more) |(N bytes) | + *+---------------------------------------------------------------------------------+ + * + * For PES and PSI, see ISO/IEC 13818-1 / ITU-T Rec. H.222.0 (05/2006), + * section 2.4.3.3 "Semantic definition of fields in Transport Stream packet + * layer", which says much the same thing. */ static void mp2t_process_fragmented_payload(tvbuff_t *tvb, gint offset, guint remaining_len, packet_info *pinfo, |