3G-324M bắtbuộcsửdụng AMR codec,nhưngcũngcóthểsửdungh G.723.1 nếusửdụng 1 sốthiếtbịđầucuối H.323AMR làchuẩnđượcpháttriểnbởi ETSI cho GSMTốiưuhóacácmạngđiệnthoại di động,tựđộngđiềuchỉnhsốlượngcác bit dduwwocphânbốchomãhóatiếngnói,lỗiđiềukhiển,cungcấpchấtlượngâmthanhtốtnhấttrongđktruyềnvôtuyến.1 lợiíchkhácnữalà AMR thíchứngrấttốtvớicácchuyểnkênhgiữacácchếđộkhiđang bay
1.MPEG-4 (ISO/IEC 14496-2) : phươngthứcnénâmthanhhìnhảnhdữliệukỹthuậtsố(AV),2.H.263 : là 1 chuẩnnéndữliệnhưđãthiếtkế,nhưnéntốcđộ bit thấpcho video3.
1.Cung cấp 1 cáchlinhhoạttrongpháthiệnvàsữalỗinângcaohiệuquả,thíchhợpchotruyền video dung lượnglớn,quamạngkodây.2.Cung cấpkhảnawgkhắcphụclỗithông qua: dữliệuđượcphânvùng,RVLC,resynchronisation marker, and header extension code vàcókophứctạplắm
Video telephony chanel
Video telephony channel There are 4 channel in 3G-324: Control channel Voice channel Audio channel Video channel
Channels• Control channel 3G-324M uses H.245 as a terminal control protocol. H.245 requires the numbered simple retransmission protocol (NSRP) and control channel segmentation and reassembly layer (CCSRL) sublayer support to ensure reliable operation. H.245 call control with the CCRL and NSRP to assure that the H.245 channel will be highly reliable and can use large packets during operation..
H.245• Master-slave determination is provided to determine which terminal is the master at the beginning of the session.• Capability exchange is provided to exchange terminal capabilities, such as optional modes of multiplexing, type of audio/video codecs, data sharing mode and its related parameters, and/or other additional optional features.• Logical channel signaling is provided to open/close the logical channels for media transmission.• Round-trip delay measurement is provided to enable accurate quality characteristic measurement.
Voice Channel—The AMR Codec• The 3G-324M specifications define the AMR codec as mandatory. 3G-324M also recommends the use of G.723.1, which is used by many H.323 terminals today.• The AMR codec was originally developed and standardized by ETSI for GSM cellular systems.• Optimized for mobile networks, it dynamically adjusts the amount of bits allocated to voice coding and error control, providing the best possible voice quality based on radio conditions• Another benefit of AMR is the adaptive rate adaptation for switching smoothly between codec modes on the fly.
The video channel• MPEG-4 (ISO/IEC 14496-2) : Is a method of defining compression of audio and visual (AV) digital data.• H.263 : Is a video compression standard originally designed as a low bitrate compressed format for videoconferencing.• The 3G-324M standard specifies the H.263 codec as mandatory, with MPEG-4 as a recommended codec for video processing. H.263 is a legacy codec that is used by many existing H.323 wireline devices
MPEG-4 interface to multiplex• MPEG-4 is much more flexible and offers advanced error detection and correction services, which are a big value add when delivering video over a wireless network.• Provides error resilience (through data partitioning, RVLC, resynchronisation marker, and header extension code) and low complexity.
The table lists a number of video channels 3G-324m