ATM交换技术AAL部分.ppt

ATM业务分类和ATM业务适配的思想
ITU-T标准委员会根据以下三个参数对用户平面高层业务进行分类:
Timing relation between source and destination(required or not required)
Bit rate (constant or variable)
Connection mode(connection-oriented or connectionless)
基于以上三个参数,用户高层业务可被划分成四类:
Class A: Connection-oriented constant bit rate (CBR)service, such as
circuit emulation and CBR video
 Class B: Connection-oriented variable bit rate (VBR) service with a timing relation between the source and the destination, such as VBR video and audio
 Class C: Connection-oriented VBR service without a timing relation
between the source and the destination, such as connection-oriented
file(., data) transfer
 Class D: Connectionless VBR service, such as LAN data
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ATM Adaptation Layer Traffic Types
 AAL1-ATM Adaptation Layer Type 1: CBR service, which allows ATM
to emulate voice or DSn(n=0,1,or 3) traffic.
举例:PCM 64kb/s Voice, coded video transmission,etc.
 AAL2-ATM Adaptation Layer Type 2: VBR service with timing relation
between the source and destination-Under studying.
举例:可变比特率分组传输,可变比特率视频编码MPEG-1/2
etc. Rt-VBR/nrt-VBR
 AAL3/4-ATM Adaptation Layer Type 3/4:VBR service without timing
relation between source and destination.
举例:帧中继, etc. AAL3是面向连接的业务,AAL4是
无连接数据业务
 AAL5-ATM Adaptation layer Type 5: Connectionless traffic.
举例:IP,SMDS
(SEAL: Simple and Efficient Adaptation Layer )
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ATM ITU ATM/B-ISDN Service Classes
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Applications of AAL and ATM Layer Service Category
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高层、AAL层和ATM层
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Generic AAL Protocol Sublayer Model
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Mapping of AAL、ATM SDU/PDU
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Summary of Adaptation Layer Process
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ATM适配层协议-AAL1
面向的业务(class A)
-信源与信宿之间有严格的定时要求
-恒定比特率编码
-面向连接方式
业务举例:话音业务、电路仿真(如E1仿真)、恒定比特率的图象编
码业务。
 AAL1向AAL层用户提供四种层服务
-以恒定比特率传送业务源的SDU,并在目的地以同样的比特率
递交这些SDU
-在源和目的地之间信送数据结构信息
-根据需要,指示出AAL1本身无法恢复的丢失或错误信息
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ATM适配层协议-AAL1
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