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Q.931

维基百科,自由的百科全书
Q.931
ISDN用户网络接口第3层基本呼叫控制规范
状态已生效
开始年1988
最新版本May 1998
预览版本(12/02)
组织ITU-T
有关标准H.323
网站https://www.itu.int/rec/T-REC-Q.931

Q.931ITU-T 制定的ISDN网络层界面协议(ISDN network layer interface protocol)。[1]

Q.931一般不进行数据运送。Q.931并没有直接相当于在互联网协议栈,但跟SIP相比,由于底层的协议被认为是可靠的协议并且电路交换网络的带宽调整是固定的方式, 所以Q.931不提供流量控制和重传机制.

Q.931是ISDN相关的协议, Q.931最近被用来作为H.323协议(即H.225)的一部分,在某种形式的移动电话传输系统。H.323包括Q.931、H.225H.245ASN.1, 为了提供呼叫资讯,H.323部分融合了H.225和Q.931标准。Q.931流程包括呼叫建立和拆除。

一个 Q.931 frame包含以下元素:

  • 协议鉴别器(Protocol discriminator, PD)-指定的信令协议是用于连接(如PD = 8为DSS1 )
  • 呼叫参考值(Call reference value, CR) - 针对不同的连接,可以同时存在。 只有在实际连接的一段时间值有效。
  • 消息类型(message type, MT) - 指定的第3层消息类型的呼叫控制(如设置)设置在Q.931定义的消息类型。 有呼叫建立,呼叫释放和通话功能的控制定义的消息。
  • 资讯元素(information element, IE) - 指定关联到实际的消息的进一步资料。Q.931 分组(packet)包含多个称为资讯单元的参数。一个 IE浏览器包括IE浏览器的名称(如承载能力),其长度和变量字段的内容。

讯息示例

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  • SETUP:指示建立一个连接
  • CALL PROCEEDING
  • ALERTING
  • CONNECT
  • RELEASE
  • RELEASE COMPLETE

中断原因

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十六进制 十进制 原因
0x1 1 未分配或未指定的号码
0x2 2 没有路由到指定的运输网络 (Transit Network Identity)
0x3 3 没有到目的地的路由
0x4 4 发送特殊信息
0x5 5 Misdialled trunk prefix
0x6 6 频道不可接受
0x7 7 Call awarded and being delivered in an established channel
0x8 8 Prefix 0 dialed, 但不允许
0x9 9 Prefix 1 dialed, 但不允许
0xA 10 Prefix 1 not dialed, 但需要
0xB 11 More digits received than allowed, call is proceeding
0x10 16 Normal call clearing
0x11 17 User busy
0x12 18 No user responding
0x13 19 T.301 expired: - User Alerted, No answer from user
0x15 21 Call rejected
0x16 22 Number changed to number in diagnostic field.
0x17 23 Reverse charging rejected
0x18 24 Call suspended
0x19 25 Call resumed
0x1A 26 Non-selected user clearing
0x1B 27 Destination out of order
0x1C 28 Invalid number format or incomplete address
0x1D 29 EKTS facility rejected by network
0x1E 30 Response to STATUS ENQUIRY
0x1F 31 Normal, unspecified
0x21 33 Circuit out of order
0x22 34 No circuit/channel available
0x23 35 Destination unattainable
0x24 36 Out of order
0x25 37 Degraded service
0x26 38 Network out of order
0x27 39 Transit delay range cannot be achieved
0x28 40 Throughput range cannot be achieved
0x29 41 Temporary failure
0x2A 42 Switching equipment congestion
0x2B 43 Access information discarded
0x2C 44 Requested circuit channel not available
0x2D 45 Preempted
0x2E 46 Precedence call blocked
0x2F 47 Resource unavailable, unspecified
0x31 49 Quality of service unavailable
0x32 50 Requested facility not subscribed
0x33 51 Reverse charging not allowed
0x34 52 Outgoing calls barred
0x35 53 Outgoing calls barred within CUG
0x36 54 Incoming calls barred
0x37 55 Incoming calls barred within CUG
0x38 56 Call waiting not subscribed
0x39 57 Bearer capability not authorized
0x3A 58 Bearer capability not presently available
0x3F 63 Service or option not available, unspecified
0x41 65 Bearer service not implemented
0x42 66 Channel type not implemented
0x43 67 Transit network selection not implemented
0x44 68 Message not implemented
0x45 69 Requested facility not implemented
0x46 70 Only restricted digital information bearer capability is available
0x4F 79 Service or option not implemented, unspecified
0x51 81 Invalid call reference value
0x52 82 Identified channel does not exist
0x53 83 A suspended call exists, but this call identity does not
0x54 84 Call identity in use
0x55 85 No call suspended
0x56 86 Call having the requested call identity has been cleared
0x57 87 Called user not member of CUG
0x58 88 Incompatible destination
0x59 89 Non-existent abbreviated address entry
0x5A 90 Destination address missing, and direct call not subscribed
0x5B 91 Invalid transit network selection (national use)
0x5C 92 Invalid facility parameter 93 Mandatory information element is missing
0x5D 93 Message type non-existent or not implemented
0x5F 95 Invalid message, unspecified
0x60 96 Mandatory information element is missing
0x61 97 Message type non-existent or not implemented
0x62 98 Message not compatible with call state or message type non-existent or not implemented
0x63 99 Information element nonexistent or not implemented
0x64 100 Invalid information element contents
0x65 101 Message not compatible with call state
0x66 102 Recovery on timer expiry
0x67 103 Parameter non-existent or not implemented - passed on
0x6F 111 Protocol error, unspecified
0x7F 127 Internetworking, unspecified
0x80+ 128 or

higher

Proprietary diagnostic code (not necessarily bad). Typically used to pass proprietary control or maintenance messages between multiplexers.

限制

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Q.931是基于原语(primitive)的,但Q.931并没有规定原语的字义,Q.931和H.225都定义了呼叫资讯流程,但定义不充分,Q.931的原语缺乏充分的文字说明。另一方面, Q.931和H.225融合不够好,H.225将Q.931中的消息标记成“禁用”,但却没有规定出新流程。Q.931界面是不可移植的, 这是因为H.225只提到原语而没有提供包含参数的资讯,使得H.323的发展大受影响, SIP有取代H.323的趋势。

Q.2931

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Q.2931是Q.931修改和扩展B-ISDN的变种。

参考资料

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