Q.931

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

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.225、H.245和ASN.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

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

中断原因

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

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

Q.2931是Q.931修改和扩展B-ISDN的变种。