ITU-T Q.424

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INTERNATIONAL TELECOMMUNICATION UNION

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TELECOMMUNICATION

STANDARDIZATION SECTOR

OF ITU

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(Extract from the "LUE"OOK)

NOTES

1 ITU-T Recommendation Q.424 was published in Fascicle VI.4 of the Blue Book. This file is an extract from

the Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, the

contents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).

2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a

telecommunication administration and a recognized operating agency.

 ITU 1988, 1993

mechanical, including photocopying and microfilm, without permission in writing from the ITU.

Fascicle VI.4 - Rec. Q.424 1

Recommendation Q.424

Fascicle VI.4 - Rec. Q.424

3.3 PROTECTION AGAINST THE EFFECTS OF FAULTY TRANSMISSION

Faulty transmission conditions in PCM systems can lead to degradation of the speech channels and erroneous

signalling. In the case of primary PCM multiplex equipment operating at 2048 kbit/s failures due to loss of frame or

multi-frame alignment and/or failure of any other important function results in both PCM terminals going into alarm

condition in accordance with Recommendations G.732 and G.734.

Thus both PCM terminals apply the state corresponding to state 1 on the PCM line on each "receive"

signalling channel at the interfaces with the switching equipment, as indicated in Table 4 of Recommendation G.732.

In this way, the incoming switching equipment receives the equivalent of af = 1, bf = 1 on the PCM line and the

outgoing switching equipment receives the equivalent of ab = 1, bb = 1.

These characteristics are taken into account in the present specifications (see § 3.2.4) so that:

- at the outgoing end (see Table 3/Q.422) a PCM fault results in a blocked state, seizure acknowledged

state or clear-back state. This means that all circuits in the idle state of a faulty PCM multiplex will be

blocked against seizure and that seized circuits will go to or remain in the seizure acknowledged or clear-

back state;

- at the incoming end (see Table 4/Q.422) a PCM fault can be identified and appropriate actions can be

taken.

When the signalling equipment is a part of a digital exchange, it may receive alarm indications in a form other

than both signalling bits in state one. The failure may be detected by the signalling equipment or an indication be

received from the PCM terminal according to Recommendation G.734.

When the signalling equipment recognizes a failure it must:

- block the detection of signalling transitions to avoid recognition of erroneous signalling codes caused by

the failure. This action must be taken as soon as possible and at least within 3 ms as specified in

Recommendation G.734 for a PCM terminal,

- react as specified in Tables 3/Q.422 and 4/Q.422 when a signalling code a = 1, b = 1 is detected at the

input of signalling equipment situated at the analogue access of a PCM terminal equipment complying

with Recommendation G.732.

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摘要：

ITU-T Q.424 是国际电信联盟电信标准化部门（ITU-T）发布的一项技术标准，主要针对通信网络中信令系统的接口与协议规范。该标准通常涉及与No.7信令系统（SS7）相关的网络节点间信令传输、呼叫控制及业务处理流程，旨在确保不同厂商设备之间的互操作性与网络可靠性。对于通信工程师、网络规划人员及电信设备开发者而言，Q.424标准有助于优化信令网络设计、提升呼叫建立效率并降低故障风险。掌握其内容对于维护现有PSTN网络及向下一代网络演进中的信令兼容性具有重要意义。

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