ITU-T Recommendation Q.850 (10/2018), Usage of cause and location in the Digital Subscriber Signalling System No. 1 and the Signalling System No. 7 ISDN user part

Publisher

International Telecommunication Union (ITU-T)

URL

https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-Q.850-201810-I!!PDF-E&type=items

Published

2018-10-14

Updated

unknown

Accessed

2026-09-15

HTTP status

200

License

ITU-T Recommendation; ITU copyright, free public download; no-redistribution; short excerpts and locators only

Source notes citing this source

• Cause 127 interworking unspecified indicates interworking with a network that does not provide causes for its actions, so the precise cause cannot be ascertained. in context
• Cause 13 call completed elsewhere is the one Q.850 cause whose application column reads SIP rather than DSS 1 or ISUP, and its definition is a rule about what an S-CSCF puts in the Reason header field of a CANCEL after a forked INVITE receives a 2xx. in context
• Cause 16 normal call clearing indicates that one of the users involved requested that the call be cleared, and Q.850 states that under normal situations the source of this cause is not the network. in context
• A cause 16 whose location field names a network element is worth stopping on in a trace, because Q.850 says the source of a normal call clearing is not normally the network, and nothing in the record says why the network cleared the call. inferred in context
• Cause 18 no user responding is used when the called party does not respond to call establishment within the allotted time, while cause 19 no answer from user is used when the called party was alerted and did not answer, so the pair separates a device that never signalled from a device that rang. in context
• Cause 41 temporary failure and cause 38 network out of order both indicate that the network is not functioning correctly and are separated only by expected duration: a 41 invites an immediate retry and a 38 says an immediate retry is not likely to succeed. in context
• A Q.850 cause value is a class in bits 5 to 7 and a value within the class in bits 1 to 4, so the cause number is the class times 16 plus the value, and that arithmetic holds for all 70 cause values in Table 1. field report in context
• Two bits of the cause element select the coding standard as ITU-T standardized, ISO/IEC, national, or specific to the identified location, and Q.850 states the other standards should be used only when the desired cause value cannot be represented with ITU-T coding. in context
• The diagnostics that may accompany a cause are given per cause value in Table 1 and Q.850 states that diagnostic information is not available for every cause. in context
• Each Q.850 class carries an unspecified cause used only when no other cause in that class applies, and the definitions say so in the same words for each: 31 normal, 47 resource unavailable, 63 service or option not available, 79 service or option not implemented, 95 invalid message, 111 protocol error and 127 interworking. field report in context
• The in-force components of Q.850 are the edition of 10/2018 and Amendment 1 of 04/2019, and the 1993 and 1998 editions are listed as superseded. in context
• Causes carried in the ISDN user part and not marked for national use are the minimum set of cause values that shall be supported over the international interface. in context
• Location is a separate four-bit field of the same cause element with 8 defined values from user through international network and network beyond interworking point, so a cause value quoted without its location does not say who cleared the call. in context
• The normal class holds 25 of the 70 Q.850 causes, more than any other class, and the interworking class holds exactly one. field report in context
• ITU-T Q.850 defines 70 cause values and every one of them is both a row of Table 1 and a numbered definition subclause under clause 6.2.7; the two lists are identical. in context
• The Recommendation subfield of the cause element is not supported by the ISDN user part and its default interpretation there is Q.763, and when the field defaults the octets carrying it are omitted entirely rather than sent as zero. in context
• Clause 6.2.5 names class 000 and class 001 both as normal event, and clause 6.2.7 groups both under a single heading called the Normal class, so the eight class codes carry seven names. in context

Cite this source record

APA

WarmTransfer. (2018, October 14). ITU-T Recommendation Q.850 (10/2018), Usage of cause and location in the Digital Subscriber Signalling System No. 1 and the Signalling System No. 7 ISDN user part. WarmTransfer. https://warmtransfer.net/knowledge/sources/itu-t-q850-2018

BibTeX

@misc{warmtransfer-itu-t-q850-2018,
  title  = {ITU-T Recommendation Q.850 (10/2018), Usage of cause and location in the Digital Subscriber Signalling System No. 1 and the Signalling System No. 7 ISDN user part},
  author = {{WarmTransfer}},
  year   = {2018},
  url    = {https://warmtransfer.net/knowledge/sources/itu-t-q850-2018},
  note   = {International Telecommunication Union (ITU-T), accessed 2026-09-15}
}