RFC 3578: Mapping of Integrated Services Digital Network (ISDN) User Part (ISUP) Overlap Signalling to the Session Initiation Protocol (SIP)

Publisher

RFC Editor / IETF

URL

https://www.rfc-editor.org/rfc/rfc3578.html

Published

2003-08-01

Updated

unknown

Accessed

2026-09-24

HTTP status

200

License

IETF Trust Legal Provisions; no-redistribution; short excerpts and locators only

Source notes citing this source

• Under RFC 3578, when timer T10 expires the gateway sends an INVITE containing the digits collected so far. in context
• RFC 3578's preferred approach is for the gateway to convert overlap to en bloc, collecting digits by number analysis and timers and sending one INVITE once the number is complete. in context
• RFC 3578 states that native SIP endpoints never generate overlap signalling; SIP carries the complete number en bloc in the INVITE Request-URI. in context
• RFC 3578 allows a gateway to generate SIP overlap signalling (multiple INVITEs) only if the SIP routing infrastructure ensures the INVITEs reach a single gateway. in context
• A 484 seen on a trunk configured for overlap dialling is expected signalling for a partial number, whereas a 484 on an en-bloc trunk indicates the sender truncated or malformed the dialled number. inferred in context
• RFC 3578 states that in overlap operation all INVITEs except one typically receive 4xx responses such as 484 Address Incomplete. in context
• RFC 3578 warns that successive overlap INVITEs may be routed to different gateways, so that more than one gateway generates an ISUP IAM. in context
• RFC 3578 prefers converting ISUP overlap signalling to en-bloc SIP, where the gateway waits for all parts of the called number before generating a single INVITE. in context
• When overlap signalling is carried in SIP under RFC 3578, the gateway sends a new INVITE as digits arrive, each carrying all digits received so far in the Request-URI and a higher CSeq. in context
• RFC 3578 says the gateway should not CANCEL a previous overlap INVITE transaction when sending a new one, to avoid race conditions. in context
• RFC 3578 warns against SIP overlap where a number and a shorter prefix of the same number can both be valid PSTN addresses. in context
• In RFC 3578 en-bloc conversion the gateway sends an INVITE with the digits collected so far when ISUP timer T10 expires. in context
• When overlap is carried into SIP under RFC 3578, each arriving SAM refreshes timer T10 and triggers a new INVITE with the accumulated digits, and 4xx-6xx responses do not trigger an ISUP REL until T10 expires with no more SAMs. in context
• RFC 3578 states that the preferred approach for a gateway handling PSTN overlap signalling is to convert it into SIP en-bloc signalling. in context

Cite this source record

APA

WarmTransfer. (2003, August 1). RFC 3578: Mapping of Integrated Services Digital Network (ISDN) User Part (ISUP) Overlap Signalling to the Session Initiation Protocol (SIP). WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-3578-isup-overlap-sip

BibTeX

@misc{warmtransfer-rfc-3578-isup-overlap-sip,
  title  = {RFC 3578: Mapping of Integrated Services Digital Network (ISDN) User Part (ISUP) Overlap Signalling to the Session Initiation Protocol (SIP)},
  author = {{WarmTransfer}},
  year   = {2003},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-3578-isup-overlap-sip},
  note   = {RFC Editor / IETF, accessed 2026-09-24}
}