RFC 4028: Session Timers in the Session Initiation Protocol (SIP)

Publisher

IETF / RFC Editor

URL

https://www.rfc-editor.org/rfc/rfc4028.txt

Published

2005-04-01

Updated

unknown

Accessed

2026-09-30

HTTP status

200

License

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

Source notes citing this source

• 422 (Session Interval Too Small) is generated by a UAS or proxy when a request's Session-Expires duration is below its minimum timer. in context
• If no session refresh arrives, the side not performing refreshes should send BYE slightly before the session expires; the recommended margin is the smaller of 32 seconds and one third of the session interval. in context
• When the Min-SE header field is absent its default value is 90 seconds. in context
• It is RECOMMENDED that the refresher send the session refresh once half the session interval has elapsed. in context
• If a session refresh request times out or receives a 408 or 481 response, the UAC sends a BYE. in context
• For session refresh, UPDATE is RECOMMENDED over re-INVITE when the peer is known to support it; a refresh UPDATE is recommended to carry no offer, whereas a refresh re-INVITE SHOULD contain one. in context
• The absolute minimum Session-Expires value is 90 seconds and 1800 seconds (30 minutes) is RECOMMENDED. in context
• SIP session timers are a keepalive: user agents send periodic re-INVITE or UPDATE requests, called session refresh requests, to keep the session alive. in context

Cite this source record

APA

WarmTransfer. (2005, April 1). RFC 4028: Session Timers in the Session Initiation Protocol (SIP). WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-4028-session-timers-b

BibTeX

@misc{warmtransfer-rfc-4028-session-timers-b,
  title  = {RFC 4028: Session Timers in the Session Initiation Protocol (SIP)},
  author = {{WarmTransfer}},
  year   = {2005},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-4028-session-timers-b},
  note   = {IETF / RFC Editor, accessed 2026-09-30}
}