	SIP Reference Guide
Table Of Contents
DNS Example
Elements and Architectures
Header Fields
Header Fields – Compact Forms
Header Parameters & Values
INVITE Client Transaction
INVITE Server Transaction
INVITE/200
Mapping Between SS7 USI and the SIP SDP (SS7 Origination)
Mapping Between the SIP SDP and SS7 USI/HLC (SIP Origination)
Mapping ISUP Cause Codes to SIP-I/SIP-T Responses
Mapping SIP-T Responses to ISUP Cause Codes
Mechanics: Location
Mechanics: Registration
Namespaces and Priority Values for the Resource Priority Header Field
NAPTR Records
Non-INVITE Client Transaction
Non-INVITE Server Transaction
Option Tags for SIP Extensions
Response Code
Security Mechanism Names
Session Description Protocol
SIP Events
SIP Methods
SIP Response to a Call Progress (CPG) Message
SIP Timers
SIP/SIPS URI Parameters
SIP-I Responses - ISUP Cause Codes
SIPS's Use of DNS
SRV Records
Types of DNS Resource Records
URI Purposes
Warning Codes
Glossary of SIP Acronyms
SIP References

SIP Timers

Other SIP Resources

	SIP Pocket Guide
	SIP Signaling Router Use Cases Multimedia
	SIP Sessions Blog
	SIP Signaling Router Application Handbook
	SIP Signaling Router (SSR) Use Cases Application Guide

RFC 3261

Timer	Value	Section	Meaning
T1	500 MS default	Section 17.1.1.1	RTT Estimate
T2	4s	Section 17.1.2.2	The maximum retransmit interval for non-INVITE requests and INVITE responses
T4	5s	Section 17.1.2.2	Maximum duration a message will remain in the network
Timer A	initially T1	Section 17.1.1.2	INVITE request retransmit interval, for UDP only
Timer B	64*T1	Section 17.1.1.2	INVITE transaction timeout timer
Timer C	> 3min	Section 16.6	Proxy INVITE transaction timeout
Timer D	> 32s for UDP	Section 17.1.1.2	Wait time for response retransmits
Timer E	initially T1	Section 17.1.2.2	Non-INVITE request retransmit interval, UDP only
Timer F	64*T1	Section 17.1.2.2	Non-INVITE transaction timeout timer
Timer G	initially T1	Section 17.2.1	INVITE response retransmit interval
Timer H	64*T1	Section 17.2.1	Wait time for ACK receipt
Timer I	T4 for UDP	Section 17.2.1	Wait time for ACK retransmits
Timer J	64*T1 for UDP	Section 17.2.2	Wait time for non-INVITE request transmits
Timer K	T4 For UDP, 0s for TCP/SCTP	Section 17.1.2.2	Wait time for response retransmits
Timer L	64*T1	draft-sparks-sip-invfix	Wait time for INVITE retransmissions
Timer M	64*T1	draft-sparks-sip-infix	Wait time for 2xx response retransmissions and any additional 2xx responses from other branches of the INVITE if it forked downstream