	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

NAPTR Records

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

NAPTR Field	Description
NAPTR	Specifies the order, from lowest to highest, in which to process multiple NAPTR records for a name. Processing stops once a suitable record is found.
Preference	The order, from lowest to highest, in which to process multiple NAPTR records with the same order value. Higher numbered records can be tried if lower numbered records fail or aren’t acceptable in some other way.
Flags	Always “s” for SIP, which means to do an SRV lookup on whatever is in the replacement field.
Service	Specifies the service available by following this rule. For SIP: • SIP+D2U: SIP over UDP • SIP+D2T: SIP over TCP • SIP+D2S: SIP over SCTP • SIPS+D2T: SIPS over TCP
Regexp	Always empty for SIP services.
Replacement	For SIP, a DNS name to use in an SRV query.

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