8 Using Compact and Long Header Formats for SIP Messages

This chapter describes how to use the Oracle Communications Converged Application Server SipServletMessage interface and configuration parameters to control SIP message header formats:

• Overview of Header Format APIs and Configuration

• Summary of Compact Headers

• Assigning Header Formats with WlssSipServletMessage

• Summary of API and Configuration Behavior

Overview of Header Format APIs and Configuration

Applications that operate on wireless networks may want to limit the size of SIP headers to reduce the size of messages and conserve bandwidth. JSR 289 provides the SipServletMessage.setHeaderForm() method, which enables application developers to set a long or compact format for the value of a given header.

One feature of the SipServletMessage API provided in JSR 289 is the ability to set long or compact header formats for the entire SIP message using the setHeaderForm method.

In addition to SipServletMessage, Converged Application Server provides a container-wide configuration parameter that can control SIP header formats for all system-generated headers. This system-wide parameter can be used along with SipServletMessage.setHeaderForm and SipServletMessage.setHeader to further customize header formats.

Summary of Compact Headers

Table 8-1 defines the compact header abbreviations described in the SIP specification (http://www.ietf.org/rfc/rfc3261.txt). Specifications that introduce additional headers may also include compact header abbreviations.

Table 8-1 Compact Header Abbreviations

Header Name (Long Format)	Compact Format
Call-ID	i
Contact	m
Content-Encoding	e
Content-Length	l
Content-Type	c
From	f
Subject	s
Supported	k
To	t
Via	v

Assigning Header Formats with WlssSipServletMessage

All instances of SipServletRequest, SipServletResponse, and WlssSipServletResponse can be cast to WlssSipServletMessage in order to use the extended API.

A pair of getter/setter methods, setUseHeaderForm and getUseHeaderForm, are used to assign or retrieve the header formats used in the message. These methods assign or return a HeaderForm object, which is a simple Enumeration that describes the header format:

• COMPACT: Forces all headers in the message to use compact format. This behavior is similar to the container-wide configuration value of “force compact,” as described in use-header-form in the Converged Application Server Administrator's Guide.

• LONG: Forces all headers in the message to use long format. This behavior is similar to the container-wide configuration value of “force long,” as described in use-header-form in the Converged Application Server Administrator's Guide.

• DEFAULT: Defers the header format to the container-wide configuration value set in use-header-form.

WlssSipServletResponse.setUseHeaderForm can be used in combination with SipServletMessage.setHeader and the container-level configuration parameter, use-compact-form. See "Summary of API and Configuration Behavior".

Summary of API and Configuration Behavior

Header formats can be specified at the header, message, and SIP Servlet container levels. Table 8-2 shows the header format that results when adding a new header with SipServletMessage.setHeader, given different container configurations and message-level settings with WlssSipServletResponse.setUseHeaderForm.

Table 8-2 API Behavior when Adding Headers

SIP Servlet Container Header Configuration (use-compact-form Setting)	WlssSipServletMessage.setUseHeaderForm Setting	SipServletMessage.setHeader Value	Resulting Header
COMPACT	DEFAULT	“Content-Type”	“Content-Type”
COMPACT	DEFAULT	“c”	“c”
COMPACT	COMPACT	“Content-Type”	“c”
COMPACT	COMPACT	“c”	“c”
COMPACT	LONG	“Content-Type”	“Content-Type”
COMPACT	LONG	“c”	“Content-Type”
LONG	DEFAULT	“Content-Type”	“Content-Type”
LONG	DEFAULT	“c”	“c”
LONG	COMPACT	“Content-Type”	“c”
LONG	COMPACT	“c”	“c”
LONG	LONG	“Content-Type”	“Content-Type”
LONG	LONG	“c”	“Content-Type”
FORCE_COMPACT	DEFAULT	“Content-Type”	“c”
FORCE_COMPACT	DEFAULT	“c”	“c”
FORCE_COMPACT	COMPACT	“Content-Type”	“c”
FORCE_COMPACT	COMPACT	“c”	“c”
FORCE_COMPACT	LONG	“Content-Type”	“Content-Type”
FORCE_COMPACT	LONG	“c”	“Content-Type”
FORCE_LONG	DEFAULT	“Content-Type”	“Content-Type”
FORCE_LONG	DEFAULT	“c”	“Content-Type”
FORCE_LONG	COMPACT	“Content-Type”	“c”
FORCE_LONG	COMPACT	“c”	“c”
FORCE_LONG	LONG	“Content-Type”	“Content-Type”
FORCE_LONG	LONG	“c”	“Content-Type”

Table 8-3 shows the system header format that results when setting the header format with WlssSipServletResponse.setUseHeaderForm given different container configuration values.

Table 8-3 API Behavior for System Headers

SIP Servlet Container Header Configuration (use-compact-form Setting)	WlssSipServletMessage.setUseHeaderForm Setting	Resulting Contact Header
COMPACT	DEFAULT	“m”
COMPACT	COMPACT	“m”
COMPACT	LONG	“Contact”
LONG	DEFAULT	“Contact”
LONG	COMPACT	“m”
LONG	LONG	“Contact”
FORCE_COMPACT	DEFAULT	“m”
FORCE_COMPACT	COMPACT	“m”
FORCE_COMPACT	LONG	“Contact”
FORCE_LONG	DEFAULT	“Contact”
FORCE_LONG	COMPACT	“m”
FORCE_LONG	LONG	“Contact”