Administrator's Guide

Appendix A. More About SIP
The Telecommuting Module always rewrites the Contact when a SIP request is forwarded
through. To prevent this rewriting, the URI Encoding and Preserve Username For All
Requests settings can be used.
Via
The Via header is used to keep track of which route the SIP request was sent. The response
is sent back the same route.
The Via header is always rewritten by the Telecommuting Module when the SIP signaling
crosses a NAT border (when the IP addresses change).
The Telecommuting Module can remove Via headers, when the server receiving the SIP re-
quest will not accept requests with more than one Via header. This is done using the Remove
Via Headers setting.
Record-Route
The Record-Route header is used to make subsequent signaling for this request to be sent
via the Telecommuting Module.
The Record-Route header is always rewritten by the Telecommuting Module when the SIP
signaling crosses a NAT border (when the IP addresses change).
You can force the Telecommuting Module to add Record-Route headers using the Force
Record-Route for Outbound Requests and Force Record-Route for All Requests set-
tings.
Route
The Route header is used to send SIP signaling via a predefined route. All Record-Route
headers added to the original SIP request will be converted into Route headers in later SIP
requests within the same SIP session.
The Route header is always rewritten by the Telecommuting Module when the SIP signaling
crosses a NAT border (when the IP addresses change).
Content-Type
The Content-Type header is used when the SIP packet has a body. A body is used to convey
information about something, like call parameters when a voice call is set up. The Content-
Type header defines the body type to help the client read the content correctly.
Some content types are automatically allowed through the Telecommuting Module, but most
types must be allowed by configuration. For this, the Content Types table is used.
If a SIP packet is not allowed because of the content type, this error message is shown in the
log: SIP unaccepted content - deny.
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