Support SIP Max Forward in INVITE Message


This feature allows the CSP to insert the Max-Forwards header in outbound requests from the CSP SIP stack.

The Max-Forwards header is optional and is disabled by default. The host can also configure the Max-Forwards value.

Specification Built From

RFC 3261


Max-Forwards header limits the number of hops a request can make on the way to its destination. It consists of an integer that is decremented by one at each hop. If the Max-Forwards value reaches 0 before the request reaches its destination, it is rejected with a 483 (Too Many Hops) error response.

For example, this feature is needed by customer applications that require the Max-Forwards header in the inbound INVITE message so the application can respond to it. The host inserts this header in the INVITE message generated by the CSP SIP stack.

This feature applies to the following requests generated by the CSP SIP stack:











Example: Below is an example of the INVITE message with this feature enabled:


INVITE sip:35751@ SIP/2.0

Via: SIP/2.0/UDP

To: 35751<sip:35751@>

From: 00000000<sip:00000000@>;tag=734407b2

Call-ID: EXCEL-CSP16.7.1970.350@

Contact: 00000000<sip:00000000@>

User-Agent: Excel_CSP/84.10.1

Supported: timer

Session-Expires: 1800

Min-SE: 300


Max-Forwards: 80

Content-Type: application/sdp

Content-Length: 100



o=sip 0 0 IN IP4


c=IN IP4

t=0 0

m=audio 8028 RTP/AVP 0

API Configuring and Querying

To enable this feature using the EXS API, use the SIP Max Forwards (0x0286) TLV in the VoIP Protocol Configure (0x00EE) message. Refer to 0x2946 - SIP Request URI Password .

You can query this feature with the VoIP Protocol Query (0x00EF) message.

CSA Configuring and Querying

Follow the steps below to configure or query this feature from SwitchKit CSA.

1 To open the CSP SIP Configuration dialog box, do one of the following:

Select the CSP Matrix Series 3 Card in the node view. Go to the Configuration menu and select SIP®SIP Configuration.

Right-click the node view window (outside the card slots) and select SIP Configuration from the menu list.


2 Click the Show Advanced button. The SIP Configuration, Advanced dialog box opens.

3 Select SIP MAX Forwards.



Call Flow