Skype Exchange 4U

Microsoft Skype Exchange Server Blog

How SIP Requests (extensions) Work on Lync/Skype:

REQUEST TYPE  METHOD / PURPOSE 
SUBSCRIBE  Enables a user to subscribe to certain events. This means that the user should be informed when such events occur. 
NOTIFY  Used to inform the user that a subscribed event has occurred.
MESSAGE  Used to carry the body of an instant message to another user
INFO  Used for transferring information during a session, such as user activity.
SERVICE  Used to carry a Simple Object Access Protocol (SOAP) message as its payload.
NEGOTIATE  Used to negotiate various kinds of parameters, such as security mechanisms and algorithms.

SIP Responses Type :

When a request is received the SIP server issues a response with status code :

RESPONSE CODE

STATUS

DESCRIPTION

100-199

Informational or

Provisional

Request received, continuing to process the request. For example, 180 indicates that the phone of the called user is ringing.

200-299

Success

Action was successfully received, understood, and accepted. Only 200 OK and 202 ACCEPTED have been defined in this class.

300-399

Redirection

Further action needs to be taken to complete the request. For example, a front-end server sends 302 to redirect the client to a home server.

400-499

Client Error

The request contains a bad syntax or cannot be fulfilled at the server

500-599

Server Error

Server failed to fulfill a valid request.

600-699

Global Failure

Request cannot be fulfilled at any server. This is a new class defined for SIP.