Independentsoft.Sip.Methods Namespace

The Ack class represents ACK method. The ACK method is used to acknowledge final responses to INVITE requests. An ACK may contain an "application/sdp" message body. This is permitted if the initial INVITE did not contain a SDP message body. If the INVITE contained a message body, the ACK may not contain a message body.

The Bye class represents BYE method. The BYE method is used to terminate an established media session.

The Cancel class represents CANCEL method. The CANCEL method is used to terminate pending INVITE attempts.

The Info class represents INFO method. The INFO method is used by a client to send call signaling information to antoher client with which it has an established media session. This is different from a re-INVITE since it does not change the media characteristics of the call. An INFO method typically contains a body. The contents may be signaling information, a midcall event, or some sort of stimulus.

The Invite class represents INVITE method. The INVITE method is used to establish media sessions between clients. Responses to INVITEs are always acknowledged with the ACK method. An INVITE usually has a body containing the media information of the caller. If an INVITE does not contain media information, the ACK contains the media information of the client. A successful INVITE request establishes a dialog between the two clients, which continues until a BYE is sent by either party to end the session.

The Message class represents MESSAGE method. The MESSAGE method is used to transport instant messages. Instant messages usually consists of short message exchanged in near-real time by participants engaged in a "conversation". MESSAGEs may be sent within a dialog or outside a dialog. The actual message content is carried in the body.

The Notify class represents NOTIFY method. The NOTIFY method is used by a client to convey information about the occurrence of a particular event. A NOTIFY is always sent within a dialog when a subscription exists between the subscriber and the notifier. However, it is possible for a subscription to be established using non-SIP means (no SUBSCRIBE is sent) and may also be implicit in another SIP request type (for example, a REFER establishes an implicit subscription). NOTIFY requests contain an Event header field indicating the package and a Subscription-State header field indicating the current state of the subscription. A NOTIFY is always sent at the start of a subscription and at the termination of a subscription.

The Options class represents OPTIONS method. The OPTIONS method is used to query a client or server about its capabilities and discover its current availability. The response to the request lists the capabilities of the client or server. A success response can contain Allow, Accept, Accept-Encoding, Accept-Language, and Supported headers indicating its capabilities. An OPTIONS request may not contain a body.

The Prack class represents PRACK method. The PRACK method is used to acknowledge receipt of reliably transported provisional responses (with status code 1xx). The reliability of 2xx, 3xx, 4xx, 5xx, and 6xx responses to INVITEs is achieved using the ACK method. However, in cases where a provisional response, such as 180 Ringing, is critical in determining the call state, it may be necessary for the receipt of a provisional response to be confirmed. The PRACK method applies to all provisional responses except the 100 Trying response, which is never reliably transported.

The Publish class represents PUBLISH method. The PUBLISH publishs event state. The PUBLISH is similar to REGISTER in that it allows a user to create, modify, and remove state in another entity which manages this state on behalf of the user. The body of a PUBLISH request carries the published event state.

The Refer class represents REFER method. The REFER method is used by a client to request another client to access a URI or URL resource. The resource is identified by a URI or URL in the required Refer-To header field. A REFER request can be sent either inside or outside an existing dialog.

The Register class represents REGISTER method. The REGISTER method is used by a client to notify a SIP network of its current Contact URI (IP address and port) and the URI that should have requests routed to this Contact. Depending on the use of the Contact and Expires headers in the REGISTER request, the registrar server will take different action.

The Subscribe class represents SUBSCRIBE method. The SUBSCRIBE method is used by a client to establish a subscription for the purpose of receiving notifications (via the NOTIFY method) about a particular event. A successful subscription establishes a dialog between the client and the server or another client. The subscription request contains Expires header field, which indicates the desired duration of the existence of the subscription. After this time period passes, the subscription is automatically terminated. The subscription can be refreshed by sending another SUBSCRIBE within the dialog before the expiration time. A server accepting a subscription returns a 200 OK response also containing an Expires header. There is no "UNSUBSCRIBE" method used in SIP—instead a SUBSCRIBE with the Expires=0 requests the termination of a subscription and hence the dialog. A terminated subscription (either due to timeout out or a termination request) will result in a final NOTIFY indicating that the subscription has been terminated.

The Update class represents UPDATE method. The UPDATE method is used to modify the state of a session without changing the state of the dialog. In an established session, a re-INVITE is used to update session parameters. However, neither party in a pending session (INVITE sent but no final response received) may re-INVITE—instead, the UPDATE method is used.