SIP

Carrier-grade Signalware® SIP provides a complete development and deployment environment for customer-developed applications based on the SIP signaling protocols. This includes the combination of flexible SIP protocol access and platform management features that simplify the development process. Signalware SIP is a robust solution that is built on the same proven fault-resilient platform as Signalware SS7 and SIGTRAN.

 

Signalware SIP's high availability and scalability distinguish it from other SIP offerings. Features such as multiple computer element clusters and application failover and restart ensure revenue will not be lost due to downtime. Signalware SIP APIs can be added along side of SS7 or SIGTRAN signaling nodes to take advantage of Signalware's proven operational environment. Signalware SIP can also be deployed in a standalone environment, reducing product life cycle costs since one signaling platform supports multiple customer products.

 

The SIP architecture is modular and provides a simple, easy to use development environment for handling SIP session control. Signalware SIP allows developers to maintain state information at either the transaction level or at the call level. Because it is modularized, the underlying transport protocol (UDP, TCP, SCTP) is transparent from the user application. This transparency hides the communication details so developers can concentrate on the application.

 

Signalware applications can access the SIP protocol stack using any of the three abstraction levels as shown below: Protocol Function, Transaction Function, and Call Function. In addition, Signalware SIP includes important Routing and Management Functions that support the high availability features of the product.

 

Protocol Function
The Protocol Function provides low level encoding and decoding of SIP message formats. This is the lowest level that the developer can use to access SIP communications services. Signalware SIP is compliant with the latest IETF standards (RFC 3261, RFC 2327). The SIP library performs SIP parsing of standard requests (INVITE, ACK, BYE, CANCEL, REGISTER, OPTIONS) and responses. Optional SIP extensions (INFO, PRACK, SUBSCRIBE, NOTIFY, UPDATE, REFER, MESSAGE) support 3G wireless requirements for presence, availability and instant messaging services. The protocol function does not reject unrecognized extensions. Any unrecognized data is passed on as raw data to the application for further deciphering. This allows the developer to handle many proprietary extensions or special encoding defined by a SIP extension.

 Transaction Function
The Transaction Function API simplifies the handling of SIP by presenting a more abstract interface for applications that benefit from access at the transaction level. A transaction consists of one request and its corresponding response. Signalware SIP implements the transaction state machine and handles all retransmissions upon failure conditions. State information is maintained in a distributed fashion so that in the event of a failure, the standby process or standby Computer Element (CE) can recover any pending transactions without loss of service. This function is important for SIP applications that require a transaction stateful mode of operation or in carrier-grade SIP environments where high availability is critical.

Call/Dialog Function
Signalware SIP maintains persistent state information at the SIP call and dialog level using the services of the Transaction Function. Like the Transaction Function, call states are distributed so that a standby process or CE can resume call process in the event of a fault. The Call Function manages one or multiple SIP call legs associated with the dialog call. Signalware SIP can manage the state information for all transactions that occur for each call from the initial (INVITE) message to the last (BYE) message. This greatly simplifies applications that handle multipoint calls by managing all of the call legs of a multipoint session. Signalware SIP performs the typical call handling functions including APIs to support timer management so that the application can issue retransmission requests in the event of timer expiration.

Specifically, at the call level, Signalware SIP performs:

• Transaction sending/receiving within the same call leg
• SIP session timer management
• Protocol error handling (invalid call state transitions)
• Call Functions that can handle multiple call legs (To, From, Call-id) within the same call
• Call-Ids and Cseq values assignments

Routing Function
The SIP router uses the underlying reliable and unreliable transport services (TCP, SCTP, and UDP) over IPv4 or IPv6. TCP and UDP are provided by the commercial operating system (OS). SCTP protocol is provided either by Ulticom or the commercial OS as a selectable option. Once an application registers for Signalware SIP services, the router listens for incoming messages on the designated port number(s) and sends SIP messages to the application based on the combination of Call-Ids and port number. The SIP router sends outbound messages based on the following criteria:

• To a configured local outbound proxy
• To a specific IP address
• To a hostname or domain name by resolving the address using DNS

Management Functions
SIP management functions include SIP stack management, virtual IP management, and events and measurements. The SIP stack manager handles initialization and registering applications with the SIP stack. The virtual IP manager is a distributed function that monitors the IP connections to the network and initiates IP-takeover in the event of a failure of a connection within the Signalware cluster. Signalware SIP collects and stores measurement information, handles event logging via standard Signalware methods, provides debug tracing and monitoring capabilities, and handles MML commands for the SIP stack management. Ulticom's Signalware SIP product is easy to use and provides low-level access to SIP messages.