The VoIP Peering Puzzle�Part 28: SBC Architectures�Stratus Technologies

Stratus Technologies, Inc., headquartered in Maynard, Mass., is a 750-person, $250M revenue-per-year global solutions provider, focused on network solutions for customers that can’t afford to have network downtime. You might recognize this company by its former name, Stratus Computer, which built a 25-year reputation of delivering very high (99.999+ percent) availability computing solutions to their customers. Stratus servers have enjoyed a reputation as downtime-preventing machines, and as a result, have been deployed in some of the world’s largest financial, life sciences, manufacturing, public safety, airline, telecommunications, and retail industries. Stratus claims to be the first and only server vendor to perform a daily calculation of its server reliability, based upon field data, and then have the courage to display that information on their homepage (check out and look in the lower right hand corner). Today’s value is 99.9997% worldwide uptime—an impressive achievement.

In September 2006, Stratus purchased Emergent Network Solutions, a small Dallas-based company with significant expertise in VoIP softswitches, gateways, and session controllers. The Emergent Network Solutions group is specifically focused on the telecommunications industry, and provides IMS-ready solutions for customers who are looking to build or grow new infrastructure, or to add new services to existing infrastructure. The Stratus networking solutions focus specifically on customizability, scalability, and continuous availability.

From the Emergent acquisition has come the Stratus Session Controller, which is now available on the fault-tolerant servers from Stratus, running the Red Hat Enterprise Linux operating environment on an Intel processing platform. At Stratus, session control is key to their network architecture, and the Session Controller network element is included in the product suite along with other offerings that either build upon or supplement it. These associated solutions include: an IMS-compliant Call Session Control Function (CSCF), a tandem/gateway solution, a residential broadband voice solution, a hosted Centrex enterprise solution, and related service solutions such as billing, unified messaging, service brokering, and interworking. Stratus’ standards-based solutions are modular, and can be used either to build and grow new infrastructure or to add services to existing infrastructure.

The Stratus Session Controller allows full access to all the communications flows required to establish media sessions and provide services in a packet network. Designed to bridge the gap between disparate infrastructure and service networks, the Session Controller offers protocol translation, interworking, media access, and control functions that reliably and effectively deliver services to solve security and vendor-compatibility issues, and provide call detail records for billing. Based upon an open solution telecommunications infrastructure, the Session Controller can resolve the issues that are faced when building new VoIP networks, or interconnecting networks with different VoIP equipment, such as connections to customers behind firewalls (including Network Address Translation (NAT) firewalls), and secure interconnection with other service providers—such as Internet Telephony Service Providers (ITSPs) or Application Service Providers (ASPs). All calls going to or from adjacent service providers are sent to the Session Controller, which will groom and route the signaling and bearer traffic according to the needs of the carriers.

The Session Controller includes a number of key SBC features, including H.323 gatekeeper and back-to-back gateway services; Session Initiation Protocol (SIP) proxy and redirect servers, plus back-to-back user agent services; H.323/SIP protocol conversion and interworking; media redirection, grooming, and monitoring; security; NAT transversal; support for STUN (the Simple Transversal of UDP through NATs); and least-cost routing (LCR).

The gatekeeper functionality allows the Session Controller to interwork with other H.323 and SIP gatekeeper/gateway devices, providing a full spectrum of routing, translation, and screening capabilities for H.323 and SIP traffic. Back-to-back gateway capabilities allow the signaling and bearer traffic to be groomed according to the unique requirements of each network. In a similar manner, the SIP proxy/redirect services provide routing, translation, and screening capabilities for SIP traffic, while the back-to-back user agent function allows the SIP signaling and bearer traffic to be groomed according to the needs of the network. Another component, called the virtual media server, allows the media path to be intercepted, groomed, and monitored, thus eliminating most firewall traversal issues.

The Session Controller also includes integrated billing capability, which stores all of the call-by-call information in easily integrated call detail records, which in turn provide the basis for creating customer bills and mediating billing records between carriers. Access to application programming interfaces (APIs) for the Session Controller is also available, which lets customers create custom solutions to meet specific application requirements.

Further details on the Stratus architecture and products can be found at Our next tutorial will continue our examination of vendors’ SBC architectures.

Copyright Acknowledgement: © 2007 DigiNet Corporation ®, All Rights Reserved

Author’s Biography
Mark A. Miller, P.E. is President of DigiNet Corporation®, a Denver-based consulting engineering firm. He is the author of many books on networking technologies, including Voice over IP Technologies, and Internet Technologies Handbook, both published by John Wiley & Sons.

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