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Feature Article
November 2000


Leveraging SS7 To Provide Enhanced Services: SCTP: IP Telecom's First Protocol


The Internet has grown at a rate that far exceeds the growth of any other industry, ever. This phenomenal growth, the expanding freedoms and knowledge available, ever-increasing transmission speeds, and the addition of voice and associated signaling, may be pushing the envelope of the technology. The safety and the quality of other industries are regulated. Take, for instance, the automobile industry. Would anyone deem cars safe if they developed free of safety checks? Holding to the standards of proven telecommunications protocols, while at the same time developing more suitable protocols and technologies, is, and will continue to be, a key issue in the emerging Internet world.

It was understood that the critical first mission was to craft a signaling transport protocol for the IP realm. In the PSTN world, Signaling System 7 (SS7) was developed in the 1970s to define procedures and protocols by which the public switched telephone network elements exchange information over a packet network, with signaling carried on an overlaid network apart from actual information flows. It since has been nearly universally adopted as the primary signaling protocol for call setup as well as to provide for an array of enhanced services ranging from toll-free 800 numbers, calling cards, and caller ID, to wireless services such as PCS, roaming, and mobile subscriber authentication. Now it's "back to the future" time for SS7 as it accommodates similar functionality in the IP world.

We take for granted the high reliability of the phone network, but are we prepared to accept Internet time as a unit of measurement for the dynamic setup of our IP voice services? That's the issue the Internet Engineering Task Force's (IETF) Signaling Transport (sigtran) Working Group was challenged to tackle. Specifically, the mandate was to address the transport of packet-based PSTN signaling over IP networks, taking into account functional and performance requirements of the PSTN signaling network. Simply put, we were to expose the strengths of SS7 to the IP community and come up with something equally reliable for the IP networks.

The sigtran design team was constituted of several dozen dedicated and knowledgeable telecom engineers from around the globe. Between bi-weekly conference calls and numerous face-to-face meetings, we managed to focus on a list of core issues and produce, from a series of papers submitted by group members, an evolving proposal for a reliable IP transport protocol. As it evolved, a number of issues arose concerning functionality, the scope of the protocol, and naming conventions.

After more than a year's collaboration, the team published comments regarding the Stream Control Transmission Protocol (SCTP) and a number of signaling adaptation layers. This first low-layer protocol will be the foundation for an emerging array of new protocols to be layered on top of it as time goes on. As interest from the networking community increased and we received feedback, SCTP made its way into the hands of the Internet Engineering Steering Group (IESG) for approval, which eventually came after several final iterations, alterations, and interoperability "bake-offs."

SCTP is welcome as the newest member of the IP transport layers, sitting alongside transmission control protocol (TCP) and user datagram protocol (UDP) as it operates directly on top of IP. It provides ordered message delivery on multiple logical streams for QoS and message throughput and supports network fault tolerance where multi-homing environments are available. It is also an alternative to TCP -- basically a replacement for TCP where it has proven to have limitations. One of the group's most popular discussion threads hypothesized on using SCTP as a transport for hypertext transport protocol (HTTP).

SCTP itself cannot provide transport for SS7 services. It requires user adaptation layers that transform SS7 layer interfaces into a series of messages and procedures. A number of these user adaptation layers now are being defined by the sigtran design team for signaling protocols. For SS7, the message transfer part (MTP) Level 2 user adaptation (M2UA) covers SS7 datalinks, effectively allowing SS7 long haul over IP. The MTP Level 3 and Signaling Connection Control Part (SCCP) user adaptation layers (M3UA and SUA) allow media gateway controllers or other next-generation switches and services engines to access SS7 through a signaling gateway -- effectively bypassing the complexities of SS7 networking. More proposals covering ISDN, session initiation protocol (SIP), and other non-SS7 user adaptation layers are emerging as more industries realize the potential of SCTP as a transport protocol.

Standard protocols and procedures are vital to the evolution of services in this expanding information age. The entire Web is based on a handful of well-defined protocols designed decades ago that allowed for the acceptance and explosive growth of the Internet. As we find new services to deploy, we will continually re-evaluate the tools at hand and appropriately add to the arsenal. A standard like SCTP will enable the telecom industry to develop functional, interoperable tools to support efficient and reliable services over IP.

Personally, I am banking on these developments: With any luck, sometime in the next few decades, I'll be able to get safely teleported to work each day, no longer worrying about beating the highway traffic in my car. And perhaps I'm dreaming, but I'm sure my boss will be using various media transported over SCTP to find a way to reliably teleport his image to my home each morning to deliver my to-do list personally. 

Norm Glaude is the chief engineer of SS7/IP Signaling Products at Performance Technologies, Inc., and is a member of the Internet Engineering Task Force's Signaling Transport Working Group. 

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Intelligent Optimization Of Bandwidth For Next-Generation Networks


The new public network changes so many things for service providers. To compete in the fast-paced telecom market, their business plans must be focused on varied and value-added services. Carriers are shaping their infrastructures to take advantage of everything a next-generation network offers. They are ramping up to fully utilize high-speed optical capacity at the core. But at the access and edge of the network, carriers are forced to make compromises and deal with complexity.

The high cost of overlay networks is the largest barrier in becoming a multiservice carrier. This led carriers to take an evolutionary direction toward offering all their services over a single unified infrastructure. This unified approach has created the need for a new breed of multiservice edge switch. Vendors developed this new class of edge devices to fill this need and aggregate a variety of traffic types and send them over the appropriate backbone network. These aggregation switches simplified network operations and were less expensive. They were scalable, reliable, and had robust network management capabilities for a multi-vendor environment.

Converging different types of access devices and essentially taking advantage of the core optical network were the primary goals of the first-generation aggregation switches. These switches were problematic though, as they were really only aggregation devices, performing the conversion between legacy and next-generation networks and creating large pipes through the optical core. They weren't able to converge voice and data and lacked intelligence and SS7 signaling capabilities for any other types of functions.

The market has responded to this deficiency by creating another type of edge switch that combines aggregation capabilities with intelligence. These next-generation switches are a combination of multiservice edge switch and softswitch technology and are typically referred to as intelligent multiservice or convergent switches. The next-generation switches go beyond aggregation and provide a large pipe into the core: Integrated call control to the SS7 network is performed on these switches, covering such functions as 800 number and DNS-to-IP translations. The softswitch portion of the switch performs the call control function and bridges the gap between the public switched telephone network (PSTN) and the Internet.

The question remains: How should enhanced services be implemented intelligently across multiple access technologies? The solution is to implement intelligence on the high bandwidth multiservice switches at the edge of network. This intelligence has two specific applications: Multiplexing the data effectively on the transport side to get the best results; and allowing a unified service logic to be delivered to an end user, regardless of type of access. The requirements for an intelligent multiservice switching system include: Simplicity, scalability, availability, and support for services.

The winning strategy for service providers is to facilitate, not force, the migration and convergence to the new public network. Therefore, products that fit this new evolving paradigm must perform like a class 4/5 central office switch to the PSTN network while providing the bandwidth, density, latency, and interconnection of converged public networks and diverged access types. Access types should include broadband, such as DSL and 3G wireless, as well as narrowband TDM voice and data dial-up. Such a product is achieved through the support of these multiple access types and the integration of signaling, call control, circuit and session termination, and service intelligence, as well as aggregation and grooming in a highly-scalable system node. This node can be deployed as a single platform or in a distributed architecture, feeding the unified core network with efficient voice and data traffic. This is the new intelligent edge that is required to meet carriers' needs in the new public network.

John St. Amand is co-founder, president and CEO of Telica, Inc., a developer of intelligent multiservice broadband switching systems. 

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Enhancing Services Using SS7: Real Benefit From Link Monitoring System Data


Every traditional telecom network is built around two main networks -- one carrying voice and the other carrying the signals required to set up and tear down these voice calls. The information carried by this second network -- known as the SS7 network -- is incredibly rich. But how can this mass of information be harnessed and put to good use?

A link monitoring system (LMS) can monitor all the messages sent along the SS7 links in a non-intrusive, switch-independent way and can correlate all messages from a single call into a call detail record (CDR). These CDRs can either be processed at the point of monitoring or delivered into a central repository, typically a large database.

Now difficult as this may sound, the hardest part is actually how to process and arrange this huge mass of data with more information arriving by the minute. Many of the world's most forward-looking telecom service providers use a data management component that cleanses and enriches the data as it arrives, loads the enriched data into a database, and manages the database in a way that enables efficient access, both current and future.

Enrichment takes two forms: The first adds extra information to each call from an external source, for example recording the state and LATA a call originated and terminated, and determining if the call was made to an ISP; the second adds information to a call that came from another part of a call, for example recording the entry and exit of a transit call, or back-filling a calling party number of an inter-state call if lost by the long-distance carrier. Current uses of this kind of system include:

  • Finding ISP PoPs by analyzing call profiles to every called number in the network;
  • Network planning, i.e., deciding whether a new tandem is really needed or if the congestion could be solved simply by additional direct trunks; and the ability to track and offload ISP traffic to packet-switched networks;
  • Reciprocal compensation/interconnect billing including separating out ISP calls, automatic verification for state and LATA jurisdiction, as well as percentage of calls with no calling party number;
  • Measuring interconnect Service Level Agreements (SLAs) including checking call completion rates and verifying the correct mix of peak and off-peak traffic; and
  • Detecting deliberate disguising of the true nature of a call (arbitrage detection).

However, the possibilities for further mining this rich vein of data are many:

  • How many calls did a residential customer miss while surfing the net? Enough to persuade the customer to take a second line or ADSL?
  • How many calls did a business miss because they had too few lines? How many of those calls phoned back?
  • What was average call setup time by switch? By route? By time of day? By IXC?

As these systems evolve to include information from next-generation telecom networks, the possibilities are even greater.

John Macartney is R&D project manager for Agilent Technologies, Telecom Systems Division (TSD). Its businesses excel in applying measurement technologies to develop products that sense, analyze, display and communicate data.

[ Return To The November 2000 Table Of Contents ]

SS7 -- Providing The Key For Converged Service Provision


Three major trends are shaping the telecommunications industry today: Deregulation, with the increased competition this implies; a huge surge in the volume of data traffic; and the advent of a new breed of sophisticated communications services "consumer," who moves with ease between fixed, mobile, and data-based appliances.

Against this backdrop, service providers have recognized the potential benefits of merging these different types of traffic and delivering them over a unified infrastructure. These benefits range from the significant cost savings of running a single network, particularly for business customers, to the possibility of creating value-added services that combine voice and data in innovative new ways. This is what is meant by the term "network convergence."

The technical challenge facing service providers, therefore, is how to seamlessly deliver the complete range of communications services -- those that are traditionally delivered over the PSTNs and those that are associated with packet-switched networks -- over a converged infrastructure.

Early experiments in this field have not lived up to expectations. Some ISPs have indeed succeeded in transporting voice over the Internet, but these offerings have not been able to match the quality of service, nor provide the range of value-added services, delivered by the traditional PSTN network.

A ready solution lies in SS7 technology, which can be used to provide a bridge between PSTN and packet-switched networks. For, in truth, while we refer to the converged network, the reality is more likely to be the coexistence of voice and data networks running alongside a dominant IP network, with SS7 technology acting as the unifying element allowing seamless service delivery across all three.

SS7 technology is one of the most critical components of today's PSTN infrastructure. It provides for call setup on circuit-switched networks via high-speed, out-of-band connections, as well as offering transaction capabilities that harness remote database interaction. If the signaling capabilities afforded by SS7 technology are combined with intelligent network (IN) architecture, it becomes possible not only to deploy service across PSTN and IP networks, but also to create advanced, value-added services that combine voice and data.

Jean-Rene Bouvier is the general manager of Hewlett-Packard's Telecom Infrastructure Division, based in Grenoble, France. 

[ Return To The November 2000 Table Of Contents ]

Natural Selection In VoIP


As competitive service providers race to build networks that support next-generation services, they must also be mindful to not sacrifice, for the sake of a "next-generation" label, the advanced intelligent network (AIN)-based services customers already expect. While AIN and next-generation aren't mutually exclusive, it is a rare combination. The carrier's cash register will ring "No Sale" without AIN support for basic services such as enhanced 911, 800 number translation, Custom Calling services (CLASS features), including Caller ID, Calling Name Delivery (CNAM), Call Waiting, Automatic Call Back, Selective Call Acceptance/Rejection, Local Number Portability, and PCS services.

Signaling System 7 (SS7) must play a major role in the success of the next-generation network because of these high standards. Fortunately for competitive carriers, SS7 support does not mean a multi-million dollar investment in "big-iron" switching gear. Thanks in part to support for SS7, today's next-generation Class 5 switch technology can enable this new breed of carrier to build an effective network that leverages the best of the PSTN with the best of IP-based networks.

A Class 5 switch can leverage the SS7 protocol to make service creation simple, and by supporting the protocol, competitive carriers can offer all the essential features of a traditional network, while providing a platform for service migration. Using the AIN network architecture, the AIN-capable Class 5 switch provides a set of generic triggers and events during call processing, which can be set to invoke service logic in an AIN service control point (SCP). The creation of this service logic is accomplished through interaction with the service creation environment (SCE). The Class 5 switch adopts industry-standard open APIs that enable service providers to deliver value-added services regardless of platform vendor or network access. The SCP defines the service logic, determines the next action for the service, and executes the service.

SS7 plays a vital role in AIN service creation and delivery in the IP environment. It ensures full service transparency of SS7 switch-to-switch features, via ISUP-functionality, and provides interconnect across multiple country variants. In the multi-vendor, multi-service network environment, SS7 over IP maintains service integrity, service performance, and high reliability. For example, it will enable database access for 800, LIDB, and CNAM via SCPs directly from the IP network. The IP/SS7 signaling gateway provides consolidation and PSTN access.

SS7 not only allows IP networks to migrate to carrier-class services that could be enhanced with the use of SS7, ISUP, and TCAP protocols, but also allows new types of services from the Internet such as "Click-to-dial-back" and "Click to Fax." The idea is to trigger PSTN services from the Web and execute service on the AIN SCP. SS7 also allows PSTN to IP host communication for applications such as Internet call-waiting where the IN needs to alert the Internet node.

New service creation environments allow application creation and protocol independence by leveraging Internet protocols such as XML and JAVA. Service providers looking to create competitive differentiation can use new service creation tools and protocols that allow the re-programming of the end-office switch to rapidly create value-added services. 

Nitin Patel is product manager, signaling at Taqua Systems, Inc., based in Hyannis, MA. Taqua's Open Compact Exchange (OCX) embraces today's technology to provide a migration path for the delivery of tomorrow's services. The company is led by an experienced team of telecommunications professionals.

[ Return To The November 2000 Table Of Contents ]

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