ing feature could limit the flexibility of the IT manager and potentially drive up
costs for the enterprise. Introduction. Session Border Controllers (SBCs) are de-.
W H I T E
PA P E R John Warner,
Director, Multicore & Media Infrastructure Business Texas Instruments
Session Border Controller Selection Introduction
Today, SBCs typically use a general-purpose processor to implement control, signaling and
Session Border Controllers (SBCs) are de-
management function. Specialized hardware in the form of digital signal processors (DSPs)
signed to provide security and interwork-
is added for efficient transcoding, tone processing, facsimile and any other signal-processing
ing based upon established policies for
operations that require more intense processing. In this white paper we explore how DSPs
traffic entering and exiting a network. In
can add value and flexibility to SBCs and provide a “turbo-charged” solution.
service provider networks there is normally an access SBC and a peering network SBC, as depicted in Figure 1. SBCs are now taking on a larger role in the enterprise environment as well. Enterprise SBCs are typically on premise and terminate SIP trunks from a service provider. In the signaling domain, SBCs normally perform session management in the form of topology hiding, call admission control, policy enforcement and support for billing. In the packet domain, the role of SBCs is to provide media interworking and security. Each vendor will have a specific set of capabilities in
Understanding the codec environment In most circumstances, it is desirable that codec selection is performed by the endpoint. The industry has seen a rapid evolution of codec technology. HD audio and multimedia applications are two domains that have led recent advancements. As the list of eligible codecs is constantly increasing it is often the case that endpoints have disparate capabilities that require interworking. Disparate endpoints are continually being introduced as new highdefinition voice and video codecs make their way through the standardization process. In order to keep pace with these developments the SBC needs to be flexible in terms of transcoding support. This is especially true in an enterprise environment where codecs in the enterprise may need transcoding in order to work in the outside world. A lack of this transcoding feature could limit the flexibility of the IT manager and potentially drive up costs for the enterprise.
each of these areas that need to be evaluated Service Provider IP Network
based upon a user’s specific environment.
(Continued on next column) SIP Trunks
E-SBC
Figure 1. Session border controllers
Access SBC
Peering SBC Peering Service Provider
2
Texas Instruments
In the carrier realm, multiple evolving voice coding standards are driving the need for transcoding. In addition, when service providers need to offer hosted services, such as voice, an SBC’s transcoding capability can be used to ensure that all sessions use the appropriate voice coding. A consistent coding format at the network edge translates into predictable traffic patterns and increased control over voice quality. For wireless carriers moving to 4G, multiple handsets will exist in the same network using differing voice codecs requiring transcoding. In the crossover period from 3G to 4G handsets, a common set of codecs will not be possible. Some service providers want to limit their core networks to a specific voice coding. This simplifies the network design and allows some control over network bandwidth. Additionally, as enterprises become SIP enabled, the door is opened to interconnect with a multitude of service providers, other enterprises, and the “outside” world. Today’s enterprise SBCs use a service provider to talk with the outside world. When two enterprises desire to connect with one another the carrier’s role becomes one of “hairpining” in which calls are routed to the carrier, then to the other enterprise’s carrier and finally to the destination enterprise. Alternatively, a “federation” can be established that allows direct connection between the two enterprises and multiple other enterprises that are part of this federation. An SBC with transcoding capability provides the critical flexibility in making these type connections.
Application breadth
Video codec selection is also a potentially significant challenge without a specialized processor. Using DSPs to interwork video can increase the corporate reach to remote employees and trusted partners driving business efficiencies. The ability to manage these video applications effectively will add to worker productivity and allow for video-conferencing solutions across a wider range of organizations. IVR, or Intelligent Voice Response systems, drive business critical applications and rely on the ability of the IVR host or server to accept DTMF digits sent by the user. In traditional VoIP systems these digits are intercepted by the DSP and a control message is sent to the other party’s end device informing it that there is a digit being pressed. This is done mostly for reliability reasons and to save bandwidth. The other party’s device recreates a clear, unambiguous tone for the user (piece of mind) or server. DSP technology performs this function with a fraction of the processing power required by generalized solutions and provides a highly reliable method of processing tones. Facsimile, or fax services, is another area where DSPs provide value. The variable delay of an IP network can introduce anything from slow fax transmissions to failed transmissions. Fax is normally assumed to be 5 percent of the overall network traffic but accounts for 95 percent of the network headaches. DSP technology can transmit fax reliably using a spoofing technology that perceptually eliminates the IP network delay and enhances the user experience. As with IVR-type applications, it is possible to use other technologies to create this solution; however, DSP technology can perform this function for a fraction of the cost and with much higher reliability.
Session Border Controller Selection
February 2012
Texas Instruments 3
Fax is a special case of point-of-sale type applications (e.g., credit card swipes) and there are indications that with taxi-based credit authorizations and other new applications on the rise, this same mode of transmissions could take advantage of DSP processing capabilities. When selecting an SBC, the breadth of media-processing applications should be taken into consideration. Requirements for audio, video, tone processing, fax, and newer applications will drive the need for DSPs in SBC products.
VoIP quality monitoring
Whether or not a transcoding solution is applicable, the SBC provides a logical point in the network for monitoring voice quality. Today’s leading VoIP quality-monitoring solutions enable enterprises or service providers to monitor voice quality on a real-time basis. This is accomplished through a protocol extension in the IP packet. A voice quality score is generated and can be used to accurately describe the subjective voice quality. These measurements rely on sophisticated algorithms that consume very little overhead when executed on a DSP. This information can be shared with both endpoints in a call. Use of a DSP in this environment also opens up the potential for measurement of a full battery of other impairments that effect VoIP quality which can be shared with network policy entities to dynamically adjust call-routing policy. Both service providers and enterprises can use this voice quality monitoring capability for policy routing decisions and monitoring service level agreements.
Multicore DSP solutions
While the applications discussed in this paper could be supported by a general-purpose processor, performance is negatively impacted, limiting scale and requiring high power. DSPs can perform these operations at a fraction of the cost and power and achieve performance and scale that cannot be achieved with generalpurpose processors. Most of today’s solutions provide an optional DSP add-on capability. With diverse technologies coming together this is becoming a more significant option to consider to drive value for applications that support media processing. TI’s latest DSP technology, based upon the KeyStone architecture, provides a scalable solution targeted at the SBC environment. Specifically, a combined security and network coprocessor block provides a front end to a high-performance set of DSP processors set in a System-on-Chip environment. All of today’s latest interfaces are supported including PCIe, SRIO, 1GbE, and many more. In addition, an embedded three-port GbE switch provides a daisy chaining capability to drive even higher scale. TI’s latest high-performance DSP incorporates eight C66x cores that provide up to 10 GHz of processing power at a fraction of the cost of competing technologies. Please visit www.ti.com/multicore for the latest updates on TI’s DSP processors and more information on the Keystone architecture.
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