ITEXPO begins in:   New Coverage :  Asterisk  |  Fax Software  |  SIP Phones  |  Small Cells

Feature Article
February 2005

Software Media Servers Step Up

BY Ken Osowski, Vice president of marketing and product management of Pactolus Communications Software Corp.

Software-based media servers are the next iteration in the SIP community’s drive to move to a pure-IP services infrastructure that will allow service providers to increase revenues and lower infrastructure costs. Not only will software-based media servers increase profitability, but they will help to make technology choices future-proof.

Media servers play a crucial role in the delivery of advanced IP network services. An industry-wide movement to deploy IP-based, converged network infrastructure has opened up new markets and revenue opportunities for traditional service providers with their existing legacy networks, and for emerging carriers with IP-based, next-generation networks.

Media servers have, until recently, been almost exclusively hardware-based. Hard-coded DSP logic was the only solution for providing the ability to handling the media processing workload in phone networks. But software-based media servers can be deployed as a stand-alone IP-based media server solution to support SIP-based entities throughout a SIP-enabled network or in combination with an application server running SIP-based services. While used in its purest application to enable call signaling for call control, the SIP protocol by design was built to be extensible; many new innovative services will emerge, with SIP evolving from call control to more generic event control where events could be triggered by instant messages, voice messages, presence state changes, or even video sessions.

While hardware-based software media servers will continue to thrive in large-scale telephone networks, software-based media servers can supplant DSP-based hardware servers for “commodity IVR” functionality. “Commodity IVR” is the small set of features required for prepaid and most other IVR applications, including:

  • Streaming pre-recorded prompts.
  • Detecting DTMF entries.
  • Standard IVR controls (e.g., barge-in, digit timers).
  • Recording and playback.

Unshackling Service Providers
These software-only media servers will unshackle service providers from reliance on proprietary (read: expensive) hardware for base functionality. Utilizing off-the-shelf Linux-based systems, software-based solutions can support a variety of media processing functions, including announcement generation, DTMF detection and generation, message play and record, conference recording, audio bridging for small n-way conferences, and other advanced capabilities. Currently, software-only media servers are deployed operationally with prepaid IVR systems supporting more than 300 million minutes a month of calls. A single Intel processor today can support 400 full duplex IVR sessions with DTMF detection.

Traditional carriers are using PSTN/IP media gateways to perform Internet offload functions and in so doing defer expensive upgrades on their TDM switches; emerging carriers along with some traditional carriers (both wireline and wireless) are using media gateways to convert PSTN voice calls to “packetized” voice and route these calls to lower cost IP network infrastructure (IP trunking). Carriers are utilizing these media gateways to deploy proven revenue-generating services such as calling card services, conference calling, broadband telephony, and voice mail services. These solutions are incorporating an IP-based services architecture that includes IP media servers and SIP-based application servers connected to media gateways.

Service Logic Runs on Application Server
The IP-based media server takes DSP logic that ran deep inside traditional service nodes and makes these functions available to the service logic execution environment running on an application server. These functions include interactive voice response capabilities such as playing prompts and collecting DTMF digits, automatic speech recognition (ASR), bridging calls together for conferencing applications, as well as recording greetings, announcements, and messages to a server.

As call flow logic executes, the application server requests these functions when needed from the media server using either SIP or MGCP protocols. This decomposed service node model speeds up application development and allows these components to scale independently so that new services and capacity can be easily added.

As noted earlier, most implementations today rely on hardware-based media servers. But the capability of software-based media servers is growing by leaps and bounds. Because software runs on industry-standard hardware running Linux, it offers a lower cost-per-port than DSP-based IP media servers. As faster hardware becomes available, carriers can scale capacity without expanding their hardware footprint and without disrupting services. Common hardware components also means hardware spares can be reduced, eliminating the need to inventory dedicated, DSP-based media server hardware platforms. Carriers have the added flexibility of choosing a variety of cost-effective Linux platforms.

Software-based media servers run media handling logic to process media streams — usually written in C++ — directly on general purpose processors running off-the-shelf operating systems such as Linux. Hardware-based media servers run this same logic in firmware on DSPs that are designed to perform analog signal processing functions; they are optimized to perform media processing functions and can scale to thousands of “ports” in a relatively small footprint. But software media servers can deliver up to 800 ports of IVR in a 1RU form factor, and given that this processing logic is written to run under Linux, it can be more readily changed to add new feature sets without requiring that DSPs are replaced to introduce new features.

In the case of a prepaid calling card application, a subscriber would typically call an 800 number provisioned on a media gateway to get access to the service. Based upon the number called, the media gateway “forwards” the call to the application server by issuing a SIP invite request. The application server then starts prepaid service logic that plays an introductory service greeting and prompts the subscriber to enter their PIN code. During this part of the call flow, the application server asks the media server (usually under MGCP control) to play the prompts (“Please enter your PIN code”) and collects the subscriber’s PIN code that was entered using DTMF input on the subscriber’s phone. The “bearer channel” or voice path that enables the subscriber to hear the voice prompts is established between the media gateway and media server as RTP streams. In this type of application, the software-based media server can be used to play the welcome prompt, collect PIN information about the subscriber, or play “whisper prompts” to the subscriber telling them how many minutes they have left on their card.

In the case of residential broadband telephony with integrated voice mail, the software media server is used to perform IVR functions in conjunction with an application server. When a caller reaches a subscriber’s voice mailbox or the subscriber accesses their messages, IVR menus are presented to the caller by application server service logic requesting the media server to play a prompt, to collect DTMF to navigate messages or collect password information. The media server also records voice messages to the message store or plays them back using RTP media streams. The audio streams are mixed by the media server to create a conference call or possibly bridge in an operator to assist the subscriber.

Scaling Gracefully As Needed
One commercially successful prepaid calling card service provider is using these technologies to scale to over 300 million minutes of monthly long distance voice traffic. This deployment takes software-based media processing functions and combines it with application server logic that runs the prepaid calling card application. This allows the service provider to scale very gracefully by adding one server at a time to increase its overall capacity. This eliminated the need to manage a hardware-based media server resource as yet another network element that needs to be maintained and capacity managed separately.

Software-based media servers are very real and readily support a breadth of applications today. Will hardware media servers ever get replaced by software media servers? For commodity IVR and voice messaging functions the answer is yes. Because it is possible to run these software-based media servers on industry-standard hardware running Linux, service providers are able to benefit from a low cost-per-port.

For proven, carrier-deployed, revenue generating services such as calling card, voice messaging, and broadband telephony, software media servers will emerge as the most economic and flexible alternative to DSP-based media servers. Intel processors running Linux will continue to deliver more raw MIPS for media processing tasks and provide to carriers an all-software alternative to deploying next generation communication services. IT

Ken Osowski is vice president of marketing and product management of Pactolus Communications Software Corp. For more information, please visit the company online at

[ Return To The February 2005 Of Contents ]

Today @ TMC
Upcoming Events
ITEXPO West 2012
October 2- 5, 2012
The Austin Convention Center
Austin, Texas
The World's Premier Managed Services and Cloud Computing Event
Click for Dates and Locations
Mobility Tech Conference & Expo
October 3- 5, 2012
The Austin Convention Center
Austin, Texas
Cloud Communications Summit
October 3- 5, 2012
The Austin Convention Center
Austin, Texas