Media servers play an important role in telecommunications networks, and will only grow in importance as media traffic volume and variety increase in the future. This role includes the processing of real-time transport protocol media such as voice and video; the routing of media service requests in the network; quality of service enforcement; media transcoding, transizing, and transrating to reduce network bandwidth; recording, playback, and archiving of media; and the delivery of real-time media streaming. Media servers also manipulate media streams to improve the user experience (e.g., echo cancellation for voice) and extend media functionality (e.g., fax interoperability, speech recognition, text-to-speech, etc.). Media servers are here to stay.
As the telecom world moves closer to software-based infrastructure, many questions are being asked about scalability of these software-based infrastructure solutions, including software-based media servers. After all, when there are hardware cards full of digital signal processors you could simply plug in more boards or add more systems (at greater cost) to get to the scalability desired. In the software world, when using a single machine, the scalability is directly related to the power of the processor used in the box.
One model to obtain higher scalability with software would be to use software-based infrastructure software to start, and then use a DSP assist to get higher scalability. But this defeats the purpose of going with software in the first place. First of all, it’s no longer software running on COTS hardware, so expensive purpose-built hardware will need to be deployed. And employing virtualization even on the same server means even more efficiency because multiple software programs can share the same COTS environment. These are core tenets of the move to network functions virtualization.
Additionally, time to innovation is much faster with software. New features and enhancements can be added to a software-based solution more easily via a software upgrade as opposed to trying to upgrade a piece of hardware. For instance, with WebRTC a software-based media server can support VP9 much faster than a DSP can.
What is the alternative though? There are software mechanisms for scaling that have been tried and true with many software programs of the past. Bringing these techniques to software-based communications network infrastructure enables these programs to scale as well. A media server has historically been chock full of DSPs because of the intense media resource requirements described above. Huge inroads have been made with software-based media servers over the past few years that allow them to run in service provider environments. For one, Moore’s Law has now enabled 2,000 channels of voice to run comfortably on a single machine. That will continue to contribute going forward. But those kinds of densities are not good enough for the movement to software-based media servers.
The media server in the IMS network is referred to as a media resource function. The MRF spec calls out an element referred to as the media resource broker, which is a media resource controller and software load balancer that provides scalability, resiliency, and redundancy of media services in the network. The MRB (News - Alert) is described in Internet Engineering Task Force RFC 6917 as well as in the 3GPP specification for IP multimedia session handling (TS 23.218).
The MRB essentially controls multiple media servers at one time and in this way scalability is achieved. Additionally, the presence of the MRB in the network ensures that media service requests are handled in the most efficient manner possible. The MRB has visibility into both the capabilities (e.g., codec support) and availability of each media server in the network, and routes media service requests to the most appropriate media server accordingly. The current Dialogic MRB can control up to 30,000 sessions at a time. We know how to get higher sessions as well and continue to work on that.
Another benefit is high availability since the MRB can be used to manage multiple media servers in different locations. A software MRB can be deployed in a standalone configuration or as a redundant pair for high availability/scalability scenarios.
When large numbers of media sessions are required, software-based media servers can meet your needs.
Jim Machi is vice president of product management at Dialogic.
Jim Machi is vice president of product management at Dialogic (News - Alert) Inc. (www.dialogic.com).
Edited by Maurice Nagle