Sorell Slaymaker
Sorell Slaymaker has 25 years of experience designing, building, securing, and operating IP networks and the communication services that run...
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Sorell Slaymaker | April 22, 2013 |


Dynamic Session Management

Dynamic Session Management Not all sessions and applications are equal, and the network can only do so much with QoS and call admission control; a new architecture is needed.

Not all sessions and applications are equal, and the network can only do so much with QoS and call admission control; a new architecture is needed.

Current communications architectures based on IMS/SIP treat all established sessions the same, which limits the ability to optimize the end user's experience based on available network capacity. As UC applications that utilize voice and especially video consume more network bandwidth, network resources should be allocated according to business value.

An emerging method for providing this flexibility is called dynamic session management, defined as the ability to prioritize, limit, and optimize communication sessions in real-time as the network becomes congested. Enterprises should look at supplementing their Network QoS and static call admission control (CAC) policies with dynamic session management.

Traditionally, a UC solution is unaware of network capacity. CAC is used to limit the utilization of network links by communications applications: A UC solution will have a predefined limit on the number of voice and video sessions that a link can handle, and a Wide Area Network will be designed to handle the predicted busy hour/minute of traffic. Because WAN bandwidth is deemed expensive, highly compressed voice and video codecs are typically used, which lowers the end user experience while putting a cap on the number of sessions that are carried. Even though the majority of the time, bandwidth is available for a high-quality end user experience, the pre-defined, static configuration of the network inhibits the use of the available bandwidth.

In a VoIP/SIP connection, once a voice/video session is established, the media is designed to flow peer to peer and the session is set. The codec type and all the other communication negotiations are done prior to session establishment. If the network runs out of bandwidth mid-session, then the communication will suffer either quality degradation or total drop of the call. Adaptive codecs were introduced to address this problem, and the network communicates to the session by the means of dropping packets and/or adding jitter.

The flaw in this model is the premise that all established sessions are equal and all must adapt in the same way. The business reality is that not all sessions are equal and that under network congestion, some sessions should get higher priority than others.

Figure 1. Current UC/SIP Deployment Architecture

Figure 1 illustrates a multi-vendor Unified Communications SIP deployment. The key components are:

1) SBC: Termination of SIP trunks to the PSTN

2) Session Manager: SIP proxy that manages the dial plan and session policy rules across platforms

3) Communications Services: Manage the communications to the endpoints/services that it supports; these services include:
a. Telephony: Provides the standard telephony and media for all hard- and some softphones
b. Contact Center: IVR, Routing, CTI/desktop, recording, reporting
c. Collaboration: Instant messaging, presence, unified messaging, file sharing
d. Conferencing: Audio, video (room and desktop), and web conferencing

4) End Users: In the office, home, mobile, and at third-party sites

This model works the majority of the time, but under high load, it falls apart. A few examples:

1) Large Conference Call: At the top of the hour, a large conference call starts and consumes all available voice sessions to a site. Contact Center calls cannot get to available agents, emergency calls cannot get out, and local customer calls get a fast busy.

2) Training Video: Marketing is launching a new product and wants to update the sales force on it and requires that everyone watch the 30-minute video. All video sessions are used up and a sales person that would like to show the video to a prospective client that is on-site has to wait.

3) Critical Issue: An overseas manufacturing plant is having production problems and needs to establish a HD video link back to HQ and to the R&D team. The bandwidth is not available due to other voice, video, and data sessions currently running.

4) Desktop Video: A team member wants to collaborate on a new idea with folks at 4 other sites, but is not permitted to do so because the organization does not allow desktop video, because IT cannot manage the bandwidth it may consume, and they worry that it may impact other applications--even though at this moment in time, there may be plenty of network capacity.

Next Page: The Solution: Dynamic Session Management


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