Media Flow Controller Assuredflow; Admission Control - Juniper MEDIA FLOW CONTROLLER 2.0.4 - ADMINISTRATOR S GUIDE AND CLI Administrator's Manual

Media Flow Controller Overview

Media Flow Controller AssuredFlow

The AssuredFlow feature assures that Media Flow Controller provides the required bandwidth
for a connection so that media encoded at different bit-rates are delivered at approximately the
encoded bit-rate rather than the fastest possible. This helps optimize use of the available
bandwidth per session along with contributing to the viewing experience of the end user.
It also may be tied to the end-user's service level agreement (SLA). This ensures that
bandwidth is not wasted by sending data at a rate higher than the rate at which it is being
consumed (decoded) by the client. Furthermore, it ensures sufficient bandwidth is available
(reserved) for clients that need higher bit rate video. Examples include:
•
Full-screen mode clients (higher bit rate) versus small window client (lower bit rate).
•
Premium content (higher bit rate) versus free content (lower bit rate).
•
Content delivery to a primary site visitor with higher bit rate versus content delivered to a
viewer redirected from a partner site.
Assured-flow rate (AFR) is the parameter through which Media Flow Controller provides
customer control of the AssuredFlow feature. AFR is specified in Kbps, and its intent is to
ensure that Media Flow Controller reserves at least the configured rate in bandwidth for each
delivery session. Clearly, the sum of AFR cannot exceed the aggregate bandwidth of the
server. To be more specific, if an interface, say, GbE, has "n" sessions, AssuredFlow can
guarantee that the sum of AFR assigned to each active session does not exceed the capacity
of the GbE port, or 1Gbps. An active session is one that is sending data at any one particular
instance. We recommend that the sum of AFR be configured to 80 to 90 percent of the link
speed, for best performance. Further, the configured AFR should reflect the average
bandwidth the target origin server is set to deliver media. For example, if a portal delivers
video to users at an average rate of 750 Kbps, AFR should be configured to reflect this value
(for example, 750 Kbps). Assured-flow rate can be configured globally or through a virtual
player configuration. Traffic is served at the configured AFR, or the dynamic AFR set by the
virtual player, up to the configured maximum session bandwidth.
It is not uncommon to have portals set the logic in their player to signal the AFR on each
session. In that case, the signaled AFR overrides the configured AFR. AFR is disabled by
default, which means Media Flow Controller does not assure a delivery rate. When AFR is
disabled in Media Flow Controller, player-signaled AFR is still effective.

Admission Control

Session admission control provides a mechanism to avoid bandwidth overload; this is an
important part of AssuredFlow. Before a new session is admitted, a series of checks across
various resources determines whether the session can be admitted. A new session is defined
as the first GET request received within a new network connection. Existing sessions are not
subject to this control. The following are the various checks that can reject a new session.
1. A new connection is rejected if the incoming interface is already serving at its bandwidth
limit.
2. After a new connection is accepted, the first GET request can be rejected (with an HTTP
error code) during various stages of processing:
50 Media Flow Controller AssuredFlow
Media Flow Controller Administrator's Guide
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