Open Caching Request Routing Functional Specification (Version 2.0)

Project Status:

(roll over for info)


The project has been completed.


March 1, 2019

Estimated Completion:

March 6, 2020
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Problem Statement

There are a number of different methods by which rewrites can be handled in-session. One of those methods, manifest rewrites, was not included in the original Open Caching Request Routing specification. The specification needed to be updated to address this common rewrite technique for segmented HLS streaming video.

Project Description

With Manifest rewrite, a video platform can change the URLs for individual segments by rewriting the manifest. This works best with HLS which has complete URLs for each segment in the media playlists, so any segment can be pointed to any source. For live, the segment list is fetched again by the client as new segments are created, and a server can change the latest segment to point to an alternate source (such as another CDN) the segments were not pointing at before. This effectively moves clients to the new source in a controlled fashion. However, this requires an explicit list of URLs and, thereby, does not work with DASH which uses the same URL for all segments in a bitrate variant. Changing the manifest during the session does not work for VoD either, since the manifest or playlist is only downloaded once when the stream is initialized which results in all segment requests being directed to the CDN, or CDNs, decided at the start of the session. Manifest rewrite can be used to redirect part of the traffic to a separate server with diagnostic capabilities and collect server side metrics to gain insights into the session.

Project Type


Project Leads


There are no SMEs associated with this project.

Published Documents

Goals and Objectives

This project has the following goals and objectives:
  • To update the Version 1.1 Open Caching Request Routing Functional Specification document to Version 2.0 which will include details on how the Open Caching system can make use of the Manifest Rewrite method

Project Scope

The document produced by this project will PROVIDE:
  • An updated Request Routing Functional Specification document which includes the Manifest Rewrite method
The document will NOT PROVIDE:
  • Any additional updates to the Request Routing Functional Specification


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Additional References


The following presentations delivered during Open Caching working group sessions may provide additional information about this project.

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