Back-to-source of range

Introduction

• The Back-to-source of Range function allows a client to notify an origin site server to return partial content within a specified range. It accelerates delivery of large files by reducing the consumption of back-to-source traffic and improving the resource response speed.

• When the Back-to-source of Range function is enabled, a parameter request can be returned to an origin site. In this case, the origin site returns the file byte range according to the Range parameter and the CDN node returns the content in the byte range to the client.

  For example, if a request sent from a client to a CDN node contains range:0-100, the range:0-100 parameter will also be contained in the request received on the origin site. When the origin site returns the parameter content to the CDN node, the node returns the content in 101 bytes ranging from 0 to 100 to the client.

• When the Back-to-source of Range function is disabled, a CDN higher-level node will request an origin site for all files. However, the requested files will not be cached on the CDN node because a client will automatically disconnect HTTP links after receiving bytes specified by Range. This causes a low cache hit rate and large back-to-source traffic.

  For example, if a request sent from a client to a CDN node contains range:0-100, the range:0-100 parameter will not be contained in the request received on the server. The origin site will return a complete file to the CDN node and the CDN node will return only 101 bytes to the client. However, the file cannot be cached on the CDN node because the link is disconnected.

Considerations

To use the Back-to-source of Range function, an origin site must support Range requests, meaning that the origin site must be able to return correct 206 Partial Content for an HTTP request header containing a Range field.

Procedure

This function is optional and is disabled by default.

1. Log on to the CDN console.

2. On the left-side navigation pane, click CDN Domain Name List.

3. Select a domain to enter the management page and find Back-to-source of range: