Caching Servers and Streaming

Hogrod

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I'd like to start what could potentially be a technical thread and one that may require the intervention of Iburst to resolve the situation. However, I'd like some information from those that understand how caching servers may effect the streaming of recorded content from an International website.

THE SITUATION

I like to listen to a radio station in the UK called BBC Radio 1. They provide the ability to listen again to shows that have already aired using their 'Listen Again' functionality. Basically a new show is uploaded to their servers every week for anyone to listen to.

For this problem I'd like to refer to this weeks show as SHOW1 and last weeks show as SHOW2.

Every week SHOW2 is overwritten by SHOW1.

THE PROBLEM:
While listening to SHOW1, parts of SHOW2 appear in SHOW1. According to BBC technical support this may be caused by caching servers not realising that there is a new SHOW1 and it still has SHOW2 on its server. Therefore it appears to switch between content in SHOW1 and SHOW2 instead of just playing SHOW1.

This problem not only occurs on my Iburst connection but also when I use other ISPs such as those utilising DSL services from Telkom.


BBC Technical support made the following report to me:

"The fault you described does sound like a caching problem we have had reported several times in the past. We know some ISPs do not stream media directly from our servers. Instead they keep their own local copy and stream from that. As we overwrite the same files every week the ISP's system gets confused between their own copy and the new one and flips between the two. As result people hear a mixture of an old stream from the ISP's cache and the new one from our streaming servers. It can be a few seconds of an old show or it can be a whole hour, and it can flip between them many times.

It would be impossible for our streaming servers to produce the problem you describe. Radio programmes are automatically recorded and given a unique filename. The old programme is then deleted from our streaming servers. Finally the new one is uploaded to the stream servers and renamed so it has the same file name as the old one."


YOUR HELP:
So who or what is at fault for this problem I've described here, and what do you think can be done about it?
 
If BBC renamed the files instead of keeping the same name, then it wont be a problem. The cache servers look at the name of the file, it doesnt verify the content.

R
 
Thanks! That seems like a very simple solution. I will suggest it to them and see what they say.
 
A simpler solution would be for them(the isp) not to cache the content in question.
 
Last edited:
if the host sets the HTTP headers correctly, the ISP should not cache the content. my guess is that the header is not set correctly!

for more info on caching in HTTP1.1, have a look at the rfc.
 
andres101 said:
if the host sets the HTTP headers correctly, the ISP should not cache the content. my guess is that the header is not set correctly!

for more info on caching in HTTP1.1, have a look at the rfc.

Hi, would this apply to a realmedia file being called from a HTTP page? It's the media file that is being cached and not the HTTP page.
 
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