Downloads hanging

[Vangelis forthnet]

On Wed May 13 2255:35 BST 2015, Nick Payne wrote:

> which virtually always defaults to flashhd1, 
> that my downloads will chug along at about 1.5Mbit/sec.
> If instead I use --tvmode=flashhd2, 
> the downloads will run at pretty much my full 
> connection speed of just under 15Mbit/sec.

Hi Nick

 There's probably a logical explanation for that.
 
 As already said, the Akamai CDN (geo-blocked at FMS 
level for non-UK IPs) is the default CDN for 
all UK IPs accessing iPlayer TV content; this includes 
access from all RTMP-served devices and, 
of course, GiP users. 
 More often than not, flashhd1=Ak CDN.
However, the Akamai CDN is also used by default to serve 
the lower quality variants too (flashvhigh, flashhigh etc.), 
not only HD, so the bandwidth demands on the servers 
are significantly high. 
 For SD content, the alternate RTMP CDN is Limelight; 
this is NOT the default CDN in the UK; I do not know 
the intricacies of the iPlayer infrastructure that are 
responsible for bandwidth management between CDNs; 
I suspect there's a mechanism that shifts traffic from the 
default CDN (Akamai) to the contingent CDN (Limelight), 
when the first is overloaded... 
 I bet if you did a speed comparison between 
flashhigh1 (Ak) and flashhigh2 (Ll), you'd also find 
that the latter downloads at greater speeds...
 
 On the other hand, flashhd2 corresponds (usually) 
to the Level3 CDN - this is a dedicated HD-only CDN 
that hosts and serves only the 720p flavour of 
TV files - in normal traffic circumstances, when Akamai 
serves HD adequately, there's little bandwidth pressure 
on the back-up Level3 CDN. When asking - through 
GiP - specifically for the L3 hosted file, you'll be among 
few users on that server, so it can afford to "send" you 
the file at increased speeds... 
 While the above logic may not completely explain the 
almost tenfold speed increase (compared to Ak), 
you could also be exceptionally lucky in being 
very closely located to a Level3 CDN node...
 Enjoy your high speeds!

Cheers, 
Vangelis.