Impact of upstream load on downstream in ADSL

My simple understanding of ADSL was that it is ADSL because more 'bandwidth' is allocated to the downstream data than upstream.

Although mainly via overhead wires, our BT ADSL consistently tests here at around 6500/375 and services such as BBC iPlayer on the @Internet TV stream well, even in HD.

However, since installing CrashPlan (which for the next week or so will be continuously backing up my 'server' upstream at 300) the inbound streaming (eg to the TV) has started to occasionally pause - unless I suspend the CrashPlan.

Should upstream traffic have any affect on downstream in ADSL?

When you are downloading a large amount, like streaming, it has to frequently send ACKnowledgements back on the Upstream. If the Upstream is full then these ACKs get delayed and the download pauses to wait for them.

You can see this happen a lot for some people using p2p while sharing out the programs.

Have a look if your program has a setting for the upload bandwidth, and pull it down a little, this should leave enough upstream left for the ACK to get sent back up, the results are instant.

Thanks for the insight and suggestions.

The CrashPlan utility appears to be configured to use 300 upload when 'idle' otherwise 200.

Problem is that is when the PC/server is 'idle' (which it nearly always is) not when the local network (TV, netbook, smart phone etc.) is 'idle'. (Not sure if it would be practical for them to monitor local network traffic rather than PC activity, but might suggest it to them).

100% this ^

You can see this impact speedtests as well if other people on the network are browsing etc while you run a speedtest

Can you not configure it to just use say 250 upload when idle?

Might be a plan once the 101GB base load has been backed up and we are into just incremental backups.

However, at that point it might be more practical to just schedule backups to run overnight.

Purely from an academic interest (worked in IT since the early 60s but been retired 10 years) was just wondering if it would be technically feasible for CrashPlan to monitor local traffic levels rather than local PC activity?

I'm afraid I have no idea, I am not familiar with that application.

Some makes of router will allow you to prioritise traffic on certain ports or from certain machines. Have a look in the config pages on your router for QoS or something similar

If your network is NOT using a switch, which it most likely is, then they could monitor it using software.
Otherwise they would need SNMP access to your router, ie. difficult to do for all router models on the market.
In short possible, but difficult to get it working reliably for all customers.