Slow Modem Router?

I've had a Zoom X5 ADSL modem router for about 2 years now and its been...'okay'. However, I've noticed that whenever I use P2P that opens many ports my whole internet connection slows to a crawl. I can barely view webpages or open emails. So normally I only have a choice between having a P2P app open or browsing the web.

I've looked around tentatively and found it may be the router's poor speed/capacity. As slower routers can't handle large numbers of connections generated by P2P software and so they keel over and crawl. Considering I have an 8Mb line this is really harsh.

Now I've done numerous speed tests and all check out fine. I'm getting good speeds through. Its ONLY when I use apps that open lots of ports.

Is it likely to be the router? My ISP? Or something else?

I never used to get this level of slowdown when using P2P when I was in my student house with an NTL cabale connection at 2Mb and that was being shared between 4 people! When all 4 were using P2P THEN and only then would we experience slowdown in web browsing.

If anyone can shed any light I'd be very grateful. It'd be useful to know what I need to change - ISP, router, etc?

Thanks.

most routers with firewalls have a limited number of open ports or data streams they can handle, in some cases this is set as an explicit number - my office router will only allow 2000 connections through at once. P2P is suckware opening so many ports the vast majority of which are doing nothing.

Some ISP's are known to throttle connections when P2P is being used.

One possibility is that the upstream is saturated by the p2p traffic, delaying such necessary things as the ACK packets your browser needs to send to make connections. If the X-modem does not have some sort of QoS filter on the upstream, then you possibly could apply this to the PC you're using the p2p application on.