The Origin of Random iChat video failu

Question

I hope this topic gets a lot of response and reply from as many people as we can get involved. If you are like me you have been using iChat more of less happily for some months and then suddenly all **** breaks loose and you cannot initiate chats with one or another of your usual partners when neither of you have changed anything. PERIOD. Maybe it comes and goes, maybe you "fix" it with a seemingly random change. I would love to hear from someone and everyone about what can truly cause these problems. I have two brand new macs, an iMac about 5 months old and a 2 month powerbook. There are days that the powerbook will work on a video chat while the iMac fails every time (trust me we tried a LOT of times). In this case they are BOTH sitting behind the same cable modem,using the same wireless router and have been identically configured (trust me I checked, I looked in all the places etc etc). So, in my mind that eliminates the usual carbon copy post most people make telling everyone to check their router, firewall, NAT, uPnP, port forwarding etc etc etc.
My question to everyone is, what can POSSIBLY work in this way, ie which component is iChat having issues with.
OR
Is it more likely a network issue EXTERNAL to my house and my chat partners home, i.e. bandwidth, routers etc etc... I don't think it could be speed. During a repeated failure I and my chat partner both went to speedcheck.com and both had well in excess of 500 kbps up and down, more like 1Mbps but I cannot recall the number so I dont want to exagerate here. . I am leaning this way just a bit because it works, then stops, then works, then fails with a different individual, then all is good etc etc you get the idea.
Basically what can get you failures that act this way. I am STUMPED. Is it apple code and an iChat bug? Is it just complicated (poor excuse), or is something really broken somewhere that somehow works most of the time until it decides not to work and then suddenly heals itself (you can see why I feel this is a bunk excuse).
Anyhow... chime in

Answer 1

Yes, I think weʼre a growing lot of people who experience the severe limitations of iChat AV while other IM-clients have no problems and Skype is getting through everywhere. Textchatting is the only thing which works, but well...
Anyway, so far I have found out that one of the main reasons for these kind of problems, is that iChat is being a very "law abiding" citizen. It obeys rules and follow protocols while no one else seem to do so and that leaves a lot of us with problems.
There are ISPs who are blocking certain ports iChat needs to establish AV-chats and they do this mainly because they sell similar products like VoIP-telephony. The problem then, if you use a laptop and are travelling, it all depends on the network you connect to. Then it of course depends on the network your buddy is connected to.
To give an example; I used the landlordʼs internet the last two places I lived and I could not initiate a AV conversation nor accept one. I am still living in one of the places but decided to get my own internet and asked specifically that the ISP didnʼt block such ports as needed by iChat and I found the one for me - and it works again! But that will of course change if I take to the road with my iBook...
So, Apple, please make iChat a more forgiving and flexible application! If others can do so - MSN, Yahoo Messenger, Skype - it canʼt be that hard. And iChat is good when it works, maybe even the best. But my mother canʼt see her children and not hear them as we all intended her to do. Others cannot stay in touch with spouses and friends and colleagues when they are away.
Well, I hope my two øre can contribute to understand what the problem is. And to move Apple to do something about it.