Mon May 17 16:31:06 GMT 2004 IP telephony- No training
I had a client install an ip phone at a remote warehouse today. It was a frustrating experience for all concerned, and the frustration came because the phone guy really had no concept of tcp/ip and networks. Of course, I have no idea how his equipment works either, but maybe between us we could get there.
He knew enough to ask for port forwarding and for internal ip addresses. I gave him the addresses he'd need at both ends, and set the port forwarding as he indicated. As expected, it didn't work. Well, that's what I expected, anyway. Call me jaded, but it's rare to find any of these people with a genuine clue. Nice guy, and it's not his fault that nobody bothers to explain ip basics to installers.
Well, after a bit of a struggle, I realized that he had programmed his remote phones to access the internal ip of his phone card. What would be the point of port forwarding, I asked. He had no idea what I meant. I tried to convince him to change them, but he said "No, that doesn't work, I get the customer's web page!". Huh? Turns out he's configuring the main card with a web browser using a machine that has a pptp vpn connection, so of course he could use the internal address for http. I tried explaining to him that his ip phones did NOT have a pptp vpn connection and therefore needed to use the external ip - which is why we did port forwarding. No comprehension. "But I need to access the internal machine". Sigh. Yes, and that's why I did the port forwarding for you. "But I can't use the browser!". Right, we're not forwarding port 80. "And I can't ping!". Right, ping is icmp.
Finally convinced him to make the change and it ALMOST worked - the devices saw each other, but he had no audio. He had happened to mention that port 5004 was the audio port, but had said it was tcp. I asked if it might be udp.
"It's not either. 5566 is tcp, 5567 is udp". Oh, ok.. I added a udp forward for 5004, and asked him to try it again. Of course, it now worked. I told him to remember that 5004 was udp (or maybe he needs both; I didn't tear down the tcp rule) so that the next job doesn't have to be so confused. He said he would. That's helpful, and as long as the expenses from our ignorance are less than the income from our knowledge, we all make out fine.
Got something to add? Send me email.
More Articles by Tony Lawrence © 2012-06-27 Tony Lawrence
C++ is just an abomination. Everything is wrong with it in every way. So I really tried to avoid using that as much as I could and do everything in C at Netscape. (Jamie Zawinski)