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Pound Key as Call Key
  
March 20, 2009
Early IP phone and ATA users were "forced" to use '#' key to call out. Unlike PSTN, the devices usually didn't know when was the end of dialing. In old H.323 days lots of IP to IP calls were made, especially when testing with NetMeeting which came free with Windows system. Since '*' key was used in internet address as '.', the only choice was to use '#' as key to call out.
PSTN service providers did not like H.323 at all. But when their backbone network were changing into IP, they guess they need something at the terminal side too. MGCP protocol was the answer, but it is really a bad one. The only good thing for MGCP is that it has "digit maps", so devices know when the numbers are completed.
SIP and IAX2 protocol did not consider the dialing difficulty at first. But later they added things like "Overlapped Sending" and "Server's Dial Plan" to solve this problem.
Inspired by MGCP "digit maps", AR1688 and PA1688 devices can set private "digit maps" to enable call out without special call key or '#'.
PSTN service providers actually used a lot of '#' in special services. So when we were testing PA1688 devices with Huawei and UTStarcom systems, we added special "service type" as "huawei" and "utstarcom" to disable '#' key to call out.
When we started AR1688 software, we decided to discard '#' key as call key from the beginning. However, many old customers still like to use '#' key, we had to add an option "Use '#' To Call" later.
In United States, people call '#' as pound key. For a long time I had been wondering: what is the relationship between '#' and a pond?

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