VoIP strives for simplicity
Analog phones continue its service, as the users can buy an inexpensive phone set, plug it into the network and immediately start calling. The use and connection of IP phones are still difficult, but perhaps the situation will be improved by the IAX protocol.
It was designed to minimize bandwidth consumption by signaling and data transmission systems, as well as for internal support for NAT transparency (network address translation). Instead of the RTP (Real-time Protocol) protocol, IAX uses the User Datagram Protocol (UDP) over a single Internet port (port 4569) to transmit signaling information. IAX traffic easily crosses firewalls and uses much less overhead than RTP. This protocol can triple the number of calls sent with the G.729 compression codec. So, the combination of G.729 with IAX allows you to transmit at least 103 calls with a bandwidth of 1 Mbit / s.
Instead of parsing text commands, IAX uses binary data, as this is a natural way of computers communication with each other. The answers are sent back by the IAX protocol, no matter where the packets came from. IAX transmits audio packets with only 4 bytes of headers each, so commands use very low bandwidth. For multiple calls, IAX reduces the amount of overhead information of each channel by combining the data of several channels into one packet. The protocol reduces not only the number of headers but also the number of packets, which is especially important for wireless networks.
The IAX protocol is so simple and straightforward that the entire IP stack including IAX support, TDM interface, echo cancellation and subscriber identification are implemented in the analog terminal adapter (ATA). The ATA is equipped with an Ethernet interface and a telephone jack. Thus, ATA turns any analog phone into an IP phone. The adapter can be built using only an 8-bit microprocessor, 4 Kbytes of RAM and 64 Kbytes of internal flash memory. In the near future, there will be an enthusiast who can make an IP phone for $ 10, using such inexpensive components.
IAX can be extended and supplemented with encryption and intercom functions. The lack of a documented standard for IAX is the main obstacle for its use by telecom industry leaders. But a number of vendors still created products based on IAX or expanded the functionality of their solutions by supporting this protocol. If he can simplify the use of VoIP terminals to the level of analog communications, one day it will be possible to connect an inexpensive IP-phone to the network and immediately start calling using it.