IP telephony (Internet Protocol telephony) uses the “Internet” to transmit voice and fax instead of connections over public switched telephone network (PSTN) lines. IP telephones are connected to an ethernet network to communicate internally and externally. IP Telephone systems revolutionized the telecom market by allowing a single dedicated network jack to connect both the user’s computer and telephone.
I looked up the internet to find the history of the IP Telephone and two different stories exist out there. The first one is that Selsius Networks created the first IP Telephone and was eventually acquired by Cisco. According to Wikipedia, the first commercially available IP phone was the Selsius 30SP. In November, 1997 the company sold five 30SP phones to the TRI lab of Southwestern Bell in San Antonio. The company was acquired by Cisco in 1998 and Selsius provided the evolution path to most of the Cisco phones you see today on desktops throughout the world.
The second story is that Nortel Networks or Northern Telecom was experimenting with Unistim IP phones prior to 1997, with the first Nortel IP Phone (i2004) introduced commercially in 1998. Unlike the Cisco’s phones which were largely developed out of data and networking, Nortel’s IP phones were developed out of telephone and voice technology. While Nortel may have been a little late to the IP phone rollout to desktops throughout the world, they were very successful and achieved parity with Cisco in the number of IP Phones rolled out. Many legacy Nortel IP sets are still in service today (being supported by E-MetroTel and Avaya) and are operating on desktops with the most current technology.
IP phones run on many different protocols. Cisco uses SCCP and SIP, legacy Nortel uses Unistim and SIP, while Avaya uses H.323 and SIP. Various software versions and firmware are available for these phones that will allow users and administrators to flash different firmware to the phones. For example if you have a Nortel Unistim set that you want to convert to SIP for use on an IP Office, you simply obtain the SIP firmware from Avaya’s website and then use a TFTP server to upload the SIP firmware to the Unistim phone.
IP trunks use the same internet based protocols such as SIP to provide VOIP PSTN service (instead of analog or digital PRI’s) to telephone systems. You don’t need IP phones to run on IP trunks. Conversely you don’t need IP trunks to run IP Phones. For example, if you buy a Nortel BCM50 system with 30 IP sets, it is possible to use analog POTS trunks on the main system for incoming and outgoing trunk calls. The IP based technology only exists internally on the networks.
On the other hand, you can buy an Avaya IP Office with 50 digital sets and use VOIP trunking for incoming and outgoing calls, without having an actual IP phones active on the system. In this case IP based technology is only used externally on the network.
Lastly, you can have a system such as the E-MetroTel UCx where you have digital, analog, and IP phones on the same system and a mix of analog POTS and IP trunks on the same system. Programming on the system can allow certain lines to use analog for incoming only or IP for outgoing calls only. Systems with this type of flexibility are commonly referred to as a full IP-PBX.
Analog | Digital | IP | |
Voice quality | ♦♦♦ | ♦♦♦♦♦ | ♦♦♦♦ |
Reliability | ♦♦♦♦♦ | ♦♦♦♦♦ | ♦♦♦♦ |
Features | ♦ | ♦♦♦ | ♦♦♦♦♦ |
Cost | ♦♦♦♦ | ♦♦♦♦♦ | ♦♦♦ |
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