VoIP - Introduction to Voice over IP

Introduction to Voice-Over-IP


1&2 Port gateways	4 Port gateways	VoIP Phones	VoIP PBX	VoIP Sundries

The Promise of Voice over IP

For over a decade now the prospect of using the internet to carry voice calls has been ‘next years technology’. Although there has not yet been any revolution in the way we route our phone calls, a number of enabling technologies, services and providers are now in place which can finally deliver a reliable, high-quality solution at very low cost.Most businesses and individuals who are serious internet users now have un-timed and effectively un-limited connection to the internet. Users can spend all day downloading data from the other side of the world at no added cost. And yet, when those same users make a phone call they are charged by the minute, whether the call is local, national or international. In practice the data may well travel over exactly the same route, on the same wires, owned by the same people. Only the billing mechanism and price is different. Wouldn’t it be better for the end user if the telephone call went with the internet traffic with the attendant price saving?Another attractive application for many businesses would be to connect home workers and sub-offices. The only on-going cost at each site would be the charge for an always-on internet connection. The remote sites could use the internet connection to log-in to the main office network and also run their telephones as extensions to the main office phone system.

A third use of Voice-over-IP technology is to replace the expensive telephone system that most companies require. The idea is to use existing computer hardware such as servers and Ethernet cabling to handle telephone traffic. Telephone system functions such as call-transfer and hold could be handled by software and telephone devices could just be plugged into a network point instead of dedicated wiring.

The three applications outlined above can be summarised as:
· Long-distance call routing.
· Point-to-point connections.
· In-house PBX systems.

We consider each of these applications in greater detail and look further at the hardware in our article The Promise of Voice over IP

The Hardware

VoIP Phones Voice over IP

VoIP Phones connect directly to your LAN via an RJ45 ethernet connection and provide quick and easy access to internet based telephony.

Gateways

A VoIP Gateway is a device which connects a telephone device or line to a computer network.
On the computer connection side, devices may just have an ethernet connection or they may incorporate a cable-modem or ADSL modem. All the products available from Solwise have 10/100 Mbps ethernet ports for their network side connection.
At the telephone side, all the Solwise products provide standard analogue (also called PSTN or POTS) connections. These connections come in two flavours:

FXS	use with devices like phones, fax machines or PBX trunk ports
FX0	connect to a trunk line from BT or a PBX extension.

The Channel

In principle you can use a VoIP gateway to communicate with anyone else on the internet who is similarly equipped, or has software to drive their PC/Soundcard. For best performance it is preferred that both ends have some for of broadband connectivity.

A more common use is to connect two or more sites for free calls between the sites. There may already be a data-link between the sites or the prospect of free-calls may be the spur to set this up.

Each telephone conversation requires a channel of less than 10k, so any data-link from 64k up would be reasonable as long as it is fairly stable, has a small delay and is not already congested.
Suitable choices for the channel are

Direct wired/RF/IR/Microwave ethernet connection
Leased Line
ISDN/ADSL/CableModem dialup/FRIACO accounts with suitable ISP

Of these the most 'asked about' is the last. Here is a list of requirements for such a dial-up account system

Must have fixed (though not necessarily public) IP
ISPs must not block VoIP protocols (some ISP's may have a vested interest in not allowing you to do telephone calls via the internet)

We can help with arranging suitable fixed monthly 'always-on' accounts if required

The protocols and call-routing

The two principle protocols for using VoIP are MGCP and H.323. Each of these protocols is supported by the Solwise products along with many others. The principle difference between the two protocols for the beginner is that MGCP requires a call agent. This is a piece of software or hardware responsible for the routing of calls. A simple H.323 setup can be configured with all routing information held within the voice gateway itself.
In a very simple H.323 setup a call can be placed between two phones, connected to gateways, by just dialling the IP address of the other gateway.

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