by Philip Carden

A full-blown IP telephony solution

Toll bypass is a straightforward, cost-saving solution that can be implemented easily today. But what will a complete IP telephony solution look like? The following diagram illustrates the major components.

In a full IP telephony solution, all end-user devices (both PCs and phones) connect to the network via LAN connections (typically Ethernet). There are two major classes of end-user device: Software IP telephones and hardware IP telephones (i.e., telephones that rely on client software on PCs or stand-alone IP telephones). When these devices communicate with one another they do so directly, via an IP connection (using RTP). Another component, the gateway, is required so that calls can be placed to and from the public network. And finally, there’s the servers that support IP telephony -- helping provide both basic call setup functions as well as the advanced features users have come to expect from traditional PBXs. Let’s explore these components in a little more detail.

IP telephones

You can, of course, use IP telephony by means of a speaker and microphone, or a headset, plugged into a PC. The problem is that people like telephones. That dilemma can be solved in either of two ways: provide a telephone that speaks IP directly, or attach a handset to a PC. Examples of the former include Cisco’s IP Telephones, Nokia’s IPCourier range, Siemens’ HiNet range and Lucent’s Defintity Hardphone. Each of these ranges includes full-featured handsets that seem pretty much the same as regular corporate handsets, except that they have a 10BASE-T port instead of plugging into a phone jack. The only other difference that users will notice is that these telephones currently need to be plugged into a power jack; however, that’s likely to change as we see switches introduced that provide power via cat-5 cabling (for example, Cisco claims that its Catalyst 6000 will support this feature). Once the power issue is resolved, the solution becomes quite compelling — one cabling system that users can plug any device into.

The disadvantage is also pretty obvious: More cat-5 jacks will be required. One way to avoid this, while potentially providing tighter integration with PC applications, is to use a software-based IP telephony solution in conjunction with a telephone attached to the PC. This may be achieved in a few different ways — either you can get a purpose-built phone that attaches to a serial port (like Nokia’s SerialSet) or you can plug a traditional analog phone into a PC card or external adapter. And of course there may be some corporate users (like callcenter operators) for whom the PC-attached headset really is suitable.

If you’re taking the PC-based route you’ll also need client software capable of supporting IP telephony. The client software may be stand-alone, standards-based IP telephony or multimedia software (such as Microsoft’s NetMeeting) or it may be part of a broader IP telephony family (most of the major vendors offer such a product).

When you’re selecting IP telephones, bear in mind the following considerations:

• Central Office. Also called an End Office or Local Exchange. This is where your local phone lines first connect into the public network.
• Central Office Switch. The local switch in the Central Office.
• Tandem Switch. Switches that provide inter-connection between Central Office Switches in a local area network (or, in the United States, within a LATA).