Another important consideration is Quality of Service. QoS ensures that voice packets receive priority over data traffic on a business's network. Bandwidth providers are beginning to take QoS seriously as it applies to VoIP. Carriers are starting to implement various kinds of QoS options. You pay more for these options, but the carriers then guarantee transit times. These carriers structure their networks so that the networks route voice packets ahead of data traffic, which results in an asynchronous kind of communication.
Conventional 10Base-T and 100Mb networking hubs aren't qualified to provide the QoS capability that's necessary to guarantee that the voice and video will always sound good and look good, no matter what happens with the data traffic on the network. If you have such hubs and you want to implement a VoIP system, you must replace the hubs with Ethernet switches that ensure the voice packets get priority over data and video traffic on the network. I recommend that you also use routers whose algorithms favor voice traffic over data traffic.
Because voice packets are so sensitive to delays, I also recommend that you use a VoIP system that provides low-latency queuing. Low-latency queuing treats voice data preferentially by letting voice packets be sent before any other types of packets.
Voice packets can consume a lot of bandwidth, so another consideration is call-admission control and provisioning. For example, when you use G.729A as the coder-decoder (codec) and compressed Real Time Protocol (RTP) as the packet mechanism, you need to plan for 12,000 bits per second (bps) per simultaneous phone call over a WAN. (For information about VoIP codecs and packet mechanisms, see "Valuable VoIP," July 2001, http://www.winnetmag.com, InstantDoc ID 21130.) Admission control is possible only if you provision the system with enough bandwidth to handle simultaneous calls. For example, you might configure the system to handle five simultaneous calls at 12,000bps, which totals 60,000bps. If someone were to place a sixth call between the two sites, the call-admission control system would cause a dialed overflow through the network. In this respect, the call-admission control system acts like a PBX. If two PBXs were to have a tied line with five circuits in it and someone placed a sixth call, the PBXs would create a dialed overflow as well. Without a call-admission control system, the sixth call would cause all six calls in that circuit (not just the sixth call) to degrade and begin to sound bad.
VoIP Solutions
A variety of VoIP products are available—far too many to cover them all here. So, let's look at a few of the more interesting products on the market. These products fall into three broad categories: complete systems, hardware (e.g., VoIP-enabled phones, VoIP gateways), and software (e.g., applications, softswitches).
Complete systems. Several manufacturers produce complete VoIP systems. Perhaps the largest is Cisco Systems, which according to some analysts has more than 50 percent of the VoIP market. Cisco's integrated systems incorporate IP telephony, conferencing, a contact center, and messaging to create a complete customized IP communications system for a business.
CommWorks, a 3Com subsidiary that's dedicated to IP-based networking solutions, also produces complete VoIP systems. CommWorks' platform is based on common hardware that lets the company deliver multiple services, regardless of the transport medium (i.e., wired, wireless, narrowband, or broadband) or the type of traffic (i.e., voice, data, fax, or video).
Hardware. VoIP hardware vendors include such companies as 3Com, Cisco, Polycom, and SMC Networks. 3Com produces a full line of VoIP-enabled phones. For example, the 3Com NBX 2102-IR infrared (IR)enabled business phone features 18 programmable buttons, a full-duplex speakerphone, IR port, and 10/100Mbps switched Ethernet connectivity. 3Com also produces call processors that you can set up for VoIP. The 3Com SuperStack 3 NBX and 3Com NBX 100 call processors combine call-processing capabilities, telephony applications, and multisite IP connectivity options. You can use the 3Com NBX 100 with as many as 200 phones and the 3Com SuperStack 3 NBX with as many as 1500 phones.
In addition to offering complete VoIP systems, Cisco offers VoIP hardware products, including VoIP-enabled phones. For example, Cisco introduced the Cisco IP Phone 7905G in late 2002 as part of its Cisco 7900 Series IP Phones. The 7905G supports inline power, which lets the phone receive power over the LAN and gives the network administrator centralized power control. Cisco also produces high-end individual user phones, such as the Cisco IP Phone 7960G, which has an LCD display and six programmable buttons for lines, and the Cisco IP Conference Station, a VoIP-enabled conference room speakerphone.
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