The most effective way to measure network health is to use an autodiscovery tool. Autodiscovery tools allow you see to how the network sees itself. They point out errors such as incorrect subnets, and will indicate which devices are Simple Network Management Protocol (SNMP)-enabled. Double-clicking on these will provide you with statistics, including bit errors, traffic passed, retransmissions, etc.
Once you identify which ports are experiencing errors, root out the causes. An easy way to evaluate device errors is to export the information to a spreadsheet and then sort into columns.
If you do see errors, retest cables to make sure they're performing as expected. If the cables aren't the problem, check out the electronics. A faulty network interface card could be the culprit. If autodiscovery reveals too many retransmissions, another common error, the buffers on switches may simply be too low for the traffic.
Enable SNMP Version 3 on all servers, switches and routers at least 30 days prior to running your autodiscovery tool. This allows your autodiscovery tool to see an entire month's worth of statistics, including traffic for peak periods like end-of-month processing.
Preparing the network for voice
Once you deem your network healthy, determine if your electronics will support voice quality of service. Data retransmissions are not as critical and certainly should take a back seat to real-time voice packets, so you should set voice traffic as the highest priority. You can do this in the options panel on your router and switch ports.
Talk to your wide-area carriers as well. They can provide a wealth of information, including traffic passed over your network, peak bandwidth utilization, etc. With voice, plan for peak traffic as if it is the norm -- otherwise, when peaks occur, voice traffic will suffer. If possible, have extra bandwidth on hand, above and beyond peak demand. You can also look to Erlang calculators to determine how much bandwidth you will need.
Some small and medium-sized businesses (SMBs) use separate circuits for voice and data. This is certainly acceptable and, in some cases, less expensive than upgrading your current data network. To ensure the best performance of voice traffic, voice equipment can be housed on a separate virtual LAN. The manufacturer of your VoIP equipment can provide you guidance on this.Be sure to make VoIP packets your network's highest priority.
Decide what VoIP equipment and protocols you will use. Session Initiation Protocol (SIP)is vastly becoming the most popular protocol for VoIP, and plenty of good SIP-based equipment is available. Check with your manufacturer to ensure that peripheral equipment, such as speakerphones, are interoperable with your switches before committing. Also check to see what security enhancements or upgrades to your network will be necessary.
Choosing a VoIP installer
Finally, and most importantly, select an installation company. This is a critical decision. Choose a reputable company to install your VoIP system. Ask basic but important questions such as how many VoIP installations of that size and caliber it's done. Also ask for recent references. This will allow you to find out if the company has suffered any unbudgeted expenses or other negative issues, as well as help you gauge the responsiveness of your installer.
Better yet, find references not offered by that vendor, who are apt to provide you with a more honest assessment.
If you follow these steps, your network will be ready to handle VoIP and your SMB can begin enjoying its benefits in no time.
Carrie Higbie, global network applications market manager at The Siemon Co., has been involved in the computing and networking industries for nearly 20 years. Higbie has taught classes for Novell Inc., Microsoft and Cisco Systems Inc. certifications, as well as computer-aided design/computer-aided engineering, networking and programming on a collegiate level, and serves as the "Preparing your network for VoIP" site expert on SearchEnterpriseVoice.com.
This was first published in October 2007