Voice switching systems have a typical economic life of around 8 to 10 years, which means that systems that were installed prior to the year 2000 (perhaps in response to anticipated Y2K issues) are currently in the process of being replaced. In our last two tutorials, we have looked at some ways to evaluate a switching system vendor, and how the switching system purchase or upgrade must be considered in the context of the larger enterprise network. In this, our concluding tutorial in the series, we will drill down a little deeper to look at how the features, management, and support capabilities might influence a system purchase decision.
At the risk of being a bit simplistic, one could say that most voice switching systems have pretty much identical call processing characteristics: If you compare features such as call conferencing, call forwarding, caller ID, automatic redial, and so on, between two vendors' products, the end users experience of those functions is going to be about the same. A similar case could be made for many of the adjunct features of a voice communication system, such as the automatic attendant, voicemail system, call detail recorder (CDR), automated call director (ACD), and unified messaging capabilities. For example, if you consider the voicemail feature of several different products, the end resultleaving and retrieving messageswill be about the same.
When you ponder these assertions for a little while, you realize that the purpose of a switch simply is to connect two end users for a voice, data, or video communication session, and once that is accomplished, there is little else visible to the end user.
By contrast, the network management and support functions of a switching system are a completely different story. Let's look at some of the issues that may not be as prominently strutted on the vendor's glossy brochure:
- What type of handsets will your constituents be using? Switching vendors typically quote a price on a per-port basis; this does not include the end-station handsets that will be incorporated into the system. In some cases, a switch vendor manufactures its own station sets; in other cases they recommendor have some type of collaborative agreement withspecific handset manufacturers. But are these the correct sets for your enterprise? With an increasingly mobile workforce, requirements to integrate in-building wireless handsets and cellular telephones into the switching system are becoming more common. What about existing handsets: Can they be integrated into a new switching system to save on the overall cost? Remember that the station set is the interface though which your end-users will access this communications system, and if these end stations are not functional and easy for your constituents to usefor whatever reasonyou could have a major uprising on your hands.
- How well does this product scale? Unless your organization is different than most, the number of end usersas well as the number of applications supporting those end users (especially multimedia applications)will likely grow over time. How will your vendor's switching architecture handle this growth? Can the line and trunk port boards from your existing switch be reused in another larger model, or do you have to change out the entire system? Better to confront these questions now than several years down the road.
- What survivability factors are built into this system? Voice communication systems are one of those "good news, bad news" stories: When they work, life is good, but if they should crash, you may well be dead in the water. So, the type of survivability provisions built into this system is a significant issue. For example, how will the system handle the failure of commercial power, a PSTN trunk, an IP trunk or Internet connection, a gateway to another system, or a single end station? Are the port boards hot-swappable, without bringing down the entire system? If you are like most, you will experience some type of outage, so it is better to ask the questions beforehand, rather than scrambling for answers during a crisis.
- What reliability factors are quoted for this system? Communication systems designers frequently quote three factors that describe the reliability of their product:
- Mean Time Between Failure (MBTF): the average time, measured in hours, between system failures
- Mean Time to Repair (MTTR): the average time, measured in hours, to restore the system to working order
- Availability = MTBF/(MTBF + MTTR)
As an example, there are 8,760 hours in a year (24 hours/day * 365 days/year), so if you had one failure per year, and that failure took two hours to repair, your system availability would be:
8,760/(8,760 + 2) = 8,760/8,762 = 0.99977 or 99.977%
- How complicated are typical moves, adds and changes to administer? Depending on the survey that you read, changes to telephone extensions because of end user movement and rearrangements can occur up to once a year. Is this something that can be accomplished by the user himself, or does the system administrator have to intervene? In either event, is there an easy web interface for these tasks, or something more complicated? If you get lost in the process, is there someone at the vendor that you can call?
- What warranty and support options are available? If you have a multi-location network, and especially if the individuals at the remote locations are not techies, then perhaps an extended warranty or support contract would be a good idea. Are these options available through this vendor? If so, what are the quoted response times?
As you can see, managing a VoIP network, which needs to be up and running on a 24 x 7 x 365 basis can turn into a challenge. Fortunately, there are a number of network management and analysis systems available that can make this job quite a bit easier. Our upcoming tutorial will begin a new series that expands on this very topictools and techniques for effectively managing the VoIP network.
Copyright Acknowledgement: © 2007 DigiNet Corporation ®, All Rights Reserved
Mark A. Miller, P.E. is President of DigiNet Corporation®, a Denver-based consulting engineering firm. He is the author of many books on networking technologies, including Voice over IP Technologies, and Internet Technologies Handbook, both published by John Wiley & Sons.