Answers to your VoIP questions

If you’re seriously considering making the voice-over-IP plunge, you no doubt have loads of questions ranging from the technical to the financial to the political.

Can VoIP traffic traverse firewalls? Can it really save us money? What is the best way to get IT and telecom staffs to work together?

In wrapping up our series on convergence, we’ve taken a crack at answering a few of those questions.

Can my LAN handle VoIP?

IP telephony works best on LANs running switched 10/100M bit/sec Ethernet to the desktop and switched Gigabit Ethernet in the backbone. If you’re still connecting desktops with hubs, and you want IP telephony, an upgrade is probably in order.

Having LAN switches that support quality-of-service (QoS) technologies, such as 802.1p traffic prioritization, virtual LAN tagging or Differentiated Services, also is important. Many IP telephony vendors build QoS into their equipment, so a network lacking QoS-enabled switches also is a candidate for an upgrade if IP telephony is your goal – though there are users who have QoS-capable switches and get by without flicking the QoS switch, preferring to just tolerate the occasional snaps and pops on the line.

Do I have to throw out my PBX?

Companies such as Cisco Systems Inc. and 3Com Corp., which have no traditional PBX installed base, have pushed their customers to make a wholesale swap from circuit-switched telephony to IP. Avaya Inc., Siemens AG, Nortel Networks Corp., NEC Corp. and other sellers of traditional PBXs offer IP cards for their systems as a way to “IP-enable” them. IP enabling a PBX lets customers extend their PBXs to branch offices via IP WAN connections, or even to IP or digital phones inside a corporate headquarters.

What’s the voice quality like?

It can be as good or better than standard voice quality. But quality is in the ear of the beholder, so the answer depends on how discriminating your company’s end users are. Some companies don’t worry much about the quality of VoIP for certain internal calls. But if the calls are involved directly with revenue generation, companies typically have a higher standard.

If you want to measure the quality of a VoIP call, there are methods, including the MedianOpinion Score (MOS) test, endorsed by the International Telecommunications Union (ITU). MOS involves gathering people into a room to listen to calls, after which group members rate quality on a scale from 1 to 5. Voice-quality testing tools based on computer algorithms also are available from vendors such as Agilent Technologies Inc. and Empirix Inc.

Is VoIP really less expensive?

You can make a good case for it, but it’s hard to give a blanket answer. Theoretically you can get rid of some phone trunks if you use a single network for all traffic. You can avoid expensive toll fees, particularly for international calls. You can cut the administrative cost of moving phones when someone changes offices or someone is hired or fired. You might get by with fewer employees if you merge data and telecom staffs. But you have to factor in the cost of new equipment, increased traffic on your data network that can require bigger, more expensive links to service providers and higher-priced services based on stringent service-level agreements that voice requires. Some users worry that because VoIP is relatively new, software updates will be more frequent than with traditional PBXs, making the maintenance of IP PBXs more expensive. You have to crunch your own numbers and determine whether it makes sense for you.

If the power goes out, does the VoIP network stay up?

In the traditional voice world, phones are powered by the PBX, which is usually powered by a back-up power source, which can sustain the system through most outages. Running voice over a LAN introduces more devices into the voice network equation – and that means there are more points along the network that can be affected by an outage and create phone service problems.

One preventive measure to take is to put back-up power supplies on all LAN switches that connect IP phones and IP PBXs. Most crucial to ensuring phone connectivity in an outage, however, is to make sure phones are powered over their network connections. Vendors such as Avaya, Cisco and Nortel sell Ethernet switches that can deliver electrical power along with Ethernet LAN connectivity.

What happens to VoIP if the network fails?

In VoIP deployments where a centralized IP PBX controls remote-office phones, the WAN connection is a voice and data lifeline. If the link goes down, dial tone as well as Internet and network access can be lost. Some vendors include technology in their routers or remote gateways that lets remote IP phone users to continue making phone calls through a back-up T-1 or ISDN line if the main links to a central IP PBX are lost.

Do I have to buy special phones?

If you do VoIP to the desktop you need IP phones, and not just any IP phones. Even though all LAN telephony gear is Ethernet-based, it does not yet offer the same level of interoperability as Ethernet computer networking. This is because most vendors have proprietary protocols and software running on their phones and call servers that don’t work with those in others’ products. Some IP phone systems support standards protocols such as H.323, Session Initiation Protocol (SIP) and Media Gateway Control Protocol. This lets users purchase commodity IP phones from vendors such as Pingtel Inc., Polycom Inc. and Symbol Technologies Inc.

Many vendors also have gateways that allow analog or digital sets to be used on their IP-based call servers.

What protocol do I use?

The choice now is between the tried-and- true and the cutting edge. H.323 products are available, stable and deployed. SIP holds promise for new and more dynamic applications, but has not been put through the paces in many corporate networks.

What cool new capabilities do we get?

Tops on the list is unified messaging. Most VoIP gear makers have crafted products that let end users read e-mail and listen to voice mail from a single in-box, integrated with applications such as Microsoft Corp.’s Exchange and IBM Corp.’s Lotus Notes.

Telecommuters are benefiting from IP telephony also. Workers with home VPN connections and IP phones (or PC-based “softphones”) can extend their four-digit extensions to the home office.

Many IP phones are becoming more like thin IP clients than phones. Many come with LCD displays that let users interface with Web-based applications or even surf the Internet. Some users enabled IP phones to tap into back-end XML or Java application servers.

How secure is VoIP?

VoIP gear is based on servers that are as susceptible to attacks as any others. They are vulnerable to viruses, so a regular regimen of updates and patches is required. Many of these devices have Web-based management, which also must be monitored and remedied for bugs and vulnerabilities.

Isn’t it hard to get IP voice through a firewall?

Yes, but this can be worked out. Unless every phone at a site has a public IP address, the firewall will change the source IP address as packets pass from the phone and out onto the WAN IP link. But the firewall only does this in the headers, not on internal parts of the packet. When IP phone gear picks up that the source addresses in different parts of the same packets don’t match, it drops the packets. Firewalls and firewall add-ons are being developed so they can take care of this problem, but it’s something you have to know about and deal with. Another firewall problem is that because they are designed to keep out all but authorized traffic, they would keep out legitimate inbound phone calls as well. A port could be left open as a hole through which to initiate such calls, but your security experts might not like that. New gear called session controllers establish persistent connections from outside firewalls to IP phones inside firewalls to create a more secure hole for inbound calls.

If I’m running voice on what was previously just a data network, what becomes of my telecom staff?

This is a tricky one. Some IT executives who propose transitions to IP voice cite the cost savings their companies will experience by laying off the telecom staff. In an effort to save their jobs, the telecom staff members often respond by attacking the viability of IP voice in an effort to put off the projects. Successful transitions have included a recognition of this conflict and dealt with it. In some cases, cross-training IT and telecom staff has resulted in much better phone and data service. This merging of staff might not be possible in all cases, but IT executives should anticipate that the conflict will come up and plan for how to deal with it.

What happens to QoS when I pass traffic off to my service provider?

It could go right out the window unless you make arrangements with your carrier. You need to let the carrier know that you are transporting voice to its network and ask how the carrier can guarantee the traffic will get priority treatment.

The carrier might have a network that uses the same priority markers you use on your LAN or might be able to map your priority scheme into its priority scheme. The capability will likely cost you extra, but the service should come with measurable service-level guarantees to give you some degree of comfort that voice will be treated well.

Does 911 still work?

It had better. The technology exists so that when an end user takes his phone and moves it to another office, the 911 system knows about the new location, and emergency personnel can find the person. Depending on whose gear you buy, updating the location database might require manual entries or it might limit the number of times a phone can be moved per day.