Many small- to medium-sized businesses (SMBs) are transitioning to Voice-over-IP (VoIP) phone systems, either hosted or self-hosted (IPPBX).  When preparing your SMB local area network (LAN) for VoIP, there are three main areas you need to focus on: your Internet Firewall, your voice and data cabling and your LAN Switches.

We are Firewalled!

The Internet Firewall is of special concern for SMBs because some folks still have very old firewalls out there. Some of these old firewalls were not designed to recognize SIP (Session Initiation Protocol) and RTP (Real Time Protocol) protocols or, if they were, the firmware is so out-of-date that they will not process today’s protocols correctly. SIP and RTP are the network protocols that underlie most VoIP systems. So, the first thing we need is a current, up-to-date SIP- and RTP-aware Firewall. Once that firewall is in place, we will want to block all uninvited SIP/RTP traffic except that from service providers (e.g., hosted provider or SIP Trunk Provider) or from fixed remote sites. ‘Real world’ note: If your firewall provides a SIP Application Layer Gateway (ALG) turn it off. If you find you need it later you can turn it back on, but many SIP ALGs cause more problems than they solve.

The Cable Guy

The typical SMB environment includes a Voice and Data cable plant. Typically, voice cable consists of a Category 3 or Category 5 cable to each desktop, terminated on terminal blocks back in the telephone room. (In some older buildings, the phone room may be in a different location from where your data cables are terminated.) Data cable will typically be a Category 5e cable to each desktop, terminated on patch panels in the server room. You need to decide which cable you want to use for VoIP.

So you have two options here: you could maintain the separation between voice and data and run your VoIP over the existing voice cable plant. Even though this seems to contradict one of the primary goals of VoIP, that of unifying the voice/data infrastructure, there are actually advantages to this approach. This scenario would involve re-terminating the voice cable on patch panels and providing voice only LAN switches (see below).

The other, more common approach is to unify the cable plant using the existing data cable. Using the single data cable to each workstation, the IP phone will plug directly into the wall jack and the PC will plug into the phone. The disadvantage to this approach is that your PC data speed is limited by the speed of the phone. To put it another way, when you want to upgrade your data speed (say from 100 Mbps to 1 Gbps), you will have to replace all your 100 Mbps phones.

Making the Switch

The final task is updating your LAN Switches. Having voice on your LAN is a whole new world and brings some special requirements.

First of all, you have to decide how you want to power your phones. That’s right. Remember, with your legacy phone system, power was provided to the phones over the dedicated voice cable plant. Now, the only connection to the phone is an Ethernet cable. You have two options: power the phone locally (using an AC adapter) or provide Power Over Ethernet (POE). POE is a standard (802.3af) that allows power to be delivered to the device over the Ethernet cable. The local power option provides many more points of failure and is a bit of an administrative headache, but for very small businesses it may be the right solution. POE is much simpler to administer, but requires a capital investment in new POE switches.

Port of Call

When you look at POE switches, read the specs carefully. There are a lot of POE switches out there that only provide POE on some of the ports, or do not have sufficient power to support POE devices on all ports. Plan carefully, know how many devices you need to power and make sure the switch you select will support that.

Depending on the complexity of your network, there may be other considerations in selecting a POE switch. Do you need VLANs (for example to separate voice and data) or layer 3 routing? Costs go up as you get into L3 POE switches. And keep in mind, you may not be able to  completely segment voice and data traffic on the LAN. If you are using an IPPBX, you may have Unified Communications and/or Call Control applications that require desktop PC access to the IPPBX. Just one final ‘real-world’ note on your LAN switches. There are some LAN switches out there that have IGMP snooping turned on by default. Turn it off. This feature can wreak havoc on your VoIP network, so check your default settings before deployment.

Is your data network ready for VoIP? Have you already deployed VoIP on your data network? What pitfalls did you find? Share your thoughts in the comments.

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