Lync Enterprise Voice Misconceptions #2 - External Access Prefixes

During my travels across the Lync Enterprise Voice landscape, I come across numerous Lync deployments that make some fundamental mistakes in how to manage phone numbers, call routing and other details.  I've covered a lot of these details in parts of my OTHER Enterprise Voice Best Practices, but its obviously a lot to take in, and I've seen enough of the same sort of errors in the wild that prompted me to do this series.

Last week's episode talked about common errors when setting up resiliency/failover routing. This week, we're talking about...

#2 - External Access Prefixes

A lasting legacy of the PBX era is the concept of dialing an external access prefix to make a call to the outside world.  In many deployments, you have to dial a 9 or 8 or something to open a channel to the PSTN.  In some systems, when you press 9 (or whatever the prefix is, I'm going to assume the external access prefix is 9 throughout this article), you can hear the change in dial tone as you actually open a connection to the PSTN.

There are many reasons for using an external access prefix, one of the biggest is to provide a clear demarcation between internal and external calls. When dialing "off-hook" - meaning the user picks up the handset, hears a dialtone then starts dialing the number on the keypad - the PBX needs to know where to send the call based on the digits entered on the keypad.  This might sound obvious, but if you've punched in the digits 2-1-2-3, the PBX needs to know if you want to connect to someone at extension 2123, or if you're just in the process of dialing an external New York number that happens to start with 2123.  If you punched in 2123 and meant to reach extension 2123, then the PBX will connect your call to that extension and everybody's happy. But if you meant to dial New York number 2123334444, then you will be understandably frustrated that you were connected to extension 2123 instead.

The external access prefix deals with this issue in a neat and tidy way. When you dial off-hook, if you enter the external access prefix before dialing your number, then the PBX will not attempt to connect you to an internal extension as you punch in digits.  So, when you dial 92123, the PBX won't attempt to route your call to extension 2123, and will instead wait for the user to enter the remaining digits necessary to complete a call on the PSTN.

In many Lync Enterprise Voice deployments, Lync is connected to the PSTN through an existing PBX which gives Lync both access to the PSTN as well as phones on the PBX. Since Lync's PSTN access is via the PBX, then this means that calls that come from Lync usually needs to have the PBX's external access prefix added in front of PSTN-bound calls.

I've seen many deployments where administrators do one of two things:

1. They normalize dialed numbers in Lync to include the 9
2. They create a normalization rule where users have to dial 9, but they strip it out, leaving a properly formatted E.164 number, using a rule like ^9(\d{10})$ --> +1$1. They then add the 9 using a trunk translation rule before sending to the PBX.

With #1, this breaks Ken's universal E.164 rule, which states: "NORMALIZE EVERY NUMBER TO E.164!!!"  If you don't know what E.164 is, I recommend you check out this post on the topic.  For example, if your normalized number for our earlier example is +912123334444, that number is technically a phone number in Chinchwad, India (which incidentally is now on my list of funny-sounding place names).  91 is the country code for India, and 212 is the area code for Chinchwad.

The ramifications of choosing this path is that you have to adjust everything else in Lync to accommodate what you started with adding the 9 to all normalized numbers.  This means routes, and even phone numbers in Active Directory.  You may argue that this is OK for you, because you have a single site, and you don't have any need to call India. But AD phone numbers can populate users' contact lists on their mobile phones, and they most certainly don't want to be dialing India when they mean to call New York. You could do some additional work to deal with this situation, but it gets messy very fast and doesn't scale beyond a single site.  For example, what if you have a second site that doesn't use 9 for dialing externally?  If you have to route calls from the first site for redundancy, then you'd have to make all sorts of rules in Site B to deal with how you initially set things up in Site A.  As you add sites, this scheme would quickly become unmanageable. 

Case #2 is closer to the correct way to do things. Dialed numbers are ultimately formatted to E.164 standards which is good. Since the PBX ultimately requires numbers are prepended with a 9, we can do this with trunk translation rules. Its trivial to add a 9 to every call that routes out to the PBX. However, you shouldn't have to manually create normalization rules that force users to enter a 9.  If you recall from the beginning of this article, the external access prefix is meant to help people who do off-hook dialing. When dialing from the Lync softclient, there is no off-hook dialing.  You enter the digits, then you press the call button, or ENTER or whatever. Entering a 9 is superfluous in those cases.  However, you do want to ensure a good experience when people do off-hook dialing from a Lync desk phone. How do you support on-hook and off-hook dialing without forcing EVERYONE to enter an external access prefix in Lync?  Use the External Access Prefix option in the Lync dial plan, as shown below.   

This option does several things, firstly it allows people to dial phone numbers in Lync the same way they're accustomed to on the PBX without having to adjust normalization rules.  It also makes Lync work the same way a PBX phone works when dialing off-hook.  The kicker is that you're not forced to enter a 9 when dialing. You either enter a 9 when dialing from the Lync softclient, or you don't. Either way, the call goes through as expected. Same thing for the Lync deskphone. You're not forced to enter a 9, but if you habitually dial off-hook, then you'll want to, or you'll stand a good chance of reaching an internal extension instead of the PSTN number you dialed. 

Rather than rehash what's been said before, have a read of one of my blog posts from waaay back in Lync 2010 days on this topic (don't worry, things haven't changed since then).  It shows how to set your Lync deployment up for extension dialing and external access prefixes the no-muss, no-fuss way. It also shows some examples on how the Lync softclient behaves when using an external access prefix.

You can use this in pure Lync Enterprise Voice deployments, or when integrated with an existing PBX.  In cases where you connect to a PBX, you still have to create a trunk translation rule to add the 9, if necessary. For more information on trunk translation rules, you can read my blog post on the subject, or refer to Technet. 

Tune in next week, where we talk about inter-trunk routing, and how people inadvertently set it up without meaning to.

Lync Enterprise Voice Misconceptions #1 - Failover Routing

During my travels across the Lync Enterprise Voice landscape, I come across numerous Lync deployments that make some fundamental mistakes in how to manage phone numbers, call routing and other details.  They're always fixed by the end of the engagement, but I'd like to share some of these to help keep others from making the same mistakes.  This will be an ongoing series of unknown duration.

#1 - Failover/Resiliency Routing

This is one of the more misunderstood concepts in Lync Enterprise Voice. Its a question that often trips people up on the Lync Voice exam (70-337), and is something that even respected websites like Windows IT Pro gets wrong (despite my attempts to get them to correct it).

The idea behind failover or resiliency routing is that you want to use a particular PSTN gateway for your normal day-to-day call routing, but have a backup PSTN trunk ready in case the primary one is down. This is different from load-balanced routing, where your goal is to evenly spread call traffic between two or more trunks.

For example, say you have a Lync deployment in your Boston office and another one in your Seattle office.  For reasons that should be obvious, you want to ensure that your Boston users always use the Boston PSTN gateway for outbound calls to reduce WAN traffic and call latency. If the Boston trunk is down, calls should failover to the Seattle PSTN trunk.  The same goes for your Seattle users. We could make things more interesting by bringing least-cost routing into play, but we're going to keep it simple here.

A common error people make in an attempt to make things simple and easier to manage is to create a single route for all calls, and place both the Boston and Seattle trunks inside that route.  Since they added the Boston trunk first, it appears first in the list, and they are lulled into thinking that calls will always use the Boston trunk unless its down, at which point the Seattle trunk is used.

In actual fact, calls will load-balance themselves between the Boston and Seattle trunks. Sure, if Boston is down, all calls will route via Seattle, but any well-designed EV deployment should never needlessly send calls across the country on the corporate WAN unless absolutely necessary.  If your other site is in a different country, you could be left with some pretty high phone bills since half of your national calls will be routed out the other country's gateway as an international call.

Voice Policy	PSTN Usage	Route	Trunks
Global	AllCalls	AllCalls	BostonGW SeattleGW

A clue to this behaviour can be found when you look at a route in the Control Panel.  You'll notice that while you can add/remove trunks to a route, there is no way to change the order of the trunks. This should be a clue to the fact that you have no control over which trunk is used within a route.

The proper way to achieve failover routing is via PSTN Usage ordering. Instead of creating a single route with multiple gateways inside it, you create a Boston PSTN Usage with a route to the Boston PSTN gateway, and another Seattle PSTN Usage with a route to the Seattle gateway.  In the voice policy assigned to your Boston users, add both the Boston and Seattle PSTN usages, ensuring the Boston one is above the Seattle one.  For your Seattle voice policy, put Seattle first.

Voice Policy	PSTN Usage	Route	Trunks
Boston	Boston-AllCalls	Boston-AllCalls	BostonGW
	Seattle-AllCalls	Seattle-AllCalls	SeattleGW

Now, you have achieved true failover routing.  For Boston users, all calls will route out the Boston trunk, unless it is down.  The same thing works for your Seattle users.

Incidentally, putting multiple trunks  in a single route does have its uses. If you have multiple PSTN gateways within the same datacentre for redundancy, its OK to do things this way, since you usually don't really care which trunk is used for outbound calls. Calls will be load-balanced between all the trunks, skipping any gateways marked as down. The above picture shows exactly that situation (although its not obvious since most of the trunk name is truncated). However this should never be considered failover routing, simply round-robin or load-balanced routing.

Voice Policy	PSTN Usage	Route	Trunks
Boston	Boston-AllCalls	Boston-AllCalls	BostonGW1 BostonGW2
	Seattle-AllCalls	Seattle-AllCalls	SeattleGW1 SeattleGW2

Essentially, you want to avoid placing trunks from different locations within the same route. This ensures you have control over how your calls are routed, keeping WAN utilization and costs low.

Tune in next week for our next exciting episode: "PBX External Access Prefixes"