In the previous article “Lync Integration with Polycom SIP Phones” the ability for native Lync registration was introduced for many of the standard SIP handsets with the firmware release version 4.0.1.  Recently a new firmware version of 4.0.2B was released containing some minor updates and hotfixes.  Included in this release was the ability to support extension dialing when registered to Lync Server.

Previous Behavior

In the previous 4.0.1 version a preceding ‘+’ was automatically added to all dialed numbers when the call was sent to the Lync Server, thus only the full E.164 number could be manually dialed.  For example to call a Lync user with a Line URI value of “tel:+13125557501” the user would need to dial ‘13125557501’ and then the phone would automatically add the + before sending the call, in which the SIP INVITE would appear like this on the Lync Server:

Start-Line: INVITE sip:+13125557501@mslync.net;user=phone;transport=tls SIP/2.0
From: “vvx1500” <sip:vvx1500@mslync.net>;tag=244EA9C6-BF641E55;epid=0004f2be8eb4
To: <sip:+13125557501@mslync.net;user=phone>
CSeq: 1 INVITE

This basic SIP Phone behavior would prevent non-E164 dial strings from working as if a extension was dialed (e.g. 7501) the resulting SIP INVITE would be formatted as an invalid number:

Start-Line: INVITE sip:+7501@mslync.net;user=phone;transport=tls SIP/2.0
From: “vvx1500” <sip:vvx1500@mslync.net>;tag=3D51BA91-C61AB03A;epid=0004f2be8eb4
To: <sip:+7501@mslync.net;user=phone>
CSeq: 1 INVITE

When Lync Server receives an inbound call from an endpoint or gateway and the + is included in the dial string the translation engine assumes that the string as already globally unique and will not perform any server-side normalization of the digits.  This is a hardcoded behavior that has been in the product since Enterprise Voice was introduced in OCS 2007.

The following information comes from logging the TranslationApplication component in the Lync Server 2010 Logging Tool during a call and shows Lync Server identifying the number as ‘global’ and then passes it on as-is.

INVITE, reqUri=sip:+7501@mslync.net;user=phone;transport=tls newHostPart=NULL
Global number, no further processing. RequestUri=sip:+7501@mslync.net;user=phone;transport=tls
Retargeting [ReqUri=sip:+7501@mslync.net;user=phone;transport=tls]

Clearly this call would fail as the targeted user’s Line URI is not +7501, but +1312557501.

Updated Behavior

In the 4.0.2 release the ‘+’ is no longer added by default, yet omitting the plus alone is not enough to provide for successful call routing for partial digit strings.  The call will need to specify the desired Lync dial plan in the SIP INVITE so the server knows which set of normalization rules to apply to the call.  Some Lync deployments may only include these normalization rules in the default Global dial plan while other deployments may contain multiple dial plans for different pools, sites, or users.

For example, if the plus is left off the dialed string on an incoming call but a dial plan is not assigned then the call will fail to be completed since the retargeted URI will not match the user’s defined Line URI.

INVITE, reqUri=sip:7501@mslync.net;user=phone;transport=tls newHostPart=NULL
Missing phone-context, no further processing.  RequestUri=sip:7501@mslync.net;user=phone;transport=tls
Retargeting [ReqUri=sip:7501@mslync.net;user=phone;transport=tls]

Thus the desired dial plan needs to be included in the invitation so the Translation engine knows which normalization rules to apply the call’s digit string to.  In this example the URI has been properly formatted to tell the Lync Server to use the default dial plan’s normalization rules to the call, which includes a rule named “Extension Dialing” to translate 4-digit extensions starting with 75 or 77 into a full RFC3966-compliant number.

INVITE, reqUri=sip:7501;phone-context=defaultprofile@mslync.net;user=phone;transport=tls newHostPart=NULL
calledNumber=’7501′
added attribute DefaultProfile, key 0

regex: ^(7[5,7]\d{2})$
regex: ^(7[5,7]\d{2})$, prefix 7, num leading zeroes 0
added regex ^(7[5,7]\d{2})$ to list with prefixes
ruleName=’Extension Dialing’ matched Num=’7501′, txNum=’+13125557501′
MATCH: New request Uri=’sip:+13125557501@mslync.net;user=phone;transport=tls’
Retargeting [ReqUri=sip:+13125557501@mslync.net;user=phone;transport=tls]

Configuration

To provide the above dialing behavior to Polycom SIP phones running the 4.0.2B release an additional configuration parameter needs to be defined. This custom mapping rule will be used to send all digits dialed on the phone exactly as dialed along with the name of the desired Lync dial plan so that server-side normalization can be utilized.

Identify Lync Dial Plan

Because these phones are able to register to multiple SIP platforms at one time the default digit mapping behavior of the device should not modified specifically for Lync interoperability as that could impact dialing to an existing registration to other non-Microsoft SIP platforms.  Instead a line-specific parameter should be defined to be used specifically for the Lync Server registration.  But before the configuration parameter is added the desired Lync dial plan must be identified.

• From the Lync Server Management Shell issue the Get-CsDialPlan cmdlet to list any and all defined dial plans in the topology.

PS C:\> Get-CsDialPlan

Identity                 : Global
Description              :
DialinConferencingRegion : Chicago
NormalizationRules       : {Description=;Pattern=^(7[5,7]\d{2})$;Translation=+1
                           312555$1;Name=Extension Dialing;IsInternalExtension=
                           False, Description=Prepend Area Code to 555 prefix;P
                           attern=^(555\d{4})$;Translation=+1312$1;Name=Prefix
                           Dialing;IsInternalExtension=False, Description=Norma
                           lize 10 and 11 digit number strings;Pattern=^\+?1?(\
                           d{10})$;Translation=+1$1;Name=Basic;IsInternalExtens
                           ion=False}
CountryCode              :
State                    :
City                     :
ExternalAccessPrefix     :
SimpleName               : DefaultProfile
OptimizeDeviceDialing    : False

• Alternatively the Lync Server Control Panel can also be used by navigating to the Voice Routing > Dial Plan section.

The result above show a single defined dial plan listed which happens to be the Global default dial plan.  The majority of deployment may still utilize this built-in dial plan.  Review the various NormalizationRules to identity the desired dial plan in the event that multiple dial plans are defined in the environment.

• Once the desired dial plan is selected then identify the SimpleName attribute as this is the name which must be included as the phone-context value in the invite, not the common name shown as the Identity.  The default Global dial plan’s Simple name will always be DefaultProfile.

Identity : Global
SimpleName : DefaultProfile

Update Device Configuration

In this example a per-device configuration file which matches the guidance originally detailed in this previous article is used along with XML Notepad 2007 to facilitate easy manipulation of the XML-based configuration files.

• Whether using FTP provisioning or manually importing configuration files into the devices locate the source configuration file (e.g. lync.cfg) and add an additional parameter in the format of dialplan.x.digitmap where x is the number of the line registered to the Lync server. (If unsure look at the number in the existing configuration file used in the reg.x.address parameter and use the same line number; typically it will just be line ‘1’.)

dialplan.1.digitmap

• For the value of the new attribute the following string must be entered in identical to the example, paying close attention to character case as the digit mapping fields in the Polycom phones use uppercase characters to perform translation actions.  Only the Lync dial plan’s Simple Name should be altered in the event that the default dial plan is not desired; make sure to not omit the ‘R’ character at the end of the pattern.

x.TRR;phone-context=defaultprofileR

Basically this rule will send all dialed digits (x) to the phone without any manipulation and then append any characters located between the ‘RR’ and ‘R’ characters, which happens to be the string “;phone-context=<Dial Plan Simple Name>”

Using either Notepad or an XML editor update the configuration file with the new parameter and import the new file or trigger FTP provisioned devices to update their configuration (or wait for an automatic refresh).

dialplan.1.digitmap=”x.TRR;phone-context=defaultprofileR”

Notice

This approach of manually configuring the digit mapping parameter is specifically for the 4.0.2 release.  This will not be required in the next software release as client-side number normalization will be handled automatically and natively, displaying the same behavior as the Lync Phone Edition client currently does by consuming the normalization rules from the assigned dial plan via in-band provisioning of Lync policies.