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Configure a ThinkTel SIP Trunk

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If you're looking for a solution that enables you to connect your Office Communications Server infrastructure to the PSTN, you will want to consider configuring a SIP Trunk. A SIP trunk configuration is a great way to go if you don't already have an IP/PBX.

Author: Rui Maximo, Mike Wood (ThinkTel)

Publication date: March 9, 2010

Product version: Microsoft Office Communications Server 2007 R2

If you're looking for a solution that enables you to connect your Office Communications Server infrastructure to the PSTN, you will want to consider configuring a SIP Trunk. A SIP trunk configuration is a great way to go if you don't already have an IP/PBX. If you already have an IP/PBX, connecting your Office Communications Server to your IP/PBX using Direct SIP is an option that will take advantage of your existing IP/PBX investment. A SIP trunk is less complex to set up and requires no extra hardware, such as an IP/PBX, to deploy. This article covers how to set up a SIP trunk from ThinkTel (www.ThinkTel.ca). ThinkTel is a supported SIP trunk provider that participates in the Open Interoperability Program (OIP) (go.microsoft.com/fwlink/?LinkId=178632) for Communications Server 2007 R2 and is based in Canada.

To configure a ThinkTel SIP trunk with your Office Communications Server infrastructure, you'll need to complete the following steps. These can be performed easily in less than 15 minutes:

  1. Order your SIP trunk from ThinkTel.
  2. Configure your external firewall to allow communication between ThinkTel and your Mediation Server.
  3. Create a phone route to route outbound calls to your SIP trunk.
  4. Configure your Mediation Server to use your SIP trunk as the PSTN gateway.
  5. Enable users for Enterprise Voice.

 Order Your ThinkTel SIP Trunk

To order your SIP trunk, go to <support.thinktel.ca/siptrunk/retail>. The process is simple. On the SIP trunk order form shown in Figure 1, specify your information. In particular, the following settings must be set to specific values:

  • Select the closest location to your office where your Mediation Server is located for the Pilot Number (Local Calling Rate Centre) .
  • If your Mediation Server is deployed behind a NAT firewall, select the PBX behind NAT box.
  • In the PBX make and model field, enter Office Communications Server to indicate to ThinkTel that your PBX model is Office Communications Server. ThinkTel supports over 100 different PBX models.
  • In the Channel Commit field, specify the number of simultaneous active calls you wish to purchase. A channel is equivalent to an active call.
  • If you experience a call volume that is more than the number of channels ordered, and you want to accept those calls without callers getting a busy signal, specify in the Channel Burst field the maximum number of simultaneous calls you want to allow. Keep in mind that each additional active call (channel) is charged an additional fee per day. This allows you to purchase additional channels on a per day basis when you go over your monthly commitment. The typical cost for a channel is $3.00 per day, which will save you money if you host large conference calls a few days a month. According to ThinkTel, bursting will pay off if you go over your channel commitment eight or less times a month. If you are regularly using more channels than you commit to, ThinkTel recommends that you increase the maximum number of simultaneous calls to your Office Communications Server. This change can be made at any time in the month. You can move your committed number of channels up or down during the month and your bill will be pro-rated accordingly.
  • Enter the publicly reachable IP address of your Mediation Server in the IP address field. If your Mediation Server is behind a firewall or proxy, this will be the address of the firewall/proxy assigned to route traffic to your Mediation Server. Please ensure that the following ports are opened on your firewall:
    • TCP port 5060 for signaling traffic
    • UDP port range 60,000 through 65,535 for media traffic

Figure 1. ThinkTel SIP trunk order

After you submit your order form, ThinkTel will send you an e-mail that has a ticket number for your order. Typically within 24 to 48 hours, you will get an e-mail back from the system that has your pilot number (used as your billing number) and SIP proxy. You can use this pilot number as a regular DID; however, it is recommended that you assign new numbers for your organization and users and leave this unused to make bill consolidation easier. The SIP proxy will be used to configure the PSTN Gateway IP address field of your Mediation Server.

To manage your ThinkTel account, go to https://dims.thinktel.ca and log on by using the credentials sent to you in e-mail. You can allocate more phone numbers by clicking the PBX DID Orders link on the right side of the page. On this site you can also add and edit 911 listings on a per DID basis, review your bill, download CDRs, and monitor the usage on your trunks to ensure you always have capacity available.

In addition to making changes to your account, you can request access to a Web-based API that enables you to take inventory of your existing numbers, locate rate centers with available numbers, and order new numbers. The API is available through a REST or SOAP interface.

 Configure Your External Firewall

Because your ThinkTel SIP trunk connects to your Mediation Server, all you have to do is allow incoming and outgoing traffic between your Mediation Server and ThinkTel. Generally, by default, outgoing traffic that originates from your internal network is allowed by most firewalls. Consequently, you need to configure firewall rules to allow only incoming traffic originating from the Internet. Two firewall rules are required to flow through your firewall:

  • SIP traffic: this rule allows signaling traffic from your ThinkTel provider to your Mediation Server over TCP on port 5060.
  • Media traffic: this rule allows audio traffic from your ThinkTel provider to your Mediation Server over UDP across a range of ports. By default, this range of ports is 60,000 through 65,535. However, you can customize it.

 Create a Phone Route to Route Outbound Calls to Your SIP Trunk

Before your users can initiate outbound calls to your ThinkTel SIP trunk, you must specify a route. This route defines where to send outbound calls to. Because calls going to the SIP trunk must first pass through your Mediation Server, you must route outbound calls to your Mediation Server first. The Mediation Server will then route calls to your SIP trunk. To keep things simple, we'll define a rule that routes all outbound calls to your Mediation Server.

  1. Click Start, click Programs, click Administrative Tools, and then click Office Communications Server 2007 R2 to open the Office Communications Server 2007 R2 snap-in for the Microsoft Management Console (MMC).
  2. Right-click the forest node, select Properties, and then select Voice Properties.
  3. Click the Routes tab.
  4. Click Add to create a new route.
  5. Enter a period and an asterisk (.*) in the Target regular expression field. This regular expression will capture all number formats that your users dial. This is a good way to verify that your configuration is properly routing calls to your SIP trunk before you decide to constrain your routing rules.
  6. Under Gateways, click Add to select your Mediation Server and associated port number.
  7. Under Phone usages, click Configure to select a phone usage. You can select the Default Usage or create a custom usage. Defining the phone usage is what ties the phone route you just created to the location profile that you will create next.

Figure 2 illustrates this configuration.

Figure 2. Phone Route

The next step is to create a location profile. A location profile defines a set of normalization rules. This location profile will be assigned to your Mediation Server and users so they can dial out to the SIP trunk. The normalization rules specify which phone number formats are acceptable and what format phone numbers will be converted to. You can define the phone number formats to accept any format as long as the phone number is not ambiguous. However, the resulting format these phone numbers are translated to must conform to E.164 format to be accepted by your SIP trunk provider.

To create a location profile:

  1. On the Voice Properties dialog box, click the Location Profiles tab.
  2. Click the Add button.
  3. Enter a name and description to identify the purpose of this new location profile.
    To keep our example simple, we will create a basic normalization rule that prepends a plus sign (+) to a 10-digit number to conform to the E.164 numbering format as shown in Figure 3. You can customize these normalization rules to your needs.
  4. Click Add to create a normalization rule.
  5. Enter a name and description to identify the purpose of the new rule.
  6. In the Phone pattern regular expression field, enter ^(1\d{10})$ . This regular expression matches exactly 10 digits and saves it to register 1.
  7. In the Translation pattern regular expression field, enter +$1. This regular expression prepends a plus sign (+) to the content of the register 1, which is a 10-digit phone number.
  8. You can test your regular expressions by entering a phone number in the Sample dialed number field, and analyzing the resulting output in the Translated number field.

Figure 3. Normalization rule

 Configure Your Mediation Server

Assuming your Mediation Server is already installed, activated, and set up to communicate with your Communications Server infrastructure, we'll focus on assigning the location profile that you just created to your Mediation Server (Figure 4) and configuring it to connect to your ThinkTel SIP trunk as its PSTN gateway (Figure 5).

  1. Click Start, click Programs, click Administrative Tools, and then click Office Communications Server 2007 R2 to open the Office Communications Server 2007 R2 snap-in for the MMC.
  2. Expand the Mediation Servers node, and then select your Mediation Server.
  3. Right-click your Mediation Server, and then click Properties.
  4. On the General tab, select the location profile that you just created from the Default location profile drop-down list (Figure 4). This assigns a Location Profile to the Mediation Server.

Figure 4. Assign Location Profile to Mediation Server

  1. Select the Next Hop Connections tab to configure the SIP trunk as the Mediation Server's PSTN gateway (Figure 5).
  2. Under Office Communications Server next hop:
    • Select the FQDN of an existing Communications Server as the next hop connection to which your Mediation Server will route traffic.
    • Unless you are not using MTLS with your Office Communications Server infrastructure, specify port 5061.
  3. Under PSTN Gateway next hop:
    • Specify the SIP proxy address provided by ThinkTel in the Address field.
    • Set the port number to 5060.
    • Set the transport to TCP.

Figure 5. Mediation Server SIP trunk configuration

 Configure Your Users

The direct inward dialing (DID) numbers provided by your SIP trunk provider must be associated to the user accounts in your organization for inbound call routing to work. These DID numbers should be assigned to users in E.164 format. When an incoming call originates from the SIP trunk, Communications Server performs a reverse number lookup (RNL) of the DID to determine which user account is assigned this number. Office Communications Server translates the TEL URI number to the corresponding user's SIP URI and routes the call to the user.

To configure a user with a DID number (Figure 6):

  1. Click Start, click Programs, click Administrative Tools, and then click Office Communications Server 2007 R2 to open the Office Communications Server 2007 R2 snap-in for the MMC.
  2. Right-click the user that you want to configure to assign a DID number, and then click Properties.
  3. Under Telephony Settings, click Configure.
  4. By default, the Enable PC-to-PC communication only option is selected. Change this selection to Enable Enterprise Voice and make sure Enable PBX integration is not selected.
  5. In the Line URI field, enter the DID number in E.164 format. The line URI is prepended by tel: followed by a plus sign (+) sign followed by the country code, area code, and phone number.
  6. Select the same location profile that you created earlier so that outbound calls initiated by the user will be properly routed to your SIP trunk.

Figure 6. User Configuration for Enterprise Voice

 Summary

Configuring a SIP trunk provides PSTN access to Communications Server 2007 R2 users. In working with our partner, ThinkTel has streamlined the process and user interface for ordering a SIP trunk for Office Communications Server 2007 R2 making the entire process simple. ThinkTel Communications is a partner in the Microsoft Unified Communications Open Interoperability Program. Acknowledgements go to the ThinkTel team for providing a test SIP trunk and explaining their offering so I could author this article. In particular, I would like to thank Mike Wood for his expertise and assistance.

 Additional Information

To learn more, check out the following articles:

 Communications Server Resources

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