Many people are aware of Microsoft Lync as a business tool for instant messaging, presence display, and web conferencing. In addition to these, one of its more powerful features is making a “soft-phone” out of the client software installed on your PC by hooking it up to your firm’s telephone services. Microsoft calls this feature Enterprise Voice. With this feature you have the ability to make outbound calls, and access to an extension or DID (direct inward dialing) number for inbound calls. This blog goes over some of the ways that you can be connected via Lync to the PSTN (the public switched telephone network), and it introduces you to some commonly used terminology for discussing these approaches as well.
Lync’s impact on telephony—and business
Microsoft Lync has made a dramatic impact on the landscape in terms of what solutions enterprises are investigating for telephony, to wit…
- 70% of Fortune 500 companies now use Lync, resulting in 3 Million+ users worldwide*
- 86% of those firms deploy Enterprise Voice
- Over 11% of these implementations (double from last year) use Lync as their PBX (Public Branch Exchange), the solution that connects employees to phone service and other users in the outside world via the PSTN, which all individuals and businesses connect to worldwide in order to make telephone calls.
Connecting Lync servers to telephony systems
The diagram above shows a typical corporate environment where Lync is used. To begin to understand it, let’s explore two basic approaches for hooking up Lync servers to telephony systems, and why you would use each.
1. Connect Lync to the company’s PBX, which in turn connects to the PSTN
These types of solutions are known as using Direct SIP …. These are connections using the SIP (Session Initiation Protocol) network protocol that do not cross a firm’s local network boundary. Instead, they connect to an IP-PBX, or to a PSTN Gateway which then connects to a PBX. This all happens within your company’s internal network. Here are more details on each option:
- IP-PBX Option: Lync can connect to an IP-PBX which is digital gear that uses IP network protocols for voice communications. Some leading vendors of IP-PBX products are Alcatel, Avaya, and Cisco.
- PSTN Gateway Option: A second option is to route voice traffic through a PSTN Gateway, which then connects to a PBX, if the PBX is an older TDM (Time Domain Multiplexed) analog type. This type of PBX needs a PSTN gateway, such as those made by AudioCodes or Sonus/NET, in order to translate signals.
A company may choose to use one of the above approaches if they have recently invested in a PBX that they wish to retain, or if it has specific features that they need. So users with PBX phones will co-exist with users that use Lync. One advantage to this scenario as compared to the next one is the current capital investment in the PBX can still deliver value. The other feature of this solution is that users can have the legacy PBX phone as well as the Lync soft phone, until they are comfortable with giving up the PNX phone and using only Lync.
2. Connect Lync directly to the PSTN via an Internet telephony service provider
ITSPs (Internet telephony service providers), also known as VoIP providers, can deliver telephone service directly to the Lync servers. Some providers often used are Level 3, XO Communications, Interoute, Global Crossing, and AT&T (IP Flexible Reach Service). This type of connection is known as a SIP trunk. A SIP trunk is an IP connection that establishes a SIP communications link between your organization and an Internet telephony service beyond your firewall.
This approach might be pursued when a new company is being setup, i.e. there is no PBX present and there is Greenfield environment. Or it may be pursued for certain branch offices with Lync servers which need survivability of phone service when the connection to the main office PBX is broken. Finally, a feature of ITSPs is their ability to help meet regulatory requirements when the branch site and central site are in different countries, which then requires at least one SIP trunk per country. For example, in the European Union, calls cannot leave a country without terminating locally in that country onto the PSTN.
Note: The above voice topologies aren’t all currently available with Microsoft’s Office 365 Lync service, but they are generally available for a company deploying Lync on their premise or accessing Lync via a Telco or application service provider. The material presented here is targeted to the currently available Lync 2010 version. Lync 2013 will be addressed in a future post.
What’s your take?
Does your firm have Lync? Have you completed a pilot implementation of Enterprise Voice with PSTN connectivity? If so, what was your experience? How are you leveraging Lync for your business?