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Lync and the role of the media gateway

This is part one of a twelve post series, to see an index of all twelve posts click here.
On the first day of Lync’mas my UC Team gave to me: a media gateway for PSTN connectivity.
In the song, “The Twelve Days of Christmas” the first day is the building block for the other eleven days.  In a Lync Enterprise Voice deployment, PSTN (Public Switched Telephone Network) access is the building block for the rest of the deployment.  The ability for your users to make and receive calls with the outside world and access to dial-in conferencing all hinge on connectivity to the PSTN.  For most Lync Enterprise Voice deployments, PSTN access comes in the form of a media gateway.
A media gateway is a device that connects Lync to the PSTN or another vendor’s PBX.  In simplistic terms, think of a media gateway as a language interpreter sitting in between two people speaking different languages.  On one side of the conversation  the media gateway “speaks” SIP with Lync using Lync’s native language.  On the other side of the conversation the media gateway “speaks” to the PSTN using it’s native language through analog lines, digital trunks or even SIP trunks.  The media gateway could also “speak” to a PBX using these same forms of connectivity – analog lines, digital trunks or SIP trunks.
There are a number of manufacturers of media gateways, but the best place to start is the Microsoft Unified Communications Open Interoperability Program (UCOIP).  I mostly work with the AudioCodes Mediant line of media gateways.  As you can see from looking at the Qualified IP PBX and Gateways list, AudioCodes is qualified for both Lync 2010 and Lync 2013 as an “Enhanced” Gateway.  An “Enhanced” Gateway supports all of the following features whereas a “Basic” gateway may only support a limited set: TLS/SRTP, Media Bypass, Comfort Noise, Refer processing, DNS Load balancing, qualified Lync Survivable Branch Appliance (SBA), NAT and Firewall traversal.
One of the reasons I like the AudioCodes Mediant line, specifically the Mediant 1000, 2000 and 3000 products, is the flexibility of the product.  The Mediant 1000 supports a combination of modules, up to 4 digital trunks or 24 analog ports or any combination in between.   Say, for example, I have a scenario where I need to connect Lync users to the PSTN via PRI while at the same time providing analog services for a handful of fax machines, alarm systems and/or keysets.  I also have a requirement to provide backup life line services via analog lines.  In the image below, you can see that I have an AudioCodes Mediant 1000 outfitted with all of the modules necessary to address the example scenario.  In slot 1 we have a 4 port FXO module for backup analog life line services.  Slot 3 contains our digital PRI interface module.  Slot 4 contains the FXS module to provide analog services for the fax machines, alarm systems and keysets.  Slots 2, 5 and 6 are empty but could be filled with additional modules based on future needs.  You will also see that the Mediant 1000 supports redundant Ethernet network interfaces (on the CPU module) as well as redundant power supplies.

AudioCodes Mediant 1000

AudioCodes Mediant 1000

As you can see, a media gateway is an important and critical component to a Lync Enterprise Voice deployment.  Any of the manufacturers’ products listed on the UCOIP can fulfill the basic need for PSTN connectivity.  However, careful evaluation of your connectivity needs should be considered and weighed against the various solutions before a final purchase decision is made.

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Scott Middlebrooks

I am a Senior Technical Architect within the Microsoft practice at Perficient. In this role, I am responsible for strategy, delivery, operations, and technical sales support aspects of enterprise infrastructure projects, especially Microsoft Unified Communications projects. I have extensive experience in traditional telephony, voice over IP, network design and architecture, systems engineering and infrastructure security. Prior to joining Perficient, I served as the Chief Information Officer at Northridge. Northridge was a leading Microsoft consultancy based in Atlanta, Georgia and was acquired by Perficient in July of 2012. I posses several Microsoft Certifications including: Microsoft Certified Systems Engineer (MCSE) on both the Windows NT 4.0 platform as well as the Windows Server 2003 platform, Microsoft Certified Technology Professional for Lync and Microsoft Certified Technology Specialist for Virtualization. I hold a Bachelor of Business Administration degree in Management Information Systems from the University of Georgia, GO DAWGS! In my time away from the office I enjoy time with my family and friends, UGA football, anything aviation related and I love cooking, especially on my Big Green Egg!

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