Being able to replace a traditional PBX is an important new feature of Lync Server 2010. New functions like enhanced delegate handling and resilient telephony are a big step forward but support of analog devices is important as well. Although telephony is normally based on VoIP there are still situations where a few analog lines are needed: Elevator phones with two-wire connections, existing fax machines or special devices like door phones or pagers still use traditional interfaces.
To qualify for Lync Server 2010, Enhanced Media Gateways (EMG) as well as gateways integrated into Survivable Branch Appliances (SBA) have to support analog connections at least as an option. Both PSTN-side (FXO) and device-side (FXS) connections must be offered. This article will take a closer look at FXS support and administration.
Analog devices are completely managed using Lync Management Shell since Control Panel is not aware of them. Creation of related contact objects in Active Directory is done using the Cmdlet New-CsAnalogDevice:
New-CsAnalogDevice -LineUri tel:+49301234567 -SipAddress sip:email@example.com -DisplayName “Analog fax machine” -RegistrarPool sba.lynctest.lan –AnalogFax $True -Gateway ferrari-gw.lynctest.lan -OU “CN=Users,DC=lynctest,DC=lan”
“SipAddress” and “DisplayName” are optional parameters. Instead of “OU” it is also possible to specify a “DN” value. An interesting parameter is AnalogFax – why does Lync care whether a normal phone or a fax machine is connected on a given port?
Lets take a look at a distributed Lync deployment with gateways installed in two sites A and B where both gateways support analog devices. Phone calls from an analog port at site A directed to another analog device at site B would normally take use of WAN infrastructure and VoIP protocols. If site A and B are not connected through a “low-latency network” and are not using media bypass, the RTP stream will be converted to RTAudio by the local Mediation Server and typically converted back to G.711 at the destination. While an adaptive codec like RTAudio is great for voice calls, it fails on modem communications. Therefore if Lync needs to connect two analog devices configured as fax and residing on different gateways it will route the call through PSTN since TDM-based faxing will work much better.
Another nice feature in Lync is that normalization rules apply to analog phones the same way as to Lync or IP phone users. How does that work? Numbers dialed by such a device are forwarded to the Mediation Server without any conversion. If Lync finds the senders line URI in Active Directory (and only then) it will apply policies, dial plan with associated number normalization and routing decisions. Also call detail records (CDR) are written for analog devices.
Gateways do not need to know anything about that – they only know the line URI for each analog port. This information has to be maintained on two sides: in AD by using Lync Cmdlets and in the gateway configuration supported by the hardware vendor. To help assigning analog contacts to FXS ports and to avoid mistyping, gateway configuration UI may provide additional support like in our OfficeMaster SBA. It uses a Lync Cmdlet to query for analog devices hosted on its gateway and offers a simple way of assigning those line URIs to local FXS ports: