Is Microsoft VoIP ready for prime time?

Enterprise Voice

Enterprise Voice is the VoIP component of OCS, and it’s an important point of the Unified Communications goal of OCS (along with audio conference calling ,video conference calling, conferencing, IM, and Outlook/Exchange integration). OCS makes VoIP an integral part of working with Office applications. Users can make phone calls in a “click-to-call” manner to Outlook and Communicator contacts.

OCS also provides a similar sort of functionality as services such as Google’s GrandCentral, which allow users to integrate all their phone numbers. Users can register their mobile phones and other devices with OCS; they then receive calls simultaneously on all registered endpoints and can choose which to answer. Through the Enterprise Voice client software, users can also choose whether to forward unanswered calls to another number or log them for notification.

In addition, the voice functionality doesn’t limit users to calling within the local area network. Users with Internet connections can call into the office remotely. They don’t have to use a VPN or pay long-distance charges.

Cost savings go beyond substituting VoIP for PSTN calls. When calls do need to go through the PSTN, Enterprise Voice uses least-cost algorithms to determine how to route those calls.
PBX integration

Based on the SIP standard, OCS offers integration with a company’s existing IP PBX if it supports SIP and native PBX integration. That means users can use existing handsets to make and take phone calls, as well as Office Communicator 2007 on their computers.

A mediation server mediates signaling and media between the OCS and PBX systems. It’s necessary if you’re using a basic media gateway. If you have an advanced media gateway, however, the gateway handles mediation, and you don’t need a mediation server. Media gateways are devices that translate the signaling and media between the Enterprise Voice software and the PSTN.

When the PBX routes calls to users, it also sends the call to OCS. OCS then routes the call to the user’s registered SIP endpoints while the PBX sends it to the PBX phone on the user’s desk.

Another option is to set up OCS to handle phone calls for an individual department within a company while the rest of the company uses the existing PBX. This allows you to roll out OCS in increments within the organization and/or to deploy OCS only for those groups that need its features.

A media gateway can connect the OCS/VoIP group with the PBX. The members of these groups don’t necessarily have to be in the same physical location. If the team members are in disparate locations, they can use OCS for communications, which can save a significant amount of money in long-distance charges.

You can place Enterprise Voice either in front of or behind the PBX. Each option has advantages and disadvantages. Placing Enterprise Voice in front of the PBX means incoming calls come into the media gateway, and it routes calls to the PBX or OCS as appropriate. Placing Enterprise Voice behind the PBX means incoming calls go to the PBX first, and it routes calls for Enterprise Voice users to the media gateway.

OCS and Exchange Server 2007 Unified Messaging (UM) can work together to provide users with Outlook Voice Access. This makes e-mail messages, faxes, and voice messages all accessible from Outlook on a computer or over the phone via an access number assigned by the Exchange UM administrator. Exchange UM can provide voice mail services when you use OCS without PBX integration.
Drawbacks

Of course, like any VoIP solution, a network or power outage may cause you to lose telephone service. In addition, problems with the OCS server itself may result in a voice outage.

You’ll want to have an alternative calling method available for emergency services (i.e., 911) in such cases. OCS doesn’t automatically provide physical location information to emergency services when a caller dials 911.

Another consideration is that when using PBX integration, users can’t use the OCS voice mail. That means you have to either use the voice mail system on the PBX or configure voice mail on Exchange Unified Messaging.

Deploying Enterprise Voice can be complex. If you have outside callers who use Office Communicator, you need an Access Edge Server and Audio/Video Edge Server so their calls can go through the firewall or NAT device.

The A/V Edge Server includes an A/V Authentication service that authenticates outside callers. In addition, you need to translate phone numbers to the E.164 format, create dialing plans, define usage records to assign call permissions to users, and populate a routing table for determining how to route which calls to which gateways.
Source:http://blogs.techrepublic.com.com/networking/?p=363