In part 1 of this post, we examined the core pool roles for Microsoft Office Communications Server 2007. Specifically, we covered front-end servers, directors, the three variants of conferencing servers, and the archiving and CDR server. There are still several key roles to be covered to understand the full breadth of the OCS offering. These roles fit into three key areas: edge servers, telephony servers, and “other”. Before we get into the specifics of the roles, please take a brief moment to review the vocabulary from part 1:
- Office Communications Server: A Microsoft product designed to facilitate communications both inside and outside the office.
- Presence: A metric that takes into account both your availability (available, idle, away) and your willingness (available, busy, on a call) to communicate.
- Endpoint: Any device (SIP phone) or software package that registers itself with Office Communications Server as belonging to a user, meaning that the user can be contacted through the device or software package.
- Enterprise Voice: Probably the most noteworthy addition to the product since 2005; allows calls to enter and exit Office Communications Server. This means that from any endpoint, users can make or receive calls to traditional phone numbers.
- Public Switched Telephone Network (PSTN): The traditional telephone network that delivers telephone service over dedicated copper cables.
Edge Servers
Access Edge Server
The access edge server provides three very key services: authenticating and enables connectivity for remote users, negotiating federated communications, and connecting to public IM services such as MSN, AOL, and Yahoo. Authentication and communications with remote users is unequivocally the most common usage of access edge server. This server is critical whenever an employee needs to use Communicator but is outside of the corporate LAN. Traveling sales representatives with Communicator Mobile, home-based employees and other situations are supported when using Access Edge Server. Federation is the term used to refer to two Active Directory domains that have set up a federated relationship. Note that a federated relationship is not the same thing as a domain trust, but is similar. Generally federation happens along corporate boundaries. Two companies in a strategic alliance or other partnership will federate to allow key contacts greater visibility and easier access to communications. Microsoft OCS can also allow connectivity with public IM services, enabling communications from Communicator to MSN Messenger, AIM, or Yahoo! Messenger.
Personal Side-note: Access edge server is one of the most amazing roles in my opinion. I have been witness to quite literally taking an OCS endpoint, moving it outside of the network, and having it seamlessly connect back up to OCS without any additional configuration. Imagine being able to grab your desk phone and go home for the day! We currently have a Cisco UCCX system in place. In order to take my phone home, I have to take a hardware VPN home, hook it up directly to my cable modem (in the basement) and then hook my phone straight to that. With OCS, I was able to take my laptop home, turn on my wireless and connect immediately. If I can say one thing that would be the most important thing for a Cisco customer to hear, it’s this:
Our Cisco system is technically capable of achieving everything we need it to achieve, but our experience with OCS has blown us away. Actually getting your hands on to a sample OCS setup is the best thing that you can do for yourself.
To summarize, the access edge server:
- Authenticates and enables connectivity for remote users
- Allows two entities to federate, which in turn allows greater visibility for communications
- Allows connectivity to public IM networks
A/V Edge Server
The A/V edge server enables audio and/or video conferences to happen with users outside of the corporate LAN. It is important to note that telephony conferences are considered distinct from this scenario and are covered by the telephony conferencing server (see part 1). The A/V edge server allows remote users authenticated by access edge server to establish internal audio or video calls, or VoIP calls for enterprise telephony scenarios.
Web Conferencing Edge Server
Similar to the A/V edge server, the web conferencing edge server enables Live Meeting 2007 sessions to include users outside of the corporate LAN. Many companies will use this role slightly differently than they will the other edge server roles. Where access edge server and A/V edge server are deployed to allow external known users to connect and conference, Web conferencing edge server may arguably be used to conference in more anonymous users (who are still actually authenticated by digest authentication) than known users. This allows companies an internally controlled, paid-for mechanism similar to WebEx that allows public sharing of desktops and other information.
Requirements** (for all edge servers):
- Dual processor, dual core 3.0GHz+ processor
- 2 x 18GB HDD
- 4GB+ RAM
- 2 x Gigabit NIC
- Windows Server 2003 SP1+*
* I was not able get the OCS primary installer to run successfully on Windows Server 2008 RTM. It may be that the individual installers would run successfully, but I have not confirmed this. The only role I have successfully installed on Windows Server 2008 is Speech Server 2007.
** The work of mixing audio channels is intense; A/V servers will benefit from more robust hardware.
Communicator Web Access
Communicator Web Access (CWA) is to Office Communications Server what Outlook Web Access is to Exchange Server 2007. It provides an attractive, AJAX (slick update without refresh) based interface for internal or external users to use. CWA functions much like the director role in that it proxies connections, but differs in that it also proxies internal connections. Also, CWA is restricted to communicating via instant messaging. There is no support for audio/video conferences, Live Meeting, or enterprise voice.
Requirements:
- Dual processor, 3.2GHz+ processor
- 1 x 36GB HDD
- 4GB+ RAM
- Gigabit NIC
- Windows Server 2003 SP1+*
* I have not yet attempted to install this role on Windows Server 2008.
Web Components Server
This role has probably the least visible functionality of all server roles: it’s primary responsibilities are to allow users to join Web conferences by clicking a URL, allow download of Address Book data, and expand membership in distribution groups (in ways, simply an expansion of the Address Book functionality).
Requirements:
- Dual processor, dual core 2.6GHz+
- 2 x 18GB HDD
- 2GB+ RAM
- Gigabit NIC
- Windows Server 2003 SP1+*
* I have not yet attempted to install this role on Windows Server 2008.
Mediation Server
Contrary to the Web components server, the mediation server role has profound visibility and is arguably as important as a front-end, back-end, or edge server. The mediation server is what makes enterprise voice possible. When Microsoft implemented enterprise voice, they elected to use proprietary codecs (RTAudio and RTVideo) in order to overcome some significant hurdles such as inconsistent bandwidth. However, their choice to use these proprietary codecs meant that right from the beginning, Microsoft wasn’t able to play nicely with many pieces of PSTN hardware. In their defense, the enterprise voice market is very confused right now. There are many competing standards such as ICE, SIP, and others that still aren’t fully or consistently supported. Microsoft saw this and decided that it would be easier to simply draw a strong line between external and internal voice traffic. That line is drawn right through mediation server.
Microsoft states that there are three ways to connect Office Communications Server to the PSTN. The first is through a basic media gateway. A basic media gateway is simply a piece of hardware that terminates PSTN lines (whether in FXS/FXO or T/E/DS form). The media gateway’s responsibility is to accept incoming calls on the PSTN lines and hold the line open until the call is complete. To know when the call is completed, the basic media gateway talks to the mediation server, generally via G.711. The mediation server does the job of decoding G.711 voice traffic and encoding into RTAudio (and vice versa, for outbound voice traffic).
A basic hybrid gateway does essentially the same thing except that it merges the mediation server role directly onto the media gateway. The benefit of a basic hybrid gateway over a basic media gateway fundamentally boils down to TCO: it’s cheaper and easier to manage one box than it is to manage two.
The final means of connecting Office Communications Server to the PSTN is for the media gateway itself to directly support the native OCS protocols (like RTAudio and ICE). Microsoft calls this an advanced media gateway. Please note that the difference between the advanced media gateway and the basic hybrid gateway is that in the basic hybrid scenario there are two functions coexisting on one box – they are still distinguishable functions. With advance media gateways, the functions are no longer distinguishable. The media gateway natively speaks OCS’ language.
In the next post in this series, we’ll consider a final smattering of server roles that don’t always require a full server, consider coexistence scenarios and some final “gotchas” that I wish I’d known about when I started deploying OCS.
