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DISTRIBUTED  VOIP  ARCHITECTURE 
PROMOTES  ENTERPRISE  PROVISIONING 

	By William Flanagan, Editor & Publisher

Scalability is always an issue for the largest organizations, those with more than 50,000 phones.  But mid-size and smaller enterprises face similar issues, particularly when deploying Voice over IP (VoIP) across multiple locations.  One of the key issues is the trade-off between localized (distributed) call processing versus centralized.  "Distributed" offers an opportunity for redundancy, but "centralized" (one unit) is usually easier to manage.

ShoreTel (www.shoretel.com, formerly Shoreline) has been pushing their call processor platforms (ShoreGear) to support larger and larger networks.  They just announced they are now up to 10,000 phones, reaching that level in a way that facilitates provisioning within an enterprise.  For more capacity, add another "box".

Each ShoreGear unit handles up to 120 lines (and 30 trunks), the number varying with the types of ports (analog, IP, ISDN).  Additional units may be added all in one location (centralized) or at branch offices (distributed).  

The architecture is fully distributed:  every ShoreGear runs the full software suite (ShoreTel 5, Rel. 2).  For example, hunt groups and group paging (through IP phones) consist of ports or devices at any location.  However, to the manager, all the devices (up to 200) appear as a single system at one management console, the "Director" workstation.  The GUI workstation simplifies supervisory functions.  

Help in provisioning new sites comes from an automated process that trains new switches with routing information and the numbering plan from other ShoreGear devices that exist on the network.  Web-based provisioning features let each user set preferences and activate features permitted by administrative policy.  User take these configurations with them when the move between locations--logging in gives each users his own feature set, on a phone he brings or one that he borrows.

On a global basis, the distributed architecture works in several languages (English, German, Spanish--and American).  A language may be assigned to a user or a site, ensuring the local people will understand the prompts and get familiar ringing patterns.  

To avoid the problems of differing national standards for voice signaling (often a barrier to provisioning new systems internationally), ShoreGear offers two choices for the almost universally availble ISDN Primary Rate Interface (PRI):  for North America (T-1;  NI-1) and for Europe (E-1;  Q.sig).  No need to worry about R-2 signaling any more.

To address the rising concern about network security for VoIP, ShoreGear runs an embedded operating system, VXworks.  This OS handles replication of data bases for newly added switches, and updates all devices when a change is made in any location.  For high availability, configuration information and the dialing plan are stored in flash--no hard drive to fail.

When a user is migrating from a traditional PBX, ShoreTel offers to ease the transition by:
--upgrading site-by-site to control capital expenditures,
--replace the PBX but keep the voice mail system (SMDI interface),
--replace the voice mail (with unified messaging) while leaving the PBX.

Depending on the strategy, the migration might leave existing phones in place or deploy new IP phones.  To simplify the installation, IP phones contain an IP switch that prioritizes voice packets over data from an attached PC.  Depending on the configuration and capacity of the IP LAN, the amount of additional configuration for the addition of voice traffic can be minimized.

And isn't that the goal of new deployments?