Melissa Swartz, Swartz Consulting
Elizabeth English, EE and Associates
Comparing Three Solutions
Case studies of live sample projects
May or may not have been implemented with most
redundant configurations
ShoreTel Premises
Avaya Premises
Cisco Hosted
Interactive discussion of strengths and weaknesses of
each design. (based on design as implemented, not
manufacturer issues)
Case Study 1 Description
Two Data Centers: Data Center and Head Quarters
250 Remote sites (most small)
SIP trunks into both data center and HQ (distributed
load)
Primary and backup Servers all in Data Center
(Director and DVS)
MPLS and SIP on shared Ethernet from Sprint
Case Study 1 Strengths
Dual SIP connectivity
SIP failover from the carrier‐ if connection fails, calls
are routed by Sprint to predetermined numbers
Redundant SBCs in both Data Center and HQ (2 each)
Redundant servers
Site switches will maintain calls if connectivity to
servers is lost
Case Study 1 Design Improvements
Separate MPLS and SIP on different Ethernet circuits/carriers
Separate redundant Directors geographically (different
buildings, different parts of the country)
Add 3
rd
party software to automatically failover to second
Director (Double Take)
Separate DVS between DC and HQ and/or add to some sites
ShoreTel fails “up”
Cross connect DVS at DC to HQ Director, DVS at HQ to DC director
Add backup power to servers, gateways, and switches at DC and
HQ
N+1 Shoregear switches at Data Center and HQ. N+1 switches at
At least one server is always required in a ShoreTel deployment and is referred to as the Headquarters (HQ), or root, server. Additional servers can be added for better fault tolerance, redundancy and survivability. Whether referred to as Distributed Voice Mail servers (DVMs) or, more recently, Remote Application Servers, these additional servers rely on the HQ server to receive configuration changes but, otherwise, can run entirely independent from the HQ server for extended periods of time. An additional server can be added to a remote site to keep local Auto Attendant (AA) and Voice Mail (VM) traffic off the WAN and to provide survivable AA & VM access even when connectivity to the Headquarters site/server has been lost. An additional server can be added to the Headquarters site to enable failover & redundancy in case the HQ server is taken off‐line for maintenance or upgrades. All the servers communicate with each other and work together to "back each other up" in case one server is unreachable. ShoreGear Switches: Selection of Primary and Secondary Servers
Each ShoreGear switch, starting with full knowledge of all ShoreTel servers in it's own site and all sites above it, will select a primary server and a backup, or secondary, server. When a ShoreGear switch needs any server‐based service (such as an Auto Attendant prompt or a Voice Mail box) the switch will first try to connect to its primary server and, if that server is unreachable, will connect to it's secondary server.
The selection of primary and secondary servers is done dynamically by the switches and is done by each switch individually and from its unique position and perspective of the ShoreTel site hierarchical tree. If there are two (or more) ShoreTel servers at a site, then the ShoreGear switches at that site will always select those local servers for their primary and secondary servers. In fact, different switches will select different servers for their primary and secondary to effectively load‐balance across all servers at a site. If there is only one server at a site, then that server will always be selected as the primary server for each switch at that site. The switches then select the next "nearest" server by looking up the ShoreTel site hierarchical tree. This hunting will continue up the tree until each switch has selected both its primary and secondary server or it reaches the HQ site and has run out of servers to choose from. In practice, with most simple, hierarchical tree structures, this often will mean that each switch will use it's local DVM server as it's primary server and the HQ server as its secondary server. Note: When a switch is selecting it's primary and secondary servers it will always hunt up the site tree (towards parent sites and the root/HQ site) and will never hunt to the side or down the tree (to a sibling site or a child site). Distributed Server Services Many of the ShoreTel server‐based services are fully distributed, such as all AA prompts and the recorded names of all users. When one of these services is needed by a ShoreGear switch it will connect, as always, to its primary server and that server will be able to service the request locally.
But some server‐based services are performed only by one, single server, such as the storage of each individual users Voice Mail messages and greetings. When a ShoreGear switch needs, for example, to route a caller to leave a voice mail message for a particular user the switch will connect to it's primary server and that server will then redirect the call to the appropriate server that hosts the specified user's voice mail box.
Since Servers fail from "child" to "parent" you may consider the HQ server at the DR site and DVM's as your main voice mail servers.
