Of course, all situations are unique but here are some some validated steps for your consideration. Of course, if you don’t have any PBXs you can skip that step and others that don’t apply nor possible but there is always something you forgot to do.
1 – Locate PBXs physically close to your IP gateways.
2 – Locate IP gateways and Unified Messaging servers on the same VLAN (with 802.1p and q) and the same physical site.
3 – Locate Unified Messaging servers within the same physical site as other servers that have Exchange 2007-2010 server roles installed, including Mailbox, Hub Transport, and Client Access servers.
4 – Terminate your WAN network connections physically close to where all SIP equipment is located with both diverse (separate trench/aerial wireline and wireless) and redundant physical routes.
5 – In branch office scenarios or over WAN connections, create VLAN set routers to prioritize voice and use the G.723.1 codec where feasible instead of the G.711 codec to minimize voice network traffic.
6 – Add multi-level UPS power systems for systems, HVAC, staff, and network management including fire suppression.
7 – Plan for multiple geographic route terminations for voice traffic.
8 – Apply corporate risk and IT security and social media security practices including before and after disaster policy reviews.
9 – Train redundant staff and contract for backup “hotsite.”
10 – Conduct monthly “stress tests.” One example is “stress testing” power systems shared neutrals resulting from power sags.
Click here for animated tutorial in case you want the details.