OnSIP uses redundant servers, routers, Tier 1 Internet connections, and upstream carriers to provide an extremely reliable VoIP service. Today, OnSIP has two data centers, located in renowned carrier hotels at 60 Hudson St, New York, NY and One Wilshire Blvd, Los Angeles, CA

OnSIP Hosted PBX is built using a substantially different paradigm than competing services, resulting in industry-leading reliability, geographic scalability, and low cost. Unlike competing services, OnSIP is not a collection of customer PBXs deployed in a datacenter. The latter setup is associated with limitations such as sub-optimal call routing (affecting call quality) through the customer’s dedicated box, service outages if the particular box fails for any reason, and scaling inflexibility.

Many open source projects such as OpenSIPS, FreeSWITCH and Asterisk are used in the implementation of the current OnSIP platform. The "core" of the OnSIP platform consists of a geographically distributed cloud of SIP proxies. These SIP proxies appear as one entity, sip.onsip.com. Restated, OnSIP presents itself as a single SIP server, sip.onsip.com, to the outside world, which is a key characteristic: Instead of registering to a single box, OnSIP phones will connect to the geographically closest SIP proxy in the cloud. These proxies also handle NAT and firewall traversal on the server side, freeing customers from excess NAT or firewall administration.

OnSIP Platform Guide