Here are some key features of "TekSIP":

· Supports features described in RFC 3261 and ENUM (e164.arpa domain only, ENUM lookup is performed just for INVITE requests).
· Logs system messages, errors and session information to a log file.
· All parameters can be configured through management GUI.
· Provides NAT traversal between registered SIP UAs. TekSIP also supports UPnP.
· Supports RADIUS Authentication (RFC 2865) and RADIUS Accounting (RFC 2866) with the method described in draft-sterman-aaa-sip-00.txt and draft-schulzrinne-sipping-radius-accounting-00.txt respectively.
· Can optionally act as a B2BUA for incoming 3xx SIP responses.
· You can define a default SIP route or prefix based routes for particular SIP endpoints for outgoing calls (One ITSP account can be shared by internal users). TekSIP can register to upstream SIP servers to receive incoming calls.
· You can redirect calls to alternate endpoint when called endpoint is unavailable (Off-line, busy…).
· You can monitor active registrations and SIP calls in real-time.
· TekSIP has a built-in Presence Server (SIP/SIMPLE based).
· Clears expired registrations automatically.
· Stores configuration data in the installation directory (.ini file).
· Can act as a RTP Proxy and record audio streams if RTP proxy enabled. Recorded audio streams are saved in wave format can be played using TekSIP Manager.
· Quick and easy installation.
· Runs as a Windows service.

Requirements:

· 512 MBytes of RAM
· Microsoft.NET Framework v2.0.50727 (Min.)
· 1 MByte for installation