SIP Application Server is a fully functional application server solution that can also act as soft switch that can take wholesale or retail traffic. SIP Application Server is tightly integrated with the LCR (Least Cost Routing) engine, Registrar and VoIP Billing. It supports all services provided through VoIP Applications Pack.
Features:

• Fully compliant SIP based Application Server
• Support for flexible dialling rules with its own GUI
• Support for IP and TechPrefix based Authentication
• Support for IP and username / password authentication for terminators
• Flexible TechPrefix support for terminators.
• Support for thousands of Originators at one time.
• Support for hundreds of terminators at one time.
• Integration with optional components like Radius and VoIP applications pack
• Support for file based Accounting in addition to database Accounting

Media Proxy: In a typical VoIP setup, voice (media) goes directly from the sending party to the receiving party without going through the SIP Application Server or the Softswitch. The softswitch only does the match making between the two end points and once this is done, the voice goes directly from point to point. At times it is required to pass the media through the softswitch as well. This may be needed to:
1. Hide the IP address of one party from the other.
2. Reach an end point which is behind NAT and cannot be reached by their public IPs.
3. Monitoring the Quality of Service of the call.
4. Conversion of voice from one codec to the other.
SIP Application Server provides complete Media Proxy features and choose to remain in media path if required by the service provided by VoIP Application Path.
Same module is also used in the detection of DTMF digits which are used for different applications in VoIP Application Pack
Registrar:
Registrar is an optional add-on module to the SIP Application Server. Registrar is used to register those end points which do not have a permanent IP address and therefore use a username /  password to identify themselves. Such users are typically customers using Dialers, IP Phones or ATA devices. At times, terminators also use Registrar and this is in case when their terminating equipment (Gateways, SIM boxes etc.) are behind NAT or requires VPN tunnels to reach to them.
VPN Tunnel:
VPN Tunnel is a further optional part of the registrar. It allows the end points to establish two types of layer 2 VPN tunnels with the SIP Application Server:

• PPTP (Point to Point Tunnelling Protocol
• IPSEC

A VPN puts all the SIP messages inside an encrypted tunnel. This is required in the following scenarios:
1. The standard SIP ports are blocked in company's firewall.
2. VoIP is restricted or banned in a country and VoIP traffic is stopped.
3. More secure communication is required.
In these cases, the Tunnelling add-on module to the registrar can be applied. This is a server that can be installed and communicates with the clients. The client side is usually built into the device. If not then, a tunnel is established through a PC connected in between the client and the registrar.
The encrypted SIP messages received over the Tunnel are decrypted at the server side and handed over to the SIP Application Server or the Softswitch.
Guaranteed Capacity:
On a high end dedicated server, the SIP Application Server can handle up to 1,000 concurrent calls or 10 million minutes of VoIP traffic in a month.
On a server shared with database and billing, the soft switch can still take 500 concurrent calls or 5 million minutes of VoIP Traffic in a month.
Operating Systems support:
All flavours of Linux.
Preferred Linux flavour: CentOS 5.4 or later
Optional Add-Ons:
LCR (Least Cost Routing) Engine
VoIP Applications Pack
Radius Server