Smartvox Products: Gateways and Border Controllers

VoIP Gateways Explained

Basic Function of a VoIP Gateway
A VoIP gateway provides the interface between the IP telephony network and the conventional public switched telephone network (PSTN). For example, a gateway can be used to link a VoIP call to a PRI-30 ISDN trunk, a BRI two channel ISDN circuit or an analogue line.

In fact, a gateway can be used as the interface between any disparate telephony protocols. It might provide the bridge between analogue and digital circuits or allow VoIP calls using the SIP protocol to connect to remote peers using the IAX protocol. If it supports "transcoding", then a gateway may also be used to interconnect end points that would not otherwise be able to negotiate a common codec.

Dial Plans - Intelligent Routing of Calls
All but the most basic of gateways will have a configurable set of rules that are used to determine the correct path for each new call that arrives on the system. The rules can range from very simple ones like "every call arriving on port 1 send it out on port 2" to quite complex decisions based on examination of the dialed number, the caller id and the current status of the connections and ports available.

The Smartvox product range includes gateway and proxy server solutions with pre-set internal rules to determine routing and call delivery, but we also offer you the option to link the gateway to an Application Server. Using this option, the logic for all routing decisions is pushed out to the Application Server thereby giving you almost unlimited flexibility.

Must I have my own gateway?
The simple answer is no. You can have an IP phone that registers directly with a remote VoIP Service Provider through the Internet. When you make a call, the IP phone will send the request to your VoIP Service Provider and your call can reach the entire public telephone network because your Service Provider has a PSTN gateway - this means you don't need one on your premises.

However, if you want even a slightly more sophisticated solution than the simple IP phone example described above, then the chances are that you will need a gateway or a PBX that acts as a gateway. It is very common these days for new PBX's to be IP enabled in some way. This could mean they support VoIP trunk connections, IP phones as extensions or both.

For small and medium sized businesses that do not want the expense and disruption of replacing existing telephony equipment (PBX, phones, cabling etc), the addition of a VoIP gateway makes very good sense. The solution we recommend is the addition of a Vegastream gateway in series with the trunk before it connects to the existing PBX.

Advanced Gateway Solutions

Session Border Controllers
When a gateway is used as the interface between the Internet and a private network segment, along with rules to control connections between the two, then it is known as a Session Border Controller or SBC.

Some products marketed as Session Border Controllers also include other facilities such as SIP Proxy, Registrar and Location server. While a basic SBC may be a useful addition for a business that wants to allow controlled access to its IP enabled PBX, the more sophisticated versions with additional features are mostly aimed at Service Providers or larger enterprises.

Load Balancing and Failover
Smartvox has developed its own gateway and SIP proxy products offering load balancing and failover. These products, aimed primarily at the ITSP and service provider market, allow calls to be delivered to a bank of call handling servers such as IVR's or Media Servers.

Transcept: Asterisk based Solutions

Asterisk as a VoIP Gateway
Asterisk, when used as a gateway, offers superb flexibility because several different telephony interfaces can be accommodated in a single unit and the dial plan can be customised to almost any level. Also, because it runs on a standard Linux platform, it allows more versatile integration with other services on your network such as database and mail servers or application servers.

Transcept GUI: Monitoring application for Windows
Illustration of the Transcept real-time monitoring screen To complement an Asterisk based solution, Smartvox can provide an optional monitoring application. The application runs on any Windows desktop PC and shows in real-time how many calls are being handled on each port of the Asterisk server. Options are available to include automated fault detection and alarms.

Load Balancing option
For heavy duty applications where you need to distribute calls to a number of end points, we are able to offer the enhanced load balancing version of our Asterisk gateway. The load balancing option adds an extra target type within your dial plan - a load balancing group. The group may contain several pre-set target devices and you control distribution to those targets in real-time simply by changing a few values in a database.

Asterisk as a Session Border Controller
Equip the Asterisk server with two ethernet ports, connect one to the Internet and the other to your internal network; set up the firewall, configure the dial plans and you've got everything you need for a fully functional Session Border Controller.

IP phones can register with the SBC either from the internal network or from the Internet.
Use your SBC as an Inbound and/or Outbound proxy to have complete control over incoming and outbound calls
Use it to control access to your IPBX and to overcome the usual problems associated with interfacing VoIP between your private network and the Internet
Solve one-way audio and other notoriously difficult and annoying NAT traversal problems while, at the same time, improving your systems security