Considerations for VoIP Dial-Plan Design & Security

Considerations for VoIP Dial-Plan Design & Security


Designing of dial-plan of the IP Telephony network is one of the crucial tasks as the integration with other networks is difficult because the other networks might not be designed for integration.

One of the scenarios when integration with other networks is done is when two different companies merge. For integration, the companies’ data networks that include IP addressing, inventory data base an ordering information must be joined. Both companies should use the same strategies and methodologies when implementing integration otherwise problems can arise.

When two companies merge, their telephony system including voicemail, supplementary features, billing, and dial plan might be incompatible with each other.

When designing an IP telephony network, always use these methodologies that will be compatible with other companies for integration in future if integration is required.

Let’s have a look at the considerations required when designing a dial plan of IP telephony network.

Dial Plan Rules to Consider

Extension Addressing: Decide how many digits will be used to identify user’s extension.

Extension Dialling: The number of digits to dial any extension.

Dialling Privileges: Pre-define allowing or not-allowing certain types of calling.

Selection of Path: Either the IP network will be used for on-net calls, or one carrier will be used for local PSTN network calls and for international calling.

Calling number Transformation: Replacement of caller’s extension with the office’s main number when calling any local PSTN number.

Called number Transformation: Retaining the last dialled numbers.


Key Elements of a Dial Plan

Path Selection: When dialling from an IP phone, different paths can be selected to reach the dialled destination. Primary and secondary paths are generally used that means PSTN network may be used in case of IP network failure.

Digit Manipulation: DM is very important as in some cases you need to modify calling or called party number.

Calling Privileges: Set some conditions to every calling party which allows them to call some specific numbers only.

Endpoint Addressing: Directory numbers should be provided to every device within an office, so that they may be accessed locally.

VoIP Security Considerations

VoIP calls are majorly harmed by Denial-of-Service attacks. These attacks result in hacked gateways leading to malicious call redirection, call eavesdropping and unauthorized free calls. DoS attacks target weak VoIP network elements that can flood the network with bogus voice calls traffic, degrading network performance and may shut down both voice and data communications.

VoIP gateways should be secured as in hacking of gateways results in free calls. Unprotected voice packets can be stolen or sniffed out and listened to in real time.

The following are some security tips for ensuring secure voice communication:

VoIP Protocols: Select the equipment and protocols that meet your needs.

Use only necessary protocols:  There are advantages and dis-advantages of using various protocols. You should implement only the required protocols as unnecessary protocols may cause the chance of harmful attacks.

Keep VoIP servers separate from other servers: Some security devices used in LAN networks do not recognize voice commands. This will allow attackers to penetrate in your network and access critical information.

Network Address Translation: NAT converts internal IP addresses into a globally unique IP address for routing over the Internet. The security solution you deploy should allow you to enable NAT on the LAN, as well as allows callers from outside the network to find users with dynamic and non-routable IP addresses.

Remote Connections: Allow only authorized persons to access VoIP network from remote locations. As unauthorized person may attack on your network server.

Use separate infrastructure for VoIP: It is highly recommended to use separate infrastructure for VoIP communications and other IP based communications.

Security system for VoIP: Deploy a security system specifically for voice calls that analyses call state and makes sure that all parameters are consistent.           

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