VoIP – James Batchelor

Zen Digital Voice – Connecting to SIP

If like me you still have a requirement for a landline, or at least a landline number. Zen Internet offers a “digital voice” package as an accompaniment to its broadband service.

Traditionally this service is provided via its supplied Fritzbox router, utilising its FXS port to supply telephony to analogue devices.

As the service is SIP based, it is possible to connect direct via SIP phones or Asterisk which is ideal should the Fritzbox not be suitable for your requirements. While this is permitted by Zen, it is unsupported.

Here are a couple of examples of getting connected to Zen DV without the use of the Fritzbox.

Asterisk Monitoring Over SNMP

The aim of deploying Zabbix and adding SNMP to Gentoo was to gain better insight on how an Asterisk PBX was performing.

Last of the hurdles was to get data from Asterisk in order to send to Zabbix, however the traditional way of loading the res_snmp.so module in Asterisk was not available, as while the PBX in question utilises Asterisk, its buried under proprietary licensing and a non-standard api, therefore being unable to either add the SNMP module or to query it.

If you are experiencing a similar situation, here is how to extract some stats from Asterisk 16 using SNMP, but without the SNMP module…

Yealink OpenVPN to Draytek Router

The firewalls in front of our PBX’s are configured to only allow SIP traffic from UK IP addresses, this reduces the attack surface and is usually not an issue as almost all legitimate traffic is from the UK.

As we expand there is greater need for international connections, this is fine if they have a static WAN IP or FQDN, but the more recent requirements are for “home” users with phones on their residential connections where dynamic IPs are the standard.

Changing the whitelisted IP every time their IP changes is not only tedious, but gives poor service, plus due to recent events (here and here) I’m not prepared to open access to another country for a single extension.

In my case, these internationals are satellites of a UK based office, so the idea is having the overseas phone route all voice traffic through the UK office where its free to connect to the PBX…

Provisioning Polycom Phone

Yealink is our go to vendor for telephony hardware, mainly due to its ease and variety of configurability. But recently have been tasked with adding a Polycom VVX250 to the system for a charity to use.

While the setup between different manufacturers normally follows the same general path. This is a journey of how Polycom interprets it…

Provisioning a Cisco 7940/7960

2021 is here and so returns (In the UK at least) one of my favourite shows to Netflix, The Office (US). Since starting working in VoIP its hard not to notice what phones turn up in TV shows, here the Cisco 7960, was prolific for showing up in shows around this era.

So why not, nearly 16 years after the show started, try and get one of these working on an Asterisk PBX? At work we had a number of similar 7940 models that hadn’t be used for years, so why not give it a try…

Testing a New PBX

Recently I’ve had the opportunity to deploy and test a call centre PBX product to gauge if its viable to offer as a product and how it will sit within our infrastructure.

Installing and poking around the GUI is all well and good but to really find out how a PBX behaves it needs some traffic, to find outs its performance in regards to resources but also to find out what a vendor’s interpretation of an advertised feature actually is.

To generate sample calls, instead of registering handsets/softphones and dialling manually it would be better to automate this, and SIPp is the perfect tool for this.

Yealink Remote Factory Reset

When a phone is no longer required on your service, there is always trepidation on what will happen to it, the hope is that’s its unplugged, stuffed in a drawer and never sees the light of day again. But in reality, there’s a good chance that it will end up on the likes of eBay and Gumtree, and since a phone is already provisioned with your server details, the next person to get their hands on it could have unauthorised access to the system.

The simple step to prevent unauthorised access is to delete / change the secret to the extension, if your will to put up with the constant failed registration attempts. But what about the personal data on the phone? BLFs, local directories and the like.

Yealink devices since firmware version 81 have had the ability to factory reset via a SIP notify command, meaning should a phone still be online, a factory reset can be handled remotely and without end user intervention.