Testing Gigabit VoIP Systems with TALAN 3.0


The TALAN is capable of detecting VoIP packets on VoIP phone systems using the 10/100 Mbps rate. The TALAN VoIP Test Adapter will force some Gigabit VoIP systems to auto-negotiate to the  10/100 Mbps rate. However, some VoIP network systems may not be fully compatible with the VoIP Test Adapter, or have been set up not to auto negotiate down. Below are compatibility issues that may be encountered and also solutions:

  1. Gigabit VoIP phone systems that do not auto-negotiate down to the 10/100 Mbps rate supported by the TALAN Ethernet card.
  2. Gigabit network systems where the VoIP phone system requires Power over Ethernet (PoE).
  3. Gigabit network systems where the VoIP phone system is shared with the test site’s data network. These systems may not desire to have the data network slowed to 100 Mbps speeds.
  4. VoIP traffic collections where both transmit and receive sides of the phone traffic may be required simultaneously for determination of possible threats.

Solution – A Configurable Ethernet Switch

There are third-party configurable Ethernet switches on the market which will enable the TALAN to analyze the IP packets to/from the network switch and local device even when the network may be incompatible. When purchasing a configurable Ethernet switch to use for VoIP Analysis with the TALAN, there are several features that you want to look for:

  1. Port Mirroring– in order to monitor the VoIP traffic on a phone line, it will be necessary to mirror the port connected to the phone line to another port. This second port will connect to the Ethernet port on the TALAN.
  2. Auto Negotiation– the switch will need to auto-negotiate down to 100 Mbps speeds when connected to the TALAN. This will only occur on the mirrored port connected to the TALAN – the other network connections will remain at the speeds supported by the network.
  3. PoE support– In a VoIP system that uses PoE, the phones might not have a separate AC adapter for power; they instead receive their power from the Ethernet cabling. For gigabit systems which use PoE, you will need an Ethernet switch that supports PoE.
  4. Auto-sensing or 802.3af support– Applying power through the Ethernet cabling to devices which are not designed to support PoE could potentially damage those devices. Select an 802.3af switch, also known as an active/smart switch or end-span device – one that uses auto-sensing to poll connected devices – to determine whether they support PoE before applying voltage (typically 48V).

This is an excerpt from REI’s TSCM Quarterly Newsletter. Click here to download the full edition.