Ethernet Cards for Silent Monitor
On a site with IP telephony, the Unified CM and the IP Phones normally use a Virtual Local Area Network (VLAN) that logically separates voice from data. Although both traffic types are on the same physical channel, they are sent on different VLANs, one for voice and other for data. This configuration enables you to send voice with higher priority than data.
In a call center with silent monitoring, the agent desktop system uses one single physical channel to interact with two different VLANs. You connect the agent desktop system to the PC port on the back of the IP phone. Then, the silent monitor subsystem can collect the voice packets reaching the phone and forward the packets to the supervisor workstation.
The agent desktop system accesses the physical channel through an Ethernet Network Interface Controller (NIC). The NIC monitors the channel and collects Ethernet frames addressed to the agent's computer. The NIC runs a preprocessing step to extract IP packets from the Ethernet frames and deliver them to the TCP/IP stack on the operating system.
During internal testing, Cisco identified that some Ethernet NIC card drivers cannot preprocess Ethernet frames that have an IP packet encapsulated in a VLAN frame. The NIC card driver discards the Ethernet frame if the IP packet is encapsulated in an 802.1Q frame. Some vendors can provide a configuration setting that allows their NIC card driver to forward VLAN traffic to the TCP/IP stack.
If an agent desktop's NIC card driver discards VLAN traffic, then the silent monitor subsystem on that desktop cannot collect and forward voice packets. Silent monitor cannot function properly on such a NIC. Cisco developed a procedure to determine if a particular Ethernet NIC card driver works with the CTI OS silent monitor. The procedure is described in the following sections.