On a site where IP telephony is or will be deployed, the
Unified CM and the IP Phones are normally configured to use a Virtual Local
Area Network (VLAN) such that voice is logically separated from data. Although
both traffic types are carried on the same physical channel they are
transmitted on different VLANs, one for voice and other for data. This
configuration allows voice to be transmitted with higher priority than data.
In a call center that will use silent monitor you must connect the agent desktop system to the PC port on the back of the IP
phone, such that voice packets reaching the phone can be collected by the
silent monitor subsystem to then forward to the supervisor workstation. The
agent desktop system then uses one single physical channel to interact
with two different VLANs.
The agent desktop system accesses the physical channel via an
Ethernet Network Interface Controller (NIC). The NIC monitors the channel and
collects Ethernet frames addressed to the agent's computer. The NIC then 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 available in the market are not capable of pre-processing
Ethernet frames that have an IP packet encapsulated in a VLAN frame; that is
the NIC card driver discards the Ethernet frame altogether 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
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 to the supervisor workstation and silent monitor cannot function properly. 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.
The test involves sending sample VLAN packets to a
Test Target NIC card and verifying that the packets are not
discarded by the pre-processing step but are passed onto the TCP/IP stack on
the operating system at the computer hosting the NIC card.
The test requires a configuration as shown in the following
Figure 1. Silent Monitor Ethernet Card Test Configuration
The Test Target NIC is connected to one port of a simple Hub.
The Hub is connected to the network backbone or subnet. You also need a
Packet Generator Host capable of generating Ethernet traffic. You must connect the
Packet Generator Host to another port on the
Packet Generator Host equipment can be either a dedicated packet
analyzer or a computer with a software-based packet analyzer with capabilities
to generate Ethernet traffic.
WinPcap utility. The WinPcap installation program is located
at the root directory on the Cisco Computer Telephony Integration CTI Object
Create a directory on the
Test Target computer named
From the Cisco Computer Telephony Integration CTI Object Server
CD, copy WinDump.exe and place it in the directory you created in Step 2.
(WinDump is located on the CD under CtiOS\Tools\VLANTest\WinDump.)
Open a console window. Go to the directory where you copied
Determine the MAC address of the
Test Target NIC by executing
ipconfig /all at the command prompt. Write down the number
that appears for the Physical Address. For example, the
"Intel Pro/100" NIC card has a MAC address of
Figure 2. Determining the Test Target NIC MAC Address
Determine the device interface number of the
Test Target NIC. Execute
windump –D and write down the number of the NIC
you want to test. In this example, you would choose interface number 1, which
corresponds to the
"Intel Pro/100" NIC card.
If you are not sure which number to pick, repeat the test for
each card until the test succeeds for one (sufficient to pass) or this fails
for all cards.
Start WinDump to monitor the
Test Target NIC for incoming VLAN packets. To do this execute
windump –i <device_number> vlan. In the
following example the
device_number is 1.
Figure 3. Monitoring the Test Target NIC for Incoming VLAN
Prepare Packet Generator Host
Perform the following steps to prepare the packet generator
Load the packet analyzer software onto your
Packet Generator Host.
Load the sample capture file provided in the Cisco Computer
Telephony Integration CTI Object Server CD
(Ctios\Tools\VLANTest\VLANCapture\VLANSamplePackets.cap). The capture file was
generated in a format that is used by most dedicated and software packet
Select the Decode view from the tab at the bottom of the screen.
Executing a Test
The test involves sending sample VLAN packets to a
Test Target NIC card and verifying that the packet is not
discarded by the pre-processing step but is passed onto the TCP/IP stack on the
computer hosting the NIC card.
The test case to determine whether or not the
Test Target NIC is qualified to work with CTI OS silent monitor
is as follows. (In the test case nomenclature, PA stands for Packet Analyzer
and WD stands for WinDump.)
Table 1 SMNIC- 1 Send Sample VLAN Packets to Test Target NIC Card
Verify that the Test Target NIC can pre-process VLAN
packets and forward them to the TCP/IP stack on the Test Target Host.
Select one of the loaded sample VLAN Packets.
Select or right-click
"Send Current Frame".
Modify the destination MAC address to use the MAC address of
the Test target NIC (for more information, see the figure
"Modifying the destination MAC address" below).
Send the new frame to the Test Target NIC five times.
Verify that there is activity reported on the Test Target NIC.
Test Target computer
windump displays five packets for VLAN ID = 85 (for more information, see
"Sample output showing successful packet capture" below).
If the test fails, no packets appear.
If the outcome of this test is successful, then your
Test Target NIC works with the CTI OS silent monitor. Otherwise,
contact your NIC card provider and ask what settings are necessary to allow
your NIC card driver to forward all packets including VLAN packets to the
TCP/IP stack on the computer so that your packet analyzer tool can capture and
display them. Then apply the appropriate adjustments and rerun this test