Hi Ed,
You may use either a Y/USB-A cable or USB-A/USB-A cable to connect the Cisco 562 multi-base to the Cisco 8851 phone.
When using the Y-cable, the AUX port must be configured properly for headset operation.
If the 8851 is running 12.7(1) or later firmware release, follow the instructions below to configure the AUX port operation mode.
- Press the Applications button on the phone.
- Select Admin settings > Aux port.
- Use the navigation key to select Connect e-hook headset.
- Press Set.
If the 8851 is running an older firmware release, configure the AUX port operation mode from the CUCM.
- Login to the CUCM Administration page.
- Click Device > Phone.
- Find and click on the 8851 phone to configure the AUX port.
- On the CUCM's Phone Configuration page, set the parameter Wireless Headset Hookswitch Control to Enabled.
NOTE: If the parameter is not displayed on the CUCM, then the phone AUX port operation mode must be set from the phone and may require an upgrade of the phone firmware. - Click Save and then Apply Config.
I would advise checking the Y-cable is correctly plugged into the phone as shown below. The RJ-9 of the Y-cable should be connected to the headset (top RJ-9) port when looking at the backside of the phone. The RJ-11 of the Y-cable should be connected to the AUX port.