8.2 Issues with Devices Roaming Between Sites

This topic describes issues that occur when users roam between sites with their devices.

Device can be an IP phone or, more likely, a softphone of a roaming user.

When users roam between sites, they might take their phones with them. This situation typically does not apply to Cisco IP phones, but is very common with softphones or Cisco Unified Wireless IP phones.

Issues with Roaming Devices

When phones move between different Cisco Unified Communications Manager sites, some settings can become inaccurate.

If a user is moving between sites and is using a phone, the following situation occurs:

  • Location-dependent settings are set per phone (MAC).
  • The physical device location is assumed to be constant.
  • The constant settings become inaccurate:
    1. Region
    2. Location
    3. SRST reference
    4. AAR group
    5. CSS
    6. MRGs and MRGLs
    7. Other settings

The configuration of an IP phone includes personal settings and location-dependent settings that are all bound statically to the MAC address of the phone and hence to the device itself. The physical device location is assumed to be constant.

If a phone, or more likely a softphone, is moved between sites, the location-dependent settings become inaccurate. Some of these settings and their errors are as follows:

  • Region: This setting might cause wrong codec settings.
  • Location: This setting might cause wrong CAC and bandwidth settings.
  • SRST reference: This setting might cause malfunction of Cisco Unified Survivable Remote Site Telephony (SRST).
  • AAR group: The AAR group setting might cause malfunction of the call redirection on no bandwidth.
  • CSS: The CSS setting might cause usage of remote gateways instead of local gateways.
  • MRGs and MRGLs: The MRG and MRGL settings might cause allocation of wrong media resources, such as conference bridges or transcoders.

To maintain the correct settings, the Cisco Unified Communications Manager must be aware of the physical location of all phones, including moving devices.

Using Device Mobility to Solve Roaming Device Issues

Cisco Unified Communications Manager Device Mobility offers functionality that is designed to enhance the mobility of devices within an IP network.

Issue Without Device Mobility Issue Solved with Device Mobility Feature
When mobile user moves to different location, CAC settings are not adjusted. Location settings are dynamically assigned.
When mobile user moves to different region, codec settings are not adjusted. Region settings are dynamically assigned.
SRST reference is fixed. SRST reference is dynamically assigned.
Media resources are assigned independent of location. Media resource list is dynamically assigned.
PSTN gateways to be used are fixed. Dynamic phone CSS allows for site-independent local gateway access.
AAR does not work for mobile users. AAR calling search space and AAR group of directory numbers are dynamically assigned.

Issues with PSTN gateway selection and AAR apply only to deployments that do not use globalized call routing.

The device still registers with the same Cisco Unified Communications Manager cluster, but it adapts some of its behavior to the actual site where it is located. Those changes are triggered by the IP subnet in which the phone is located. The table shows the issues that are solved by Device Mobility.

Basically, all location-dependent parameters can be dynamically reconfigured by Device Mobility. Thus, the phone keeps its user-specific configuration, such as directory number, speed dials, and call-forwarding settings, but adapts location-specific settings like region, location, or SRST reference to the actual physical location.

Device Mobility can also be configured so that dial plan-related settings, such as the device CSS, AAR group, and AAR CSS, are modified. These dial plan-related settings only need to be modified if different sites require different CSSs. When using local route groups and globalized call routing, the device-level CSSs are the same at all sites.