9.6 Cisco Extension Mobility Considerations

This topic describes the issues that must be considered when implementing Cisco Unified Communications Manager Extension Mobility.

  • Cisco Extension Mobility does not modify the device CSS
  • Cisco Extension Mobility modifies only the line CSS
  • When using the line-device CSS approach or globalized call routing and local route groups:
    1. Line CSS of user device profile is applied; CoS settings of the user are enforced.
    2. Device CSS is not modified; gateway selection remains device-dependent.
  • When using only one CSS at the device level, the same CSS is used all the time; no CoS can be applied.
  • When using only one CSS at the line level, proper gateway selection requires Local Route Groups.
  • AAR CSS is configurable only at the device and is never updated by Cisco Extension Mobility, so local gateway can be used for AAR calls.

Cisco Extension Mobility does not modify the device CSS or the AAR CSS (both of which are configured at the device level). Cisco Extension Mobility does replace the line configuration of a phone, including the CSS that is configured at the line, with the line configuration of the device profile of the logged-in user.

Thus, in an implementation that uses the line-device approach, the following applies:

  • The line CSS of the login device is updated with the line CSS of the user. This update is used to enforce the same CoS settings for the user, independent of the physical device to which the user is logged in.
  • The device CSS of the login device is not updated, and the same gateways (those gateways that were initially configured at the phone before the user logged in) are used for external route patterns. Because the phone did not physically move, the same local gateways should be used for PSTN calls, even when a different user is currently logged into the device.

When using globalized call routing (including local route groups), the implications of Cisco Extension Mobility CSSs are similar to the above scenario with the line-device approach. The only difference is that the gateway selection is done by the local route group and not by site-specific device CSS.

If only one CSS is used to implement partitions and CSS, the following applies:

  • If only the device CSS is used, the CSS is not updated, and no user-specific privileges can be applied. The user inherits the privileges that are configured at the device that is used for logging in.
  • If only line CSSs are used, the line CSS that is configured at the device profile of the user replaces the line CSS of the login device. In a multisite environment, this configuration can cause problems in terms of gateway choice because the same gateway is always used for external calls. To avoid gateway-selection problems in such an environment, you should use local route groups.

Alternatives for Mismatching Phone Models and CSS Implementations

To avoid issues with mismatching IP phone models or with calling privileges when the traditional approach for implementing partitions and CSSs is used, multiple device profiles can be configured per user.

  • Alternative to using the default device profile and the (applicable) settings of the user device profile:
    1. Create multiple device profiles for the user (one per phone model family).
    2. Alternative is applicable only if users use Cisco Extension Mobility across phone-model families that do not support feature safe.
  • Alternative to line-device CSS or local route groups:
    1. Create multiple device profiles for the user (one per physical location), giving each profile the appropriate CSS to enforce CoS and to choose the correct gateway.
  • Neither alternative scales well.

When different phone model series are used, issues can arise when the settings of the default device profile are applied. Different users might require different settings. This problem can be solved by creating multiple device profiles per user. When you configure and associate one device profile (per phone model) with a username, Cisco Unified Communications Manager displays this list of profiles after successful login. The user can choose a device profile that matches the phone model of the login device. However, if many users need to use Cisco Extension Mobility and many different phone models are used, this solution does not scale well.

The same concept can be used as an alternative to local route groups or the line-device approach for implementing CSSs. A separate device profile can be created per site and is configured with the appropriate CSS to allow local gateways to be used for external calls. Again, the user chooses the corresponding device profile after logging in, and the correct CoS and gateway choice are applied without depending on a separate line and device CSS or local route groups. The recommendation, however, is to use globalized call routing with local route groups in a multisite environment, because that approach simplifies the dial plan and scales better.