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Unified CM Extension Mobility and cross-cluster Extension Mobility

Verified 2026-09-24 · 60 sources · tier 2

Also known as Cisco Extension Mobility, EMCC, Extension Mobility Cross Cluster.

Cisco Extension Mobility allows users to temporarily access their phone configurations, including line appearances, services, and speed dials, from other phones across the Unified CM system 7. When a user logs in, the Extension Mobility device profile serves as a virtual device mapped to the physical phone, and the device automatically reconfigures itself using the profile's settings 840.

How Extension Mobility works

When a user logs in, Unified CM automatically applies the profile if only 1 profile exists, or presents a selection list if the user has multiple device profiles 49. If the physical phone model differs from the device profile, Unified CM copies device-independent settings—such as user hold audio source, user locale, user ID, speed dials, and directory number configuration (excluding the line setting for this device)—from the profile onto the phone 45. For model mismatches, the system applies the login phone model's default profile settings for the phone button template, softkey template, and supported add-on modules 46. If the user locale on the user or profile differs from the device locale, the phone restarts and then resets following a successful login 39.

Users log out by selecting logout under the Services button, through configured service parameter timeouts, or when another user logs them out from the phone 41. Following logout, Unified CM sends the logout profile to the phone and restarts the physical device 42.

Unified CM maintains the device's authentication and encryption status during Extension Mobility use 51. For SIP phones supporting Extension Mobility, Unified CM applies the digest credentials of the logged-in end user configured in End User Configuration 53.

An intercom line is presented only on the default device when Extension Mobility is used 38. For call display restrictions, Extension Mobility operates as usual, provided that Ignore Presentation Indicators (internal calls only) is checked on both the Device Profile and the Phone Configuration 5.

Service configuration and parameters

Extension Mobility requires a reachable TFTP server, and administrators must verify phone model support in device documentation because EM extends to most, but not all, Cisco IP phones 50. In Unified Contact Center Enterprise deployments, phones set to an IP Addressing Mode IPv6 Only cannot be used for Cisco Extension Mobility 59.

The Release 15 EM task flow runs in this order: generate a phone feature list; activate EM services; configure the EM phone service; create a device profile; associate the profile to the user; subscribe to EM; configure the Change Credential service; optionally configure EM service parameters 55.

Service activation requires the Cisco CallManager, Cisco Tftp, and Cisco Extension Mobility services in Cisco Unified Serviceability 1. The Extension Mobility IP phone service uses the URL http://<IP Address>:8080/emapp/EMAppServlet?device=#DEVICENAME# 52. The Change Credential IP phone service enables users to update their PIN from the phone using the URL http://server:8080/changecredential/ChangeCredentialServlet?device=#DEVICENAME#, with an optional secure URL on port 8443 6.

The Enable Extension Mobility check box must be checked in the Phone Configuration window under Device > Phone 33. Additionally, both the IP phones and the device profiles must be subscribed to the Extension Mobility service 54.

Key service parameters control login behavior and scaling:

Intra-cluster Multiple Login Behavior: Offers three options: Multiple Logins Allowed, Multiple Logins Not Allowed, and Auto Logout 48. The default is Multiple Logins Not Allowed, restricting a user to a single device 47. Selecting Auto Logout ensures that logging in to a second device—via standard Extension Mobility or Extension Mobility Cross Cluster—automatically logs the user out of the first device 3. For Unified CCE agents on hard phones, Cisco advises setting the multiple-login service parameter to Auto Logout so agents do not remain logged in to devices, avoiding a 'shared line' error for the next agent 58.
Intra-cluster Maximum Login Time: Accepts values from 0:00 to 168:00 in HHH:MM format 44.
Maximum Concurrent Requests: Limits simultaneous login and logout operations to safeguard system resources, defaulting to 5 43.
Extension Mobility Cache Size: Controls the device cache retained by the service; it defaults to 10000, with a minimum of 1000 and a maximum of 20000 4. Logged-in user information is cached for 2 minutes 57.
Allow Proxy and Trusted List of IPs: Setting Allow Proxy to True permits login and logout operations routed through a web proxy 2. The Trusted List of IPs parameter takes hostnames or IP addresses separated by semicolons for source IP validation 56.

The EM troubleshooting section lists login errors including Authentication Error (201), Blank User ID or PIN (202), User Profile Absent (205) and User Logged in Elsewhere (25) 36.

Cross-cluster Extension Mobility

Extension Mobility Cross Cluster (EMCC) gives users EM functionality while letting them move from their home cluster and log in to a temporary phone on a remote visiting cluster 10. In cloud environments, Webex Calling provides Hoteling as a counterpart to temporarily load a guest user's calling profile onto a host phone, though the Control Hub documentation does not mention Unified CM Extension Mobility 60.

Extension Mobility Cross Cluster (EMCC)

EMCC allows users to travel from their home cluster and log in to a physical phone on a remote visiting cluster 10. The visiting phone registers directly to the user's home cluster and applies home cluster settings 22.

EMCC deployment characteristics include:

Registration and Device Limits: Unified CM supports a MaxPhones value of 60,000, where EMCC devices count double according to the formula: Phones + (2 x EMCC devices) = MaxPhones 16. The physical phone device name must not be configured in both clusters, or login fails with duplicate device error 37 11. IPv6-only phones are not supported; devices must use IPv4 or dual-stack addressing 14.
User and Cluster Provisioning: The home cluster user must have the Enable Extension Mobility Cross Cluster check box selected; failure to do so yields login results 31 or 38 12. If the home cluster lacks an entry for the visiting cluster, login fails with result 35 13.
Certificates: Setup requires bulk certificate management where each cluster exports all certificates (Certificate Type All) to a shared SFTP server, consolidates them, and imports them back into each cluster 9.
Trunks and Routing: Local calls and E911 calls route through the visiting cluster's local PSTN gateways 15. Up to 2 SIP trunks are required: a PSTN Access SIP trunk routes outbound PSTN calls through visiting gateways, and an RSVP Agent SIP trunk handles RSVP-based call admission control 2027. A single trunk can combine both functions 27. Location-based CAC is unsupported, while RSVP-based CAC is supported 18.
Security and Parameters: EMCC operates with secure or nonsecure phone profiles across nonsecure or mixed-mode clusters, providing cross-cluster security by default 24. The feature parameter Default TFTP Server for EMCC Login Device specifies the TFTP server for remote login devices and has no default value 26. The intercom feature is not supported 17.

Extension Mobility Roaming Across Clusters (EMRAC)

EMRAC allows users to roam across clusters and handle calls even if their home cluster is offline 28. With EMRAC the phone registers only in the roaming cluster 22.

EMRAC requires at least Cisco Unified Communications Manager 12.0(1)SU1 30. Directory numbers are synchronised across clusters using ILS; if the hub ILS fails, spokes cannot synchronise until it recovers 29. Logins are restricted to superusers assigned to the Standard EM Roaming Across Clusters Super Users access control group, and superuser information must be shared across all clusters 32. Superusers may log in from multiple devices within the same cluster, but cannot do so across clusters 31.

Applicability

EMRAC requires at least Cisco Unified Communications Manager 12.0(1)SU1 30.

What remains uncertain

How UCM-to-Webex Calling migration tools treat Extension Mobility device profiles regarding Hoteling or hot desking is not covered by the sources below. Compliance with Kari's Law and RAY BAUM'S Act dispatchable location requirements under EMCC is not covered by the sources below. Webex Calling hot desking sign-in mechanisms (such as QR codes or voice portals) as a cloud counterpart to Extension Mobility are not covered by the sources below. Extension Mobility login and logout throughput rates and scaling limits per node are not covered by the sources below. Specific phone models and protocols (SIP vs SCCP) supported under EMCC are not covered by the sources below. Release 15 SU release-note modifications impacting Extension Mobility or EMCC are not covered by the sources below. Whether an HTTPS port 8443 URL is documented for the main Extension Mobility phone service in Release 15 is not covered by the sources below. The factory default value of the Intra-cluster Maximum Login Time parameter is not covered by the sources below.