Which service must you restart, in order to enable file transfers on the Cisco Unified Communications Manager IM and Presence server?

Cisco SIP Proxy handles SIP session signaling between endpoints and the IM and Presence server; it has no involvement in XMPP-based file transfer functionality.

Cisco Presence Engine processes presence subscriptions and NOTIFY publications but does not control or route file transfer sessions.

The Cisco XCP Router is the central service responsible for routing all XMPP-based traffic on the IM and Presence server, including file transfer requests which are negotiated via XMPP extensions. File transfer capability is governed by the XCP framework, so any configuration changes enabling file transfers require the XCP Router to be restarted before they take effect. Restarting this service reloads all XCP component configurations including file transfer settings.

Cisco Sync Agent synchronizes user, device, and licensing data between CUCM and IM and Presence Service and has no role in enabling or routing file transfers.