Which protocol does Jabber use to communicate with the Cisco IM and Presence server when instant messages are sent and received?

MSNP (Microsoft Notification Protocol) is a proprietary protocol used by the legacy MSN Messenger client and is unrelated to Cisco Jabber or IM and Presence.

SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions) is an IM protocol built on top of SIP used by some enterprise systems, but Jabber does not use SIMPLE to communicate with the Cisco IM and Presence server.

XMPP (Extensible Messaging and Presence Protocol), defined in RFC 6120, is the protocol Cisco Jabber uses to communicate with the IM and Presence server on TCP port 5222 for instant messaging and presence subscriptions. Cisco IM and Presence acts as an XMPP server, and Jabber clients authenticate and exchange messages using this open standard.

OSCAR (Open System for Communication in Realtime) is AOL's proprietary protocol used by the legacy AIM and ICQ clients and has no role in Cisco communications.