When a Mobile and Remote Access (MRA) client logs in and uses phone services, the Cisco Expressway-E and Expressway-C pair proxies specific protocols. The initial login, authentication, and retrieval of configuration/service information (such as from CUCM User Data Services) are handled over HTTPS. The Expressway pair proxies this secure web traffic from the external client to the internal Unified Communications servers. For call signaling, registration, and presence, MRA uses SIP. The Expressway pair acts as a SIP Back-to-Back User Agent (B2BUA), effectively proxying all SIP communications between the MRA client and the internal CUCM.

B. H.323: MRA does not utilize the H.323 protocol for endpoint registration or call signaling; it is exclusively a SIP-based solution for this purpose.
D. SCCP: MRA does not support SCCP (Skinny Client Control Protocol). Endpoints must be configured for SIP to register through an Expressway pair.
E. SRTP: SRTP (Secure Real-time Transport Protocol) is the media protocol. While media traffic is relayed through the Expressway-E, SRTP is not a signaling protocol that is proxied for login or service establishment.

1. Cisco Expressway Series Configuration Guide (X14.2)

"Mobile and Remote Access on Expressway

" Section: "MRA Prerequisites and Assumptions." The guide states

"MRA requires SIP-enabled endpoints. It does not support H.323 or SCCP endpoints." This confirms that H.323 and SCCP are incorrect.

2. Mobile and Remote Access Through Cisco Expressway Deployment Guide (X14.0)

"Solution Overview

" Section: "About Mobile and Remote Access." The document explicitly states

"The key components of the Mobile and Remote Access solution are: ... A secure traversal between the Expressway-C and the Expressway-E for SIP and HTTPS traffic." This directly supports the selection of SIP and HTTPS.

3. Cisco Collaboration System 12.x Solution Reference Network Designs (SRND)

Chapter: "Cisco Expressway

" Section: "Mobile and Remote Access." This document details the architecture

stating

"For MRA

the Expressway-C and Expressway-E provide secure firewall traversal for SIP registration

IM and Presence

and HTTPS-based services for Cisco Jabber and IP phone clients." This confirms that SIP and HTTPS are the core protocols proxied for MRA services.