Server Roles in CRM 2015

Server Role Group Server Roles
Front End Server 
Web Application Server
Discovery Web Service
Organization Web Service
Help Server
Back End Server
 Asynchronous Service
Sandbox Processing Service
SharePoint Integration Service
Deployment Administration Server
Deployment Tools
Deployment Web Service

Full Server Includes the Front End Server, Back End Server, and Deployment
Administration Server role groups

SQL Server A logical role that is set during installation. Not part of a Server Role Group.
SRS Data Connector (for
SQL Server Reporting
Services)