Which type of multicast message is sent periodically by Maintenance End Points (MEPs) to monitor service connectivity?

The type of multicast message that is sent periodically by Maintenance End Points (MEPs) to monitor service connectivity is known as the Continuity Check Message (CCM). This message plays a critical role in the management of Ethernet networks, particularly for ensuring that paths remain operational and that connectivity between various endpoints is consistently maintained.

CCMs are periodically transmitted to verify that the connection between MEPs remains intact, allowing for the proactive identification of any service interruptions or faults. By sending these periodic messages, MEPs can locally detect issues and report them as needed, thus maintaining the integrity of the service across the Ethernet network.

The other options, while related to network maintenance and performance, do not fit the specific role that CCMs play in periodic connectivity monitoring. Link Trace Messages (LTMs) are used primarily for tracing the path through the network, while Service Level Agreement Messages (SLAMs) deal with the consistency of service parameters against defined agreements. Performance Monitoring Messages (PMMs) are typically focused on measuring performance metrics rather than on maintaining service connectivity directly. Therefore, CCMs are distinctly positioned as the ongoing connectivity monitor through periodic multicast messaging.