There are several protocols that exist in the session layer. Although most protocols may originate in other layers, these protocols begin in part in the session layer:

• Real-Time Transport Control Protocol (RTCP): This works along with RTP to deliver control information to all participants in a call.
• Domain Name System (DNS): This resolves a hostname to an IP address in order for a session to take place.
• Point-to-Point Tunneling Protocol (PPTP): This creates a VPN by using a generic routing encapsulation tunnel to provide a more secure way to deliver data than using plain text.
• Remote Procedure Call (RPC): This allows a program to run a subroutine on another host on a shared network.

At the session layer, the PDU is data. The following is a summary of the session layer:

The session layer manages all aspects of a session that enable hosts to communicate in a conversation with one another. At this point, the data then moves to the transport layer, where it now becomes a segment that has the necessary port addressing in the transport layer header.