Frame relay is a synchronous HDLC protocol based network. Data is sent in HDLC packets, referred to as "frames". The diagram below of an HDLC frame may be familiar, since without adding specific definitions of how the Address, Control and CRC is used, the diagram is applicable to IBM's SDLC, to X.25, to HDLC, to Frame Relay, as well as other protocols.
Address Control Data CRC Error Correction
The protocol is similar to that of an X.25 network, except all circuits are permanently assigned
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https://www.dcbnet.com/notes/framerly.html
this is for Frame Relay in detail ..
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Routher is a device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect.
Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.