Frame Relay vs. X.25

There are various differences between X.25 and Frame Relay. The most significant are:

1. Call Control

X.25 connection establishment and release (call control) use in-band signaling within the same virtual channel used for user data transmission causing additional overhead. Frame Relay call control uses separate virtual channels identified by reserved DLCI using the LMI (Local Management Interface) protocol.

2. Routing vs. Switching

X.25 performs packet switching on OSI layer 3 (network layer); Frame Relay performs packet switching on OSI layer 2 (data-link). Frame Relay does not use any layer 3 protocol.

3. Flow Control

Frame Relay (FR) doesn't perform flow control between frame handlers (FR routers). X.25 routers have to acknowledge each frame; in case of frame errors frames have to be retransmitted and acknowledged. Frame Relay relies on flow control performed by higher layer protocols.