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X25 versus Frame Relay

The most important thing to remember with X25 is that it was a predecessor Frame Relay.

If one thinks back to when X25 was in it's prime, digital technology was still emerging and the quality of service of lines, both analogue and digital was far from what it is today. Therefore X25 was created with the intention to operate up to the 3rd level of the OSI model.

Frame Relay only operates at the first two layers of the OSI model. FR is basically "dumb" and relies upon customer equipment or DTE gear to monitor and govern flows and do error correction.

FR call control signalling is carried out separate from the actual data connection. This eliminates nodes having to store tables of routing information
An entire OSI layer is non-existent with FR
There is no low or hop control, or error correction. Other applications operating above FR must carry this out.
FR can operate upto 2Mbps (32 timeslots), rather than the paltry 64kbps of X25 (1 timeslot).

Comparison of X25 and Frame Relay
...	X25	FR
Multiplexing of virtual circuits	Y	Y
Port Sharing	Y	Y
Sensitive to Protocols	Y	No
Efficient with Bursty traffic	Y	Y
High volume of Data	No	Y
Transmission Speed	Slow/Med	Med/Fast
Delay	High	Low

OSI Layer 7: Application

OSI Layer 6: Presentation

OSI Layer 5: Session

OSI Layer 4: Transport

OSI Layer 3: Network

OSI Layer 2: Data Link

OSI Layer 1: Physical

the Open Systems interconnection model

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