I would disagree with the statement below. Ethernet, Token Ring etc are
interacting with the upper layers. For example Ethernet II has an Ethertype
value that identifies the upper layer for 0x0800 is IP, the same goes for
DSAP/SSAP values in the 802.3 header. The OSI layers are somewhat
independent of each other except at the borders where they interact. For IP
the interaction between the layer 3 and higher uses a Protocol ID field in
the header to specify TCP UDP EIGRP etc.
Regarding Frame Relay this is done in the encapsulation part. For example if
you would use the IETF encapsulation method you (the system) would use a
NLPID that identifies the upper layer protocol. For more info on this see
http://andrew2.andrew.cmu.edu/rfc/rfc1490.html . Cisco uses a proprietary
encapsulation as well where 2 bytes are used for indicating packet type.
Willy Schoots
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Rik Guyler
Sent: Thursday, February 01, 2001 3:29 PM
To: Cisco Groupstudy (E-mail)
Subject: RE: Frame Relay
Layer 2
Seriously, FR is a Layer 2 protocol, as is Ethernet, Token Ring, etc. As
those other protocols support numerous Layer 3 (or higher) protocols, so
will FR. The beauty of the OSI model is that there is separation of the
layers without too much interaction between them. In other words, the Layer
4 datagrams get encapsulated into the Layer 3 packets, which in turn get
encapsulated into Layer 2 frames. FR doesn't care for the most part what is
"inside" the Layer 3 stuff coming down the pipe. ;-}
Rik
-----Original Message-----
From: Pierre-Alex [mailto:[EMAIL PROTECTED]]
Sent: Thursday, February 01, 2001 8:41 AM
To: [EMAIL PROTECTED]
Subject: Frame Relay
What element in a frame relay packet allows support for multiple protocols?
Pierre-Alex
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