[EMAIL PROTECTED] wrote:
2Q: Or would it also contain an extra flag to
indicate whether the packet is a DTE->DCE or DCE->DTE packet?
2A: LAPB contains direction ( DCE to DTE or vice versa) encoded in the
Address byte.
Actually, what X.25 (10/96) says is:
Frames containing commands transferred from the DCE to the DTE will
contain the address A for the single link operation and address C for
the multilink operation.
Frames containing responses transferred from the DCE to the DTE will
contain the address B for the single link operation and address D for
the multilink operation.
Frames containing commands transferred from the DTE to the DCE shall
contain the address B for the single link operation and address D for
the multilink operation.
Frames containing responses transferred from the DTE to the DCE shall
contain the address A for the single link operation and address C for
the multilink operation.
with the address A being 0x03, B being 0x01, C being 0x0F, and D being
0x07, so, for example, DCE->DTE frames can contain any one of those four
addresses, as can DTE->DCE frames.
I.e., for frames going in a given direction, the address encodes whether
the frame is a request or a response and whether single-link or
multilink operation is being used.
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