tcpdump mailing list archives
Re: DLT_LAPB value assignment
From: Guy Harris <guy () alum mit edu>
Date: Wed, 15 Aug 2007 11:11:11 -0700
Mirko.Karanovic () ttc ca 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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Current thread:
- DLT_LAPB value assignment Mirko.Karanovic (Aug 13)
- Re: DLT_LAPB value assignment Guy Harris (Aug 13)
- Re: DLT_LAPB value assignment Mirko.Karanovic (Aug 14)
- Re: DLT_LAPB value assignment Guy Harris (Aug 15)
- Re: DLT_LAPB value assignment Mirko.Karanovic (Aug 17)
- Re: DLT_LAPB value assignment Guy Harris (Aug 17)
- Re: DLT_LAPB value assignment Fulko Hew (Aug 17)
- Re: DLT_LAPB value assignment Mirko.Karanovic (Aug 14)
- Re: DLT_LAPB value assignment Guy Harris (Aug 13)