d96\d96n165.txt
                                                Alan Chambers
                                                7/9/96 11am
        Mapping the Problem Space
        -------------------------
        -2 basic services for (end-station) MAC users:
                -Ethernet
                -LLC
        These need to be supported over:
        -2 basic kinds of LAN:  -CSMA/CD
                                -"RING" (802.5. FDDI)
        -2 kinds of vLAN environment:   -Implicit
                                        -Explicit
                ===>
        -8 MAC-frame + encapsulation formats to consider
                 (2 * 2 * 2)
        -24 possible heterogeneous bridging functions 
                between the different LAN vLAN environments.
                ("one-way": 12 symmetrical two-way.)                1
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picture:        Circle, transected by two diagonal lines
                 extending beyond the edges of the circle,
                 determining 4 quadrants.
                -Upper Right half is "RING" environment
                -Lower left half is CSMA/CD environment
                -Upper left half is Implied tagging environment
                -Lower Right half in Explicitly tagging environment (Tagged)
 
                Each quadrant has 2 different services; 
                        -dashed lines: Ethernet
                        -solid lines: LLC.

                Quadrant denotations:
 
                                (Ring,Implied)
                        E|R,I  ----  Enet, Ring, Implied
                        L|R,I  ____  LLC, Ring Implied
 
E|C,I  ----  Enet, CSMA/CD, Implied             E|R,T  ---- Enet, Ring, Tagged
L|C,I  ____  LLC, CSMA/CD, Implied              L|R,T  ____ LLC, Ring, Tagged

                        E|C,T  ----  Enet, CSMA/CD, Tagged
                        L|C,T  ____  LLC, CSMA/CD, Tagged

Figure 1: Services and Environments                                 2
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picture:

Figure 2: Heterogeneous Bridging Functions                          3
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Frame Formats

E|C,I                   DA,SA,                PT,data
E|C,T                   DA,SA,VT,VI,          PT,data
E|R,I                   DA,SA,SLZO,           PT,data
E|R,T                   DA,SA,SLZO,VT,VI,     PT,data  [A]  -or-
                        DA,SA,SLZO,VT,VI,SLZO,PT,data  [B]

L|C,I                   DA,SA,      Len,data
L|C,T                   DA,SA,VT,VI,Len,data
L|R,I                   DA,SA,data

L|R,T                   DA,SA,SLZO,VT,VI,Len*,data   -or-
                        DA,SA,SLZO,VT,VI,SLZO,data  

where   SLZO=SNAP LLC header and zero OUI (AA-AA-03-00-00-00)
        VT=vLAN ethertype
        VI=Rest of vLAN tag                                         4
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Bridging Functions

B1:     (vLAN free)
        802.1D conversion for L                         |
        RFC 1042 encapsulation/decapsulation for E      | 8021.H
        (or 802.1H bridge tunnel, if required)          |
B2:     (vLAN entry/exit, homogeneous CSMA/CD)
        802.1Q will specify tagging to be inserted/removed
B3:     (combined vLAN entry/exit, CSMA/CD <--> Ring
        (tagged Ring, implied vLAN id on CSMA/CD)
        vLAN entry: [A] ==      vLAN entry in CSMA/CD followed by
                                RFC 1042 encapsulation.
        vLAN exit: [A] ==       RFC 1042 encapsulation followed by
                                vLAN exit in CSMA/CD
        vLAN entry: [B] ==      RFC encapsulation followed by vLAN
                                entry in Ring domain (10-octet vLAN 
                                instead of 4) for E frames.
                                Special double encapsulation, L frames
        vLAN exit [B] ==        vLAN exit in Ring domain followed by
                                RFC 1042 decapsulation, for E frames.  
                                L frames need special double decapsulation.
--------------------------------------------------------------------5
B4:     (tagged vLAN, CSMA/CD <--> Ring)
        for [A]         802.1D conversion for L frames  |
                        RFC encapsulation for E frames  |       802.1H
        for [B]         New double encapsulation, conversion in
                        place on 802.1H operation
 
B5:     (vLAN entry/exit. homogeneous Ring)
        802.1Q will specify insertion.removal of vLAN tags.
        for [A]         4-octet tag (E-frames)
                        12-octet (tag & length) (L frames)
        for [B]         10-octet tag (E frames)
                        10-octet tag plus 8 octet extra encapsulation
                        (L frames)                                  6
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B6:     (combined vLAN entry/exit, CSMA/CD <-->Ring
        (tagged CSMA/CD, implied vLAN id on Ring
vLAN entry:     -RFC 1042 decapsulation followed by vLAN entry in CSMA/CD, 
                for E frames
                -802.1D conversion followed by vLAN entry in CSMA/CD, 
                for L frames
(A/B not relevant since no tagging on Ring)                         7