FYI - Media Frame Types
-----------------------

The following information, adapted from several pages of the 'Open Data-Link
Interface Developer's Guide for NetWare 386 Server Drivers', gives the Media
Frame Types for ARCNET, Ethernet, and Token Ring.

Additional notes are supplied in between the descriptions of each Frame
and at the end of the document.


ARCNET
------

*       Source Address
*       Destination Address
*       Long Packet Flag (Set to 00h if this is a Long Packet)
*       Byte Offset
***     )
***     )
.       ) Unused
.       )
***     )
***     )
*       Protocol Type
*       Split Flag (Set to a number other than FFh if this is a Long Packet)
**      Packet Sequence Number
.
.       Protocol Header & Data
.

Short Packets     : Byte Offset <> 00h
Long Packets      : Long Packet Flag = 00h, Split Flag <> FFh
Exception Packets : Long Packet Flag = 00h, Split Flag = FFh

A Long Packet is defined as one between 253 and 504 bytes

Note that Source and Destination Address are only 1 byte (00h to FFh), which
is the reason for ARCNETs limitation of 255 decimal (FFh) nodes per LAN.


ETHERNET 802.2
--------------

******  Destination Address                 \
******  Source Address                      | 802.3 Header
**      Frame Length                        /
*       DSAP                                \
*       SSAP                                | 802.2 Header
*       Control                             /
.
.       Protocol Header & Data
.

In Ethernet 802.2 the Frame Length field contains a value less than 1500
decimal (05DCh).



ETHERNET RAW 802.3
------------------

******  Destination Address                 \
******  Source Address                      | 802.3 Header
**      Frame Length                        /
**      Data (always FFFFh)
.
.       Protocol Header & Data
.

In Ethernet 802.3 the Frame Length field contains a value less than 1500
decimal (05DCh) and the first two bytes of Data must contain FFh.



ETHERNET II
-----------

******  Destination Address                 \
******  Source Address                      | Ethernet II Header
**      Frame Type (8137h for NetWare)      /
.
.       Protocol Header & Data
.

In Ethernet II the Frame Type field contains a value greater than 1500
decimal (05DCh). Examples of values in this field are :

0600h  -  XNS
0800h  -  IP
0805h  -  X25
0BADh  -  Banyan
809Bh  -  Appletalk
80D5h  -  SNA
8137h  -  NetWare
814Ch  -  SNMP



ETHERNET SNAP
-------------

******  Destination Address                 \
******  Source Address                      | 802.3 Header
**      Frame Length                        /
*       DSAP (always AAh)                   \
*       SSAP (always AAh)                   | SNAP Header
*       Control (always 03h)                |
*****   Protocol ID                         /
.
.       Protocol Header & Data
.

DSAP and SSAP fields are always set to AAh. The Control field is always 03h.



TOKEN RING 802.2
----------------

*       Access Control                      \
*       Frame Control                       | 802.5 Header
******  Destination Address                 |
******  Source Address                      /
*       Route Control Broadcast / Length
*       Route Control Direction
**      Route Designator 1
**      Route Designator 2
.
.
.
*       DSAP                                \
*       SSAP                                | 802.2 Header
*       Control                             /
.
.       Protocol Header & Data
.



TOKEN RING SNAP
---------------

*       Access Control                      \
*       Frame Control                       | 802.5 Header
******  Destination Address                 |
******  Source Address                      /
*       Route Control Broadcast / Length
*       Route Control Direction
**      Route Designator 1
**      Route Designator 2
.
.
.
*       DSAP (Always AAh)                   \
*       SSAP (Always AAh)                   | SNAP Header
*       Control (Always 03h)                |
*****   Protocol ID                         /
.
.       Protocol Header & Data
.

DSAP and SSAP fields are always set to AAh. The Control field is always 03h.


Notes
-----

The number of asterisks (*) indicates the number of bytes reserved for each
piece of information. A number of full stops (.) indicates a variable amount
of data at that position.

Hexadecimal values are represented in the form NNh where each NN represents
one byte. Thus, for example, FFFFh is two bytes representing 65535 decimal.

SNAP Packets, whether Ethernet or Token Ring, always have DSAP and SSAP
fields set to AAh and the Control field set to 03h.


DSAP = Destination Service Access Point
SSAP = Source Service Access Point
SNAP = Simple Network Access Protocol



FRAME.TXT

Marcus Williamson
Novell Consulting (Europe)
Duesseldorf, Germany
71333,1665