RAS Frame Format Diagram

 Last reviewed: May 8, 1997
Article ID: Q103026

The information in this article applies to:
  • Microsoft Windows NT operating system, version 3.1
  • Microsoft Windows NT Advanced Server, version 3.1

Below is a diagram indicating the format of Remote Access Service (RAS) frames: 

                  +---+---+---+---+------  --------+---+---+---+
   RAS 1.0 frame  |SYN|SOH| LENGTH| <--> Data <--> |03h|  CRC  |
   asybeui frame  +---+---+---+---+------  --------+---+---+---+
                       ^
                       |--SOH_BCAST or SOH_DEST

                  +---+---+---+---+---+------  --------+---+---+---+
   RAS 2.0 frame  |SYN|SOH| LENGTH|COH| <--> Data <--> |ETX|  CRC  |
   asybeui frame  +---+---+---+---+---+------  --------+---+---+---+
   with compress       ^
                       |--(SOH_BCAST|SOH_COMPRESS)
                          or (SOH_DEST|SOH_COMPRESS)

                  +---+---+---+---+---+------  --------+---+---+---+
   RAS 2.0 frame  |SYN|SOH| LENGTH|COH| <--> Data <--> |ETX|  CRC  |
   asybeui frame  +---+---+---+---+---+------  --------+---+---+---+
   with compress   ^   ^
   with XON/XOFF   |   |--(SOH_BCAST|SOH_COMPRESS)
                   |      or (SOH_DEST|SOH_COMPRESS)
                   |
                   +-------(SYN | SYN_XONXOFF)


                  +---+---+---+---+---+---+-----  -------+---+--+--+
   RAS 2.0 frame  |SYN|SOH| LENGTH| E-TYPE|<--> Data <-->|ETX| CRC |
   with TCP/IP    +---+---+---+---+---+---+-----  -------+---+--+--+
   no compress         ^
                       |--(SOH_BCAST|SOH_TYPE) or (SOH_DEST|SOH_TYPE)

                  +---+---+---+---+---+---+---+----  ------+---+--+--+
   RAS 2.0 frame  |SYN|SOH| LENGTH| E-TYPE|COH|<-> Data <->|ETX| CRC |
   with TCP/IP    +---+---+---+---+---+---+---+----  ------+---+--+--+
   and compress        ^
                       |--(SOH_BCAST|SOH_TYPE|SOH_COMPRESS)
                          or (SOH_DEST|SOH_TYPE|SOH_COMPRESS)

   NOTE: Compression is performed after COH and before ETX. This does
   mean that E-TYPE is not compressed. Also, when CRC is performed,
   SOH through ETX (inclusive) is checked. ETX is included because RAS
   1.0 also checked ETX.

   SYN          = 0x16
   SOH_BCAST    = 0x01
   SOH_DEST     = 0x02
   SOH_TYPE     = 0x80
   SOH_COMPRESS = 0x40
   SYN_XONXOF   = 0x20
   CRC          = 16 bit CRC polynomial (Big-Endian format)
   LENGTH       = length of Data part of frame (two-byte Big-Endian)

Additional query words:
Keywords : kbnetwork ntras NTSrvWkst
Version : 3.1
Platform : WINDOWS

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Last reviewed: May 8, 1997
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