引言

NWG/RFC 11 已在 UCLA 作了修改, 并将重新发布。在此期间, 似乎有必要报告一种新的控制报文格式, 它不使用 7 位 ASCII 字符传输方式。

所有 HOST-HOST 控制报文均由形如下式的 8 位字节序列构成:

   <control byte> <parameter byte l> ... <parameter byte n>

在任一给定报文中传输不止一条控制报文是合理的, 尽管这并非强制要求。

目前, UCLA 已定义 9 条控制报文; 下表连同其参数一并给出。解释是从发送主机的角度给出的。("L" 或 "Li" 表示 Link#, 均为二进制值。)

   Control byte     Parameter      Interpretation

    <0>             <L>           Please establish primary connection;
                                  our output link # is L

    <1>             <L,> <L2>     Please establish auxiliary connection
                                  parallel to our primary output link L.
                                  The auxiliary output link is L2.

    <2>             <L1> <L2>     DK primary.  Your primary output link
                                  to us was L; our primary output link
                                  to you is L2.

    <3>             <L1> <L2>     OK auxiliary.  Your auxiliary output
                                  link is Li, our auxiliary output link
                                  is L2.

    <4>             <L>           Not OK primary.  We cannot establish a
                                  primary connection.  Your primary
                                  output link number was L.

    <5>             <Li> <L2>     Not OK auxiliary.  We cannot establish
                                  an auxiliary connection.  Your primary
                                  output link no was L2.

    <6>             <L>           Please stop transmitting over link
                                  number L.  This is called the CEASE
                                  directive.

    <7>             <L>           We are CLOSING our output link number
                                  L.  You may get this message before
                                  the last message arrives over this
                                  link since control messages are higher
                                  priority than regular data messages.

    <8>             <L>           UNCEASE: that is, you may resume
                                  transmitting over output link number
                                  L.

每条控制报文都嵌入在相应的报文结构中, 例如:

               <-------------32 bits --------------->
               |           HEADER                   |
               |____________________________________|
               |      |       |           |         |
               | mark |  l    |  <L1>     |  <L2>   |
               |______|_______|___________|_________|
               |                 |                  |
               |     checksum    |     Padding      |
               |_________________|__________________|
                 typical control message (please
                 establish auxiliary link #L2
                 parallel to our primary link #l)

所有 HOST-HOST 控制报文的首部如下:

   0     3  4   7  8  9   10   14   LINK#      24              31
   _______________________________________________________________
   |       |      |     |       |               |////////////////|
   | FLAGS | TYPE |  H  |  SITE | 00000001      |////////////////|
   |_______|______|_____|_______|_______________|________________|

   where  FLAGS - 0000
          TYPE  - 0000 (regular message)
          H     - host #(0-3) at SITE (usually 0 for single HOST sites)
          SITE  - Site #
          LINK# - 00000001 (HOST-HOST control link)

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注: 本 RFC 由 Alison De La Cruz 于 12/00 转为机器可读形式, 以便录入在线 RFC 档案库。