COMMENT ⊗   VALID 00003 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002		      Format of an IMP message header (32 bit words)
C00007 00003		      Format of an IMP message header (36 bit words)
C00011 ENDMK
C⊗;
	      Format of an IMP message header (32 bit words)

    (In 1822, IMP-host header bits are numbered 1-96.  Here they are
     numbered starting at 0 in word 0.)

     0			 1		     2			 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-------+-------+---------------+-------+-+-----+---------------+
0   |unused | New   |  Destination  |unused |T|Ldr  |  Message	    |
    |	    | Format|  Network	    |	    |r|Flags|  Type	    |
    +-------+-------+---------------+-------+-+-----+---------------+
1   |  Handling     |  Destination  |	  Destination		    |
    |  Type	    |  Host	    |	  IMP			    |
    +---------------+-------+-------+-------------------------------+
2   |  Message ID	    |Sub-   |	  Message Length	    |
    |			    |Type   |				    |
    +-----------------------+-------+-------------------------------+


Internet (IP) header  (IHL = Internet header length, in 32-bit words)

     0			 1		     2			 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-------+-------+---------------+-------------------------------+
3   |Version|  IHL  |Type of Service|	       Total Length	    |
    +-------+-------+---------------+-----+-------------------------+
4   |	      Identification	    |Flags|	 Fragment Offset    |
    +---------------+---------------+-----+-------------------------+
5   |  Time to Live |	 Protocol   |	      Header Checksum	    |
    +---------------+---------------+-------------------------------+
6   |			    Source Address			    |
    +---------------------------------------------------------------+
7   |			 Destination Address			    |
    +-----------------------------------------------+---------------+
    |			 Options		    |	 Padding    |
    +-----------------------------------------------+---------------+


TCP header

     0			 1		     2			 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-------------------------------+-------------------------------+
8   |	       Source Port	    |	    Destination Port	    |
    +-------------------------------+-------------------------------+
9   |			     Sequence Number			    |
    +---------------------------------------------------------------+
10  |			 Acknowledgement Number			    |
    +-------+-----------+-+-+-+-+-+-+-------------------------------+
    |  Data |		|U|A|P|R|S|F|				    |
11  | Offset| Reserved	|R|C|S|S|Y|I|		 Window		    |
    |	    |		|G|K|H|T|N|N|				    |
    +-------+-----------+-+-+-+-+-+-+-------------------------------+
12  |		Checksum	    |	       Urgent Pointer	    |
    +-------------------------------+---------------+---------------+
    |			 Options		    |	  Padding   |
    +-----------------------------------------------+---------------+
13  |				  data				    |
    +---------------------------------------------------------------+


(IP and TCP options are optional.  Padding fills to 32-bit boundary.)

	      Format of an IMP message header (36 bit words)
			  (assuming no options)

     0			 1		     2			 3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-------+-------+---------------+-------+-+-----+---------------+-------+
0   |unused | New   |  Destination  |unused |T|Ldr  |  Message	    |Handling
    |	    | Format|  Network	    |	    |r|Flags|  Type	    |Type
    +-------+-------+-------+-------+-------+-+-----+-------+-------+-------+
1   Handling|  Destination  |	  Destination		    |  Message ID
     Type   |  Host	    |	  IMP			    |
    +-------+-------+-------+-----------------------+-------+-------+-------+
2    Message|Sub-   |	  Message Length	    |IP     |  IHL  |Type of
     ID     |Type   |				    |Version|	    |Service
    +-------+-------+-----------------------+-------+-------+-------+-------+
3    Type of|	       Total Length	    |	      Identification	    |
     Service|				    |				    |
    +-----+-+-----------------------+-------+-------+---------------+-------+
4   |Flags|	 Fragment Offset    |  Time to Live |	 Protocol   |Cksum
    +-----+-----------------+-------+---------------+---------------+-------+
5      IP Header Checksum   |	       Source Address
    +---------------+-------+-----------------------------------------------+
6    Source Address |		Destination Address
    +-------+-------+-----------------------+-------------------------------+
7   Dest Adr|	       Source Port	    |	    Destination Port	    |
    +-------+-------------------------------+-----------------------+-------+
8   |			     Sequence Number			    |ACK No.
    +-------------------------------------------------------+-------+-------+
9		 Acknowledgement Number			    |  Data | Reser-
							    | Offset| ved
    +---+-+-+-+-+-+-+-------------------------------+-------+-------+-------+
	|U|A|P|R|S|F|				    |
10  Rsvd|R|C|S|S|Y|I|		 Window		    |  TCP checksum
	|G|K|H|T|N|N|				    |
    +---+-+-+-+-+-+-+-----------------------+-------+-----------------------+
11    Cksum |	       Urgent Pointer	    |	   (beginning of data)
    +-------+-------------------------------+-------------------------------+