2b1d5a A link disconnect message is sent to B from A.

                  2b1d5b A panic routine is called(error).

   2c Auxilliary Links

      2c1 Auxilliary links are established by a call to the monitor from
      a user program.

         2c1a The request must specify pertinent data about the desired
         link to the monitor

            2c1a1 The number of the primary link to B.

         2c1b The request for an auxilliary link must be made by a user
         program in each of the HOSTs (A and B).

         2c1c If Na > Nb, then HOST A proceeds to establish a link to
         HOST B in the manner outlined above (getlink).






 
RFC 2


         2c1d If Na<Nb, then A waits:

            2c1d1 For HOST B to establish the link (after looking to see
            if B has already established the corresponding link).

            2c1d2 For a specified amount of time to elapse.

               2c1d2a This means that HOST B did not respond to the
               request of HOST A.

               2c1d2b The program in HOST A and B should be able to
               specifiy the amount of time to wait for the timeout.

3 ERROR CHECKING

   3a All messages sent over the network will be error checked initally
   so as to help isolate software and hardware bugs.

   3b A checksum will be associated with each message, which is order
   dependent.

      3b1 The following algorithm is one which might be used:

         3b1a A checksum of length 1 may be formed by adding successive
         fields in the string to be checked serially, and adding the
         carry bit into the lowest bit position of the sum.

              +--------------+
              |              |
              +---FIELD 1----+

          ADD +--------------+
              |              |
              +----FIELD 2---+

            +-+--------------+
            | |              |
            +-+--------------+
              \
               \          +--+
          ADD   CARRY---> |  |
                          +--+

              +--------------+
              |              |
              +----RESULT----+

            3b1a1 This process is known as folding.




 
RFC 2


            3b1a2 Several fields may be added and folded in parallel, if
            they are folded appropiately after the addition.

              +---------+---------+---------+---------+
              | FIELD 4 | FIELD 3 | FIELD 2 | FIELD 1 |
              +---------+---------+---------+---------+

              +---------+---------+---------+---------+
              | FIELD 8 | FIELD 7 | FIELD 6 | FIELD 5 |
              +---------+---------+---------+---------+
            ADD
            +-+---------+---------+---------+---------+
            | |         |         |         |         |
            +-+---------+---------+---------+---------+