[ih] TCP RTT Estimator (JNC history site contents)

[Greg Skinner]

On Mar 27, 2025, at 12:41 PM, John Gilmore <gnu at toad.com> wrote:
> 
> Greg Skinner via Internet-history <internet-history at elists.isoc.org> wrote:
>> BTW, Jim Mathis' TIU implementation is available on Noel Chiappa's ana-3.lcs.mit.edu <http://ana-3.lcs.mit.edu/> site. [1]
>> The documentation is dated April 1979.
>> --gregbo
>> [1] http://ana-3.lcs.mit.edu/~jnc/tech/mos/
> 
> Noel's ana-3 site is dead now, but it has apparently moved to:
> 
>  http://mercury.lcs.mit.edu/~jnc/

Odd, because I have been able to access it.  Here is part of the documentation on TCP retransmission, from  http://ana-3.lcs.mit.edu/~jnc/tech/mos/docs/tiunv2.lpt:

     2.   Output Packet Processing          ______ ______ __________

[…]

         d.   Retransmission of Unacknowledged Text or Control               ______________ __ ______________ ____ __ _______


               At present, the TCP process gets signaled every second

and counts down the signals by using the WAKEUP counter in the TCB.

When this counter reaches zero, the retransmission is triggered; a new

value for the retransmission interval (RTXDLY) is calculated; and WAKEUP

is initialized to that value.  Currently, the new value for RTXDLY can

either be constant or increase linearly or exponentially with the number

of unsuccessful retransmissions of a packet.







                                  111

17 April 1979                  D R A F T                        at 11:10



               When the retransmission time-out expires, the TCP

determines whether the head of the retransmission queue has been

retransmitted the maximum number of times; if so, the remote TCP is

declared "not responding," and the connection is marked as suspended.  A

count is kept in the RETRY field of the TCB, is incremented on every

retransmission, and is reset to zero whenever a new packet has been

received.  If the connection is not in a usable state (i.e., if it is

attempting to open or close), the connection is aborted.


               After deciding to retransmit, the TCP checks the head of

the retransmission buffer to see whether it contains control or data;

these two cases are handled separately.  If it contains control, a

packet containing this control function is constructed and transmitted.

If it contains data, a packet is constructed that contains all the data

from the head of the retransmission buffer to its end or to the first

control function indicator, with the amount of data not exceeding the

maximum allowed in a single packet.  Thus the data packet boundaries are

not preserved.