Subject: Re: Flow Control Issues

From: Choon Lee <[email-masked]>
Date: Tue, 10 Aug 1993 15:14:55 -0700

This would preserve the TCP connection between two DLSw nodes at 2. 
I am still interested in hearing about responses to your earlier suggestion
of having a Transport connection for each DL circuit. That would really
simplify things.

Regards,
Choon Lee
3Com Corp.

>> > 
>> > 
>> > Hi,
>> > 
>> > If the proposed pacing scheme were to work well, we need to figure out a way
>> > by which the the IPM could be delivered to the peer without the possibility
>> > of a closed TCP send window. One way to do that is to ensure that the
>> > receiving TCP always has receive window open. The other way is to have a
>> > "control channel" which is used to send only control messages.
>> > 
>> > Consider the connection,
>> > 
>> > 
>> >         --------------                         --------------
>> >         |             |        1              |               |
>> >         |               ======================>               |
>> >         |             |            2          |               |
>> >         |    A        |<--------------------- |    B          |
>> >         |             |                       |               |
>> >         |             |                       |               |
>> >         |             |        3              |               |
>> >         |              <===================== |               |
>> >         |             |            4          |               |
>> >         |             |---------------------->               |
>> >         |-------------                         ---------------
>> > 
>> > 
>> > 1 and 2 form a full duplex  TCP connection while 3 and 4 form another. 
>> > Whenever A wants to send data to B it sends on 1 and B sends data to A on 3.
>> > We could use 2 and 4 for control messages. Whenever a circuit in A is
>> > beginning to get congested, A can send an IPM to B on 4 and B can respond on
>> > 2. This way we have a larger bandwidth for control messages and we don't have
>> > to really depend upon the transport flow control. This also ensures that the
>> > control messages which are important and are the basis for Dlsw flow control
>> > reach the peer faster. Thus we could use the existing transport connection
>> > scheme in the RFC and get around the "urgent data" problem.
>> > 
>> > If this suggestion is agreeable, we can explore other issues further with
>> > this approach and nail them.
>> > 
>> > 
>> > I had sent a mail sometime back regarding TCP connection management on July
>> > 30th. So far I have received only one response. If the existing implementors can come out and explain how this has been done or how it ought to be done, it 
>> > would be of great help to all of us so that we could avoid inconsistencies in
>> > implementation.
>> > 
>> > 
>> > Thanks,
>> > 
>> > 
>> > andy
>> > 
>> > 
>> > -- 
>> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> > | UUCP:  {ames,apple,sun,mtxinu}!excelan!andy         (Anand Subramaniam) |
>> > | INTERNET:  [email-masked]                          Ph : (408)-473-8413 |
>> > | " Now and then I go off in to my own little world; But they know me     |
>> > |   there"                                                                |
>> > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>> >

---

From: [email-masked] (Anand Subramaniam)
Date: Tue, 10 Aug 93 17:46:11 PDT

Hi,

What I was suggesting was to have a single TCP connection per DL connection.
This means we don't have to worry about the sharing of transport bandwidth
across many DL connections. This would also simplify flow control to a great
extent as we can exploit the available transport level flow control. OSI
seems to follow this strategy for X400 by using a transport connection per
network connection(TP-0).  The multiplexing class TP-2 is used only when the
traffic is not very heavy.

We would need only one port which is a listener port per DLSw node.

As far as the responses, I haven't received any. We can accelerate the
discussion on this topic and arrive at one conclusion or the other.

Regards,

andy