On 4 Jul, 17:25, mark.berg...@thales-is.com wrote:
> I have a TCP/IP socket connection from a Linux machine (RHEL 4) to a
> Terminal Server port, with data going back and forth to equipment at
> the other end of a serial line. Every few hours, the Terminal Server
> stops transmitting the data down the serial line, and stops replying
> to the Linux machine.
> In netstat, I see the queue to the Terminal Server port building up,
> and the light on the Terminal Server for the physical port stops
> flashing.
> If I close and reopen the socket, all is OK.
>
> If I connect my previous system (Tru64) to the Terminal Server, it
> works fine, with no pauses.
>
> Any ideas?

I would start with tcpdump'ing the connection an analyzing the output
around the point when it stops.

On 4 Jul, 20:24, Maxim Yegorushkin
wrote:
> On 4 Jul, 17:25, mark.berg...@thales-is.com wrote:
> > Every few hours, the Terminal Server stops transmitting the data
> > down the serial line, and stops replying
> > In netstat, I see the queue to the Terminal Server port building up,

> I would start with tcpdump'ing the connection an analyzing the output
> around the point when it stops.

Right, when I noticed the link quiet yesterday, I ran tcpdump - got
one line printed, then a big pause (nearly a minute):

# tcpdump host ts03 and port port14
tcpdump: verbose output suppressed, use -v or -vv for full protocol
decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
16:54:21.363443 IP NN.46215 > ts03.port14: P 3797484301:3797484305(4)
ack 953507769 win 5840

during this time, tcpdump showed queue building up:
# netstat | grep ts03
tcp 0 0 NN:46625
ts03ort02 ESTABLISHED
tcp 0 0 NN:45509
ts03ort15 ESTABLISHED
tcp 0 444 NN:46215
ts03ort14 ESTABLISHED
# netstat | grep ts03
tcp 0 0 NN:46625
ts03ort02 ESTABLISHED
tcp 0 0 NN:45509
ts03ort15 ESTABLISHED
tcp 0 532 NN:46215
ts03ort14 ESTABLISHED

(After that, tcpdump started outputting, but port14 disappeared from
netstat - it could be that my application tries a different port at
this point, I'd need to check:
16:55:18.426493 IP NN.46215 > ts03.port14: FP 4:836(832) ack 1 win
5840
16:55:18.428453 IP NN.46687 > ts03.port14: S 864774909:864774909(0)
win 5840
16:55:18.428726 IP ts03.port14 > NN.46215: . ack 0 win 3584
16:55:18.430105 IP ts03.port14 > NN.46687: R 0:0(0) ack 864774910 win
0
16:55:19.431559 IP NN.46688 > ts03.port14: S 874636630:874636630(0)
win 5840
16:55:19.432999 IP ts03.port14 > NN.46688: R 0:0(0) ack 874636631 win
0
16:55:20.435416 IP NN.46689 > ts03.port14: S 872546385:872546385(0)
win 5840 )

TIA
Mark

On Wed, 04 Jul 2007 09:25:41 -0700, mark.bergman wrote:

> I have a TCP/IP socket connection from a Linux machine (RHEL 4) to a
> Terminal Server port, with data going back and forth to equipment at
> the other end of a serial line. Every few hours, the Terminal Server
> stops transmitting the data down the serial line, and stops replying
> to the Linux machine.
> In netstat, I see the queue to the Terminal Server port building up,
> and the light on the Terminal Server for the physical port stops
> flashing.
> If I close and reopen the socket, all is OK.
>
> If I connect my previous system (Tru64) to the Terminal Server, it
> works fine, with no pauses.

Some wild guesses, since you seem to be stuck...
IIRC the (ds90?) terminal servers have a way of
converting TCP(options?) into serial flow-control.
(you can even specify "hard" or "soft" flow-control)
Maybe the flow control is just stuck in a XOFF-like state.
(does the initialisation/connection build-up differ between TRU64 and
linux?)
BTW: once it is booted&up you can log into the ds90 and
check/alter the status/settings of it's ports.

Thought 1: keep-alive/idle (but that would probably disconnect the serial
session)
Thought 2: telnet options negotiation.
Thought 3: CR/LF handling.
Thought 4: ARP/routing/RARP. /subnetting/
Thought 5: MSS/fragmentation.

HTH,
AvK