Terminal Server connection pauses; traffic building up on queue - TCP-IP

This is a discussion on Terminal Server connection pauses; traffic building up on queue - TCP-IP ; 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 ...

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Thread: Terminal Server connection pauses; traffic building up on queue

  1. Terminal Server connection pauses; traffic building up on queue

    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?
    TIA
    Mark


  2. Re: Terminal Server connection pauses; traffic building up on queue

    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.


  3. Re: Terminal Server connection pauses; traffic building up on queue

    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



  4. Re: Terminal Server connection pauses; traffic building up on queue

    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


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