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Packets Out of Order

Posted on 2005-04-27
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Last Modified: 2012-06-21
We are having a serious problem with some RAD gear that takes TDM voice and
converts it to IP and then back to TDM.  The gear (which I don't look after or
know much about) keeps complaining about "packets out of order"..... the
connection is a pair of 6509's and a pair of 2924 switches in between them
using a 100 Meg LAN extension (via local telco).

I ran the ttcp utility between them and get the same issue with packets out of
order but I'm not sure why... looking for input on the below capture..

Thanks,

Paul

gw-6509#ttcp
transmit or receive [receive]:
perform tcp half close [n]:
receive buflen [8192]:
bufalign [16384]:
bufoffset [0]:
port [5001]:
sinkmode [y]:
rcvwndsize [0]:
ack frequency [2]:
delayed ACK [y]: n
show tcp information at end [n]: y

ttcp-r: buflen=8192, align=16384/0, port=5001
rcvwndsize=0, delayedack=no  tcp
ttcp-r: accept from 216.168.103.2
ttcp-r: 16777216 bytes in 107768 ms (107.768 real seconds) (~151 kB/s) +++
ttcp-r: 30866 I/O calls
ttcp-r: 0 sleeps (0 ms total) (0 ms average)
Connection state is CLOSEWAIT, I/O status: 1, unread input bytes: 1
Local host: 216.168.100.1, Local port: 5001
Foreign host: 216.168.103.2, Foreign port: 11006

Enqueued packets for retransmit: 0, input: 0  mis-ordered: 0 (0 bytes)

Event Timers (current time is 0x4195F05C):
Timer          Starts    Wakeups            Next
Retrans             1          0             0x0
TimeWait            0          0             0x0
AckHold             0          0             0x0
SendWnd             0          0             0x0
KeepAlive       32770          0      0x4196DAB8
GiveUp              0          0             0x0
PmtuAger            0          0             0x0
DeadWait            0          0             0x0

iss:  640436363  snduna:  640436364  sndnxt:  640436364     sndwnd:   4128
irs: 3499076369  rcvnxt: 3515853587  rcvwnd:       3976  delrcvwnd:    152

SRTT: 37 ms, RTTO: 1837 ms, RTV: 1800 ms, KRTT: 0 ms
minRTT: 16 ms, maxRTT: 300 ms, ACK hold: 200 ms
Flags: passive open, retransmission timeout, keepalive running
 gen tcbs, no delayed ACK

Datagrams (max data segment is 536 bytes):
Rcvd: 32771 (out of order: 688), with data: 32768, total data bytes: 16777216
Sent: 63452 (retransmit: 0), with data: 0, total data bytes: 0

gw-6509-1#ttcp
transmit or receive [receive]: transmit
Target IP address: 216.168.100.1
perform tcp half close [n]:
send buflen [8192]:
send nbuf [2048]:
bufalign [16384]:
bufoffset [0]:
port [5001]:
sinkmode [y]:
buffering on writes [y]:
show tcp information at end [n]: y

ttcp-t: buflen=8192, nbuf=2048, align=16384/0, port=5001  tcp  -> 216.168.100.1
ttcp-t: connect
ttcp-t: 16777216 bytes in 107768 ms (107.768 real seconds) (~151 kB/s) +++
ttcp-t: 2048 I/O calls
ttcp-t: 0 sleeps (0 ms total) (0 ms average)
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Local host: 216.168.103.2, Local port: 11006
Foreign host: 216.168.100.1, Foreign port: 5001

Enqueued packets for retransmit: 7, input: 0  mis-ordered: 0 (0 bytes)

Event Timers (current time is 0x418B9750):
Timer          Starts    Wakeups            Next
Retrans         32257         65      0x418B986F
TimeWait            0          0             0x0
AckHold             0          0             0x0
SendWnd             0          0             0x0
KeepAlive           0          0             0x0
GiveUp              0          0             0x0
PmtuAger            0          0             0x0
DeadWait            0          0             0x0

iss: 3499076369  snduna: 3515850218  sndnxt: 3515853586     sndwnd:   4128
irs:  640436363  rcvnxt:  640436364  rcvwnd:       4128  delrcvwnd:      0

SRTT: 300 ms, RTTO: 303 ms, RTV: 3 ms, KRTT: 0 ms
minRTT: 12 ms, maxRTT: 348 ms, ACK hold: 200 ms
Flags: higher precedence, retransmission timeout

Datagrams (max data segment is 536 bytes):
Rcvd: 63443 (out of order: 0), with data: 0, total data bytes: 0
Sent: 32887 (retransmit: 65), with data: 32885, total data bytes: 16836696
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Question by:kpmas
3 Comments
 
LVL 32

Assisted Solution

by:harbor235
harbor235 earned 750 total points
ID: 13875353
I would start by calling the RAD gear vendor, sounds like the mux and demux operations of the RAD device are injecting/reassembling packets out of order. Are you up on the latetest versions of code for these devices?


harbor235
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LVL 2

Author Comment

by:kpmas
ID: 13875430
Yes we are running the latest code.  We have talked to RAD directly and they claim this problem is always from not prioritizing voice traffic over data traffic.  While it's true that we don't run priority on these connections, the link is barely at 10% of it's capacity....

Also, relating to my above posting we are seeing packet loss on the link which would be related to the RAD issue we believe.  Have talked numerous times to the LAN extension provider (local telco) and they claim there is nothing wrong with the circuit.  I wanted to ensure our end was ruled out first...

Thanks.
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LVL 13

Accepted Solution

by:
eatmeimadanish earned 750 total points
ID: 13888588
This problem stems from either an improper setup of QOS in the network, or lacking it altogether.  What happens is data makes it way through the router bus, and then is divied out as info comes in from multiple sources.  Without QOS the data can stay in the buffer until it is grabbed while other data is past through.  The caching on some routers are ineffecient simply because TCP/IP is designed with that in mind.  You need to use some sort of QOS in order to force certain data through at the required interval.  
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