On Fri, 26 Oct 2007 15:14:18 -0700, karthikbalaguru
<karthikbalaguru79@gmail.com> wrote:
>On Oct 27, 1:13 am, Aaron Leonard <Aa...@Cisco.COM> wrote:
>> ~ Hi,
>> ~
>> ~ How to avoid packet duplication ?
>> ~
>> ~ Thx in advans,
>> ~ Karthik Balaguru
>>
>> Implement sequence numbers.
>>
>> Refrain from transmitting packets.
>
>Like any other protocol, i use sequence number (for segmentation, re-
>assembly, re-transmit,
>transmission/reception)
>
>To put it in other way :
>If i am transmitting(Tx) 2 packets with sequence number 1 and sequence
>number 2.
>I should received only packets with sequence number 1 and sequence
>number 2 on the Receiver(Rx) side.
>But, i get 4 packets with sequence number 1 and another 4 packets with
>sequence number 2.
>I am sending only once(Only one time) the 2 packets with sequence
>number 1 and sequence number 2.
>Till the point it is going into the Air, i have only 2 packets.
>But at the reception end (after the Air travel), i get duplicated
>packtes in sequence.
>
>But, how does it get replicated(duplicated) on the receiver side ?
>(It is flooding my Receiver).
>
>Any ideas to avoid it ?
>
>Thx in advans,
>Karthik Balaguru
In wireless, duplicates and retransmissions are difficult to avoid.
The problem is that there receiving end is trying to acknowledge
reception of your packets 1 and 2. If the receiving end either does
not receive the packet *OR* the sending end does not receive the
ACK's, the sending end will retransmit the packets until TTL is
reached. Such retransmissions are difficult to prevent unless you
first deal with the interference, timing problems, broken firmware,
junk hardware, or other common causes of delivery failures. Note that
the retransmissions can happen at either layer 2 (MAC) or layer 3
(IP). Usually, they're all at the MAC layer, and not visible at the
IP layer. However, if you're seeing them at the IP layer, my
guess(tm) is that you have a broken IP stack at one end or the other.
A simple test to check for interference is with ping. Just ping the
IP address of the wireless access point or whatever unspecified piece
of wireless hardware you haven't bother to disclose. You should get a
very consistend 1 to 4 msec latency with no lost packets. However, if
the latency varies radically and there are lost packets, you probably
have an interference problem.
In the future, if you have a question, I suggest you supply:
1. What problem are you trying to solve?
2. What do you have to work with? (Hardware, software, versions,
numbers).
3. What have you done so far and what were the results?
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
jeffl@comix.santa-cruz.ca.us
#
http://802.11junk.com jeffl@cruzio.com
#
http://www.LearnByDestroying.com AE6KS
Avoiding Packet duplication 
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