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When 3 Duplicate Acks arrive TCP halves its congestion window, but when only 1 or 2 Duplicate Acks arrives what does TCP do ? Does it increase the congestion window like any other non duplicate Ack ?
That reaction to 3 duplicate acks is in TCP Reno. When it receives 1 or 2 duplicate ACK's it shouldn't do anything. The increase of the congestion window occurs after original ACK's are received because they indicate the communication is good and TCP is tries to get to the maximum possible throughput.
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I am reading about ipv4 and I wonder how scientist determine the perfect size of packet for example here in RFC 791 said 512 B for payload + 64 B for ip-header
how they do that?
also what parameters they considered?
Another question is that why until now this is the same as that time?? how it still working properly, even today it get smaller!
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A packet contains an IPv6 header with no options and a 20-byte TCP header. Is the IPv6 packet here smaller than the Ethernet minimum packet size, and, if so, by how much?
Yes, the example that you give is smaller than the minimum Ethernet frame size; packet refers to things at Layer 3 and above, frames to layer 2.
The minimum frame size is 64 bytes. An Ethernet frame consists of 14 bytes of Ethernet header and a 4 byte trailer (Frame Check Sequence). This leaves 46 bytes (64 - 14 - 4). Note that you will not be able to see the trailer in any typical sniffer; the network card will not deliver it to the networks stack of the operating system.
The TCP/IP packet that you have described would be 40 bytes in length. This means that the remaining 6 bytes will consist of padding.
I leave it to you to apply the same logic to figuring out the size of an IPv6 header/packet.
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Closed 9 years ago.
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how is the smallest value for tcp_rmem_default and tcp_wmem_default? Becauase im doing tcp tuning and my windows size is 6250 bytes (10mbit bandwith, delay 5ms and loss %0.00001) so i put tcp_rmem_default='6250' and tcp_wmem_default='6250' but it didn't work and decreased troughput. Then i put tcp_rmem_default='65536' and tcp_wmem_default='65536'and increase the Throughput, but this value default. Also i calculate windows size with 10mbit bandwith and delay 5ms and the result was 6250 bytes! So i can't understand! I hope someone can help me! Sorry for my English
I calculate windows size with 10mbit bandwith and delay 5ms and the result was 6250 byte
No it isn't.
bandwidth = 10Mbits/s = 10*1024*1024/8 bytes/s = 1310720 bytes/s
delay = 5ms = 0.005s
product = 1310720*0.005 = 6553.6
However 6250 is far too small for a TCP send or receive buffer, and has been for many years. Linux probably agrees and enforces a higher minimum.
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I've been asked in a assignment to analyze a packet trace and determine what kind of VNIC the user has on his or her machine. I'm finding this to be quite difficult however; I'm not quite sure what to look for. I'd appreciate getting pointed in the right direction. I mean whether the connection is through ethernet or a wireless 802.11 card
If you have the capture file with you already then open the file with wireshark, and on the display filter type "wlan", then click Apply to filter out 802.11 packets. The display filter expression for ethernet is "eth". If there are any packets on display after you apply the display filter, then there were packets that used the protocol. You can look into the packets with Wireshark to see the ethernet II or 802.11 header.
You can download some sample captures of 802.11 and Ethernet II from http://wiki.wireshark.org/SampleCaptures.
Do you mean the manufacturer of the Ethernet/WLAN card? The first 6 bytes of the Ethernet address are called the Organization Unique Identifier, and you can look them up here:
http://standards.ieee.org/regauth/oui/index.shtml
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TCP and UDP(sometimes) use a simple checksum to make sure the contents are correct.
What I want to know is any empirical data or estimate, of how often a packet is corrupted, but has the correct checksum for a person with a standard computer and internet connection.
Now I know that this probably all varies widely with ISP quality, hardware quality, and more, but I just want to hear any information on this.
You're asking how long a piece of rope is. In general, unless there's something wrong, the error rate should be less than 10-7. On the other hand, wireless, 3G, and such can have significantly higher error rates.
This Google search will show you there's a lot of literature.
From Microsoft Research,
Traces of Internet packets from the
past two years show that between 1
packet in 1,100 and 1 packet in 32,000
fails the TCP checksum, even on links
where link-level CRCs should catch all
but 1 in 4 billion errors. For certain
situations, the rate of checksum
failures can be even higher: in one
hour-long test we observed a checksum
failure of 1 packet in 400. We
investigate why so many errors are
observed, when link-level CRCs should
catch nearly all of them.
http://academic.research.microsoft.com/Paper/22436.aspx
Basically transmit 100MB+ over a typical Internet connection and you are very likely to see a silent failure.