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TCP global synchronization

Discussion in 'Networks' started by cobirad, May 28, 2010.

  1. cobirad

    cobirad Bit Poster

    Routers on the Internet normally have packet queues, to allow them to hold packets when the network is busy, rather than discarding them.
    Because routers have limited resources, the size of these queues is also limited. The simplest technique to limit queue size is known as tail drop. The queue is allowed to fill to its maximum size, and then any new packets are simply discarded, until there is space in the queue again.
    This causes problems when used on TCP/IP routers handling multiple TCP streams, especially when bursty traffic is present. While the network is stable, the queue is constantly full, and there are no problems except that the full queue results in high latency. However, the introduction of a sudden burst of traffic may cause large numbers of established, steady streams to lose packets simultaneously.
    TCP has automatic recovery from dropped packets, which it interprets as congestion on the network (which is usually correct). The sender reduces its sending rate for a certain amount of time, and then tries to find out if the network is no longer congested by increasing the rate again subject to a ramp-up. This is known as the slow-start algorithm.
    Almost all the senders will use the same time delay before increasing their rates. When these delays expire, at the same time, all the senders will send additional packets, the router queue will again overflow, more packets will be dropped, the senders will all back off for a fixed delay... ad infinitum.
    This pattern of each sender decreasing and increasing transmission rates at the same time as other senders is referred to as "global synchronization" and leads to inefficient use of bandwidth, due to the large numbers of dropped packets, which must be retransmitted.
  2. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

    The source..


    Certifications: C&G Electronics - MCSA (W2K) MCSE (W2K)
  3. cobirad

    cobirad Bit Poster

    Yeah you're correct thats the source.Its Actually a good article isn't it ?
  4. zebulebu

    zebulebu Terabyte Poster

    You've missed the point. Just chucking a paragraph of text up on a public forum without citing its source as provenance is extremely bad form.
    Certifications: A few
    WIP: None - f*** 'em

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