tailieunhanh - Network Congestion Control Managing Internet Traffic phần 3

đạt được thông lượng cao nhất có thể trong khi vẫn duy trì một tỷ lệ tổn thất thấp và sự chậm trễ nhỏ. Tắc nghẽn phải được tránh vì nó dẫn đến hàng đợi tăng trưởng và tăng trưởng hàng đợi dẫn đến sự chậm trễ và mất, do đó, tránh tắc nghẽn "đôi khi được sử dụng. | 38 CONGESTION CONTROL PRINCIPLES too long as there should be no loss during the increase phase until the limit is reached while the bandwidth reduction due to multiplicative decrease is quite drastic. Another common problem is that some Internet providers offer a satellite downlink but the end-user s outgoing traffic is still sent over a slow terrestrial link or a satellite uplink with reduced capacity . With window-based congestion control schemes this highly asymmetric kind of usage can cause a problem called ACK starvation or ACK congestion in which the sender cannot fill the satellite channel in a timely fashion because of slow acknowledgements on the return path Metz 1999 . As we have seen in Section enqueuing ACKs because of congestion can also lead to traffic bursts if the control is window based. Mobility As users move from one access point base station cell. . . depending on the technology in use to another while desiring permanent connectivity two noteworthy problems occur 1. Normally any kind of link layer technology requires a certain time period for handoff during which no packets can be transmitted before normal operation can continue. 2. If the moving device is using an Internet connection which should be maintained it should keep the same IP address. Therefore mechanisms for Mobile IP come into play which may require incoming packets to be forwarded via a Home Agent to the new location Perkins 2002 . This means that packets that are directed to the mobile host experience increased delay which has an adverse effect on RTT estimation. This list contains only a small subset of network environments - there are a large number of other technologies that roughly have a similar influence on delay and packet loss. ADSL connections for example are highly asymmetric and therefore exhibit the problems that were explained above for direct end user satellite connections. DWDMbased networks using optical burst or packet switching may add delay overhead or even