tailieunhanh - Satellite networking principles and protocols - p9

truyền hình vệ tinh băng thông quản lý tài nguyên Các hệ thống TDMA được sử dụng với chiều dài khung 20 ms được chia sẻ bởi các trạm mặt đất. Mỗi trạm mặt đất được giới hạn trong các khe thời gian tương ứng với dung lượng truyền dẫn cấp lên tối đa 960 tế bào (tương đương với 20,352 Mbit / s). TDMA chung định dạng | 270 Satellite Networking Principles and Protocols the packet was sent out and the acknowledgement returned as Mn and the average RTTn calculated with a weight factor a typically a 7 8 and RTT0 is set to a default value as RTTn aRTTn-1 1 - M The deviation is calculated with the same weight factor a as Dn aDn-1 1 - M - RTTn-1 Then the time out can be calculated as Timeout RTTn 4Dn We will now discuss some TCP enhancement techniques. These are optimised to deal with particular conditions in satellite network configurations but may have side effects or may not be applicable to general network configurations. It is also a great challenge for the enhancement to interwork with existing TCP implementations. TCP for transactions In a transaction service particularly for short data size and TCP session the utilisation is significantly affected by the connection set-up and connection close-down time. TCP uses a three-way handshake to set-up a connection between two hosts. This connection set-up requires one or RTT depending upon whether the data sender started the connection actively or passively. This start-up time can be eliminated by using TCP extensions for transactions T TCP . After the first connection between a pair of hosts is established T TCP is able to bypass the three-way handshake allowing the data sender to begin transmitting data in the first segment sent along with the SYN - synchronisation number . This is especially helpful for short request response traffic as it saves a potentially long set-up phase when no useful data are being transmitted. As each of the transactions has a small data size the utilisation of satellite bandwidth can be very low. However it has the potential for many TCP session hosts to share the same bandwidth to improve bandwidth utilisation. T TCP requires changes of both the sender and the receiver. While T TCP is safe to implement in shared networks from a congestion control perspective several security implications of .