现代计算机网络讲义6(英语)+传输层.ppt

* * 6.6.4 Fast TPDU Processing (2)* (a) TCP header. (b) IP header. In both cases, the shaded fields are taken from the prototype without change. * * 6.6.4 Fast TPDU Processing (3) A timing wheel. * * 6.6.5 Protocols for Gigabit Networks (1) Using 32-bit sequence numbers will fail. Communication speeds have improved much faster than computing speeds. Go back n protocol performs poorly Delay limited rather than bandwidth limited in that long gigabit lines * * 6.6.5 Protocols for Gigabit Networks (2) Time to transfer and acknowledge a 1-megabit file over a 4000-km line. * * Some ways to deal with the problems Design for speed, not for bandwidth optimization To build fast network interfaces in hardware To avoid feedback The header should contain as few fields as possible, to reduce processing time The header and data should be separately checksummed The maximum data size should be large The protocol software To concentrate on the successful case To minimize copying time 6.6.5 Protocols for Gigabit Networks (3) * * 6.3.2 The Example Transport Entity(2) . The network layer packets type used in example * * 6.3.2 The Example Transport Entity (3) Each connection is in one of seven states Idle – Connection not established yet. Waiting – CONNECT has been executed, CALL REQUEST sent. Queued – A CALL REQUEST has arrived; no LISTEN yet. Established – The connection has been established. Sending – The user is waiting for permission to send a packet. Receiving – A RECEIVE has been done. Disconnecting – a DISCONNECT has been done locally. * * 6.3.2 The Example Transport Entity (4) Transitions occurs when the following events occur a primitive is executed a packet arrives the timer expires. A flow control mechanism different from the sliding window. When RECEIVE is called, a special credit message is sent to the sending machine When SEND is called, the transport entity checks to see if a credit has arrived on the specified connection. If so, the message is sent and th