3. Buffer size and restrictions affect the size of the IP datagram. 1) IPv4 datagram, maximum size is 65535.2) The MTU specified by the hardware. The Ethernet MTU is a 1500-byte, slip-link 1006-byte or 296-byte 3-Path MTU. The smallest MTU in a path between two hosts. 1500 bytes Common path MTU4) IP datagram >mtu,ipv4 perform shard 5) IPV4,DF bits are set (not fragmented). When the router receives a IPV4 datagram that exceeds its outgoing link MTU size and has a DF bit set, it generates an error message that ICMPV4 "destination unreachable, fragmentation needed but DF bit set". The DF bit is used for Path MTU Discovery. 6) Minimum reassembly buffer size, IPv4 576 byte 7) TCP has an MSS that advertises to the peer TCP the maximum amount of TCP data that can be sent in each sub-section.
4.TCP Output Description: Call write call 1. When an application process calls write, the kernel copies all data from the buffer of the application process to the send buffer of the abbreviated socket. If the socket send buffer does not fit, the application process is put to sleep, and if all data in the application process buffer is assigned to the socket send buffer, the success is returned. 2. The successful return of a write call to a TCP socket simply means that we can reuse the original application process buffer and does not indicate that the TCP or application process on the end has received the data. TCP handles data 1.TCP in MSS-sized or smaller chunks to transmit the data to the IP, while attaching a TCP header to each block of data to form a TCP subsection. 2.IP assigns an IP header to each TCP sub-section to form an IP datagram, locates the routing table entry according to its destination IP address to determine the egress interface, and then passes the datagram to the appropriate data link. 3. Each data link has an output queue, and if the queue is full, the new packet is discarded and an error is returned along the protocol stack: from the data link to the IP, then from IP to TCP. TCP will notice this error and retransmit the appropriate section at a later point in time. The application process is unaware of this temporary situation.
Transport Layer (3)-buffer size and limit, TCP output
