TCP retransmission timeout to determine the time of RTO:
Adaptive algorithm: first sampling the RTT (round trip time), record the recent round trip time value, and then do the smoothing calculation, the current retransmission timeout time estimate accurate to adjust RTO.
Ignore retransmission mechanism: not to retransmission RTT (round trip time) to do the sampling.
Improvements to ignore retransmission mechanism: as long as the retransmission occurs, doubling the existing RTO value.
An IP address and MAC address:
MAC address is the data link layer to distinguish, distinguish between physical addresses on each physical network device used. IP address is the logical address of the network layer and above use, it is assigned a unique logical address to each host and the Internet network, to mask the differences in the physical address.
5 and the intermediate layer architecture each layer used in the device:
- Application layer: to accomplish specific network applications through the interaction between the application process. Application layer protocols: HTTP, SMTP, DNS (Domain Name System), File Transfer Protocol: FTP, TFTP
- Transport Layer: provides inter-process communication between two hosts. The main protocols: TCP, UDP
- Network layer: Routers
- The data link layer: a bridge or switch bridge
- Physical Layer: transponder
TCP / IP Architecture
- Application layer
- Transport Layer
- Internet layer / IP layer
- Network Interface Layer
OSI7 layer architecture and the protocol layers used:
- Application layer: to accomplish specific network applications through the interaction between the application process. Application layer protocols: HTTP, SMTP, DNS (Domain Name System), File Transfer Protocol: FTP, TFTP
- Presentation Layer:
- Session layer:
- Transport Layer: provides inter-process communication between two hosts. The main protocols: TCP, UDP
- Network Layer: Address Resolution Protocol ARP, Internet Control Message Protocol ICMP, routing protocol (Internal Gateway Protocol RIP, OSPF exterior gateway protocols: the BGP)
- Data link layer: Point to Point Protocol PPP, CSMA / CD protocol
- Physical layer:
TCP and UDP difference:
Why not ask tcp handshake twice? Why not four?
Two not: tcp is a full duplex communication, two-way handshake only determine the data communication link is, does not guarantee a normal communication reverse
Not four:
Originally shake hands and waved, like all need to be confirmed in both directions can Unicom have been the model should be:
1. The client sends to the server syn0
2. The server receives syn0, reply ACK (syn0 + 1)
3 server sends SYN1
4. client receives SYN1, reply ack (syn1 + 1)
as tcp is full duplex, the upper four data confirmed in both directions can be arrived correctly, steps 2 and 3 but there is no up and down links that can be combined to accelerate the efficiency of the handshake, all becomes a 3-way handshake.
TCP packet header How long? How long is the longest overall message?
TCP packet size 1500 - IP header (20B) - TCP header (20B) = 1460B which is the maximum MSS
The maximum length of the TCP header is 60 bytes, the data offset field is given by "offset data" four bits (4-bit binary represents maximum 15), in units of 32-bit words (4 bytes), the TCP the maximum length of the header portion = 15 * 4 = 60 bytes. ( "Computer Network seventh edition of" Xie Xiren P218 page)