(A) Transport / Reliability (transmission / reliability)
1. Transport Layer (Transport Layer)
- Introduction: the transport layer is responsible for providing services to communications between two hosts in the process. Having a demultiplexing and multiplexing functions. The transport layer provides transparent transfer of data between end users, to provide reliable data transmission service to an upper layer. Reliability is guaranteed by the flow control, segmentation / reassembly and to achieve error control.
- The origin of the transport protocol (TCP) is: when in 1987, when more than 10Mbit of 56Kbit campus network using leased lines connected together, there were network congestion, leading to network collapse.
- TCP features: TCP buffer will be stored in the transmission system and the target system to hold the data has arrived, if necessary, be further retransmit the data, a separate TCP connection between applications.
2. Van Jacobson - Slow Start Algorithm ( Van - Jacobson - slow start algorithm)
- Van Jacobson (Van Jacobson) Internet technology-based TCP / IP protocol stack main drafters. He is known for its network upgrade and optimize the performance of pioneering achievements.
- Thinking slow start algorithm: When the host starts sending data, if immediately inject large amounts of data to the network, then it may cause network congestion, because the load condition of the network is not clear at the beginning. Experience has shown that a better approach is to conduct surveys, namely small to large gradually increasing the transmission window, that is, from small to big gradually increasing congestion window value. Usually in the beginning send a message segment, first congestion window cwnd is set to a maximum segment MSS value. In acknowledgment of the receipt of each new segment, the congestion window is increased up to the MSS a value, in such a way gradually increase the congestion window cwnd sender, the packet can be injected into the network is more reasonable rate .
3.The Domain Name System (DNS Domain Name System)
- DNS: Domain Name System is the Internet of a service. As the domain name and IP address of each map one distributed database , so that people can more easily access the Internet .