1. Resource subnet
Resources subnet that contains a number of hosts (Host), which are types of computers (or servers) to provide services to users.
Resources subnet is composed of a host in the network perimeter, whose task is responsible for information processing , provide resources available to the network. Users can not only share resources through resource subnet subnet communication, but also share hardware and software resources resources subnet.
2. subnetworks
Switch nodes by a communication link and network configuration information for exchange. Inner subnetworks in the network. The main task of the communication subnet is responsible for the whole network and data communications network interconnection.
Communication subnet data exchange technology employed main circuit switching, packet switching and packet switching three.
Circuit switched 2.1
1 Introduction
Must be "connected to the communication connection release" step three way connection-oriented networking.
Circuit switched Examples
A and B, four switches calls through the
call in the connection A to B is
C and D only through a local call switch
call C to be connected in the D
2. Features
Circuit switched data transfer of a computer inefficient
computer having a data burst.
This led to the communication line utilization is very low.
2.2 Packet Switched
2.2.1 Introduction
Packet switching using store and forward technology.
? Packet (message): the data block to be transmitted
packets or packages (package):? Packets into segments of equal length, with the necessary control information for each segment consisting of a front header (header) . The packet header is also referred to Baotou.
2.2.2 The basic principles of packet switching network
2.2.3 Features
The advantage of packet switching:
efficient: the process of dynamic allocation of packet transmission bandwidth occupied by the communication circuit piecewise
flexibility: Each intelligent node are independently selected for each packet forwarding route.
Quickly: As a packet transfer unit may not establish a connection to send packets to other hosts; high-speed network links.
Reliable: comprehensive network protocol; distributed multi-route the packet-switched network using the network have good survivability.
Packet switching problems:
there is a certain time delay
control information in each group carried will cause some overhead (overhead)
require specialized management and control mechanisms.
2.3 message exchange
2.3.1 Introduction
Message exchange (message switching)
packet switching based on the principle of store and forward
message switching center to each packet as a unit, according to the destination address of the packet, performing a respective forward.
2.3.2 Features
Disadvantages: the longer the delay time, a few minutes to several hours.
Comparison:
packet switching and packet switching as are used store and forward principle , but due to the computer and the switching nodes are grouped into fixed-length, not the length, can switch on a memory node for processing, which on the very fast packet forwarding.
2.4 circuit switching, packet switching, packet switching comparison between
A and D represent the source node and the destination node B, and C are intermediate nodes between A and D
