First, the concept
Switching technology means that each station between hosts , each between communication devices or between a host and a communication device (simply understood: between your PC and my PC, your PC and my router, routers) to exchange information used in the data exchange apparatus and formats manner.
Second, the exchange of technology classification
2.1 a circuit switched (Circuit Switching)
2.1.1 What is the circuit-switched?
Anderw S.Tanenbaum in " Computer the Network " circuit switched to a definition:
Conceptually, when you or your computer places a telephone call, the switching equipment within the telephone system seeks out a physical path all the way from your telephone to the receiver’s telephone. This technique is called circuit switching.
Conceptually, when you or your computer that you want to make calls, switching equipment within the telephone system will look from your phone to a physical path between the telephone receiver. This technique is known as circuit switching. During the call, we need to understand a few concepts. It corresponds to the source node calling party, the receiving party corresponding to the telephone destination node, from which we pick up the handset, dial-up, waiting call, hang a series of process we call it a complete circuit exchange process. So in short, it is to establish a dedicated circuit switched path between the source node and the destination node for data transmission.
2.1.2 Circuit Switched specific process
Corresponding to our everyday telephone communication step of: dialing, call, hang up, the main switching circuit includes three stages, namely to establish a connection, data transmission, disconnected .
- establish connection
Communications transmission medium is required between the two nodes, called versa. So we need our phone lines to transmit voice signals. So when we need to talk, the first thing to do is to establish a communication line, that is, to take up a dedicated telephone line ( Occupy the BETWEEN A Dedicated path both-ends ).
- transfer data
Establishing a communication line is implemented communication system base end (the communication connection-oriented). When the link is established, we can call a voice signal transmitted through the channel, of course, which may also involve the coding and modulation data.
- Disconnect
After the end of the two-node communication, in order to improve the data transfer rate and resource utilization, we need to need to make a communication line node communication. So we have to release the connection.
In real life, we call behavior similar to this picture:
After the dial-up wait time is equivalent to the left side of the telephone in an unoccupied by selecting a multi-port switch telephone line. Switching Office intermediate needed to implement the data relay. When the communication ends, the switch is equivalent to poke disconnected.
Advantages and disadvantages of the circuit switched 2.1.3
a) the advantages
- Small communication delay
- Orderly transfer
- No data conflicts
- And real time
- Simple control
b) shortcomings
- Establishing a long connection time (typically from 10 seconds to dial the ON time, it is compared to the network communication delay lot !!!)
- Exclusive line, the channel utilization is low
- Fault-resistant properties of the difference circuit (fault point, reconnection)
- Normalized difficult (no direct data cache, it is difficult to communicate signals with different rates)
2.2 message exchange (Message Switching)
2.2.1 What is packet switching?
Is essentially a packet switching using store and forward techniques , between the source node and the destination node is achieved through exchange of packets intermediate nodes (routers), enabling the transmission of packets.
The message can be exchanged for us to understand the reality of life in a relay race, the first swimmer took the baton from the starting point, then the middle will pass the baton to the next teammate, finally taking over teammate excitedly run to the line! Where the message is like the baton, which halfway participation relay athletes who switch node is the middle of it. After this analysis, we have a good grasp of the characteristics of packet switching.
2.2.2 newspaper features of message exchange
a) the advantages
- Without establishing a connection (circuit switched different)
- Dynamic distribution line (routing algorithm to select the best route)
- Strong anti fault line (no "a little off, multi-paralysis" situation)
- Improve the utilization of the line (with respect to the circuit switching, does not tie up the channel)
- Provides multi-target service (a message can be broadcast to multiple destinations)
b) shortcomings
- Extended forwarding
- Large storage overhead
These two points from the point of view of time and space study the shortcomings of packet switching. Because the message (data) into the switch node to be subjected to the storage, queuing, forwarding and other process (unlike the circuit-switched connection established directly send a), it will cause additional forwarding delay. Of course, because of using store and forward techniques, it requires the intermediate nodes need to have certain cache space to temporarily store the received packets , and each packet routed to select the appropriate next node before followed.
2.3 Packet Switched (Package Switching)
2.3.1 What is packet switching?
In essence, packet switching and packet switching are the same , they have a "store - forward" thinking, the only difference is that packet switching to more detailed consideration, it gives the message length limit . In other words, packets can not be transmitted to any length , it must be within a fixed length, and if it exceeds a predetermined range needs to be divided into two or more message packets for transmission. We therefore in packet switching technology, data is generally referred to as a "packet" (Packet). Similar to the IP packet.
2.3.2 Characteristics of the packet switched
a) the advantages
In addition to the same advantages of packet switching, but also has:
- Simplifies storage device (with respect to packet switching, packet length is fixed, ease of operation)
- Pipelined transfer acceleration (a plurality of packets queued waiting transmission in parallel)
- Lower error rate and the retransmission (packet length is shorter, reducing the probability of error)
b) shortcomings
- There is transmission delay
- Additional information needs to be transmitted (each packet specify the source address, the destination address of the additional information, the packet number, etc.)
- Additional processing time (packet segmentation to achieve large datagrams, it also brings the cost of the extra work group assembling, sorting, etc.)
Three three switching technology Comparison
Long author Anderw S.Tanenbaum provide a comparison of the indicators of circuit-switched and packet-switched :( packet switching and packet switching essence is the same drop)
References the current scenario, the circuit-switched technology are generally used for cable television, telephone systems finite fields requiring reliable transmission, and the like. The message exchange only circuit-switched to packet switching transition alternatives have become history. Packet-switched applications on a more extensive, such as IP packets, ICMP packets and so the use of packet switching technology.
He did not get the security research places, on balance, chose to study section, just to continue to upgrade themselves. Either from a technical or psychological, heart always firm: less talk and more work.