0. Introduction
In the era of parallel SCSI bus and no complicated link layer protocol, "even" reflected on the cable, like copper wire connection between the CPU and the Northbridge same, but SCSI cable is made of soft external cable only. In this short on basic cable do not have to consider the content of the communication level, because the distance is short, the line is stable, no need to add things such as transport security mechanism and the like. At the same time, this case also corresponds to a circuit switched connection-oriented communication between the parties to a pre-established path (virtual circuit) on a physical, whether or not the data stream, this path is always present, and the fixed bandwidth, others grab do not take the right to use this circuit, which both parties to the communication provides maximum stability and quality assurance. In such a link, the underlying transport protocol without undue overhead.
In contrast, in the non-oriented packet-switched network connection, the data stream is encapsulated into packets, and flow control transmission security becomes very important factors. Because the network is shared, Best Effort best effort network in forwarding packets. FC and Ethernet switched networks are of this (except for the type of service in FC Class1) connectionless oriented technology.
While the switched telephone network, parallel SCSI bus network belonging to the connection-oriented network. When you pick up the phone dial, telephone office telephone exchange will be between you and your partner communicate establish a physical circuit, so that the two communicating parties.
提示:
大家可以观察一下电话交换机，每当有外线拨入的时候，就可以听到交换机里有吧嗒吧嗒的声音，这就是交换机在做继电器开合动作。
Connection-oriented and connectionless (FC knowledge) -1086825-2 for parallel SCSI bus, when the initiator of communication needs and a node communication, it will apply for bus arbitration, after obtaining the bus resources, and the other to initiate direct communication, and at this time there is no explicit connection establishment process. Physical access is always present, there are between any two points, but this path is a bus, is for all to share, you need to obtain the right to use the bus through arbitration, it is equivalent to establish exclusive connection. SCSI commands and data may be directly transferred on the bus, it does not require too much additional protocol overhead.
1. Achilles' heel for connection
However, there are three connection-oriented communication fatal weakness. The first weakness for connection to the network is a waste of resources. Particularly in switching environment, since there is no data transmission on the path matter, this connection must be pre-established and maintained
Only two sides to use specific communication, data communication with other nodes regardless of how congestion can not use this path. Connection-oriented network like a city bus system, each bus lines are fixed, regardless of the traffic on this route number, even if no one take this route, the buses have to run back and forth. The connectionless networks of like a taxi. In the absence of people, a taxi can wait for the arrival of guests. Once guests arrive, a taxi will be on the road, but the route is not fixed, the driver can follow the current road traffic conditions, select a free path to the destination.
The second weakness of the connection-oriented network is to maintain costs and high maintenance cost of this connection. The two sides near distance communication, no problem, but once very far away, to maintain this physical connection, you need a very high cost. To solve the interference problem of long distance transmission, relay and other needs, which is why a long-distance telephone charges are high.
A third disadvantage connection-oriented network, is the lack of high availability. Once established good VC disconnected for some reason, we need to re-establish communication initiator circuit to continue the communication between the two sides. This phenomenon is often encountered when the long-distance calls, then had to re-call. For packet-switched network, the communicating parties without a fixed data flow paths, switching or routing devices on their own judgment data stream should reach the other side through which path. Once a strip of dynamic path is no longer available, switching equipment will immediately choose a different path to reach the other side, and this short-term interruption of transmission safeguards agreement will be forwarded to the impact caused by the operation of the two sides to deal with communication, lost packets will It is retransmitted. The user does not have to be concerned about this, most feel there is a short delay, and the other without having to re-establish the connection.
2. Connectionless oriented advantages
No connection-oriented packet-switched network has many advantages over connection-oriented network. For connectionless packet-switched network is a trend in network communication, the current VOIP, IPTV applications are wanted to use packet-switched network instead of a normal switched telephone network and a cable network.
Do not put "connectionless" and "TCP connection is" confused together. TCP is an end to end protocol that runs on both sides of communication, rather than communication through a network device. TCP connection is not a physical connection but a logical connection. TCP is actually a state, itself remains a state machine is used to detect whether the data stream between the two sides successfully sent or received. Actual communication connection between two points over the packet switched network, also may pass through the connection-oriented network. That is, the "connection-oriented" and "connectionless" refers to the concept of the link layer, the transport layer TCP concept.
Author: Jian Yun
link: https://forum.huawei.com/enterprise/zh/thread-194991.html
Source: Huawei Enterprise interactive community
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