Services provided in the transport tier, transport services in the transport tier

Some technical means are used to make up for the difference between the user's requirements for the network and the services that the network can provide to the user, so that the user does not need to understand the details of the network transmission and obtains a relatively stable data transmission service. The main technical means used are:

1) Diversion merging technology: the network with low throughput, low rate and high transmission delay can support the requirements of users for high-speed data transmission;

2) Demultiplexing technology and splicing segmentation technology: make the network with high throughput, high speed, low transmission delay, and high cost support the user's requirements of low transmission cost;

3) Segmentation and merging technology: The network that transmits user data (packets) of limited length can support the transmission of unlimited length of user data.

4) Error detection and recovery technology: The network with a high error rate can support the user's high-reliability data transmission requirements.

5) Flow control technology: limit the number of protocol data units for continuous transmission to avoid network congestion.

The transport layer is the most important and critical layer of the seven-layer model, and it is the only layer responsible for overall data transmission and control. The transportation layer serves two main purposes: first, to provide reliable end-to-end communication; Second, provide network-independent transportation services to the session layer.

The services provided in the transport layer are the (establishment) (dismantling) (management) of the transport connection

The ultimate goal of the transportation layer is to provide users with effective, reliable and reasonable services. The diagram shows the relationship between the transportation layer, the network layer, and the transportation service users. In a system, the transport entity communicates with other transport entities through network services to provide transport services to transport layer users (which can be application processes or session layer protocols).

The services of the transportation layer include: service type, service level, data transportation, user interface, connection management, fast data transportation, status reporting, security and confidentiality, etc. The transport agreement entity should allow users of the transport layer to choose the level of service provided by the transport layer in order to facilitate more efficient use of the resources of the links, networks and interconnected networks provided.

The services available include the degree of error and data loss, the average and maximum latency allowed, the average throughput rate allowed, and the priority level. Based on these requirements, the transport layer agreement service levels can be subdivided into the following four categories:

1) Reliable connection-oriented protocol. 2) Unreliable connectionless protocols. 3) Voice transport agreements that require sequencing and timed transportation.

4) Need for fast and highly reliable real-time protocols. This includes secure and confidential services such as confirmation of the sender and receiver, encryption of data, and passage and decryption, as well as routing of confidential links and nodes.