osi七层模型传输层

传输层-OSI模型 (Transport Layer - OSI Model)

The basic function of the Transport layer is to accept data from the layer above, split it up into smaller units, pass these data units to the Network layer, and ensure that all the pieces arrive correctly at the other end.

传输层的基本功能是接受来自上一层的数据，将其拆分成较小的单元，然后将这些数据单元传递到网络层，并确保所有数据块正确到达另一端。

Furthermore, all this must be done efficiently and in a way that isolates the upper layers from the inevitable changes in the hardware technology.

此外，所有这些工作必须高效完成，并且必须将上层与硬件技术中不可避免的变化隔离开。

The Transport layer also determines what type of service to provide to the Session layer, and, ultimately, to the users of the network. The most popular type of transport connection is an error-free point-to-point channel that delivers messages or bytes in the order in which they were sent.

传输层还确定要提供给会话层，并最终提供给网络用户的服务类型。 传输连接中最流行的类型是无错误的点对点通道 ，该通道按消息发送顺序发送消息或字节。

The Transport layer is a true end-to-end layer, all the way from the source to the destination. In other words, a program on the source machine carries on a conversation with a similar program on the destination machine, using the message headers and control messages.

从源到目的地，传输层始终是真正的端到端层。 换句话说，源机器上的程序使用消息头和控制消息与目标机器上的类似程序进行对话。

传输层的功能 (Functions of Transport Layer)

1. Service Point Addressing: Transport Layer header includes service point address which is port address. This layer gets the message to the correct process on the computer unlike Network Layer, which gets each packet to the correct computer.服务点寻址：传输层标头包含服务点地址，即端口地址。 与网络层不同，该层将消息发送到计算机上的正确进程，而网络层将每个包发送到正确的计算机。
2. Segmentation and Reassembling: A message is divided into segments; each segment contains sequence number, which enables this layer in reassembling the message. Message is reassembled correctly upon arrival at the destination and replaces packets which were lost in transmission.分段和重组：消息分为多个部分； 每个段都包含序列号，这使该层可以重新组合消息。 消息在到达目的地后会正确重组，并替换传输中丢失的数据包。
3. Connection Control: It includes 2 types: 连接控制：它包括2种类型：
   • Connectionless Transport Layer : Each segment is considered as an independent packet and delivered to the transport layer at the destination machine.
     无连接传输层：每个段都被视为一个独立的数据包，并在目标计算机上传递到传输层。
   • Connection Oriented Transport Layer : Before delivering packets, connection is made with transport layer at the destination machine.
     面向连接的传输层：在传送数据包之前，在目标计算机上与传输层建立连接。
4. Flow Control: In this layer, flow control is performed end to end.流控制：在此层中，端到端执行流控制。
5. Error Control: Error Control is performed end to end in this layer to ensure that the complete message arrives at the receiving transport layer without any error. Error Correction is done through retransmission.错误控制：在该层中端到端执行错误控制，以确保完整的消息到达接收传输层而没有任何错误。 纠错是通过重传完成的。

传输层的设计问题 (Design Issues with Transport Layer)

• Accepting data from Session layer, split it into segments and send to the network layer.
  从会话层接受数据，将其拆分为多个段，然后发送到网络层。
• Ensure correct delivery of data with efficiency.
  确保高效地正确传输数据。
• Isolate upper layers from the technological changes.
  将上层与技术变化隔离开。
• Error control and flow control.
  错误控制和流控制。

翻译自: https://www.studytonight.com/computer-networks/osi-model-transport-layer

osi七层模型传输层