osi 模型 会话层
会话层-OSI模型 (Session Layer - OSI Model)
The Session Layer allows users on different machines to establish active communication sessions between them.
会话层允许不同计算机上的用户在它们之间建立活动的通信会话。
It's main aim is to establish, maintain and synchronize the interaction between communicating systems. Session layer manages and synchronize the conversation between two different applications. In Session layer, streams of data are marked and are resynchronized properly, so that the ends of the messages are not cut prematurely and data loss is avoided.
其主要目的是建立，维护和同步通信系统之间的交互。 会话层管理和同步两个不同应用程序之间的对话。 在会话层中，数据流被标记并正确地重新同步，这样消息的末端就不会过早地被切断，从而避免了数据丢失。
会话层的功能 (Functions of Session Layer)
- Dialog Control : This layer allows two systems to start communication with each other in half-duplex or full-duplex. 对话控制：此层允许两个系统以半双工或全双工方式开始相互通信。
- Token Management: This layer prevents two parties from attempting the same critical operation at the same time.令牌管理：此层可防止两方同时尝试相同的关键操作。
- Synchronization : This layer allows a process to add checkpoints which are considered as synchronization points into stream of data. Example: If a system is sending a file of 800 pages, adding checkpoints after every 50 pages is recommended. This ensures that 50 page unit is successfully received and acknowledged. This is beneficial at the time of crash as if a crash happens at page number 110; there is no need to retransmit 1 to100 pages.同步：此层允许进程将检查点添加到数据流中，这些检查点被视为同步点。 示例：如果系统正在发送800页的文件，则建议每50页之后添加检查点。 这样可确保成功接收并确认50页单位。 这在崩溃时很有好处，就像崩溃发生在第110页时一样； 无需重新传输1至100页。
会话层的设计问题 (Design Issues with Session Layer)
- To allow machines to establish sessions between them in a seamless fashion. 允许计算机以无缝方式在它们之间建立会话。
- Provide enhanced services to the user. 为用户提供增强的服务。
- To manage dialog control. 管理对话框控件。
- Token management and 令牌管理和Synchronization.同步等服务 。
翻译自: https://www.studytonight.com/computer-networks/osi-model-session-layer
osi 模型 会话层