计算机网络有几层，用英语回答

The computer network is typically divided into seven layers, which are known as the OSI (Open Systems Interconnection) model. The seven layers are as follows:

1. Physical Layer: It deals with the physical transmission of data over the network, including the electrical and mechanical aspects of the network hardware.

2. Data Link Layer: It provides error-free transmission of data frames between two directly connected nodes, and it also handles flow control and error detection.

3. Network Layer: It is responsible for the logical addressing and routing of data packets across different networks. It determines the best path for data transmission.

4. Transport Layer: It ensures reliable and efficient end-to-end delivery of data. It breaks down large data into smaller segments and reassembles them at the receiving end.

5. Session Layer: It establishes, manages, and terminates communication sessions between applications on different network devices.

6. Presentation Layer: It is responsible for data representation, encryption, and compression. It ensures that data from the application layer of one system can be understood by the application layer of another system.

7. Application Layer: It provides network services to end-user applications, such as email, web browsing, file transfer, etc.

--Related Questions--
1. What is the purpose of the physical layer in computer networks?
2. How does the transport layer ensure reliable data delivery?
3. What are some examples of protocols used in the application layer?
4. How does the network layer handle routing of data packets?