name requests is not defined

时间: 2023-04-22 13:02:24 浏览: 148

MidtermExam_吴先_13000128171

ork, a path is established between the sender and the receiver before data transmission starts. This path is defined by a sequence of virtual circuit identifiers (VCIDs) assigned to each link along the way. Each node on the network is aware of the VCID and uses it to forward packets along the predetermined route. Virtual circuits allow for more efficient packet routing since the setup phase determines the best path and minimizes the need for frequent routing decisions during transmission. Question 1.1 discusses flow control, a crucial aspect in computer networks to prevent buffer overflow at the receiver. Flow control mechanisms ensure that the sender does not overwhelm the receiver by adjusting the transmission rate according to the receiver's capacity. Techniques like stop-and-wait, sliding window, and selective acknowledge (SACK) are used to implement flow control in various protocols. Question 1.2 focuses on queuing delay, which occurs when data packets arrive at a router's buffer and wait to be forwarded. Queuing delay can be affected by factors such as traffic volume, router processing speed, and buffer size. High queuing delay can lead to increased packet loss or latency. Question 1.3 explains how HTTP is a stateless protocol, meaning that each request from a client to a server is treated independently. Cookies are used to maintain session state across multiple HTTP transactions. They are stored in the client's browser and sent back to the server in subsequent requests, allowing the server to remember user preferences or session information. Question 1.4 highlights the three-way handshake required to establish a TCP connection, which typically takes two round-trip times (RTTs). Persistent and non-persistent connections refer to how multiple data segments are handled after the connection is established. While they can impact overall transmission efficiency, they do not alter the initial 2 RTTs needed for connection setup. Question 1.5 introduces the concept of authoritative name servers in the Domain Name System (DNS). These servers are responsible for providing authoritative responses to DNS queries for a specific domain. When a client looks up a hostname, it communicates with local, root, and top-level domain (TLD) DNS servers before reaching the authoritative server for the queried domain. Question 1.6 emphasizes the role of transport layer ports in identifying and directing data to the appropriate application. Each port number corresponds to a specific service or protocol, ensuring that data is correctly demultiplexed to the correct process running on the host. Question 1.7 describes different mechanisms in the transport layer, specifically slow start, flow control, and error control. Slow start is a congestion avoidance technique where a sender initially sends a small number of packets and gradually increases its rate. Flow control ensures the sender doesn't exceed the receiver's capacity, while error control is responsible for detecting and recovering from errors using techniques like acknowledgments and retransmissions. Question 1.8 introduces virtual circuit networks, contrasting them with datagram networks. In a virtual circuit network, all packets belonging to the same connection follow the same predefined path, reducing the overhead of routing decisions for each packet. This is particularly useful in wide area networks (WANs) with high traffic loads, where establishing a circuit beforehand can improve performance. In summary, these questions cover essential topics in computer networks, including flow control, queuing delay, HTTP cookies, TCP connection establishment, DNS hierarchy, transport layer functions, and virtual circuit networks. These concepts are fundamental to understanding the functioning and design of modern internet protocols and services.

name requests is not defined 是一个错误提示，意思是请求名称未定义。这通常是因为在代码中使用了requests模块，但是没有正确导入或安装该模块。需要检查代码中是否正确导入了requests模块，并且确保已经安装了该模块。

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name requests is not defined

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发生异常: NameError name 'headers' is not defined File "C:\Users\riseon\Documents\python\test.py", line 7, in <module> response = requests.get(url, headers=headers) # 发送 GET 请求 NameError: name 'headers' is not defined

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