• 802.11 supports CSMA/CA (CSMA with collision avoidance) for MAC protocol. Suppose there are 4 stations. A wants to send to B. C is within range of A. D is within range of B but not within range of A. A begins by sending an RTS (request to send) frame to B to request permission to send. If B decides to grant permission, it replies a CTS (clear to send) frame. Upon receipt of the CTS, A sends its frame and starts an ACK timer. Upon the correct receipt of the data frame, B responds with an ACK frame, terminating the exchange. For C, it is within range of A, it will receive the RTS frame. Then it asserts a kind of virtual channel busy for itself, indicated by NAV (network allocation vector). For D, it does not hear the RTS, but it does hear the CTS, so it also asserts the NAV signal for itself翻译
时间: 2024-02-14 16:03:05 浏览: 33
802.11标准支持使用CSMA/CA(带冲突避免的CSMA)作为MAC协议。假设有4个站点,A想向B发送数据,C在A的范围内,D在B的范围内,但不在A的范围内。协议流程如下:
1. A先向B发送一个请求发送(RTS)帧,请求发送数据。
2. 如果B决定允许发送,它会回复一个清除发送(CTS)帧。
3. 收到CTS帧后,A会发送数据帧并启动一个确认(ACK)定时器。
4. 在正确接收到数据帧后,B会回复一个ACK帧,结束交换过程。
5. 对于C,它在A的范围内,会收到RTS帧。然后它为自己声明一种虚拟信道忙状态,即使用网络分配向量(NAV)信号表示。
6. 对于D,它没有收到RTS帧,但它会收到CTS帧,因此它也会为自己声明NAV信号。
相关问题
Discuss the Ethernet and its two types in detail with a diagram. Classic Ethernet Physical Layer, Classic Ethernet MAC Sublayer Protocol, CSMA/CD with Binary Exponential Backoff, Switched Ethernet
Ethernet is a widely used networking technology that is used for connecting devices in a local area network (LAN). It was first developed by Xerox Corporation in the 1970s and has since become a standard technology used for LANs worldwide. Ethernet uses a bus topology, where all devices share the same communication medium.
There are two main types of Ethernet: Classic Ethernet and Switched Ethernet.
Classic Ethernet:
The Classic Ethernet is the original Ethernet technology that was developed in the 1970s. It is also known as the "thicknet" or "thinnet" Ethernet. The Classic Ethernet uses coaxial cables as the communication medium. In the Classic Ethernet, data is transmitted using baseband signaling.
The Classic Ethernet has two main layers: the Physical layer and the MAC sublayer protocol.
1. Classic Ethernet Physical Layer:
The Classic Ethernet Physical Layer is responsible for transmitting data over the communication medium. It uses coaxial cables as the communication medium. There are two types of coaxial cables used in Classic Ethernet: Thicknet and Thinnet.
a) Thicknet:
Thicknet is a thick coaxial cable that is 0.4 inches in diameter. It is also known as 10Base5 because it supports a maximum data rate of 10 Mbps and can transmit data up to a distance of 500 meters. Thicknet uses a transceiver to transmit and receive data.
b) Thinnet:
Thinnet is a thin coaxial cable that is 0.2 inches in diameter. It is also known as 10Base2 because it supports a maximum data rate of 10 Mbps and can transmit data up to a distance of 185 meters. Thinnet uses a BNC connector to connect devices to the network.
2. Classic Ethernet MAC Sublayer Protocol:
The Classic Ethernet MAC (Media Access Control) Sublayer Protocol is responsible for controlling access to the communication medium. It uses the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol to avoid collisions between data frames.
a) CSMA/CD with Binary Exponential Backoff:
CSMA/CD is a protocol used by Classic Ethernet to avoid collisions between data frames. It works by sensing the communication medium to check if it is free before transmitting data. If the medium is busy, the device waits for a random amount of time before trying again. If a collision occurs, the devices involved in the collision wait for a random amount of time before retransmitting data. The amount of time the device waits before retransmitting data increases exponentially with each collision, which is known as Binary Exponential Backoff.
Switched Ethernet:
The Switched Ethernet is a newer Ethernet technology that was developed in the 1990s. It uses switches instead of hubs to connect devices to the network. In the Switched Ethernet, data is transmitted using broadband signaling.
The Switched Ethernet has two main layers: the Physical Layer and the MAC Sublayer Protocol.
1. Switched Ethernet Physical Layer:
The Switched Ethernet Physical Layer is responsible for transmitting data over the communication medium. It uses twisted-pair cables or fiber optic cables as the communication medium. The most common type of twisted-pair cable used in Switched Ethernet is the 100Base-TX, which supports a maximum data rate of 100 Mbps and can transmit data up to a distance of 100 meters.
2. Switched Ethernet MAC Sublayer Protocol:
The Switched Ethernet MAC Sublayer Protocol is responsible for controlling access to the communication medium. It uses the same CSMA/CD protocol as Classic Ethernet but is rarely used since collisions are avoided by using switches instead of hubs.
Diagram:
Here is a diagram showing the differences between Classic Ethernet and Switched Ethernet:
```
Classic Ethernet Switched Ethernet
Communication Medium Coaxial cables Twisted-pair or fiber optic cables
Data Transmission Baseband signaling Broadband signaling
Maximum Data Rate 10 Mbps 100 Mbps or higher
Distance Up to 500 meters (Thicknet) Up to 100 meters (100Base-TX)
Access Control CSMA/CD with Binary Exponential Backoff CSMA/CD or Switches
```
In conclusion, Ethernet is a widely used networking technology that is used for connecting devices in a local area network (LAN). There are two main types of Ethernet: Classic Ethernet and Switched Ethernet. Classic Ethernet uses coaxial cables as the communication medium and has a maximum data rate of 10 Mbps while Switched Ethernet uses twisted-pair or fiber optic cables and has a maximum data rate of 100 Mbps or higher. Both Classic Ethernet and Switched Ethernet use the CSMA/CD protocol to avoid collisions between data frames.
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This website provides comprehensive documentation for the Selenium testing framework. Selenium is an open-source tool used for automating web browsers. It allows users to write test scripts in various programming languages such as Java, Python, C#, etc. Selenium supports different web browsers like Chrome, Firefox, Safari, etc., and can be integrated with other tools like TestNG, JUnit, Maven, etc.
The documentation on this website covers various aspects of Selenium, including installation, getting started with Selenium WebDriver, working with different web browsers, handling various web elements, debugging tests, and more. It also provides examples and sample code for users to understand and implement Selenium in their projects.
Additionally, the website offers a community forum where users can ask questions, share knowledge, and get help from other Selenium users. There is also a blog section where users can find articles related to Selenium and web automation.
Overall, the Selenium documentation website is a valuable resource for anyone who wants to learn or use Selenium for web automation testing.
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