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1. IEEE 802.11 && Wireless LAN
1.802.11 MAC frame header format
2. Classification of wireless local area networks
1. There is a fixed infrastructure wireless LAN
2. Ad hoc network without fixed infrastructure WLAN
2. PPP protocol & HDLC protocol
1. Characteristics of PPP protocol
2. Requirements to be met by the PPP agreement
3. Requirements that the PPP protocol does not need to meet
4. The three components of the PPP protocol
5. State diagram of PPP protocol
6. Frame format of PPP protocol
4. PPP protocol & HDLC protocol
1. Physical layer extended Ethernet
2. Link Layer Extended Ethernet
3. Collision domain and broadcast domain
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1. IEEE 802.11 && Wireless LAN
1.802.11 MAC frame header format
2. Classification of wireless local area networks
- Wireless LAN with fixed infrastructure
- Ad Hoc Networks for Wireless Local Area Networks without Fixed Infrastructure
1. There is a fixed infrastructure wireless LAN
2. Ad hoc network without fixed infrastructure WLAN
2. PPP protocol & HDLC protocol
1. WAN
- Wide Area Network (WAN, Wide Area Network), usually spanning a large physical range, covering a range from tens of kilometers to thousands of kilometers, it can connect multiple cities or countries, or span several continents and provide remote Distance communication to form an international long-distance network.
- The communication subnet of the WAN mainly uses packet switching technology. The communication subnet of the wide area network can use the public packet switching network, the satellite communication network and the wireless packet switching network, which will be distributed in different regions and
局域网或计算机系统interconnected to achieve the purpose of resource sharing . Such as the Internet (Internet) is the world's largest wide area network.
2. PPP protocol
1. Characteristics of PPP protocol
- Point-to-Point Protocol PPP (Point-to-Point Protocol) is currently the most widely used data link layer protocol. Users generally use the PPP protocol when they use dial-up phones to access the Internet.
- Only full-duplex links are supported .
2. Requirements to be met by the PPP agreement
简单: For link layer frames, no error correction, no sequence number, and no flow control are required.封装成帧: frame delimiter透明传输: How data with the same combination of bits as the frame delimiter should be handled: byte stuffing for asynchronous lines, bit stuffing for synchronous lines.多种网络层协议: Encapsulated IP datagrams can use multiple protocols.多种类型链路: Serial/Parallel, Synchronous/Asynchronous, Electrical/Optical….差错检测: Discard if wrong.检测连接状态: Whether the link works normally.最大传送单元: The maximum length MTU of the data part.网络层地址协商: Know the network layer addresses of both communicating parties.数据压缩协商
3. Requirements that the PPP protocol does not need to meet
纠错流量控制序号不支持多点线路
4. The three components of the PPP protocol
- A method to encapsulate IP datagrams into serial links (synchronous serial/asynchronous serial).
- Link Control Protocol LCP: Establish and maintain data link connections. Authentication
- Network Control Protocol NCP: PPP can support a variety of network layer protocols, each of which requires a corresponding NCP to configure, to establish and configure logical connections for network layer protocols.
5. State diagram of PPP protocol
6. Frame format of PPP protocol
3. HDLC protocol
1. Concept
- High-Level Data Link Control (High-Level Data Link Control or HDLC for short) is a data link layer protocol for transmitting data over a synchronous
面向比特network . ) protocol extension developed.- Data packets can be transparently transmitted, and the " 0-bit insertion method " used to achieve transparent transmission is easy to implement in hardware
- full duplex communication
- All frames are used
CRC检验, and the information frames are sequenced编号to prevent missed or duplicated copies, and the transmission reliability is high.
2. HDLC Station
- Master station, slave station, composite station
- 1. The main function of the master station is to send command (including data information) frames, receive response frames, and be responsible for the initial start of the control system of the entire link, process control, error detection or recovery, etc.
- 2. The main function of the slave station is to receive the command frame sent by the master station, send the response frame to the master station, and cooperate with the master station to participate in link control such as error recovery.
- 3. The main function of the composite station is to send and receive command frames and response frames, and is responsible for the control of the entire link.
- Three data operation modes:
①, normal response mode
②, asynchronous balance mode
③, asynchronous response mode
3. HDLC frame format
- The first bit of the information frame (I) is 0 , which is used to transmit data information , or use piggybacking technology to confirm data
- Supervision frame (S) 10, used for flow control and error control , to perform functions such as confirmation of information frames, request for retransmission and request for suspension of transmission
- Unnumbered frame (U) 11, used to provide various control functions such as link establishment and teardown.
4. PPP protocol & HDLC protocol
- HDLC and PPP only support full- duplex links.
- Transparent transmission can be achieved. [ PPP protocol: can be filled with bytes or bits; HDLC protocol: can only be filled with bits ]
- Error detection can be achieved, but errors are not corrected.
3. Link Layer Devices
1. Physical layer extended Ethernet
2. Link Layer Extended Ethernet
- Bridges & Switches
- The bridge sums
MAC帧的目的地址the framesbased转发the过滤. When the bridge receives a frame, it does not forward the frame to all interfaces, but first checks the destination MAC address of the frame, and then determines which interface to forward the frame to, or discards (ie, filters) it. .
1. Bridge
(1) Bridge classification - transparent bridge
- Transparent Bridge & Source Routing Bridge
- Transparent bridge : "Transparent" means that the station on the Ethernet does not know which bridges the frame will pass through. It is a plug-and-play device - self-learning.
(2) Bridge classification - source route bridge
- Source-routing bridge : When sending a frame, put the detailed best route information (least route/shortest time) in the header of the frame.
- Method : The source station
广播方式sends one to the destination station to be communicated发现帧.
2. Ethernet switch
(1) Multi-interface bridge - Ethernet switch
(2) Two switching modes of Ethernet switches
3. Collision domain and broadcast domain
冲突域: Every node in the same collision domain can receive all transmitted frames. Simply put, it is the range where only one device can send information at the same time. [As long as a link layer device is a port, it is a collision domain]广播域: The set of all devices in the network that can receive broadcast frames sent by any device. Simply put, if a site sends out a broadcast signal, the range of all devices that can receive the signal is called a broadcast domain. [Determine the broadcast domain through the router]
