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1. Basic concepts and architecture of local area network
4. LAN media access control method
5. Classification of Local Area Networks
6. MAC sublayer and LLC sublayer
2. Ethernet provides connectionless, unreliable service
3. Development of Ethernet transmission medium and topology
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1. Basic concepts and architecture of local area network
1. LAN
- Local Area Network (Local Area Network): Abbreviation
LAN,某一区域refers to a group of computers interconnected by multiple computers, using broadcast channels .- Features:
①. Feature 1: The coverage is small, and it is only connected within a relatively independent local area, such as a single or centralized building complex.
②, Feature 2: Use specially laid transmission medium (twisted pair, coaxial cable) for networking, and the data transmission rate is high (10Mb/s ~ 10Gb/s).
③, Feature 3: The communication delay time is short, the bit error rate is low, and the reliability is high.
④, Feature 4: Each station is in an equal relationship and shares the transmission channel.
⑤、Characteristic 5: Distributed control and broadcast communication are mostly used, which can broadcast and multicast.- The main factors that determine the local area network are: network topology , transmission medium and medium access control method .
2. LAN topology
3. LAN transmission medium
4. LAN media access control method
- CSMA/CD: commonly used in bus-type LANs , but also in tree-type networks
- Token bus: commonly used in bus-type local area networks , but also in tree-type networks.
It forms a logical ring by arranging various workstations in a bus-type or tree-type network in a certain order, such as according to the size of the interface address. Only the token holder can control the bus and have the power to send information.- Token Ring: For ring LANs such as Token Ring
5. Classification of Local Area Networks
- Ethernet : Ethernet is the most widely used local area network, including standard Ethernet (10Mbps), Fast Ethernet (100Mbps), Gigabit Ethernet (1000 Mbps) and 10G Ethernet, all of which conform to the IEEE802.3 series of standard specifications. Logical topology bus type, physical topology is star or extended star. Use CSMA/CD.
- Token Ring Network : Physically adopts a star topology, and logically is a ring topology. "Tomorrow's Yellow Flower"
- PDDI network (Floer Distrilouked Data inervece) : Physically adopts a double-ring topology, and logically is a ring topology.
- ATM network (Asynchronous Transler Mode) : a relatively new type of unit switching technology, which uses 53-byte fixed-length units for switching.
- Wireless Local Area Network (Local Area Network WLAN) : The IEEE 802.11 standard is adopted.
- IEEE 802 standard : The IEEE 802 series of standards are local area network and metropolitan area network technical standards formulated by the IEEE 802 LAN/MAN Standards Committee (established in February 1980). Among them, the most widely used are Ethernet, Token Ring, wireless local area network and so on. Each sub-standard in this series of standards is under the responsibility of a dedicated working group within the committee.
- IEEE 802.3 : Ethernet Media Access Control Protocol (CSMACD) and Physical Layer Specifications 2.
- IEEE 802.5 : Medium Access Control Protocol and Physical Layer Technical Specification for Token-Ring.
- IEEE 802.8 : Optical Fiber Technical Advisory Group, which provides technical advice on fiber optic networking.
- IEEE 802.11 : Media Access Control Protocol and Physical Layer Specifications for Wireless Local Area Networks (WLAN).
6. MAC sublayer and LLC sublayer
The local area network reference model described by the IEEE 802 standard only corresponds to the data link layer and physical layer of the OSI reference model. It divides the data link layer into the logical link layer LLC sublayer and the medium access control MAC sublayer.
2. Ethernet
1. Ethernet Overview
- Ethernet ( ) refers to the baseband bus local area network specification
Ethernetcreated by Xerox Corporation and jointly developed by Xerox, Intel and DEC Corporation . It is the most common communication protocol standard used by existing local area networks today. Ethernet uses CSMA/CD (Carrier Sense Multiple Access and Collision Detection) technology.- Ethernet occupies a
统治性position in various technologies of local area network:
1. Low cost (less than 100 Ethernet network cards);
2. It is the most widely used local area network technology;
3. It is cheaper and simpler than token ring network and ATM network;
4 .满足网络速率要求：10Mb/s~10Gb/s.- Two Ethernet standards:
①,DIX Ethernet V2：第一个局域网产品（以太网）规约。
②,IEEE 802.3：IEEE 802委员会802.3工作组制定的第一个IEEE的以太网标准。(the frame format has been slightly changed)
2. Ethernet provides connectionless, unreliable service
- Connectionless: There is no "handshake process" between sender and receiver.
- Unreliable: The data frame is not sent to the
编号sender, the receiver does not send it to the sender确认, the error frame is directly discarded, and the upper layer is responsible for error correction.- Ethernet only achieves error-free reception, not reliable transmission.
3. Development of Ethernet transmission medium and topology
4. 10BASE-T Ethernet
10BASE-T is a twisted pair Ethernet that transmits baseband signals . T means twisted pair. Now 10BASE-T uses unshielded twisted pair (UTP), and the transmission rate is 10Mb/s .
5. Adapter and MAC address
- The connection between the computer and the external local area network is through the communication adapter .
- In a local area network, a hardware address is also called a physical address, or a MAC address. [actually an identifier]
- MAC address: Each adapter has a globally unique 48-bit binary address, the first 24 bits represent the manufacturer (specified by IEEE), and the last 24 bits are specified by the manufacturer. It is usually represented by 6 hexadecimal numbers, such as 02-60-8c-e4-b1-21.
6. Ethernet MAC frame
7. Fast Ethernet
- Ethernet with a rate of ≥100Mb/s is called high-speed Ethernet.
1. 100BASE-T Ethernet
- The star topology Ethernet that transmits the 100Mb/s baseband signal on the twisted pair still uses the CSMA/CD protocol of IEEE802.3.
- Support full duplex and half duplex , can work in full duplex mode without conflict.
2. Gigabit Ethernet
- 1Gb/s signal is transmitted over fiber or twisted pair .
- Support full duplex and half duplex , can work in full duplex mode without conflict.
3. 10 gigabits
- 10 Gigabit Ethernet carries 10 Gb/s signals over fiber .
- Only supports full duplex , no contention issues