Ethernet & IEEE 802.3 802.X 802.1AG-MEP

ISO/IEC 7498, which defines the 7-tier framework for network interconnection, the Open Systems Interconnect Reference Model (OSI model ).

A switch is like a neighboring street, and a router is the intersection of a street. (The second layer of the switch , the data link layer, also has four layer, seven layer switch; the router works on the third layer).

See (http://www.he.edu.cn/learn/wlxy/netlan/index.html)

Crossover and direct-attached network cables

First, direct connection interconnection

Both ends of the network cable are pressed T568B to connect the host and device, i.e. DTE and DCE, as

1. Computer ←-→ADSL Cat

2. ADSL Cat ←-→ADSL WAN Port of Router

3. LAN Port of Computer ←-→ADSL router

4. Computer ←-→ hub or switch

Second, cross-interconnection

One end of the network cable is pressed T568B, the other end is connected by T568A, which is used to connect the host and host, or the device and device, such as

1. Computer ←-→ computer, that is, peer network connection

2. Hub ←-→ Hub

3. Switch ←-→ switch

RJ45 is a type of various connectors (for example: RJ11 is also a type of connector, but it is used on the telephone); RJ45 head according to the order of the line is divided into two kinds, one is white orange, orange, white green, blue, white blue, green, white Brown, Brown, and the other is white green, green, white orange, blue, white blue, orange, white brown, brown So there are two kinds of lines that use RJ45 connectors: (12345678 corresponds to 12345678), crossover line (12345678 corresponds to 36145278).

Media and connected devices

Interconnection devices for communications refer to the interconnection devices between DTE and DCE. DTE both data terminal equipment, also known as physical devices, such as computers, terminals, etc. are included. The DCE is a data communication device or circuit connection device, such as a modem. The data transfer is usually through DTE──DCE, then through the Dce──dte path.　 Interconnection devices are devices that connect DTE and DCE, such as various plugs and sockets. Various coarse and fine coaxial cables, T-connectors, plugs, receivers, transmitters, repeaters, etc. in LAN are all media and connectors of the physical layer.

Main functions of the physical layer
⑴ provides a path for data-end devices to transmit data, which can be either a physical medium or multiple physical media connections. A complete data transfer, including activating physical connections, transmitting data, and terminating physical connections. So-called activation, no matter how much physical media involved, Should be connected between the two data terminals of the communication to form a pathway.
⑵ transfer data. The physical layer is to form an entity suitable for data transmission, which is to be transmitted to the service. One is to ensure that the data can be passed correctly on it, and the other is to provide enough bandwidth (the bandwidth is the number of bits per second that can pass through) to reduce congestion on the channel. The way data is transferred to point-to , serial or parallel, half-duplex or full-duplex, synchronous or asynchronous transmission is required.
⑶ complete Some management work on the physical layer.

The physical layer provides the transmission medium and its connection to the data communication between the terminal devices. The media is long-term, the connection has the survival period. During the lifetime of the connection, Both ends of the transceiver can be unequal for one or more data communication. Each communication must be established through communication and the removal of communication between the two processes. This established data-sending relationship is called a data link . The most common of the independent link products is the NIC, the bridge is also the link product. The Data link layer turns the inherently unreliable transmission media into a reliable transmission path to the network layer.

Main functions of the ⑴ link layer
The link layer provides the data transfer service for the network layer, which relies on the functions of this layer. The link layer should have the following functions:
① link Connection establishment, demolition, separation.
② frame and Frame synchronization. The data transmission unit of the link layer is the frame, the protocol is different, the frame length and the interface also differ, but the frame must be bound in any case.
③ sequential control, which refers to the control of the order of receiving and transmitting frames.
④ error detection and recovery. There are also link identification, flow control, and so on. Error detection multi-square code check and cyclic code check to detect the data on the channel error, and frame loss, such as serial number detection. The recovery of various errors is often done by the feedback re-send technique.

The generation of network layer is also the result of network development. In the context of online systems and circuit switching, the functionality of the network layer does not make much sense.

⑴ Network layer main function
The network layer should have the following main functions for establishing network connection and providing service to the upper layer.
① route selection and trunking. ② activation to terminate the network connection.
③ multiplexing multiple network connections on a single data link, and takes time-sharing multiplexing techniques.
④ error detection and recovery. ⑤ sorting, flow control.
⑥ service Selection. ⑦ Network Management.

The Transport Layer is the first end-to-end level when two computers are communicating over a network, because it is the last layer of low to high control of data transfer from the source end to the destination.

ISO/IEC 15802----MAC sub-layer definition

__________________
Network 3rd Layer
__________________
Logical Link Control
-----------------2th Layer
Medium Access Control

___________________
Physica 1st Layer

Related definitions in the IEEE STD 802.1ag-2007:3.5 down MEP A MEP residing in A Bridge that receives CFM PDUs from, and transmits them Towa Rds,the direction of theLAN.3.43 up mep:a MEP residing in A Bridge that transmits CFM PDUs towards, and receives them from, thedirection of theBridge Relay Entity.The main difference between the down MEP and the up MEP is that the direction of the CFM PDU is different, and the direction of the down MEP is the direction of the Lan,up MEPBridge Relay Entity, thisBridge Relay Entity can simply be thought of as a switch, that is, the down MEP is sending and receiving PDUs directly from the LAN and terminating on that port, but the up MEP is a PDU obtained from a different port that is forwarded to that port and terminated on that port.  Up MEP and down MEP also have other names in different places, such as outgoing and inward MEP: is up MEP, sending a paper to relay entity, also called an introverted MEP. Is the down MEP, which sends the PDU to the network direction

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Ethernet ( Ethernet ) is a computer LAN networking technology. the IEEE 802.3 standard developed by IEEE gives the technical standard of Ethernet. It largely replaces other LAN standards, such as token Ring , FDDI, and ARCNET.

Ethernet is still used Bus Type topology , and CSMA/CD (Carrier Sense multiple access/collision detection is a bus contention technique for carrier-monitored multiple access with collision detection.)

The carrier monitor multi-access CSMA technology, also known as the first to listen to say LBT (Listen before talk).

In CSMA , because of the propagation delay of the channel, there is still a conflict when two stations are sending frames when they hear no signal on the bus. Because the CSMA algorithm has no conflict detection function, even if the conflict has occurred, the destroyed frames will be sent out , so that the utilization of the bus is reduced. The improvement is to enable the site to continue to listen to the media during transmission time, once the conflict is detected, immediately stop sending, and send a short packet of blocking messages (JAM) to the bus, notify the bus The collision of the above stations has already occurred, can improve the utilization of the bus. this is called Carrier monitoring multi-access/Collision Detection Protocol (CSMA/CD) , this protocol has been widely used in Ethernet and the IEEE802.3 standard.

CSMA/CD Carrier-listening multi-access/collision detection (Carrier sense Multiple access with Collision Detection, CSMA/CD), this scenario applies to the Ethernet (DIX Ethernet V2) Standard, IEEE 802.3 standard.

Working principle

CSMA/CD is a distributed media access control protocol, each station (node) in the network can independently determine the data frame transmission and reception. Each station before sending a data frame, the first to carry out carrier monitoring, only when the media is idle , only allow the sending of frames. At this point, if more than two stations at the same time to listen to the media idle and send frames, there will be a conflict phenomenon, the sent frames are invalid frames, sent immediately declared failure. Each station must have the ability to detect whether a conflict occurs at any time, in the event of a conflict, you should stop sending, so that the media bandwidth due to the transfer of invalid frames and wasted, and then randomly delay a period of time, and then re-contention media, resend the frame. The CSMA/CD protocol is simple and reliable, and its network systems (such as Ethernet) are widely used.

CSMA/CA Carrier Listener multipath Access/collision Avoidance (Carrier sense Multiple Access with collision AVOIDANCE,CSMA/CA)

This scenario applies to the IEEE 802.11 standard for wireless LANs.

logically, it can be divided into two parts: Data Link Layer of the Media access Control Child Layer (MAC) and Physical Layer .

In order to better adapt the Data link layer to a variety of LAN standards, the 802 committee has split the data link layer of the LAN into two sub-tiers:
Logical Link Control LLC (Logical link controls) sublayer
Media access controls the Medium access control sub-layer.

Media access Control (media access controls, abbreviated: MAC) sublayer , which is the lower part of the data link layer in the LAN , provides control of addressing and media access, the Mac sub-layer acts as a medium for the communication between the logical link Control sub-layer and the physical layer, and provides an addressing method called the Physical address or MAC address . MAC addresses are unique and each network card has a different MAC address, so you can transfer packets to a specific destination device in one subnet. The subnet here refers to a physical network (such as Ethernet) without a router.

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IEEE 802.3 The standards are not entirely independent, IEEE 802 some of the standards in the series were once 802.3 A strong competitor of the standard, such as 802.4 Standard description of Token Bus and the 802.5 Standard description of Token Ring , these LANs have disappeared today. in a picture of the IEEE STD 802 Standard document, you can see where the IEEE 802.3 Standard is located.

Other network protocols related to IEEE 802:
IEEE 802.1-overview, architecture and network interconnection, and network management and performance measurement.
IEEE 802.2-Logical Link Control LLC. The highest level protocol interfaces with any one of the LAN Mac sub-tiers.
IEEE 802.3-CSMA/CD Network that defines the specification of the MAC sub-layer and the physical layer of the CSMA/CD bus network.
IEEE 802.4-Token bus network.   Defines the specification of the MAC sub-layer and the physical layer of the token delivery bus network. Standard for---token network
IEEE 802.5-Token Ring network. Defines the specification of the MAC sub-layer and physical layer of the token-passing ring network.
IEEE 802.6-metropolitan area network.
IEEE 802.7-Broadband technology.
IEEE 802.8-Optical fiber technology.
IEEE 802.9-integrated voice data LAN.
IEEE 802.10-Security for interoperable LANs.
IEEE 802.11-Wireless LAN.
IEEE 802.12-Priority high-speed local area network (100MB/S).
IEEE 802.13-Cable TV (CABLE-TV).

IEEE802.4 is the token bus access method and the physical layer protocol. examples of token bus topologies are "ARCNET"

In the process of studying the 802 standard, the industrial community (general motor, etc.) proposed a map (manufacturing Automation Protocol) protocol, which was adopted by IEEE and became the IEEE 802.4 standard. This network absorbs the advantages of bus network and Token Ring network, and is an important network technology in industrial automation.

The token bus LAN is a system that can determine the delivery delay time.
The time limit for the token to wrap around the net for a week is <=nt seconds. In a token bus LAN, there must be a valid Mac sub-layer protocol to manage the network tokens. Thus the MAC sub-layer protocol of the token bus LAN is very complex.

1802.4 is completely incompatible with the physical layer of 802.3.
Token: A special frame in which only the node that gets the token can send the frame. IEEE 802.4 uses tokens to avoid frame collisions caused by multiple nodes accessing the bus at the same time.

features.
1, the physical is the bus network, the logic is the token network
2, physical layer: The transmission medium is 75W wideband coaxial cable, the data rate is 1mb/s, 5mb/s or 10mb/s;
3, the transmission mechanism for the combination of Ethernet and Token Ring:
The physical transmission uses the broadcast mode;
Media access control takes the form of tokens.

Ethernet & IEEE 802.3 802.X 802.1AG-MEP