CCNA Notes--osi--Physical layer, Data link layer

OSI seven-layer model

Application Layer

Presentation Layer

Session Layer

Transport Layer Core Layer

Network Layer aggregation Layer

Data Link Layer Access layer

Physical Layer

First, the physical layer

1. Transmission unit: bit bitstream

2. Device NIC, Hub hub, transfer media

Professional Terminology broadcast: A pair of all multicast: one to many Unicast: One to all full duplex: Receive and send simultaneously

Half Duplex: Receive and send two select one

Broadcast domain: A certain range of a pair of all

Conflict domains: Within a certain range, packets are generated by sending or receiving conflicting domains

Dividing broadcast domains: a network segment

Vlan

Router

RJ-45: Crystal head on twisted pair

RJ-11: The head on the phone line

Each port of the switch is a separate conflict domain

All interfaces on a hub hub are in the same conflict domain

4. Transmission media: Fiber Type: Indoor and outdoor

Function: Single Film (Gold * * *) Multi-Film (orange)

Pigtail: Round Head square head

Effective transmission distance: 1000 m

No electronic signal interference, can not bend radius less than 15cm

Coaxial cable 10base2 Thin cable 30 crystal head effective transmission distance: 185 m

10BASE5 thick cable 100 crystal head effective transmission distance: 500 meters

10 refers to the transfer rate of one m/s calculation

Twisted pair 10baseT effective distance: 100 m

5. Network by geographical division: WAN, LAN, metropolitan area network

Wan is made up of good metropolitan area network

6. The network is divided by topology type: Bus, star, ring, tree, net

The most used are: stars and trees

Second, Data link layer

　　1. Transmission Unit: Data frame

The Start field of the a data reminder frame comes up

Address field destination address and source address for B-frames

C Length Type controls the length and type of field frames

d data field raw data

e-Frame Check sequence field Check frame integrity

2. LLC Logical Link Control sub-layer

Mac Encapsulation

3. MAC address 48-bit hexadecimal number consisting of the first 24 bits is the manufacturer's identity

The rear 24 bits are the device number

4. Features: Only the Mac does not know IP

5. Concept: The 1> Data link layer provides physical transmission of data, which would mean that in a local area network using a hardware address, the data link layer ensures that the information is transmitted to the correct device, and the information from the network layer is converted into a bitstream form to facilitate the transfer of the physical layer.

2> encapsulates the information into frames and adds a custom header, which contains the destination address and source address in hardware form, which surrounds the original information to the Apollo program.

6. The difference between the network layer and the data link layer

Routers work at the network layer, they only care about the best path to reach these networks and the location of the network, the router does not care about the internal network, the data link layer is responsible for residing in the local networks unique identity.

7. Features of the data link layer

Physical Address definition

Physical media access

Link parameters

Error verification

Network topology structure

Flow control

8. LLC Sublayer Features

Responsible for identifying the network protocol, burning fire to its door encapsulation, the LLC header tells the data link layer, one but the frame is accepted should be how to handle the packet.

9. The limitation of physical layer and the solution of Data link layer

One layer can not communicate with high-level communication Layer Two through the LLC sublayer

One layer does not identify the computer two layer identifies the computer with a Mac addressing scheme

The first layer can only describe the bit stream layer two to organize or group bits with frames

10. Device switches, bridges,

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CCNA Notes--osi--Physical layer, Data link layer