// This note is only a learning record
| level | equipment |
|---|---|
| Physical layer | Repeater, hub, amplifier |
| data link layer | Bridge, LAN switch, wireless AP |
| Network layer | router |
| Above the network layer | Gateway |
1. Physical layer
1. Repeater
- Between two nodes, the signal is amplified and transmitted, to be exact, it is regenerated, not amplified
- Strengthen the baseband signal for the transmission of digital signals
- Repeaters can reduce distortion
2. Hub
- A hub is a repeater with multiple ports
- The hub does not isolate the conflict domain, that is, any incoming data will be forwarded from all ports (except the port that comes in)
- The bandwidth of the hub needs to be divided by the number of hosts connected to it, and the switch does not
3. Amplifier
- Enhancing broadband signals for the transmission of analog signals
- Using an amplifier will also amplify noise and cause distortion
2. Data link layer
- Can isolate the conflict domain, but not the broadcast domain
- Use physical address forwarding
1. Bridge
- Connect the bridge between two LANs
- Can isolate the safety network segment
- Can interconnect heterogeneous networks
- Expand the physical scope
The bridge forwards according to the destination MAC address. With filtering function, that is to say, when the bridge receives a frame, it is not forwarded to all ports, but according to the destination MAC address, the port is selected for forwarding.
2. LAN Switch
- Multi-port bridge, VLAN realized by LAN switch can isolate conflict domain and broadcast domain
- The bandwidth of the switch will not decrease because of the increase in the number of port nodes, but the total bandwidth increases with the increase of nodes. For example, if there are n users in a shared Ethernet, the average bandwidth of each user is only 1/n, while using an Ethernet switch, it can reach n times the bandwidth.
- Because it works at the data link layer, the physical address is used for forwarding
- Join the switch to connect to 10Mb/s Ethernet for 10 users. In half-duplex , the rate of each user is 10Mb/s, and in full-duplex , the rate of each user is 20Mb/s.
- When data frames enter the switch, the switch must perform self-learning (recording the source MAC address of the frame and the port that entered) and forwarding (see below)
Forwarding
6. First find the entry in the forwarding table.
7. If there is a clear entry and the ingress port and the forwarding port are different, forward from the forwarding port.
8. If there is a clear entry, but the ingress port and the forwarding port are the same, then discard
9 . If there is no clear entry, flood forwarding from all ports (except the incoming port)
Two switching modes
10. Straight-through, the switch only checks the destination address of the frame at this time
11. Storage dedicated
Multiplexing mode: The
switch adopts statistical time division multiplexing
3. Wireless AP
3. Network layer
Can isolate conflict domain and broadcast domain
1. Router
- The transmission delay of the router is the largest among these network devices because of the selection and grouping
- Used to connect different local area networks and wide area networks, providing routing and packet forwarding functions
- The meaning of a router connecting a heterogeneous network: that is, the protocols of the physical layer, the data link layer and the network layer can be different, but the protocols above the network layer must be the same
2. Layer 3 Switch
- Definition: a layer 2 switch with layer 3 routing function (switch with routing function)
- Features: The use of hardware to realize the forwarding of messages and routes, and the use of fast backplane switching technology to improve the processing speed of key nodes (higher efficiency than traditional routers)
4. Above the network layer
1. Gateway
Can realize network interconnection above the network layer