Computer network data link layer
concept
link
NIC
The work of a node
Receiving a bitstream from the physical layer, the identification data frame, post-processing to the upper layer (network layer)
Three questions
Framing package
Transparent transmission
Error detection
Point to point network: PPP protocol
composition
Frame format
Establish a PPP session
Broadcast network data link layer protocol
local area network
advantage:
Ethernet
Standard: 802.3
Ethernet physical address
Hardware address, physical address, MAC address
48, 6 bytes
Ensure that the products of the adapter does not duplicate address (can be changed at the software level)
| 3 bytes | 3 bytes |
|---|---|
| Organizationally Unique Identifier | Extended Unique Identifier |
Least significant bit of the first byte I / G
Single station address I / G = 0
Group address I / G = 1
Only broadcast address as the destination address
Adapter MAC address checking
Promiscuous mode working Ethernet adapter
Ethernet frame format
| 8 | 6 | 6 | 2 | 46-1500 | 4 |
|---|---|---|---|---|---|
| Preamble information | Destination address | source address | Frame Type | data | CRC |
One of the Ethernet protocol: CSMA / CD
Ethernet-to-many broadcast communications.
Media Sharing Technology
Static divided channel
Dynamic Media Access Control
Random access
Controlled Access
CSMA / CD: to resolve the conflict shared channel
sender
Carrier Sense Multiple Access / Collision Detection
- Listen starters
- Listen and hair
- Stop conflict
- Delayed retransmission
receiver
Judgment: the frame is too short? correct address? Check correct? Frame length correct?
Using CSMA / CD Ethernet protocol is only half duplex (two-way alternate communication)
The minimum frame length
From the destination address to the checksum, the minimum frame length of 64 bytes
The recipient : less than 64 bytes in all frames are invalid frames abnormally terminated due to collision.
Why is the minimum frame size is 64 bytes?
One wireless network protocol: CSMA / CA
Error-free and reliable.
Limited coverage.
Sender: End ACK frame is transmitted after waiting for a recipient.
Receiver: with CSMA / CA.
device
Hub
The use of an Ethernet hub is still a logical bus network using CSMA / CD, a shared bus logic.
Operate at the physical layer.
switch
No mac address
Is essentially a device multiple interfaces
Each interface with a single host, or connected to another Ethernet switch, operate in full-duplex mode
Having parallelism , can simultaneously communicate with multiple interfaces on the host can communicate simultaneously on multiple
Ethernet switch exchange
Store and forward mode
First cache
Straight way
Simultaneously receiving a data frame determined forwarding interface (destination MAC address according to the data frame)
Disadvantages: error detection is not performed
Self-learning algorithm maintains switching table (address mapping table)
Feature
advantage
Radio & domain collision domain
Broadcast domains: a broadcast communication sent by any device can be received by all other devices in the network section.
All computers connected to the Ethernet switches are in the same broadcast domain.
Collision domains: each interface Ethernet switch is a collision domain.
Fast Ethernet
100BASE-T Ethernet
Fast Ethernet: meet / exceed 100Mbps
Fast Ethernet: 100BASE-T
Features:
Full-duplex mode, no conflict.
Do not use full-duplex CSMA / CD
(Column outline, will supplement da ~ ~ ~)