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LAN and MAN
Teacher Summer's soft exam LAN summary outline introduced the Ethernet protocol, virtual LAN VIAN, Spanning Tree Protocol STP, Wireless LAN protocol, etc.
Edited at 2024-04-18 22:16:52- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- Project Management Process Template
Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
LAN and MAN
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- One Hundred Years of Solitude Character Relationship Chart
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
- Project Management Process Template
Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
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- Outline
LAN and MAN
IEEE
Ethernet protocol (802.3)
Carrier Sense Multiple Access/CSMA
Principle: Before sending data, first monitor whether someone is sending on the channel. If there is, it means that the line is busy, and then decide according to the predetermined strategy.
algorithm
Non-persistent type: After a collision, it backs off for a random time, which reduces the probability of collision, but the channel utilization also decreases and increases the transmission delay;
1-Persistent monitoring: As long as the channel is idle, data is sent immediately, and the channel utilization rate and conflict probability are both increased (double high)
P-persistent algorithm: When the channel is idle, it is sent with probability P; In case of conflict, delay one time unit by (1-P), and the size of P is adjustable.
Clash Detection/CSCD
Principle: CSMA (monitoring) can only reduce the probability of conflict, but cannot completely avoid it, so the collision detection method of listening and transmitting is adopted
method
Receive at the same time during sending, and compare the received data. If they are consistent, continue sending;
If they are inconsistent, a conflict occurs, transmission is stopped immediately, and a jamming signal (Jamming) is sent out, and all stations stop transmitting.
After sending interference signals, wait for a random time, listen again, and try to send
Binary exponential backoff algorithm
Principle: After detecting a conflict, immediately stop sending, send interference signals, wait for a random time before sending data
Random time formula: waiting time = t*Random[0,1,...2k-1 (k is the square)], so the backoff time is not necessarily longer than the previous one. The greater the number of retransmissions, the larger the backoff window, thereby reducing the probability of collision.
After 16 consecutive collisions, it is considered that the network is busy or faulty and no longer is sent.
Minimum frame formula: Lmin=2R*d/v R is the network data rate, d is the maximum distance, and v is the propagation speed
Ethernet frame structure
1. The preceding pilot field (7 bytes) and start identifier (1 byte) are not included in the frame length; 2. The data length is 46-1500 bytes. If it is not enough, it will be filled to 46 bytes; 3. Check bit 4 bytes, CRC cyclic redundancy check 32 bits 4. Destination address 6 bytes, source address 6 bytes, length: 2 bytes 5. Minimum frame: 64 bytes; (46 6 6 2 4) 6. The longest frame: 1518 bytes (1500 6 6 2 4)
1. Ethernet header: destination source address length = 6 6 2 2. IP header: 20 bytes 3.TCP header: 20 bytes 4. Application data: minimum 46 - IP - TCP =6 bytes 5. Application data: Maximum 1500 - IP - TCP = 1460 bytes 6. Checksum: 4 bytes
physical specifications
Fast Ethernet (100M)
100Base-TX (4B5B encoding): using two pairs of Category 5 UTP (unshielded twisted pair), two pairs of STP (shielded twisted pair), transmission 100M
100Base-FX: One-to-many or one-to-one optical fiber, 2KM and 40KM respectively
100Base-T4: Four pairs of Category 3 UTP, 100 meters
100Base-T2: Two pairs of 3 UTP, 100 meters
Gigabit Ethernet (1000M)
1000Base-SX: multi-mode, 550M
1000Base-LX: single mode (10um) or multi-mode, 5KM
1000Base-CX: two pairs of STP, 25 meters, transmission in the same room
802.3z
1000Base-T: Four pairs of Category 5 UTP, 100 meters, using 8B\10B encoding
802.3ab
10 Gigabit Ethernet (10G)
10GBase-S: multi-mode fiber, 62.5um=65 meters, 50u=300 meters
10GBase-L: single-mode fiber, 10 kilometers
10GBase-E: single-mode fiber, 40km, 1550nm serial
10GBase-LX4: Wavelength Division Multiplexing (WDM)
802.3ae, no more shared bandwidth, no conflict detection
Virtual LAN VLAN
Features
A logical network formed by segmenting a switched LAN based on management function, organization, or application type.
Different VLAN communications must pass through three-layer devices: routers, three-layer switches, and firewalls.
A hub or repeater is a collision domain, a VLAN is a broadcast domain, and an interface on a switch is a collision domain.
Collision domain: A collection of all nodes on the same shared medium. All nodes in the collision domain compete for the same bandwidth. Messages (single, group, broadcast) sent by one node are received by the other nodes.
Broadcast domain: The entire access range that broadcast messages can reach is called the Layer 2 broadcast domain. Hosts in the same broadcast domain can all receive broadcast domain messages.
VLAN division
Static VLAN: based on switch port
Dynamic VLAN: based on MAC address, based on policy, based on network layer protocol, based on network layer address
VLAN function:
Controlling network traffic helps control broadcast storms, reduce conflicts, and improve network bandwidth utilization;
Improve network security, different VLANs cannot communicate;
Flexible network configuration, VLAN configuration can break through geographical location restrictions and use management functions to divide;
802.1Q tag
PRI (3 bits): Priority indicates priority, providing a total of 8 priorities from 0 to 7. When multiple frames are waiting, data packets are sent in order of priority.
VID (12 bits): VALN identifier, up to 2^12=4096 VLANs, of which VID0 is used to identify priority, VID4095 is reserved for use, up to 4094 VLANs can be configured, the default VLAN1, cannot be deleted
Note: The Vlan labeling process of the switch is implemented by dedicated hardware and will not cause too much delay in data.
VLAN tags are transparent to users. When the PC receives data, the VLAN tags will be torn off;
switch port
Access interface: can only transmit single Vlan data, generally used for PCs, cameras, etc.;
Trunk interface: capable of transmitting multiple VLAN tags, generally used between switches;
Hybrid interface: hybrid interface, including Access interface and Trunk interface
QINQ (802.a1d): double-layer label, generally used in carrier metropolitan area networks;
MAC-IN-MAC: also called PBB, 802.1ah
MAN technology
Spanning Tree Protocol STP
background: 1. There is a single point of failure in a single link of the switch, and the network has no redundancy; 2. If any link or equipment fails, the network will be directly disconnected; 3. After adding redundant equipment, there is a layer 2 data loop problem;
broadcast storm
Once broadcast data frames appear, these data will be continuously broadcast and flooded by interconnected switches, causing broadcast storms;
After a broadcast storm occurs, it will seriously occupy CPU resources and network bandwidth;
Phenomenon: The network is slow, all indicators flash at high speed, CPU usage is high, and CLI freezes
MAC table oscillation
Since all switches are connected together, the ports will automatically learn the MAC address, so when a PC sends out a message, each switch will continuously forward the information, causing the switch to continuously change the device MAC address.
Principle: Block specific ports through logic to break loops and ensure normal use of the network.
Bridge ID
8 bytes, consisting of 2 priority bytes and 6 bytes of MAC address (default: 32768)
The smaller the value, the higher the priority. When manually modifying it, it must be a multiple of 4096.
Path cost: The path cost is inversely proportional to the domain port bandwidth.
Implementation process
Determine the root bridge: choose the bridge with the smallest priority and MAC address
Determine the root ports of other bridges: the port closest to the root bridge from the non-root bridge port
Select a designated port for each segment: the designated bridge is given priority, and the designated port is on the designated bridge.
Select non-specified ports
Transmit BPDU messages
protocol
Spanning Tree Protocol: 802.1d STP (slow, convergence takes 30S-50S)
Rapid Spanning Tree Protocol: 802.1W RSTP (fast, 6S)
Multiple Spanning Tree Protocol: 802.1S MSTP (to achieve multiple Vlan load balancing)
Wireless LAN protocol (802.11)
Simplified formula: conflict probability 1/2^n (n is the number of conflicts that have occurred, n<=10)