4、 LAN and man

LAN architecture and topology

The data link layer is divided into logical link control LLC and MAC Sublayer

802.3  CSMA/CD Ethernet

802.11  WLAN WLAN

Bus type

Ring

Star type

Tree form

CSMA/CD And listening algorithm

Access control protocol CSMA/CD  ( Carrier Sense Multiple Access/Collision Detection )

continuity 16 Secondary collision , Do not send . The more conflicts , The longer the backward time .

Non persistent listening algorithm

1- Persistent monitoring algorithm ： High conflict probability and utilization

P- Persistent monitoring algorithm

Conflict detection principle ： send out Jamming frame , Wait for a random period of time

Minimum frame length calculation ：Lmin/R= 2 d/v  (R Network data rate ,d Maximum distance ,v Speed of propagation )

Out of Collision detection The consideration of

Ethernet frame structure and physical layer specification

Ethernet frame structure

Purpose mac Address      Source mac Address       length          data                                         The checksum

   6                           6                2         46~1500             4( byte ),CRC Cyclic redundancy check 32 position

Frame length 64-1518 byte

100 BASE T

100Mbps,BASE Baseband transmission ,T Twisted pair F Optical fiber 5 Express 500 rice

Fast Ethernet

802.3u 100M

100Base-TX          100m   4B/5B

100Base-FX

Gigabit Ethernet

802.3Z

1000Base-SX         550m

1000Base-LX         10km

1000Base-CX         25m

802.3ab

1000Base-T           100m   8B/10B

1000Base-ZX        100km

10 Gigabit Ethernet

802.3ae full duplex Optical fiber / Twisted pair No conflict detection Point to point

Virtual LAN VLAN

Virtual Local Area Network

Different VLAN The communication goes through three layers of equipment （ Router 、 Three layer switch 、 Firewall, etc ）

A repeater and a hub are a conflict domain . One VLAN For a broadcast domain , An interface of the switch is a conflict domain .

Static partition VLAN： Based on the switch port

Dynamic partition VLAN： be based on MAC Address 、 Based on Strategy 、 Based on network layer protocol 、 Based on network layer address

Switch port type ：

Access Interface ： Connect PC/ Camera and other terminals

Trunk Interface ： Interconnection between switches

Hybrid

QinQ: Metropolitan area network

Add and remove VLAN Marking is implemented by hardware

Partition in LAN VLAN. Different VLAN Through between Relay port signal communication .

802.1Q

Purpose mac Address     Source mac Address    Tag    length     data      The checksum

Tag4 byte , Last 12 position VID（VLAN identifier ）212 -2 = 4094 individual VLAN

Used to carry multiple VLAN The traffic protocol group is 802.1q and ISL( Cisco private )

Spanning tree protocol STP

Redundant topology brings about layer 2 loop problems ： Broadcast storm 、MAC Watch shakes

Third floor ring road IP package TTL Maximum 255

STP The protocol prevents the layer 2 loop .

1、 Identify the root bridge RB Priority and MAC Address minimum

2、 The nearest port from the non root bridge to the root bridge is the root port RP

3、 Find the specified bridge DB, To RB The cost is minimal .DB The upper port is the designated port dp

4、 Find the unspecified port

Bridge ID

      priority                      MAC Address

2 byte （32768）            6 byte

Path overhead

bandwidth         802.1d

10M          100

100M         19

1000M        4

10G            2

Metropolitan area network foundation

802.1ad    QinQ user VLAN Mark the operator on the outer layer VLAN Mark

802.1ah    MAC-IN-MAC