5、 Wireless communication network

WLAN Basics

                 2G          3G

Move         GSM      TD-SCDMA Independent research and development

Unicom         GSM       WCDMA

telecom         CDMA     CDMA2000

                       802.11     802.11b    802.11a      802.11g          802.11n

Working frequency band        2.4GHZ     2.4GHZ    5.8GHZ     2,4GHZ       2.4GHZ、5.8GHZ

Non overlapping channel         3                3                  5            3                     3+5

Maximum transmission rate  2Mbps         11                54          54            300(MIMO 600)

WLAN Network classification

Infrastructure networks ： Wireless access point AP（ Working in OSI Model Data link layer ）

Ad Hoc

Not in IEEE802.11 What is used in WLAN is CDMA.

WLAN Spectrum Introduction

ISM Frequency band

Industry 900M    Science 2.4G     Medical 5.8G

2.4G Frequency band 13 Channels ,3 Non overlapping channels （1,6,11）

5.8G Frequency band 12 Channels ,5 Non overlapping channels （ At home 149,153,157,161,165）

802.11 MAC layer

802.11 The standard for the MAC The sublayer defines three access control mechanisms ：

1、CSMA/CA Distributed coordination

  Wired CSMA/CD Collision detection , Wireless conflict avoidance , because Hide nodes problem .

2、RST/CTS Channel reservation

3、PCF Point coordination function

802.11 Three inter frame intervals

IFS Distributed coordination IFS  The lowest priority       Asynchronous frame contention access

PIFS A little coordination IFS        Priority centered      PCF operation

SIFS short IFS              The highest priority      ACK/ The reply    

Move AD Hoc The Internet

MANET

Network topology changes , Not applicable to traditional routing protocols

Every node It is the host , It is also a router , No central node

Limited energy

WLAN Security

1、SSID Access control ： hide SSID

2、 Physical address filtering ： Wireless router settings MAC Black and white list of addresses

3、WEP Authentication and encryption ：PSK Preshared key authentication ,RC4 encryption

4、WPA（802.11i The draft ）

authentication ：IEEE802.1X（ user name ＋ password ）

For users connected to switch ports / equipment MAC Address authentication

encryption ：RC4（ enhance ）+TKIP（ Temporary key integrity protocol , Dynamically change the key ）

5、WPA2（802.11i）

encryption ： be based on AES Of CCMP and TKIP