1. Lecture 16 Medium Access Control Sublayer Broadband Wireless 802.16
CS 453 Computer Networks
Lecture 16
Medium Access Control Sublayer
Broadband Wireless

2. Broadband Wireless
While fills a niche for wireless networking in very limited area…
These seems to be an equally compelling need to have a wireless networking technology on a somewhat larger scale rangewise
Getting that “final mile”
A wireless local loop

3. Broadband Wireless
IEEE was commissioned address this issue…
And Local Multipoint Distribution Service was invented to do this
In principal a much more cost effective way to provide broadband services that running cable or fiber to local houses and buildings

4. 802.16 Broadband Wireless 802.16 started in July, 1999
Standard approved in April, 2002
Officially “Air Interface for Fixed Broadband Wireless Access Systems”
Often called –
Wireless local loop
WMAN – wireless Metropolitan Area Network
WiMax

5. Broadband Wireless
heavily influence by other 802 efforts and by OSI Reference model
So, why not just make a bigger, stronger ?
It fills a difference niche.
It has different objectives

6. Broadband Wireless
Both were designed to provide high bandwidth wireless network access
was designed to deal with
mobility
Multiple end-point stations
Moving within cells and
In and out of cells

7. 802.16 Broadband Wireless 802.16 is intended for connecting buildings…
…houses --- fixed location points
… no mobility (yet)
range in 10s of meters
range in miles

8. 802.16 Broadband Wireless 802.16 transmitting over city, etc.
is omni-directional
is uni-directional – can be pointed
operates in th Ghz band (much higher than )
Millimeter wavelengths –
Tend to be absorbed by water
So error handling is more important
transmitting over city, etc.
Means securing and privacy very important

9. 802.16 Broadband Wireless 802.16 protocol stack Follows OSI model
Lower layer have several sublayers
Physical layer has several “modules” depending distance/modulation

10. 802.16 Broadband Wireless … continued 802.16 Physical Layer
Because of millimeter band signal strength falls off rapidly with distance…
Difference modulation techniques are used at different distances to achieve different data rates
… continued

11. 802.16 Broadband Wireless Modulation and data rates
Short distance = QAM-64 – 6 bits/baud
Medium distance = QAM-16 – 4 bits/baud
Long distance = QPSK – 2 bits/baud
At 125 MHz of bandwidth
QAM-64 = 150 Mbps
QAM-16 = 100 Mbps
QPSK = 50 Mbps

12. 802.16 Broadband Wireless 802.16 allocations bandwidth
Frequency Division Multiplexing (FDM)
Time Division Multiplexing (TDM)
Frames contain subframes (time slots)
Base station decide how many subframes are for Downstream data and how many are for upstream data
Base station can adjusts proportion of downstream/upstream subframes depending on data flow
A station can request a bandwidth allocation

13. 802.16 Broadband Wireless 802.16 Uses RSA Public Key encryptions
Only encrypts payload
…rest of frame in clear

14. 802.16 Broadband Wireless 802.16 – Four classes of services
Constant bit rate service
Automatic allocation of subframes
Voice and similar applications
Real-time variable bit rate service
Compressed video
Needs to transmit but irregular flow OK
Non-real-time variable rate service
Heavy transmission, but not real time
Data file transfers
Best-effort service
As available bandwidth

15. 802.16 Broadband Wireless Frame Structure
O = data frame 1= bandwidth frame
EC = payload encrypted
CI = type(pack/fragmenting
EK = Ids encryptions keys
Length = Len of frame
Connection Identifier = which connnection
Header CRC = CRC of header only
From: Tanenbaum (2003) pg. 309

16. Bluetooth More Information: http://www.bluetooth.com/bluetooth/

17. Bluetooth
Developed out of an interest by a cell phone manufacturer for a way for cell phone to connect to other devices sans cables
SIG created from Erricson, IBM, Intel, Nokia, and Toshiba…
… to develop standards
Bluetooth SIG standards in 1999
IEEE jumped in later
…became

18. Bluetooth Ever wonder where the name came from?
Harold Gormson (Harold I of Denmark), a Viking king

19. Bluetooth 802.11 intended to serve buildings
Range ~ hundred meters
Bluetooth intended to serve a room
Much more of a personal area network
Short run cable replacement (at least originally)
Range: 10 meter (that was the idea anyway)

20. Bluetooth Bluetooth architecture Small radio cell – piconet
Piconet about 10 meters
Multiple piconets can be bridged
Cell has one master node…
… and up to seven slave nodes
Can have up to 255 parked nodes
Master does all parking (valet?)

21. Bluetooth Bluetooth architecture Master does all control
Slave only does what Master says
This allow very cheap slave electronics (plan was for under $5 per chip
All communications must be master/slave, slave/master…
Never slave/slave
Bandwidth allocation via TDM

22. Bluetooth Bluetooth architecture 3 classes of radios used in Bluetooth
Class 3 radios – have a range of up to 1 meter or 3 feet
Class 2 radios – most commonly found in mobile devices – have a range of 10 meters or 30 feet
Class 1 radios – used primarily in industrial use cases – have a range of 100 meters or 300 feet
From:

23. Bluetooth Bluetooth architecture Uses 2.4 Ghz ISM band Uses FHSS
1600 Hops/second
Dwell time 625 microseconds
79 channels 1 Mhz each
FSK modulation
Uses same band/same channels as
802.11, garage door remotes, cordless phones, etc.

24. Bluetooth Bluetooth application profiles
From: Tanenbaum, 2003, pg. 312

25. Bluetooth Bluetooth links ACL – Asynchronous Connection Less
Packet switching irregular data
Slave can only have one ACL link with master
Synchronous Connection Oriented
Real-time data
Like voice, etc.
Slave can have up to 3 SCO links to master

26. Bluetooth Bluetooth SCO payload always 240 bits
ACL payload 80, 160, 240
Master uses even slots
Slave uses odd slots

27. Bluetooth Bluetooth frames Ack = piggybacking Ack on frame
Seq = number frames (one bit?)
Header repeated 3 times
Addr = address of one of eight active devices
Type = ACL, SCO, Polling, null
Flow = slave wants pause