Wireless Infrastructure: Networks and Issues (2)

H. Scott Matthews

February 26, 2003

Recap of Last LectureWireless generally a ‘radio’ technology

Dependent on antennas (cell sites) Cell sizes getting generally smaller

Spectrum allocation has become an increasingly complex problem as there have been more demands for it (FCC)

Number wired/wireless users ~ equal

FCC’s involvement In telecom, the government tends to

regulate the devices not the network E.g. licenses spectrum for use Certifies devices (e.g. phones) compliant

Industry/professional groups (e.g. IEEE) generally set equipment/network standards

Management Metrics Different type of problem since networks are generally

private Subscribers

Number, growth, net additions Voice quality Time to login to system, call access time Percent completed calls or call failure rate

Coverage area Percent of US, Percent of population, ..

Financial Margin (profit) per minute, subscriber

Others?

Wireless ‘Data’ Networks IEEE 802.11b (used on campus)

11 Mbps, using 2.4 GHz spectrum (unlicensed!) 14 channels, 2.4 to 2.4835 GHz (80 MHz) Different channels legal around world, only chan. 1, 6,

and 11 have no overlap Designing a big network means reusing channels and

considering overlaps Usually uses PC cards, access points + wired Industry group (WiFi alliance) certifies products

802.11a: 54Mbps @ 5 Ghz, 12 channels no overlap - 500 MHz of frequency

802.11g backwards compatible with 802.11b, but boosts speed to 54 Mbps

CMU Campus Wi-Fi Network

CMU campus: ubiquitous wired, wireless networks Every room on campus ‘wired’, every space

‘wireless’ 10,000 users; 350 wireless antennas (about 30

users each) How much electricity used?

Functional, but not equivalent, comparison Show energy “to network 10,000 users

wired/wireless” Only ‘network’ - not ‘attached devices’ - in boundary

Campus Network Model

120 Wiring Closets

Office/room equipment

350 WirelessAntennas

Main computer center

Two Data Sources Campus has building-level electricity meters

installed Several buildings have more than one meter when

areas have higher than average use Used for “Main computer center electricity” Not so useful for electricity of room/equipment

Portable power meters to measure electricity use of pieces of equipment Measure one of each, scale up via inventory

Summary of EstimatesAnnual

Electricity(MkWh)

Power (kW)

Main Computing Center 4.2 480Office Network Equipment 0.01-0.11 15Wiring Closets – Wired Switches 0.2 30Wireless Transceivers & Switches 0.03 3Total 4.4 – 4.6 520

Network electricity 6% of total campus - 1.7 kWh/ft2

Wireless endpoints use 10x less electricity than wired Caveats: speeds, installation and maintenance requirements

different Wireless speed bump coming (10x) but electricity use

expected go up only 50% Relevance: more voice wireless than wired in the world

Overall Voice Network ElecDo similar analysis, estimate PSTN and

wireless voice network electricity use PSTN = Public Switched Telephone Net

Consider number and kW of cell sitesTotal energy use of sector, etc.Get estimate of 30 TWh/yr

< 1% of US electricity consumption

Other Issues Ad hoc = latin for ‘for this (time)’

Ad hoc networks are temporary, maybe one use systems

Difference in use and design of networks Don’t have to be ‘operating’ all the time

‘Beaming’ with palm pilots is an example New ‘Bluetooth’ devices will be too

Useful for sensor networks (coming soon!) Issues with designing/managing ad hoc?

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Seepublicinternetproject.orgFor details, more research

Open/Public Wireless Nets Example of more formalized/larger ad hoc networks

(not fully “ad hoc”) Campus wireless is not an example because you need to be

registered to use Communities building small-medium wireless networks

with their own broadband connection and wireless points (hotspots)

Could have ‘network name’ commonality but no password/authentication/registration

There are people who drive around looking for ‘open’ wireless networks just for fun Note: these guys need more work / less free time

Implications of Open NetsCoordination (e.g. same network name)Security!

Preventing questionable traffic Hacking/cracking/spamming

Leeching (free rider problem)