Transcript 1998-11-19-MIEM-WirelessWANs

Wireless WANs In-Depth
Presented by:
Paul Melson, CNE
Mark Lachniet, MCNE
Holt Public Schools
“Wireless WANs”
session agenda
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Case example - Holt Public Schools
The solution - Install wireless WAN
Applications for wireless networking
Cost, speed, and configurations
Radio Frequency Networks
Spread Spectrum
IEEE 802.11
Available Hardware
Build Your Own?
Case Example
Holt Public Schools
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District-wide network installed through
bond passage around 1993
Fiber optics wherever possible (local
campuses)
11 Novell 4.0 fileservers
Lan2Lan WAN cards & 56k
DSU/CSU’s between remote locations
and Education Center
The Problem:
56k Leased Lines
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Too slow to be useful for anything other than EMail and simple applications
Loading GroupWise Administrator 4.1 took 15
minutes!
Routed solution - protocol specific and
complicated (subnetting TCP/IP)
EXPENSIVE = $12,000 per year budgeted for
recurring fees on leased lines
Frequently down due to problems with
Telephone Company
Holt’s Original WAN design
The solution:
Install wireless
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Remove leased line equipment
Replace all 56k lines with 4mb/s wireless
Move from routed to bridged networking
Installed Linux proxy servers for Internet
Original specification bid at $42,000 (but
increased as & locations features added)
Will pay for itself within 5 years
The New Holt Schools WAN
Physically Installing the Network
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Originally installed telescoping masts
Had to upgrade to true tower segments
because they weren’t high enough
Supporting guywires required so
placement on the building was difficult
Required drilling through brick to run the
2 coaxial cables to an inside location
Placed “Pinnacle Link” CPU in closet or
storage room
Physically Installing the Network
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Had to install and ground surge suppressors
and lightning arrestors
Had to run UTP cable or fiber optic from the
closet to the rest of the network
Overall, installing the physical components
was hard work!
My advice: contract the vendor to do it for
you, and set up your agreement so you pay
when it is all working (we didn’t have this
problem ourselves, but you never know)
Directing the Signal
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Relatively small data beam must be aimed
Use GPS to determine general directions
One person climbs the tower with a walkie-talkie while
another watches the signal strength on the monitor
Signal can go through some obstructions such as sparse
leaves
CANNOT go through buildings, tree trunks, or hills
Our product has a “test mode” for reporting signal
strength but we used a free UNIX program called
TCPspray to measure actual throughput
The bandwidth was sometimes low when the signal was
reported as good - so test your system!
Path Analysis
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Provided by a service with a geographical database
Shows the altitude, etc. of the land between two
points
Path Analysis
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Also shows the best height to mount the
antenna on the tower
Logically Installing the Network
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Simply had to add an NE2000 Ethernet card to one
fileserver at every campus location
Plugged bridge and fileserver into the same
Ethernet hub
Had to “bind” a common network address to the
wireless network
We used the IPX network number “314159” - in
other words “the Pi in the sky”
Could also have done it as one big network with
everyone on it - but why?
From this point on, the network works just as if it
were on Ethernet (except bridged)
Signal Strength
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Having good signal is essential to having a
good connection
Height is a big factor - the higher the
better
The length of the coaxial cable from the
antenna to the CPU is also a big factor the bigger the distance, the bigger the loss
Use of amplifiers can greatly boost the
signal of the links (this is what we use)
An Ethernet Bridge
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Reduces traffic across WAN link
Forwards or doesn’t forward information
based upon the destination MAC address of
the network packet
Maintains a table of which MAC address is
on which side (wireless or Ethernet)
Will not forward traffic across the WAN link
if it knows the recipient computer is on its
own network
Modern units do more sophisticated routing
Wireless WANs
a good fit for:
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Areas where no Telco solution is available
Areas with major obstructions (freeways,
railroad tracks, property owned by others, etc.)
where fiber optics are not possible
The tight budget - especially long term
Institutions that need more speed
Campus areas (many buildings in a small area)
Over harsh terrain
Data Security
Configurations
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Many different configurations available
No FCC licensing necessary
Many use the Lucent “WaveLAN” card
Point to Point vs. Omni-Directional
915MHz vs. 2.4GHz
2.4GHz - 5 separate channels
Wide variance in speed, but most modern units
are 2mb/s to 10mb/s
Some (all?) spread spectrum 10mb/s solutions
use all 5 2.4GHz channels, but is this good?
Omnidirectional vs. Point to Point
$ The Cost $
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Wide variance of price and quality
Good luck getting it funded by USF - the Telco companies lose
money on wireless :(
On the plus side, if you go all wireless, you might not have to
fill out USF forms!
Don’t forget about installation costs, costs of towers, labor, etc.
Must buy 2 units to make a link, for a minimum of $6490 for a
2mb/s solution if you already have line of sight
This is based only on our vendor - your mileage will vary
From Pinnacle Communications of Dayton
PinnacleLINK 2/E Wireless Ethernet Bridge, 2mb/s + Antenna
$3,295
PinnacleLINK 2/E Multi-Port Repeater, 4mb/s + OMNI antennas $4,395
Microwave, both ends, including towers and assembly, 10mb/s
$39,885
Administrative Analysis:
The Good Points
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A good sell - recurring fees are bad
Generally, the links are upgradable in the future by
simply replacing the wireless network card
Once properly configured, need little maintenance
Easy to assimilate into any network design
Fast - a 2mb/s wireless link is better than a T1
Resistant to adverse weather, fog, etc
Good data security
More control over your network
All E-Mail is now Air-Mail!
Administrative Analysis:
The Bad Points
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Not easy to set up by yourself
Initial investment requires up-front money
Can’t always service the wireless equipment yourself
(district insurance policies)
May require a service call from a far away vendor this means waiting
Possibility of interference from Cell towers, etc.
Limited distance (generally 10 miles)
Minor hassle from weather (ice storms, extreme
winds)
Requires line-of-sight to remote locations
Radio Frequency Networks
RF signals, including microwave, operate at
frequencies from 30KHz to 300GHz. They break
down into sub-bands from LF to EHF. Most
commercial networking solutions use subchannels the UHF band, with a frequency range
of 300Mhz to 3GHz, and a variable wavelength
of 1meter to one tenth of a meter.
Radio Frequency Networks
RF networks are not limited to data applications.
They can support audio/video content, voice
communications, cellular and PCS signals. RF LANs
and WANs are the current state-of-the-art in
networking mobility. The ability to connect people,
computers, and other resources without cables and
without requiring FCC licenses will change the way
the world works, and has the potential to revolutionize
the way in which schools work together.
Spread Spectrum
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Military Background
Low Probability of Intercept (LPI) and
low interference through pseudo-noise
algorithms.
Modulation Schemes (DSSS, FHSS, and
THSS or “Chirp”)
Spread Spectrum History
Invented in Germany during WWII, both the Axis
Powers and the Allies experimented with simple
frequency-hopping algorithms. SS has been adopted as
a staple means of field communication by the US
military because of its LPI and anti-jamming
characteristics. Despite the military’s reliance on this
medium, it has only been within the past 5 years that
commercial uses have become prevalent.
Direct Sequence Spread
Spectrum (DSSS)
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High-speed code sequence manages
frequency modulation
Produces signal centered at carrier frequency
Frequency Hopping Spread
Spectrum (FHSS)
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Code function determines “hops” to
manage frequency modulation
Carrier is flat across spectrum
Spread Spectrum Note
Frequency modulation types are all
exclusionary, meaning that a point-topoint link can not use FHSS on one end
and DSSS on the other. Also, modulation
is often hardware specific, making a
heterogenous environment a wise option.
IEEE 802.11
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MAC layer protocol
802.3 - Ethernet
 802.5 - Token Ring
 802.11 - Wireless LAN/WAN
 New IEEE Standard
 Open Industry Standard
 Allows for third-party interoperability
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IEEE 802.11 Features
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Robust (because of ACK, RTS/CTS, and
fragmentation features)
Multi-channel roaming
Automatic rate selection (2Mbps will fall back
to 1Mbps instead of dropping packets to
increase reliability)
Security WEP (Wired Equivalent Privacy based on RC4)
Protocol level error correction
Lucent's WaveLAN Card
 Uses IEEE Standard 802.11
 2Mbps Raw Data
 Supports 2.4Ghz
 Direct Sequence (DSSS)
Cards Available for:
 PC2 (PCMCIA)
 ISA (PC Clone)
 PCI (Mac Only)
Spectrum24’s LA2400
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Uses IEEE Standard 802.11
1Mbps Raw Data
Supports 2.4GHz & 2.5GHz
Frequency Hopping (FHSS)
Cards Available for:
 PC2 (PCMCIA)
Build Your Own?
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Hardware is cheap and available
802.11 standard bolsters interoperability
between commercial and “homegrown”
equipment
Open Source solutions like Linux available for
free to handle network management
Build firewalls, routers, bridges and proxies,
all for less than $1500/each
QUESTIONS?
Paul Melson, CNE
[email protected]
Mark Lachniet, MCNE
[email protected]
This presentation at http://lachniet.com