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Wireless WANs In-Depth Presented by: Paul Melson, CNE Mark Lachniet, MCNE Holt Public Schools
“Wireless WANs” session agenda s s s s s 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 s s District-wide network installed through bond passage around 1993 Fiber optics wherever possible (local campuses) 11 Novell 4. 0 fileservers Lan 2 Lan WAN cards & 56 k DSU/CSU’s between remote locations and Education Center
The Problem: 56 k Leased Lines s s Too slow to be useful for anything other than EMail and simple applications Loading Group. Wise 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 s s s Remove leased line equipment Replace all 56 k lines with 4 mb/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 s s s 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 s s 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 s s s s 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 s s Provided by a service with a geographical database Shows the altitude, etc. of the land between two points
Path Analysis s Also shows the best height to mount the antenna on the tower
Logically Installing the Network s s s Simply had to add an NE 2000 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 networks just as if it were on Ethernet (except bridged)
Signal Strength s s 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 s s s 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: s s s s 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 s s s s Many different configurations available No FCC licensing necessary Many use the Lucent “Wave. LAN” card Point to Point vs. Omni-Directional 915 MHz vs. 2. 4 GHz - 5 separate channels Wide variance in speed, but most modern units are 2 mb/s to 10 mb/s Some (all? ) spread spectrum 10 mb/s solutions use all 5 2. 4 GHz channels, but is this good?
Omnidirectional vs. Point to Point
$ The Cost $ s s s 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 2 mb/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 Pinnacle. LINK 2/E Wireless Ethernet Bridge, 2 mb/s + Antenna $3, 295 Pinnacle. LINK 2/E Multi-Port Repeater, 4 mb/s + OMNI antennas $4, 395 Microwave, both ends, including towers and assembly, 10 mb/s $39, 885
Administrative Analysis: The Good Points s s s s 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 2 mb/s wireless link is better than a T 1 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 s s s s 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 30 KHz to 300 GHz. They break down into sub-bands from LF to EHF. Most commercial networking solutions use subchannels the UHF band, with a frequency range of 300 Mhz to 3 GHz, and a variable wavelength of 1 meter 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 s s s 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) s s High-speed code sequence manages frequency modulation Produces signal centered at carrier frequency
Frequency Hopping Spread Spectrum (FHSS) s s 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 s MAC layer protocol 802. 3 - Ethernet s 802. 5 - Token Ring s 802. 11 - Wireless LAN/WAN s New IEEE Standard s Open Industry Standard s Allows for third-party interoperability s
IEEE 802. 11 Features s s Robust (because of ACK, RTS/CTS, and fragmentation features) Multi-channel roaming Automatic rate selection (2 Mbps will fall back to 1 Mbps instead of dropping packets to increase reliability) Security WEP (Wired Equivalent Privacy based on RC 4) Protocol level error correction
Lucent's Wave. LAN Card s Uses IEEE Standard 802. 11 s 2 Mbps Raw Data s Supports 2. 4 Ghz s Direct Sequence (DSSS) Cards Available for: s PC 2 (PCMCIA) s ISA (PC Clone) s PCI (Mac Only)
Spectrum 24’s LA 2400 s s Uses IEEE Standard 802. 11 1 Mbps Raw Data Supports 2. 4 GHz & 2. 5 GHz Frequency Hopping (FHSS) Cards Available for: s PC 2 (PCMCIA)
Build Your Own? s s 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