Practical Aspects of Wireless Networking

Stephen Stuart

Table of Contents

• Stan Barber's Notes
• Sharif Torpis's Notes
• June 1997 NANOG Home Page

Sharif Torpis from PAC*BELL volunteered his notes for this talk. They are included along with my own.

Stan Barber's Notes

Altavista says there about 1000 responses to a search for wireless networking.

There are two basic technologies:

• point-to-point
• Wireless LANs

This talk is mostly going to be about Wireless LAN

Ricochet is one and WaveLan/WaveNet & compatibles is the other.

Ricochet uses a band around 915Mhz and attempts to emulate modems (14.4 or 28.8k).

WaveLAN/WaveNet --Developed by NCR/AT&T -- Digital calls it RoamAbout and Lucent calls it WaveLAN. Some countries don't license things in 915Mhz.

WaveLAN is the "air interface" and is IEEE 802.11 -- CSMA/CA

WaveNet is the roaming spec.

WaveNet provides bridged access to a wired network. Access points announce themselves to mobile stations and to other mobile stations.

These parameters control roaming: Domain ID, Network ID and Beacon Key.

Mobile stations need to know Network ID to transmit to an AP. Mobile Stations can receive without knowing the network ID. However, without the beacon key, the network ID can't be decrypted.

A Mobile station listens to multicast announcements from the various access points. Choose one based on quality (and access information).

Roaming may not be required and doesn't have to be used.

There are risks. Unwanted access to your network can happen. Anyone can listen to your network. Anyone with network id can transmit. Treat the network like an untrusted public network. Noise is bad. But, others are also authorized to use spectrum that can interfere with this unit (and probably with each other). Microwave ovens can interfere.

Some things can be opaque. Metal is hard to get through and hard to get around. Reinforced concrete walls can be a problem. Heavy foliage can absorb signals.

Some things can bounce.

Designing the network involves lots of decisions and work in the environment to determine what works.

Sharif Torpis's Notes

• point to point circuits (microwave, laser, 10Mb/s ethernet, FDDI, OC3)
• wireless LANs (Ricochet serial line, Wavelan/Wavenet and competitors ethernet)
• Ricochet
  • 14.4-28.8Kbps
  • 40 Kbps in peer to peer mode
• 915MHz (902-928MHz really, with 160KHz subchannels, ~300m)
• 2.4GHz (~180m, shorter wavelength)
• Wavelan/Wavenet
  • DEC's name is Roamabout
  • Lucent's name is Wavelan
  • 915MHz and 2.4GHz versions
  • check for country specific frequency specifications
  • Wavelan is the "air interface" spec (IEEE 802.11, CSMA/CA)
  • Wavenet is the roaming spec (how stations roam among providers, bridge access to wired net)
• how Wavelan works
  • domain ID
  • network ID: identifies an AP, different AP == different NWID
  • beacon key: encrypts NWID for APs w/ same DOMID
  • APs send multicast announcements on wireless i/f
  • MS needs NWID to xmit to AP
  • MS can recv w/o knowing NWID!
  • MS sets NWID to promiscuous mode during initial connect to AP or when switching APs
• don't need roaming?
  • routed access to wired net
  • set radios to common NWID
  • bridged access using APs
  • could be consider a point to point mode
• risks
  • unwanted access to your net
  • anyone with NWID can xmit (NWID is 16 bit int 0-FFFF)
  • with one attempt every 10 secs, it would take ~3 weeks/8hr/day to find NWID
  • anyone can listen period
  • anyone with beacon key can decode multicast annnouncements to get NWIDs
  • life is even easier for hacker if you provide DHCP address assignments
  • firewall, SSH, end to end encryption
• noise is bad
  • 915MHz crowded
  • new PCS in 2.4GHz
  • microwave ovens (largest occupant of 2.4GHz spectrum), workstation with cover off, AC units
• architecture good or bad
  • metal (hard to get through/around)
  • reinforced concrete
  • heavy foliage
  • reflective (e.g. at Memphis IETF, signal bounced off hotel across street and reached upper floors of hotel)
• designing
  • roaming required?
  • routing/bridging?
• RF analysis tools on MS
  • ID noise sources, permanent and variable
  • ID range
  • walking around with laptop is fun and scares humans
• geek stuff
  • Win95 driver support, BSDI, FreeBSD, Linux
  • RF experiments: weird antenna can increase range, directional gain, etc.
• monitoring software demo
  • signal level
  • S/N ratio
  • signal quality