CPET 260 – Network I Wireless Networks Bluetooth

Wireless Networking: IEEE (Wi-Fi) and Home RF Advantages Fast installation Adaptable to changing environment Reduced costs in many situations Applications Hospitals Older buildings Temporary setups Warehouse & Factor Floors

Ad-Hoc Networks & Access Points (Aps) Ad-Hoc networks are established ‘on the fly’ A number of computers, each with wireless NIC adapters Communications is established by the computers interchange Peer to Peer network AKA – Basic Service Set (BSS) or Independent Basic Service Set (IBSS)

Access Point An AP acts as an intermediary in the network – potentially extending the distance between far points of the net. AP can be added to a wired net to provide extend or provide additional services.

Examples D-Link DWL-1000AP 11Mbps, 5.5Mbps, 1Mbps or auto Supports DHCP 100 to 300 meters

Examples D-Link DL-713 Wireless Gateway Wireless + 3 switch ports Supports Network Address Translation (NAT) – security IEEE b & ‘Wi-Fi’ compatible

IEEE Standards Spread Spectrum radio Frequency Hopping Spread Spectrum (FHSS) Original std used FHSS 1Mbps Direct Sequence Spread Spectrum (DSSS) Supported both 1Mbps & 2Mbps IR is included – at 1Mbps & 2Mbps Not implemented to any great amount

IEEE Standards The MAC layer – Ethernet used CSMA/CD – Carrier Sense Multi-Access/Collision Detect Required that transmission be monitored while sent RF cannot perform monitoring while sending CSMA/CA – Carrier Sense Multi-Access / Collision Avoidance

CSMA/CA As with CSMA/CD – the NIC listens for a carrier already in use If detected – backs off & waits If no detection, sends packet Waits for ACK packet – to acknowledge receipt of data packet. If no ACK – the lost packet is retransmitted. Also known as Distributed Coordination Function (DCF)

CSMA/CA In a wireless network, since each node needs only to communicate to the AP – not to each other, they may be out of range of one another. Hidden Node problem Solved by sending RTS (request to send) + amt of time needed to the AP AP responds with CTS

CSMA/CA All units on net receive CTS + time required Other units back off the time granted by AP Known as Point Coordination Function – PCF DCF is required by IEEE , PCF is not

Association / Reassociation Provides for migration from one BSS to another, as the node moves physically MAC layer provides

Radio Wave Transmissions FHSS versus DSSS On – GHz range Known as the ISM band (Industry, Scientific, Medical) Spread Spectrum Developed in WWII for security As apposed to narrowband

Spread Spectrum Radio transmission is transmitted on a greater bandwidth than the actual transmitted data. Resulting bandwidth is determined by a method other than by data transmitted. Up to 1000 times wider BW

FHSS versus DSSS FHSS – uses a narrowband transmission in the range of the SS transmission Both ends must know the starting frequency and the pattern used No data burst longer than 400 ms for one frequency. May skip from one to next May skip on preset pattern

FHSS versus DSSS DSSS uses pseudo-noise signal on all frequencies not used by data burst. Both ends know the algorithm for generating the pseudo-noise pattern Noise is removed at receiver, leaving data

What is Wi-Fi Wireless Ethernet Compatibility Alliance (WECA) produces products using IEEE b standard Wi-Fi extends to 11 Mbps Designed for both home/business wireless solutions

Security standard is Wired Equivalent Privacy (WEP) Shared 40 bit key for security RC4 encryption algorithm Can be ‘broken’ easily Work is underway for WEP2 (IEEE e)

HomeRF A home version of wireless on 2.4G ISM band Uses FHSS technology SWAP 2.0 Shared Wireless Access Protocol 1.6Mbps

References IEEE DSSS Overview fi.com/downloads/weca80211boverview.pdfhttp:// fi.com/downloads/weca80211boverview.pdf IEEE Technical Tutorial fi.com/downloads/IEEE_80211_Primer.pdf fi.com/downloads/IEEE_80211_Primer.pdf Reliability of IEEE Hi Rate DSSS WLANs in a High Density Bluetooth Environment fi.com/downloads/Coexistence_Paper_Intersil_ Aug18.pdfhttp:// fi.com/downloads/Coexistence_Paper_Intersil_ Aug18.pdf

Bluetooth Voice and Data Performance in DSSS WLAN Environment fi.com/downloads/BT_inf802_June_8.pdfhttp:// fi.com/downloads/BT_inf802_June_8.pdf Wi-Fi WEP Security Update fi.com/pdf/Wi-FiWEPSecurity.pdfhttp:// fi.com/pdf/Wi-FiWEPSecurity.pdf Does Frequency Hopping Enhance Security? fi.com/pdf/ _frequencyHopping.pdf fi.com/pdf/ _frequencyHopping.pdf

Wi-Fi Security Update fi.com/pdf/ _WEP_Security.pdf fi.com/pdf/ _WEP_Security.pdf Operating Rules, PDF b/Rules/WPAN-Rules.pdf Operating Rules, PDF b/Rules/WPAN-Rules.pdf