Wireless Service Engineering
Properties of Communication technologies
- Communication range
- Lower frequency → less power required to gain longer distance,
- Latency
- Data transfer rate
- Architecture
- Price for creating network
Wireless LANs
- IEEE 802.11 family, HiperLAN…
- IEEE Standards dominant
- Wi-Fi (Wireless Fidelity)
- Certified 802.11 standard family compliant product
- Trademark of Wi-Fi Alliance
- Supported by most types of devices
- built-in on most laptops and some PDA's and evenn mobile phone
- Adding the capability to the device
- PCMCIA cards
- CF cards
- Global standard → same client works everywhere.
- Core elements of Ethernet present
- 48-bit MAC
- Frames delivered based on MAC
- Additional reliability mechanisms
- HiperLAN is ETSI standard
- co-operation on 2.4Ghz spectrum
- Topology
- Infrastructure mode/network
- Terminals connected to access point
- Peer-to-peer or ad hoc mode or independent network
- Terminals connected to each other directly
- Access points
- Directional or omnidirectional RF
- range is from tens to hundreds of meters
- Access points usually have an ethernet connection.
- Many brands to choose from
- Lower cost
- 2.4GHz ISM band (Industrial Scientific Medical) (used by most WLAN standards)
- Free for using, no regulations
- Maximum transmission power
- Creating own network free, no licenses needed
- No regulation → interference problems
- s
- No strong authentication
- Nominal speed from 1Mb/s to 100Mb/s
- Power consumption rather high
IEEE 802.11 family
| spec | speed | Frequency | |
| 802.11a | 54Mbps | 5Ghz | non free frequency |
| 802.11b | 11Mbps | 2.4Ghz | Wi-FI |
| 802.11g | 54Mbps | 2.4Ghz | speed update to b |
| 802.11n | 100Mbps | 2.4Ghz | next step after g |
Connectivity
- Connection forming between AP and mobile or between several mobiles
- The desired network is found through scanning
- SSID is the identifier of network (service set identifier)
- Active scan
- Sending probe frame to inform SSID of the network the device wants to join
- using Broadcast SSID in probe results response from all networks within range
- Passive scanning
- Listening communication on each WLAN channel to found out which is used by desired SSID
- Responses
- Access points responses to the probes
- On ad hoc networks station that generated last beacon frame responds
- After the desired network is found authentication and association is conducted
- Open system authentication
- Authentication based on MAC address
- Shared key authentication
- WEP must be enabled
- One access point can serve up to 100 devices
- Latency
- from few milliseconds to hundreds of illiseconds
- Processing the connections increase latency
- The more there is users the higher the latency
- Roaming is possible
- Not always supported
- Some compatibility issues between different vendors products.
Things to consider
- Who creates network?
- How big network is required?
- What is the cost for upkeeping own network?
- What kind of billing we can arrange?
- Rely on TCP/IP?
- How to conduct service discovery?
- Dedicated SSID for a device providing certain type of service?
- How about security?
