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Wireless LAN Standards

◼ IEEE 802.

◼ HiperLAN

◼ BlueTooth

Introduction

◼ The IEEE 802. 11 specification is an international

standard describing the characteristics of a Wireless

Local Area Network (WLAN).

◼ The name Wi-Fi (short for "Wireless Fidelity”),

corresponds to the name of the certification given by

the Wi-Fi Alliance, formerly WECA (Wireless

Ethernet Compatibility Alliance), the group which

ensures compatibility between hardware devices

that use the 802. 11 standard.

◼ IEEE Created standard, but Wi-Fi Alliance certifies

products.

Disadvantages of WLAN

◼ QOS : lower quality because of lower bandwidth due to limitation radio communication, higher error rates due to interference; higher delay due to extensive error detection and correction mechanisms ◼ Proprietary solutions : slow standardization procedures ◼ Restrictions : products have to comply with national regulations; takes time to establish global solutions ◼ Safety and security : radio waves for data communications might interfere with other high-tech equipment; open radio interface makes eavesdropping easier; standards must offer additional mechanisms for encryption, privacy, anonymity etc.

Design Goals ◼ Global operation : for selling the products globally, national and international regulations have to be considered ◼ Low power : wireless devices run on battery power, design must implement special power saving modes and power management functions ◼ License free operation : equipment must operate in license-free band ( 2. 5 GHz ISM band) ◼ Robust transmission Technology : WLANs operate under difficult conditions; interference from other electrical devices, antennas are omnidirectional not directed, senders and receivers may move ◼ Simplified spontaneous operation : should not require complex set-up routine ◼ Easy to use : should not require complex management, should work on simple plug-and-play basis ◼ Protection of investment : should be interoperable with existing networks ◼ Safety and security : should be safe to operate; low radiation; use of encryption to avoid reading of user data, user privacy during roaming ◼ Transparency for applications : Existing applications should continue to run hiding the fact of wireless access and mobility

WLAN : Transmission Technologies

◼ Disadvantages

❑ Low bandwidth as compared to other LAN technologies ( 4 Mbits/s) ❑ Quite easily shielded ❑ Cannot penetrate walls or other obstacles ❑ For good transmission quality and high data rates, a LOS is needed ❑ Standardized only by IEEE 802. 11

WLAN : Transmission Technologies

◼ Radio Transmission

◼ Advantages

❑ Can cover larger areas ❑ Can penetrate obstacles (thinner) ❑ Additional coverage gained by reflection ❑ Does not need a Los if frequencies are not too high ❑ Higher transmission rates ( 54 Mbits/s)

WLAN : Types of Network

◼ Infrastructure based networks does not

necessarily imply a wired fixed networks

WLAN : Types of Network Infrastructure based ◼ Provide access to other networks also including forwarding functions, MAC etc. ◼ Communication takes place between wireless nodes and access points, not directly between nodes ◼ Access points control medium access and also act as bridge to other networks. Design of networks is simpler; most of the functionality lies with access point, wireless clients remain simple ◼ Can use different access schemes with or without collision ◼ Lose some of the flexibility wireless networks can offer ◼ Typical cellular phone system and satellite based cellular phones systems are infrastructure based

WLAN : Ad-hoc Network

◼ Do not need any infrastructure

◼ Each node can communicate directly with

other nodes

◼ No access point controlling media access is

necessary

◼ Complexity of each node is higher as every

node has to implement

❑ medium access mechanisms ❑ handle hidden and exposed terminal problem ❑ provide certain QOS.

WLAN : Ad-hoc Network

◼ Self organizing and adaptive

◼ Can be deformed on the fly

◼ No system administration

◼ Most often battery operated devices

◼ Multiple hops may be needed, i.e. each node

may act as a router

IEEE 802.11 - Goals ◼ Primary goal was specification of a simple & robust WLAN offering time-bound & asynchronous services. ◼ Mac layer should be able to operate with multiple physical layers, each of which exhibits a different medium sense and transmission characteristic. ◼ Candidates for physical layer: infra red & spread spectrum radio transmission techniques. ◼ Support of power management, handling of hidden nodes & ability to operate worldwide. ◼ Standard use 2. 4 GHz ISM band available in most countries around the world. ◼ Data rates envisaged were 1 Mbit/s mandatory and 2 Mbit/s optional

System Architecture : Infrastructure based ▪ Station (STA) ▪ Terminal with access mechanisms to the wireless medium and radio contact to the access point ▪ Basic Service Set (BSS) ▪ Group of stations using the same radio frequency ▪ Access point (AP) ▪ Station integrated to the wireless LAN and the distributed system ▪ Portal ▪ Bridge to the other (wired) network ▪ Distribution System ▪ Interconnection network to form one logical network; connects several BSSs via the AP to form a single network extending the wireless coverage area, also known as the Extended Service Set (ESS)

System Architecture : Ad-hoc based ▪ IEEE 802. 11 allows building of ad-hoc networks between stations forming one or more independent BSS (IBSS) ▪ The standard does not specify special nodes that support routing, exchange of data or exchange of topology information ▪ Two IBSS can be separated either by distance or using different frequencies or code

Protocol Architecture ◼ The adjoining figure illustrates a typical scenario; IEEE

802. 11 connected to switched
803. 3 Ethernet via a bridge ◼ Except lower BW & higher access time no difference; WLAN behaves like a slow wired LAN ◼ Upper part of Data Link Control layer, the LLC covers differences of MAC layers needed for different media ◼ The standard covers only the physical layer PHY and medium access layer MAC