Wireless LANs Part 1 - Introduction

Wireless Local Area Networks (Part 1) - Introduction

• Wireless LANs are networks that use radio waves to connect devices.
• Key elements of wireless networks include wireless hosts, wireless links, and base stations.
• Networks topologies include point-to-point, star, tree, switched star, and mesh.
• WLAN devices include client adapters, infrastructure, and bridging components.

Outline

• Elements of Wireless Networks
  • Wireless hosts, wireless links, base stations
• Topologies of Wireless Networks
  • Point-to-point, Star, Tree, Switched Star, Mesh
• WLAN devices
  • Client adapters, infrastructure, bridging
• IEEE 802.11 WLAN Standards
  • IEEE 802.11 WLAN Architecture
  • Discovering and Joining an IEEE 802.11 WLAN
  • MAC sub-layer standards
  • PHY layer standards
  • Network layer standards

Wireless Hosts

• Devices like laptops, PDAs, and IP phones can be wireless hosts.
• Hosts can be stationary or mobile.
• Wireless does not always mean mobility.

Base Stations

• Typically connect to the wired network.
• Relay packets between the wired network and wireless hosts within their coverage area.
• Examples include cell towers and 802.11 access points.

Wireless Links

• Typically used to connect wireless hosts to base stations.
• Employ multiple access protocols for coordinated link access.
• Support varying data rates and transmission distances.

Topologies of Wireless Networks

• Wireless point-to-point topology: common in wireless networks but may have various forms that apply in different technologies.
  • Examples: WLAN peer-to-peer (ad hoc) mode, WMAN backhauling, LAN wireless bridging, WPAN main topology (e.g., Bluetooth), and wireless optical communications (e.g., infra-red).
• Wireless star topology: a central device plays the role of a hub; it can be an access point, a base station, etc.
• Wireless tree topology: an access point switch or controller manages interconnections and data delivery among access points; simplifies management.
• Wireless switched star topology: the central device spatially divides stations using sectored or array antennas; overall throughput is multiplied by the number of transmitters (similar to switches in wired networks).
• Wireless mesh topology: consists of mobile nodes, stationary routers, and wired access points to create a reliable, self-healing network using multi-hop routing.

WLAN Devices

• Wireless LAN devices categorize as client devices, infrastructure devices, or WLAN antennas.
• Client devices include network interface cards (NICs), while infrastructure devices involve access points, outdoor wireless bridges, wireless switches or controllers.

WLAN Client Devices

• Wireless Network Interface Cards (NICs) transform network-capable devices like desktops, laptops, and PDAs into wireless devices (stations) that enable communication with other wireless devices or access points.
• Wireless NIC antennas may be internally integrated or externally connected/detachable.

WLAN Client Devices

• Wireless NICs are available in various form factors, including PCMCIA (obsolete), PCI, Mini-PCI cards, USB dongles, and fully integrated chipsets.

Access Point (AP)

• Acts as a switch/gateway for wireless hosts/stations, connecting them to a backbone network.
• Provides connectivity to wired resources.
• Offers security features (e.g., authentication, encryption, access control lists), network configuration capabilities (e.g., SNMP), and optional networking features (e.g., Internet gateways, LAN switching, wireless bridging, wireless repeaters).

Types of Access Points

• Multiple types of access points exist, each varying in form and appearance.

Outdoor Wireless Bridge

• Provides a point-to-point link between two remote wired and/or wireless network segments.
• Usually built for outdoor use with weatherproof enclosures.
• Employ high-gain directional antennas.

Wireless Switch or Controller

• Used in large-scale WLAN deployments (with tens or hundreds of access points).
• Aims to simplify deployment, configuration, and management of access points.
• Works with "thin" or "lightweight" dependent access points, handling most functionality.
• Offers lower hardware costs, simplifying configurations, improving mobility, and streamlining updates.

Sample Wireless Switch Layout

• Shows a layout example of a wireless switch and how it connects to access points.

WLAN Antennas

• Traditional fixed-gain antennas come in different types with various radiation patterns.
• Smart antennas, using antenna arrays, allow multiple nodes to transmit simultaneously, increasing throughput.

IEEE 802.11 WLAN Standards

• The FCC opened the 900 MHz, 2.4 GHz, and 5.8 GHz unlicensed frequency bands in 1985, triggering IEEE WLAN standardization.
• Various IEEE 802.11 standards have been ratified, each with differing generations, years of ratification, raw data rates, and operating frequencies.

Other IEEE 802.11 Standards

• Different versions have key characteristics like specific data rates, using different modulation, technologies (like OFDM or DSSS).

The Main Characteristics of 802.11 WLANs

• IEEE 802 standards cover Physical (PHY) and Media Access Control (MAC) sublayers.
• IEEE divides the Data Link Layer into Logical Link Control (LLC) and Media Access Control (MAC) sub-layers.

The IEEE 802.11 WLAN Components

• Stations (STA): devices implementing PHY and MAC layer protocols.
• Access Point (AP): Provides an interface between stations, often incorporated in a basic service set (BSS) and a distribution system (DS).
• Distribution System (DS): Connects multiple access points (APs) and their associated basic service sets (BSS) to form an extended service set (ESS).

The Basic Service Set

• A cellular structure.
• Each cell is a basic service set (BSS) with a unique identifier (BSSID).

The Extended Service Set

• Multiple BSSs are linked into an extended service set (ESS) with common distribution systems (DS).

The Independent Basic Service Set

• A peer-to-peer network, allowing wireless nodes to connect directly.

The IEEE 802.11 MAC Sublayer Standards

• Functions, services, frame formats, frame types, addressing mechanisms, WLAN discovery, WLAN joining, wireless media access.

MAC Sublayer Functions and Services

• Access control, discovering WLANs, gaining/maintaining connections during mobility, reliable data transfers of LLC frames, security services.

IEEE 802.11 MAC Sublayer Services

• MAC service data units (MSDU) delivery and WLAN access/security.

MSDU Delivery Related Services

• Association, reassociation, disassociation, MSDU delivery, distribution.

Access and Security-Related Services

• Authentication, deauthentication, privacy

MAC Sublayer Frames

• Frame formats, including frame controls fields and their components (like addresses, durations, and sequence controls).

Frame Types

• Management (e.g., beacon, authentication, association) frames
• Control (e.g., RTS,CTS,ACK) frames
• Data frames (carrying or not LLC data).

Discovering and Joining a WLAN

• Steps involved in finding a WLAN and joining it, such as scanning, beaconing, and authentication.

Beaconing

• Regular AP transmissions; broadcast frames announcing the presence of a WLAN BSS and providing other information to join.

The Contents of the Beacon Frame

• Fields within beacon frames like the beacon interval, timestamp of the beacon source clock, Service Set Identifier (SSID), supported data rates, parameter sets, capability information.

Scanning

• Method for discovery.
• Passive or active.

Authentication

• Verifying a device's identity.
• Open system authentication: simply checking shared SSID
• Shared key authentication: needs a shared pre-configured key.

Association

• Final step toward allowing a station to join a WLAN after authentication.

Association-Related Services

• Services for transferring MSDUs among STAs, relevant to different types of transitions based on the STA mobility.

Station Location

• The DS (distribution system) needs station location data to deliver MSDUs.

A Sample Scenario of a STA Mobility Among APs

• Illustrative diagram of station (STA) movement and how wireless systems manage the transition between access points (APs) during mobility. 

Explore the fundamentals of Wireless Local Area Networks (WLANs) in this quiz. Learn about the key elements of wireless networks, various topologies, and the essential devices involved. Additionally, get familiar with the IEEE 802.11 WLAN standards that govern these networks.