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WLAN Topologies Overview

Module 7: WLAN Topologies

This module focuses on the various wireless networking topologies and the related standards that define their operation, design, and implementation in real-world environments.

Wireless Networking Topologies

Wireless Wide Area Network (WWAN)

WWANs cover extensive geographical areas, typically utilizing cellular technologies such as GPRS, CDMA, TDMA, LTE, and GSM. These networks are crucial for enabling connectivity for various devices including smartphones, tablets, and modems across regions where wired connections may not be feasible. They facilitate mobile communications and data services over significant distances.

Wireless Metropolitan Area Network (WMAN)

WMANs provide radio frequency (RF) coverage across metropolitan regions, such as urban cities and their surrounding suburbs. They often utilize the 802.16 standard (WiMAX), which allows for high-speed wireless connections that integrate various wireless technologies for service delivery. WMANs serve to bridge the digital divide by offering broadband access to underserved areas.

Wireless Personal Area Network (WPAN)

WPANs are designed for close-proximity wireless communication among devices, typically within a range of 10 meters. Technologies such as Bluetooth (operating via radio-frequency) and Infrared (which uses light-based mediums) facilitate communication among devices like laptops, smartphones, cameras, and wearable tech, supporting a range of applications from file transfers to audio streaming.

Wireless Local Area Network (WLAN)

WLANs support wireless networking within confined locations such as buildings or campuses, harnessing the 802.11 standards. This makes WLANs the most common deployments both in residential and commercial settings due to their high data transfer speeds and range. They enable a network of connected devices to share resources and access the internet seamlessly.

802.11 Stations

Stations (STA)

The cornerstone of WLANs includes stations, which comprise radios that either exist inside an Access Point (AP) or as client stations (CS). Every station is assigned a unique Media Access Control (MAC) address essential for communication over the network.

Client Station

Client stations refer to non-AP radios found within devices like laptops or smartphones. These stations contend for half-duplex RF medium access, allowing them to communicate with the AP while maintaining layer 2 connections when associated.

Access Point (AP) Station

Access Points act as wireless portals, facilitating connections for client stations and managing communications via the Distribution System Access Function (DSAF). They are pivotal in creating robust wireless networks that ensure connectivity for multiple devices simultaneously.

Integration and Distribution Service

Integration Service

Defined by the 802.11-2020 standard, the Integration Service enables the transfer of MAC Service Data Units (MSDUs) between various distribution systems. This is vital for frame transfer via access points or WLAN controllers.

Distribution System (DS)

The Distribution System interconnects multiple Basic Service Sets (BSS) through integrated Local Area Networks (LANs), forming what is known as an Extended Service Set (ESS). The DS consists of several components:

  • Distribution System Medium (DSM): A logical medium linking access points, typically based on the IEEE 802.3 standard.

  • Distribution System Service: Responsible for forwarding network information from layer 3 to layer 7 (MSDUs).

Wireless Distribution System (WDS)

WDS functionality employs interconnected APs to create mesh deployments, effectively enhancing coverage and providing backhaul capabilities. This is commonly utilized in outdoor bridge links for establishing connections between buildings.

802.11 Service Sets

Types of Topologies

  • Basic Service Set (BSS): The fundamental part of a WLAN consisting of one AP and multiple client stations.

  • Extended Service Set (ESS): Multiple identically configured BSS connected by Distribution System Medium (DSM); supports seamless roaming across overlapping AP coverage.

  • Independent Basic Service Set (IBSS): A peer-to-peer network comprising solely client stations without an AP.

  • Personal Basic Service Set (PBSS): Engages in direct communication among 802.11ad stations without centralized control, managed by the PBSS Control Point (PCP).

  • Mesh Basic Service Set (MBSS): APs relay traffic in a mesh network configuration to extend coverage and connectivity.

  • Quality of Service Basic Service Set (QBSS): Prioritizes traffic management across 802.11 service sets to enhance performance.

Service Set Identifier (SSID)

The SSID is a logical name (up to 32 characters) used to identify 802.11 networks, enabling users to distinguish between different networks within the range.

Basic Service Set

Definition

The Basic Service Set (BSS) is defined as a core topology where one AP manages multiple client stations that associate with it for effective communication.

Basic Service Area (BSA)

The coverage area provided by an AP is referred to as the Basic Service Area (BSA). Stations can maintain communication as long as signal strength remains within acceptable limits.

Basic Service Set Identifier (BSSID)

The Basic Service Set Identifier (BSSID) is the MAC address of the AP's radio element, functioning as the layer 2 identifier for each BSS. In scenarios involving multiple BSSIDs on a single radio interface, these identifiers typically increment based on the MAC address.

Extended Service Set

Configuration

An Extended Service Set comprises multiple BSS that are identically configured and interconnected via Distribution System Medium (DSM). This supports seamless roaming, allowing mobile devices to maintain connections as they move through overlapping AP coverage.

Nomadic Roaming

When client devices move between disjointed cells, they experience a loss in connectivity that must be reestablished, exemplifying the challenges associated with mobility in wireless networks.

Extended Service Set Identification (ESSID)

The ESSID is similar in function to the SSID and is crucial for maintaining consistent network credentials across multiple APs in an Extended Service Set.

Independent Basic Service Set

Structure

An Independent Basic Service Set (IBSS) is structured solely of client stations which allow them to communicate directly with one another, operating much like a wired crossover cable setup without the need for an AP.

Personal Basic Service Set

Characteristics

In a Personal Basic Service Set (PBSS), communication occurs directly between 802.11ad stations without relying on a centralized AP. The group is led by a specific client termed the PBSS Control Point (PCP), facilitating peer-to-peer communication.

Mesh Basic Service Set

Functionality

In a Mesh Basic Service Set (MBSS), APs function to distribute wireless traffic across the network, forming a mesh that can enhance coverage and connectivity. A designated mesh portal connects to a wired infrastructure, while various mesh points relay traffic among each other.

Quality of Service Basic Service Set

Implementation

The Quality of Service Basic Service Set (QBSS) incorporates mechanisms that ensure the efficient management and prioritization of traffic across all 802.11 service sets, thereby improving overall performance and user experience across the network.

Configuration Modes - Access Points

Default Modes

Access points may operate in various modes:

  • Root Mode: Serves as the default mode wherein the AP functions as a wired network portal.

  • Mesh Mode: For deploying a mesh topology.

  • Sensor Mode: Utilized for sensor networks.

  • Bridge Mode: Interconnects wired and wireless segments.

  • Workgroup Bridge Mode: Allows client access to an AP.

  • Client Mode: Connects client devices directly to the network.

Configuration Modes - Clients

Operational States

Clients can operate in:

  • Infrastructure Mode: The default mode where clients connect through access points.

  • Ad Hoc Mode: Allows peer-to-peer communication within an Independent Basic Service Set (IBSS) without the necessity for an AP.

Questions

Exam Preparation

This module includes 20 questions designed to assess comprehension and reinforce learning pertaining to WLAN topologies and configurations.