Сервисы Wi-Fi | Курс "Компьютерные сети"

Introduction to Wi-Fi Services in Wired Networks

Overview of Wi-Fi and Ethernet

• The lecture introduces the topic of Wi-Fi services within wired networks like Ethernet, highlighting that Ethernet has a single data transmission service.

• Unlike wired connections, Wi-Fi operates in an open environment using radio waves, necessitating additional services for reliable network operation and data protection.

Key Services in Wi-Fi Networks

• Before transmitting data over a wireless network, users must authenticate themselves to prove their right to access the network.

• Data encryption is crucial due to the accessibility of wireless signals; thus, protecting transmitted information is essential.

Basic Service Set (BSS)

Understanding Basic Service Set

• The basic service set consists of one access point that can operate independently or connect to a distribution system for internet access.

• Access points broadcast identifiers such as the MAC address and a human-readable service identifier when advertising available networks.

Authentication Process

• Users must undergo authentication by sending a management frame request to the access point. If approved, they receive a positive response.

• There are three authentication modes:

• Open authentication allows anyone to connect without restrictions but lacks encryption.

• Personal authentication uses a shared password for all devices, suitable for home use.

• Enterprise mode provides individual credentials stored on servers for higher security.

Association and Data Transmission

Associating with the Network

• After successful authentication, clients send an association request detailing compatible parameters. A successful response allows data transmission through the access point.

Data Handling Between Clients

• All client-to-client communications still route through the access point to manage shared airspace effectively.

Advanced Scenarios in Wireless Networking

Additional Authentication Requirements

• In some cases, clients may need further authorization after initial association before being allowed to transmit data.

Example of Captive Portals

• Public networks often require users to log in via captive portals after connecting without passwords; this typically involves entering phone numbers or other credentials.

Extended Service Set (ESS)

Overview of Extended Service Set

• An extended service set is used for larger areas requiring multiple coordinated access points managed by an external controller.

Roaming Capabilities

Access Points and Client Information Management

Client Connection Process

• Information is retained not only at the access point but also in the controller. When a client moves into another access point's range, the controller already has information about that client.

• The client sends a reassociation request to the new access point, allowing it to retrieve client information from the controller for seamless reconnection.

Scanning Methods

• Clients can identify available access points through a process called scanning, which includes two types: passive and active scanning.

• In passive scanning, clients receive broadcast frames from access points containing network identifiers and service set identifiers (SSID).

• Active scanning allows clients to send out broadcast probe requests to all access points, prompting them to respond with their network information.

Data Security in Wireless Networks

• Data transmitted over wireless networks is accessible to anyone; thus, sensitive information like passwords or credit card numbers should be encrypted.

• Wi-Fi employs data encryption using specific header flags (protection frame), sometimes referred to as WEP value, ensuring privacy akin to wired connections.

Encryption Standards

• The original WEP standard is now obsolete due to its vulnerability; current practices utilize WPA2 (Wi-Fi Protected Access 2), which offers robust security measures.

• Users connecting to open Wi-Fi networks without encryption should be cautious as data is transmitted unprotected and can be intercepted by malicious actors.

Service Sets in Wi-Fi Networks