Wireless Reading
For this assignment, we were to read several chapters from the CCNA Wireless 200-355 Official Cert Guide accessed through the University of Houstons library. this included three chapters:
- Chapter 1 - RF Signals and Modulation
- Chapter 2 - RF Standards
- Chapter 5 - Wireless LAN Topologies
Brief Synopsis of Chapter 5 - Wireless LAN Topologies
This chapter expalins the topologies used to control access and to provide data exchanges between devices. The following topics are covered:
- Types of Wireless Networks
- Wireless LAN Topologies
- Other Wireless Topologies
Types of Wireless Networks
There are 4 different types of Wireless Networks.
- Wireless Personal-Area Netowrk (WPAN) which uses low powered transmitters to create a network with a very short range (20-30 feet). WPANs include technology such as bluetooth and Zigbee.
- Wireless Local Area Network (WLAN) is a service that connects multiple devices using the IEEE standard over a medium sized range.
- Wireless Metropolitan-Area Network (WMAN) is a wireless service over a large geographic are, such as a portion of a city.
- Wireless Wide-Area Network (WWAN) is a service for mobile phones that is offered over a very large geographic area by telecommuniations carriers.
Wireless LAN Topologies
Basic Service Set
- Basic Service Set (BSS) Wireless service provided by an AP to one or more associated clients.
- At the heart of every BSS is an Access Point (AP) - A device that provides wireless service for clients within its coverage area or cell.
- The AP operates in Infrastructure Mode - The operating mode of an AP that is providing a BSS for wireless clients.
- BSA - Basic Service Area - the BSS is bounded by the area where the AP's signal is usable.
- The AP serves as a single point of contact for every device that wants to use the BSS and advertises the existence of the BSS so devices can find it and try to join.
- The AP also advertises the wireless network with a Service Set Identifier (SSID) - a text string containing a logical name (a non-unique, human-readable name tag that identifies the wireless service.
- Membership with the BSS is called an association. A device must send an association request and the AP must grant or deny that request. Once associated, a device becomes a client of the BSS.
Distribution System
- Distribution System (DS) - The wired Ethernet that connects to an AP and transports traffic between a wired and wireless network.
- The AP is in charge of mapping a virtual local are network (VLAN) to an SSID.
- When AP uses multiple SSID's, it is trunking VLANs over the air to wireless clients.
- Even though an AP can advertise and support multiple logical wireless networks, each of the SSIDs covers the same geographic area because they use the same transmitter, receiver, antennas andchannel for every SSID that it supports.
Extended Service Set
- Normally one AP cannot cover the entire area where clients might be located
- To cover more area than a single AP's cell, you simply need to add more AP's and spread them geographically
- When AP's are placed at different geographic locations, thehy can be interconnected by a switchd infrastructure
- The 802.11 standard called this an extended service set (ESS)
- The idea is to make multiple APs cooperate so that the wireless service is consistent and seamless from the client's perspective.
- In an ESS, a wireless client can associate with one AP while it is physicallhy located near that AP. If the client later moves toa different location, it can associate with a different newarbyh AP automatically (called Roaming).
Independent Basic Service Set
- independent basic service set (IBSS) An impromptu wireless network formed between two or more devices without an AP or a BSS; also known as an ad hoc network.
Other Wireless Topologies
Repeater
- Repeater - A device that repeats or retransmits signals it receives, effectively expanding the wireless coverage area.
- If the repeater has a single radio, there is a possibility that the AP's signal will be received and retransmitted by the repeater, only to be received again by the AP-halving the effective throughput
- As a remedy, some repeaters can use two radios to keep the original and repeated signals isolated. One radio is dedicated to signals in the AP's cell, while the other radio is dedicated to signals in the repeater's own cell.
Workgroup Bridge
- Suppose you have a device that supports a wired Ethernet link but is not capable of having a wireless connection. You can use a workgroup bridge (WGB) to connect the device's wired network adapter to a wireless network.
- You might encounter two types of workgroup bridges:
Universal workgroup bridge (uWGB)-A single wired device can be bridged to a wireless network.
Workgroup bridge (WGB)-A Cisco-proprietary implementation that allows multiple wired devices to be bridged to a wireless network.
Outdoor Bridge
- An AP can be configured to act as a bridge to form a single wireless link from one LAN to another over a long distance. Outdoor bridged links are commonly used for connectivity between buildings or between cities.
- If the LANs at two locations need to be bridged, a point-to-point bridged link can be used.
Mesh Network
- In a mesh topology, traffic is bridged from AP to AP, in a daisy-chain fashion
- To provide wireless coverage over a large area, it is not always practical to run Ethernet cabling to every AP that is needed. Instead, you could use multiple APs configured in mesh mode.
- Mesh APs can leverage dual radios-one in the 2.4-GHz band and one in the 5GHz band. Each mesh AP usually maintains a BSS on a 2.4-GHz channel, with which wireless clients can associate.
- Client traffic is then usually bridged from AP to AP over 5-GHz channels as a backhaul network. At the edge of the mesh network, the backhaul traffic is bridged to the wired LAN infrastructure
- The mesh network runs its own dynamic routing protocol to work out the best path for backhaul traffic to take across the mesh APs.
