1. Wireless Networking WAN Design Module-06
Jerry Bernardini
Community College of Rhode Island
4/17/2017
Wireless Networking J. Bernardini

2. Presentation Reference Material
CWNA Certified Wireless Network Administration Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett
Chapter-5 Pages
The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project
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Wireless Networking J. Bernardini

3. IEEE 802.11 Service Sets Basic Service Sets – 3 types
Independent Basic Service Set (IBSS)
Infrastructure Basic Service Set (BSS)
Extended Basic Service Set (ESS)
Note: The BSS is the fundamental building block for all wireless networks.
Note:
for IEEE each device on the network is a node or host
for IEEE each device on the network is a Station (STA)

4. Basic Service Set
BSS - The Basic Service Set is a term used to describe the collection of Stations which may communicate together within an WLAN.
Basic Service Set (BSS): Group of wireless devices served by single AP
infrastructure mode
BSS must be assigned unique identifier
Service Set Identifier (SSID)
Serves as “network name” for BSS
Basic Service Area (BSA): Geographical area of a BSS
Max BSA for a WLAN depends on many factors
Dynamic rate shifting: As mobile devices move away from AP, transmission speed decreases

5. Extended Service Set ESS - is comprised of a number BSS’s
ESS stations must have the same SSID
The BSSID is the “name” of the BSS (not same as SSID)
APs can be positioned so that cells overlap to facilitate roaming
Wireless devices choose AP based on signal strength
Stations going from one BSS to another will deal with Handoff
ESS
SSID
Wired LAN
BSS2
(BSSID2)
An Extended Service Set is comprised of a number of IEEE BSS (Basic Service Set) that share the same SSID (not BSSID) and enables limited mobility within the WLAN (Wireless Local Area Network). Stations are able to move between BSS within a single ESS yet still remain “connected” to the fixed network and so continue to receive s etc. As a Station moves into a new BSS, it will carry out a reassociation procedure with the new AP (Access Point).
BSS3
(BSSID3)
BSS1
(BSSID1)

6. IEEE Wireless LAN Configurations: Independent Basic Service Set
Independent Basic Service Set (IBSS): Wireless network that does not use an AP
Wireless devices communicate between themselves
Peer-to-peer or ad hoc mode
BSS more flexible than IBSS in being able to connect to other wired or wireless networks
IBSS useful for quickly and easily setting up wireless network
When no connection to Internet or external network needed

7. Service Set Identifiers - SSID and BSSID
SSID -Service Set Identifier is a 1-32 byte alphanumeric sequence that uniquely names an ESS (the network name).
Any SSID or Null SSID is a blank SSID used to associate with anyone.
BSSID- Basic Service Set Identifier is a 48-bits that uniquely identifies a BSS
Wired LAN AP
Only using one access point all clients connect to that AP. The BSSI ID is the mac address of the AP.
An Infrastructure Basic Service Set (BSS) is a type of IEEE network comprised of both Stations and AP (Access Point) which are used for all communication within the BSS , even if the Stations reside within the same area. The process involves the Station first sending the information to the AP which in turn forwards it to the destination Station. Alternatively, should the information be destined for a wired node, the AP will forward it onto the fixed network.
An networking framework in which devices communicate with each other by first going through an Access Point (AP). In infrastructure mode, wireless devices can communicate with each other or can communicate with a wired network. When one AP is connected to wired network and a set of wireless stations it is referred to as a Basic Service Set (BSS). An Extended Service Set (ESS) is a set of two or more BSSs that form a single subnetwork. Most corporate wireless LANs operate in infrastructure mode because they require access to the wired LAN in order to use services such as file servers or printers.
ESS
Id = SSID
BSS
Id = BSSID

8. Reassociation Wired LAN Access Points 1 2 1 Wireless Clients
A station may decide that its link (faded gray double arrow) to its current access point is poor. The station can use a scanning function to find another access point. The station would then send a Reassociation Request (small green arrow) to the new access point. If a successful Reassociation Response (small red arrow) is returned then the station has roamed to the new access point. Otherwise, the station can continue scanning for another access point. If an access point accepts a Reassociation Request, the access point indicates a Reassociation to the gateway server or router servicing that station. Normally the old access point is also notified about the Reassociation, yellow double arrow. Also the old access point is buffering the data for client 1 and is then passed to AP2. Also in a switched network the MAC of the client must be transferred.

9. Load Balancing or Sharing
Wired LAN
Access Points 1 2 2 2 1 1 1
Wireless Clients
In a multi-cell structure with several co-located APs sharing the load. The coverage area of the AP’s illuminate the same physical area of the network. Note that the laptops in the slide are divided equally between the APs for improved throughput. 2

10. WLAN IP Addressing
In standard networking, IP protocol responsible for moving frames between computers
Network layer protocol
TCP/IP works on principle that each network host has unique IP address
Used to locate path to specific host
Routers use IP address to forward packets
Prohibits mobile users from switching to another network and using same IP number
Users who want to roam need new IP address on every network

11. Mobile IP
Provides mechanism within TCP/IP protocol to support mobile computing
Computers given home address,
Static IP number on home network
Home agent: Forwarding mechanism that keeps track of where mobile computer located
When computer moves to foreign network, a foreign agent provides routing services
Assigns computer a care-of address
Computer registers care-of address with home agent

12. Mobile IP-Computer relocated

13. Infrastructure Mode
CWNA Guide to Wireless LANs, Second Edition

14. Channel reuse
CWNA Guide to Wireless LANs, Second Edition

15. Flip flop between access points
CWNA Guide to Wireless LANs, Second Edition

16. Wireless Networking J. Bernardini
WLAN Design Models
Point-to-Point (PtP)
Point-to-Multipoint (PtMP)
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17. Wireless Networking J. Bernardini
WLAN Modes
Single MAC Model
Edge, Autonomous, Stand-Alone, Fat-AP
Split MAC Model
Centralized, Thin-AP
Mesh Network
Distributed, Multipath, IEEE s
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Wireless Networking J. Bernardini

18. Wireless Networking J. Bernardini
Single MAC Model
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19. Wireless Networking J. Bernardini
Split MAC Model
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20. Wireless Networking J. Bernardini
WLAN Model Evolution
Intelligent Edge(Distribution)
Quick to setup but for small-medium networks
Difficult to mage for large networks
WLAN Network Management Systems
Centralized Management Distribution Processing
For large networks
Centralized WLAN Architecture (Split MAC)
For large networks with centralized controller
Large amount of wiring needed
Distributed Data Forwarding (DDF) WLAN
Similar to Split MAC but uses Fat-AP
Unified WLAN Architecture
Wireless built in to every thing including switches
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Wireless Networking J. Bernardini

21. WLAN Power Management Features
Active Mode
No power saving but improved station and AP performance
For desktops and line powered laptops
Power Save Mode
Dozing and Wake modes
Switches to wake to check for frames
WMM Power Save
U-APSD Unscheduled Automatic Power-Save Delivery
This is an industry certification
IEEE e-2005
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Wireless Networking J. Bernardini

22. Power Management
A WLAN laptop must remain “awake” in order to receive network transmissions
Original IEEE 802 standard assumes stations always ready to receive network messages
Power management: Allows mobile devices to conserve battery life without missing transmissions
Transparent to all protocols
Differs based on WLAN configuration
AP records which stations awake and sleeping
Buffering: If sleeping, AP temporarily stores frames

23. Power Management At set times AP send out beacon to all stations
Contains traffic indication map (TIM)
At same time, all sleeping stations switch into active listening mode
Power management in ad hoc mode:
Ad hoc traffic indication message (ATIM) window: Time at which all stations must be awake
Wireless device sends beacon to all other devices
Devices that previously attempted to send a frame to a sleeping device will send ATIM frame indicating that receiving device has data to receive and must remain awake

24. Continuous Aware Mode
Constantly Awake Mode provides the best performance allowing the client a strong connection between the wireless card and the AP; however, it also rapidly drains the client’s battery, resulting in shorter battery life.

25. Power Management with TIM/DTIM/ATIM
Traffic Indication Map (TIM)
A table stored on the AP of all STA’s in Power Save mode
TIM is used to determine which STA’s require frame buffering
Every Beacon contains a TIM
Delivery Traffic Indication Message (DTIM)
Used to manage STAs and to program wakeup
Sent on every few (third or some interval)Beacon
Ad Hoc Traffic Indication Message (ATIM)
Use to power manage IBSS
4/17/2017
Wireless Networking J. Bernardini