Information and communication technologies principles and perspectives

1. Information and Communication
Technologies(ICT)
Principles and Perspectives
Lecture : Distributed multimedia systems
Chapter 18th Study guide, 6th essential

2. Wireless networks
• A network in which wireless (and possibly mobile) users are connected into
the larger network infrastructure by a wireless link at the network’s edge.
• Wireless Vs Mobile
• Main elements of wireless network
• Wireless hosts
• Wireless links
• Base station

3. Main elements
• Wireless host: End systems devices that run application
• A wireless host might be a laptop, palmtop, smartphone, or desktop
computer. The hosts themselves may or may not be mobile
• Base Station: this is typically connected to a wired network and acts as a
relay, responsible for sending packets between wired network and wireless
host(s) in its coverage area
• Cell towers, access points

5. Main elements
• Wireless link: A host connects to a
base station or to another wireless
host through a wireless
communication link
• Different links have different
transmission rates and transmit
over different distances

6. Infrastructure Vs Ad hoc
• Hosts associated with a base station are often referred to as operating in
infrastructure mode
• all traditional network services (e.g., address assignment and routing) are provided by
the network
• In ad hoc networks, wireless hosts have no such infrastructure with which
to connect.
• the hosts themselves must provide for services such as routing, address assignment,
DNS-like name translation etc.

7. Infrastructure Vs Ad hoc

8. Handoff
• When a mobile host moves beyond the range of one base station and into the range
of another, it will change its point of attachment into the larger network
• how does one find the mobile host’s current location in the network so that data can
be forwarded to that mobile host?
• How is addressing performed, given that a host can be in one of many possible
locations?
• If it moves during TCP connection or phone call how data continues uninterrupted

9. Classification
• A packet crosses one wireless hop or multiple
• Whether there is infrastructure such as a base station in the network:

10. Wireless link characteristics
• Decreasing signal strength
• Interference from other sources : For example, 2.4 GHz wireless phones and
802.11b wireless LANs transmit in the same frequency band.
• Multipath propagation: the radio signal reflects off objects on the ground,
resulting in paths of different lengths between sender and receiver, blurring
the received signal.

11. Hidden terminal and fading

12. IEEE 802.11

13. 802.11 ac
• For most current deployments,
802.11ac devices use an 80 MHz
channel width compared to 40 MHz
for 802.11n, effectively doubling the
data rate. IEEE 802.11ac also has the
option of providing 160 MHz channel
bandwidth with contiguous and non-
contiguous 80+80 MHz channel
bonding

14. The 802.11 Architecture

15. Terminologies
• Basic service set ( BSS)
• Service Set Identifier (SSID) : This is the name which you view when you
click on available networks
• Channel on which AP transmit or receive data
• For instance, in the IEEE 802.11b standard, its 2.4 GHz–2.485 GHz spectrum is
divided into 11 channels at different frequencies
• Wi-Fi jungle is any physical location where a wireless station receives a
sufficiently strong signal from two or more APs

16. Connect with Wi-Fi jungle
• How would we associate with a particular AP in Wi-Fi jungle
• Each AP sends beacon frames with AP’s SSID and MAC address
• Typically the host chooses the AP whose beacon frame is received with the highest
signal strength
• it’s possible that the selected AP may have a strong signal, but may be overloaded
with other affiliated hosts
• Beacon frames scanning and listening process is passive scanning
• In active scanning a probe frame that will be received by all APs within the
wireless host’s range

17. Active Vs Passive Scanning