1. Mobile and Wireless Networks and Applications: Introduction/Overview
Notes from Stanford Univ.

2. What is Mobility? A device that moves A person who moves
Between different geographical locations
Between different networks
A person who moves
Between different communication devices
Between different applications

3. Device mobility Plug in laptop at home/work on Ethernet
Occasional long breaks in network access
Wired network access only (connected => well-connected)
Network address changes
Only one type of network interface
May want access to information when no network is available: hoard information locally
Cell phone with access to cellular network
Continuous connectivity
Phone # remains the same (high-level network address)
Network performance may vary from place to place

4. Device mobility, continued
Can we achieve best of both worlds?
Continuous connectivity of wireless access
Performance of better networks when available
Laptop moves between Ethernet, WaveLAN and Metricom networks
Wired and wireless network access
Potentially continuous connectivity, but may be breaks in service
Network address changes
Radically different network performance on different networks

5. People mobility Phone available at home or at work Cell phone
Multiple phone numbers to reach me
Breaks in my reachability when I’m not in
Cell phone
Only one number to reach me
Continuously reachable
Sometimes poor quality and expensive connectivity
Cell phone, networked PDA, etc.
Multiple numbers/addresses for best quality connection
Continuous reachability
Best choice of address may depend on sender’s device or message content

6. Mobility means changes
How does it affect the following?
Hardware
Lighter
More robust
Lower power
Wireless communication
Can’t tune for stationary access
Network protocols
Name changes
Delay changes
Error rate changes

7. Changes, continued Fidelity Data consistency
High fidelity may not be possible
Data consistency
Strong consistency no longer possible
Location/transparency awareness
Transparency not always desirable
Names/addresses
Names of endpoints may change
Security
Lighter-weight algorithms
Endpoint authentication harder
Devices more vulnerable

8. Changes, continued, again
Performance
Network, CPU all constrained
Delay and delay variability
Operating systems
New resources to track and manage: energy
Applications
Name changes
Changes in connectivity
Changes in quality of resources
People
Introduces new complexities, failures, devices

9. Example changes Addresses Network performance Network interfaces
Phone numbers, IP addresses
Network performance
Bandwidth, delay, bit error rates, cost, connectivity
Network interfaces
PPP, eth0, strip
Between applications
Different interfaces over phone & laptop
Within applications
Loss of bandwidth triggers change from color to B&W
Available resources
Files, printers, displays, power, even routing

10. Summing up Generally, mobility stresses all resources further: CPU
Power
Bandwidth
Delay tolerance
Radio spectrum
Human attention
Physical size
Constraints on peripherals and GUIs (modality of interaction)
Locations (body parts!) for device placement