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

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

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

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

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

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

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

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

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

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