Mobile and Wireless Networks and Applications IntroductionOverview CS

Mobile and Wireless Networks and Applications: Introduction/Overview CS 444 N, Spring 2002 Instructor: Mary Baker 1

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

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 3

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, Wave. LAN 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 4

People mobility • Phone available at home or at work – 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 5

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 6

Changes, continued • Fidelity – 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 7

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 8

Example changes • Addresses – Phone numbers, IP addresses • Network performance – Bandwidth, delay, bit error rates, cost, connectivity • Network interfaces – PPP, eth 0, 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 9

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 10