Mobility and Networking

1. Mobility and Networking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute shivkuma@ecse.rpi.edu http://www.ecse.rpi.edu/Homepages/shivkuma Based in part on slides of Hari Balakrishnan, Srini Seshan, Pravin Bhagwat

2. Wireless: Introduction • 802.11, Bluetooth, CDPD • Mobility: IP Addresses and location • Solutions: Mobile IP, TCP Migrate • Service discovery, Configuration: current work • iNAT, zero-conf Overview

3. Mobile vs Wireless • Mobile vs Stationary vs Nomadic • Wireless vs Wired • Wirelessmedia sharing issues • Mobilerouting, location, addressing issues • Nomadic => terminate existing communications before leaving point-of-attachment. Later, reconnect. Mobile Wireless

4. Wireless Challenges • Force us to rethink many assumptions • Need to share airwaves rather than wire • Don’t know what hosts are involved • Host may not be using same link technology • Other characteristics of wireless • Noisy  lots of losses • Slow • Interaction of multiple transmitters at receiver • Collisions, capture, interference • Multipath interference

5. 10 W P1 dBm = 10 log (-------) 1mW 101 Power 1 mW 10-3 1 W 10-6 d1 source d2 Path Loss in dBm = 40 dBm + 10,000 times = 0 dBm - 1,000 times = -30 dBm

6.   r3.3 r2 Radio propagation: path loss near field path loss in 2.4 Ghz band Pr r  8m r > 8m Pt far field near field r Pr path loss = 10 log (4r2/) r  8m = 58.3 + 10 log (r3.3 /8) r > 8m

7. Fading and multipath Fading: rapid fluctuation of the amplitude of a radio signal over a short period of time or travel distance Tx Rx Effects of multipath • Fading • Varying doppler shifts on different multipath signals • Time dispersion (causing inter symbol interference)

8. Bandwidth of digital data Fourier transform Frequency domain Time domain • Baseband signal cannot directly be transmitted on the wireless medium • Need to translate the baseband signal to a new frequency so that it can be transmitted easily and accurately over a communication channel Signal amplitude 1 Mhz 0.5 MKhz 1.5 Mhz baseband signal (1 Mbs)

9. ISM band 902 – 928 Mhz 2.4 – 2.4835 Ghz 5.725 – 5.785 Ghz VHF UHF SHF EHF LF MF HF 300MHz 30MHz 30GHz 300GHz 3GHz 3MHz 30kHz 300kHz  10m 1m 100mm 100m 10cm 10km 1km 1cm EM Spectrum FM radio S/W radio AM radio TV TV cellular  X rays Gamma rays visible UV infrared  1 MHz 1 GHz 1 kHz 1 THz 1 EHz 1 PHz Propagation characteristics are different in each frequency band

10. Unlicensed Radio Spectrum  12cm 5cm 33cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 2.4 Ghz 5.725 Ghz 2.4835 Ghz 5.785 Ghz 928 Mhz unused 802.11 Bluetooth Microwave oven cordless phones baby monitors Wireless LANs

11. Bluetooth radio link 1Mhz • Frequency hopping spread spectrum • 2.402 GHz + k MHz, k=0, …, 78 • 1,600 hops per second • GFSK modulation • 1 Mb/s symbol rate • transmit power • 0 dbm (up to 20dbm with power control) . . . 79 1 2 3 83.5 Mhz

12. Wireless link layers • Cellular Digital Packet Data (CDPD): • Send IP packets over unoccupied radio channels within the analog cellular-telephone systems • Not circuit switched => no per-call/call-duration charges • Usage-based billing (contract w/ CDPD providers who have roaming agreements w/ other providers) => a wide area mobility solution (limited by availablility) • Carrier provides IP address, but link layer protocols are responsible for ensuring packets are delivered • Max data rate of 11 kbps

13. Wireless link layers (contd) • IEEE 802.11 • Wireless LANs: 2 or 11 Mbps. • Defines a set of transceivers which interface between wireless/wired • Link layer protocols make entire network of transceivers appear as one link at network layer => mobility within 802.11 invisible to IP • Changing router boundaries => interrupts communications.

14. Wireless link layers (contd) • Bluetooth: • A cable replacement technology • 1 Mb/s symbol rate; Range 10+ meters • Single chip radio + baseband • Target: low power & low price point

15. Ideas: Cellular Reuse • Transmissions decay over distance • Spectrum can be reused in different areas • Different “LANs” and “forwarding mechanisms” • Decay is 1/R2 in free space, 1/R4 in some situations

16. Multiple Access • TDMA, FDMA like wired networks • CDMA (code division multiple access) • Multiple senders at a time (like FDMA) • Senders cause interference to each other • Each sender has unique code known to receiver • Codes chosen to be distinguishable, even when multiple sent at same time • Code “spreads” actual transmission • Codes can be applied in different ways • Direct sequence – controls transmitted bits • Frequency hopping – controls hopping sequence

17. CSMA/CD Does Not Work • Carrier sense problems • Relevant contention at the receiver, not sender • Hidden terminal • Exposed terminal • Collision detection problems • Hard to build a radio that can transmit and receive at same time Hidden Exposed A A B B C C D

18. RTS/CTS Approach • Before sending data, send Ready-to-Send (RTS) • Target responds with Clear-to-Send (CTS) • Others who hear defer transmission • Packet length in RTS and CTS messages • If CTS is not heard, or RTS collides • Retransmit RTS after binary exponential backoff

19. Adding Reliability • Noise can corrupt packets • Add an ACK after DATA transmission • If ACK not received, sender restarts RTS/CTS again • If ACK was lost, receiver sends ACK instead of CTS A B C

20. IEEE 802.11 • Standard for wireless communication • MAC-layer uses many of the ideas discussed • RTS/CTS/ACK • Careful backoff • Allows two modes • Ad-hoc • Wired/wireless

21. Applications IP IP SDP RFCOMM Control Control Data Data Audio L2CAP Link Manager Baseband RF Bluetooth Protocols Applications SDP RFCOMM Audio L2CAP Link Manager Our Focus Baseband RF

22. m s m s s • Piconet • Master can connect to 7 slaves • Each piconet has max capacity (1 Mbps) • hopping pattern is determined by the master s Bluetooth Physical link • Point to point link • master - slave relationship • radios can function as masters or slaves

23. Master Active Slave Parked Slave Standby Piconet formation • Page - scan protocol • to establish links with nodes in proximity

24. Addressing • Bluetooth device address (BD_ADDR) • 48 bit IEEE MAC address • Active Member address (AM_ADDR) • 3 bits active slave address • all zero broadcast address • Parked Member address (PM_ADDR) • 8 bit parked slave address

25. Piconet channel FH/TDD f5 f1 f4 f3 f2 f6 m s1 s2 625 sec 1600 hops/sec

26. Multi slot packets FH/TDD f1 f5 f4 f6 m s1 s2 625 µsec Data rate depends on type of packet

27. Mobility at IP, Transport Layers • Mobile IP: independent of link layer technology • Mobility-aware routing: home/foreign agent • Transparent to end hosts (“seamless”) • Often inefficient packet routes • TCP Migrate: new MIT proposal • Locate hosts through existing DNS • Secure, dynamic DNS is currently deployed and widely available (RFC 2137) • Maintains standard IP addressing model • Seamless connectivity thru connection migration • No home agent or foreign agents: “end-to-end”

28. Mobile IP drivers • IP Address is used for two purposes: • To identify an endpoint • To help route the packet • Move from subnet ("link") => need to change address to allow routing • Problem 1: How to route packets to this node at its new link ? • Problem 2: Can we avoid changing the addresses seen by higher layer protocols ? • Several protocols affected by address change: DNS, TCP, UDP.

29. How to Handle Mobile Nodes? • Dynamic Host Configuration (DHCP) • Host gets new IP address in new locations • Problems • Host does not have constant name/address  how do others contact host • What happens to active transport connections? • Naming • Use DHCP and update name-address mapping whenever host changes address • Fixes contact problem but not broken transport connections

30. Basic Solution to Mobile Routing • Add a level of indirection! • Keep some part of the network informed about current location • Need technique to route packets through this location (interception) • Need to forward packets from this location to mobile host (delivery) • TCP connections not broken! • Remote hosts just use the home address in their socket pair

31. Interception • Somewhere along normal forwarding path • At source • Any router along path • Router to home network • Machine on home network (masquerading as mobile host) • Clever tricks to force packet to particular destination • “Mobile subnet” – assign mobiles a special address range and have special node advertise route

32. Delivery • Need to get packet to mobile’s current location • Tunnels • Tunnel endpoint = current location • Tunnel contents = original packets • Source routing • Loose source route through mobile current location

33. Mobile IP (RFC 2290) • Interception • Typically home agent – hosts on home network • Delivery • Typically IP-in-IP tunneling • Endpoint – either temporary mobile address or foreign agent • Terminology • Mobile host (MH), correspondent host (CH), home agent (HA), foreign agent (FA) • Care-of-address (CoA), home address

34. Mobile IP model • Two-level addressing: • Home address: fixed (permanent) address used by other nodes to communicate with the mobile node. • Care-of-address: address on a (foreign) link to which the mobile is currently attached. • Home agent: • Tracks care-of-address of mobile • Re-addresses packets destined to home address and tunnels them to the care-of-address • Foreign agent: • Gives mobile node its care-of-address. Optimizes IP address use.Terminates tunnel from home agent • Default router for packets from mobile node

35. Correspondent Home Agent ForeignAgent MobileHost IP HeaderTo: Mobile Info Encapsulation/Tunneling • Home agent intercepts mobile node's datagrams (using proxy ARP) and forwards them to care-of-address through a tunneling mechanism • Decapsulation: Extracted datagram sent to mobile node IntermediateRouters IP HeaderTo: COA

36. Mobile IP (MH at Home) Packet Correspondent Host (CH) Internet Visiting Location Home Mobile Host (MH)

37. Mobile IP (MH Moving) Packet Correspondent Host (CH) Internet Visiting Location Home Home Agent (HA) Mobile Host (MH) I am here

38. Mobile IP (MH Away – Foreign Agent) Packet Correspondent Host (CH) Mobile Host (MH) Internet Visiting Location Home Encapsulated Home Agent (HA) Foreign Agent (FA)

39. Mobile IP (MH Away - Collocated) Packet Correspondent Host (CH) Internet Visiting Location Home Encapsulated Home Agent (HA) Mobile Host (MH)

40. Other Mobile IP Issues • Route optimality • Resulting paths can be sub-optimal • Can be improved with route optimization • Unsolicited binding cache update to sender • Authentication • Registration messages • Binding cache updates • Must send updates across network • Handoffs can be slow • Problems with basic solution • Triangle routing • Reverse path check for security

41. TCP Migrate Approach • Locate hosts through existing DNS • Secure, dynamic DNS is currently deployed and widely available (RFC 2137) • Maintains standard IP addressing model • IP address are topological addresses, not Ids • Fundamental to Internet scaling properties • Ensure seamless connectivity through connection migration • Notify only the current set of correspondent hosts • Follows from the end-to-end argument

42. DNS Server Connection Initiation Mobile Host foo.bar.edu Migrate Architecture Location Query (DNS Lookup) Location Update (Dynamic DNS Update) Connection Migration Correspondent Host xxx.xxx.xxx.xxx

43. Spontaneous networking • Automatically obtain map of region & discover devices, services and people there • Locate other useful services (e.g., nearest café) Where? Location-dependent wireless services • Access, control services, communicate with them • Handle mobility & group communication App should be able to conveniently specify a resource and access it

44. Resource discovery • Why is this hard? • Dynamic environment (mobility, performance changes, etc.) • No pre-configured support, no centralized servers • Must be easy to deploy (“ZERO” manual configuration) • Heterogeneous services & devices • Approach: a new naming system & resolution architecture

45. iNAT: Design goals Names must be descriptive, signifying application intent Expressiveness Name resolvers must track rapid changes Responsiveness System must overcome resolver and service failure Robustness Name resolvers must self-configure Easy configuration

46. Intentional Naming System (INS) principles • Names are intentional, based on attributes • Apps know WHAT they want, not WHERE • INS integrates resolution and forwarding • Late binding of names to nodes • INS resolvers replicate and cooperate • Soft-state name exchange protocol with periodic refreshes • INS resolvers self-configure • Form an application-level overlay network

47. Summary • Wireless: Introduction • 802.11, Bluetooth, CDPD • Mobility: IP Addresses and location • Solutions: Mobile IP, TCP Migrate • Open areas: new directions... • iNAT, zero-conf