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Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobility and Networking
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
http://www.ecse.rpi.edu/Homepages/shivkumaBased in part on slides of Hari Balakrishnan, Srini Seshan, Pravin Bhagwat
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Wireless: Introduction802.11, Bluetooth, CDPD
Mobility: IP Addresses and location Solutions: Mobile IP, TCP Migrate Service discovery, Configuration: current work
iNAT, zero-conf
Overview
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Wireless Challenges
Force us to rethink many assumptions Need to share airwaves rather than wire
Don’t know what hosts are involvedHost may not be using same link technology
Other characteristics of wirelessNoisy lots of lossesSlow Interaction of multiple transmitters at receiver
Collisions, capture, interferenceMultipath interference
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Path Loss in dBm
1 W
d2
10 W
source d1
1 mW
+ 10,000 times
- 1,000 times
= 40 dBm
= 0 dBm10-3
101
10-6
Power
dBm = 10 log (-------) P1
1mW
= -30 dBm
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Radio propagation: path loss
Pt
Pr
Pr
near field
path loss = 10 log (4r2/) r 8m
= 58.3 + 10 log (r3.3 /8) r > 8m
r
path loss in 2.4 Ghz band
near field far field
r2
r 8m r > 8m
r3.3
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fading and multipath
Tx
Rx
Fading: rapid fluctuation of the amplitude of a radio signal over a short period of time or travel distance
• Fading• Varying doppler shifts on different multipath signals• Time dispersion (causing inter symbol interference)
Effects of multipath
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Bandwidth of digital data
• 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
Time domain Frequency domain
1 Mhz 1.5 Mhz0.5 MKhz
Sig
na
l am
plit
ud
e
Fourier transform
baseband signal (1 Mbs)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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EM Spectrum
Propagation characteristics are different in each frequency band
LF HF VHF UHF SHF EHFMF
AM ra
dio
UV
S/W ra
dioFM
radio
TV TVce
llula
r
1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz
infrared visible
X raysGamma rays
902 – 928 Mhz2.4 – 2.4835 Ghz
5.725 – 5.785 Ghz
ISM band
30kHz300kHz 3MHz 30MHz 300MHz 30GHz 300GHz
10km 1km 100m 10m 1m 10cm 1cm 100mm
3GHz
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Unlicensed Radio Spectrum
902 Mhz
928 Mhz
26 Mhz 83.5 Mhz 125 Mhz
2.4 Ghz
2.4835 Ghz5.725 Ghz
5.785 Ghz
cordless phonesbaby monitorsWireless LANs
802.11BluetoothMicrowave oven
unused
33cm 12cm 5cm
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Bluetooth radio link
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)
. . .
1Mhz
1 2 3 79
83.5 Mhz
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Wireless link layers (contd) IEEE 802.11
Wireless LANs: 2 or 11 Mbps. Defines a set of transceivers which interface
between wireless/wiredLink 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.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Wireless link layers (contd)
Bluetooth:A cable replacement technology1 Mb/s symbol rate; Range 10+ metersSingle chip radio + baseband Target: low power & low price point
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Ideas: Cellular Reuse Transmissions decay over distance
Spectrum can be reused in different areasDifferent “LANs” and “forwarding mechanisms”Decay is 1/R2 in free space, 1/R4 in some
situations
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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 receiverCodes chosen to be distinguishable, even when
multiple sent at same timeCode “spreads” actual transmission
Codes can be applied in different waysDirect sequence – controls transmitted bitsFrequency hopping – controls hopping sequence
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
A
B
C
A
B
C
D
Hidden Exposed
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
Bluetooth Protocols
RFCOMMSDPIP
Applications
RF
Baseband
AudioLink Manager
L2CAP
Data Con
trolSDP RFCOMM
IP
Applications
Our Focus
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Bluetooth Physical link
Point to point link master - slave relationship radios can function as masters or slaves m s
ss
m
s
Piconet Master can connect to 7 slaves Each piconet has max capacity (1 Mbps) hopping pattern is determined by the master
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Piconet formationMaster
Active Slave
Parked Slave
Standby
Page - scan protocol to establish links with
nodes in proximity
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Piconet channel
m
s1
s2
625 sec
f1 f2 f3 f4
1600 hops/sec
f5 f6
FH/TDD
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Multi slot packets
m
s1
s2
625 µsec
f1 f4 f5 f6
FH/TDD
Data rate depends on type of packet
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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”
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Basic Solution to Mobile Routing
Add a level of indirection! Keep some part of the network informed about
current locationNeed 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Delivery
Need to get packet to mobile’s current location Tunnels
Tunnel endpoint = current locationTunnel contents = original packets
Source routingLoose source route through mobile current
location
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobile IP (RFC 2290)
InterceptionTypically home agent – hosts on home
network Delivery
Typically IP-in-IP tunnelingEndpoint – 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
IP HeaderTo: COA
IP HeaderTo: Mobile
Info
IntermediateRoutersCorrespondent
Home Agent
ForeignAgent
MobileHost
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobile IP (MH at Home)
Mobile Host (MH)
Visiting Location
Home
Internet
Correspondent Host (CH)
Packet
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobile IP (MH Moving)
Visiting Location
Home
Internet
Correspondent Host (CH)
Packet
Home Agent (HA) Mobile Host (MH)I am here
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobile IP (MH Away – Foreign Agent)
Visiting Location
Home
Internet
Correspondent Host (CH)
Packet
Home Agent (HA) Foreign Agent (FA)Encapsulated
Mobile Host (MH)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Mobile IP (MH Away - Collocated)
Visiting Location
Home
Internet
Correspondent Host (CH)
Packet
Home Agent (HA) Mobile Host (MH)Encapsulated
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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 IdsFundamental 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Migrate Architecture
DNS Server
Mobile Hostfoo.bar.edu
Location Query(DNS Lookup)
Connection Initiation
Location Update(Dynamic DNS Update)
Connection Migration
xxx.xxx.xxx.xxx
CorrespondentHost
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Location-dependent wireless services
Access, control services, communicate with them
Handle mobility & group communication
Spontaneous networking
Locate other useful services (e.g., nearest café)Where
?
App should be able to conveniently specify a resource
and access it
App should be able to conveniently specify a resource
and access it
Automatically obtain map of region & discover devices, services and people there
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Resource discovery
Why is this hard?Dynamic environment (mobility,
performance changes, etc.)No pre-configured support, no centralized
serversMust be easy to deploy (“ZERO” manual
configuration)Heterogeneous services & devices
Approach: a new naming system & resolution architecture
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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iNAT: Design goals
Responsiveness Name resolvers must track rapid changes
Robustness System must overcome resolver and service failure
Easy configuration Name resolvers must self-configure
Names must be descriptive, signifying application intentExpressiveness
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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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