Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 Mobility and Networking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute [email protected]

Shivkumar KalyanaramanRensselaer Polytechnic Institute

1

Mobility and Networking

Shivkumar Kalyanaraman

Rensselaer Polytechnic Institute

[email protected]

http://www.ecse.rpi.edu/Homepages/shivkumaBased in part on slides of Hari Balakrishnan, Srini Seshan, Pravin Bhagwat


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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


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 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


5

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


6

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


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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


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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)


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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


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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


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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


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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


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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.


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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


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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


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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


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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


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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


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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


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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


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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


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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


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Piconet formationMaster

Active Slave

Parked Slave

Standby

Page - scan protocol to establish links with

nodes in proximity


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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


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Piconet channel

m

s1

s2

625 sec

f1 f2 f3 f4

1600 hops/sec

f5 f6

FH/TDD


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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


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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”


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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.


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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


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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


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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


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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


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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


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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


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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


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Mobile IP (MH at Home)

Mobile Host (MH)

Visiting Location

Home

Internet

Correspondent Host (CH)

Packet


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Mobile IP (MH Moving)

Visiting Location

Home

Internet


Packet

Home Agent (HA) Mobile Host (MH)I am here


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Mobile IP (MH Away – Foreign Agent)

Visiting Location

Home

Internet


Packet

Home Agent (HA) Foreign Agent (FA)Encapsulated

Mobile Host (MH)


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Mobile IP (MH Away - Collocated)

Visiting Location

Home

Internet


Packet

Home Agent (HA) Mobile Host (MH)Encapsulated


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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


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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


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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


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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


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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


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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


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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


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Summary

Wireless: Introduction802.11, Bluetooth, CDPD

Mobility: IP Addresses and location Solutions: Mobile IP, TCP Migrate Open areas: new directions...

iNAT, zero-conf

Documents

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 Mobility and Networking Shivkumar Kalyanaraman Rensselaer Polytechnic Institute [email protected]