Transcript Mobile IP - ECSE - Rensselaer Polytechnic Institute

Mobility and Networking
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
[email protected]
http://www.ecse.rpi.edu/Homepages/shivkuma
Based in part on slides of Hari Balakrishnan, Srini Seshan, Pravin Bhagwat
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
1
Overview
Wireless: Introduction
 802.11, Bluetooth, CDPD
 Mobility: IP Addresses and location
 Solutions: Mobile IP, TCP Migrate
 Service discovery, Configuration: current work
 iNAT, zero-conf

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
2
Mobile vs Wireless
Mobile
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.
Shivkumar Kalyanaraman
Rensselaer
Polytechnic Institute

3
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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10 W
Path Loss in dBm
= 40 dBm
P1
dBm = 10 log (-------)
1mW
101
+ 10,000 times
Power
10-3
1 mW
= 0 dBm
- 1,000 times
1 W = -30 dBm
10-6
source
d1
d2
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
5
Radio propagation: path loss
near field
path loss in 2.4 Ghz band
Pr
r  8m
Pt
r > 8m
far field
near field
r
 r3.3
 r2
Pr
r  8m
path loss = 10 log (4r2/)
= 58.3 + 10 log (r3.3 /8)
r > 8m
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
6
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)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
7
Bandwidth of digital data
Signal amplitude
Time domain
Fourier transform
Frequency domain
1 Mhz 1.5 Mhz
0.5 MKhz
baseband signal (1 Mbs)
• 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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
8
EM Spectrum
ISM band
902 – 928 Mhz
2.4 – 2.4835 Ghz
5.725 – 5.785 Ghz
LF
MF
VHF
HF
30kHz 300kHz
3MHz
30MHz
10km
100m
10m
1km
UHF
300MHz
1m
SHF
EHF
30GHz
3GHz
10cm
1cm
300GHz
100m
m


X rays

infrared visible UV
1 kHz
1 MHz
1 GHz
1 THz
1 PHz
Gamma rays
1 EHz
Propagation characteristics are different in each
frequency band
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Unlicensed Radio Spectrum

33cm
26 Mhz
902 Mhz
12cm
83.5 Mhz
2.4 Ghz
928 Mhz
cordless phones
baby monitors
Wireless LANs
5cm
125 Mhz
5.725 Ghz
2.4835 Ghz
802.11
Bluetooth
Microwave oven
5.785 Ghz
unused
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
10
Bluetooth radio link
1Mhz
. . .
79
12 3
83.5 Mhz
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)

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
11
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 Kalyanaraman

Rensselaer 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/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.
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
13
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
14
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
15
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
Shivkumar Kalyanaraman
Rensselaer 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
Hidden
A
B
C
Exposed
A
B
C
D
Shivkumar Kalyanaraman
Rensselaer 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 Kalyanaraman
Rensselaer 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 Kalyanaraman
Rensselaer Polytechnic Institute
19
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 Kalyanaraman
Rensselaer Polytechnic Institute
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Bluetooth Protocols
Applications
IP
RFCOMM
SDP
Data
Audio
L2CAP
Our Focus
Link Manager
Baseband
RF
Shivkumar Kalyanaraman
Rensselaer 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
m
 Piconet
Master can connect to 7
slaves
 Each piconet has max
capacity (1 Mbps)
 hopping pattern is determined
by the
Rensselaer Polytechnic
Institutemaster

22
s
s
s
Shivkumar Kalyanaraman
Piconet formation

Page - scan protocol
 to establish links
with nodes in
proximity
Master
Active Slave
Parked Slave
Standby
Shivkumar Kalyanaraman
Rensselaer 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 Kalyanaraman
Rensselaer Polytechnic Institute
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FH/TDD
f1
Piconet channel
f2
f4
f3
f5
f6
m
s1
s2
625 sec
1600 hops/sec
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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Multi slot packets
FH/TDD
f1
f4
f5
f6
m
s1
s2
625 µsec
Data rate depends on type of packet
Shivkumar Kalyanaraman
Rensselaer 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 Kalyanaraman
Rensselaer Polytechnic Institute
27
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 Kalyanaraman
Rensselaer 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 Kalyanaraman
Rensselaer 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 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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
30
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 Kalyanaraman
Rensselaer Polytechnic Institute
31
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
32
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
33
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 Kalyanaraman
Rensselaer Polytechnic Institute
34
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
Home Intermediate Foreign Mobile
Correspondent
Routers
Agent
Agent
Host

IP Header
To: COA
IP Header
To: Mobile
Info
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
35
Mobile IP (MH at Home)
Packet
Correspondent Host (CH)
Internet
Visiting
Location
Home
Mobile Host (MH)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
36
Mobile IP (MH Moving)
Packet
Correspondent Host (CH)
Internet
Visiting
Location
Home
Home Agent (HA)
Mobile Host (MH)
I am here
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
37
Mobile IP (MH Away – Foreign Agent)
Packet
Correspondent Host (CH)
Mobile Host (MH)
Internet
Visiting
Location
Home
Encapsulated
Home Agent (HA)
Foreign Agent (FA)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
38
Mobile IP (MH Away - Collocated)
Packet
Correspondent Host (CH)
Internet
Visiting
Location
Home
Encapsulated
Home Agent (HA)
Mobile Host (MH)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
39
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 Kalyanaraman
Rensselaer Polytechnic Institute
40
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
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
41
Migrate Architecture
Location Query
(DNS Lookup)
Location Update
(Dynamic DNS Update)
DNS Server
Connection Initiation
Connection Migration
Correspondent
Host
Mobile Host
foo.bar.edu
xxx.xxx.xxx.xxx
Shivkumar
Kalyanaraman
Rensselaer Polytechnic Institute
42
Location-dependent wireless
services

Spontaneous networking

Automatically obtain map of
region & discover devices,
services and people there

Access, control services,
communicate with them
Handle mobility & group
communication


Where?
Rensselaer Polytechnic Institute
Locate other useful services (e.g.,
nearest café)
App should be able to conveniently
Shivkumar
Kalyanaraman
specify a resource and
access
it
43
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
44
iNAT: Design goals
Expressiveness
Names must be descriptive,
signifying application intent
Responsiveness
Name resolvers must track
rapid changes
Robustness
System must overcome
resolver and service failure
Easy configuration
Name resolvers must
self-configure
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
45
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

Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
46
Summary
Wireless: Introduction
 802.11, Bluetooth, CDPD
 Mobility: IP Addresses and location
 Solutions: Mobile IP, TCP Migrate
 Open areas: new directions...
 iNAT, zero-conf
Shivkumar Kalyanaraman

Rensselaer Polytechnic Institute
47