Download Ad hoc communication

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Course element content for Ad hoc
•Lecture 1 (Ad hoc concept and networking overview)
•Ad hoc concept
•Ad hoc basic functionality
•Ad hoc possible usage areas
•Background of ad hoc
•Networking: OSI, Protocols, routing, TCP/IP
•Project description (briefly)
•Lecture 2 (Networking and routing in depth)
•TCP/IP in depth
•Routing protocols: purpose, conceptual function and review
•Standardization work: IETF, IEEE current protocols
•Additional ad hoc routing features
•Lecture 3 (Advanced concepts)
•MAC layer
•ARP
•Quality of Service (QoS): SNR, Bandwidth constraints, Neighbor solicitation errors
•IPv6
•Security considerations
Ad hoc communication: Concept, OSI and TCP/IP
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OSI layer 1 802.11 PHY Sublayer
Defines the physical and electrical characteristics of the network. The NIC
cards in your PC and
the interfaces
on your routers
run rates
at this level since,
Examples
of modulation
andall
data
eventually, they have to pass strings of ones and zeros down the wire!
IEEE 802.11a
Examples:
Ethernet/802.3 Token Ring (802.5) SNAP/802.2 X.25 FDDI ISDN Frame
Data rate
Modulation
Coding rate
Relay SMDS ATM Wireless (WAP, CDPD, 802.11)
6 DDS/DS0/T-carrier/E-carrier
BPSK
½
Fibre Channel
SONET/SDH
DWDM
PPP HDLC9 SLIP/CSLIP xDSL
Cable Modem (DOCSIS)
BPSK
¾
4-QAM
½
802.11 phy 12
18 of encoding and
4-QAM
¾
Defines a series
transmission schemes
24
36
FHHS (802.11
2Mbps)
48
16-QAM
½
16-QAM
¾
64-QAM
½
DSSS (802.11b
11Mbps)64-QAM
54
¾
OFDM (802.11a 54Mbps)
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OSI layer 2 MAC
802.11 MAC Frame
The 802.11 MAC frame, as shown in the following figure, consists of a MAC
header, the frame body, and a frame check sequence (FCS). The numbers in the
following figure represent the number of bytes for each field.
802.11 MAC Frame Format
02312
MAC Header
2
Frame
Control
2
6
Duration/
ID
Address
1
6
6
Address
2
Address
3
6
Sequence
Control
2
Address
4
Frame
Body
4
FCS
Frame Control Field
2 bits
Protocol
Version
2
Type
4
Subtype
1
1
1
To
DS
From
DS
More
Fragments
1
1
Retry Power
Mgt.
1
1
More
data
WEP
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1
Order
802.11 MAC Layer Overhead
Network Capacity Approximations for 802.11b, 802.11g and 802.11a
Data rate (Mbps)
Approximate Throuput
(Mbps)
802.11b
11
6
802.11g (802.11b in cell)
54
8
802.11g (no 802.11b in cell)
54
22
802.11a
54
25
Source: Cisco Systems, Inc.
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OSI reference model
Application
TCP
/ UDP
Transport
IP
Network
Data
link
MAC
Physical
ARP
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Address Resolution Protocol (ARP)
•
•
•
•
ARP translates Ethernet addresses (MAC) to Internet Protocol addresses
(IP)
Data communication (IPv4) is initiated by ARP messages.
ARP messages are sent automatically.
Has been deprecated in IPv6 and replaced by the Neighbor Discovery
Protocol (NDP) which is a pure layer 4 protocol.
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ARP Illustrated by Ping Example
Node:
IP Address:
MAC Address:
1
192.168.0.1
00-0D-56-3C-DE-C0
Node:
IP Address:
MAC Address:
2
192.168.0.2
00-0D-56-3C-DB-9D
Who has 192.168.0.2? Tell 00-0D-56-3C-DE-C0
192.168.0.2 is at 00-0D-56-3C-DB-9D
ICMP Request to 192.168.0.2
Who has 192.168.0.1? Tell 00-0D-56-3C-DE-C0
192.168.0.1 is at 00-0D-56-3C-DE-C0
ICMP Reply to 192.168.0.1
ICMP Request to 192.168.0.2
ICMP Reply to 192.168.0.1
ICMP Request to 192.168.0.2
ICMP Reply to 192.168.0.1
ICMP Request to 192.168.0.2
ICMP Reply to 192.168.0.1
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Standard Internet ARP Message
Hardware Type
Protocol Type
Hardware Address Len
Protocol Address Len
Operation Code
Sender Hardware Address
Sender IP Address
Recipient Hardware Address
Recipient IP Address
The operation code defines what type of message that is transmitted / received.
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Concept of Multi-hop Enabled ARP (MEARP)
•
•
•
•
Reuses existing data traffic
Introduced resending of ARP requests
Introduced forwarding of ARP replies
Mechanisms to treat the new ARP messages
•
•
•
Cross-layer issues
•
•
•
Flood avoidance
Pending request list
Link quality observations
Traffic observations
Multi-hop gateway support
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ARP Enabled Ad Hoc Routing
Node:
IP Address:
MAC Address:
1
192.168.0.1
00-0D-56-3C-DE-C0
Who has 192.168.0.3?
Tell 00-0D-56-3C-DE-C0
Node:
IP Address:
MAC Address:
2
192.168.0.2
00-0D-56-3C-DB-9D
Who has 192.168.0.3?
Tell 00-0D-56-3C-DB-9D
Node:
IP Address:
MAC Address:
3
192.168.0.3
00-0D-56-3C-E2-4C
192.168.0.3 is at
00-0D-56-3C-E2-4C
Use 192.168.0.2 to reach
192.168.0.3
ICMP Request 192.168.0.3
ICMP Request 192.168.0.3
192.168.0.1 is at
00-0D-56-3C-DE-C0
Who has 192.168.0.1?
Tell 00-0D-56-3C-DB-9D
Who has 192.168.0.1?
Tell 00-0D-56-3C-E2-4C
Use 192.168.0.2 to reach
192.168.0.1
ICMP Reply 192.168.0.1
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ICMP Reply 192.168.0.1
Security considerations in ad hoc networks
Issues:
• Information integrity – Unauthorized should not be able to read our
data.
• Transmission security – Unauthorized should not be able to
eavesdrop on out transmitted information.
• Denial of Service (DoS) – No one should be able to report
unusable routes, drown the network with bogus data in order to
cause congestions etc.
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Security considerations in ad hoc networks
Information is relayed by someone you do not trust. How do you
protect your information?
Solution:
OSI layer 3 cryptography, e.g. IP Security
(IPSec, AH, ESP).
Solution:
OSI layer 6 cryptography, e.g. the Secure
Socket Layer (SSL).
An unauthorized person eavesdrops on our transmitted data packets.
Solution:
Issues:
OSI layer 2 cryptography, e.g. WEP or WPA for
IEEE 802.11x. Frequency hopping etc.
Distribution of new authentication keys.
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Security considerations in ad hoc networks
An unauthorized person is injecting invalid routes, to much data traffic
etc. into the ad hoc network.
Solution:
Issues:
A node must be authenticated before it can be
trusted in the ad hoc network. Nodes that are
not authenticated should not be trusted and
their information should not be forwarded.
Distribution of new authentication keys.
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Security summary
•
•
•
Secure communication and information integrity can be performed at
different OSI layers.
Ad hoc routing algorithms have to be able to authenticate other nodes.
Difficulties to distribute authentication keys to all ad hoc nodes, since all
nodes may not be in reach of radio transmission.
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How an ordinary router works – 1 of 2
Definition:
•
•
•
•
•
A device that connects multiple networks together and forwards packets (of
data) between them.
Uses multiple network interfaces.
Routing is preformed at the network layer (layer 3), i.e. a router does not
care about higher layers.
A router has a routing table, specifying which IP address (or group of
addresses) should belonging to which interface.
The Internet is hierarchy designed, which allows routers to group similar
addresses to the same interface.
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How an ordinary router works – 2 of 2
1. An inbound packet is received on one interface.
2. The MAC Header is removed. (It is only valid for one link)
3. The destination of the IP packet is examined to find out on which interface
the packet should be transmitted. If no route is found, the packet is dropped
and an Internet Control Message (ICMP) is sent to the source of the IP
packet.
4. The Data Link Layer adds a MAC Header on the packet.
5. The Physical Layer transmits the packet.
SOURCE
ROUTER(S)
DESTINATION
HTTP
HTTP
TCP
TCP
IP
IP
IP
Ethernet
Ethernet
Ethernet
100BASE-TX
100BASE-TX
100BASE-TX
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Wireless routing
• The Physical Layer receives all wireless communication. All filtering,
i.e. packets that are not destined for the local device, is performed at
the Data Link Layer.
• Power is consumed when receiving and computing data.
• Most ad hoc routing algorithms performs routing at the Network
Layer.
• Routes are set by saying:
To reach C, send to B.
A
B
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C
Dynamic Source Routing
(DSR)
• Reactive routing protocol.
• Modifies every IP packet with an additional header, DSR Header.
Example:
IP
DSR
TCP
HEADER HEADER
HEADER
TCP PAYLOAD
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Dynamic Source Routing (DSR)
DSR Header
IP
DSR
TCP
HEADER HEADER
HEADER
Next
Header
F
TCP PAYLOAD
Reserved
Payload Length
(Option1)
(…)
(Option N)
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Dynamic Source Routing (DSR)
DSR Header options
Options:
• Variable-length field;
• The length of the Options field is specified by the Payload
Length field in this DSR Options header.
• Contains one or more pieces of optional information (DSR
options).
Next
Header
F
Reserved
Payload Length
(Option1)
(…)
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Dynamic Source Routing (DSR)
DSR Header options
Next
Header
F
Reserved
Payload Length
(Option1)
(…)
•
•
•
•
•
•
•
•
Route
Requestoption
option
Route Request
Route
Replyoption
option
Route Reply
Route
Erroroption
option
Route Error
Acknowledgement
Request
option
Acknowledgement Request
option
Acknowledgement
option
Acknowledgement option
DSR Source
Routeoption
option
Source Route
Pad1 option
option
PadN option
option
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Dynamic Source Routing (DSR)
DSR options example
ROUTE REQUEST
Option Type
•
•
•
Opt Data length
Target Address
Address[1]
Address[2]
…
Address[N]
Identification
Opt Data Len 8-bit unsigned integer. Length of the option, in octets, excluding the
Option Type and Opt Data Len fields.
Identification A unique value generated by the initiator (original sender) of the Route
Request.
Target Address The address of the node that is the target of the Route Request.
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Dynamic Source Routing (DSR)
DSR options example
ROUTE REPLY
Option Type
Opt Data length L
Target Address
Address[1]
Address[2]
…
Address[N]
Reserved
L: Set to indicate that the last hop given by the Route Reply (the link from Address[n1] to Address[n]) is actually an arbitrary path in a network external to the DSR
network.
Addresses: The source route being returned by the Route Reply.
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DSR Considerations
• DSR packets can not be traversed on the Internet.
• If the DSR network is interconnected with another network, e.g. the
Internet, all DSR information, i.e. the DSR Header, has to be
removed in the packet!
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Why have QoS techniques? – 1 of 2
•
•
Ideal QoS = unlimited throughput + no delay + no drops
But…
1.
2.
3.
4.
•
Links have limited bandwidth.
Applications/nodes compete for bandwidth.
Some applications try to take all available bandwidth.
Transmissions takes time and packets get queued.
Different applications have different QoS requirements.
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Why have QoS techniques? – 2 of 2
1.0
file server 1
voip
A
R1
2.0
0.064
1.5
R2
2.0
voip
B
R3
2.0
1.0
0.064
R4
news server 1
1.5
unit: Mbps
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news server 2
Issues in QoS-aware MANETs
Quality of Service metrics
•
•
•
Delay, bandwidth, probability of packet loss, and delay variance (jitter).
Power consumption and service coverage area.
QoS metrics could be defined in terms of one of the parameters or set of
parameters in varied proportions.
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QoS in MANETs: Issues and difficulties
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•
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•
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Unpredictable link properties.
Node mobility.
Limited battery life.
Hidden and exposed terminal problems.
Route maintenance.
Security.
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Hidden and exposed terminal problems
currently transmitting
wants to transmit
Range of
terminal A
A
Range of
terminal C
B
Range of Range of
terminal B terminal C
A
C
will collide with
transmission from A at B
Hidden Terminal Problem
B
C
D
cannot send to D due
to carrier sense
Exposed Terminal Problem
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QoS Support in the Physical Layer
•
Channel estimation
•
•
•
Signal-to-noise ratio in channels fluctuates  adaptive modulation
Accurate channel estimation at the receiver and then reliable feedback of the
estimation to the transmitter.
Joint source-channel coding
•
Takes both source characteristics and channel conditions into account
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QoS Provisioning at the MAC Layer
•
Fully distributed scheme is needed that should first solve the hidden and
exposed terminal problems.
•
Multihop access collision avoidance (MACA)
•
•
•
MACA for Wireless (MACAW)
•
•
Request-to-send/clear-to-send (RTS/CTS) dialogs
Does not completely eliminate the hidden terminal problem
Extension to MACA to provide faster recovery from hidden terminal collisions
IEEE 802.11
•
•
Collision avoidance feature of MACA and MACAW by its distributed control
function (DCF)
Carrier sense multiple access with collision avoidance (CSMA/CA)
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QoS-aware routing at the Network Layer
•
Types of MANET routing protocols:
•
•
•
•
Proactive, table-driven routing schemes.
Reactive, on-demand routing schemes.
These algorithms are based on the discovery of shortest paths.
QoS-aware routing protocol should find a path that satisfies the QoS
requirements in the path from source to the destination.
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Transport Layer issues for QoS
TCP performs poorly in terms of end-to-end throughput in MANETs
•
The assumption used in Internet that packet losses are due to congestion is not
valid in MANET environments
TCP performance improvement in wireless networks
•
•
Local retransmissions
Split-TCP connections (Use of multi-path)
Explicit feedback mechanisms to distinguish between losses due to errors and
congestion is necessary for QoS provisioning in MANETs.
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QoS Summary
•
•
Quality of Service is the idea that transmission rates, error rates, and other
characteristics can be measured, improved, and, to some extent,
guaranteed in advance.
Cross-layer, OSI layers that is, issues needs to be examined. (Interaction
between layers that is)
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IPv6 overview
IPv6
Motivation for developing IPv6:
• Header fields simplification, including removal of fields.
• Revision of fields.
• New fields were added.
• Fixed header size. (Improves routing efficiency)
• Increased amount of addresses.
• Scalability. (Introduction of extension headers)
IPv6
Note! IPv6 only affect layer 3 and 7 in the OSI model.
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IP header overview
From IPv4 toIPv6
Version
IP header
IH
L
Identification
Type of Service
Time
Live
HopTo
Limit
Next
Header
Protocol
Payload
length
Total Length
Flags
Fragment offset
Header Checksum
Source Address
Destination Address
(Option 1)
(Option line 1)
(Option
10)10)
(Option
line
Destination
Address
Transport
Layer
Data….
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IP header overview
IPv6
Version
Flow Label
Traffic Class
Payload length
Next Header
Hop Limit
Source Address
Base
Header
Hop-by-hop
options
Destination
options
Routing
header
ESP
…….
Destination Address
TCP header
Application
payload
Extension
headers
( Extension Headers)
( Extension Header)
( Extension Header)
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IPv6 effect on ad hoc routings
• IPv6 currently uses two different types of addresses:
1. Link Local addresses (Used for point-to-point communication – not
routable!)
2. Global addresses (Used on the Internet – Routable!)
Issue:
Solution:
A neighbor (point-to-point) could move, i.e. the node
is no longer our neighbor. If the Link Local address is
used, it should not be routed!
Only use Global addresses!
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IPv6 effect on ad hoc routings
IPv6 Routing Header
• Similar to the DSR Header.
• Allows the source of an IP packet to choose the packets path.
• Ad hoc routing algorithms could take an advantage of this additional
header.
Issue:
Solution:
IPv6 addresses are large (128 bits), which reduces
the amount of available space for IP payload.
IPv6 header compression!
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Ad hoc communication
References
•
Internet Protocol version 6:
http://www.ipv6.org
•
How 802.x Wireless Works:
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/Te
chRef/370b019f-711f-4d5a-8b1e-4289db0bcafd.mspx
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