CPSC 441: Wireless 1 Instructor: Anirban Mahanti Office: ICT 745 Email: [email protected]Class Location: ICT 121 Lectures: MWF 12:00 – 12:50 hours Notes derived from “Computer Networking: A Top Down Approach Featuring the Internet”, 2005, 3 rd edition, Jim Kurose, Keith Ross, Addison- Wesley. Slides are adapted from the companion web site of the book, as modified by Anirban Mahanti (and Carey Williamson). Wireless and Mobile Networks
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CPSC 441: Wireless 1
Instructor: Anirban MahantiOffice: ICT 745Email: [email protected] Location: ICT 121Lectures: MWF 12:00 – 12:50 hoursNotes derived from “Computer Networking: A Top
Down Approach Featuring the Internet”, 2005, 3rd edition, Jim Kurose, Keith Ross, Addison-Wesley.
Slides are adapted from the companion web site of the
book, as modified by Anirban Mahanti (and Carey Williamson).
Wireless and Mobile Networks
CPSC 441: Wireless 2
Outline
Introduction Standards and Link Characteristics IEEE 802.11 Wireless LANS Mobility Wireless/Mobility Performance Issues Summary
CPSC 441: Wireless 3
What is Wireless Networking? The use of infra-red (IR) or radio frequency
(RF) signals to share information and resources between devices
promise anytime untethered Internet access Two important (but different) challenges
communication over wireless link handling mobile user who changes point of
attachment to network Buzz words!
Mobile Internet, Pervasive Computing, Nomadic Computing, M-Commerce, Ubiquitous Computing …
CPSC 441: Wireless 4
Wireless Networking Technologies Mobile devices – laptop, PDA, cellular
phone, wearable computer, …
Operating modes Infrastructure mode (Access Point) Ad hoc mode
Access technology Bluetooth (1 Mbps, up to 3 meters) IEEE 802.11 (up to 55 Mbps, 20 – 100
meters)
CPSC 441: Wireless 5
Infrastructure Mode
network infrastructure
infrastructure mode base station
connects mobiles into wired network
handoff: mobile changes base station providing connection into wired network
CPSC 441: Wireless 6
Ad hoc Mode
Ad hoc mode no base stations nodes can only
transmit to other nodes within link coverage
nodes organize themselves into a network: route among themselves
CPSC 441: Wireless 7
Outline
Introduction Standards and Link Characteristics IEEE 802.11 Wireless LANS Mobility Wireless/Mobility Performance Issues Summary
CPSC 441: Wireless 8
Wireless link standards
384 Kbps384 Kbps
56 Kbps56 Kbps
54 Mbps54 Mbps
5-11 Mbps5-11 Mbps
1 Mbps1 Mbps
802.15
802.11b
802.11{a,g}
IS-95 CDMA, GSM
UMTS/WCDMA, CDMA2000
.11 p-to-p link
2G
3G
Indoor
10 – 30m
Outdoor
50 – 200m
Mid rangeoutdoor
200m – 4Km
Long rangeoutdoor
5Km – 20Km
CPSC 441: Wireless 9
Two Popular 2.4 GHz Two Popular 2.4 GHz Standards:Standards: IEEE 802.11
Fast (11b) High Power Long range Single-purpose Ethernet
replacement Easily Available
• Apple Airport, iBook, G4
• Cisco Aironet 350
Bluetooth Slow Low Power Short range Flexible Cable
replacement
CPSC 441: Wireless 10
Wireless Link CharacteristicsDifferences from wired link ….
Decreasing signal strength: radio signal attenuates as it propagates through matter (path loss)
Interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well
Multi-path propagation: radio signal reflects off objects ground, arriving at destination at slightly different times
…. make communication across (even a point to point) wireless link much more “difficult”
CPSC 441: Wireless 11
Wireless Network CharacteristicsMultiple wireless senders and receivers create
additional problems (beyond multiple access):
AB
C
Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each
othermeans A, C unaware of their
interference at B
A B C
A’s signalstrength
space
C’s signalstrength
Signal fading: B, A hear each other B, C hear each other A, C can not hear each other
interfering at B
CPSC 441: Wireless 12
Outline
Introduction Standards and Link Characteristics IEEE 802.11 Wireless LANS Mobility Wireless/Mobility Performance Issues Summary
home agent: entity in visited network that performs mobility functions on behalf of mobile.
correspondent: wants to communicate with mobile
CPSC 441: Wireless 29
How do you contact a mobile friend:
search all phone books?
call her parents? expect her to let you
know where he/she is?
I wonder where Alice moved to?
Consider friend frequently changing addresses, how do you find her?
CPSC 441: Wireless 30
Mobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
Let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
CPSC 441: Wireless 31
Mobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
not scalable
to millions of mobiles
CPSC 441: Wireless 32
Mobility: registration
End result: Foreign agent knows about mobile Home agent knows location of mobile
wide area network
home network
visited network
1
mobile contacts foreign agent on entering visited network
2
foreign agent contacts home agent home: “this mobile is resident in my network”
CPSC 441: Wireless 33
Mobility via Indirect Routing
wide area network
homenetwork
visitednetwork
3
2
41
correspondent addresses packets using home address of mobile
home agent intercepts packets, forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
CPSC 441: Wireless 34
Indirect Routing: comments Mobile uses two addresses:
permanent address: used by correspondent (hence mobile location is transparent to correspondent)
care-of-address: used by home agent to forward datagrams to mobile
foreign agent functions may be done by mobile itself triangle routing: correspondent-home-network-
mobile inefficient when correspondent, mobile are in same network
CPSC 441: Wireless 35
Indirect Routing: moving between networks suppose mobile user moves to another
network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile
(but with new care-of-address) mobility, changing foreign networks
transparent: on going connections can be maintained!
CPSC 441: Wireless 36
Mobility via Direct Routing
wide area network
homenetwork
visitednetwork
4
2
41correspondent requests, receives foreign address of mobile
correspondent forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
3
CPSC 441: Wireless 37
Mobility via Direct Routing: comments
overcome triangle routing problem non-transparent to correspondent:
correspondent must get care-of-address from home agent what if mobile changes visited network?
CPSC 441: Wireless 38
wide area network
1
foreign net visited at session start
anchorforeignagent
2
4
new foreignagent
35
correspondentagent
correspondent
new foreignnetwork
Accommodating mobility with direct routing
anchor foreign agent: FA in first visited network data always routed first to anchor FA when mobile moves: new FA arranges to have
data forwarded from old FA (chaining)
CPSC 441: Wireless 39
Mobile IP
RFC 3220 has many features we’ve seen:
home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)
three components to standard: indirect routing of datagrams agent discovery registration with home agent
CPSC 441: Wireless 40
Outline
Introduction Standards and Link Characteristics IEEE 802.11 Wireless LANS Mobility Wireless/Mobility Performance Issues Summary
CPSC 441: Wireless 41
Wireless, mobility: impact on higher layer protocols
logically, impact should be minimal … best effort service model remains unchanged TCP and UDP can (and do) run over wireless,
mobile … but performance-wise:
packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff
TCP interprets loss as congestion, will decrease congestion window un-necessarily
delay impairments for real-time traffic limited bandwidth of wireless links
CPSC 441: Wireless 42
Summary
Wireless wireless links:
capacity, distance channel impairments CDMA
IEEE 802.11 (“wi-fi”) CSMA/CA reflects
wireless channel characteristics
Mobility principles: addressing,
routing to mobile users home, visited networks direct, indirect routing care-of-addresses