Transcript Voice over Mobile IP

Ch 6. Wireless and Mobile Networks
Myungchul Kim
[email protected]
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Wirless hosts
Wireless links
Base station: (e.g., cell towers, access points) handoff
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Infrastructure mode
Ad hoc mode
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Wireless network taxonomy
single hop
infrastructure
(e.g., APs)
no
infrastructure
host connects to
base station (WiFi,
WiMAX, cellular)
which connects to
larger Internet
no base station, no
connection to larger
Internet (Bluetooth,
ad hoc nets)
multiple hops
host may have to
relay through several
wireless nodes to
connect to larger
Internet: mesh net
no base station, no
connection to larger
Internet. May have to
relay to reach other
a given wireless node
MANET, VANET
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Wireless links and network
characteristics
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Differences between a wired link and a wireless link
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Signal-to-noise ration (SNR)
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Decreasing signal strength
Interference from other source
Multipath propagation
A relative measure of the strength of the received signal and the
noise.
dB
Bit error rate (BER)
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Physical-layer characteristics of higher-layer wireless
communication protocols
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For a given modulation scheme, the higher the SNR, the lower
the BER.
For a given SNR, a modulation technique with a higher bit
transmission rate will have a higher BER.
Dynamic selection of the physical-layer modulation technique
can be used to adapt the modulation technique to channel
condition.
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CDMA
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A partitioning protocol in that it partitions the codespace and
assigns each node a dedicated piece of the codespace.
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WiFi: 802.11 Wireless LANs
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802.11n: multiple-input multiple-output (MIMO) antennas, over
100Mbps, compatible with 802.11a/b/g devices
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The 802.11 architecture
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Basic service set (BSS): service set identifer (SSID)
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Channels and association
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11 partically overlapping channels
Separated by four channels (e.g., 1, 6, and 11)
AP sends beacon frames (AP’s SSID and MAC address)
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Association with authentication
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A station’s MAC address
Usernames and passwds by RADIUS or DIAMETER
The 802.11 MAC protocol
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CSMA/Collision Avoidance
Differences from Ethernet
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Collision avoidance
Link-layer acknowledgement/retransmission
No collision detection
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Costly to build hardware that can detect a collision
No detect all collisions due to the hidden terminal problem and
fading
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Dealing with hidden terminals: RTS and CTS
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RTS (including the total time required to transmit the DATA and
the ACK) and CTS to reserve access to the channel
CTS: gives the sender explicit permission to send and also
instructs the other stations not to send for the reserved duration.
RTS/CTS is used only when the frame is longer than the
threshold.
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Collision Avoidance: RTS-CTS exchange
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AP
B
reservation collision
DATA (A)
defer
time
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The IEEE 802.11 frame
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The fourth address: APs forward frames to each other in ad hoc
mode.
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Address 3 contains the MAC address of the router interface.
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802.11 frame: addressing
R1 router
H1
Internet
AP
R1 MAC addr AP MAC addr
dest. address
source address
802.3 frame
AP MAC addr H1 MAC addr R1 MAC addr
address 1
address 2
address 3
802.11 frame
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Mobility in the same IP subnet
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Advanced features in 802.11
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802.11 rate adaptation: select the underlying physical-layer
modulation technique to use based on current channel
characteristics.
Power management: alternate between sleep and wake states,
250 microseconds for wakeup.
Bluetooth
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IEEE 802.15.1
Wireless personal area network
4Mbps
Ad hoc networks
A piconet of up to eight active devices
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WiMAX
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IEEE 802.16
Wireless ADSL
Speeds of 70-80 miles per hour
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Cellular Internet Access
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Air interface access technologies
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A combination of FDM and TDM
CDMA
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1G
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Analog FDMA
Voice only
2G
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Digital for voice
Global system for mobile communication (GSM)
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Combined FDM/TDM
IS-95 CDMA
2.5G
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General packet radio service (GPRS): up to 9.6kbps packetbased data
Enhanced data rates for global evolution (EDGE): 384 kbps
CDMA-2000 phase: packet-data up to 144.4 kbps
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3G
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144 kbps at driving speeds
384 kbps for outside stationary use or walking speeds
2 Mbps for indoors
CDMA-2000
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Universal Mobile Telecommunication Service (UMTS)
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Evolved from IS-95
1xEVDO for 3 Mbps data
WCDMA for data
HSDPA/HSUPA up to 14 Mbps
4G
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Ubiquitout Internet access
The highest bit rate at that time and place
Vertical handoff
Seamless moblity
Voice and real-time video over IP
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Mobility management: principles
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Routing to a mobile node
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A mobile-node-to-foreign-agent protocol
A foreign-agent-to-home-agent registration protocol
A home-agent datagram encapsulation protocol
A foreign-agent decampsulation protocol
Direct routing to a mobile node
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Triangle routing problem
A mobile-user location protocol
Anchor foreign agent
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Mobile IP
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Agent discovery
Registration with the home agent
Indirect routing of datagrams
Agent discovery
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Via agent advertisement or via agent solicitation
An extension to the router discovery protocol
Home agent bit (H), foreign agent bit (F), registration required bit
(R), M and G encapsulation bits, care-of-address (COA) fields.
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Managing mobility in cellular networks
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GSM
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Indirect routing
Home location register (HLR), Visitor location register (VLR)
Mobile station roaming number
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Handoffs in GSM
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GSM: handoff with common MSC
VLR Mobile
Switching
Center 2
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1
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old BSS
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new BSS
1. old BSS informs MSC of impending handoff,
provides list of 1+ new BSSs
2. MSC sets up path (allocates resources) to
new BSS
3. new BSS allocates radio channel for use by
mobile
4. new BSS signals MSC, old BSS: ready
5. old BSS tells mobile: perform handoff to new
BSS
6. mobile, new BSS signal to activate new
channel
7. mobile signals via new BSS to MSC: handoff
complete. MSC reroutes call
8 MSC-old-BSS resources released
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Wireless and mobility: impact on higher
layer protocols
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Packet loss in TCP
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Network congestion
Handoff
Wireless communication
Approaches
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Local recovery
TCP sender awareness of wireless links
Split-connection approaches: two tranport-layer connections
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