Transcript Document

Wireless & Mobile Networking
Prof. Malathi Veeraraghavan
Elec. & Comp. Engg. Dept/CATT
Polytechnic University
[email protected]
Welcome to the first class of
EL604: Wireless & Mobile Networking
M. Veeraraghavan
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Polytechnic University
Outline
• Review of basic concepts in networking
–
–
–
–
Prerequisite: A first course on networking
Communication links and switches
Types of networks
Shared links: media access control (MAC)
• How does the “wireless” dimension change the
networking problem?
• How does the “mobile” dimension change the
networking problem? “Mobile” vs. “Portable”
M. Veeraraghavan
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What is a
communication network?
• Simplest “network”
– Single link between two pieces of end-user
equipment (e.g., PC, telephone)
– Types of communication links
•
•
•
•
Twisted pair
Coaxial cable
Optical fiber
Wireless links
End-user
equipment
End-user
equipment
– Radio frequencies
– Infra-red frequencies
M. Veeraraghavan
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What is needed to send data on
communication links?
• Error control
– Error detection:
• Parity checks, Checksum, Cyclic Redundancy Code (CRC)
– Error correction:
• ARQ (Automatic Repeat reQuest)
• FEC (Forward Error Correction)
• Flow control: handles rate mismatch between
sender and receiver
– x-ON/x-OFF
– Window based flow control
– Rate based flow control
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Switches
• Connect multiple links and route traffic
from one link to another
End-user
equipment
End-user
equipment
Switch
End-user
equipment
M. Veeraraghavan
End-user
equipment
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Why use a switch?
• If there are N endpoints (end-user
equipment), then how many links are
needed for full mesh connectivity?
• How many physical links are needed if
these endpoints are connected through a
switch?
M. Veeraraghavan
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Answers
• Number of direct links needed to connect N
nodes is N ( N  1)
2
• N links – since we only need one link from
an endpoint to a switch
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Cost of using a switch?
• Switch cost
• Can all endpoints have full connectivity at
all times to all other endpoints?
– Yes, with multiplexing on the links
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Concept of multiplexing
• Time division multiplexing
– Allows data from different sessions to be
combined at different times on to the same line
– How many DS0s in a T1?
• Wavelength division multiplexing
– Difference between FDM (Frequency Division
Multiplexing) and WDM?
– Relation between frequency and wavelength
M. Veeraraghavan
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Answers
• 24 DS0s in a T1
• Term WDM is the same as FDM at optical
frequencies – see EM spectrum chart
• Speed of light c = f
• : wavelength; f: frequency
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Transceiver rate
• Rate of transmission and reception at
endpoints and the switch
– Needs to be sufficient for “full mesh”
connectivity “all the time”
– e.g., if DS0s used between endpoints in full
mesh network, then T1s can be used in 25
endpoint network with a switch for full mesh
connectivity
M. Veeraraghavan
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Types of switches
• Circuit switches: Position-based switching
– Switch consults a table to determine output port on which to send
data bits based on their arriving position
• “Position”: Interface (space), time slot and/or wavelength
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–
–
–
Space division switch: switch based on input interface
Time division switching: interface + time slot
Wavelength division switching: interface + wavelength
No buffers
• Packet switches: Label-based switching
– Switch consults a table to determine output port on which to send
the packet based on value of label (in packet header)
– Label could be changed on outgoing port or could stay the same
– Have buffers to hold packets
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Network of switches
• Expand 1-switch network to a multi-switch
network
• Why not build one gigantic switch?
– Scalability limitations
End-user
equipment
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Switch
End-user
equipment
Switch
End-user
equipment
Switch
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Different types of networks
•
•
A network is defined by its “switching mode” and its “networking mode”
Circuit switching vs. packet switching
– Circuit-switching: switching based on position (space, time, ) of arriving bits
– Packet-switching: switching based on information in packet headers
•
Connectionless vs. connection-oriented networking:
– CL: Packets routed based on address information in headers
– CO: Connection set up (resources reserved) prior to data transfer
Switching modes
Networking modes
Connectionless
Packet-switching
IP, SS7
MPLS
IP + RSVP
ATM, X.25
Telephone network,
SONET/SDH, WDM
Circuit-switching
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Connection-oriented
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Types of data transfers
An application could consist of different types of data transfers
— An http session has an interactive component, but could also
have a non-real-time transfer
Consuming end
Live
Sending end
Live
Stored
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Stored
Interactive/
Live streaming
Recording
Stored streaming
File transfers
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Types of data transfers
An application could consist of different types of data transfers
— An http session has an interactive component, but could also
have a non-real-time transfer
Consuming end
Live
Sending end
Live
Stored
M. Veeraraghavan
Stored
Interactive/
Live streaming
Recording
Stored streaming
File transfers
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Matching applications & networks
Data transfers
Non-real-time
(stored at sender and receiver ends)
Real-time
(consumed or sent live)
Interactive (two-way)
(consumed and sent live)
e.g. telephony, telnet, ftp, http
Streaming (one-way)
(consumed live;
sent from live or stored source)
e.g. radio/TV broadcasts
Recording (one-way)
(stored at receiver end;
sent from live source); e.g. Replay
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Packet-switched CO networks
Short transfers
(e.g. short email)
Connectionless
networks
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Ideal networks
Long transfers
(e.g. large image,
audio, video or data)
Circuit-switched
networks
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Congestion control
• What is it?
– The purpose of a network is to allow sharing of
resources
– This means if demand is high, there could be
competition for resources from multiple users
– What are network resources:
• Link capacity (bandwidth)
• Switch buffer space (only in packet switches)
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Congestion control
• In CO networks
– Congestion control: mostly preventive
– Connection Admission Control (CAC)
• Check availability of bandwidth and buffer resources before
admitting a connection
• CS CO networks: congestion will not occur once circuits are
admitted
• PS CO networks: congestion can occur after connection is
admitted if connection admission is based on statistical
multiplexing
– Have some supplemental reactive congestion control scheme
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Congestion control
• In CL networks
– Have packet switches detect congestion and
send reactive messages asking sender to slow
down
– e.g., datagram routers in SS7 networks send
such messages; SRP (Spatial Reuse Protocol)
switches in 802.17 MANs send such messages
– IP routers implement Explicit Congestion
Notification (ECN) procedures
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End-to-end path
• Transport protocols
– Ensure reliable transfer across a communication
path consisting of many links (“zero” loss)
– OR ensure delay-controlled path across a
communication path consisting of many links
– Error control and flow control
– Delay control (e.g., RTP)
– Congestion control and connection control –
special in TCP
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Applications
• Most Internet applications are client-server based
End-user
equipment
Network
Web server
(Usually runs
on fixed hosts)
Web clients
Network
Network
End-user
equipment
Email-sending clients
(outlook,
messenger)
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Outgoing
email servers
(pop, imap)
Network
Incoming
email servers
(smtp)
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End-user
equipment
Polytechnic
University
Email-receiving
clients
(outlook, messenger)
Protocol Stacks
AL
AL
TL
TCP/UDP
NL
NL
NL
IP
DLL
DLL DLL
DLL DLL
DLL
PHY
PHY PHY
PHY PHY
PHY
Switch
Switch
Endpoint
Endpoint
•
OSI model: two more layers between AL and TL
–
•
Session layer and presentation layer
PHY: Physical; DLL: Data Link Layer; NL: Network Layer; TL: Transport Layer;
AL: Application Layer
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Example protocols
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•
•
•
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AL protocols: http, smtp, ftp, PCM voice
TL protocols: TCP, UDP, RTP
NL protocols: IP, ATM
DLL protocols: PPP, HDLC
PHY protocols: DS0, DS1
Ethernet: PHY+DLL+NL
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Functions of protocol layers
• PHY: sends bits across a link
• DLL: error control and flow control on a
link
• NL: switching (routing), multiplexing,
congestion control
• TL: error control and flow control on an
end-to-end basis
• AL: Functions specific to the application
M. Veeraraghavan
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Congestion control and
connection control in TCP
• IP routers did not implement ECN until recently
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–
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TCP performs congestion control
Senses whether network switches (routers) are congested or not
Adjusts rate accordingly
Slow start and congestion avoidance
• Concept of a “connection” at the TL
– End hosts maintain state information regarding a TCP connection
to track sequence numbers and ACKs
– Connection open (SYN) and close (FIN) procedures
– Contrast with a “connection” at the NL, where each switch
maintains state about the connection
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User plane, control plane, and
management plane
• Management plane: consists of all the protocols needed to “configure”
data tables for the operation of the network
– For example, protocols for routing data dissemination (distributed or
centralized)
– Other functions: performance, fault mgmt., accounting, security
• Control plane:
– Connection control protocols
• in CO networks, this includes connection setup at each switch (connections at
the network layer)
• in CL networks, this includes connection setup only at the endpoints
(connections at the transport layer, if the TL protocol is reliable)
– Call control protocols
• User plane: protocols for the actual flow of data
M. Veeraraghavan
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Routing protocol in all three types of
networks - Phase 1
Dest.
Next hop
B
B
II
Host A
I
Dest.
Next hop
III-*
IV
Routing
protocol
Routing
protocol
Routing
protocol
IV
Dest.
Next hop
III-*
III
Host B
III
V
Routing tables
• Routing protocols exchange
topology/loading/reachability information
• Routes to destinations are precomputed and stored in
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routing tables
Signaling protocol for NL connection setup in
a PS CO network - Phase 2
Connection
setup (B)
II
d/L1
b
a
Host A
IN
Port /Label
I
c
Connection
setup
b
a
a/L1
OUT
Port/Label
c/L2
Connection
setup
IV
III
d
IN
Port /Label
b
Host B
c
V
d
Connection
setup
OUT
Port/Label
a/L2
•
b/L3
a
c
IN
Port /Label
OUT
Port/Label
c/L1
Virtual circuit
Connection setup consists of each switch on the path
– Route lookup for next hop node to reach destination
– CAC (Connection Admission Control) for buffer and BW
– Writing the input/output label mapping tables and programming the scheduler
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Signaling protocol for NL connection setup in
a CS CO network - Phase 2
Connection
setup (B)
Host A
II
d/2
b
a
I
IN
OUT
Port /Timeslot Port/Timeslot
c
a
Connection
setup
b
Connection
setup
a
a/1
c/2
IV
III
d
c
IN
OUT
Port /Timeslot Port/Timeslot
b/1
b
Host B
c
V
d
Connection
setup
IN
OUT
Port /Timeslot Port/Timeslot
a/2
c/2
Circuit
• Connection setup consists of each switch on the path
– Route lookup for next hop node to reach destination
– CAC (Connection Admission Control) for BW (note: no buffers)
– Writing the port/timeslot/
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TL connection setup in a CL PS
network - Phase 2
• Notion of transport layer connections
– Exchange initial sequence numbers end-to-end to allow for ARQ
(Automatic Repeat reQuest) based error correction, i.e., retransmissions in
case of errors
Dest.
Next hop
B
B
II
Host A
I
Dest.
Next hop
B
II
M. Veeraraghavan
Host B
III
SYN
ACK
SYN
V
IV
Dest.
Next hop
B
III
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Routing tables
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User-plane packet forwarding in a PS
CO network - Phase 3
II
L1
b
Host A
IN
Port /Label
a/L1
a
I
c
L1
III
c
d
b
a
OUT
Port/Label
c/L2
L3
a
IV
d
b
Host B
c
V
L2
• Labels are VPI/VCIs in ATM
• Labels are translated from link-to-link
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User-plane actions in a circuit-switched
network - Phase 3
II
1
2
b
Host A
a
I
1
a
1
c
2
b
d
c
a
IV
III
d
2
b
Host B
c
V
IN
OUT
Port /Timeslot Port/Timeslot
a/1
c/2
1
2
• Bits arriving at switch I on time slot 1 on
port a are switched to time slot 2 of port c
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User-plane packet forwarding in a CL PS
network - Phase 3
II
b
Host A
a
I
c
B
B
a
B
III
c
d
b
a
IV
d
b
Host B
c
V
B
• Packet headers carry destination host address (unchanged
as it passes hop by hop)
• Each CL packet switch does a route lookup to determine
the outgoing port/next hop node
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Addressing
• Where are endpoint addresses used:
– In CL PS networks, endpoint addresses are
carried in packet headers
– In CO networks, be it PS or CS, endpoint
addresses are carried in connection setup
messages
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Summarized addresses
• What are summarized addresses?
• Why summarize addresses?
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Summarized addresses
• What are summarized addresses?
– An address that represents a group of endpoint
addresses
– e.g., all 212 numbers, 128.238 IP addresses
• Why summarize addresses?
– Reduces routing table sizes – hold one entry for a
summarized address instead of a large number of
individual addresses
– Reduces routing message lengths that convey
reachability information
M. Veeraraghavan
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Examples of signaling protocols
• SS7 (Signaling System No. 7) network
(with its SS7 protocol stack) carries
signaling messages to set up and release
circuits in a telephone network
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Examples of routing protocols
• In the Internet:
– Link-state routing protocols, such as Open Path
Shortest First (OSPF)
– Distance-vector based routing protocols, such
as Routing Information Protocol (RIP)
• In telephone networks:
– Real-Time Network Routing (RTNR)
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Examples of addressing schemes
• Internet
– 4-byte IP addresses
• Telephone networks
– 8-byte E.164 address (telephone number)
• ATM networks
– 20-byte ATM End System Address (AESA)
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Broadcast links
• Wireless
• Copper: ethernet hubs
• Optical fiber: Passive star couplers
Dest: A
Ethernet hub
or
WDM Passive Star Coupler
A
Ethernet switch
(packet switch)
Blind broadcast
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MAC protocols
• Medium Access Control (MAC) protocols are used in broadcast links
to allow a node to access medium and send information
• As if “switch” is in endpoints
• Wasteful of resources because all endpoints receive all packets
B’s MAC layer checks destination address to
determine whether the packet should be “switched” to
the application or dropped
End-user
equipment
A
To B
M. Veeraraghavan
C’s MAC layer checks destination address to
determine whether the packet should be “switched” to
the application or dropped
End-user
equipment
B
To B
End-user
equipment
C
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Outline
• Review of basic concepts in networking
–
–
–
–
Prerequisite: A first course on networking
Communication links and switches
Types of networks
Shared links: media access control (MAC)
 How does the “wireless” dimension change the
networking problem?
• How does the “mobile” dimension change the
networking problem? “Mobile” vs. “Portable”
M. Veeraraghavan
43
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The “wireless” dimension
• Naturally broadcast medium
• Poor link quality
• Low power
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Protocol impact
• Need a MAC protocol to share the
“naturally broadcast” wireless medium
• High error rate because of the poor link
quality
– Need link-level error correction
• Low power causes high error rate
M. Veeraraghavan
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Outline
• Review of basic concepts in networking
–
–
–
–
Prerequisite: A first course on networking
Communication links and switches
Types of networks
Shared links: media access control (MAC)
• How does the “wireless” dimension change the
networking problem?
 How does the “mobile” dimension change the
networking problem? “Mobile” vs. “Portable”
M. Veeraraghavan
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Portable vs. mobile
• A portable end user device is one that can
be removed easily from its network point of
attachment and connected to a different
point in the network
– usually nodes that run “client” software not
server
• A mobile end user device is one that can be
moved while engaged in a communication
session
M. Veeraraghavan
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Impact of “portable” nodes
• When a node connects to some switch (router) of a network, it should
be assigned an endpoint address derived from the network address of
switch
– Allows for routing information in the rest of the network to not require an
update
– e.g., DHCP (Dynamic Host Configuraion Protocol)
get address
Dest: 24.3.5.10; Src: yahoo
24.3
yahoo
web
server
My laptop
@Home R
Dest: yahoo; Src: 24.3.5.10
Dest: 128.238.24.5; Src: yahoo
Poly network R
address: 24.3.5.10
get address
My laptop
Dest: yahoo; Src: 128.238.24.5 128.238address: 128.238.24.5
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Node: client or a server
• If the node that is portable is a client, i.e., no other
host tries to reach this node, then this solution of it
obtaining a temporary address works.
• But in cellular telephone network, this is not
applicable because all endpoints can be “called”
• “Server” receives calls/session requests
• “Client” only makes calls, initiate sessions
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What happens if the
server (called end) moves?
• The server is known to all nodes in the
network by some address
• If the server changes its point of connection
to the network, its location should be
“managed”
• This is the problem of location
management.
• Any ideas for how to solve this problem?
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Location management problem
in IP networks
To A
R2
Host C
Dest
R1
Next-hop
R4
128.238.42 R2
110.54.66 R4
128.238.42
R3
.110
110.54.66 .11
R5
Host A
Host B
128.238.42.110
Host A
• How is the IP packet destined to A delivered?
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Location management in
cellular telephone networks
setup(718-261-5678)
S2
S1
Dest
718-261
415-555
Next-hop
S4
S2
S4
718-261
718-261-5678
S3
S5
415-555
415-555-1234
718-261-5678
• How is a call delivered to A?
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A user moves
while in a connection
• If a user moves while communicating
– how does the network reroute data destined to
the user?
– this is called handoff management
• Examples
– In cellular networks, a user traveling in a car
while communicating keeps changing his
connection point to the network (base station)
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Cellular network handoffs
S2
S1
718-261
718-261-5678
S3
S4
S5
Have to preserve the connection as the user moves
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718-261-5678
Polytechnic University
Handoffs in a data network
• In an IP network, there is a similar need for
a handoff if a mobile wireless user moves
while the user’s laptop is engaged in a TCP
connection (say for email download or web
file download)
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Big difference between these two
types of handoffs
• In CO networks, every switch on the path has been
configured with translation tables specifying how
to route bits arriving on each connection
– Handoff involves a rewriting of this data
• In CL networks such as IP, with TCP as a CO
transport protocol, state information is only held at
the end hosts
– Handoff is a lot simpler
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Mobility management
• Mobility management includes both
– Handoff management
– Location management
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Summary
• Reviewed networking concepts
• To support wireless links, need
– MAC protocols
– Location management
– Handoff management
• To support mobile servers on wireless links, need
– Location management
– Handoff management
• To support mobile clients on wired or wireless links
(portables), need support for dynamically allocated
addresses
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