Telemedicina e eSaúde Telecommunication Networks Introduction 1 d cc ] [ Telecommunication Networks Introduction Telemedicina e e-Saúde 2019/20 Pedro Brandão d cc ] [ References • These slides are the companions of “Computer Networking: A Top Down Approach 5th edition. Jim Kurose, Keith Ross Addison- Wesley, April 2009” oWith adaptations/additions by Rui Prior and Pedro Brandão Telemed eSaúde 19/20 - Networks Intro - pbrandao 2
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Telemedicina e eSaúde
Telecommunication Networks Introduction 1
d cc][
Telecommunication Networks IntroductionTelemedicina e e-Saúde
2019/20
Pedro Brandão
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References
• These slides are the companions of “Computer Networking: A Top Down Approach 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009”oWith adaptations/additions by Rui Prior and Pedro Brandão
Telemed eSaúde 19/20 - Networks Intro - pbrandao
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Telecommunication Networks Introduction 2
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Digital, Analogic
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Analogic Digital
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Sampling
Quantification
Images from Wikipedia
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A few words on audio compression
• Audio signal sampling at a fixed rate:o telephone: 8 000 samples/sec
o CD: 44 100 samples/sec
• Each sample is quantized, rounded:o Ex.:, 28=256 possible values
• Each quantized value is represented by bitso 8 bits for 256 values
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
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The Network Core
• mesh of interconnected routers
• the fundamental question: how is data transferred through net?o circuit switching: dedicated circuit per
call: telephone net
o packet-switching: data sent thru net in discrete “chunks”
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Network Core: Circuit Switching
End-end resources reserved for “call”
• link bandwidth, switch capacity
• dedicated resources: no sharing
• circuit-like (guaranteed) performance
• call setup requiredo Establishing connection
oData transfer
o disconnecting
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Network Core: Circuit Switching
• Developed to transmit voice
• “Intelligence” resides on the network
• Dedicated resources per calloNo sharing (capacity wasted)
oGuaranteed performance
• Good resource usage for voice callso Someone is always talking most of the
time…
• For datao Inactive line most of the time
• Dividing link bandwidth into “pieces”o Frequency division (FDM)
o Time division (TDM)
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Circuit Switching: FDM and TDM
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FDM
frequency
time
TDM
frequency
time
4 users
Example:
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Numerical example
•How long does it take to send a file of 640 000 000 bits from host A to host B over a circuit-switched network?oAll links are 153.6 Mbps
oEach link uses TDM with 24 slots/s
o500 ms to establish end-to-end circuit
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100 s + 500 ms = 100,5 s
* In practice we need to add propagation delay… More on that later
153.6 𝑀𝑏𝑝𝑠
24= 6.4 𝑀𝑏𝑝𝑠
640 000 000 𝑏𝑖𝑡𝑠
6.4 𝑀𝑏𝑝𝑠= 100 𝑠
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Network core: packet switching
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Network core: packet switching
Each packet is dealt with independently:
• No relation with preceding packets
• Each node chooses next hop per packet
• Packets for the same destination do not necessarily follow the same route (although they usually do)
• Packets may arrive out of ordero Destination re-orders them
• Packets may be dropped or corrupted in transit
• Source and destination are responsible for dealing with losses and corruption
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Network Core: Packet Switching
idea: divide end-to-end data flow in small pieces (packets)
• Packets of different users share network resources
• each packet uses full link bandwidth
• resources used as needed
resource contention:
• aggregated resource demand can exceed resources available
• congestion: packets queue, wait for link use
• store and forward: packets move one hop at a timeo Node receives complete packet before
forwarding
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Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
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Packet Switching: Statistical Multiplexing
• Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing.
• In TDM: each host gets same slot in revolving TDM frame.
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A
B
CEthernet100 Mb/s
1.5 Mb/s
D E
Statistical multiplexing
queue of packetswaiting for output
link
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Packet-switching: store-and-forward
• takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
• store and forward: entire packet must arrive at router before it can be transmitted on next link
• delay = 3L/R (assuming zero propagation delay)
Example:
• L = 7.5 Mbits (~0.94 Mbytes)
• R = 15 Mbps
• Transmission delay = 1.5 s
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R R R
L
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Packet switching versus circuit switching
• 1 Mb/s link
• Each user:o100 kb/s when “active”
oactive 10% of time
• circuit switching: o10 users
• packet switching : oWith 35 users, probability > 10 active at same time is less than 0.000424
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N users
1 Mbps
Packet switching allows more
users to use network
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Packets vs. Circuits
• Great for bursty datao resource sharing
o simpler, no call setup
• excessive congestion:packet delay and lossoprotocols needed for reliable
data transfer, congestion control
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Is packet switching a “slam dunk winner?”
Q: How to provide circuit-like behavior?• bandwidth guarantees needed for audio/video apps• still an unsolved problem• Over-provisioning is the current answer…
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Internet: network of networks
Internet is composed of
• Backbones: infrastructures to interlink networks, like NSFNET, in the USA, GÉANT in Europe, as well as commercial operators backbones like PT/Altice
• Regional networks, connecting for example universities and research institutes, e.g. FCCN
• Commercial networks, e.g. internal usage or for supplying services to customers, like internet connections, e.g. PT/Altice, NOS, Vodafone…