Welcome to COE321: Logic Design
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Transcript Welcome to COE321: Logic Design
What’s the Internet: “nuts and bolts” view
PC
server
wireless
laptop
cellular
handheld
Mobile network
millions of connected
computing devices: hosts
Global ISP
= end systems
communication links
access
points
wired
links
router
running network
apps
fiber, copper,
radio, satellite
transmission rate
= bandwidth
Home network
Regional ISP
Institutional network
routers: forward packets
(chunks of data)
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What’s the Internet: “nuts and bolts” view
protocols control sending,
receiving of msgs
e.g., TCP, IP, HTTP, Skype,
Ethernet
Internet: “network of networks”
loosely hierarchical
public Internet versus private
intranet
Internet standards
RFC: Request for comments
IETF: Internet Engineering
Task Force
Mobile network
Global ISP
Home network
Regional ISP
Institutional network
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What’s the Internet: a service view
communication infrastructure
enables distributed applications:
Web, VoIP, email, games,
e-commerce, file sharing
communication services
provided to apps:
reliable data delivery from
source to destination
“best effort” (unreliable)
data delivery
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What’s a protocol?
human protocols:
“what’s the time?”
“I have a question”
introductions
… specific msgs sent
… specific actions taken
when msgs received, or
other events
network protocols:
machines rather than
humans
all communication activity
in Internet governed by
protocols
protocols define format, order of
msgs sent and received
among network entities, and
actions taken on msg
transmission, receipt
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What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
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Computer networks: overview
Two most important aspects of computer networks
Hardware
And, software
Network hardware can be classified by
Transmission technology
And, scale
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Classification of hardware by
transmission technology
Communication is a primary concern in a network
=> we are dealing with both computers and
Communication (transmission) technologies
Types of transmission technology
Broadcast links
A single communication channel is shared by all machines
Restricting transmission to a set of machines => multicasting
Point-to-point links
Many connections between individual pairs of machines
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Broadcast communication networks
Examples:
satellite networks
multi-access Ethernet.
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General rule
Smaller networks
Larger networks
Broadcasting
Point-to-point
An alternative criterion for classifying networks
Their scale
Personal area networks, and local area networks
Metropolitan are networks, and wide are networks
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Classification of interconnected
processor by scale
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Local area networks
LANs
are privately owned networks
Within a single building or campus of few kilometers in size
Various topologies are possible for LANs
Bus
A single shared cable connect all devices
Example: IEEE 802.3 Ethernet
Ring
All messages travel thru a ring in the same direction
Example: FDDI (Fiber Distributed Date Interface)
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LANs topologies
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Metropolitan Area Networks
A MAN
Covers a city
The best known example is
Cable television network available in many cities
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Wide area networks
WANs
Within a country or even whole continent
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Connectionless WAN
packet-switched networks
In an IP network,
a user can send packets to a destination
without having to set up a connection first, i.e.,
without informing the network prior to transmitting them.
This simplifies the network,
as there is no need for a special signaling protocol.
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Routing in IP
User A
User B
IP network
The routing of a packet through the network is done on a
hop-per-hop basis based on the destination IP address
carried in the IP packet’s header.
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Quality of Service (QoS) in IP
Typically, an IP router does not offer QoS.
It cannot distinguish packets
belonging to different service classes
based on their destination address.
IP is almost ubiquitous.
There is a lot of interest in introducing QoS
in the IP network,
and MPLS seems to be the architecture for introducing QoS.
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Internetworks
Internetwork or internet
A collection of interconnected networks
Deals with how to connect different kinds of networks
It is formed when distinct networks are interconnected
Resulting in the Internet
That really covers the whole Planet
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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 required
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Network Core: Circuit Switching
network resources (e.g.,
bandwidth) divided into
“pieces”
pieces allocated to calls
resource piece idle if not
used by owning call (no
sharing)
dividing link bandwidth into
“pieces”
frequency division
time division
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Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
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Numerical example
How long does it take to send a file of 640,000 bits
from host A to host B over a circuit-switched
network?
All links are 1.536 Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit
Let’s work it out!
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Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
end systems, access networks, links
1.3 Network core
circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
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How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link exceeds output link capacity
packets queue, wait for turn
packet being transmitted (delay)
A
B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
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Four sources of packet delay
1. nodal processing:
check bit errors
determine output link
2. queueing
time waiting at output
link for transmission
depends on congestion
level of router
transmission
A
propagation
B
nodal
processing
queueing
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Delay in packet-switched networks
3. Transmission delay:
R=link bandwidth (bps)
L=packet length (bits)
time to send bits into link
= L/R
transmission
A
4. Propagation delay:
d = length of physical link
s = propagation speed in
medium (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very
different quantities!
propagation
B
nodal
processing
queueing
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Transmission vs. propagation
applet
An applet
Illustrating the difference between
Transmission delay and propagation delay
An interactive animation
Speaks a thousand words
http://media.pearsoncmg.com/aw/aw_kurose_network_2/apple
ts/transmission/delay.html
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Nodal delay
dnodal dproc dqueue dtrans dprop
dproc = processing delay
typically a few microsecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= L/R, significant for low-speed links
dprop = propagation delay
a few microsecs to hundreds of msecs
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Queueing delay (revisited)
R=link bandwidth (bps)
L=packet length (bits)
a=average packet arrival
rate
traffic intensity = La/R
La/R ~ 0: average queueing delay small
La/R -> 1: delays become large
La/R > 1: more “work” arriving than can be
serviced, average delay infinite!
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Queuing delay vs. packet loss
Applet can be found at:
http://media.pearsoncmg.com/aw/aw_kurose_network_2
/applets/queuing/queuing.html
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“Real” Internet delays and routes
What do “real” Internet delay & loss look like?
Traceroute program: provides delay measurement from
source to router along end-end Internet path towards
destination. For all i:
sends three packets that will reach router i on path towards
destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes
3 probes
3 probes
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“Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
* means no response (probe lost, router not replying)
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
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Tracing LAU’s webserver
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Tracing webserver (cont’d)
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Packet loss
queue (aka buffer) preceding link in buffer has finite
capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous node,
by source end system, or not at all
buffer
(waiting area)
A
B
packet being transmitted
packet arriving to
full buffer is lost
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Throughput
throughput: rate (bits/time unit) at which bits
transferred between sender/receiver
instantaneous: rate at given point in time
average: rate over longer period of time
link
capacity
that
can carry
server,
with
server
sends
bits pipe
Rs bits/sec
fluid
at rate
file of
F bits
(fluid)
into
pipe
Rs bits/sec)
to send to client
link that
capacity
pipe
can carry
Rfluid
c bits/sec
at rate
Rc bits/sec)
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Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
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Throughput: Internet scenario
per-connection endend throughput:
min(Rc,Rs,R/10)
in practice: Rc or Rs is
often bottleneck
Rs
Rs
Rs
R
Rc
Rc
Rc
10 connections (fairly) share
backbone bottleneck link R bits/sec
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