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)
1
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
2
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
3
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
4
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?
5
Computer networks: overview


Two most important aspects of computer networks

Hardware

And, software
Network hardware can be classified by

Transmission technology

And, scale
6
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
7
Broadcast communication networks

Examples:

satellite networks

multi-access Ethernet.
8
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
9
Classification of interconnected
processor by scale
10
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)
11
LANs topologies
12
Metropolitan Area Networks

A MAN

Covers a city

The best known example is

Cable television network available in many cities
13
Wide area networks

WANs

Within a country or even whole continent
14
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.
15
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.
16
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.
17
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
18
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
19
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
20
Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
21
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!
22
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
23
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
24
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
25
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
26
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
27
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
28
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!
29
Queuing delay vs. packet loss

Applet can be found at:

http://media.pearsoncmg.com/aw/aw_kurose_network_2
/applets/queuing/queuing.html
30
“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
31
“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
32
33
Tracing LAU’s webserver
34
Tracing webserver (cont’d)
35
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
36
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)
37
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
38
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
39