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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
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-1
What’s the Internet: a service view
 Communication infrastructure
• enables distributed
applications
• Web, VoIP, email, games, ecommerce, social nets, …
mobile network
global ISP
home
network
regional ISP
 Communication services
• provides programming
interface to apps
• hooks that allow sending
and receiving app programs
to “connect” to Internet
• provides service options,
analogous to postal service
institutional
network
Introduction 1-2
What’s the Internet: “nuts and bolts” view
 hosts or end systems:
PC
mobile network
• billions of connected
computing devices
• running network apps
server
wireless
laptop
global ISP
smartphone
 communication links:
wireless
links
wired
links
home
network
regional ISP
• fiber, copper, radio,
satellite
• transmission rate:
bandwidth
 routers & switches:
router
 forward packets
(chunks of data)
institutional
network
Introduction 1-3
What’s a protocol?
protocols define
format, order of messages sent and
received among network entities,
TCP connection
request
TCP connection
response
<file>
and actions taken on message
transmission, receipt
Get http://www.awl.com/kurose-ross
Introduction 1-4
What’s the Internet: “nuts and bolts” view
 Internet: “network of networks”
mobile network
• Interconnected ISPs
global ISP
 Internet standards
• IETF: Internet Engineering Task Force
 RFC: Request for comments
home
network
regional ISP
• IEEE for links/hardware
 Ethernet, 802.11,
 protocols
• control sending, receiving of messages
• e.g., TCP, IP, HTTP, Skype, 802.11
institutional
network
Introduction 1-5
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-6
A closer look at network structure:
 network edge:
mobile network
• hosts: clients and servers
• servers often in data
centers
 access networks, physical
media:
global ISP
home
network
regional ISP
 wired, wireless
communication links
 network core:
• interconnected routers
• network of networks
institutional
network
Introduction 1-7
Access networks
Q: How to connect end systems
to edge router?
 residential access nets
 enterprise/institutional access
networks
 school, company,
 mobile/wireless access
networks
Introduction 1-8
Residential access networks
wireless
devices
to/from headend or
central office
often combined
in single box
cable or DSL modem
wireless access
point (54 Mbps)
router, firewall, NAT
wired Ethernet (1 Gbps)
Introduction 1-9
Enterprise access networks (Ethernet)
institutional link to
ISP (Internet)
institutional router
Ethernet
switch
institutional mail,
web servers
 typically used in companies, universities, etc.
 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
 today, end systems typically connect into Ethernet switch
Introduction 1-10
Mobile/wireless access networks
 shared wireless access network connects end system to router
• via base station aka “access point”
wide-area wireless access
wireless LANs:
 within building (100 ft.)
 802.11b/g/n (WiFi): 11, 54, 450
Mbps transmission rate
 provided by telco (cellular)
operator, 10’s km
 between 1 and 10 Mbps
 3G, 4G: LTE
to Internet
to Internet
Introduction 1-11
Host: sends packets of data
host sending function:
 takes application message
 breaks into smaller
chunks, known as packets,
of length L bits
 transmits packet into
access network at
transmission rate R
• link transmission rate,
aka link capacity, aka
link bandwidth
packet
transmission
delay
=
two packets,
L bits each
2 1
R: link transmission rate
host
time needed to
transmit L-bit
packet into link
=
L (bits)
R (bits/sec)
Introduction 1-12
Physical media
 bit: propagates between
transmitter/receiver pairs
 physical link: what lies
between transmitter &
receiver
 guided media:
• signals propagate in solid
media: copper (twisted
pair), fiber, coax
 unguided media:
• signals propagate freely,
e.g., wireless
Twisted pair cable
Coaxial cable
fiber optic cable
Introduction 1-13
Unguided media
 signal carried in
electromagnetic spectrum
 no physical “wire”
 bidirectional
 propagation environment
effects:
• reflection
• obstruction by objects
• interference
radio link types:
 terrestrial microwave
• e.g. up to 45 Mbps channels
 LAN (e.g., WiFi)
• 54 Mbps
 wide-area (e.g., cellular)
• 4G cellular: ~ 10 Mbps
 satellite
• Kbps to 45Mbps channel (or
multiple smaller channels)
• 270 msec end-end delay
Introduction 1-14
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-15
The network core
The fundamental question:
how is data transferred
through net?
 circuit-switching: dedicated
circuit per call: telephone
nets
 packet-switching: data sent
thru net in discrete
“chunks”
Introduction 1-16
Network core: packet-switching
100 Mb/s
Ethernet
A
B
C
1.5 Mb/s
Packet-switching:
 Source breaks application-layer message into packets
 Forward from one router to the next until reaching destination
Introduction 1-17
Network core: packet-switching
100 Mb/s
Ethernet
A
B
C
1.5 Mb/s
Packet-switching:
 no dedication/reservation: all streams share resources
 no setup is required
 resources used as needed
 each packet uses full link bandwidth
 aggregate resource demand can exceed capacity
 no guarantee
Introduction 1-18
Packet Switching: statistical multiplexing
A
B
R = 100 Mb/s
statistical multiplexing
R = 1.5 Mb/s
C
D
E
queue of packets
waiting for output link
Sequence of A & B packets does not have fixed pattern, shared on
demand  statistical multiplexing
Introduction 1-19
Packet-switching: store-and-forward
L bits
per packet
source
3 2 1
R bps
 takes L/R sec to transmit (push
out) L-bit packet into link at R
bps
 store and forward: entire packet
must arrive at router before it
can be transmitted on next link
 end-end delay = 2L/R (assuming
zero propagation delay)
R bps
destination
one-hop numerical example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 one-hop transmission delay =
5 sec
more on delay shortly …
Introduction 1-20
Packet Switching: queueing delay, loss
A
C
R = 100 Mb/s
R = 1.5 Mb/s
B
queue of packets
waiting for output link
D
E
queuing and loss:
 if arrival rate (in bits) to link exceeds transmission rate of link
for a period of time, then there will be consequences:
• delay: packets will queue, wait to be transmitted on link
• loss: packets can be dropped if memory (buffer) fills up
Introduction 1-21
Two key network-core functions
routing: determines sourcedestination route taken by
packets
 routing algorithms
forwarding: move packets from
router’s input to appropriate
router output
routing algorithm
local forwarding table
header value output link
0100
0101
0111
1001
3
2
2
1
1
3 2
destination address in arriving
packet’s header
Introduction 1-22
Alternative core: circuit switching
 reserved resources:
• resources divided into
‘pieces’
• end-end resources are
reserved for each “call”
• in diagram, each link has four
circuits
• call gets 2nd circuit in top link
and 1st circuit in right link.
 no sharing:
• dedicated resources:
 guarantees:
• circuit-like performance
Introduction 1-23
Alternative core: circuit switching
 wasted if not used:
• circuit segment idle if not
used by call (no sharing)
 overhead:
• call setup is required
• admission control
 same path for all chunks
 commonly used in
traditional telephone
networks
Introduction 1-24
Circuit switching: FDM versus TDM
 Multiplexing: Combining
multiple signals such
that individual signals can be retrieved at the
destination.
 Signals occupy the same channel, so the
channel must be shared
 Two ways of dividing bandwidth into “pieces”
 frequency division
 time division
Introduction 1-25
Circuit switching: FDM versus TDM
Example:
Freq. Division Multiplexing (FDM)
4 users
frequency
time
Time Division Multiplexing (TDM)
frequency
time
Introduction 1-26
Circuit switching: FDM versus TDM

Frequency Division: Divides the channel into
multiple, but smaller frequency ranges.
(+) Supports more user at one time
 (+) Low latency, no time turn, preferred for real-time
applications, limited
 (-) But limited in terms of frequency availability


Time Division: Allocates certain time periods to
each channel in an alternating manner.
(+) Much more flexible, can support many users but at
different times
 (-) Slower, have to wait the turn
What is the best option?


Introduction 1-27
Packet switching versus circuit switching
A
Circuit switching
B
B: has no
packets to send
A
2 Mb/s
• 2 circuits (use TDM)
• A reserves 1 circuit
• B reserves 1 circuit
Utilization = 50% only = 1 Mb/s
Packet switching
B
2 Mb/s
• statistical multiplex.
• B uses full link since
A is not using it
Utilization = 100% = 2 Mb/s
Introduction 1-28
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?
• The link’s transmission rate = 0.64 Mbps
• Each link uses TDM with 10 slots/sec
• 0.5 sec to establish end-to-end circuit
Solution:
Bandwidth of circuit (in kbps)= .64x1000/10 = 64 kbps
 Time to send: 640 kbits/64 kbps + 0.5s = 10.5s

Introduction 1-29
Packet switching versus circuit switching
Packet switching
Circuit switching
resources
sharing
no sharing
congestion
-
may lead to
needs congestion control
admission control
overhead
-
less overhead
no connection setup
-
more overhead
need to reserve
resources first
guarantee
-
best-effort model
no guarantees
-
provides guarantees
good for multimedia
Introduction 1-30
Packet switching versus circuit switching
packet switching allows more users to use network!
 3 Mb/s link
 each user:
• 1 Mb/s when “active”
• active 1/3 of time
 circuit-switching:
N
users
3 Mbps link
• 3 users
 packet switching:
• With N=4 users, what are the chances that a user won’t get 1 Mb/s?
I.e., what is the prob. that more than 3 (strictly) users are active?
• With N=5 users, what are the chances that a user won’t get 1 Mb/s?

…….
Introduction 1-31
Internet structure: network of networks
Question: given millions of access ISPs, how to connect them
together?
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
Introduction 1-32
Internet structure: network of networks
Option: connect each access ISP to every other access ISP?
access
net
access
net
access
net
access
net
access
net
access
net
access
net
connecting each access ISP
to each other directly doesn’t
scale: O(N2) connections.
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
Introduction 1-33
Internet structure: network of networks
Option: connect each access ISP to one global transit ISP?
Customer and provider ISPs have economic agreement.
access
net
access
net
access
net
access
net
access
net
access
net
access
net
global
ISP
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
Introduction 1-34
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
….
access
net
access
net
access
net
access
net
access
net
access
net
access
net
ISP A
ISP B
access
net
access
net
access
net
ISP C
access
net
access
net
access
net
access
net
access
net
access
net
Introduction 1-35
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
…. which must be interconnected
Internet exchange point
access
access
net
net
access
net
access
net
access
net
IXP
access
net
ISP A
access
net
ISP B
IXP
access
net
access
net
access
net
ISP C
access
net
peering link
access
net
access
net
access
net
access
net
access
net
Introduction 1-36
Internet structure: network of networks
… and regional networks may arise to connect access nets to
ISPs
access
net
access
net
access
net
access
net
access
net
IXP
access
net
ISP A
access
net
ISP B
IXP
access
net
access
net
access
net
ISP C
access
net
access
net
regional net
access
net
access
net
access
net
access
net
Introduction 1-37
Internet structure: network of networks
… and content provider networks (e.g., Google, Microsoft,
Akamai) may run their own network, to bring services, content
close to end users
access
net
access
net
access
net
access
net
access
net
IXP
access
net
ISP A
Content provider network
IXP
ISP B
access
net
access
net
access
net
access
net
ISP C
access
net
access
net
regional net
access
net
access
net
access
net
access
net
Introduction 1-38
Internet structure: network of networks
Tier 1 ISP
Tier 1 ISP
IXP
IXP
Regional ISP
access
ISP
access
ISP
Google
access
ISP
access
ISP
IXP
Regional ISP
access
ISP
access
ISP
access
ISP
access
ISP
 at center: small # of well-connected large networks
• “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national &
international coverage
• content provider network (e.g., Google): private network that connects
it data centers to Internet, often bypassing tier-1, regional ISPs Introduction 1-39
Tier-1 ISP: e.g., Sprint
Introduction 1-40
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-41
Four sources of packet delay
transmission
A
propagation
B
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dproc: nodal processing
 check bit errors
 determine output link
 typically < msec
dqueue: queueing delay
 time waiting at output link
for transmission
 depends on congestion
level of router
Introduction 1-42
Four sources of packet delay
transmission
A
propagation
B
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay:
 L: packet length (bits)
 R: link bandwidth (bps)
dtrans and dprop
 dtrans = L/R
very different
dprop: propagation delay:
 d: length of physical link
 s: propagation speed (~2x108 m/sec)
 dprop = d/s
* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
* Check out the Java applet for an interactive animation on trans vs. prop delay
Introduction 1-43
“Real” Internet delays and routes
 what do “real” Internet delay & loss look like?
 traceroute program: provides delay
measurement from source to router along endend 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
Introduction 1-44
“Real” Internet delays, routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
3 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
Introduction 1-45
Exercise 1
Packet length = L bits
trans. rate R = 1 Mbps
Host A
Host B
distance = 1 km, speed = 2x108m/s
Question:
 Which bit is being transmitted at the time the first bit arrives at Host B
Answer:
First bit arrives after
1/R + d/s = 1/106 + 103/(2x108) = 10-6 + 5x10-6 = 6x10-6 = 6 µsec
After 6 µsec
6 bits are already transmitted; so 7th bit is being transmitted
Introduction 1-46
Exercise 2
Transmission vs. propagation
L=100Bytes
trans. rate R = ?
Host A
Host B
distance = 2 km, speed = 2x108m/s
Question:
 At what rate (bandwidth) R would the propagation delay equal the
transmission delay of packet?
Answer:
 Propagation delay = 2x103 (m)/2x108 (m/s) = 10-5 sec
 Transmission delay = 100x8 (bits)/R
 Prop. delay = trans. delay => R=105x100x8 = 80 Mbps
Introduction 1-47
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-50
Protocol “layers”
Networks are complex,
with many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware,
software
Question:
is there any hope of
organizing structure of
network?
Introduction 1-51
Internet protocol stack
 application: supporting network
applications
• FTP, SMTP, HTTP
 transport: process-process data
transfer
• TCP, UDP
 network: routing of datagrams from
source to destination
• IP, routing protocols
 link: data transfer between
neighboring network elements
application
transport
network
link
physical
• Ethernet, 802.11 (WiFi), PPP
 physical: bits “on the wire”
Introduction 1-52
Encapsulation
source
message
segment
M
Ht
M
datagram Hn Ht
M
frame
M
Hl Hn Ht
application
transport
network
link
physical
link
physical
switch
M
Ht
M
Hn Ht
M
Hl Hn Ht
M
destination
Hn Ht
M
application
transport
network
link
physical
Hl Hn Ht
M
network
link
physical
Hn Ht
M
router
Introduction 1-53
ISO/OSI Model
application
presentation
session
transport
application
transport
network
network
link
data link
physical
physical
7-layer ISO/OSI model
(OSI: open system interconnections)
5-layer Internet
Protocol Stack
Introduction 1-54
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
 end systems, access networks, links
1.3 network core
 packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 end-to-end throughput analysis
Introduction 1-55
Nodal delay: four delay components
d nodal  d proc  d queue  d trans  d prop
 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
Introduction 1-56
How does packet loss occur?





queue (aka buffer) preceding link has finite capacity
packets may arrive at rate exceeding output link capacity
packets are queued in router buffers
packet arriving to full queue are dropped (aka lost)
lost packet may be retransmitted by previous node, by
source end system, or not at all
buffer
(waiting area)
A
packet being transmitted
B
packet arriving to
full buffer is lost
* Check out the Java applet for an interactive animation on queuing and loss
Introduction 1-57
Queueing delay (more insights)
Packet arrival rate
= a packets/sec
queue
Packet length
= L bits




Link bandwidth
= R bits/sec
Every second: aL bits arrive to queue
Every second: R bits leave the router
Question: what happens if aL > R ?
Answer: queue will fill up, and packets will get dropped!!
aL/R is called traffic intensity
Introduction 1-58
Queueing delay (more insights)
1 packet arrives
every L/R seconds
queue
Link bandwidth
= R bits/sec
Packet length L bits
Arrival rate: a = 1/(L/R) = R/L (packet/second)
Traffic intensity = aL/R = (R/L) (L/R) = 1
Average queueing delay = 0
(queue is initially empty)
Introduction 1-59
Queueing delay (more insights)
Packet arrival rate
= a packets/sec
queue
Packet length
= L bits
 La/R ~ 0: avg. queueing delay small
Link bandwidth
= R bits/sec
La/R  1
La/R ~ 0
 La/R -> 1: delays become large
 La/R > 1: more “work” than can be
serviced, average delay infinite!
(this is when a is random!)
Introduction 1-61
Store-and-forward (revisited)
L
R
R
R
Entire packet must arrive at router before it can be
transmitted on next link: store and forward
 Takes L/R seconds to transmit (push out) packet of L bits on
to link of R bps
 delay = 3L/R (assuming zero propagation delay)
more on this next…
Introduction 1-62
Store-and-forward (more insights)
 distance = d meters; speed of propagation = s m/sec
 transmission rate of link = R bits/s
L
d
R
L
d/2
R
d/2
R
 delay (one packet only)
= L/R + d/s
 delay (one packet only)
Example:
 d/s = 0.5 sec
 L = 10 Mbits
 R = 1 Mbps
 delay = 10.5 sec
Example:
 d/s = 0.5 sec
 L = 10 Mbits
 R = 1 Mbps
 delay = 20.5 sec
= L/R + ½d/s + L/R + ½d/s
= 2L/R + d/s
Introduction 1-63
Store-and-forward (more insights)
 distance = d meters; speed of propagation = s m/sec
 transmission rate of link = R1 and R2 bits/s
 Consider sending two packets A and B back to back
L d/2
R1
 Case 1: Assume R1 < R2
d/2
R2
 Case 2:Assume R1 > R2
Q: is there a queuing delay? how much is this delay?
Answer (queue is empty initially):
Time for last bit of 2nd pkt to arrive at router: t1= L/R1 + L/R1 + d/(2s)
Time for last bit of 1st pkt to leave router: t2= L/R1 + d/(2s) + L/R2
Queueing delay = t2 – t1 = L/R2 – L/R1 if positive, otherwise 0. Hence:
when R1 < R2, queueing delay = t2 – t1 = 0
when R1 > R2, queueing delay = t2 – t1 = L/R2 – L/R1
Introduction 1-64
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
server,
withbits
server
sends
file of into
F bitspipe
(fluid)
to send to client
linkpipe
capacity
that can carry
Rs bits/sec
fluid at rate
Rs bits/sec)
linkpipe
capacity
that can carry
Rc bits/sec
fluid at rate
Rc bits/sec)
Introduction 1-65
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
Bottleneck link on end-end path is what constrains end-end throughput
Introduction 1-66
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
* Check out the online interactive exercises for more
examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
Introduction 1-67
Throughput analysis
Host A
L
R
R
R
Host B
 Suppose: Host A has huge file of size F bits to send to Host B
 File is split into N packets, each of length L bits (i.e., N=F/L)
 Ignore propagation delay for now
 Question 1: how long it takes to send the file?
A: (N+2)L/R = (F+2L)/R
 Question 2: what is the average end-to-end throughput
achieved when sending the file?
A: NL/[(N+2)L/R]=NR/(N+2) = FR/(F+2L) = R/(1+2L/F)
Introduction 1-68
Introduction: summary
Covered a “ton” of material!
 Internet overview
 Network protocol
 Network edge, core, access network
 Packet-switching versus circuit-switching
 Internet/ISP structure
 layering and service models
 performance: delay and throughput analysis
Introduction 1-69