CS 352
Internet Technology
Dept. of Computer Science
Rutgers University
Administrative




Instructor :
Richard Martin
TA:
TBA
Textbook
 James F. Kurose and Keith W. Ross, Computer Networking, 3rd
edition.
Class webpage
 http://remus.rutgers.edu/cs352/S06/
 Announcements
 Lecture notes
 Projects
 Homeworks
 Old exams
CS352
Fall, 2005
2
Course Goals




Understand the basic principles of computer
networks
Understand the Internet and its protocols
Understand the key design principles used to
build the Internet
Experience building network systems
CS352
Fall, 2005
3
Course goals (cont.)

Course is not about specific skills


E.g. configure a router from company X vs. learn
principles of how all routers work
Success means you are confident to tackle a
range of network programming, design and
maintenance.
CS352
Fall, 2005
4
Course Approach

Lectures: theory behind how networks
operate



Tested in exams
See last semesters’ classes for sample problems
Programming assignments:



CS352
Real world experience with networks
Program design
Communicating your design
Fall, 2005
5
Course Work

2 Mid-terms (15% each)


Final (35%)


No electronic devices or notes allowed. No cheat sheets
allowed
You must send the instructor email at least 2 weeks before
the final if you need to take the makeup!
Project (35%)
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CS352
Part 1 (10%)
Part 2 (10%)
Part 3 (15%)
Fall, 2005
6
Programming assignments

Single long project
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Broken into three parts
Can work in a group of 2
Both program and write-up required
Background needed to get started:

Java (112+ level)


CS352
Comfortable using data structures(stacks, trees, vector)
Unix (login, handin, permissions, javac)
Fall, 2005
7
Programming Assignment

2 Code reviews




Make improvements for next level of the
assignment.


10-15 minute oral question and answer period.
TA and instructor will critically review your assignment.
“lost art” of program design.
Grade depends on level of improvement in code quality as
well as functionality.
No late handin

CS352
Failure to meet the deadline will result in a zero for all team
members. No exceptions!
Fall, 2005
8
Academic integrity

No cheating on projects and exams



Run code similarity detectors on the projects &
code review
Scrutinize exams for copying
Department academic integrity policy


CS352
http://www.cs.rutgers.edu/policies/academicintegri
ty/
Acknowledge your awareness of this policy by the
end of September to continue to access
department computing facilities
Fall, 2005
9
Facilities

“Cereal” machines and lab


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~20 UltraSparc machines
~30+ Linux machines
Cardkey Access: student ID card
Romulus and remus for general use


CS352
Create your accounts now!
http://remus.rutgers.edu/newaccount.html
Fall, 2005
10
CS352 Fundamentals
Why Study Networks?

Integral part of society


Pervasive


Work, entertainment, community
Home, car, office, school, mall …
Huge impact on people and society
CS352
Fall, 2005
12
Impact of the Net on People

Anytime access to remote information


Person-to-person and group
communication


email, blogs, chat
Form and strengthen communities

CS352
HW assignments from my server
chat rooms, MUDs, newsgroups
Fall, 2005
13
Impact of the Net on Society

Huge impact!

Continuation of technologies that reduce
problems of time & space


Good, bad and ugly


mirror of society
Changes still on the horizon

CS352
(e.g. railroads,phone,autos,TV)
Commerce, services, entertainment, socializing
Fall, 2005
14
Concepts for this week

What is the Internet?



Network delay analysis



Core and Edge of the Internet
Circuit, message and packet switching
Single link
Multi-link
Layering and encapsulation
CS352
Fall, 2005
15
What is the Internet?
What is Internet Technology?

What is an internet?


What is the Internet?


A global internet based on the IP protocol
To what does “Internet technology” refer?


CS352
Network of networks
Architecture
Services
Fall, 2005
Protocols
17
Architecture-wise
Company A
Internet Service Provider 1
ISP 2
Company B
Core Networks (ISP tiers)
Network
Host:
Machine
:
Collection
running
of
interconnected
user
application
machines
Media:
Channel:
Router:
Physical
decide
Logical
process
where
line
of
to
used
communication
send
(copper
data
next
wire,
fiber
optics,
satellite
• Tier
1:link)
Biggest ISPs
Edge Networks: Companies, organizations
with
a “default
route”
•Tier 2 and 3: Regional
CS352 Fall, 2005
18 and
Service-wise (applications)

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Electronic mail
Remote terminal
File transfer
Newsgroups
File sharing
Resource distribution
World Wide Web
Video conferencing
Games
CS352
Fall, 2005
19
Protocols

Protocol


Architecture  Service
Rules of communication
FTP
HTTP
RTP
TFTP
UDP
TCP
IP
Ethernet
CAT-5
CS352
Fall, 2005
802.11
Single-Mode
Fiber
…
PPP
RS-232
20
Core Network Switching
Schemes
How much “state” about the connection
between two hosts does each node/router
along a path through the network maintain?
CS352
Fall, 2005
21
Switching Schemes
(1)
(2)
(3)
CS352
Circuit Switching
Message Switching (Store-and-Forward)
Packet Switching (Store-and-Forward)
Fall, 2005
22
Circuit Switching


Provides service by setting up the total path
of connected lines hop-by-hop from the origin
to the destination
Example: Telephone network
CS352
Fall, 2005
23
Circuit Switching (cont’d)
1. Control message sets up a path from origin
to destination
2. Return signal informs source that data
transmission may proceed
3. Data transmission begins
4. Entire path remains allocated to the
transmission (whether used or not)
5. When transmission is complete, source
releases the circuit
CS352
Fall, 2005
24
Circuit Switching (cont’d)
Call request signal
Time
Propagation Delay
Transmission
Delay
Call accept signal
Data
Transmission
Time
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Fall, 2005
Data
A
B
C
D
Routers/Switches
25
Message Switching




Each message is addressed to a destination
When the entire message is received at a router, the
next step in its journey is selected; if this selected
channel is busy, the message waits in a queue until
the channel becomes free
Thus, the message “hops” from node to node
through a network while allocating only one channel
at a time
Analogy: Postal service
CS352
Fall, 2005
26
Message Switching (cont’d)
Header
Time
Msg
Transmission
Delay
Msg
Queueing
Delay
Msg
CS352
Fall, 2005
A
B
C
D
Routers/switches
27
Packet Switching



Messages are split into smaller pieces called
packets
These packets are numbered and addressed and
sent through the network one at a time
Allows Pipelining

CS352
Overlap sending and receiving of packets on multiple links
Fall, 2005
28
Packet Switching (cont’d)
Pkt 1
Time
Header
Pkt 2
Pkt 1
Pkt 3
Transmission
Delay
Pkt 2
Pkt 1
Pkt 3
Pkt 2
Pkt 3
Pipelining
CS352
Fall, 2005
A
B
C
D
29
Comparisons
(1) Header Overhead
Circuit < Message < Packet
(2) Transmission Delay
Short Bursty Messages:
Packet < Message < Circuit
Long Continuous Messages:
Circuit < Message < Packet
CS352
Fall, 2005
30
Network delay
analysis
Why Study Network
Performance



Networks cost $
 OC-3 line ~= $10,000/month
 Cable modem: $40/month
 Are you getting your $/worth?
Why is the network “slow”?
Approach:
 Build abstract models of network performance
 Observe where real networks deviate from model
 Simple Models: Tells us average/best/worse cases->useful,
practical
 Complex Models: Hard to understand -> useless
CS352
Fall, 2005
32
Units

Bits are the units used to describe an amount of data in a network




= 1 x 103 bits = 1,000 bits
= 1 x 106 bits = 1,000,000 bits
= 1 x 109 bits = 1,000,000,000 bits
Seconds are the units used to measure time




1 kilobit (Kbit)
1 megabit (Mbit)
1 gigabit (Gbit)
1 millisecond (msec)
1 microsecond (msec)
1 nanosecond (nsec)
= 1 x 10-3 seconds = 0.001 seconds
= 1 x 10-6 seconds = 0.000001 seconds
= 1 x 10-9 seconds = 0.000000001 seconds
Bits per second are the units used to measure channel
capacity/bandwidth and throughput

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CS352
bit per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
Fall, 2005
33
Types of Delay

Processing


Queuing


Time waiting in queue to be processed
Transmission


Time to execute protocol code
Time to “get bits on wires”
Propagation

CS352
Time for bits to “move across wires”
Fall, 2005
34
Transmission vs. Prop. delay
A single transmission link as a water pipe
1.
2.
The thicker the pipe, the more water it can carry from one end
to the other in each unit time
Water is carried from one end of the pipe to the other at
constant speed, no matter how thick the pipe is
Water = Data bits
Thickness of the pipe = Channel capacity
Speed of water through the pipe = Propagation speed
CS352
Fall, 2005
35
Transmission vs. Prop. Delay
(cont)
pipe
1.
2.
CS352
Fall, 2005
Propagation delay is how long takes to cross
the pipe, irrespective of volume
Transmission (bandwidth delay) is related to
how much water can be pushed in through
the opening per unit time
36
Transmission Time
How long does it take A to transmit an entire packet onto the link?
Relevant information: packet length = 1500 bytes
channel capacity = 100 Mbps
Another way to ask this question:
If the link can transmit 10 million bits in a second, how
many seconds does it take to transmit 1500 bytes (8x1500
bits)?
100 Mbits
1 sec
CS352
Fall, 2005
=
1500 x 8 bits
t
Solving for t…
t = 0.00012 sec (or 120 msec)
37
Propagation Delay
How long does it take a single bit to travel on the link from A to B?
Relevant information: link distance = 500 m
prop. delay factor = 5 msec/km
Another way to ask this question:
If it takes a signal 5 msec to travel 1 kilometer, then how
long does it take a signal to travel 500 meters?
5 msec
1000 m
CS352
Fall, 2005
=
t
500 m
Solving for t…
t = 2.5 msec
38
Processing Delay
Stylized format required to send data
Analogy: adding and removing envelopes to letters
Host
Host
Application
Layer
Application
Layer
Transport
Layer
Transport
Layer
Router
Network
Layer
Network
Layer
Network
Layer
Host-toNet Layer
Host-toNet Layer
Host-toNet Layer
CS352
Fall, 2005
How long does it take
to execute all these
layers?
Why is this time
important?
39
Example
A
B
500 m
Protocol Processing Time = 40 msec
packet length = 1500 bytes
channel capacity = 100 Mbps
propagation delay factor = 5 msec/km
1.
2.
3.
CS352
How long to format the data?
How long does it take a single bit to travel on the link
from A to B?
How long does it take A to transmit an entire packet
onto the link?
Fall, 2005
40
Timeline Method
Host A
40
1st bit
Host B
Protocol Delay
2.5
Propagation delay
120
Transmission time
Time
last bit
40
CS352
Protocol Delay
Total time: 40+120+2.5+40 = 202.5 msec
Fall, 2005
41
Queuing Delay
Router
Network
Layer
Host-toNet Layer
Packets
waiting
processing
at input
ports
2 0
3
1 0
0
Router
0 0
1
2 2
3
Packets waiting
transmission
at output
ports
Packets arriving faster than
processing or transmission
delay
CS352
Fall, 2005
=> queuing (I.e. waiting in line)
42
Analytic Comparison of multilink network

Given choice of 2 switching schemes, how
would you compare their performance?




What would you need to know?
What are the independent variables?
What is the dependent variable?
Could you come up with a closed form
expression based on your choices?
CS352
Fall, 2005
43
Example: Circuit Switching vs.
Packet Switching

Goal: Determine which is faster


Formal definition: Least time to move a fixed
amount of data
Approach:



CS352
Compute time where circuit switching and packet
switching are equal based on all possible factors
A factor moving in one direction or the other will
tip the balance in favor of one or the other
We’ll ignore wire-line propagation delay in this
example
Fall, 2005
44
Factors:






Number of bytes in the message: N
Time to set up circuit:
c
Per-link bandwidth:
B
Size of the packet:
p
Size of the header:
h
Number of switches:
s
CS352
Fall, 2005
45
Circuit Switching Time

Time to send N bytes using circuit switching

= Set-up cost + bandwidth delay
N
C
B
CS352
Fall, 2005
46
Pipelining “Parallelogram”
for packet switching
Host A
Switch 1 Switch 2 Host B
Packet 1
Packet 2
Time
Propagation
Delay
Packet 3
Packet 4
Bandwidth
Delay
CS352
Fall, 2005
47
Note on Pipelining

The above analysis is very general:

Packets in a computer network


Instructions in a processor


Instructions are the unit of work.
Jobs through a batch Q in an operating system.


Messages/packets are the unit of work.
Processes are the unit of work.
Pipelining speeds up work over time.

CS352
How?
Fall, 2005
48
Packet Switching Time
Delay = Transmission + “Propagation” delays
“Propagation” delay:
Time for a single packet to cross
- not really prop. delay in the traditional sense
+ Transmission delay (also bandwidth delay):
Time to push all the packets into the network
( p  h)  N 
( p  h)
( S  1) *
 (    1) *
B
B
P
CS352
Fall, 2005
49
Packet Switching Time
Transmission delay
“Propagation” delay
Number of packets
Number of links/hops
( p  h)  N 
( p  h)
( S  1) *
 (    1) *
B
B
P
Time for each packet to
go through each link
CS352
Fall, 2005
50
Equilibrium Point
N

 p  h   N 
    S 
C  

 B   P 
B

Assuming all other factors equal, solve for C
Q: Can you add link propagation delay to this example?

CS352
Fall, 2005
51
Homework Questions




If we use message switching, how does the
time increase as we scale s?
How does packet switching reduce the
impact of increasing s?
Show, using an equation, how reducing the
packet size and packet switching reduces the
impact of increasing s.
Where does the approach of reducing packet
size fail to give any benefit?
CS352
Fall, 2005
52
Layering and
Encapsulation
Why Layering?


Network communication is very complex
Separation of concerns



CS352
Different vendors and organizations responsible
for different layers
Testing and maintenance is simplified
Easy to replace a single layer with a different
version
Fall, 2005
54
Protocol Hierarchy

Use layers to hide complexity

Each layer implements a service



Protocols


Layer N uses service provided by layer N-1
layer N-1 provides a service to layer N
Each layer communicates with its peer by a set of
rules
Interface

CS352
A layers interface specifies the operations
Fall, 2005
55
Protocol Hierarchy (cont’d)
Host A
Layer 7
Layer 6
Layer 5
Layer 4
Layer 3
Layer 2
Layer 1
CS352
Fall, 2005
Host B
Layer 7 Protocol
Layer 6 Protocol
Layer 5 Protocol
Layer 4 Protocol
Layer 3 Protocol
Layer 2 Protocol
Layer 1 Protocol
Physical Medium
Layer 7
Layer 6
Layer 5
Layer 4
Layer 3
Layer 2
Layer 1
56
Different Layering
Architectures


ISO OSI 7-Layer Architecture
TCP/IP 4-Layer Architecture


+ application layer = 5 layers in Kurose
Novell NetWare IPX/SPX 4-Layer
Architecture
CS352
Fall, 2005
57
Standards Making
Organizations
ISO = International Standards Organization
ITU = International Telecommunication Union (formerly
CCITT)
ANSI = American National Standards Institute
IEEE = Institute of Electrical and Electronic Engineers
IETF = Internet Engineering Task Force
ATM Forum = ATM standards-making body
...and many more
CS352
Fall, 2005
58
Why So Many Standards
Organizations?


Multiple technologies
Different areas of emphasis and history

Telecommunications/telephones


Local area networking/computers


IETF, IEEE
System area networks/storage

CS352
ITU,ISO,ATM
ANSI
Fall, 2005
59
ISO OSI Layering Architecture
Host A
Host B
Application
Layer
Application Protocol
Presentation
Layer
Presentation Protocol
Session
Layer
Session Protocol
Transport
Layer
Transport Protocol
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
CS352 Fall, 2005 Layer
Physical
Layer
Physical
Layer
Physical
Layer
Router
Router
60
ISO’s Design Principles




A layer should be created where a different level of
abstraction is needed
Each layer should perform a well-defined function
The layer boundaries should be chosen to minimize
information flow across the interfaces
The number of layers should be large enough that
distinct functions need not be thrown together in the
same layer out of necessity, and small enough that
the architecture does not become unwieldy
CS352
Fall, 2005
61
Layer 1: Physical Layer

Functions:



Transmission of a raw bit stream
Forms the physical interface between devices
Issues:





Which modulation technique (bits to pulse)?
How long will a bit last?
Bit-serial or parallel transmission?
Half- or Full-duplex transmission?
How many pins does the network connector
have?
How is a connection set up or torn down?
 Fall, 2005
CS352
62
Layer 2: Data Link Layer

Functions:





Provides reliable transfer of information between
two adjacent nodes
Creates frames from bits and vice versa
Provides frame-level error control
Provides flow control
In summary, the data link layer provides the
network layer with what appears to be an
error-free link for packets
CS352
Fall, 2005
63
Layer 3: Network Layer

Functions:

Responsible for routing decisions



CS352
Dynamic routing
Fixed routing
Performs congestion control
Fall, 2005
64
Layer 4: Transport Layer

Functions:

Hide the details of the network from the session
layer


CS352
Example: If we want replace a point-to-point link with
a satellite link, this change should not affect the
behavior of the upper layers
Provides reliable end-to-end communication
Fall, 2005
65
Transport Layer (cont’d)
Host A
first
end-to-end
layer
Host B
Application
Layer
Application Protocol
Presentation
Layer
Presentation Protocol
Session
Layer
Session Protocol
Transport
Layer
Transport Protocol
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
CS352 Fall, 2005 Layer
Physical
Layer
Physical
Layer
Physical
Layer
Router
Router
66
Transport Layer (cont’d)

Functions (cont’d):


CS352
Perform end-to-end flow control
Perform packet retransmission when packets are
lost by the network
Fall, 2005
67
Layer 5: Session Layer



May perform synchronization between
several communicating applications or logical
transmissions
Groups several user-level connections into a
single “session”
Examples:


CS352
Banking session
Network meetings
Fall, 2005
68
Layer 6: Presentation Layer


Performs specific functions that are
requested regularly by applications
Examples:



CS352
encryption
ASCII to Unicode, Unicode to ASCII
LSB-first representations to MSB-first
representations
Fall, 2005
69
Layer 7: Application Layer



Application layer protocols are applicationdependent
Implements communication between two
applications of the same type
Examples:



CS352
FTP
HTTP
SMTP (email)
Fall, 2005
70
Encapsulation
Treat the neighboring layer’s information as a
“black box”, can’t look inside or break
message
 Sending: add information needed by the
current layer “around” the higher layers’ data



headers in front
trailers in back
Receiving: Strip off headers and trailers
before handing up the stack
CS352
Fall, 2005
71
Encapsulation
Data
CS352
Application
Layer
AH
Presentation
Layer
PH
Session
Layer
SH
Transport
Layer
TH
Fall, 2005
Network
Layer
NH
Data Link
Layer
DH
Physical
Layer
PH
Data
Data

Headers

Trailer
Data
Data
Data
Data
Data
DT
72
Internet “Hourglass”
Architecture


Defined by Internet Engineering Task Force (IETF)
“Hourglass” Design
FTP
HTTP
RTP
TFTP
UDP
TCP
IP
Ethernet
CAT-5
CS352
Fall, 2005
802.11
Single-Mode
Fiber
…
PPP
RS-232
73
Internet Design Principles

Scale


Incremental deployment


Different technologies, autonomous organizations
End-to-end argument

CS352
New protocols need to be deployed gradually
Heterogeneity


Protocols should work in networks of all sizes and
distances
Some functions can only be correctly implemented at
the end hosts; the network should not provided these.
Fall, 2005
74
TCP/IP Layering Architecture

Application

A simplified model
The network layer

Transport
Internet/Network

Host-to-Net
CS352
Fall, 2005
Hosts drop packets into
this layer, layer routes
towards destination- only
promise- try my best
The transport layer

reliable byte-oriented
stream
75
TCP/IP Layering Architecture
(cont’d)
Host A
Host B
Application Protocol
Application
Layer
Transport Protocol (TCP)
Transport
Layer
Network
Layer
Host-toNet Layer
CS352
Fall, 2005
Application
Layer
IP
Network
Layer
Host-toNet Layer
IP
Network
Layer
Host-toNet Layer
Transport
Layer
IP
Network
Layer
Host-toNet Layer
76