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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:
Real world experience with networks
Program design
Communicating your design
CS352 Fall, 2005 5
Course Work
2 Mid-terms (15% each)
No electronic devices or notes allowed. No cheat sheets
allowed
Final (35%)
You must send the instructor email at least 2 weeks before
the final if you need to take the makeup!
Project (35%)
Part 1 (10%)
Part 2 (10%)
Part 3 (15%)
CS352 Fall, 2005 6
Programming assignments
Single long project
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)
Comfortable using data structures(stacks, trees, vector)
Unix (login, handin, permissions, javac)
CS352 Fall, 2005 7
Programming Assignment
2 Code reviews
10-15 minute oral question and answer period.
TA and instructor will critically review your assignment.
“lost art” of program design.
Make improvements for next level of the
assignment.
Grade depends on level of improvement in code quality as
well as functionality.
No late handin
Failure to meet the deadline will result in a zero for all team
members. No exceptions!
CS352 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
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
CS352 Fall, 2005 9
Facilities
“Cereal” machines and lab
~20 UltraSparc machines
~30+ Linux machines
Cardkey Access: student ID card
Romulus and remus for general use
Create your accounts now!
http://remus.rutgers.edu/newaccount.html
CS352 Fall, 2005 10
CS352 Fundamentals
Why Study Networks?
Integral part of society
Work, entertainment, community
Pervasive
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
HW assignments from my server
Person-to-person and group
communication
email, blogs, chat
Form and strengthen communities
chat rooms, MUDs, newsgroups
CS352 Fall, 2005 13
Impact of the Net on Society
Huge impact!
Continuation of technologies that reduce
problems of time & space
(e.g. railroads,phone,autos,TV)
Good, bad and ugly
mirror of society
Changes still on the horizon
Commerce, services, entertainment, socializing
CS352 Fall, 2005 14
Concepts for this week
What is the Internet?
Core and Edge of the Internet
Circuit, message and packet switching
Network delay analysis
Single link
Multi-link
Layering and encapsulation
CS352 Fall, 2005 15
What is the Internet?
What is Internet Technology?
What is an internet?
Network of networks
What is the Internet?
A global internet based on the IP protocol
To what does “Internet technology” refer?
Architecture
Protocols
Services
CS352 Fall, 2005 17
Architecture-wise
Internet Service Provider 1
Company A
ISP 2
Company B
Core Networks (ISP tiers)
Host: Machine line of to send application fiber optics, satellite link)
running user data next
Network : Collection of interconnected machines
Channel: decide where communication
Router: Logical Companies, organizations with a “default route”
Media: Physical process used (copper wire,
Edge Networks: • Tier 1: Biggest ISPs
CS352 Fall, 2005 •Tier 2 and 3: Regional and
18
Service-wise (applications)
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
TCP UDP
IP
Ethernet 802.11 … PPP
CAT-5 Single-Mode RS-232
Fiber
CS352 Fall, 2005 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) Circuit Switching
(2) Message Switching (Store-and-Forward)
(3) Packet Switching (Store-and-Forward)
CS352 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
Propagation Delay
Time
Transmission
Delay
Call accept signal
Data
Transmission
Time
Data
CS352 Fall, 2005 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
Msg
Time
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
Overlap sending and receiving of packets on multiple links
CS352 Fall, 2005 28
Packet Switching (cont’d)
Pkt 1
Header
Time
Pkt 2
Pkt 1
Pkt 3
Transmission
Pkt 2
Delay
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 kilobit (Kbit) = 1 x 103 bits = 1,000 bits
1 megabit (Mbit) = 1 x 106 bits = 1,000,000 bits
1 gigabit (Gbit) = 1 x 109 bits = 1,000,000,000 bits
Seconds are the units used to measure time
1 millisecond (msec) = 1 x 10-3 seconds = 0.001 seconds
1 microsecond (msec) = 1 x 10-6 seconds = 0.000001 seconds
1 nanosecond (nsec) = 1 x 10-9 seconds = 0.000000001 seconds
Bits per second are the units used to measure channel
capacity/bandwidth and throughput
bit per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
CS352 Fall, 2005 33
Types of Delay
Processing
Time to execute protocol code
Queuing
Time waiting in queue to be processed
Transmission
Time to “get bits on wires”
Propagation
Time for bits to “move across wires”
CS352 Fall, 2005 34
Transmission vs. Prop. delay
A single transmission link as a water pipe
1. The thicker the pipe, the more water it can carry from one end
to the other in each unit time
2. 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. Propagation delay is how long takes to cross
the pipe, irrespective of volume
2. Transmission (bandwidth delay) is related to
how much water can be pushed in through
the opening per unit time
CS352 Fall, 2005 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 1500 x 8 bits Solving for t…
= t = 0.00012 sec (or 120 msec)
1 sec t
CS352 Fall, 2005 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 t Solving for t…
=
1000 m 500 m t = 2.5 msec
CS352 Fall, 2005 38
Processing Delay
Stylized format required to send data
Analogy: adding and removing envelopes to letters
Host Host
Application Application
Layer Layer How long does it take
Transport Transport to execute all these
Layer
Router
Layer
layers?
Network Network Network
Layer Layer Layer Why is this time
Host-to- Host-to- Host-to-
important?
Net Layer Net Layer Net Layer
CS352 Fall, 2005 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. How long to format the data?
2. How long does it take a single bit to travel on the link
from A to B?
3. How long does it take A to transmit an entire packet
CS352
onto the link?
Fall, 2005 40
Timeline Method
Host A Host B
40 Protocol Delay
1st bit
2.5 Propagation delay
Time
120 Transmission time
last bit
40 Protocol Delay
CS352
Total time: 40+120+2.5+40 = 202.5 msec
Fall, 2005 41
Queuing Delay
Router
Network
Layer
Host-to-
Net Layer
Packets 2 0 0 0
Packets waiting
waiting 3 1
processing Router transmission
1 0 2 2 at output
at input 0 3
ports ports
Packets arriving faster than
processing or transmission
delay
CS352 Fall, 2005
=> queuing (I.e. waiting in line) 42
Analytic Comparison of multi-
link 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:
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
CS352 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
Propagation
Packet 2 Delay
Packet 3
Time
Packet 4
Bandwidth
Delay
CS352 Fall, 2005 47
Note on Pipelining
The above analysis is very general:
Packets in a computer network
Messages/packets are the unit of work.
Instructions in a processor
Instructions are the unit of work.
Jobs through a batch Q in an operating system.
Processes are the unit of work.
Pipelining speeds up work over time.
How?
CS352 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 P B
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 P B
Time for each packet to
go through each link
CS352 Fall, 2005 50
Equilibrium Point
N p h N
C P S
B 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
Different vendors and organizations responsible
for different layers
Testing and maintenance is simplified
Easy to replace a single layer with a different
version
CS352 Fall, 2005 54
Protocol Hierarchy
Use layers to hide complexity
Each layer implements a service
Layer N uses service provided by layer N-1
layer N-1 provides a service to layer N
Protocols
Each layer communicates with its peer by a set of
rules
Interface
A layers interface specifies the operations
CS352 Fall, 2005 55
Protocol Hierarchy (cont’d)
Host A Host B
Layer 7
Layer 7 Protocol Layer 7
Layer 6 Protocol
Layer 6 Layer 6
Layer 5 Protocol
Layer 5 Layer 5
Layer 4 Protocol
Layer 4 Layer 4
Layer 3 Protocol
Layer 3 Layer 3
Layer 2 Protocol
Layer 2 Layer 2
Layer 1 Protocol
Layer 1 Layer 1
CS352 Fall, 2005 56
Physical Medium
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
ITU,ISO,ATM
Local area networking/computers
IETF, IEEE
System area networks/storage
ANSI
CS352 Fall, 2005 59
ISO OSI Layering Architecture
Host A Host B
Application Application Protocol Application
Layer Layer
Presentation Presentation Protocol Presentation
Layer Layer
Session Session Protocol Session
Layer Layer
Transport Transport Protocol Transport
Layer Layer
Network Network Network Network
Layer Layer Layer Layer
Data Link Data Link Data Link Data Link
Layer Layer Layer Layer
Physical Physical Physical Physical
CS352 Fall, 2005 Layer Layer Layer Layer 60
Router Router
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
Dynamic routing
Fixed routing
Performs congestion control
CS352 Fall, 2005 64
Layer 4: Transport Layer
Functions:
Hide the details of the network from the session
layer
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
CS352 Fall, 2005 65
Transport Layer (cont’d)
Host A Host B
Application Application Protocol Application
Layer Layer
first
end-to-end
Presentation Presentation Protocol Presentation
layer Layer Layer
Session Session Protocol Session
Layer Layer
Transport Transport Protocol Transport
Layer Layer
Network Network Network Network
Layer Layer Layer Layer
Data Link Data Link Data Link Data Link
Layer Layer Layer Layer
Physical Physical Physical Physical
CS352 Fall, 2005 Layer Layer Layer Layer 66
Router Router
Transport Layer (cont’d)
Functions (cont’d):
Perform end-to-end flow control
Perform packet retransmission when packets are
lost by the network
CS352 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:
Banking session
Network meetings
CS352 Fall, 2005 68
Layer 6: Presentation Layer
Performs specific functions that are
requested regularly by applications
Examples:
encryption
ASCII to Unicode, Unicode to ASCII
LSB-first representations to MSB-first
representations
CS352 Fall, 2005 69
Layer 7: Application Layer
Application layer protocols are application-
dependent
Implements communication between two
applications of the same type
Examples:
FTP
HTTP
SMTP (email)
CS352 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
Application
AH Data
Layer
Presentation
Layer
PH Data Headers
Session
SH Data
Layer
Transport
TH Data
Layer
Network
Trailer
NH Data
Layer
Data Link
DH Data DT
Layer
Physical
CS352 Fall, 2005 PH Data 72
Layer
Internet “Hourglass”
Architecture
Defined by Internet Engineering Task Force (IETF)
“Hourglass” Design
FTP HTTP RTP TFTP
TCP UDP
IP
Ethernet 802.11 … PPP
CAT-5 Single-Mode RS-232
Fiber
CS352 Fall, 2005 73
Internet Design Principles
Scale
Protocols should work in networks of all sizes and
distances
Incremental deployment
New protocols need to be deployed gradually
Heterogeneity
Different technologies, autonomous organizations
End-to-end argument
Some functions can only be correctly implemented at
the end hosts; the network should not provided these.
CS352 Fall, 2005 74
TCP/IP Layering Architecture
A simplified model
Application The network layer
Hosts drop packets into
Transport this layer, layer routes
towards destination- only
promise- try my best
Internet/Network
The transport layer
reliable byte-oriented
Host-to-Net
stream
CS352 Fall, 2005 75
TCP/IP Layering Architecture
(cont’d)
Host A Host B
Application Application Protocol Application
Layer Layer
Transport Transport Protocol (TCP) Transport
Layer Layer
Network
IP Network
IP Network
IP Network
Layer Layer Layer Layer
Host-to- Host-to- Host-to- Host-to-
Net Layer Net Layer Net Layer Net Layer
CS352 Fall, 2005 76
