Here are the key steps to solve this problem: - Propagation delay = Distance / Speed of light - Distance = 4 km = 4000 m - Speed of light = 2 x 10^8 m/sec - Propagation delay = 4000 m / (2 x 10^8 m/sec) = 20 ms - Transmit delay = Size of data / Bandwidth - For transmit delay to equal propagation delay of 20 ms, set: - Transmit delay = 20 ms - Size of data = 1 bit (since we want minimum bandwidth) - 20 ms = 1 bit / Bandwidth - Bandwidth = 1 bit / 20 ms = 50 Mbps Therefore, the minimum

1. 1
Chapter 1
Foundation
Computer Networks: A Systems Approach, 5e
Larry L. Peterson and Bruce S. Davie
Copyright © 2010, Elsevier Inc. All rights Reserved

2. 2
Chapter
1
Problems
 How to build a scalable network that will support
different applications?
 What is a computer network?
 How is a computer network different from other
types of networks?
 What is a computer network architecture?

3. 3
Chapter
1
Chapter Outline
 Applications
 Requirements
 Network Architecture
 Implementing Network Software
 Performance

4. 4
Chapter
1
Applications
 Most people know about the Internet (a computer
network) through applications
 World Wide Web
 Email
 Online Social Network
 Streaming Audio Video
 File Sharing
 Instant Messaging
 …
 Three types of people comes in applications
 Application developers
 Network managers
 Network protocols developers.

5. 5
Chapter
1
Example of an application
A multimedia application including video-conferencing

6. 6
Chapter
1
Application Protocol
 URL
 Uniform resource locater
 http://www.cs.princeton.edu/~llp/index.html
 HTTP( download a page)
 Hyper Text Transfer Protocol
 TCP
 Transmission Control Protocol
 17 messages for one URL request
 6 to find the IP (Internet Protocol) address
 3 for connection establishment of TCP
 4 for HTTP request and acknowledgement
 Request: I got your request and I will send the data
 Reply: Here is the data you requested; I got the data
 4 messages for tearing down TCP connection
 Multimedia application how it works

7. 7
Chapter
1
Requirements
 Perspective
 Different perspective of the C.N.
 Application Programmer
 List the services that his application needs: delay
bounded delivery of data
 Network operator
 Easy to administrate and manage: faults can easily be
identified, adding of new devices.
 Network designer
 Design a cost-effective network :sharable resources,
Issues of performance

8. 8
Chapter
1
Connectivity
 Provide connectivity
 Need to understand the
following terminologies
 Scale
 Limiting the machines
 Grow the network
 Growth of orbittarily large
system
 Link
(a) Point-to-point
(b) Multiple access

9. 9
Chapter
1
 Nodes
 Point-to-point
 Multiple access
 Switched Network
 Circuit Switched
 Packet Switched
 Packet, message
 Store-and-forward

10. 10
Chapter
1
Connectivity
 Terminologies (contd.)
 Cloud
 Hosts
 Switches
 internetwork
 Router/gateway
 Host-to-host connectivity
 Address
 Routing
 Unicast/broadcast/multicast
(a) A switched network
(b) Interconnection of networks
(a)
(b)

11. 11
Chapter
1
Cost-Effective Resource Sharing
 Resource: links and
nodes
 How to share a link?
 Multiplexing
 Share a CPU by many
processes
 De-multiplexing
 Synchronous Time-division
Multiplexing
 Time slots/data
transmitted in
predetermined slots
 Frequency division
multiplexing
Multiplexing multiple logical flows
over a single physical link

12. 12
Chapter
1
Cost-Effective Resource Sharing
 FDM: Frequency Division
Multiplexing
 Statistical Multiplexing
 Data is transmitted based
on demand of each flow.
 What is a flow?
 Packets vs. Messages
 FIFO, Round-Robin,
Priorities (Quality-of-
Service (QoS))
 Congested?
 LAN, MAN, WAN
 SAN (System Area
Networks
A switch multiplexing packets from
multiple sources onto one shared
link

13. 13
Chapter
1
Support for Common Services
 Logical Channels
 Application programs should communicate with each other
 Identify the right set of common services
 Each channel provides the set of services required by that application
 Can think channel as being a pipe connecting two applications
 Application-to-Application communication path or a pipe
 The challenge is to recognize what functionality the channel should
provide to the application
 Guarantee the message is delivered
 Acceptable if some message fail to arrive
Process communicating over an
abstract channel

14. 14
Chapter
1
Common Communication Patterns
 Earliest application in any network is FTP and
NFS
 Client/Server
 Two types of communication channel
 Request/Reply Channels
 Guaranteed every message is delivered, provide privacy
 Message Stream Channels
 Used by V-O-D and videoconferencing
 Support in one way or two way.
 Ensure the message delivered arrive at the same order.
 May have to support the multicasting.

15. 15
Chapter
1
Reliability
 Reliable message delivery is the most important
function
 Network don't exists in the perfect word
 3 type of failures the designs has to handle
 Network should hide the errors
1 Bits are lost
 Bit errors (1 to a 0, and vice versa)
 Burst errors – several consecutive errors
2 Packets are lost (Congestion)
3 Links and Node failures
 Messages are delayed
 Messages are delivered out-of-order

16. 16
Chapter
1
Manageability
 Networks need to be managed
 Making changes as the network grows
 Hundered millions of hosts will be running
 Configuration of new devices such as routers
 Trouble shooting when network things go
wrong
 Make operations of the network scalable and
cost effective.
 Network management.

17. 17
Chapter
1
Network Architecture
•A computer network should provide general cost effective, fair, and robust
connectivity among a large number of network.
•Network designers have developed general blue print called NETWORK
ARCHICTURE
•Layering and protocol
•Abstraction for the applications that hides complexity from the
application writer
•Service provided by the higher layer are implemnted by the service
provided by the lower layers.

18. 18
Chapter
1
Network Architecture
Layered system with alternative abstractions available at a given layer
•Layering provide the two features
•Building the network into more
manageable components
•Provides the more modular design

19. 19
Chapter
1
Protocols
 Protocol defines the interfaces between the
layers in the same system and with the layers of
peer system
 Building blocks of a network architecture
 Each protocol object has two different interfaces
 service interface: operations on this protocol
 peer-to-peer interface: messages exchanged with
peer
 Term “protocol” is overloaded
 specification of peer-to-peer interface
 module that implements this interface

20. 20
Chapter
1
Interfaces
Service and Peer Interfaces

21. 21
Chapter
1
Protocols
 Protocol Specification: prose, pseudo-code, state
transition diagram
 Referred to as abstract interface and form of the
meaning exchanged between peers
 Module that actually implements the interfaces
 Interoperable: when two or more protocols that
implement the specification accurately
 Policies are established by
 IETF: Internet Engineering Task Force
 ISO

22. 22
Chapter
1
Protocol Graph
Example of a protocol graph
nodes are the protocols and links the “depends-on” relation
•RRR: request
replay
•MSP: message
stream protocol
•HHP: host-host
protocol

23. 23
Chapter
1
Encapsulation
High-level messages are encapsulated inside of low-level messages

24. 24
Chapter
1
Adds header
Multiplexing and demultiplexing

25. 25
Chapter
1
OSI Architecture
The OSI 7-layer Model
OSI – Open Systems Interconnection

26. 26
Chapter
1
Description of Layers
 Physical Layer
 Handles the transmission of raw bits over a communication link
 Data Link Layer
 Collects a stream of bits into a larger aggregate called a frame
 Network adaptor along with device driver in OS implement the
protocol in this layer
 Frames are actually delivered to hosts
 Network Layer
 Handles routing among nodes within a packet-switched network
 Unit of data exchanged between nodes in this layer is called a
packet
The lower three layers are implemented on all network nodes

27. 27
Chapter
1
Description of Layers
 Transport Layer
 Implements a process-to-process channel
 Unit of data exchanges in this layer is called a message
 Session Layer
 Provides a name space that is used to tie together the potentially
different transport streams that are part of a single application
 Presentation Layer
 Concerned about the format of data exchanged between peers
 Application Layer
 Standardize common type of exchanges
The transport layer and the higher layers typically run only on end-
hosts and not on the intermediate switches and routers

28. 28
Chapter
1
Internet Architecture
Internet Protocol Graph
Alternative view of the
Internet architecture. The
“Network” layer shown here
is sometimes referred to as
the “sub-network” or “link”
layer.

29. 29
Chapter
1
•4 layer archicture
•NET1… Protocols are implemented by the combination
of s/w and h/w
•Ethernet, wireless LAN
•IP
•Connects all the network
•TCP
•UDP and TCP
•Application protocols
•HTTP, FTP etc.

30. 30
Chapter
1
Internet Architecture
 Evolved from ARPANET
 Defined by IETF
 Three main features
 Does not imply strict layering. The application is free to bypass
the defined transport layers and to directly use IP or other
underlying networks
 An hour-glass shape – wide at the top, narrow in the middle and
wide at the bottom. IP serves as the focal point for the
architecture
 In order for a new protocol to be officially included in the
architecture, there needs to be both a protocol specification and
at least one (and preferably two) representative implementations
of the specification

31. 31
Chapter
1
Application Programming Interface
 Interface exported by the network
 Since most network protocols are implemented (those in
the high protocol stack) in software and nearly all
computer systems implement their network protocols as
part of the operating system, when we refer to the
interface “exported by the network”, we are generally
referring to the interface that the OS provides to its
networking subsystem
 The interface is called the network Application
Programming Interface (API)

32. 32
Chapter
1
Application Programming Interface (Sockets)
 Socket Interface was originally provided by the
Berkeley distribution of Unix
- Now supported in virtually all operating systems
 Each protocol provides a certain set of services,
and the API provides a syntax by which those
services can be invoked in this particular OS

33. 33
Chapter
1
Performance
 Performance is measured in Bandwidth and latency
 Bandwidth
 Width of the frequency band
 Number of bits per second that can be transmitted over a
communication link
 1 Mbps: 1 x 106 bits/second = 1x220 bits/sec
 1 x 10-6 seconds to transmit each bit or imagine that a
timeline, now each bit occupies 1 micro second space.
 On a 2 Mbps link the width is 0.5 micro second.
 Smaller the width more will be transmission per unit time.

34. 34
Chapter
1
Bandwidth
Bits transmitted at a particular bandwidth can be regarded as
having some width:
(a) bits transmitted at 1Mbps (each bit 1 μs wide);
(b) bits transmitted at 2Mbps (each bit 0.5 μs wide).

35. 35
Chapter
1
Performance
 Latency = Propagation + transmit + queue
 Propagation = distance/speed of light
 Transmit = size/bandwidth
 One bit transmission => propagation is important
 Large bytes transmission => bandwidth is important

36. 36
Chapter
1
Delay X Bandwidth
 We think the channel between a pair of processes as a
hollow pipe
 Latency (delay) length of the pipe and bandwidth the
width of the pipe
 Delay of 50 ms and bandwidth of 45 Mbps
 50 x 10-3 seconds x 45 x 106 bits/second
 2.25 x 106 bits = 280 KB data.
Network as a pipe

37. 37
Chapter
1
Delay X Bandwidth
 Relative importance of bandwidth and latency
depends on application
 For large file transfer, bandwidth is critical
 For small messages (HTTP, NFS, etc.), latency is
critical
 Variance in latency (jitter) can also affect some
applications (e.g., audio/video conferencing)

38. 38
Chapter
1
Delay X Bandwidth
 How many bits the sender must transmit
before the first bit arrives at the receiver if the
sender keeps the pipe full
 Takes another one-way latency to receive a
response from the receiver
 If the sender does not fill the pipe—send a
whole delay × bandwidth product’s worth of
data before it stops to wait for a signal—the
sender will not fully utilize the network

39. 39
Chapter
1
Delay X Bandwidth
 Infinite bandwidth
 RTT dominates
 Throughput = TransferSize / TransferTime
 TransferTime = RTT + 1/Bandwidth x
TransferSize
 Its all relative
 1-MB file to 1-Gbps link looks like a 1-KB
packet to 1-Mbps link

40. 40
Chapter
1
Relationship between bandwidth and latency
A 1-MB file would fill the 1-Mbps link 80 times,
but only fill the 1-Gbps link 1/12 of one time
RTT of 100 ms

41. 41
Chapter
1
Calculate the total time required to transfer a 1,000-KB file in
the following cases, assuming an RTT of 50 ms, a packet size
of 1-KB data, and an initial 2×RTT of “handshaking” before
data is sent.
(a) The bandwidth is 1.5 Mbps, and data packets can be sent
continuously.
(b) The bandwidth is 1.5 Mbps, but after we finish sending
each data packet we must wait one RTT before sending the
next.
(c) The bandwidth is “infinite,” meaning that we take
transmit time to be zero, and up to 20 packets can be sent
per RTT.

42. 42
Chapter
1
We will count the transfer as completed when the last data bit arrives
at its destination. An alternative interpretation would be to count until
the last ACK arrives back at the sender, in which case the time would
be half an RTT (25ms) longer.
(a) 2 initial RTT’s (100ms) + 1000KB/1.5Mbps (transmit) + RTT/2
(propagation= 25ms)
≈ 0.125 + 8Mbit/1.5Mbps = 0.125 + 5.333 sec = 5.458 sec. If we pay
more careful attention to when a mega is 106 versus 220, we get
8,192,000 bits/1,500,000bps = 5.461 sec, for a total delay of 5.586 sec.
(b) To the above we add the time for 999 RTTs (the number of RTTs
between when packet 1 arrives and packet 1000 arrives), for a total of
5.586 +49.95 = 55.536.
(c) This is 49.5 RTTs, plus the initial 2, for 2.575 seconds.

43. 43
Chapter
1
•Consider a point-to-point link 4 km in length. At what
bandwidth would propagation delay (at a speed of 2 ×
10^8m/sec) equal transmit delay for 100-byte packets?
What about 512-byte packets?
•Propagation delay is 4×10^3m/(2×10^8m/s) = 2×10−5
sec = 20 μs.
•100 bytes/20μs is 5 bytes/μs, or 5MBps, or 40Mbps.
•For 512-byte packets, this rises to 204.8Mbps.

44. 44
Chapter
1
For the following, assume that no data compression is
done, although in practice this would almost never be
the case. For (a) to (c), calculate the bandwidth
necessary for transmitting in real time:
(a) Video at a resolution of 640×480,3 bytes/pixel, 30
frames/second. =640X480X3X8X30= bits/sec
(b) Video at a resolution of160×120,1byte/pixel, 5
frames/second. =160X120X8X5=768000
bits/sec=.768Mbps
(c) CD-ROM music, assuming one CD holds 75
minutes’ worth and takes 650 MB.
=650X10^6X8/(75X60)=1155555bits/sec=1.15MBps

45. 45
Chapter
1
For the following, assume that no data
compression is done. Calculate the bandwidth
necessary for transmitting in real time:
(a) High-definition video at a resolution of
1920×1080, 24 bits/pixel, 30 frames/second.
=1920X1080X24X30=
(b) POTS(plain old telephone service) voice audio
of 8-bit samples at 8
KHz.=8000X8=64000=64kbps
(c) GSM mobile voice audio of 260-bit samples at
50Hz.
(d) HDCD high-definition audio of 24-bit samples
at 88.2kHz. = 88.2X1000X24=

46. 46
Chapter
1
1920×1080×24×30=1,492,992,000≈1.5Gb
ps. 8×8000=64Kbps.
260×50=13Kbps.
24×88,200=216,800≈2.1Mbps.

47. 47
Chapter
1
Summary
 We have identified what we expect from a computer
network
 We have defined a layered architecture for computer
network that will serve as a blueprint for our design
 We have discussed the socket interface which will be
used by applications for invoking the services of the
network subsystem
 We have discussed two performance metrics using
which we can analyze the performance of computer
networks