CS412 Introduction to
Computer Networking &
Telecommunication
Introduction
Chi-Cheng Lin, Winona State University
Topics
Introduction
 Metric Units
 Network Hardware
 Network Software
 Reference Models
 Example Networks
 Standards and Standards Organizations

2
Introduction

First two decades of computing
Highly centralized computer systems

Now
A large number of SEPARATE but
INTERCONNECTED computers
=> Computer networks
3
What is Computer Network?

An INTERCONNECTED collection of
AUTONOMOUS computers
Interconnected: Able to EXCHANGE
INFORMATION via transmission media
Media: copper wire, fiber optics, microwaves,
communication satellites
Autonomous: no master/slave relation
NOT autonomous:
 One computer can control another one
 e.g., a large computer with remote printers and
terminals
4
What is Telecommunication?

What is data communication?
Exchange of data between two devices via
some form of transmission media
Data are represented by bits – 0s and 1s

What is telecommunication?
Exchange of information over distance
using electronic equipment
5
What is Telecommunication?

Components of data communication
Sender, receiver, medium, message, and
Protocol: set of rules governing data
communication

Key elements of a protocol
Syntax
Structure/format
Semantics
Meaning
Timing
When and how fast
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Figure 1.1
McGraw-Hill
Five components of data communication
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©The McGraw-Hill Companies, Inc., 2004
Why Studying CS412?
The instructor looks nice … (Don’t bet on
it!)
 It is part of our daily life now
 The job market is good … (?)
 You want to understand concepts and
technologies of networking and telecom

Theory and practice
It is one of the most drastically changing
field in CS and you like challenges
 It makes you knowledgeable in this field
 It is FUN!!

8
Distributed System vs. Computer Network

Distributed system
TRANSPARENCY
A collection of independent computers appear
as a single coherent system
Single model/paradigm to users
Middleware on top of OS
Example?

Computer network
No such coherence, model, middleware
Machines visible to users
Users log onto remote machines
9
Distributed System vs. Computer Network
A distributed system is a SOFTWARE
system built on top of a network
 Distinction between network and
distributed system

Software (especially OS) rather than
hardware

However, considerable overlap between
the two subjects
10
Uses of Computer Networks

Business applications
Resource sharing
Communication medium
E-commerce

Client-server model
Client requests, server performs & then replies
E.g., one or more file servers, many clients
11
Business Applications of Networks

A network with two clients and one
server.
12
Client-Server Model
1
2
3
13
Uses of Computer Networks

Home applications
Access to remote information
On-line publishing, digital library, WWW
Person-to-person communication
Email, instant messaging, peer-to-peer
communication, videoconferencing, Internet
phone, E-learning
Interactive entertainment
Video on demand (VOD), games
E-commerce
Home shopping, electronic banking and
investment, on-line auction
14
Home Network Applications (2)

In peer-to-peer system there are no
fixed clients and servers.
15
Mobile Users
Notebook, PDA, cellular phone
 M-commerce
 Wireless networking and mobile
computing

16
Metric Units

The principal metric prefixes.
17
Network Hardware

By transmission technology
Broadcast links
smaller, geographically localized networks
Point-to-point links
larger networks

By scale
PAN
LAN
MAN
WAN
18
Classification by Scale
19
Broadcast Network
A single communication channel shared
by all machines on the network
 Packets (short messages) sent by any
machine are “received” by all the others

Address field of packet: whom it is intended

Message transmission
Unicast: one sends, one receives
Broadcasting: one sends, all receive
Multicasting: one sends, a group receives
20
Point-to-Point Networks
Many connections between pairs of
machines
 Intermediate machines (called routers)
might have to be visited by a packet
from source to destination – more than
one path is possible
 Routing algorithms are important

Routing: process of finding a path from a
source to the destination(s) in the network
21
Local Area Network (LAN)
Private-owned Networks
 Within a single building/campus
 Size: up to a few kilometers
 Characteristics

Size
Restricted by size
 worst-case transmission time bounded and
known in advance
 network management simplified
22
LAN

Characteristics
Transmission technology
Machines attached to a single cable
Speed/capacity (High): 10 - 100 Mbps, Gbps
 Mbps/Gbps: Megabit/Gigabit per second
 1 megabit=1,000,000 (not 220=1,048,576) bits
Delay (low): microseconds, nanoseconds
Errors: very few
23
LAN

Characteristics
Topology – the way in which a network is
laid out
Examples: Bus, Ring
Bus
Ring
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Figure 1.7
McGraw-Hill
Categories of topology
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©The McGraw-Hill Companies, Inc., 2004
Figure 1.8
McGraw-Hill
Fully connected mesh topology (for five devices)
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©The McGraw-Hill Companies, Inc., 2004
Figure 1.9
McGraw-Hill
Star topology
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©The McGraw-Hill Companies, Inc., 2004
Figure 1.10
McGraw-Hill
Bus topology
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©The McGraw-Hill Companies, Inc., 2004
Figure 1.11 Ring topology
McGraw-Hill
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©The McGraw-Hill Companies, Inc., 2004
LAN - Topology

Bus (linear cable)
Only one machine can transmit at a time
Arbitration mechanism needed to resolve
conflicts when two or more computers
want to transmit simultaneously
Centralized or Distributed
Example: IEEE 802.3 (Ethernet):
Bus-based broadcast network with
decentralized control operating at 10 Mbps to
10Gbps.
If two or more packets collide, each computer
just waits a random time and tries again later.
30
LAN - Topology

Ring
Bits propagate around the ring
Arbitration mechanism is needed, too
Example: IEEE 802.5 (IBM Token Ring)
Ring-based LAN operating at 4 and 16 Mbps
Arbitration is based on “token”
 Only token holder can transmit
31
LAN - Channel Allocation
Needed as all computers share one
communication pathway
 Static channel allocation

Divide up time into discrete intervals
Run a round robin algorithm
Allow each machine to broadcast only
when its time slot comes up
Problem: Wasting channel capacity
32
LAN - Channel Allocation

Dynamic channel allocation
Centralized
A central entity determines who goes next
Decentralize
No central entity
Each machine decides for itself to transmit or
not
Algorithms needed to resolve potential chaos
33
Metropolitan Area Network (MAN)
Covers city
 Examples

Cable TV network
IEEE 802.16 high-speed wireless Internet
access
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Figure 1.14
McGraw-Hill
MAN
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©The McGraw-Hill Companies, Inc., 2004
Metropolitan Area Networks

A metropolitan area network based on
cable TV.
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Wide Area Network (WAN)
Country or continent
 Components

Host (end system)
Machine running user (application) programs
Communication subnet (subnet)
Connecting hosts
Carrying messages from host to host
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Figure 1.15
McGraw-Hill
WAN
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©The McGraw-Hill Companies, Inc., 2004
WAN - Subnet Components

Transmission lines
Move bits between machines

Switching elements
Specialized computers that connect two or
more transmission lines
Determine out going line for incoming data
ROUTER
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WAN - Hosts and Subnet
H1
R1
R2
R3
R5
R4
R6
H2
: Host
: Router
40
WAN - Architecture
Contains numerous cables or telephone
lines
 Each cable connects a pair of routers
 Two routers must communicate
indirectly if they are not connected by a
cable
 There might be more than one route
between two hosts and it might change
from time to time

E.g., Route from H1 to H2
41
WAN - Architecture

An intermediate router in a WAN
Receives a packet in its entirety
Queues the packet until required output
line is free
Forwards the packet

Subnet using the principle above is
called
Store-and-forward or packet-switched
subnet
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Wide Area Networks

A stream of packets from sender to
receiver.
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Topology – LANs vs WANs

Local networks
Bus, Ring, Star
Tree

WANs typically irregular
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WAN - Broadcast Systems

Satellite system
Each router has an antenna
Sometimes routers are connected to a
substantial point-to-point subnet, with
some of them having a satellite antenna
Inherently broadcast
45
Wireless Network

System interconnection
Example: Bluetooth

Wireless LANs
Easy to install
IEEE Standard 802.11

Wireless WANs
IEEE Standard 802.16
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Wireless Networks
Bluetooth configuration
Wireless LAN
47
Wireless Network

Combinations of wired and wireless
networking (e.g., flying LAN)
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Home Network Categories

Computers
Desktop PC, PDA, shared peripherals

Entertainment
TV, DVD, VCR, camera, stereo, MP3

Telecomm
Telephone, cell phone, intercom, fax

Appliances
Microwave, fridge, clock, furnace, aircon

Telemetry
Utility meter, burglar alarm, babycam
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Internetwork

What is internetwork?
A collection of interconnected networks

"Internet" and "internet"
internet: internetwork
Internet: the worldwide internetwork using
TCP/IP protocol suite

Problem: Communication between
networks with different SW/HW
Solution: Gateways
Machines connect different, incompatible networks
Connection and translation
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Figure 1.16
McGraw-Hill
Internet today
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©The McGraw-Hill Companies, Inc., 2004
Network Software

Old computer networks:
HW main concern
SW afterthought
Not working now!

Network SW is now highly structured
Protocol Hierarchies
Implemented in hardware or firmware
52
Protocol Hierarchies

What is protocol?
Agreement between communication parties
on HOW communication is processed

Layered architecture
Reduce design complexity- Lower layer
offers service to higher layer
Hiding implementation details
Layer n on one machine talks to layer n on
another
Rules and conventions used in layer n’s talk:
Layer n protocol
53
Protocol Hierarchies

Peers
Entities comprising corresponding layers on
different machines
Virtual communication using protocol
Peer process abstraction make network design
becomes that of individual layers

Physical communication
Sender: Data and control passed to layer below
Data transmitted via physical media
Receiver: Data and control passed to layer
above
54
Layers, Protocols, and Interfaces
Virtual Communication
Physical Communication
55
Protocol Hierarchies

Interface between two adjacent layers
Defines primitive operations and services a
lower layer offers to the upper one
Minimizes amount of information passed
between two layers
Simplifies replacement of implementation
E.g., telephone lines  satellite channels
56
Protocol Hierarchies

Network architecture
Set of layers and protocols
Implementation and interface specification
not included

Protocol stack
A list of protocols used by a certain system,
one protocol per layer
57
Multilayer Communication - Example

Philosopher-translator-secretary
architecture
It is ok if
Dutch is
replaced by
Finnish
fax is
replaced by
email
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Information Flow - Example

Virtual communication for layer 5
Header: control information
00011100011100001110 …
Layer 1
protocol
00011100011100001110 …
59
Key Design Issues for the Layers
Sender/receiver identification mechanism
 Transmission direction modes

Simplex
Data only travel in one direction
Half-duplex
Data can travel in either direction, but not
simultaneously
Full-duplex
Data can travel in both directions simultaneously

Number of logical channels and properties
60
Key Design Issues for the Layers

Error control
Error-detecting
Error-correcting
Sequencing
 Flow control

Needed for fast sender, slow receiver
Approaches
Feedback mechanism
Transmission rate agreement
61
Key Design Issues for the Layers
Message disassembling, transmitting,
reassembling
 Multiplexing

The process of combining signals from
multiple sources for transmission across a
single data link
Multiple connections can share the link

Routing
Selecting the best path for sending a
packet from one point to another
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Connection-Oriented and
Connectionless Services

Two basic types of services
Connection-oriented
Connectionless

Consider reliability …
Reliable
Unreliable

Connection-oriented
Connectionless
Note that: Connection  Reliability
63
Connection-Oriented Service
A connection is established first, then
used, and then released when done.
 Works like a pipe:

Sender pushes data in at one end
Receiver takes them out, often in the same
order, at the other end

Analogy
Telephone system
64
Connectionless Service
No need to set up a connection first
 Each message carrying full destination
address is routed independently of
others

No guarantees on the order

Analogy
Postal system
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Six Service Types
66
Service Primitives
Service is formally specified by a set of
primitives (e.g., OS’s system calls)
available to users or entities
 Five service primitives for implementing
a simple connection-oriented service.

67
Service Primitives

Packets sent in a simple client-server
interaction on a connection-oriented
network.
68
Relationship of Services to Protocols

Service
Set of primitives a layer provides to the
layer above it
Define WHAT operations
not HOW implemented

Protocol
Set of rules governing format and meaning
of message exchanged by peer entities
within a layer
Used by entities to implement service
definition
69
Services to Protocols Relationship

The relationship between a service and
a protocol.
70
Relationship of Services to Protocols

Analogy: Object-oriented languages
Service :: Object
Users do not know the implementation of a
service
Protocol :: Implementation
The protocol of the service is invisible to users
Do you have to understand http (hypertext
transport protocol) before you can surf the
Internet?
71
Reference Models

Two reference models will be discussed
OSI reference model
TCP/IP model
72
OSI Reference Model
ISO/OSI (Open Systems Interconnection)
Reference Model
 NOT a network architecture itself

Exact services and protocols are not specified
Just "what should be done" in each layer
However, standards are produced for all layers
73
OSI Reference Model

Seven layers
Layer
Layer
Layer
Layer
Layer
Layer
Layer

7:
6:
5:
4:
3:
2:
1:
application layer
presentation layer
session layer
transport layer
network layer
data link layer
physical layer (lowest)
Diagram of OSI reference model
Note: this is one of the most important figures
in the whole book!!
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Physical medium
75
76
Physical medium
End-to-End
Point-to-Point
Point-to-Point
Host A
Subnet
Point-to-Point
Host B
77
Physical Layer
Transmitting raw bits (0s and 1s)
 Design issues

Representation of bits
How is 0/1 represented?
Data rate: number of bits sent per second
How long does a bit last?
Transmission mode
Mechanical, electrical, procedural
interfaces
Underlying physical transmission medium
78
Data Link Layer
Takes a raw transmission facility and
transforms it into a line (link) that
appears free of undetected transmission
errors to network layer
 Basic function

Breaks up input data to data frames
Transmits data frames
Processes acknowledgement frames sent
back from receiver
79
Data Link Layer

Responsibilities (cont’d)
Physical addressing
Framing
creating and recognizing frame boundaries
Error control (adjacent nodes)
Errors: damaged, lost, duplicate
Flow control (adjacent nodes)
Traffic regulation between fast sender and slow
receiver
Medium access control
Shared channel access control in broadcast
networks
80
Network Layer
Subnet operation control
 Responsibilities

Logical addressing
Routing
Static tables
Determined at the start of conversation
Dynamic
Congestion control
Quality of service
Accounting
Heterogeneous network interconnection
81
Transport Layer

End-to-end layer
Talk to destination machine directly (virtually)
Layers 4 through 7 are end-to-end
Layers 1 through 3 are node-to-node

Basic function
Split data from session layer into smaller units
Pass units to network layer
Ensure units arrive correctly at the other end
82
Transport Layer

Determine services provided to session
layer (and ultimately to users)
Error-free point-to-point channel that
delivers messages in the order in which
they were sent
Transport of isolated messages w/o
guarantee about order
Broadcasting

Normally, a distinct network connection
is created for each transport connection
required by session layer
83
Transport Layer

Responsibilities include
Service-point addressing
Which message belong to which connection
(application):
 Information in header
 Needed as multiprogramming in a host
(End-to-end) Flow control
(End-to-end) Error control
Compare to the
Data Link layer
84
Session layer
Session establishment between users
on different machines
 Responsibilities

Dialogue control
Deciding who sends, and when
Token management
Control of same operation not to be performed
at the same time
Synchronization
Inserting checkpoints (checkpointing)
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Figure 3-11 from Forouzan’s 2/e
Session Layer
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998
Presentation Layer
Syntax/semantics of information
 Responsibilities

Encoding
Convert from data representation used in one
host to the standard abstract data structure
and back
Encryption
Compression
87
Application Layer
Provides interface and support for
services to users (human, software,
robots)
 Application services

Network virtual terminal (telnet)
File transfer
Email
Network management
Hypertext transfer
88
Figure 3-14 from Forouzan’s 2/e
Summary of Layer Functions
WCB/McGraw-Hill
 The McGraw-Hill Companies, Inc., 1998
TCP/IP Reference Model

Goals
Internetworking
Fault tolerance
Flexible architecture

Four layers of TCP/IP Reference Model
Host-to-network layer
Internet layer
Transport layer
Application layer
90
Internet Layer
Packet-switching, connectionless
 Packets injected to network

Independent travel
Out-of-order arrival

Analogy
Mail system

IP (Internet Protocol)
Packet routing
Congestion control
91
Transport Layer

Two end-to-end protocols
UDP (User Datagram Protocol)
TCP (Transmission Control Protocol)

UDP (User Datagram Protocol)
Unreliable, connectionless
Widely used for
client-server type request-reply queries
speech, video
92
Transport Layer

TCP
Reliable connection-oriented
Incoming byte stream (form application
layer) is fragmented into discrete messages
and passed onto internet layer
Message is reassembled at destination
Flow control
Analogy
A
B
Pipe
93
Applications and Host-to-Network
Layers

Application layer
No session and presentation layers
TELNET, FTP, SMTP, DNS, NNTP, HTTP

Host-to-network layer
Host has to connect to to the network
using some protocol so it can send IP
packets
94
Initial TCP/IP Protocols and Networks
95
OSI and TCP/IP Models

Correspondence
OSI
7 Application
6 Presentation
Session
5
Transport
4
Network
3
2 Data Link
1
Physical
TCP/IP
Application
Transport
Internet
Host-toNetwork
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OSI and TCP/IP Models

Similarities
Stack of independent protocols
Layer functionality
Transport layer
Application layer
97

OSI
Differences between
OSI and TCP/IP Models
Distinction between services, interfaces, and
protocols (perhaps the biggest contribution)
Better Protocol-Hidden
Model first, then protocols
 Pro: No bias, more general
 Con: Designers did not have
 much experience with the subject
 a good idea of which functionality to put in which layer
No thought given to internetworking
7 layers
Communication
 Connection-Oriented and connectionless in network layer
 Only connection-oriented in transport layer
98
Differences between
OSI and TCP/IP Models

TCP/IP:
No clear distinction between services, interfaces, and
protocols
Worse protocol-hidden
Protocol first, then model
 Pro: Protocols fit model perfectly
 Con: Model does not fit any other protocol stacks (not
general)
4 layers
Communication
 Connectionless in network layer
 Both in transport layer (good for request-response
protocols)
99
Summary of Reference Models

OSI
OSI model exceptionally useful for
discussing computer networks
OSI protocols not popular

TCP/IP
TCP/IP model practically nonexistent
TCP/IP protocols widely used

Modified framework is used in the text
100
Summary of Reference Models

Modified framework is used in the text
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Figure 2.3
McGraw-Hill
Peer-to-peer processes
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Figure 2.4
McGraw-Hill
An exchange using the Internet model
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Figure 2.5
McGraw-Hill
Physical layer
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©The McGraw-Hill Companies, Inc., 2004
Note:
The physical layer is responsible for
transmitting individual bits from one
node to the next.
McGraw-Hill
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©The McGraw-Hill Companies, Inc., 2004
Figure 2.6
McGraw-Hill
Data link layer
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©The McGraw-Hill Companies, Inc., 2004
Note:
The data link layer is responsible for
transmitting frames from
one node to the next.
McGraw-Hill
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Figure 2.7
McGraw-Hill
Node-to-node delivery
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Example 1
In Figure 2.8 a node with physical address 10 sends a
frame to a node with physical address 87. The two nodes
are connected by a link. At the data link level this frame
contains physical addresses in the header. These are the
only addresses needed. The rest of the header contains
other information needed at this level. The trailer usually
contains extra bits needed for error detection
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©The McGraw-Hill Companies, Inc., 2004
Figure 2.8
McGraw-Hill
Example 1
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Figure 2.9
McGraw-Hill
Network layer
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©The McGraw-Hill Companies, Inc., 2004
Note:
The network layer is responsible for
the delivery of packets from the
original source to the
final destination.
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©The McGraw-Hill Companies, Inc., 2004
Figure 2.10
McGraw-Hill
Source-to-destination delivery
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Example 2
In Figure 2.11 we want to send data from a node with
network address A and physical address 10, located on
one LAN, to a node with a network address P and
physical address 95, located on another LAN. Because
the two devices are located on different networks, we
cannot use physical addresses only; the physical
addresses only have local jurisdiction. What we need here
are universal addresses that can pass through the LAN
boundaries. The network (logical) addresses have this
characteristic.
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Figure 2.11 Example 2
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Figure 2.12
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Transport layer
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Note:
The transport layer is responsible for
delivery of a message from one process
to another.
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Figure 2.12
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Reliable process-to-process delivery of a message
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Example 3
Figure 2.14 shows an example of transport layer
communication. Data coming from the upper layers have
port addresses j and k (j is the address of the sending
process, and k is the address of the receiving process).
Since the data size is larger than the network layer can
handle, the data are split into two packets, each packet
retaining the port addresses (j and k). Then in the network
layer, network addresses (A and P) are added to each
packet.
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Figure 2.14
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Example 3
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Figure 2.15
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Application layer
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Note:
The application layer is responsible for
providing services to the user.
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Figure 2.16
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Summary of duties
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Example Networks
The Internet
 Connection-Oriented Networks

X.25, Frame Relay, and ATM
Ethernet
 Wireless LANs: 802:11

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Standards and Standards Organizations
Why standards?
 Categories

de facto
de jure

Organizations
ITU-T (formerly CCITT)
ISO
ANSI
IEEE
IETF
ATM Forum
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