Transcript Basic Concepts - Mahmoud Youssef

Core Network Concepts
Chapter 1
Copyright 2003 Prentice-Hall
Panko’s Business Data Networks and Telecommunications, 4th edition
Figure 1.1: Major Network Categories

Major Network Types

The Global Internet

Internal Corporate Networks

The Worldwide Telephone System
2
Figure 1.1: Major Network Categories

Telecommunications Spans Two Concerns

Voice and Video Communication vs

Data Communication
 At least one party is a computer

The two are converging
Telecommunications
Voice and
Video
Data
Communication
3
Network

A network is a system of hardware, software
and transmission components that collectively
allow two application programs on two
different stations connected to the network to
communicate well.
4
Figure 1.2: Elements of a Network
Application
Application
Frame
Networks connect applications
on different stations
5
Figure 1.2: Elements of a Network
Frame
Client
Station
Mobile Client
Station
Server
Station
Stations are computers
and other devices
such as cellphones and PDAs
Server
Station
6
Figure 1.2: Elements of a Network
Frame
Client
Station
Mobile Client
Station
Server
Station
Stations communicate by
sending messages called
Frames
Server
Station
7
Figure 1.2: Elements of a Network
Frame
Switch
Switch
Switch
Switch
Frames may pass
through multiple switches
8
Figure 1.2: Elements of a Network
Access links connect
stations to the
first switch
Usually copper wire
Increasingly, radio links
Access
Link
Access
Link
Access
Link
Access
Link
9
Figure 1.2: Elements of a Network
Trunk
Link
Trunk
Link
Trunk Link
Trunk links
connect switches
Higher capacity
than access links
Trunk
Link
Trunk
Link
Often optical
fiber
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Network Elements: Recap

Applications

Stations

Frames

Switches

Access Links

Trunk Links
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Figure 1.3: Client/Server Architecture
Usually, two types of stations
Clients and Servers
Server
Client PC
Service
Network
Clients
Receive
Services
Servers
Provide
Services
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Key Point

Most desktop clients are Wintel computers,
which run client versions of the Microsoft
Windows operating system and use a
standard Intel Pentium microprocessor or a
compatible microprocessor from one of Intel’s
competitors.
13
Figure 1.4: Servers
PC
Server
Standard PC
Microprocessor
Windows NOS:
Network Operating Systems
Microsoft Windows Server
Novell Network
LINUX
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Figure 1.4: Servers
Fast (and Expensive)
Custom-Built Microprocessor
UNIX Operating System
Workstation
Server
Fastest Servers
Ultra-Reliable
Specialized Operating
System
Mainframe
Server
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Figure 1.5: Directory Server
Directory Server
Client
PC
Request for
Information
Policy
Information
Request for
Information
Information
Server
Server
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Figure 1.6: Increasing Server Scalability
(and Sometimes Reliability)
Multiprocessing
Programs or Parts of Programs
A
B
C
D
E
Multiprocessing Operating System (UNIX, Windows NT)
Microprocessor
1
Microprocessor
2
Microprocessor
3
Microprocessor
4
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Figure 1.6: Increasing Server Scalability
(and Sometimes Reliability)
Server Cluster
Server Cluster
acts like a
single large
server
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Figure 1.6: Increasing Server Scalability
(and Sometimes Reliability)
Load Balancing Router
Load balancing
router selects
host on the basis
of load and
applications
supported by
the host
HTTP-1
HTTP-2
HTTP-3
FTP-1
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Figure 1.7: Switching Decision
Switch receives
a frame, sends
it back out
Switch
Switch Sends
Signal out a
Single Port
Station A
Transmits
to Station C
Station
A
Station
B
Station
C
Station
D
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Figure 1.8:Packet Switching
1. Break message into
Smaller packets
AKA frames
Original Message
Packet
Switch
Computer X
A
Packet
B
C
Switching
Decision
E
Computer Y
F
D
2. Route packets individually
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Figure 1.8:Packet Switching

Packet Switching Reduces Trunk Line Costs

Packets from several conversations are multiplexed
on trunk lines

Each conversation only pays for the capacity it
uses
Trunk Link
Packet from A to B
Packet from C to D
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Figure 1.8:Packet Switching
Packet
Data Field
Header
Other
Header
Field
Address
Field
Message Structure
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Quality of Service

It is not enough that networks work



They must work well
Quality of Service (QoS) defines quantitative
measures of service quality

Speed and Delay (Latency)

Reliability
Security (not a QoS measure but crucial)
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Figure 1.9: Quality of Service (QoS)

Speed

Bits per second (bps)

Multiples of 1,000 (not 1,024)

Kilobits per second (kbps)—Note the Lower-case “k”

Megabits per second (Mbps)

Gigabits per second (Gbps)

Terabits per second (Tbps)

Petabits per second (Pbps)
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Figure 1.9: Quality of Service (QoS)

Congestion and Latency

Congestion because traffic chronically or
momentarily exceeds capacity

Latency (delay measured in milliseconds)

Especially bad for some services such as voice
communication or highly interactive applications
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Figure 1.9: Quality of Service (QoS)

Reliability

Availability
 Percentage of time the network is available to
users for transmission and reception
 Want 24 x 7 x 365 availability
 Telephone network: Five 9s (99.999%)

Error Rate
 % Lost or damaged messages or bits
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Figure 1.9: Quality of Service (QoS)

Service Level Agreements (SLAs)

Guarantees for various service parameters

Network provider pays performance penalties if
guarantees are not met
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Figure 1.10: Geographic Scope

Local Area Network (LAN)

Limited geographical distance: home, office,
building, campus, industrial part

Customer premises operation
 User firm chooses technology
 User firm needs to manage on ongoing basis

Low cost per bit transmitted
 Companies can afford high speed
 100 Mbps to the desktop is typical
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Figure 1.10: Geographic Scope

Wide Area Network (WAN)
WAN

To link sites
 Long distances

Requires the use of carriers to provide service
 Limited and complex choices but carrier manages

High cost per bit transmitted
 Companies cannot afford high speeds
 Usually low speed (56 kbps to a few megabits per
second)
30
Figure 1.10: Geographic Scope

Other Distinctions

Metropolitan Area Network (MAN)
 Single urban area (city and its suburbs)
 Faster than long-distance WANs

Personal Area Network (PAN)
 A person’s body or desk area

Storage Area Network (SAN)
 To link servers to storage devices
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Internet

An internet is a group of networks linked
together with routers in a way that allows an
application program on any station on any
network in the internet to be able to
communicate with an application program on
another station on any other network.
Network 1
Network 2
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Packets and Frames

Messages in Single Networks are Called
Frames

Messages in Internets are Called Packets
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Figure 1.11: An Internet
Multiple Networks
Each single network
Is like Figure 1.2.
Switches, etc.
Router where station
Would go.
Connected by Routers
Path of a Packet is its Route
Single Network
Routers
Packet
Single Network
Route
34
Figure 1.11: An Internet
Single Networks Have Switches
Each single network
Is like Figure 1.2.
Switches, etc.
Router where station
Would go.
Switches Connect Station-to-Router or Router-to-Router
Network X
Switches
Network Y
Network Z
Routers
Switches
35
Figure 1.12: Frames and Packets

Packet goes from source host to destination
host across multiple networks
36
Figure 1.12: Frames and Packets

Within a single network, the packet is carried
in the data field of that network’s frame,
probably across multiple switches
Packet
Frame
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Figure 1.12: Frames and Packets

Router removes packet from source network’s frame,
sends back out in receiving network’s frame format
Same
Packet
Frame
Different Frame Format
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Figure 1.12: Frames and Packets

Router removes packet from source network’s frame,
sends back out in receiving network’s frame format
Same
Packet
3d Frame
Format
Different Frame Format
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Figure 1.12: Frames and Packets

Like passing a shipment (the packet) from a truck
(frame) to an airplane (frame) at an airport.
Shipper
Same
Shipment
Truck
Airport
Receiver
Airport
Truck
Airplane
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Figure 1.13: The Internet
Browser
The global Internet has
thousands of networks
Webserver
Software
Network
Packet
Router
Packet
Route
Router
Router
Packet
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Figure 1.13: The Internet
Browser
Webserver
Software
Network
Packet
Router
Packet
Route
Router
Router
Packet
User PC
(Host)
IP Address=128.150.50.9
Webserver
(Host)
IP Address=128.171.17.13
Host name=voyager.cba.hawaii.edu
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Hosts

All computers connected to the Internet are
hosts

Server hosts (webservers, FTP servers, etc.)

Also client PCs at home, at school, and at work

Also PDAs and Internet-enabled cellphones

The Internet treats all hosts of all sizes as equals

Only application software distinguishes between
them (browsers for client PCs, webserver
applications for server hosts, etc.)
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Figure 1.14: Host Addresses and Host
Names

Host IP Address

Official address of host on the Internet

Every host must have an IP address, including
client PCs and PDAs

32 bits long

Often expressed in dotted Decimal Notation for
human reading (e.g., 128.171.17.13)

Hosts and routers work with 32-bit binary form
IP Address: 128.171.17.13
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Key Point

It is important to emphasize that hosts and routers
never work with dotted decimal notation. They always
work in pure binary (ones and zeros). Dotted decimal
notation is a way for human beings to represent IP
addresses for their use. It is a concession to human
memory weaknesses.
1001000100111… (32 bits)
(Used by Hosts and Routers)
128.171.17.13
(Human use Only)
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Figure 1.13: The Internet
Browser
Webserver
Software
Network
Packet
Router
Packet
Route
Router
Router
Packet
User PC
(Host)
IP Address=128.150.50.9
Webserver
(Host)
IP Address=128.171.17.13
Host name=voyager.cba.hawaii.edu
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Figure 1.14: Host Addresses and Host
Names

Host Name

Several labels separated by dots
(voyager.cba.hawaii.edu)

Like nickname; easy to remember

Not the official address of the host
Host Name
Voyager.cba.hawaii.edu
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Figure 1.14: Host Addresses and Host
Names

Domain Name System (DNS)

You cannot send messages to a host if you only
know its host name

Must know its official address (IP Address)

DNS provides a way of finding a host’s IP address if
only its host name is known
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Figure 1.15: Domain Name System (DNS)
Host
DNS Request Message
“The host name is Voyager.cba.hawaii.edu”
Originating
Host’s
DNS Resolver
DNS
Host
49
Figure 1.15: Domain Name System (DNS)
Host
DNS Table
Host Name
IP Address
…
…
…
…
Voyager.cba.hawaii.edu
128.171.17.13
…
…
Originating
Host
DNS Response Message
“The IP address is 128.171.17.13”
DNS
Host
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Figure 1.16: Internet Service Providers
(ISPs) and Internet Backbone Carriers
Webserver
User PC
Internet Backbone
(Multiple Carriers)
Router
ISP
ISP
Internet
Service Provider
Internet
Service Provider
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Internet Service Providers (ISPs)

Connect you to the rest of the Internet

Collect money from you to pay for their own
operation and to pay backbone carriers to
carry traffic

The Internet is almost entirely commercial
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Figure 1.17: The Internet, Intranets, and
Extranets

Defined by Communities Served

The Internet

Goal is universal community; include everyone
53
Figure 1.17: The Internet, Intranets, and
Extranets

Defined by Communities Served

Intranets

Community is a single (possibly multi-site)
organization

Use Internet transmission standards (see
Chapter 2) and applications

Controlled communication with the outside world
via firewalls
54
Figure 1.17: The Internet, Intranets, and
Extranets

Extranets

Community is a group of sellers and purchasers

Only some hosts within each company are included

Single seller with multiple buyers, or

Single buyer with multiple sellers, or

Marketplace with multiple buyers and sellers
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Security

A large and growing concern

Attacks are roughly doubling each year

Attacks are becoming more damaging when
they occur ($1 US billion per major virus
outbreak)

Companies and nations now face the prospect
of far more destructive cyberwar and
cyberterrorism
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Figure 1.18: Firewall to Pass or Deny
Messages
Deny an Attack Packet
1. Deny
Intranet
Server
Packet
Attacker
Internet
Internet
Firewall
Intranet
Client
Public
Webserver
Intranet
Client
Corporate Network
57
Figure 1.18: Firewall to Pass or Deny
Messages
Pass a
Legitimate Packet
Attacker
Intranet
Server
2. Pass
Internet
Internet
Firewall
Intranet
Client
Packet
Public
Webserver
Intranet
Client
Corporate Network
58
Figure 1.18: Firewall to Pass or Deny
Messages
Permit a Legitimate
Outgoing Packet
Attacker
Intranet
Server
Internet
Packet
Internet
Firewall
3. Pass
Intranet
Client
Public
Webserver
Intranet
Client
Corporate Network
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