Transcript Network services - The University of Vermont

Lecture 1
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An Introduction to Networking
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Chapter 1, pages 1-22
Dave Novak
BSAD 146, Introduction to Networking
School of Business Administration
University of Vermont
Sources: 1) Dean (2012), Network+ Guide to Networks, 6th Edition
Lecture Overview
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Brief introduction to networking
Network Services
LAN versus WAN
Types of architectures
Applications and programs
Signals, protocols, and standards
Internet and the WWW
URL
Intro to Networking
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Although networks are widely used, few
people understand basic networking
technologies and terminology
If you have any type of tech-related job,
your employer will likely expect you to
possess some basic understanding of
computer / data networks
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How computer networks work
Basic terminology
Intro to Networking
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Growth in networking
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20 years ago relatively few people had easy
or “high speed” access to a data network
from their desktop computer (at work or at
home)
Now it is hard to imagine not having
reasonably “high quality” access to a network
– even when we travel
What types of things brought about this
growth?
Computer / Data Networks
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A collection of computers and other
networking devices that are connected by
some type of telecommunications media
Motivation behind Networking
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What was the initial motivation behind
computer networking and how has this
changed over the past several decades?
Network Services
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Network services (in general) are the
specific functions/tasks/jobs provided by
the network
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File sharing
Printing
Communication
Mail
Internet
Management
Common Network Services
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File and print services
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Allow sharing of data files and printers
Communications services
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Such as mail services
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Internet services
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WWW, FTP, some security
Access services
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Allow remote users to connect to network
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Coordination and storage of email
Login (authorization / authentication)
Network Management Services
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Traffic monitoring, load balancing, diagnostics
3 General Categories of Networks
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We are focusing on the first two:
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1) Local Area Network (LAN)
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2) Wide Area Network (WAN)
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3) Metropolitan Area Network (MAN)
LAN versus WAN
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A LAN is a group of computers located in a
relatively small geographical area (like a
building or group of buildings)
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Typically owned by a single organization
A WAN is used to connect host computers
and sites (including other LANs) across a
wide geographic area
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Collective, distributed ownership consisting of
multiple organizations
LAN versus WAN
Data transfer
rate
Network
technology
LAN
WAN
High speed(≥ 1000 mbps)
Lower speed (≤ 155 mbps)
Tend to primarily use Ethernet and
WiFi, but also use Token Passing
WANs tend to use technology like MPLS and
ATM, and to a lesser extent (Frame Relay &
X.25) for connectivity over the longer
distances
Components
Generally consist of layer 2 devices like
switches, bridges. To a lesser extent
layer1 devices like hubs & repeaters
Layer 3 (+) devices such as routers, multilayer switches and technology specific devices
like ATM or Frame-relay Switches etc.
Fault
tolerance
LANs tend to have fewer problems
associated with them, as there are a
smaller number of systems to deal
with.
WANs tend to be less fault tolerant. as they
consist of a many different systems managed
by different organizations. There is a lower
amount of fault tolerance.
Typically owned, controlled, and
managed by a single organization
WANs are typically not owned by any one
organization but exist under collective or
distributed ownership and management over
long distances
Ownership
Costs
Low
High
Local Area Network
PC
PC
PC
Switch
PC
?
Printer
Wide Area Networks
leased lines from a larger provider
form part of the WAN
Some type of “shared” media
Architecture
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Networked computers interact with each
other in different ways
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Computers may have different roles on a
network
We refer to the ways in which computers
interact with one another on the network and
the organizational relationship between the
computers as the Logical Architecture
A word of caution: you will hear “architecture” used in place of “topology” quite frequently.
Also, there is not always a clear distinction between the two because modern software can
do so much! For this class we will try to keep the terms distinct.
Topology versus Architecture
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Architecture - specifies how functions are
laid out between the various devices on the
network which is independent of the
networking technologies being used
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How do the devices on the network interact?
Is there a designated “server”?
What is the server’s responsibility?
What is the client’s responsibility?
Topology – the physical arrangement of the
devices on the network which is affected by
the networking technologies being used
Architecture
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3 primary logical architectures (the book just
refers to these as “types” of networks)
1.
2.
3.
Host-based
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Traditional mainframe / central computer model
Client-based / Peer-to-Peer
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Historically most home-based and many small
office networks
Client-server
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Microsoft model – or what we commonly see
today
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Fairly powerful clients interacting with some
number of servers
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Model used on campus
Four major device functions
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Data storage
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Data access logic
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Where software that interacts with the data
source is located
Application logic
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Where data are stored
Where application that performs data processing is
located
Presentation logic (GUI)
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How information and data are displayed to the
user
Host-based architecture
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Host computer or server performs most
functions
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Mainframe system
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Dumb terminals
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Very large, powerful “central” computer
The clients (terminals) themselves have little or no
processing power, they just provide a user
interface to the server
Client sends keystrokes and then accepts
output
Host-based architecture
Server
Data storage
Data access logic
Application logic
Client
Presentation logic
Dumb terminals –
basically provide a
screen and keyboard
No local
processing or storage
Peer-to-Peer (P2P) Architecture
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Distributed architecture where individual
PCs have symmetric roles and can
function as client and/or server
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Ad-hoc (no hierarchy)
No centralized management or control
Highly autonomous
At the WAN level, may aggregate large
numbers of computers that may join or
leave the network on a frequent basis and
may not use permanent IP addresses
P2P architecture
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All 4 functions are responsibility of individual
computers / nodes that partition various tasks
among the peers
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P2P architectures are growing in popularity with
respect to some services
Individuals manage their own computer and “share”
resources
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Security
File sharing
Backup
No centralized server-based name resolution
or authentication
P2P architecture
Client
Data storage
Data access logic
Application logic
Presentation logic
all reside on individual
peers or nodes
Client / Server (CS)
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CS model distinguishes between client /
server devices and applications
Clients request specific services
Servers respond to individual client
requests for services
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Functionality implemented in software
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Depending on services the server provides,
physical server computers can be different than
other servers and client computers (i.e. more
processing power, more memory, etc)
Client/Server architecture
Also see Fig 1-3 from book
Client/Server (CS) architecture
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Structured architecture with specific roles
for specific devices using specific
applications
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A “managed” network
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File server, printer server
Unlike P2P will have a network admin
CS is the most commonly observed
architecture
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Most applications are designed to be used on
CS architecture
CS architecture
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Balance processing between clients and
server(s) by dividing functions
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Client – presentation and application logic
Server – Data access logic, data storage,
application logic
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Why do this?
Multi-Tier CS architecture
Application versus Program
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Program – set of instructions executed
on a computer
Application – software that directly
helps users perform specific tasks
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All applications are programs but the reverse is not
true
If it has a user interface, its generally considered an
application
Software drivers are programs
Admin tools with nice GUIs are considered to be
utility applications
Applications versus Services
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File transfer protocol (FTP)
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Protocol that provides file transfer services
between 2 or more computers over a
network
WS_FTP is an application (program with GUI
written specifically to provide FTP functions
to the end user)
Applications versus Services
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Simple Mail Transfer Protocol (SMTP)
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Internet-based protocol for email
transmission over IP networks (a mail
service)
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Email servers typically use SMTP for exchange
Microsoft Outlook is a personal information
management application (calendar, task
manager, contact manager, and email)
which provides mail services using SMTP
Signals
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Much of what occurs in the networking
process does not concern the nature of
the data passing over the network media
The lower layers of the OSI model (the
network transmission functionality, layers
1-4) don’t know about or care about the
type of data that are being transmitted
Signals
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When data are transferred from one
device to another, the data are reduced
to signals (digital or analog)
These signals must be compatible with
the transmission channels associated
with the specific medium being used
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Electrical voltage via copper cable
Pulses of light via fiber optic cable
Radio waves via WiFi
Protocols
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A communications network could consist
of identical devices all running the same
system software and using the same
application software
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OR more likely…
A variety of devices using different
hardware components, made by different
vendors, with different system software,
running a wide variety of different
applications using different data formats
Protocols
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For a modern data/communications
network to function in a way that most
organizations consider to be acceptable:
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All devices on the network MUST be able to
understand each other regardless of the
hardware, manufacturer, system software,
and applications being used
While we may take this for granted, it is
actually quite an amazing feat…
Protocols
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Protocol – set of rules used to
communicate
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Devices use MANY protocols even during
simple data exchanges
Protocols provide format, structure, and
meaning to messages
Protocols specify how communication occurs
and the form it takes
Protocols
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Enable communication between
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Different network devices
Different hardware components within a
single device
Different software components within a
single device
Hardware and software within the device
Protocols
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Some of the things protocols do:
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Packet acknowledgment – transmission of a
return message by the recipient verifying receipt of
a packet
Segmentation – division of a stream of data into
segments suitable for transmission of a LAN
Flow control – balancing the rate at which the
sending computer transmits compared to the rate at
which the receiving computer accepts data
Error detection – special codes in a packet that
are used to verify that the content of a packet was
not damaged
Data compression – reducing the amount of data
transmitted by eliminating redundant information
A Protocol Stack
When the transmitting computer generates
a packet / message, it is passed down from the
application to the topmost layer of the OSI
model and then subsequently passed down to
the lower layers one by one
The protocols at each layer perform specific
services or functions before passing the message
down to the next layer
Protocol Interaction
Functions performed at a
particular layer of the OSI
model at the sending
computer are also performed
(or undone) at the
corresponding layer of the
receiving computer
Protocols and standards
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Protocols are typically based on public
standards developed by an independent
committee - not on standards developed
by a single manufacturer
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What are standards and why are they
important in networking (or for technology use
in general)?
Protocols and standards
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Standards are needed because there are
many different manufactures making
similar (but not identical) products and/or
different products that provide similar or
identical services and there is a need to
have some baseline for interoperability and
technical guidelines
How does one ensure that both a Dell and
Apple computer can both work on a
network with Cisco and IBM components?
Segments and Backbones
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As a network grows, it is possible to
begin connect devices and LANs together
in a haphazard manner – this is NOT a
good thing
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Common to connect a number of segment
LANs together using a backbone LAN
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Segment LAN
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Backbone LAN
Backbone Network
The backbone LAN
consists of the three
routers and their media
The segments consist of
five PCs connected to
hubs at each floor
It is more common to see
switches used on this
particular LAN design than
routers
This would represent a
modern switched Ethernet
design
The Internet
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The Internet is a global WAN
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A very large WAN that spans the globe
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Connects many smaller WANs and MANs each of
which, in turn, connect many LANs
The Internet includes the SBA LAN (the
physical computer network that exists in this
building)
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SBA has some type of connection to the larger
UVM network, which has some connection to the
“outside” leased from some long distance carrier
History of the Internet
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U.S. Department of Defense Advanced
Research Projects Agency (DARPA)
pioneered research that led to the
modern Internet – ARPANET 1970s
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Nuclear attack by former Warsaw Pact
members, when central command and
control structures are taken out, data
communications can still occur via packetswitched routing systems
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When links and nodes are destroyed, packets
will re-route to other links and nodes
World Wide Web (WWW)
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World Wide Web (WWW)
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WWW is NOT synonymous with the Internet
You (as a client) are typically exposed to the Web
via a graphical browser such as IE or Firefox
Web browsers allow one to “open” a Uniform
Resource Locator (URL). The URL provides
information about the location of things on the
Web. For example http://www.bsad.uvm.edu
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When this hypertext link is clicked, we are actually
retrieving a file that is stored on another computer that is
located in the SBA building
The URL is local, what happens if we click on
http://www.microsoft.com/ms.htm ?
World Wide Web (WWW)
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WWW continued…
A URL is an address to another computer on a
communication network. It consists of 3 parts
method://host/path
Method (or protocol) indicates how information
should be retrieved. Examples: ftp, gopher, http
Host specifies the computer or group to access
Path specifies the directory and file to read
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Example: course Web site breakdown
http://www.uvm.edu/~dnovak/bsad146.html
Internet –vs- WWW (general)
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The internet is a proper name that
describes a specific network – the one and
only global network that connects most
other networks around the world
An internetwork is a generic term that
describes some arbitrary collection of
networks that are interconnected via routers
and operate as one
WWW can be viewed as a technology
because it involves devices communicating
specifically using HTTP
Summary
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Brief introduction to networking
Network Services
LAN versus WAN
Types of architectures
Applications and programs
Signals, protocols, and standards
Internet and the WWW
URL