Transcript An Introduction to Networking

Networking
• A computer network is a collection of
computing devices that are connected
in various ways in order to
communicate and share resources.
• The generic term node or host refers
to any device on a network.
1
Networking
• One of the guiding principles of network
design is “demand access” which is
implemented as the client/server model
2
Networking Clients
• Client software runs on a user’s
computer and sends requests to servers
for information.
• Some example client programs are:
– Browsers
– Mailers
– Fetch, WS-FTP
3
Networking Servers
• A file server is a computer that stores
and manages files for multiple users on
a network.
• A Web server is a computer dedicated
to responding to requests for Web
pages.
• A mail server is a computer dedicated
to sending/receiving email.
4
Packet Switching
• To improve the efficiency of transferring information
over a shared communication line, messages are
divided into fixed-sized, numbered packets.
• Network devices called routers are used to direct
packets between networks.
Messages
sent by
packet
switching
Types of Networks
• A local-area network (LAN) connects
a relatively small number of machines in
a relatively close geographical area.
• Recently, the term metropolitan-area
network (MAN) has been adopted to
refer to the communication
infrastructures that have been
developed in and around large cities.
6
Types of Networks
• A wide-area network (WAN) connects two
or more local-area networks over a potentially
large geographic distance.
– Often one particular node on a LAN is set up to
serve as a gateway to handle all communication
going between that LAN and other networks.
• Communication between networks is called
internetworking.
– The Internet, as we know it today, is essentially
the ultimate wide-area network, spanning the
entire globe.
7
Internetworking
Local-area networks connected across a distance to create a wide-area network
8
Internet Connections
• The Internet backbone is a term used to
refer to a set of high-speed networks that
carry Internet traffic.
• These networks are provided by companies
such as AT&T, GTE, and IBM.
• An Internet service provider (ISP) is a
company that provides other companies or
individuals with access to the Internet.
9
Internet Backbone
10
Regional Backbone
11
Internet Connections
• There are various technologies available that you can
use to connect a home computer to the Internet.
– A phone modem converts computer data into an analog
audio signal for transfer over a telephone line, and then a
modem at the destination converts it back again into
data.
– A digital subscriber line (DSL) uses regular copper
phone lines to transfer digital data to and from the phone
company’s central office.
– Cable modem—in this approach, the data is transferred
on the same line that carries your cable TV signals.
12
Internet Connections
• A key issue related to computer networks is
the data transfer rate, the speed with
which data is moved from one place on a
network to another.
• Both DSL connections and cable modems are
broadband connections, which generally
mean speeds faster than 128 bits per second.
13
LAN Connections
• Usually, the connections between
computers in a network are made using
physical wires or cables.
• However, some connections are
wireless, using radio waves or infrared
signals.
14
Open Systems
• As network technologies grew, the need for
interoperability became clear.
• We needed a way for computing systems
made by different vendors to communicate.
• An open system is one based on a common
model of network architecture and a suite of
protocols used in its implementation.
15
Network Protocols
• Network protocols were developed
using a layered approach in which each
layer relies on the protocols that
underlie it.
• This is called a protocol stack.
Layering of key network protocols
16
Protocol Layers
•
•
•
•
Application Layer
Transport Layer
Network Layer
Link Layer
17
Protocol Layers
Application
Layer
Application
Layer
Application
Layer
Transport
Layer
Transport
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Link Layer
Link Layer
Link Layer
18
Application Layer
• Consists of software units that communicate with
each other across the Internet.
• Examples of these “high-level” protocols include:
–
–
–
–
–
SMTP
POP3
telnet
FTP
http
• Passes complete message to the Transport Layer
19
Transport Layer
• Receives complete messages from the Application
layer
• Divides the message into packets
• Adds a sequence number to each packet
• Attaches the destination address to each packet
• Passes the packets to the Network Layer
• Examples include:
– TCP - Transmission Control Protocol
– UDP - User Datagram Protocol
20
Network Layer
• Receives addressed packets from the Transport Layer
• Adds an intermediate address
– If the destination is within the current net, the intermediate
and destination addresses are the same.
– Otherwise, the intermediate address is for a router in the
current net, which will pass the packet to an adjacent net.
• Passes the packet to the Link Layer
• IP - Internet Protocol
21
Link Layer
• Deals with the details of the particular
LAN.
– A ring topology connects all nodes in a closed
loop on which messages travel in one direction.
– A star topology centers around one node to
which all others are connected and through which
all messages are sent.
– In a bus topology, all nodes are connected to a
single communication line that carries messages in
both directions.
22
LAN Topologies
Various network topologies
Transmission Privileges
• Rings use tokens.
• Stars use polling.
• A bus uses CSMA/CD.
– Ethernet has become the standard.
24
Network Addresses
• A hostname is a unique identification
that specifies a particular computer on
the Internet.
• For example:
www.cse.yorku.ca
25
Network Addresses
• The Transport Layer translates a
hostname into its corresponding IP
address.
• For example:
130.63.236.200
26
Domain Name System
• A hostname consists of several parts.
• The very last section of the domain is
called its top-level domain (TLD)
name.
• Recall the example above:
www.cse.yorku.ca
“ca” is the TLD
27
Domain Name System
• Some common examples of TLDs:
Top-level domains, including some relatively new ones
28
Domain Name System
• Organizations based in
countries other than the
United States use a toplevel domain that
corresponds to their
two-letter country
codes.
Some of the top-level domain
names based on country codes
29
Domain Name System
• A domain name may be further separated
into sections that specify the organization,
and possibly a subset of an organization
(subdomain)
In the example above:
“yorku” is the domain
“cse” is the subdomain
“www” names the computer
30
Domain Name System
• The domain name system (DNS) is chiefly
used to translate hostnames into numeric IP
addresses.
– DNS is an example of a distributed database.
– If a server can resolve the hostname, it does so.
– If not, that server asks another domain name
server.
31
URLs
• A hostname is the core part of a
Uniform Resource Locator, or URL,
which uniquely identifies the page you
want out of all of the pages stored
anywhere in the world.
32
URLs
• The four parts of a URL are:
– protocol
– hostname
– path
– filename
• http://www.yorku.ca/yorkweb/index.htm
33
URLs
• The protocol specified in a URL determines
the type of connection that will be made.
• There are several possible. For example:
–
–
–
–
–
ftp
http
pop3
smtp
telnet
34
The World Wide Web
• The Web is an infrastructure of
distributed information combined with
software that uses networks as a
vehicle to exchange that information.
• http is the protocol used to transfer all
Web pages.
35