Transcript Networking Protocols and the OSI Model

Networking Protocols and the OSI
Model
OSI Model Overview
• The Open Systems
Interconnection (OSI)
reference model is an
industry standard
framework that is used to
divide the functions of
networking into seven
distinct layers.
• Each layer provides
specific services to the
layers above and below it
in order for the network to
work effectively.
OSI Model Overview
• A message begins at the top
application layer and moves
down the OSI layers to the
bottom physical layer.
• As the message descends,
each successive OSI model
layer adds a header to it.
• A header is layer-specific
information that basically
explains what functions the
layer carried out.
• Conversely, at the receiving
end, headers are striped from
the message as it travels up the
corresponding layers.
What is a Protocol?
• Protocol is a controlled
sequence of messages that
is exchanged between two
or more systems to
accomplish a given task.
• Protocol specifications
define this sequence
together with the format or
layout of the messages that
are exchanged.
Transmission Control
Protocol/Internet Protocol
• The Transmission Control
Protocol/Internet Protocol
(TCP/IP) suite of protocols
has become the dominant
standard for internetworking.
• TCP/IP represents a set of
public standards that
specify how packets of
information are
exchanged between
computers over one or
more networks.
Transmission Control
Protocol/Internet Protocol
Internetwork Packet
Exchange/Sequenced Packet
Exchange
• Internetwork Packet
Exchange/Sequenced
Packet Exchange
(IPX/SPX) is the
protocol suite employed
originally by Novell®.
• It delivers functions
similar to those included
in TCP/IP.
NetBEUI
• NetBIOS Extended User Interface (NetBEUI) is a
protocol used primarily on small Windows NT
networks.
• NetBEUI is a simple protocol that lacks many of the
features that enable protocol suites such as TCP/IP
to be used on networks of almost any size.
AppleTalk
• AppleTalk is comprised of
a e set of protocols that
span the seven layers of
the OSI reference model.
• AppleTalk protocols were
designed to run over the
major LAN types, notably
Ethernet and Token Ring,
and also Apple's own
LAN physical topology,
LocalTalk.
TCP/IP Utilities
Overview
• TCP/IP is a complex
collection of protocols.
• Most vendors implement
the suite to include a variety
of utilities for viewing
configuration information
and troubleshooting
problems.
Ping
• Ping works by sending an ICMP echo request to the
destination computer.
• The receiving computer then sends back an ICMP
echo reply message
• It is also possible to use Ping to find the IP address of
a host when the name is known.
ARP, RARP, NSLOOKUP
• Address Resolution Protocol
(ARP) is the means by which
networked computers map
Internet Protocol (IP)
addresses to physical
hardware (MAC) addresses
that are recognized in a local
network.
• Machines that do not know
their IP addresses use
Reverse Address Resolution
Protocol (RARP).
• It is used to obtain IP address
information based on the
physical or MAC address.
ARP, RARP, NSLOOKUP
• Nslookup returns the IP address for a given
hostname.
• It will also do the reverse and find the host name
for a specified IP address.
Netstat/tpcon
• The netstat command is used in Windows and
UNIX/Linux to display TCP/IP connection and protocol
information.
• The netstat command provides a list of connections
that are currently active.
• Netstat statistics can be useful in troubleshooting
TCP/IP connectivity problems.
Nbtstat
• The Microsoft TCP/IP
stacks included in
Windows operating
systems provide the
nbtstat utility, which is
used to display NetBIOS
information.
Ipconfig, winipcfg, config, and
ifconfig
• TCP/IP configuration
information can be
displayed using different
utilities
• Ipconfig – Windows NT
and Windows 2000
(command-line)
• Winipcfg –- Windows 95,
98, and ME (graphical
interface)
• Ifconfig – UNIX and Linux
(command-line
Tracert, iptrace, and traceroute
• It is often useful to trace the
route a packet takes on its
journey from source
computer to destination
host.
• TCP/IP stacks include a
route tracing utility that
enables users to identify the
routers through which the
message passes.
• The options depend on the
operating system:
– Tracert
– Iptrace
– Traceroute
Connecting to the Internet
Synchronous and Asynchronous
Serial• lines
Synchronous serial
transmission – Data bits are
sent together with a
synchronizing clock pulse. Builtin timing mechanism
coordinates the clocks of the
sending and receiving devices.
• Asynchronous serial
transmission – Data bits are
sent without a synchronizing
clock pulse. Uses a start bit at
the beginning of each message.
When the receiving device gets
the start bit, it can synchronize
its internal clock with the sender
clock.
Modems
• The modem is an electronic
device that is used for
computer communications
through telephone lines.
• It allows data transfer
between one computer and
another.
• There are four main types
of modems:
–
–
–
–
Expansion cards
PCMCIA
External modems
Built-in modems
Dial-Up Networking,
Modem Standards, AT Commands
• When computers use the
public telephone system or
network to communicate, it is
called Dial-Up Networking
(DUN).
• All modems require software to
control the communication
session.
• The set of commands that
most modem software uses
are known as the Hayescompatible command set. The
Hayes command set is based
on a group of instructions that
always begins with a set of
attention characters (AT).
ISPs and Internet Backbone
Providers
• Services of an Internet Service Provider (ISP) are
required to surf the Internet.
• An ISP is a company that connects computers to
the Internet and World Wide Web.
• The actual connection to the Internet is tiered.
• The ISP may link to a larger regional ISP, which in
turn might connect to one of a number of
nationwide computer centers.
ISPs and Internet Backbone
Providers
• The current U.S. Internet
infrastructure consists of a
commercial backbone and a
high-speed service known as
the Very High-Speed Backbone
Network Service (vBNS).
• The vBNS connects five
supercomputer networks across
the country:
– UUNET - a division of
WorldCom
– Cable & Wireless USA
– Sprint
– AT&T
– BBN Planet
ISPs and Internet Backbone
Providers
• The ISP that cannot connect
directly to the national
backbone is charged a fee to
connect to a regional
provider that links to the
national backbone through a
Network Access Point (NAP).
• Not all the Internet traffic
goes through NAPs.
• Some ISPs that are in the
same geographic area make
their own interconnections
and peering agreements.
Digital Subscriber Line (DSL)
• Digital Subscriber Line (DSL) is an always-on
technology. This means there is no need to dial up
each time to connect to the Internet.
• DSL comes in several varieties:
–
–
–
–
Asymmetric DSL (ADSL)
High Data Rate DSL (HDSL)
Symmetric DSL (SDSL)
Very High Data Rate DSL (VDSL)
Cable Modems
• A cable modem acts like a
LAN interface by connecting
a computer to the Internet.
• The cable modem connects
a computer to the cable
company network through
the same coaxial cabling
that feeds cable TV (CATV)
signals to a television set.
Cable Modem versus
DSL Internet Technologies
• When it comes to
comparing cable modem
and DSL Internet
technologies, both have
their pros and cons.
ISDN
• Another alternative to using
analog telephones lines to
establish a connection is ISDN.
• Speed is one advantage ISDN
has over telephone line
connections.
• ISDN uses a pair of 64Kbps
digital lines to connect, which
provides a total of 128Kbps
throughput.
• A telephone line connects at a
maximum speed of 56Kbps, and
in some areas, doesn’t even
reach that.
Satellite
• Satellite is an option for users in
rural areas or with no other
access to high speed Internet
service.
• Satellite Internet does not require
a phone line or cable. Two-way
communication, for upload and
download, is achieved with the
use of a satellite dish.
• Download speed is up to 500
kbps while the upload speed is
one-tenth of that of that.