ITI 510 Computer Networks

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ITI
-
510

Computer
Networks


ITI 510


Computer Networks

Meeting 1

Rutgers University Internet Institute

Instructor: Chris Uriarte


ITI
-
510

Computer
Networks


Welcome…

ITI
-
510 Computer Networks

Section 14

Instructor: Chris Uriarte (
chris@cju.com
)


Six Meetings, Tuesday 6:10
-
9pm

Starting November 8, 2000


ITI
-
510

Computer
Networks


About The Course…


For Who?


Anyone who has an interest in, or wants to explore,
computer networks.


Pre
-
requisites:


Basic knowledge of computers. User
-
level UNIX
and/or PC administration experience can help,
but is not required.


Use of Internet technologies like web and email.


ITI
-
510

Computer
Networks


What We Explore…


The concepts and theories behind computer
networking.


Network architectures


Network protocols and “packet
-
level” analysis


How network protocols and applications are
used in the “real world”


Introduction to network hardware components


Basic concepts in network troubleshooting and
support


Trends in computer networks today


ITI
-
510

Computer
Networks


Specific Topics…


OSI Model, network layers, Internet Protocol,
Transmission Control Protocol, Link Layer Protocols,
the Internet.


ARP, RAPR, ICMP, IP Routing, CIDR, networking
utilities, Routing algorithms and Protocols like
RIPv1/2, OSPF, BGP, etc.


TCP, UDP, TCP/IP and packet delivery


Application layers: DNS, FTP, HTTP, NNTP, SMTP,
SNMP


Multicast technologies and tools, MBONE


Security, MAC Protocols, Advanced topics


Operating system specifics, Microsoft NetBIOS


Overview of networking hardware


ITI
-
510

Computer
Networks


How we learn…


Lectures


Slides


Internet Resources


Book:
TCP/IP, Signature Edition

by Sidnie
Feit (1999, McGraw Hill)


Websites:

Official:

http://iti.rutgers.edu/II/ITI510

(username/pw: guest/guest)

Un
-
official:

http://www.cju.com/classes/ITI510
-
13


Hands on exercises


By asking lots of questions….


ITI
-
510

Computer
Networks


Instructor


Christopher Uriarte


Email: chris@cju.com



Full contact information available at:

http://www.red
-
usa.com/staff/chris/



Call or email anytime



ITI
-
510

Computer
Networks


Agenda: Meeting 1


Introduction to networks


Network devices


high level overview


LAN vs. WAN


OSI


Packet Overview


IP


The Internet Protocol



A few small Exercises

ITI
-
510

Computer
Networks


What is a computer network?


Formal Definition: Computer Network


A series of
points

or
nodes

interconnected

by communication paths. Networks can
interconnect with other networks and contain
subnetworks.


Simple Definition: Computer Network


Connecting computers and/or devices in such a
way that they can interact with each other.


ITI
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510

Computer
Networks


Characterizing Networks


Sometimes characterized by
Topology


i.e. bus, star or ring network


…by
Spatial Distance


Wide Area Network, Local Area Network


…by Type of
Data Transmission

or what it
carries


IP Network, Voice Network, Data Network


…by Type of
Physical Link


Fiber Optic Network, Ethernet Network,

ITI
-
510

Computer
Networks


Network Topology


In the context of communication
networks, a topology pictorially describes
the configuration or arrangement of a
network, including its nodes and
connecting lines.


Three general network topologies:


Bus


Star


Ring

ITI
-
510

Computer
Networks


Bus Networks


A
bus network

is a network topology in
which all devices are directly attached to a
line and all signals pass through each of
the devices. Each device has a unique
identity and can recognize those signals
intended for it.


“Single String” of network wire


Antiquated technologies such as 10Base2
are considered a bus network.


ITI
-
510

Computer
Networks


Examples of Bus Networks


A single wire or a group of small wires is
used to create one data path that all traffic
flows through.


2 simple examples:

ITI
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510

Computer
Networks


Bus Networks: Advantages and
Disadvantages


Disadvantages:


If one single point in the network is severed,
hosts may experience connectivity loss


Possible bandwidth constraints

ITI
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510

Computer
Networks


Ring Networks


Each device is attached along the same
signal path to
two

other devices, forming
a path in the shape of a ring.


Each device in the ring has a unique
address.


Information usually flows in one direction
and there is usually a controlling device
that intercepts and manages the flow to
and from the ring.


Popular ring network technologies are
Token Ring and FDDI


ITI
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510

Computer
Networks


Examples of Ring Networks


Simple Example of a Ring Network:

ITI
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510

Computer
Networks


Ring Networks: Advantages and
Disadvantages


Advantages:


If a single point of the physical cable is
detached, traffic can begin to flow in an the
opposite direction


no loss of connectivity.


Disadvantages:


Possible bandwidth constraints


one single pipe
for all traffic


In most cases, every computer sees every bit of
traffic across the ring

ITI
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510

Computer
Networks


Star Topology


Each device has a unique path to a central
point that distributes data


Each device “hangs” off of a piece of
hardware, such as a
hub

or a
switch


Very popular today: Traditional 10BaseT,
100BaseT Ethernet networks use this
topology.

ITI
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510

Computer
Networks


Example of Star Networks



ITI
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510

Computer
Networks


Advantages of Star Networks


A single cable break will usually only
disrupt service for a single host within a
local network segment.


Newer technologies allow you to dedicated
and guarantee high bandwidth rates for
each individual host or network hanging
off of a central switch.


The ability to eliminate packet broadcasts


every computers does not have to see
every packet on the network.

ITI
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510

Computer
Networks


Where Networks are Going…


10 Years ago: The 80/20 Rule


80% of all traffic stays on the LOCAL network
and only 20% of traffic is sent off to other
networks or to the network “backbone”


Typically describes the “workgroup” model of
computing: access devices on your local
network like file servers, printers, other
workstations.


Today: The 20/80 Rule


20% or all traffic stays on the LOCAL network
and 80% of traffic is sent to other networks or
the network backbone.


Cause by the Increased use of WAN
technologies and distributed computing models.



ITI
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510

Computer
Networks


LAN vs. WAN


Local Area Networks (LANs): a group of computers
and associated devices that share a common
communications line and typically share the
resources of a single processor or server within a
small geographic area like an office building.
Usually privately
-
owned.


Wide Area Networks (WANs): a geographically
dispersed network. It may be privately owned or
rented, but the term usually connotes the inclusion
of public (shared user) networks like the Internet
or the PSTN (Public Switched Telephone Network)


We may use different network technologies,
protocols, hardware, etc. to connect devices within
a WAN than we use when connecting devices in a
LAN.

ITI
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510

Computer
Networks


The OSI Model


OSI (Open Systems Interconnection) is a
standard description or "reference model"
for how messages should be transmitted
between any two points in a
telecommunication network.


Its purpose is to guide product
implementers so that their products will
consistently work with other products.


Developed by representatives of major
computer and telecommunication
companies in 1983


now a standard way
of examining computer network
technologies.



ITI
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510

Computer
Networks


The OSI 7 Layer Model


The general OSI model contains 7 layers
(layers 1
-
7 respectively):


Physical


Data Link


Network


Transport


Session


Presentation


Application


Each layer has a specific function


ITI
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510

Computer
Networks


Depiction of the 7 Layer Model


Layer 7 (Application) is a “high layer”


Layer 1 (Physical is a low layer)


APPLICATION

PRESENTATION

SESSION

TRANSPORT

NETWORK

DATALINK

PHYSICAL

Netscape, Outlook, FTP
Programs, Internet Explorer

HTTP, POP, SMTP

Application ports 25 (SMTP),
23 (Telnet) etc.

TCP, UDP

IP

Cables, ASDL, POTS, CAT5,
FDDI, etc.

SLIP, PPP, Ethernet

ITI
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510

Computer
Networks


TCP/IP 5 Layer Model


TCP/IP, a very popular protocol used in
LANs, WANs and the Internet, usually
groups the 7
-
layer model’s Application,
Presentation and Session layers into one
“Application” layer, resulting in a 5 layer
model.




APPLICATION

TRANSPORT

NETWORK

DATALINK

PHYSICAL

Web Services, Email
Services, News Services,
etc.

TCP, UDP

IP

Cables, ASDL, POTS, CAT5,
FDDI, etc.

SLIP, PPP, Ethernet

ITI
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510

Computer
Networks


Description of the 5 Main OSI
Layers (5 Layer Model)


Layer 5: The application layer
...This is the layer
at which communication partners are identified,
quality of service is identified, user authentication
and privacy are considered, and any constraints on
data syntax are identified. (e.g. Funcationality
provided by web browsers, mail reader programs
and their associated protocols like HTTP and SMTP)


Layer 4: The transport layer
...This layer
manages the end
-
to
-
end control and error
-
checking of network traffic. It checks to see if all
packets have arrived and ensures complete data
transfer between parties. (e.g. TCP and UDP
protcols)


ITI
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510

Computer
Networks


OSI Layers, con’t.


Layer 3: The network layer
...This layer handles
the routing of outgoing data (making sure that a
packet is sent to the right place) and also handles
incoming data. (e.g. IP)


Layer 2: The data
-
link layer
... This layer defines
the rules for sending and receiving data across the
physical connection between two systems. (e.g.
Ethernet, PPP, SLIP)


Layer 1: The physical layer
... This layer governs
hardware connections and byte preparation for
transmissions. It is the only layer that involves a
physical transfer of information between network
nodes. It’s usually responsible for translating
electrical impulses into 1s and 0s.



ITI
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510

Computer
Networks


Sending and Receiving Data


Layers only interact with other layers
directly above and below them.


When data is sent, it originates at the
application layer and moves “down” the
OSI layers until it is transmitted to
another host.


When data arrives, it originates at the
physical layer and moves up the OSI
model until it’s received by the application
layer.

ITI
-
510

Computer
Networks


Typical Flow From Layer to
Layer: Sending Data



APPLICATION


TRANSPORT


NETWORK


DATALINK


PHYSICAL

You use MS Outlook to send an
email to your friend,
friend@hotmail.com
. The Email
“packets” are sent to the Transport
Layer

The transport layer takes the email
and packages it in a format that
ensures it will be completely
delivered.

The Network layer makes sure the
email knows how to get to the
hotmail.com server

The physical layer creates the
necessary electrical impulses and
trasmits the data over the physical
medium.

The DLL converts the information
from the layers above into 1s and
0s that can be understood by a
“peer” on the other end of the
phone line or network connection
(e.g. your ISP’s modem?)

Email Sent

Move from Top to Bottom

ITI
-
510

Computer
Networks


Typical Flow from Layer to Layer:
Receiving Data





APPLICATION


TRANSPORT


NETWORK


DATALINK


PHYSICAL

Your email server receives the full
email from the Transport layer and
you use a client program (Outlook,
Eudora) to read it.

The transport ensures that all the
pieces of the email have arrived.
When it has, it’s passed to the
application layer.

The Network layer verifies where the
email originated from (e.g. What IP
address?)

The physical layer decodes the
electrical impulses it receives into 1s
and 0s

The DLL converts 1s and 0s
received from the physical layer
and passes them onto the network
layer

Email Arrives

Move from Bottom to Top

ITI
-
510

Computer
Networks


OSI Example Diagram

ITI
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510

Computer
Networks


OSI Points


The OSI model allows hardware and software
manufacturers to keep a limited scope when
developing and manufacturing


A vendor only has to create a product that can
function within its specific layer and interact with
only the layers directly above and below


For example, a manufacturer of network cards need
only know how to operate within the Physical layer
and how to pass data to the Data Link layer


the
network card does not need to know anything about
the network, transport or application layers.


Example 2: If you are writing a web browser
(Application layer), you only need to know how to
interact with the Transport layer (usually referred to
as the
TCP Stack

within an operating system)

ITI
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510

Computer
Networks


Introduction to the Internet


The Internet is a global network that is
comprised of smaller networks owned by
commercial entities, educational
institutions, government agencies, etc.


No one “owns” the Internet.


Traffic is carried through the Internet
using a hardware (physical layer) and
communication links (data link layer).


Host
-
to
-
host communication is
accomplished using TCP/IP or UDP/IP


the combination of the TCP or UDP
transmission layer protocols and the IP
(Internet Protocol) network
-
layer protocol.

ITI
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510

Computer
Networks


IP


The Internet Protocol


In an IP network, individual hosts are
distinguished by a unique address, known
as an “IP address”


An IP address is comprised of four Octals
(8
-
bit numbers), separated by a decimal
point, e.g.:


126.14.34.18


Each decimal number (126, 14, 34, 18,
etc.) has a BINARY equivalent that is used
many network equations.


128.14.34.18 = 10000000.00001110.
00100010. 00010010

ITI
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510

Computer
Networks


IP Networks


Internet service providers (ISPs) are
assigned blocks of IP addresses, which
they are free to use on their Internal
networks.


ISPs form “peering agreements” with
other service providers so they have a
pathway other other provider's networks.


ISP networks are connected through
hardware devices knows as
routers
, which
are responsible for directing traffic to and
from other networks.

ITI
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510

Computer
Networks


IP Networks
-

Example



Rutgers
Network

128.6.*.* IP
Block

UUNET

Network

63.*.*.* IP
Block

SPRINT

Network

24.*.*.* IP
Block

Rutgers obtains
connectivity to the
Internet from
UUNET, their
Internet Service
Provider

UUNET peers with
Sprint, which gives
UUNET access to
Sprint
-
connected
networks and Sprint
access to UUNET
networks.











= Router

ITI
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510

Computer
Networks


IP Addresses: The Numbers
Behind the Name


The “common” internet hostnames we use
everyday (www.yahoo.com,
iti.rutgers.edu, etc.) all have
corresponding IP addresses behind them.


Routers move packets and messages from
network to network based on IP address


not based on hostname.


ITI
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510

Computer
Networks


Class Exercise: Introduction to
Binary Numbers…


1’s and 0’s = on and off


Question: What is:





1




+ 1




-------





???