CS 4491 Internet Security

inexpensivedetailedNetworking and Communications

Oct 23, 2013 (3 years and 9 months ago)

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Dr. Clincy

Lecture

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CS 4491 Internet Security

Dr. Clincy

Networking Fundamentals

Note: I am still “tweaking” your syllabus in trying to get
to 16 or 17 lectures with 50% online

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Lecture

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Internet


Consists of various technologies


LAN Examples:
Ethernet, Token Ring, Wireless and
FDDI Ring


Point
-
to
-
Point WAN Examples:
Telephony Modem, DSL,
Cable/Modem, T
-
Lines, and SONET


Switched WAN Examples:
X.25, Frame Relay and ATM

Briefly explain the difference between packet switch networks and circuit
switch networks

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Lecture

3

Internet uses TCP/IP for
internetworking


why ?


Bottom Line: what makes TCP/IP so great and
unique

from other network protocols ??:


Network Technology Independence



independent of a
particular vendor’s hardware


Universal Interconnection



any 2 computers connected to
the internet can communicate


each computer has a unique
internationally recognized address


End
-
to
-
End Acknowledgements



acknowledgements
between the source and destination versus intermediate nodes


Application Protocol Standards



TCP/IP provides services
(or software) to applications needing lower level
communication services


In understanding TCP/IP, one must understand OSI

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Lecture

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Why Study OSI?


Still an excellent model for conceptualizing and understanding
protocol architectures


More granularity in functionality
-

more functional delineation


Key points:


Modular


Hierarchical (chain of command, pecking order)


Boundaries between layers (called interfaces)





NOTE:
the protocols or functionality with in the layer could change
however, the interface remains the same


this facilitates the flexibility

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Lecture

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OSI


Open Systems Interconnection



Developed by ISO

(International Organization for Standardization)



Contains seven layers



Application


Presentation


Session


Transport


Network


Data Link


Physical

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Lecture

6

A

Z

B

C

Q

T

7

1

3

1

Tx

Rx

Intermediate Nodes

What happens at the End and
Intermediate Nodes ?

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Lecture

7


between different layers on the same node or stack (INTERFACE)


between similar layers on different nodes or stacks (PEER
-
TO
-
PEER
PROCESSES)

Recap
-

OSI’s Layered Approach

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Lecture

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OSI Reference Model ?


Bottom 3 layers


Bottom 3 layers responsible for getting the info to the
destination


(Bottom 3 layers): at the lower levels of the model
protocols define the electrical and physical standards


(Bottom 3 layers) at the lower levels, the bit ordering, the
transmission of the bits, and error detecting and correcting
are defined


Top 4 layers


at the higher levels of the model, the protocols define the
data formatting, message syntax, dialogue management,
message sequences and info presentation

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Lecture

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OSI Physical Layer


Responsible for transmission of bits


Always implemented through hardware


Encompasses mechanical, electrical, and functional
interfaces


Encoding issues: how 0’s and 1’s are converted to
signals


Transport medium: Coaxial, Twisted Pair, Optical,
etc..


Transmission Rate/Data Rate


how fast to send bits


Transmission mode: transmission direction (simplex,
duplex)


Physical Topology: network layout

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Lecture

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OSI Data Link Layer


Responsible for error
-
free, reliable transmission of
data


Framing, Flow control, Error control
(detection/correction)


Makes use of physical address because with in the
same network

Network Layer

Data Link Layer

Physical Layer

Actually

sends

the

packets

(groups

of

frames)

from

node

to

node

using

a

routing

algorithm

Takes

raw

data

(bits)

and

transform

them

into

frames,

error

control,

etc
.

Transmit

and

receive

the

raw

data

(bits)

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Lecture

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OSI Data Link Layer

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Lecture

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OSI Network Layer


Responsible for routing of messages through networks


Concerned with type of switching used (circuit v.
packet)


Handles routing among different networks (Routing
across
“internetworks
”)


NOTE:

with in the same network, only the DATA
LINK layer is needed


amongst multiple networks,
the NETWORK LAYER and
routing

are needed


Makes use of
logical address

vs physical address
because not with in same network

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Lecture

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OSI Network Layer

Transport

Network Layer

Data Link Layer

Concerned

with

an

error
-
free

end
-
to
-
end

flow

of

data

Actually

sends

the

packets

(groups

of

frames)

from

node

to

node

using

a

routing

algorithm

Takes

raw

data

(bits)

and

transform

them

into

frames


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Lecture

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OSI Network Layer

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Lecture

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OSI Upper Layers


Application


Presentation


Session


Transport





Peer
-
to
-
Peer Processes …..


End
-
to
-
End nodes only

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Lecture

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OSI Transport Layer


Isolates messages from lower and upper layers


Breaks down message size (segmentation) (down) and
performs re
-
assembly (up)


Monitors quality of communications channel (oversee
all hops)


Selects most efficient communication service
necessary for a given transmission (could change over
hops)


Flow and Error control for Source and Sink

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Lecture

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OSI Session Layer


Establishes logical connections between systems
(up/down)


Manages log
-
ons, password exchange, log
-
offs
(up/down)


Terminates connection at end of session (up/down)

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Lecture

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OSI Session Layer

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OSI Presentation Layer


Provides format and code conversion services


Examples


File conversion from ASCII to EBDIC


Invoking character sequences to generate bold, italics, etc on
a printer


The source and sink could operate using different
encoding schemes


the presentation layer makes the
translations


Security


Compression


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Lecture

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OSI Application Layer


Provides access to network for end
-
user (end
-
user
being a human being or software application)


User’s capabilities are determined by what items are
available on this layer (ie. remote log
-
in, file transfer,
email service, directory service, etc.)

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Lecture

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An exchange using the OSI model

Explain encapsulation and decapsulation

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Lecture

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COMPLEXITY TO CONSIDER


Any particular node in an internetwork can be
functioning as follows simultaneously:



Tx to other internetwork nodes


Rx from other internetwork nodes


Intermediate node to some other internetwork nodes

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Lecture

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How TCP/IP maps to OSI ??

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Lecture

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Physical addresses


Physical address is also known as the link address


Physical address can be different sizes (depend on the network)


Unicast type physical addresses


single Rx


Multicast type physical address


multiple Rxs


Broadcast type physical address


all Rxs can pickup message

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Lecture

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IP Addresses

can be either
unicast, multicast or broadcast
types

Going from network A physical
address 10 to network P
physical address 95.


Can’t use the physical address
because different networks


The network layer address
contains the uniqueness we
need from source to sink.
Network layer address is A
-
P


Unit at this layer
-

datagram

Explain communications at the network layer

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Lecture

26

Addresses in TCP/IP

Application
Specific
Address

Converts to a part address

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Lecture

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Port addresses

Addresses of sending
and receiving processes
(j and k)

Add IP address

Overhead (H2, T2) added
for what ?

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Lecture

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Relation
-

ship

between

Layers
,

Addresses
,

and
Units


in TCP/IP

Signals

Bits

Frames

Datagrams (Packets)

Segments

Messages