OSI Reference Model and

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OSI Reference Model and
Security

COMP 423

The Physical Layer


Establish and terminate the physical and
logical connections to the media


Manage the flow and communication on the
media



Embed the message onto the signal carried
across the physical media

Network Media Type

Description

Comments

Coaxial Cable

One of the first LAN media.

Channel medium


it can only carry one message in one direction.



Fiber
-
Optic

cable



Essentially a tube with an

ultra
-
pure glass
or plastic core that carries light waves. The
single
-
mode cable provides data
transmission rate of approximately 10
gigabits per second over distances of up to
approximately 35 miles.

To send multiple simultaneous signals, networks use a multimode
variant. Multimode transmission speeds are up to 100 Mbps for up to 2
miles, up to 1
Gbps

for approximately 500 yards, and up to 10
Gbps

for
up to approximately 1/5 mile (300 yards).

Twisted Pair Wire




One of the most dominant cabling types in
use today. UTP has no supplemental
shielding, and because the twisting only
provides minimal protection, the cable has
a maximum

effective limit of approximately
100 yards.

When installing networks in buildings under construction, it is most
beneficial to install networks using physical cable like UTP. UPT is easy to
work with, reliable, less subject to interception or eavesdropping,

and
relatively inexpensive.

Wireless LAN

The most common alternative when
installing physical cable in existing buildings
becomes too difficult and expensive. The
standard for wireless networks falls under
IEEE 802.11


Wireless Local Area Networks
(WLAN). WANs

use one of three
architectures


peer
-
to
-
peer (P2P), basic
service set, or extended service set.

Wireless LANs (also called WLANs, or the brand name Wi
-
Fi) are thought
by many in the IT industry to be inherently insecure. The radio
transmissions used for the wireless network interface between
computing devices and access point (Aps) can be intercepted by any
receiver within range. To prevent this, the networks must use some
form of cryptographic security control.


Bluetooth

A wireless

technology not covered under
the 802.11 standard. Is a de facto industry
standard for short
-
range wireless
communications between devices.

To secure Bluetooth
-
enabled devices you must: 1) turn off Bluetooth
when you do not intend to use it and 2) refuse incoming communications
paring requests unless you know who the requestor is.

Infrared

A wireless technique for data connections
between personal devices, like personal
digital
assistans

(PDAs) and laptops.

The Infrared Data Association (IrDA) defined several standards for short
-
range infrared connections (typically less than 1 meter). Older IR LANs
mounted central

Aps in the ceiling, but these were quickly replaced with
802.11 alternatives.

Data Link Layer


Primary networking support layer


Provides addressing, packetizing, media access control,
error control, and some flow control for the local
network.


In LANs, it handles client
-
to
-
client and client
-
to
-
server
communications


Divided in two
sublayers


Logical Link Control


Primarily designed to support multiplexing and
demultiplexing

protocols


Media Access Control


Designed to manage access to the communications media(which
clients are allowed to transmit and when)

DLL Protocols



Ethernet (IEEE standard 802.3)


Wired networks


Wi
-
Fi (IEEE 802.11)


Wireless networks

Network Layer


Primary layer for communications between
networks. Has three key functions:


Packetizing


Addressing


Routing

Network Layer


Packetizing


Takes the segments sent from the transport layer
and organizes them into one or more packets for
transmission across a network

Network Layer


Addressing


Uniquely identify a destination across multiple
networks.

Network Layer


Routing


The process of moving a Network layer packet
across multiple networks.

Transport Layer


The primary function of the Transport Layer is
to provide reliable end
-
to
-
end transfer of date
between user applications.


Error control


Flow control

Session Layer


Responsible for establishing, maintaining, and
terminating communications sessions
between to systems.


Regulates whether communications are
preformed in:


Simplex mode


Half
-
duplex mode


Full
-
duplex mode

Presentation Layer


Responsible for data translation and
encryption functions.

Application Layer


The user is provided with a number of
services, perhaps most aptly called application
protocols.


E
-
mail (SMTP & POP)


World Wide Web (HTTP and HTTPS)


File transfer (FTP and SFTP)

TCP/IP Layers compared to OSI Layers

OSI Layers

Included Protocols

TCP/IP Layers

Application

SNMP

TFTP

NFS

DNS

BOOTP

FTP

Telnet

Finger

SMTP

POP


Application

Presentation

Session

Transport

UDP

TCP

Host
-
to
-
Host Transport

Network

IP

Internet

Data Link

Network Interface Cards


Network Interface

Physical

Transmission Media