Lecture No 6 Physical and Data Link Layer Tow very important ...

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Oct 26, 2013 (3 years and 5 months ago)

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Lecture No 6


Physical and Data Link Layer


Tow very important concepts for understanding Physical and Data Link Layers are:


1

LAN

Local Area Network

2

WAN

Wide Area Network


The technical definition of LAN and WAN does not depend upon the Graphical Distance
.

So, we can define LAN and WAN as follow:


The technology which we use for the communication on the Physical Layer and Data Link Layer decides
whether we are doing LAN Communication or WAN Communication.


LAN Communication:


If we are using
Ethernet Techn
ology which run on Physical and Data Link Layer
for the communication between
two computers
even they are 100 kilometers far from each other
then we are doing

LAN Communication.


WAN Communication:


If we are using
Modem Technology which runs on Physical L
ayer

and
PPP Protocol on Data Link Layer

for the
communication between two Computers
even they are placed nearer to each other

it will be

WAN C
ommunication.


--------------------------------------------------------------------------------------------------
------------------------------------------


Data Unit of Data Link Layer is Frame. On Physical Layer converts it into Bits

Signals.


Some Technologies

(Standards/Protocols)

of LAN environment on Physical and Data Link Layer
s












Ethernet is a standard which lies

on both Data Link and


Physical

L
ayer.



802.3 802.5 and FDDI are c
overing Physical Layer and Some



Portion

of Data Link Layer.




802.2 LLC covers the remaining Portion of Data Link Layer.










We can use any technology from above shown
technology
standards for LAN.

D
D
a
a
t
t
a
a


L
L
i
i
n
n
k
k


(
(
f
f
r
r
a
a
m
m
e
e
s
s
)
)


Physical

(bi
ts,
signals,

clocking)


E

t

h

e

r

n

e

t

802.2 LLC


8

0

2

.

3


8

0

2

.

5


F

D

D

I

LAN


Ethernet
/802.3

Techn
ology


It was actually a LAN standard which was originally developed
by Xerox, and it was proprietary

standard for
Xerox

(In other words we can say it was
used by

Xerox

for product development

and

any other company was
not
eligible for

using this standard
)
.

After it IEEE

(Institute for Electronics and Electrical Engineers) standardize
Ethernet for

any
Vendor
(Company)
.

IEEE introduced a new Standard 802.3 which was based on Xerox Ethernet


What is IEEE?


It is

an
I
nstitute

of Electronics and Electrical Engi
neers

which standardize the network technologies
.

I
t

can use

by every Vender.


Note:


We are using Ethernet Cards or LAN Cards

in LAN

are actually 802.3


Token Ring/802.5 Technology


Token Ring

wa
s also a standard

which
(
work on Physical and Data Link La
yer

in LAN environment
)

was
developed by IBM

but it was also proprietary standard of IBM and other

any

Venders were
not
eligible for use
this standard.

IEEE also
standardizes

Token Ring

and
gives

us
a standard
802.5
.


Note:

But this standard Token Ring/802
.5

is

now end.

Now a day

we are using only

IEEE standard

802.3/
Ethernet in

LAN environment



FDDI

(Fiber Distributed Data Interface)


It was also a standard which was used to develop a LAN with fiber optics but it was no more famous


Question:

Why IEEE na
med these LAN Technologies as
Ethernet


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Ethernet
is
a

Standard as well as
a
Protocol


When Ethernet describe the functionality of Data Link Layer it is Protocol and when Ethernet describe the
functionality o
f Physical Layer is called Standard.


Note:

We can state that Every Protocol is a Standard and Every Standard is not a Protocol
.


Physical Layer is Pure Hardware Layer and Data link Layer

is the combination of Software and Hardware
Functionality

and above

all Layers are Purely Software Layers.









Some Technologies (Standards/Protocols) of WAN Environment on Physical and Data Link Layer
s


























In WAN environment every Standard and Protocols are on Different
Layers. On

Data Link

Layer there

are Protocols and on Physical Layer there are Standards.


Note:


ATM
(
A
synchro
n
ou
s Transfer Mode
)

was another technology which
lies on both LAN and WAN

environment
.


ATM (Automated
Tariff

Machine) which
is

used in Banks is a Diffe
rent thing
.



-----------------------------------------------------------------------------------------------------------------------------
-----


Data Link Sub Layers


Only in LAN Environment w
e
divide

Data Link Layer in Two Sub Layers
because as we alread
y defined that it
has functionality of both Software and Hardware therefore it has to perform more functions than the other
Layer.


1

MAC Sub Layer



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2

LLC Sub Layer



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Remember: Data Link Layer w
ill always

be
divide
d into two Sub Layers only in LAN environment. It will be treated
as a Single Layer

in WAN environment.




WAN

D
D
a
a
t
t
a
a


L
L
i
i
n
n
k
k


(
(
f
f
r
r
a
a
m
m
e
e
s
s
)
)


Physical

(bits,
signals,

clocking)

X.25

Link


Frame

Relay

ISDN


PPP

EIA
-
530



V.35








Dial

on

Demand

SDLC

HDLC


V.24


HSSI

G.703





EIA/TIA
-
232

EIA/TIA
-
449
















LLC Sub Layer





LLC Sub Layer makes
Independent

Upper Layer Software from Lower Layer Hardware
and ma
kes

Independent

Lower Layer Hardware from Upper Layer Software.

It means if we have to change

Hardware (Network Cables, or LAN Cards etc.) then we don’t have to change Software (Operating

Software Windows)
. This Independence

provides LLC Sub Layer.


W
e buy LAN card a CD of its driver will always with it
.

Drivers Run on This LLC Sub Layer
these

Drivers behave

like Coupler
.


MAC Sub Layer




Medium which we are using to communicate is controlled by MAC Sub Layer


Types o
f Addresses


1

Physical Address
es
/MAC Address
/Ethernet Address
/Hardware Address/Burn in Address (BIA)






Exist on MAC Sub Layer these are assigned randomly

or have not logic
.



MAC Addresses are always Unique

2

Logical Addresses
/Software Address



Exist on Network Layer these are

assign
ed

order
ly or have some logic
.



Logical Addresses are always Unique


MAC Address


MAC address is of 48
-
Bits and it is burnt in the LAN card

MAC address has two

equal

Portions

of 24
-
bits

Left Portion of 24
-
Bits is Called Vendor Portion which is assigned b
y the IEEE.

Right Portion of 24
-
Bits is Called Serial Number which is assigned by the company which makes LAN Cards

Whenever any company want to make LAN cards it will go to the IEEE and take a Vender Code of 24
-
Bits
and

it can make

2
n

(n=24) 2
24

=
16777216

LAN cards from these 24
-
Bits Vender Code. And on each LAN card
Vender Code will be same but serial number will different. When it has made all range of 16777216 LAN
cards it will again go to the IEEE and will take a new Vendor Code.








Media Access Control

N
N
e
e
t
t
w
w
o
o
r
r
k
k


D
D
a
a
t
t
a
a


L
L
i
i
n
n
k
k


Phy
sical

L
L
L
L
C
C


S
S
u
u
b
b


L
L
a
a
y
y
e
e
r
r


MAC

Sub Layer

Logical Link Control






















-----------------------------------------------------------------------------------------------------------


24 bits

24 bits

0000.0c
12. 3456

Ven
dor Code

Serial Number

ROM

RAM

Actually this MAC address is represented in
HEXADECIMAL (one hexadecimal is consist of
4 bits ) so These 12 Hexadecimal digits are
actually 48 Bits.

Note: