In OSI model physical layer is the first layer.
Physical layer is responsible for sending bits from one computer to other
Functions of this layer:
In this layer data consists of bits. For transmission
those will encode in to signals to pass. Also in this layer we know how many
are transferring per second. Also, there will be topologies which devices are
There is syncoranizaion between transmitter and receiver
while passing data.
In OSI model data linklayer is the second layer. This
layer will deliver data between node to node. This layer is also responsible
for transferring bits, while decoding in this layer it will convert to packets
after data got transferred again it will convert to bits. Also while passing
data it will control the speed of processing also, if there is no control on
passing data there will be a cause of getting errors.
the link layer encapsulates the datagram received from the network layer into a
transferring data, it will receive data in any order.
Frame means while sending
data it will send in frames in data link layer, means it will convert some bits
to frames and deliver after that it will frame again with bits, like that it
will send data in frames wise in data link layer.
data link layer encapsulate the datagram received from the network layer in to
While connecting to router, it will receives frame and
router will extract the datagram through frame.
the link layer incapable of detecting an error in a received frame?
In link layer there is an error handling. This layer
also detect and it will correct errors in the frame while receiving. While
sending data it will also send extra bits to confirm whether received data is
correct or not after receiving.
There are 3 types of errors in link layer.
Sent bits: 10110
Sent bits: 10110
Sent bits: 10110
In received bits highlighted in red are errors
Detecting error in received frame by handles in 2
In the above diagram frame 3 didn’t received at
receiver after timeout sender will send the frame again and it was successful after
flow control one of the services provided by the link layer?
In data link layer flow control is the one of the
service provided by this layer. In this layer receiving layer receives more
frames (faster) than sending frames. That is the reason flow control is the one
of the main service for this layer.
If there is no flow control in this layer as the
receiver receives faster than sender at that time it will miss some bits for
operations does the link layer support?
Below are the operations data link layer support.
duplex and full duplex
brief description of the IEEE (Institute of Electrical and Electronics
Engineers)802 standard development
IEEE covers physical accepts of networking also deals
with local and metropolitan area networks. Mostly used for Ethernet cables and
for wireless connections.
IEEE format has 3 types of formats
3. Network access protocol
802 is set of networking standards
and for implementing networks.
802 network standards are below:
802.1 to 802.20
In these 802.10 and 802.13 are not in
802.1 – this standard is for
internet, used for routers, switches, cables and for all other internet
802.2 – this standard is for logical
link control, this covers the physical media and also this works between media
access control and physical layer.
802.3 – this standard is for
Ethernet, this is for implementing the Ethernet networks.
802.4 – this standard is for Bus,
this is for physical media works with bus network topology
802.5 – this standard is for Ring,
this is for physical media works with ring network topology
802.6 – this standard is for
metropolitan area networks, this is for manage large networks
802.7 – this standard is for Broadband, we use this
802.8 – this standard is for fiber
optic, this is used for digital connections
802.9 – this standard is for voice
and data networks, used for all data networks and voice networks like customer
802.11 – this standard is for
wireless network, used for cellphone signals and dish televisions and also for
802.12 – this standard is for high
speed network, used for high data rate connections
802.14 – this standard is for working
group, used for data transmission like for networks
802.15 – this standard is for
wireless standard network, used for wireless technologies
802.16 – this standard is for
metropolitan network, used for large city networks
802.17 – this standard is for packet ring,
used for ring topology
802.18 – this standard is for
wireless group, used for wireless group communications
802.19 – this standard is for
coexistence group, used for both software and hardware for basic
802.20 – this standard is for mobile
broadband, used for smartphones also for wireless devices.
brief description of WIFI
Wi-Fi is short for
wireless fidelity. It’s also known as Remote loyalty. Remote is an innovation
that enables us to interface with a web without associating with cables. One
advantage of Wi-Fi is high speed data transmission. It’s also integrated. Like
mobile Wi-Fi connected computers can send and receive data within the range of
base station. They use radio waves to transmit data. The wireless network is
used to connect system to system to the internet, wired network and to the
Ethernet. Wireless network can be connected from anywhere within the radius. It
can be connected to laptops, mobiles and iPad etc. The IEEE 802.11 (ISO/CEI
8802-11) is a worldwide standard depicting the qualities of a remote nearby
system. The name Wi-Fi is initially the name given to the affirmation conceded
by the WECA
The Wi-Fi are also called as Hot Spots. The 802.11
defines the layer of the Open system interconnection
model for the wireless communication electromagnetic waves. This offers three
types of coding.
The data link layer, composed of two
The physical layer shows
the radio waves and the attributes of the signal transmission, In between the
data layer acts as a link between bus and the machine of physical layer,
counting a strategy get to like the one utilized for a standard Ethernet
organize and the correspondence runs between the distinctive stations. It is
conceivable to utilize any convention over a remote Wi-Fi arrange and
additionally an Ethernet organize. The advantage of wireless network is speed
access of data. It transmits the data on the speed of 11 mega Bytes per sec and
100 times faster than regular dial up connection.
The wireless is also
having some flaws like it can be access within the range of network, cost, and
service billing system and security issues. Wireless networks are insecure.
Wireless network will break very frequently and connecting to wi-fi without
passwords and wireless networks available in public places can lead to hacking
brief description on the link layer sub-layers
The link layer is having two sub layers.
Logical Link Control or LLC
Media Access Control or MAC
The logical link control acts as a
transmission between different devices on a single link like multi network
operations. To provide data to users across a MAC link or LANs connected by MAC
bridges. The LLC can have different frames by sequence number then by sending
the frames. It can also have a control over the messages like ready and not
ready. There are various modes like
Connectionless Acknowledge service
Connectionless Unacknowledged service
Connection Oriented Service
Connection Oriented service without
Connection Oriented service with
In this mode, information is straightforwardly sent
between Layer2 peers with no sensible connection foundation. Be that as it may,
each casing is numbered utilizing arrangement numbers and the companion
recognizes each edge got utilizing an Acknowledgment number field. This administration
mode is utilized as a part of situations where the overhead of an association
foundation is expensive because of the additional defer included, yet where
information unwavering quality is required. The sender can track lost or harmed
edges and retransmit such casings to accomplish unwavering quality. This sort
of administration is utilized as a part of remote connections, where the nature
of connection isn’t in the same class as wired connections thus visit interface
foundation and teardown are superfluous overheads, as these control edges may
themselves be ruined or lost.
This is a best exertion
benefit like IP datagram benefit, with no association foundation between L2
peers and furthermore no affirmation for information outlines from the
companion. At whatever point there is information to be exchanged to the
associate, it is sent specifically, with no association foundation. Stream
control might be alternatively given in this administration. In Internet, since
dependability, stream control and mistake control are given at the vehicle
layer by TCP, a straightforward connectionless unacknowledged administration is
sufficient at the information interface layer, gave the connection is of good
quality with low blunder rates. Subsequently, this administration mode is the
most generally utilized mode in the Internet, where TCP/IP is the fundamental
convention stack. This mode is utilized on all excellent wired connections like
Ethernet and Optical.
In this mode it shows the
connection and disconnection of logical link. Before the data transfer
connection is set up between peers. Before information exchange begins, through
the trading of control outlines, known as Supervisory Frames. The consistent
association is shut after the information trade stage is finished. Genuine
information exchange begins after the association foundation stage and casings
conveying higher layer information are known as Information Frames. A third
class of casings, known as Unnumbered Acknowledgment outlines are utilized to
recognize gotten Supervisory edges.
In this mode as well,
there are two variations that are utilized, in particular one without
affirmation and another with affirmation.
Oriented service without Acknowledgment:
Here, however a legitimate connection is set up before
real information exchange happens, there is no understanding of edges being
numbered and recognized through Sequence number and affirmation number fields.
It is only a best exertion benefit, with unwavering quality left to the higher
layer convention. Numerous WAN conventions like HDLC, PPP, LAPB, and LAPD and
so on utilize this method of administration.
oriented Service with Acknowledgment:
Aside from a consistent connection being built up
before information exchange happens, unwavering quality and stream control
administrations are likewise given by the LLC. Dependability is given using
grouping number, affirmation number and retransmission of lost casings utilizing
techniques like Go Back N or Selective Repeat. Stream control is given by
utilizing a sliding window component. This administration mode is once in a
while utilized as a part of the Internet, since Internet utilizes TCP that
backings unwavering quality and stream control at the vehicle layer. This
administration mode is utilized as a part of proprietary conventions like
Media Access Control:
The MAC sub-layer interacts with the physical layer
and is basically in charge of surrounding/de-framing and crash determination.
Framing/De-Framing and interaction with PHY: On the
sending side, the MAC sub-layer is in charge of formation of edges from network
layer Packets, by including the header and the trailer. While the header
comprises of layer2 addresses (known as MAC address) and a couple of different
fields for control purposes, the casing trailer comprises of the CRC/checksum
of the entire edge. Subsequent to making a casing, the MAC layer is in charge
of collaborating with the physical layer processor (PHY) to transmit the
On the getting side, the MAC sub-layer gets outlines
from the PHY and is in charge of tolerating each casing, by analyzing the header.
It is likewise in charge of confirming the checksum to close whether the frame
has come uncorrupted through the connection without bit blunders. Since
checksum calculation and confirmation are register escalated errands, the framing/de-framing
usefulness is finished by committed bit of equipment (e.g. NIC card on PCs).
Collision Resolution: On shared or communicate joins,
where various end hubs are associated with a similar connection, there must be
a crash determination convention running on every hub, so the connection is
utilized helpfully. The MAC sub-layer is in charge of this undertaking and it
is the MAC sub-hinder that actualizes standard crash determination conventions
like CSMA/CD, CSMA and so on. For half-duplex connections, it is the MAC
sub-layer that ensures that a hub sends information on the connection just amid
its turn. For full-duplex point-to-point interfaces, the crash determination
usefulness of MAC sub-layer isn’t required.
brief description on NICs
NIC is a Network
Interface Card, by most of people thinks that NIC is a network adapter. A NIC
is a development card, an equipment gadget connected to a non-versatile PC
(like a work area) allowing the computer some new capacity. As an extension
card, the NIC particularly permits a PC the capacity to interface with a
system, (for example, Ethernet or Wi-Fi).NIC cards fill in as conductors
between a PC and a system (like Internet).Ethernet cards and token ring cards
are best examples for NIC cards. They
decipher the information on the PC into a frame that is transferrable through a
system link and control the information as it is sent to different gadgets on
the system. There are three types of configurable cards like jumper, software
and new technology PnP (Plug and Play).
Jumper configurable NIC cards are effective and simple
to use for more established gear. They have physical jumpers (little gadgets
that control PC equipment without the requirement for programming) that decide
settings for intrude on ask for line, input/yield address, upper memory square
and sort of handset. Software configurable NIC must be physically designed when
introduced, yet contain an exclusive programming program that enables the
administrator to arrange the NIC by means of a menu, or pick the auto setup
mode that figures out what design is generally reasonable. Most NICs today
utilize the PnP innovation as it doesn’t need to be physically designed,
however it can be. PnP NICs will auto-arrange upon establishment amid the
framework boot-up grouping, however can cause clashes with the hard drive.
Network interface cards come prepared to deal with
various, or numerous, sorts of systems. Serial links, Token Ring, Ethernet and
Wi-Fi are for the most part types of systems that interface cards are intended
to impart on. Most present day systems are made intensely out of Ethernet and
Wi-Fi associations. The system interface card gives the equipment to different
system layers to exist on, which means it can deal with having numerous
locations relying upon the system it conveys over. This enables a PC to match
up or exchange information along a nearby office server utilizing one, while as
yet having the capacity to convey over the Internet with another. System
interface cards likewise give a support to approaching and active information,
with the goal that the PC can make up for dormancy issues. Numerous cutting edge
gadgets have arrange interface cards incorporated with them, as principles have
made Ethernet and IEEE 802.11 (utilized for remote nearby access organize
associations) broad and minimal.
A wireless network interface controller (WNIC) is a network
interface controller which associates with a remote radio-based PC organize,
instead of a wired system, for example, Token Ring or Ethernet. A WNIC, much
the same as different NICs, deals with the Layer 1 and Layer 2 of the OSI
Model. This card utilizes a receiving wire to convey by means of microwave
radiation. A WNIC in a personal computer is generally associated utilizing the
PCI transport. Other availability alternatives are USB and PC card. Coordinated
WNICs are likewise accessible, (commonly in Mini PCI/PCI Express Mini Card
shape). Early remote system interface controllers were regularly executed on
extension cards that connected to a PC transport. The minimal effort and
omnipresence of the Wi-Fi standard implies that numerous more current portable
PCs have a remote system interface incorporated with the motherboard. The term
is typically connected to IEEE 802.11 connectors; it might likewise apply to a
NIC utilizing conventions other than 802.11, for example, one executing
of data link protocols
The data link layer acts
as a passing data between physical layers in network. The data link layer
connect layer guarantees that all bundles of data are passed on free of
mistakes. It ensures the proper physical convention is allocated to the
information. The information connect layer is the second layer in the OSI
Model. The three primary elements of the information connect layer are to
manage transmission blunders, direct the stream of information, and give a very
much characterized interface to the system layer. When it exchanges the
information to the system layer, it utilizes clocks and arrangement numbers to
check for mistakes to guarantee that all information is effectively gotten.
Data link protocols are in protocol layer just above
the physical layer. This data link protocol is used as a bridge between two
devices and there are multiple ways to connect to protocol. The reasons are.
Dedicated point-to-point links between two
devices, such as modem, bridges, or routers
Like LAN share links between different
The PPP (Point-to-Point Protocol) that individuals use
to associate with the Internet by means of a dial-up modem is a case of an
information interface convention. Since the connection between two frameworks
is point to point, the bits are constantly conveyed from sender to collector
all together. Additionally, dissimilar to shared-media LANs in which different
stations endeavor to utilize the system, there is no dispute.
Common Data link protocols are
SDLC: SDLC is a synchronous data link protocol. It is
1st developed by IBM as a part of system architecture. It was
utilized to interface remote gadgets to centralized server PCs at focal areas
in either point-to-guide (one-toward one) or point-to-multipoint (one-to-many)
HDLC: HDLC is a High-level data link control. This
convention depends on SDLC and gives both a best-exertion untrustworthy
administration and a solid administration. It is utilized with different serial
interface conventions characterized in the physical layer, for example,
EIA/TIA-232, V.24, V.35, and others.
SLIP: SLIP is a Serial line interface protocol. SLIP
is a data link control facility office for transmitting IP parcels, for the
most part between an ISP (Internet specialist organization) and a home client
over a dial-up interface. SLIP has a few confinements, including an absence of
any blunder recognition and revision instruments. It is up to higher-layer
conventions to play out these checks. Utilized over a great part of an
indistinguishable serial interfaces from HDLC.
PPP: It is a point-to-point protocol. It functionality
is same as SLIP. It’s not only transmits not only IP but also packets.it can be
much used as HDLC interface.
LAP: It is a Link access procedure. LAP has
dependability benefit highlights and comes in three types. LAPB (LAP Balanced)
is a convention that gives point-to-point associations on X.25 parcel exchanged
systems. LAPD (LAP D-Channel) gives the information interface control over the
D channel of an ISDN (Integrated Services Digital Network) association. LAPF
(LAP Frame-Mode Bearer Services) gives the information connect to outline
LAP used the X.25 which is highly dependable. But it
also has high negativity. Frame relay helps to improve the output.
LLC: It is a Logical Link Control. It belongs to 802.x
family. It’s a sublayer of link layer. It’s also used by ANSI FDDI. The logical
link control acts as a transmission between different devices on a single link
like multi network operations.
10. Media access control design and cyclic
redundancy check error detection scheme
Media Access Control:
access control interacts between the data link layer and the physical layer. This
is also known as Medium access control.
In this layer while sending data as frames MAC will
adjust the frames and send it to physical layer through transmission. If MAC is
not cotrolling the data there may be a cause of collision happens between
Cyclic redundancy check:
redundancy check will happen in most if the computers, this will cause due to
any of below reasons, due to this we may also loose the data in computer’s
Due to corrupt files
Due to duplicate links like this.
There is an option in windows also to clear the
redundancy error, either it was through command prompt (CHKDSK) or through
tools option in properties. Most of the time by doing this it will clear the
error and after that it is better to restart the system.