Time
3 hours 38 minutes
Difficulty
Beginner
CEU/CPE
2

Video Description

Data Link Layer- Reliable data transfer across physical link

  • Responsible of physical addressing
  • Organize the data into frames
  • Puts frames on the physical medium
  • Check frames for errors
  • Hop-to-hop addressing

Physical Address- Unique identifier

  • Not bound to geographical location
  • Used for hop-to-hop addressing
  • Burned on the NIC
  • Cannot be changed
  • Vendor oriented
  • Common example is the MAC address
  • Sometimes called hardware address

Data Link Layer- Received data packages from network layer

  • Convert data into the frames including the following:

    • Data packages
    • Sender and the receiver physical addresses
    • Error checking and control information
  • Checking and control ensures the frame has been delivered without troubles
  • If part of the frame is lost during transmission then:

    • Data link layer protocols of the receiver would see that
    • Data link layer at the receiver requests data retransmit from the sender
  • Switches and bridges devices work in data link layer

Frame Check Sequence (FCS)- Error checking mechanism is creating the unique frame check sequence (FCS)

  • FCS number based on the values of all of the preceding fields in the frame
  • The receiver's end receives data with the FCS value
  • Receiver compares FCS to the data fields in frame
  • In unlucky scenario of failed comparison the following is done:

    • Data is assumed corrupted
    • Receiver requests data resend
  • If the comparison is a success, receiver sends the message of successful data transmission back to the sender
  • If receiver did not receive the "success" message during specified time, automatically the sender resends the data frames

Data Link Layer Sublayers- Another function of Data Link layer protocols is to control the flow when manny different nodes are sending data at the same time

  • The Data Link layer has been divided into two sublayers be the IEEE as follows:

    • The top sublayer is called Logical Link Control (LLC) communicating only with Network layer and providing the following functions:

      • Hop-to-hop reliability
      • Hop-to-hop flow control
    • The bottom sublayer is Media Access Control (MAC) responsible for the following:

      • Adding physical address to the frame
      • Communication with the Physical layer

Physical Layer- Transmits bit stream over the physical link

  • Sends data signals to media and receives it
  • Adapts to the transmission media

    • Cables

      • Copper (coaxial, twisted pair)
      • Fiber optic (single mode, multi mode)
    • Wireless
  • Responsible for the representation of 1s and 0s
  • NIC, Hub, and Repeater work in Physical Layer

Video Transcription

00:00
Now let's talk about the lowest two layers. The datalink layer layer number two and the physical layer layer number one. They are important layers, as well as the third and the fourth. For the network specialists and engineers,
00:15
the data link Clear Layer number two. It's a reliable
00:20
layer for the data transfer across the physical link. It is responsible for the alien reliability on the level off hop tow hop transfer
00:29
across the physical link means that it is responsible for the reliability off data transfer from the machine. So the switch and from the switch so the router and from the outer toe, the next rotor across the land domain, it is responsible off physical. Addressing.
00:46
Physical addressing is different than logical. Addressing the physical address is not bound to geographical location
00:53
and cannot be change it. The logical address is bound to the geographical location and can be changed according to the geographical location, off the machine or off the network interface card inside this machine. But remember that both addresses are unique and cannot be repeated.
01:11
The data link clear organized the data into frames. The frame is the data unit at this layer at the Datalink Lair at layer. Two week old data frames at layer, three week old data packets and at Layer four, we call data segments and that they're one. We will call data bits or bites.
01:29
The data link lair puts the frames on tow. The physical media checks four frames errors, and this checking does not include correction. It is just other detection on Lee. It is responsible for hope Toe help addressing a dressing on the range off land domain
01:48
at dressing
01:49
with the physical address.
01:52
The physical address is a unique identify that cannot be repeated. It is not logical. It is not bound to the geographical location. It is only used for help toe hope. Addressing toe, identify the machine on the land. I mean, the physical addresses burned on the network interface court
02:09
and it cannot be changed. It is vendor oriented. Every
02:15
specific board off the physical address
02:19
comes that this network interface card belongs to this vendor, which means network interface card from a certain vendor should have a physical address that is related to this vendor.
02:30
A very common example of the physical addresses. The Mac address the medium control, the medium access control address. Sometimes the physical address is called the hardware Address.
02:42
The data link clear receives data packages from the network clear
02:46
when sending and convert this data into frames, including the following the data itself. The data package, the sender and the receiver. Physical addresses, error checking and control information. A field that helps for error. Checking for this frame
03:05
checking and control ensures the frame has been delivered without troubles. This is the functionality off such field for error, checking and control.
03:14
If part of the frame is lost during transmission than the Datalink Lair protocols off the receiver would see that they telling clear at the receiver, request data retransmit from the thunder. As you can see, this is just a retransmission request, not
03:29
a correction action that can correct the data.
03:35
Ah, that is corrupted at the frame. It is just a retransmission for the corrupted frame or for the frame that contains wrong information.
03:44
The switches and the bridges are devices that work in the datalink. Clear work in both layers, physical and datalink. Switch and bridge work in layer to
03:57
the frame check sequence. F. C. S is the error checking mechanism that is created at the Datalink Lair.
04:04
The F C S is a number based on the values off all the preceding fields in the frame.
04:10
The receiver receives data with the F. C s value.
04:15
The receiver compares the F. C S to the data field in the frame to check if this F c S is consistent with the data or not.
04:26
If, in an unlucky scenario off failed comparison, the following is done. If this F. C. S is saying that the data is not consistent with the field off F. C s, the data is assumed to be corrupted. Then the receiver requests data descending from the sender.
04:46
The F C s
04:48
is also beneficial. If the comparison is successful, the receiver sends a message off successful data transmission
04:57
back to the sender. If the receiver did not receive the success message during specific specific period of time automatically the Sunday reasons. The data frames
05:10
the day. Telling Claire is divided into two sub layers. The LLC, which is the logical link on throw layer and the make clear the medium excess controlled layer.
05:20
Another function of detailing clear is it control the flow when many different nodes are sending data at the same time. This is the layer where collision is detected and avoided. This is the layer where the schism a CD and this is Miss C. A.
05:36
If you remember collision carrier, since multiple exits, collusion, direction or carrier, since multiple excess
05:42
collision avoidance take place and are implemented
05:46
the day telling Claire has been divided into two sub layers by the IEEE, which are the logical in control, the lnc and the medium excess control.
05:56
The LLC is responsible for the Hope tow hop, reliability and helped tow hop flow control.
06:01
Reliability means that the data must reach each of the station
06:08
with no adults, and the flow control is the synchronization between the speeds off the sender and the speed off the receiver. The McClair adds the physical addresses to the frames off the sender and off the receiver. It is responsible off communication with the physical layer.
06:27
Let's talk about the physical layer. The physical air transmits bit streams over the physical league data at the physical airai. Other are either Bates or bites. It stands data signals to media and receives it
06:40
that
06:41
physical connection that really exists among the seven layers is between the two physical layers off the sender end off the receiver. Other links that exist between the datalink here and there are just logical links.
06:57
The physical layer adapts to the transmission media. Either these cables or wireless media. Either it is copper or fiber optic, either disco, excel or twisted pair. If copper or single mode or multi moody fiber optic, it is responsible for the representation off the ones and zeros responsible for the digital representation.
07:15
Is it plus five volt Oprah or Plast revolt or plus zero volt?
07:20
The voltage and the electrical representation is the responsibility of the physical layer. Devices that work in the physical layer are the nick, the network interface score. They help the repeater. All of these are devices that work in the physical layer only
07:39
as we can see
07:40
here are two stacks off seven layers for the thunder and for the receiver. We can imagine a logical link between the application layer here and the application layer there. But the physical link that really exists and that is not imaginary inside. This diagram
08:00
is really between the physical link at this underside and the physical link at the receiver side.
08:05
It is either through optical fiber or copper wire or electromagnetic waves in the wireless media that transmits a stream off bits and bytes from the physical year here to the physical layer there to represent the data off zeros and ones being sent from the sunder tow the receiver.
08:24
By this, we come to the end off the datalink. Clear and physical layer explanation. Thank you.

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