data link layer

Question 1

purpose of the data link layer

Answer 1

1.communication between end devices

2.it allows the upper layer protocols to access the physical layer media

3.it performs error detection and rejects corrupt frames

Question 2

sublayers of the data link layer

Answer 2

1.LLC: logical link control (it communicates between the upper layers software and the lower layer hardware) /// (standard 802.2 which places info in the frame about what netwrok layer protocol is being used )

2.MAC: media access control (it is responsible for encapsulation and media access control ) /// (standads 802.3 802.11 802.15 which are responsible for encapsulation and media access control and data link layer addressing )

Question 3

data link frame

Answer 3

1. header(it has the physcial address of the source and distination and its updated by each device that forwards the frame )
   2.data
   3.trailer

Question 4

data link layer protocols

Answer 4

ethernet protocol
802.11 wireless
PPP point to point protocol
HDLC
frame relay

Question 5

ethernet protocol

Answer 5

the ethernet protocol operates in the data link laer and physcial layer

it works with the IEE 802.2/802.3 standards

Question 6

data encapsulation in the IEEE 802.3 standard

Answer 6

1. ethernet frame: the internal structure of the frame

2.ethernet addressing: the ethernet frame includes a destination and source MAC address to deliver the ethernet frame from nic card to another nic card in the same LAN

3.ethernet error detection:the ethernet frame includes an ethernet frame check sequence (FCS) trailer used for error detection

Question 7

the MAC sublayer in the ethernet frames

Answer 7

the IEEE 802.3 mac sublayer includes the specifications for diffrent ethernet communication standards over types of media

legacy ethernet using a bus topology or hubs where a half duplex meduim uses the CSMA/CD (carrier sense multiple access/ collusion detection) protocol

however noadays ethernet uses switches that operate on fullduplex meduims which doesnt require the CSMA/CD

Question 8

ethernet frame size

Answer 8

any frame less than 64 bytes are considered runt frame and any frame more than 1518 bytes are considered jumbro frame both of which are dropped by the recieving device

Question 9

MAC addresses

Answer 9

the MAC address rules are identfies by the IEE

the MAC address has two parts (first part is the OUI organizationally unique identofier which is given by cisco and it s 24 bytes aka 6 hexadecimal charectars anf the next part is called vendor assigned decided by the vendor of the device and its also 24 bits and 6 hexadecimal)

Question 10

what does the ethernet frame include

Answer 10

header
distination mac
source mac
source ip
dest ip (source ip and dest ip is the ip packet )

data

trailer

Question 11

casting

Answer 11

1.unicast: we use the unique address (the process that a source host uses to determine the dest mac with the ipv4 address is the ARP protocol address resolution protocol the one thats associated with ipv6 is called ND neighbor discovery)

2.broadcast: FF-FF-FF-FF-FF-FF-FF-FF

3.multicast: