Physical Flashcards
Addressing, serial, parallel
why do we need different types of addresses?
at application layer we may want addresses to be understandable so need to convert between addresses
Why does ethernet needs addresses?
to be unique on the network
why cant we assign them manually or get the manifucaturer to number each card?
if we bought from different manufacturers they might have the same number
what do part 1 of ethernet addresses mean?
uniquely identifies the manufacturer (needs central control)
what do part 2 of ethernet addresses mean?
uniquely identifies the card (controlled by manufacturer
How many bit MAC address does ethernet use?
48
what do IP addresses need to identify?
network
machine
are IP address split in 2 as well?
yes
How do IP layer send packets across ethernet?
local network
if the machines are on the same local network they can be sent directly to that machine
what happens if they are not on the same local network?
we need to convert an IP adddress into MAC address
How do we convert IP into MAC address?
computer maintains a table in memory that maps IP to ethernet MAC address
but how do we populate the table?
we use ARP (address resolution protocol)
what does ARP contain?
the algorithm used
e.g packets sent, the response to receiving one, how theyre sent
how packets are formulated
e.g which bits of data contain IP address
what do we do if we want to send smth to machine B but dont know its MAC address?
we can use a broadcase packet and send a packet to ALL machines
how does broadcast packet work?
it uses a special address (all binary ones)
How do we get a computer to talk to another?
use RS232
What does RS232 consist of?
consists of transmit pin, receive pin, ground
connect transmit to other receive pin and vice versa and ground to ground
What is point-to-point link?
connects 2 computers together to communicate
What type of transfer does RS232 use?
serial transfer - sent bit by bit
what else is transmitted in RS232?
many parameters e.g how fast data is transmitted
what does Asynchronous mean?
sender transmits when it wants, not synchronised with the receiver
Whats the difference between serial and parallel transfer
parallel sends all at once while serial sends bits one after another at regular intervels
what happens after serial transfer?
receiver peices them back together
what needs to known for serial transfer to work?
the first bit received
how many bits are sent
how fast theyre sent
why do we need to know first bit in serial transfer?
start bit and stop bit is used to identify start and end of each character
what are the values of start and stop bit
0 and 1(line is kept at 1 until next character is sent)
how does transmission of a character work in serial transfer?
it always begins with transition from a 1 to a 0
8 transmitted bits later it will return to 1 again
what happens if it doesnt return 1
we have a framing error and need to resynchronise
