How did they change the computer to a asynchronous to synchronous to achieve this is a personal computer your forced to invest into a NIC card, this allows the pc to transmit data, in a synchronous <-= sends big blocks of data, synchronous transmission, the NIC card is the machine that is installed into your computer to allow this to happen theirs Ethernet Nics their areToken Ring NICS, they all send data in big blocks, pretend we have a nice big file, what allows asynchronous INT14, synchronous INT52, take data in memory and transfer a whole block of data and get transfer to the NIC, the NIC can receive this, one INT big block, incase of Ethernet how big is the block with either it will take data up to 1500 bytes and move it to the nic the nic has a block of data, up to 1500 bytes the NIC like a the UART, NICS also prepare the data, 1000 or 500 bytes long,
Last questions test 1 what is Ethernet and how does it work?
look at the synchronous aspect of Ethernet, it will put extra stuff in front |SourceAddress| and |DestinationAddress|, before it sends data it puts 8 bytes, the total 64 bit frame, in front of everything, this is called a Preamble, and all the bits are 0101010101010101010, The Preamble sets up the synchronization, how can this help with the timing, it would look like positive and negative pulses, on off pulses, now lets pretend we are NICs, we have to start talking to each other we have to make sure we are talking at the same speed, because we are sending big blocks of data, must talk exactly at the bps speed, this is the purpose of the Preamble, the receiving nic tunes into this and understands, both nics work at the same speed, ordinary nics to 1000billion bps, the nic does not sample at the wrong moment, Ethernet has two tricks, a 1 bit type, ur nic determines if it a 1 bit or a 0 bit, it maintains sync of the digital pulse itself, it syncs and when its reading in the bytes and it maintains sync, because the sampling of the digital signal to maintain a connection, because its doing this protocols can do an enhanced data checking, this is almost 100% error detection, all use this use this system called CRC cyclic redundancy checking, an error checking process, all protocols use this.
In the exam ten protocol questions they all do error checking in the same way
INT52 interrupt cpu, it downloads 1500 in the memory in the nic 1200 bits turn them in memory, its data, but to a nic it’s a big binary number, 1500 bytes long, nic has a micro processor, good to do division, we divide the data by a magic number, the text polynomial, x31+x17….ignore this no one can ever remember just understand the magic number is a standard magic number, the only thing, it 2 standard magic number 32 and 16 bits, soon protocols will have 64 bits, the bigger the more accuracy is built in to the CRC, …so pretend its 32 number and it does long division, what CRC does it ends up with a 32 bit remainder, which is the CRC, they stick this at the end of the data and its ready to be transmitted, when its transmitted same division same magic number and it comes up with the remainder and compares it, and if their identical then the NIC is 99% protected.
Synchronous transmission and Asynchronous transmission….5-6lines paragraph,
No comments:
Post a Comment