14 - communincation Flashcards

Question

physical network layer

Answer 1

specifies requirements of hardware to be used

Answer 2

identifies protocols in the packet header (TCP/IP in this case) and delivers packets to network

Answer 3

- System that connects a number of computers or devices to form a LAN (not Internet) - Uses protocols to control the movement of frames between devices and prevent simultaneous transmission - Local protocol - does not allow you to communicate with external devices (need IP for this)

Answer 4

* Destination - MAC address of the destination computer * Source - MAC address of the source computer * Ethernet type or length - ○ if the frame length ≤ 1539B then this is the length of the Ethernet frame ○ if the frame length > 1539B then this is the Ethernet type (IPv4 or IPv6 in our example) * Frame check - includes a checksum to allow checking of data integrity

Answer 5

- Peer to peer - but scaled up - fast file sharing over the Internet - allows many peers to share files

Answer 6

- Torrent is created - File is broken into = segments called pieces - peers wanting to download a file have to obtain the torrent and connect to the appropriate tracker - Each peer gets a piece of file and they become a source for that piece so other peers know where to find it - Once a peer has downloaded a files completely they make the file available to other peers in the swarm and become a seed. - The more seeds the faster the file downloading process - Logging off is frowned upon as comps need to be on to download from

Answer 7

small file containing metadata about the file that’s about to be shared

Answer 8

group of peers connected

Answer 9

peer that has downloaded a file and then made it available to the other peers

Answer 10

- central server that stores details about other peers, eg IP allows users to locate each other

Answer 11

a peer that has a negative impact on the swarm by downloading more than uploading * Ratio - amount uploaded/ downloaded * If >1 then positive impact * If <1 then negative impact

Answer 12

a peer that downloads files but doesn't make any new content available

Answer 13

- Method of transmission where a dedicated channel/circuit lasts the duration of communication - E.g. PSTN

Answer 14

○ Channel between sender and receiver established ○ Data transfer takes place - normally bidirectional ○ After data transfer is complete connection is terminated

Answer 15

- circuit dedicated to single transmission - whole bandwidth available - faster data transfer rate - packets arrive in same order - no lost packets as packets follow in sequence

Answer 16

- a message is broken into packets which can be sent along paths independently from each other - Packets need to be reassembled in order at destination - by TCP/IP - Each packet follows own path - Routing selection depends on number of packets waiting to be processed at each node (traffic) - Shortest available path is selected - Packets can reach destination in different order to how sent - E.g. VoIP

Answer 17

- not very flexible - has to use single dedicated line - nobody else can use the circuit - always there even when not used - if there is a failure on the line there is no alternate route - requires greater bandwidth - time to establish link can be long

Answer 18

- no need to tie up a communication line - can overcome failure of a line by rerouting - easy to expand traffic usage - charges only for duration of connectivity (cheaper) - high data transmission is possible - uses digital networks meaning digital data is transmitted dircetly

Answer 19

- protocols used can be more complex - if a packet is lost the sender must resend - does not work as well in real time data streams - channel has to share bandwidth with outer packets - delay at destination during reassembly - needs lots of RAM to handle large amounts of data

Answer 20

- when a packet goes from router to router - hop number is added to the header - each packets is only allowed a finite number of hops decided by the network protocol - each time the packet passes through the router the hop number is -1 - if the packets hop number = 0 and its not at its destination then its deleted at the next router - prevents lost packets hopping forever

Answer 21

- part of a data packet containing key data such as destination IP address, sequence number, and so on. - Packets also contain error checking eg checksum or parity - if values are different then a request is made to resend - Priority values indicate which queue should be used (shorter if higher priority)

Answer 22

- a data table that contains the information necessary to forward a package along the shortest or best route to allow it to reach its destination - When the packet reaches a router the packet header is compared with the routing table which supplies instructions to send the packet to the next router (a hop)

Answer 23

○ Number of hops ○ MAC address of the next router ○ Metrics (cost assigned to each route so the most efficient is found) ○ Network ID or pathway ○ Gateway (points to the gateway through which target network can be reached) ○ Netmask (used to generate network ID) ○ Interface (indicates which locally available interface is responsible for reaching the gateway)

14 - communincation Flashcards

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