Computer Networks Midterm

Processing Delay

checking of packet data by the device. it checks for forwarding and data integrity. Usually the smallest, after propagation

Queueing delay

this delay happens on the router. If the delay is less than 0, there is little to no queueing delay. If the delay = 1, we at max cap. for the queue. If the delay is greater than 1, there is more packets arriving than can be serviced.

Transmission delay

the time it takes for the device to get the packet ONTO the link. measured in L/R

Propagation delay

the time it takes for the packet to travel OVER the link. measured in d/s (where d is the length of the link and s is the speed of propagation)

Application layer

for supporting network applications - HTTP, IMAP, SMTP, DNS

Transport layer

for process to process data transfer - TCP, UDP. provides transmit instructions

Network layer

for forwarding and routing of datagrams for source to destination - IP, routing protocols

Link layer

for data transfer between neighboring network elements - Ethernet, WiFi (802.11), PPP

Physical Layer

bits on the wire/ signals in the air

Packet sniffing

reading the packets that are in the air that are transmitted from a device via wifi.

IP spoofing

getting the traffic that is intended for one receiver to be sent somewhere else

DDoS

distributed denial of service attack is swarming a server with so many requests that it cannot function

client-to-server architecture

where clients are communicating with servers either as a medium or as a ricochet.

• servers are always on

• clients can connect intermittenly

• clients do not connect to each other, only through the server

peer-to-peer architecture

there is no central server that is always on, instead peers request data from other peers.

• this architecture is self-scalable

• there might be a small server to start connection between devices

socket

combination of IP address and port number to designate specific request in a specific spot in memory.

stateless (for HTTP)

either side of the HTTP connection is not keeping tabs on what is going on

web cache

backup servers that get data from origin server updates and keep frequently requested websites/data. web caches turn over data pretty quickly to keep up with demand.

A and AAAA record

A record name: host name, value: IPv4. AAAA record name: host name, value: IPv6

NS record

name: domain, value: host name of authoritative server. sends back the A record because authoritative servers hold all the IP addresses

C NAME record

name: domain/hostname(ibm.com), value: canonical name(testserver2.ibm.com)

MX record

name: domain, value: mail server for indicated domain

iterative request

when each step/request is returned to the requesting server. "I don't know, here is the info for who to ask next"

recursive request

"I don't know, let me find out for you"

DASH

stands for dynamically adaptive streaming over HTTP.

• used by server to reprocess uploaded video to other resolutions

• used by device/client to monitor internet speeds and request the video quality the device can handle

CDN

content distribution networks store/serve multiple copies of videos at multiple geographically distributed sites

enter deep (CDN)

entering deep into local ISP networks which have copies of servers

• closer to users means faster downloads

• individual servers are vulnerable to attacks and harder to maintain

bring home (CDN)

puts copies of servers at IXPs which are at the heart of the Internet

• simpler distribution and more security for servers

• access is farther meaning slower downloads

multiplexing

TCP collecting packets and weaving them together to be sent out

demultiplexing

TCP taking the packets from the Internet and distributing them to their sockets

UDP header

checksum is the sum of all of the words(16 bit phrases) in a segment using binary arithmetic with overflow wrap-around and transforms to the 1’s complement.

TCP header

flow control: receive window field which has the # of bytes the receiver is willing to accept. 

congestion notification: CWR and ECE fields

connection management: RST, SYN, and FIN fields

bottleneck

Ways to add reliability (building blocks of TCP)

• numbering packets

• establish 2-way communication

• timing: TTL and RTT and determining if a packet is missing or just taking a long time

• ensure that all of the packets were received (ACK and NAK)