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CPSC 441 STUDY GUIDE
Internet - Answers - networking infastructure that provies services to distrubuted applications. network of networks Applicaiton layer - Answers - user to user deals with messages i.e emials ,web objects Transport Layer - Answers - end to end deals with sending data from segments to correct socekt i.e multi/demultiplexic Network Layer - Answers - host to host delivery of datagrams. Classic protocol is internet protocol Datalink layer - Answers - hop by hop delivery of frams i.e IP Physical Layer - Answers - transmists bits through physical media network protocol - Answers - hardware software message exchange hosts - Answers - end systems running networked apps packet switches - Answers - forward packets(chunks of data) communication links - Answers - fiber,copper, satellite wires badnwith - Answers - transmission rate networks - Answers - collection od devices routers links managed by an organization Protocols - Answers - controls ending/recieving, i.e http internet as nuts and bolts view - Answers - a network of networks, protocols everywhere internet as service view - Answers - infastructure that provides service to applocations, provides programming interface to distributed applocations LAN - Answers - local area network. Uses physical ethernet cables to connect servers in small area RFC - Answers - (Request for Comments) Documents are how standards and protocols are defined and published for all to see on the IETF website.
IETF - Answers - Internet Engineering Task Force - develops and promotes voluntary Internet standards and protocols, in particular the standards that comprise the Internet protocol suite (TCP/IP). Network edges - Answers - end systems/hosts Acess Networks, physical media - Answers - wired, wireless communication links Network core - Answers - interconnected routers, network of networks access network - Answers - network physically connection and end system to an edge router How to connect end system to edge router - Answers - residential access nets, institutional acess netowrks, mobile access networks mobile network access - Answers - WIFI 4G 5G HFC - Answers - hybrid fiber coax digital subscriber line - Answers - use existing line i.e tlephone wireless netowrk acess entworks - Answers - shared wireless connections end system to router WLAN - Answers - Wireless Local Area Network. Uses wired radio waves not physical Wide-area cellular access networks - Answers - - provided by mobile, cellular network operator (10's km)
- 10's Mbps
- 4G cellular networks (5G coming) reason its called cellular network - Answers - divided into zones enterprise networks - Answers - mix of wired, wireless link technologies, connecting a mix of switches and routers data center networks - Answers - high bandwith links connect to 100s or servers tranmission delay - Answers - L/R How does host send packets of data - Answers - takes applicaiton message, breaks into packets of legnth L, transmists packets into access network at trasmission rate R, link transmission rate bit - Answers - propagates between tramistter/reciever pair
Time Division Multiplexing (TDM) - Answers - Time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots Transit ISP - Answers - ISP that connects access provider ISPs to other access provider ISPs and transit ISPs so the end users can access different websites Point of Presence (POP) - Answers - A bank of modems, servers, routers, and switches through which Internet users connect to an Internet service provider. Multi-homing - Answers - acess ISP connects 2 or more rgional ISPS Internet Exchange Point (IXP) - Answers - hub where multiple ISPs can peer toghether nodal processing delay - Answers - The time it takes to process a packet in a network node (router, switch, hub, etc.), which is dependent on the speed of the device and congestion in the network. Queuing Delay - Answers - packets experience this as it waits to be transmitted onto the link propogation time - Answers - length of the physical link/propogation speed 4 packet delays - Answers - transmission, processing, queuing and propogation throughput - Answers - bits/time units at which bits are sent to reciever ISP - Answers - internet service provider transit ISP - Answers - global ISP handles many access ISPs. Very costly Negatives to packet switching - Answers - excessive congestion possible, great for bursty data but not for resources sharing. packet sniffer - Answers - network reads all packets passing by IP spoofing - Answers - giving packet fake source addresss Denial of Service - Answers - attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic authrntication - Answers - proving you are hwo you say you are via SIM card. confidentiality - Answers - encryptio integrity check - Answers - digital signature prevents from tampering
access restriction - Answers - The creation of different levels of authority to information which are manged through user rights and privileges. firewalls - Answers - special hardware and software to protect networks from external users Kleinrock - Answers - 1961 queuing theory shows effectiveness of packet switching Baran - Answers - 1964 packet switching in military nets ARPAnet - Answers - 1967 convieved by Advanced reaserach project agency 1969 - Answers - first ARPAnet node operational 1972 - Answers - ARPAnet public demo created and first email program Who created queing theory - Answers - Kleinrock which shows effectiveness of packet switching What did Baran create - Answers - packet switching in military nets Who conceived Arpanet - Answers - Advanced reaserarch project agency What is first network control protocol - Answers - NCP Ray Tomlinson did what in 1972? - Answers - wrote first email program What did Alohanet satellite acomplish - Answers - single broadcast network Cerf and kahn made what? - Answers - archetecture for interconnecting networks Ethernet at Xerox was innnovative how? - Answers - made wire based netowrks What year was TCP/IP deployed - Answers - 1983 What did BITNET provide? - Answers - email file transfer among Universities Minitel project - Answers - data netowrking in every home Who invented the web and when? - Answers - Tim Berners-Lee in 1989 server - Answers - always on host, permanent IP adddress, often in data centers for scaling clients - Answers - contact , ocmmunicate with server, dynamic IP addresses, do not communicate directly with each other. i.e HTTP, IMAP, FTP
Persistant HTTP - Answers - multiple objects can be sent over single TCP connection between client, server non persistant http example - Answers - http client intiates connection to server, server accepts, cleints sends message and server recievees and responds, client recieves response containg html and dislays, repeat prior steps until finished then server closes connection Clicking on hyperlink - Answers - browser intiates tcp connection between it and server, 3 way handshake, client sends tcp segement to server, server acknowledges, clinet does same back, first parts take one RTT, client sned message with 3rd part RTT - Answers - time for a small packet to travel from client to server and back HTTP response time - Answers - 2RTT + file transmission time None persistant vs Persistant HTTP - Answers - Non persistant: transaction orientated obtain one web object from one TCP connection Persisitant: session orientated os multiple web objects sent over same connection. perssistent is faster with less overhead POST and GET method - Answers - The GET and POST HTML method attributes specify how form data is sent to a web page. The POST method is more secure than GET as the GET method appends the form data to the URL allowing passwords and other sensitive information collected in a form to be visible in the browser's address bar. HEAD method - Answers - asks server to leave requested object out of response application, transport, network, link and physical layers - Answers - suporting network applications, process data transfer, routing od datagrams to destination, data transfer between neighboring elements, bits on the wire memo - Answers - applciation layer message PUT method - Answers - The put method allows a client to modify a resource state. The client can modify the representation of that resource. The server will take that representation, and modify the resource accordingly. It is not safe, because it modifies the state. Example: PUT /posts/1 HTTP/1. HTTP response - Answers - status (OK), date time, server, last modified, content length, content type
200 Ok - Answers - request suceeded 301 moved permanenty - Answers - request object moved 400 bad request - Answers - request no understood 404 not found - Answers - request message not found on server 505 HTTP version not supported - Answers - version not supported web caches - Answers - satisfy client request without involving origin server. if in cache return else cache new object and return. cookies - Answers - computer program, installed on hard drives, that provides identifying information 4 cookie components - Answers - headerline in response message, header line in request message, cookie file kept on users browser, backend database at the website. How to keep state - Answers - cookies in message or at protocol endpoints Access link (WAN) - Answers - A physical link between a service provider and its customer that provides access to the SP's network from that customer site. Conditional GET - Answers - The mechanism by which HTTP allows a cache to verify that its objects are up to date is called a 3 components of email - Answers - user agent, mail servers, SMTP simple mail transfer protocol User agent - Answers - mail reader, composes, edits and reads email email servers - Answers - mailbox contains incoming mail queue of outoging, SMTP protocl between servers to send messages SMTP RFC - Answers - uses TCP to reliably transfer messages , connected via port 25 for email three phases of SMTP RFC - Answers - handshaking, transfer, closure HTTP vs SMTP - Answers - HTTP: client pull, both ahve ASCII commands, object encapsulated in its onw response message. SMTP: client push, multiple objects sent in mltipart message, use persitant connections, require message to be in 7-bt ASCII, server use CRLF to determine end message.
stps of CDn operation - Answers - visist web page, ask local server, local DNS relays query to authorative server, LDNS sends second query to recieve from server, LDNS forwards to IP host UDP - Answers - A protocol used on the internet for fast transmission of information but with minimal error checking TCP - Answers - provides reliable, ordered and error checked delivery of a stream of packets in the internet DNS (Domain Name System) - Answers - The Internet's system for converting alphabetic names into numeric IP addresses. DNS process - Answers - dsitributed database implemented in hierarchy of many name servers, application layer protocol hosts DNS servers commicate to resolve names. DNS services - Answers - hostname to IP address translation host aliasing mail server aliasing load distribution why not centralized dns? - Answers - single point of failure would crash entire internet, doesnt scale Root server - Answers - top of the DNS hierachy TLD (top-level domain) - Answers - The highest-level category used to distinguish domain names-for example, .org, .com, and .net. A TLD is also known as the domain suffix. authorative DNS server - Answers - actually stores the name to address mapping DNS Name Resolution - Answers - When server recieves request returns IP address for authroative servers that control ending in .com for example, the query is then sent to the loacl DNS server and returns mapping to host iterated query (DNS) - Answers - contacted server replies with name of server to contact "I don't know this name, but ask this server" Recursive query (DNS) - Answers - puts burden of name resolution on contacted name server NORM (DNS) - Answers - query from host to local DNS are recursive all remaining are iterative
DNS protocl message - Answers - identification, flags, remaingin ehaders DDoS Attack - Answers - Distributed Denial of Service Attack. Typically a virus installed on many computers (thousands) activate at the same time and flood a target with traffic to the point the server becomes overwhelmed. Spoofing Attacks - Answers - attacks in which one device attempts to pose as another by falsifying IP, MAC or DHCP address data Connection orientated - Answers - Connection-oriented describes a connection that makes a three-way handshake that acknowledges the connection; the connection also requires an orderly tear-down process. Data is said to be guaranteed delivery when it is connection-oriented. Connection-less - Answers - stateless no handshake client server - Answers - data must be sequentially sent bottleneck is either NF/us or F/dmin P2P - Answers - server must upload at least on copy each cleint downloads. Bottleneck: F/u, F/dmin, NF/us+sum ui BitTorrent - Answers - file-sharing software that allows users to create "swarms" of data as they simultaneously download and upload "bits" of a given piece of content requesting chunks - Answers - roughly equalize number of copies of each chunk in the torrent sending chunks - Answers - every time interval selects another peer to start sending chuncks HTTP streaming - Answers - video is stoed on HTTP server as file or url and client establishes tcp connection with server to request that URL, Server respons by sending the video file. continuous playout constraint - Answers - once client playout begins, playback must match original timing client-side buffering and playout delay - Answers - compensate for network-added delay, delay jitter CDNs - Answers - Content Distribution Networks Steps of CDN operation - Answers - user visists web page, use clicks on video link and sends DNS query for video, local DNS realys query to authoratative server which
UDP sender actions - Answers - is passed and application alyer message, deetermined UDP segment header fields values, creates UDp segment, passes segment to IP UDp receiver actions - Answers - receives segment from IP, cehcks UDP checksum header value, extracts applicaiton layer message, demultiplexing message to applicaiton via socket what is in udp segment header - Answers - source port, dets port, length, cehcksum, application data What is UDP checksum - Answers - detects errors in transmitted segment How does UDP sender use checksum - Answers - treats UDP segment as sequence of 16 - bit integers, addition of content and updates checksum field with values. How does UDP receiver use checksum - Answers - computes checksum of recieved segment and checks if it mathces checksum field sent to it to check for errors Waht does complexity of reliable data transfer protcol primarily rely on? - Answers - the charactersitics of the unreliable channel In reliable data transfer do sender and receiver know the state of each other - Answers - No unless sent through a message What layers does reliabel data transfer occur? - Answers - both the application, transport and datalink layers What is the responsibility of the rdt protocol - Answers - to implement the abstraction that gives a relaible trsnfer layer overotp the unreliable one What are 4 mian relaible data transfer interfaces and what do they do - Answers - rdt_send: passed data to deliver to receiver upper layer udt_send: called by rdt to transfer packets over unreliable channel to reciever rdt_rcv: called when packet arrives on the receiver side of channel deliver_data: called by rdt to deliver data to upper layer Sender in reliable data transfer - Answers - send packets, wait for reply, read recieved receiver in reliable data transfer - Answers - wait for packets, read recieved packets, send reply Checksum is not used to check for errors in reliable data transfer T/F - Answers - false
ACK - Answers - tells receiver packet was received Ok NAK - Answers - negative ACk that tells sender there was error and retransmission is needed Automatic Repeat Request (ARQ) - Answers - an error-control protocol that requires the retransmission of a message until it is received without error. what happens if ACk/NAk is corrupted - Answers - sender retransmits packet sender state transitions - Answers - seq# added to packt, must check if received ACK corrupted, twice as many states receiver state transitions - Answers - mus check if received packet is duplicate How does NAK-free protocol work - Answers - same funcitonality uses ACK only. instead of NAK reciever sends ACk for last packet recieved ok and includes seq# of pkt being oked. duplicate ACk sender results in same action as NAK i.e retransmission new channel assumption - Answers - underlying channel can also lose packets Stop-and-wait protocol - Answers - protocols where the sender cannot receive more data from the upper layer until it receives an ACK or NAK stop and wait operation @sender - Answers - send packet, reset timer and wait for ack, if ack i++ repeat if NACk or timeout repeat stop and wait at receiver - Answers - wat for packet if packet OK send ACK else send NACK, repeat What does pipelining accomplish? - Answers - allows multiple packets to be in transfer, needs buffering at sender/reciever sliding window - Answers - A type of data window in which block sizes are variable. Window size is continually reevaluated during transmission, with the sender always attempting to send the largest window it can to speed throughput. Cumulative ACK - Answers - if multiple packets were delivered to a receiver, but somehow a couple of ACKs were lost. The receiver will send an ACK on the next transmission round that covers all previous packets, even though the sender wasn't expecting these ACKs. Cumulative ACKs cover the acknowledgement of multiple packets from the receiver. selective ACK - Answers - ACK indivudally acknowledges correctly received packets
TCP round trip estimate is what - Answers - exponeential moving average, influence of past sample decrease exponentially fast TCP fast retransmit - Answers - if sender receives 3 ACKs for same data ("triple duplicate ACKs"), resend unacked segment with smallest seq # likely that unacked segment lost, so don't wait for timeout What are the big 3 applications of the early interent - Answers - file transfer, email, usenet Leased transmission lines used to build early internet had data rates of about - Answers
- 56 kbps In TCP based server what are some typical system calls - Answers - listen and accept How many root servers are there in DNS - Answers - aprox 10 What happens to congestion window in slow start algorthm - Answers - cwdn increase exponenetially What is TCP slow start algorthm - Answers - set intial cwdn to small value, for each aknowledgement increase it so more data can be sent each rtt, sending increase xponetially until threshold, when congestion detected reduce cwdn by half only increase cwdn linearly to avoid congestion if still congested reduce cwnd further. TCP Reno - Answers - TCP Reno differs from TCP Tahoe at congestion avoidance. When triple duplicate ACKs are received, it will halve the congestion window, perform a fast retransmit, and enters fast recovery. If a timeout event occurs, it will enter slow- start, same as TCP Tahoe. average throughput acheived through TCP reno - Answers - inversely prporptional to the square root of the average packet loss TCP Vegas - Answers - uses delay based cogestion control encapsulation with network layers - Answers - move down protocol stack used at host deencauslation with network layers - Answers - happens at destination move up proctocl stack switch - Answers - intermediate devices the store and forward packets flow control vs congestion control - Answers - flow: between sinbgle sender and reciever to ensure sender does not send more than receiver can handle.
congestion: network wide to make sure many senders do not send more data than the network can handle. Demultiplexing - Answers - delivering the data in a transport-layer segment to the correct socket Is plain text HTTP used in email systems - Answers - Nope Pipelined Protocls are desinged to... - Answers - improve link utilization comapred to stop and wait Protoclas Cahing is used in - Answers - DNS: provides mapping between host names and IP address relies on cache hierchy. HTTP: cahce popular web objects closer to clients to reduce latency CDN: cahce large media like movies for streaming optimization Sequence Number - Answers - used to detect duplicate segments, detec loss and keep in order delivery Checksum - Answers - cehck against corrupt segmeents by matching with source checksum 16 bit The best effort service model is example of waht type of multiplexing - Answers - statistical multiplexing
