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CNT |! Midterm |! exam |! with |! precise |!
detailed |! answers
A |! ______________ |! defines |! the |! format |! and |! the |! order |! of |! messages |! exchanged |! between two |! or |! more |! communicating |! entities, |! as |! well |! as |! the |! actions |! taken |! on |! the |! transmission and/or |! receipt |! of |! a |! message |! or |! other |! event. |! - |! Correct |! answer |! ✔protocol What |! does |! a |! protocol |! specify? i. |! order |! of |! received |! messages ii. |! format |! of |! received |! messages iii. |! order |! of |! sent |! messages iv. |! format |! of |! sent |! messages v. |! all |! of |! the |! choices |! - |! Correct |! answer |! ✔v Circuit |! switching |! allows |! more |! users |! than |! packet |! switching |! when |! users |! are |! rarely active |! at |! the |! same |! time true/false |! - |! Correct |! answer |! ✔false In |! packet |! switching, |! there |! is |! no |! chance |! of |! packet |! loss
true/false |! - |! Correct |! answer |! ✔false Since |! the |! amount |! of |! buffer |! space |! in |! a |! packet-switched |! network |! is |! finite, |! an arriving |! packet |! may |! find |! that |! the |! buffer |! is |! completely |! full |! with |! other |! packets |! waiting for |! transmission. |! In |! this |! case, |! _______________ |! will |! occur |! - |! Correct |! answer |! ✔packet |! loss There |! are |! two |! approaches |! for |! circuit |! switching: |! FDM |! and |! TDM true/false |! - |! Correct |! answer |! ✔true Capacity |! and |! bandwidth |! of |! a |! link |! are |! the |! same |! as |! its |! transmission |! rate true/false |! - |! Correct |! answer |! ✔true Which |! of |! the |! following |! delays |! depend |! on |! the |! length |! of |! physical |! layer? i. |! Propagation |! delay ii. |! Queuing |! delay iii. |! Transmission |! delay iv. |! All |! of |! the |! choices |! - |! Correct |! answer |! ✔i The |! propagation speed |! depends |! on |! the |! physical |! medium |! of |! the |! link true/false |! - |! Correct |! answer |! ✔true
Web |! caching |! is |! used |! by |! HTTP |! to |! reduce |! response |! time |! for |! client request. true/false |! - |! Correct |! answer |! ✔true What |! transport |! service |! does |! an |! app |! need? i. |! data |! integrity ii. |! minimum |! throughput iii. |! security iv. |! all |! of |! the |! choices |! - |! Correct |! answer |! ✔iv In |! persistent |! HTTP |! connections, |! the |! server |! closes |! the |! connection |! only |! when |! it |! is |! not |! used |! for |! a |! certain |! configurable |! amount |! of |! time true/false |! - |! Correct |! answer |! ✔true A |! nonpersistent |! connection |! is |! the |! one |! that |! is |! closed |! after |! the |! server |! sends |! the |! requested |! object |! to |! the |! client. true/false |! - |! Correct |! answer |! ✔true With |! HTTP |! persistent |! connections, |! the |! server |! leaves |! the |! TCP |! connection |! open |! after |! sending |! responses |! and |! hence |! the |! subsequent |! requests |! and |! responses |! between |! the |! same |! client |! and |! server |! can |! be |! sent. |! true/false |! - |! Correct |! answer |! ✔true
De-multiplexing |! happens |! on |! the |! sender |! side |! of |! a |! data |! transfer. true/false |! - |! Correct |! answer |! ✔false At |! the |! receiving |! end, |! the |! transport |! layer |! examines |! these fields |! to |! identify |! the |! receiving |! socket |! and |! then |! directs |! the |! segment |! to |! that |! socket. |! This job |! of |! delivering |! the |! data |! in |! a |! transport-layer |! segment |! to |! the |! correct |! socket |! is |! called |! _____________ |! - |! Correct |! answer |! ✔demultiplexing Multiplexing |! happens |! on |! the |! network |! layer true/false |! - |! Correct |! answer |! ✔false The |! job |! of |! gathering |! data |! chunks |! at |! the |! source |! host |! from |! different sockets, |! encapsulating |! each |! data |! chunk |! with |! header |! information |! (that |! will |! later |! be used |! in |! demultiplexing) |! to |! create |! segments, |! and |! passing |! the |! segments |! to |! the |! network layer |! is |! called |! ________________ |! - |! Correct |! answer |! ✔multiplexing Multiplexing |! happens |! on |! both |! sender |! and |! receiver |! side |! of |! a |! data transfer true/false |! - |! Correct |! answer |! ✔false De-multiplexing |! and |! multiplexing |! are |! necessary |! when |! one |! host |! runs |! multiple |! processes.
Sender's |! utilization |! in |! rdt3.0 |! is |! the |! same |! as |! rdt2. true/false |! - |! Correct |! answer |! ✔true TCP |! standardizes |! handling |! of |! out-of-order |! data |! segments |! arrival true/false |! - |! Correct |! answer |! ✔false Congestion |! control |! of |! TCP |! Reno |! treats |! triple |! ACK |! duplicates |! differently |! from timeout |! events true/false |! - |! Correct |! answer |! ✔true In |! the |! slow-start |! state, |! the value |! of |! cwnd |! begins |! at |! 1 |! MSS |! and |! increases |! by |! 1 |! MSS |! every |! time |! a |! transmitted segment |! is |! first |! acknowledged true/false |! - |! Correct |! answer |! ✔true Slow |! Start |! of |! TCP |! means |! that |! the |! congestion |! window |! size |! initially |! increases |! by a |! constant |! slope |! of |! MSS/RTT. true/false |! - |! Correct |! answer |! ✔false Pick |! the |! correct |! statement
i. |! Flow |! control |! manages |! data |! traffic |! load |! in |! network |! core; |! but |! congestion |! control mitigates |! sever |! data |! traffic |! load |! in |! network |! edge. ii. |! Both |! flow |! control |! and |! congestion |! control |! manage |! data |! traffic |! load |! in |! network edge. iii. |! Both |! flow |! control |! and |! congestion |! control |! manage |! data |! traffic |! load |! in |! network core. iv. |! Flow |! control |! manages |! data |! traffic |! load |! in |! network |! edge; |! but |! congestion |! control mitigates |! sever |! data |! traffic |! load |! in |! network |! core. |! - |! Correct |! answer |! ✔iv Which |! protocol |! is |! not |! an |! application-layer |! protocol? TCP HTTP POP FTP |! - |! Correct |! answer |! ✔TCP Which |! protocol |! is |! used |! to |! make |! HTTP |! more |! secure? TCP IP SRS SSL |! - |! Correct |! answer |! ✔SSL
In |! Distance-Vector |! Algorithm, |! a |! link |! cost |! decrease |! is |! advertised |! faster |! than |! link |! cost |! increase. true/false |! - |! Correct |! answer |! ✔true In |! Broadcasting, |! messages |! must |! be |! duplicated |! by |! the |! source |! for |! the |! sake |! of |! efficiency. true/false |! - |! Correct |! answer |! ✔false How |! long |! is |! a |! MAC |! address? |! - |! Correct |! answer |! ✔ 6 |! bytes What |! are |! the |! Link |! layer |! services? |! - |! Correct |! answer |! ✔Framing, |! link |! access, |! reliable |! delivery, |! error |! detection |! and |! correction The |! _____ |! is |! a |! communication |! protocol |! used |! for |! discovering |! the |! link |! layer |! address, |! such |! as |! a |! MAC |! address, |! associated |! with |! a |! given |! internet |! layer |! address, |! typically |! an |! IPv4 |! address. |! - |! Correct |! answer |! ✔ARP ARP |! stands |! for |! - |! Correct |! answer |! ✔Address |! Resolution |! Protocol Formula |! for |! propagation |! delay |! - |! Correct |! answer |! ✔(link |! length) |! / |! (propagation |! speed) Formula |! for |! transmission |! delay |! - |! Correct |! answer |! ✔(size |! of |! file) |! / |! (link |! capacity)
Describe |! circuit |! switching |! - |! Correct |! answer |! ✔Resources |! needed |! along |! a |! path |! are |! reserved |! for |! the |! duration |! of |! the |! communication |! session |! between |! 2 |! end |! systems. Traditional |! telephone |! networks |! are |! examples |! of |! _____________ |! networks |! - |! Correct |! answer |! ✔circuit-switched In |! a |! ______________________ |! network, |! to |! send |! a |! message |! from |! a |! source |! end |! system |! to |! a |! destination |! end |! system, the |! source |! breaks |! long |! messages |! into |! smaller |! chunks |! of |! data |! known |! as |! packets. Between |! source |! and |! destination, |! each |! packet |! travels |! through |! communication |! links and |! packet |! switches |! (for |! which |! there |! are |! two |! predominant |! types, |! routers |! and |! linklayer switches). |! - |! Correct |! answer |! ✔packet-switched In |! packet-switched |! networks, |! packets |! are |! transmitted |! over |! each |! communication |! link |! at |! a |! rate equal |! to |! the |! full |! transmission |! rate |! of |! the |! link true/false |! - |! Correct |! answer |! ✔true Compare |! the |! client-server |! with |! P2P |! architecture. |! What |! are |! the |! pros/cons |! of |! each |! architecture? |! - |! Correct |! answer |! ✔Client-server |! architecture |! is |!
destination, |! port |! of |! source, |! and |! port |! of |! destination |! (all |! because |! it |! is |! connection |! oriented) UDP: |! Destination |! port |! number |! and |! destination |! IP |! address |! (because |! it's |! connectionless) Assume |! that |! an |! HTTP |! client |! is |! connected |! to |! an |! HTTP |! server |! by |! a |! TCP |! connection |! with |! RTT=50ms |! and |! throughput |! of |! 10Mbps. |! How |! much |! time |! does |! it |! take |! that |! the |! client |! requests |! a |! webpage |! containing |! 5 |! 2MB |! files |! and |! the |! server |! sends |! the |! webpage |! and |! the |! 5 |! files |! in |! it |! back |! to |! the |! client |! if: (a) |! persistent |! HTTP |! is |! used? |! (b) |! non-persistent |! HTTP |! is |! used |! - |! Correct |! answer |! ✔a) |! 1RTT |! + |! transmission |! delay |! of |! of |! 5 |! 2MB |! files b) |! 5 |! files |! * |! 2 |! RTT |! + |! transmission |! delay |! of |! of |! 5 |! 2MB |! files What |! is |! the |! formula |! for |! sender |! utilization |! (Usender)? |! - |! Correct |! answer |! ✔L/R |! / |! (RTT+L/R) How |! many |! TCP |! connections |! do |! FTP |! clients |! and |! servers |! create? |! Explain |! what |! kind |! of |! messages |! are |! exchanged |! on |! each |! connection. |! - |! Correct |! answer |! ✔FTP |! uses |! two |! TCP |! connections |! for |! communication. |! One |! to |! pass |! control |! information, |! and |! is |! not |! used |! to |! send |! files |! on |! port |! 21, |! only |! control |! information. |! And |! the |! other, |! a |! data |! connection |! on |! port |! 20 |! to |! send |! the |! data |! files |! between |! the |! client |! and |! the |! server. What |! does |! SMTP |! do |! and |! how |! it |! is |! different |! from |! mail |! access |! protocols |! like |! POP |! and |! IMAP? |! - |! Correct |! answer |! ✔SMTP |! sends |! emails, |! POP |! receives |! emails, |! IMAP |! retains |! copies
What |! is |! multiplexing? |! - |! Correct |! answer |! ✔way |! of |! sending |! multiple |! signals |! or |! streams |! of |! information |! over |! a |! communications |! link |! at |! the |! same |! time |! in |! the |! form |! of |! a |! single What |! is |! demultiplexing |! - |! Correct |! answer |! ✔The |! method |! that |! a |! destination |! computer |! uses |! to |! process |! an |! incoming |! packet |! (splitting |! the |! received |! signal |! into |! understandable |! data) What |! are |! the |! steps |! to |! do |! the |! following |! problem? What |! is |! the |! UDP |! checksum |! of |! the |! following |! data |! represented |! by |! hexadecimal |! notation? A0AAD3457E34 |! - |! Correct |! answer |! ✔Split |! into |! 4 |! bit |! number. |! Add |! first |! 2 |! numbers |! together |! then |! add |! the |! checksum. |! Then |! add |! the |! carry |! out |! to |! that |! number |! then |! add |! it |! to |! last |! hex Assume |! that |! host |! A |! uses |! RDT3.0 |! to |! send |! 4kB |! packets |! over |! a |! connection |! with |! RTT |! 40ms |! and |! throughput |! 50Mbps. (a) |! What |! is |! the |! utilization |! of |! sender |! (fraction |! of |! time |! that |! A |! is |! busy |! sending |! packets |! away)? |! (b) |! If |! we |! use |! pipelining |! to |! increase |! the |! sender's |! utilization, |! what |! would |! be |! the |! ideal |! utilization |! of |! sender |! if |! it |! sends |! n |! packets |! in |! an |! RTT? |! Find |! the |! utilization |! as |! a |! function |! of |! n. |! (c) |! How |! large |! can |! n |! possibly |! be |! chosen |! in |! previous |! part? |! - |! Correct |! answer |! ✔a) |! find |! Usender b) |! multiply |! result |! from |! part |! a |! by |! n |! and |! set |! uSender |! to |! 1, |! then |! solve |! for |! n c) |! set |! usender |! equal |! to |! one |! and |! solve |! for |! n
When |! is |! a |! transport-layer |! protocol |! considered |! to |! be |! fair? |! - |! Correct |! answer |! ✔if |! K |! TCP |! sessions |! share |! same |! bottleneck |! link |! of |! bandwidth |! R, |! each |! should |! have |! average |! rate |! of |! R/K even |! bits |! in |! parity |! = |! - |! Correct |! answer |! ✔zero odd |! bits |! in |! parity |! = |! - |! Correct |! answer |! ✔one How |! to |! solve |! for |! remainder |! - |! Correct |! answer |! ✔R |! = |! entire |! digit |! with |! 000000 |! added |! to |! end/G
