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Application Layer

20 questions · 7 topics

2013 Q1(a)Application LayerNetwork Delay· 4 marks

List two causes of network latency (i.e. delay in sending data). For each of the causes you list, explain how the latency due to that cause is calculated.

latencytransmissionpropagation
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2013 Q1(b)Application LayerNetwork Delay· 5 marks

You want to send 10GBytes of videos to a friend. You have a choice of burning them to DVD and sending by express post, which will take 1 day (24 hours) for them to arrive or you can send them by Internet on which you get an average upload data rate of 2Mb/sec. Show which method will be faster. You must show your work, no marks for just guessing an answer.

latencythroughputunit conversion
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2013 Q1(c)Application LayerSMTP· 3 marks

Why don’t SMTP servers just require all senders to be authenticated before accepting mail?

emailauthentication
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2013 Q1(d)Application LayerDNS· 5 marks

Explain how caching is used in the Domain Name System (DNS) during an iterative query. Specify what information is cached at the local host, the local DNS, the root DNS, the Top Level Domain (TLD) DNS and the authoritative DNS. Be sure to include only cached information not all information stored.

name resolutioncacheTTL
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2013 Q1(e)Application LayerHTTP· 4 marks

HTTP 1.1 introduced the use of persistent connections for downloading web objects. Explain why this improves performance over a connection using TCP congestion control (i.e. AIMD as used in TCP Reno and Tahoe)

weblatencyslow start
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2013 Q1(f)Application LayerClient/Server vs P2P· 4 marks

Under what conditions will distributing a file by a client-server architecture be faster than distributing the file by a peer to peer architecture.

file distributionscalability
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2014 Q1(a)(i)Application LayerClient/Server vs P2P· 3 marks

The equation for determining the download time for a peer-to-peer file sharing is given below. Dpsp ≥ max(F/us, F/dmin, NF/(us + Σ_{i=1}^{N} ui)) Explain what each of the following terms represents (for example: ”The time for one peer to download a single copy of the file”) α) F/us β) F/dmin γ) NF/(us + Σ_{i=1}^{N} ui)

P2Pfile distribution
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2014 Q1(a)(ii)Application LayerClient/Server vs P2P· 4 marks

The equation for determining the download time for a peer-to-peer file sharing is given below. Dpsp ≥ max(F/us, F/dmin, NF/(us + Σ_{i=1}^{N} ui)) Using the same terms, give an equation for the minimum download time for a client/server file download.

client-serverfile distribution
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2014 Q1(b)(i)Application LayerNetwork Delay· 4 marks

Two delays that contribute to the total end-to-end delay in networks are propagation delay and transmission delay. Explain what these two delays are and show how to calculate these delays.

latency
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2014 Q1(b)(ii)Application LayerNetwork Delay· 2 marks

Two delays that contribute to the total end-to-end delay in networks are propagation delay and transmission delay. What two other delays contribute to the total end-to-end delay in networks?

latencyqueuing
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2014 Q1(c)Application LayerSocket / Port· 4 marks

You have a web browser with two windows open each viewing a different web page. These two web pages are hosted on the same web server. Give one set of possible values for the source and destination port numbers and IP addresses for each of the two socket connections (one connection for each web page). For example: connection 1: src-129.127.6.24, dest-129.127.8.52, src-3456, dest-7892 (note this is *not* a correct answer, it’s just to show the format to write your answer in)

socketsportsTCP
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2014 Q1(d)Application LayerDNS· 4 marks

A local DNS server receives a request to resolve the name www.mycom.com.au There is no entry for this name in the local hosts file or the cache. What steps will the local DNS server do to resolve this name to an IP address?

name resolutioniterative query
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2014 Q1(e)Application LayerHTTP· 3 marks

Explain how persistent connections in HTTP can reduce the latency in retrieving web pages.

weblatency
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2015 Q1(a)Application LayerClient/Server vs P2P· 4 marks

The equation for determining the download time for a peer-to-peer file sharing and client/server file sharing is given below. Dp2p ≥ max(F/us, F/dmin, NF/(us + Σ_{i=1}^{N} ui)) Dcs = max(NF/us, F/dmin) Match the following terms to what they represent i) F/us ii) F/dmin iii) NF/(us + Σ_{i=1}^{N} ui) iv) NF/us 1) Time needed for server to upload one copy of the file 2) Time for cooperating peers + server to upload a copy of the file to all peers 3) Time for server to upload file to all clients 4) Time for slowest peer to download one copy of the file

P2Pclient-serverfile distribution
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2015 Q1(b)Application LayerClient/Server vs P2P· 3 marks

True or False: assuming that the server participates in the peer to peer exchange (as in the equation above), peer to peer download will always be faster than or the same speed as client/server download. Explain your answer

P2Pclient-server
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2015 Q1(c)(i)Application LayerNetwork Delay· 6 marks

You are building a communication network based on RFC 1149 "IP over avian carrier". You attach two 128GB flash drives to your pigeon. You can write data to the flash drive at the rate of 20 MB/s and you can read data from the flash drive at the rate of 50MB/s. The flying speed of a pigeon is 80km/h and pigeons do not need to stop for food or rest before reaching destination. What is the total time needed for you to send and your friend who lives in Brazil (Rio is 13600 km from Adelaide) to receive a 4 ∗ 10^9 bit file of your favourite home movies? Solve for the number of seconds delay. Show your work.

latencyRFC 1149unit conversion
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2015 Q1(c)(ii)Application LayerNetwork Delay· 4 marks

You are building a communication network based on RFC 1149 "IP over avian carrier". You attach two 128GB flash drives to your pigeon. You can write data to the flash drive at the rate of 20 MB/s and you can read data from the flash drive at the rate of 50MB/s. The flying speed of a pigeon is 80km/h and pigeons do not need to stop for food or rest before reaching destination. Under what conditions would IP over avian carrier have a lower propagation delay or transmission delay than using the Internet? Explain your answer.

latencythroughputRFC 1149
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2015 Q1(d)Application LayerDNS· 2 marks

Give two reasons why iterative DNS queries are preferred to recursive DNS queries. Explain your answer.

name resolutionrecursive query
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2015 Q1(e)Application LayerHTTP· 3 marks

Explain three techniques used by the Web (HTTP) to reduce latency

weblatencycaching
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2015 Q1(f)Application LayerProtocol Design· 2 marks

One key role of protocols is to define the syntax (ie structure) of requests and responses. To do this, protocols need to define where one exchange ends and the next one begins. Give two plausible ways in which a text based protocols can indicate the end of an exchange.

protocol designframingHTTPSMTP
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