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CS3102 Networks > 2: Application Layer > Flashcards

2: Application Layer Flashcards

1
Q

What is TCP?

A

Transmission Control Protocol is a transport-layer protocol facilitating the reliable transmission of data between two endpoints on a computer network.

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2
Q

What are TLD servers?

A

Top-level domain servers are responsible for resolving the addresses under one particular domain, e.g. .com.

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3
Q

How does socket programming work with UDP?

A

Connectionless, unreliable datagrams are sent and may or may not be received. methods of ensuring reliability must be built on top of UDP. But might be faster than TCP with less overhead for some uses.

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4
Q

Describe the P2P architecture.

A

A network topology with no always-on servers in which peers intermittently communicate with each other, requesting services from each other and providing services to others in return. P2P networks are self-scalable since new peers add serving capability as well as requests.

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5
Q

What is SSL?

A

Secure Sockets Layer is an application-layer security technology used to encrypt data to provide security.

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6
Q

What are DNS RRs?

A

Resource records are the individual data entries in name servers.

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7
Q

What is cache delay?

A

The delay between a request being made by a client and a cache returning the result of the request (rather than the origin server).

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8
Q

What are the method types in HTTP/1.0?

A

GET, POST, and HEAD.

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9
Q

What is a server?

A

An always-on computer that provides network resources to client devices.

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10
Q

How do you find access link utilisation?

A

Link utilisation = current data rate on link ÷ link capacity.

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11
Q

What is the heirarchy of DNS?

A

There are root, TLD, authoritative, and local DNS servers that handle iterative queries that are passed up through the DNS hierarchy to reduce strain.

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12
Q

What is a torrent? What is a torrent tracker?

A

A torrent is a group of peers that exchange the chunks of a file. A torrent tracker is a computer maintinging the list of peers storing different chunks in the torrent of a file.

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13
Q

What is a client?

A

An intermittently connected end device that requests resources from servers on a network.

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14
Q

What is IP?

A

Internet Protocol is a network-layer protocol that handles the routing and addressing of packets between nodes on a computer network.

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15
Q

Why is HTTP stateless?

A

Because the server maintains no information about past client requests, so each request is treated atomically.

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16
Q

What are the 2 types of HTTP messages?

A

request and response messages

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17
Q

What are cookies?

A

A small piece of data used to maintain the user-server state of a web browser across separate connections.

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18
Q

How is UDP different from TCP?

A

TCP provides reliable transport, flow control, and congestion control, and is connection-oriented. UDP does not provide any of these features. Neither provides security, timing, or a guarantee of a minimum throughput.

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19
Q

What is link utilisation?

A

The proportion of the capacity of a link which it is actively being used with traffic. Link utilisation = current data rate on link ÷ link capacity.

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20
Q

How do you find total delay when using a cache?

A

Where p = the probability a resource will be cached = cache hit rate,
total delay = p * delay to get resource from the origin server (1 - p) * delay to get resource from the cache

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21
Q

What is a conditional GET?

A

Allows you to only get a resource if a condition is true, usually if it has been modified since a chosen date. This can be used with caches to only retrieve resources if the versions of them currently cached are out of date

22
Q

What are DNS query and reply messages?

A

Query messages are sent to name servers, they respond with reply messages.

23
Q

What are mail servers?

A

A specialised server that handles the storing, distribution, and transfer of email messages on a network.

24
Q

What is P2P architecture?

A

A network topology in which each node, or peer, both requests and provides services. It has no central always-on server, as with the client-server architecture.

25
Q

What is a mailbox?

A

A set of incoming email messages for a certain user.

26
Q

What is a message queue?

A

A set of outgoing email messages to be sent on behalf of a certain user.

27
Q

How does SMTP work?

A

The mail servers have a handshake, then the message sends, then the connection closes.

28
Q

What is POP?

A

Post Office Protocol is a protocol used to allow email clients to retrieve email messages from mail servers. Once downloaded, the messages are deleted from the server.

29
Q

What is IMAP?

A

Internet Message Access Protocol is a protocol used to allow email clients to retrieve email messages from mail servers. Emails aren’t deleted on the server when they’re retrieved, and the server is the single place messages are kept.

30
Q

What are the variants of CDNs used?

A

Enter deep: close to users in many access networks

Bring home: a smaller number of larger clusters of servers in POPs near to access networks - but not in them.

31
Q

What is DNS?

A

Domain Name System is a group of technologies allowing for the resolution of domain names on the Internet. It is a distributed, hierarchical database and an application-layer protocol.

32
Q

Why are name servers distributed?

A

A single server wouldn’t scale (to the whole Internet) and would mean there is a single point of failure.

33
Q

What are authoritative DNS servers?

A

Domain name servers that provide name server mappings for the hosts of an organisation.

34
Q

What are local DNS name servers?

A

The default DNS server of an ISP that caches recent queries and their results.

35
Q

Wht are the types of DNS records?

A

A = mapping, NS = authoritative name server for a domain, CNAME = mapping for real name to alias, MX = mail server associated with a name.

36
Q

How does DNS caching work?

A

Any time a DNS server learns a mapping from a euery it caches the result, with a set time to live.

37
Q

How does BitTorrent chunk requesting and sending work?

A

Peers wanting a file periodically ask each peer which chunks they have and request the rarest first from each. Chunks are sent to the 4 peers sending you chunks at the greatest rate: tit-for-tat. The list of the top 4 peers is reevaluated every 30 seconds, randomly unchoking a new peer which may join the top 4.

38
Q

How do you find the time to distribute files in client-server networks?

A

A computer program running on a host. Server processes wait to be contacted, and client processes initiate communications.

39
Q

How do you find the time to distribute files in P2P networks?

A 
time to distribute a file of size F to N clients using P2P approach, DP2P > max{F/us, F/dmin, NF/(us   Σui)}
F = file size
us = server upload capacity
dmin = min client download rate
ui = download capacity of the ith peer
F/us = time to send 1 copy
F/dmin = minimum client download time
us   Σui = max upload rate
40
Q

What is a CBR encoding?

A

Constant bit rate = a video of a fixed encoding rate.

41
Q

Why is BitTorrent said to be tit-for-tat?

A

You only send chunks to the top 4 peers sending chunks to you at the fastest rate, choking all others. You reevaluate the list every 30 seconds, optimistically unchoking a peer which may join the top 4.

42
Q

Why is distributed, application-level infrastructure needed for video streaming services?

A

The massive number of users and variety in their capabilities.

43
Q

What is video coding? What is spatial coding? What is temporal coding?

A

Using redundancy within and between images to decrease the number of bits to encode an image, usually spatial and temporal. Spatial will be combining pixels of the same value, temporal only sending changes between frames in video rather than the whole frame each time.

44
Q

What is a VBR encoding?

A

Variable bit rate = a video of an encoding rate that changes as spatial and temporal codings change

45
Q

What is DASH?

A

Dynamic, Adaptive Streaming over HTTP is a system for sending videos over the Internet in such a way that the bandwidth is used optimally to provide the best quality possible. Video files are divided into multiple chunks that are stored at different encoding rates, whose URLs are stored in manifest files

46
Q

Why are CDNs needed?

A

A single server or collection in one place would not scale to millions of simultaneous diverse users with different capabilities.

47
Q

What are Over-the-top media services? What are their challenges?

A

Internet0based streaming services that bypass the traditional media of TV and telecommunications, such as Netflix.

48
Q

What are the protocols for transport-layer networking?

A

TCP and UDP.

49
Q

What is UDP?

A

User Datagram Protocol is a transport-layer protocol that is a barebones alternative to TCP, not providing reliable transmission but facilitating faster transmission that is useful with some applications.

50
Q

How does socket programming work with TCP?

A

A connection is created with a handshake, providing a reliable, in order “pipe” across which data may be exchanged.

51
Q

What are the method types in HTTP/1.1?

A

GET, POST, HEAD, PUT, and, DELETE.

CS3102 Networks (9 decks)

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