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Questions and Answers
How does distribution time behave in a client-server architecture as the number of peers increases?
How does distribution time behave in a client-server architecture as the number of peers increases?
What is the role of a tracker in a P2P architecture?
What is the role of a tracker in a P2P architecture?
In the BitTorrent protocol, what process allows peers to optimize their chunk exchange?
In the BitTorrent protocol, what process allows peers to optimize their chunk exchange?
When a peer first joins a torrent, what is their initial status regarding file chunks?
When a peer first joins a torrent, what is their initial status regarding file chunks?
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How often does a peer re-evaluate which peers to send chunks to in the BitTorrent protocol?
How often does a peer re-evaluate which peers to send chunks to in the BitTorrent protocol?
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What happens when a peer has downloaded the entire file in a torrent?
What happens when a peer has downloaded the entire file in a torrent?
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What does 'optimistically unchoke' refer to in BitTorrent?
What does 'optimistically unchoke' refer to in BitTorrent?
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What is a notable characteristic of peers in a P2P architecture like BitTorrent?
What is a notable characteristic of peers in a P2P architecture like BitTorrent?
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What strategy does a CDN employ for directing clients to a server cluster?
What strategy does a CDN employ for directing clients to a server cluster?
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Which method employs real-time measurements to determine the best cluster for clients?
Which method employs real-time measurements to determine the best cluster for clients?
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Which component is NOT part of Netflix's video distribution architecture?
Which component is NOT part of Netflix's video distribution architecture?
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How does Netflix prepare movie content for distribution?
How does Netflix prepare movie content for distribution?
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What is one method Netflix uses for adaptive streaming?
What is one method Netflix uses for adaptive streaming?
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Which is a potential drawback of using real-time measurements in a CDN?
Which is a potential drawback of using real-time measurements in a CDN?
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For which of the following purposes does Netflix use the Amazon cloud?
For which of the following purposes does Netflix use the Amazon cloud?
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What is an advantage of using the geographically closest server approach in CDN?
What is an advantage of using the geographically closest server approach in CDN?
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What is a key characteristic of peer-to-peer (P2P) architecture?
What is a key characteristic of peer-to-peer (P2P) architecture?
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Which of the following best describes how new peers impact a P2P network?
Which of the following best describes how new peers impact a P2P network?
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In a content delivery network (CDN), what is the primary function of edge servers?
In a content delivery network (CDN), what is the primary function of edge servers?
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What type of attack involves intercepting DNS queries and returning false information?
What type of attack involves intercepting DNS queries and returning false information?
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Which method is commonly used to amplify traffic during a DDoS attack on DNS servers?
Which method is commonly used to amplify traffic during a DDoS attack on DNS servers?
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What is the purpose of RFC 4033 in relation to DNS?
What is the purpose of RFC 4033 in relation to DNS?
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During a DDoS attack, which server is most commonly bombarded with traffic?
During a DDoS attack, which server is most commonly bombarded with traffic?
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What does the abbreviation 'MX' stand for in DNS records?
What does the abbreviation 'MX' stand for in DNS records?
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In a file distribution scenario, which variable represents the upload capacity of the server?
In a file distribution scenario, which variable represents the upload capacity of the server?
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What is the essential difference between a client-server model and a P2P model?
What is the essential difference between a client-server model and a P2P model?
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Study Notes
DNS Overview
- DNS (Domain Name System) translates domain names (e.g., www.example.com) into IP addresses (e.g., 192.168.1.1).
- This allows users to use memorable names instead of numerical IP addresses.
- A hierarchical system with different types of DNS servers working together: Root, TLD (Top-Level Domain), Authoritative, and Local.
Recursive Queries in DNS
- A recursive query puts the burden of name resolution on the contacted name server.
- This places a heavy load on the upper levels of the hierarchy.
- The contacted DNS server will query other servers until the answer is found.
DNS Caching
- DNS caching is used to improve performance and reduce the number of DNS messages on the internet.
- Caching improves performance by reducing delay.
- Caching saves bandwidth by reducing the amount of data transferred across the internet.
- Cache entries timeout after a specific time (TTL).
- TLD servers are typically cached in local name servers.
- Root name servers are not often visited due to caching.
DNS Records
- Resource records (RRs) contain name, address, and type of record.
- Type A: maps hostname to IP address of end device.
- Type NS: an authoritative name server for a domain.
- Type CNAME: maps alias hostname to canonical hostname.
- Type MX: indicates a mail server for an alias hostname.
DNS Protocol and Messages
- DNS uses query and reply messages, both with the same message form.
- Messages have identification (16-bit number) for matching queries and replies.
- Flags specify if recursion is desired or available, and whether the reply is authoritative.
DNS Messages Structure
- DNS messages have 12-byte headers.
- Identification: for query-reply matching.
- Questions: to be answered.
- Answers, Authority, Additional information: resource records providing the answer, for contact information about other servers, and additional helpful related data needed for the query.
Using nslookup
- nslookup is a command-line tool for querying DNS servers.
- It provides results showing domain names, addresses, and other relevant information (names of authoritative servers, addresses, etc).
Getting Your Information into the DNS
- Registering a domain name with a registrar.
- Providing the name, IP address of primary and secondary authoritative DNS servers.
- Using a registrar's function to put host name and A records into the relevant TLD server.
DNS Security
- DDoS Attacks target root and TLD servers with high traffic, often overwhelming them.
- Spoofing attacks intercept DNS queries and return false replies.
- DNS cache poisoning can occur where DNS servers receive bogus entries for a domain.
P2P Architecture
- No central server.
- Peers request service from other peers, and provide service in return.
- Self-scalable with new peers bringing new service, capacity, and demands.
File Distribution: Client-Server vs P2P
- Client-server distribution time increases linearly with the number of peers.
- P2P distribution time increases with the total upload capacity of all participating peers.
File Distribution: BitTorrent
- Tracker: tracks peers participating in the torrent.
- Peers in a torrent exchange file chunks and exchange portions of data in a tit-for-tat manner.
Video Streaming and CDNs
- Video traffic consumes a significant amount of Internet bandwidth.
- CDNs distribute video content over geographically distributed servers (caches) to improve performance and user experience.
- CDN placement strategies include "Enter Deep" and "Bring Home" locations.
Multimedia: Video
- Video is a sequence of images displayed at a constant rate (e.g., 24 images/second).
- Digital images are represented by an array of pixels.
- Coding techniques (spatial, temporal) reduce redundancy within and between images to decrease the number of bits needed to encode an image.
- CBR (constant bit rate) encoding maintains a fixed bit rate, while VBR (variable bit rate) adjusts the bit rate based on video content.
Streaming Stored Video
- In a simple stored video scenario, all clients receive the same encoding despite bandwidth variations.
- This can lead to a suboptimal experience.
Streaming Multimedia: DASH
- DASH (Dynamic Adaptive Streaming over HTTP) allows for adaptive encoding rates based on changing bandwidth conditions.
- Servers provide different chunks encoded at varying bit rates.
- Clients periodically measure server-to-client bandwidth and adjust playback to use more or less CPU-intensive or bandwidth-intensive encoding.
- Client-side intelligence manages buffer starvation and overflow.
Content Distribution Networks (CDNs)
- CDNs use multiple geographically distributed servers and cache content close to users to reduce latency, increase bandwidth availability, and distribute traffic load.
- CDN Placement Strategies involve choosing locations that are close to users (Enter Deep), and locations closer to ISPs (Bring Home).
CDN Services
- CDNs enhance regular hosting by reducing bandwidth consumption, minimizing latency, and scaling up for abnormal traffic loads.
- CDNs often store multiple copies of videos using a pull strategy where users request data, and store it locally.
Netflix Video Streaming Platform
- Netflix uses a combination of Amazon Cloud services and its own private CDN infrastructure.
- Netflix distributes various versions of videos in different formats suitable for different platforms and devices, with various bit rates for bandwidth optimization.
- Adaptive streaming (e.g. the DASH standard) is used for changing bandwidth and quality.
Socket Programming
- Socket programming is a way to build client-server applications that use sockets to communicate.
- Sockets provide a door between the process of a program running on an end-device and the transport protocol such as UDP or TCP.
Socket Programming with UDP
- UDP (User Datagram Protocol) is an unreliable datagram-based service.
- There is no connection or handshaking before sending client and server data.
- The sender explicitly appends the IP address and port number to each packet.
- UDP packets can be lost or arrive out of order.
Socket Programming with TCP
- TCP (Transmission Control Protocol) is a reliable byte stream-oriented service.
- A connection is required before data can be exchanged.
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