Application Layer: Content Distribution Networks

Questions and Answers

What is a primary characteristic of a Peer-to-Peer (P2P) architecture?

Peers communicate solely through dedicated channels.

Always requires a central server for data distribution.

Peers can both request and provide services to each other. (correct)

Peers are always connected to the internet.

Which DNS record type is responsible for mapping a domain name to an IP address?

CNAME

A (correct)

What happens to DNS cache entries after they timeout?

They are stored indefinitely.

They become more accurate.

They are refreshed with current data.

They are permanently deleted. (correct)

Which of the following describes a CNAME DNS record?

It provides an alias for a canonical name. Signup and view all the answers

What is a potential security threat to DNS outlined in the content?

DNS poisoning. Signup and view all the answers

What is one disadvantage of cached DNS entries?

They can become outdated. Signup and view all the answers

In DNS, which type of record indicates the authoritative server for a domain?

NS Signup and view all the answers

What is the main purpose of DNSSEC?

To enhance DNS security against attacks. Signup and view all the answers

Which of the following is a benefit of a Content Distribution Network (CDN)?

Improves latency through geographically distributed servers. Signup and view all the answers

What is a challenge specifically associated with P2P file sharing?

Managing intermittent connections and changing IP addresses. Signup and view all the answers

Study Notes

Mega-Server vs. CDN

A single large "mega-server" can be a single point of failure, leading to network congestion and inefficient long-distance routing.
Cannot scale effectively to serve millions of video streams to numerous users simultaneously.

Content Distribution Networks (CDNs)

CDNs are used to stream content from multiple servers in geographically distributed sites, enhancing scalability.
Akamai is a major CDN provider with around 240,000 servers across 120 countries as of 2015.
Content is stored in CDN nodes, allowing subscribers to request and receive videos from copies located close to them, improving retrieval times.

Over-The-Top (OTT) Streaming

OTT enables Internet host-host communication, facing challenges such as dealing with network congestion and optimizing content placement across CDN nodes.

Streaming Stored Video Challenges

Continuous playout requirements mean clients must match playback timing with variable network delays, necessitating buffering.
Interactivity features like pause, fast-forward, and rewind can affect streaming performance, as video packets might be lost and need retransmission.

Playout Buffering

Client-side buffering is crucial for managing network delays and jitter during video playback.
Ensures a smooth viewing experience by buffering and adjusting to network conditions.

DASH (Dynamic Adaptive Streaming over HTTP)

DASH divides video files into chunks encoded at various rates, with a manifest file linking to these chunks.
Clients request video chunks based on real-time assessments of available bandwidth, allowing for adaptive streaming quality.

Client Intelligence in DASH

Clients determine when to request new chunks and select encoding rates based on current network conditions to prevent buffer starvation or overflow.

DNS Caching and Management

DNS entries cache mappings of names to IP addresses, with a time-to-live (TTL) after which they may expire.
Updates on DNS mappings could lead to outdated entries until TTLs expire globally.

DNS Records

DNS operates as a distributed database with various resource record (RR) types, including A (address), CNAME (canonical name), NS (name server), and MX (mail server).

DNS Protocol Messages

Both DNS queries and replies share the same general format, including fields for identification, flags, questions, answers, authority records, and additional information.

Inserting Records into DNS

New domain registrations require authoritative name server details, with NS and A records inserted into TLD servers appropriately to establish domain mappings.

DNS Security Concerns

DNS is vulnerable to DDoS attacks, redirect attacks, and DNS poisoning, where false responses are sent to disrupt service.
DNSSEC offers a layer of security to prevent certain types of attacks by validating responses.

Overview of Application Layer

The application layer encompasses various services including P2P applications, video streaming, web services (HTTP), and email protocols (SMTP, IMAP), addressing fundamental network principles.

Peer-to-Peer (P2P) Architecture

P2P networks lack centralized servers, allowing arbitrary end systems to communicate directly.
P2P systems are self-scaling; new peers enhance capacity and demand simultaneously, supporting applications like file sharing (BitTorrent) and streaming (KanKan).

Client-Server vs. P2P File Distribution

The efficiency of file distribution from a server to multiple peers (N) involves consideration of the file size (F) and network conditions impacting distribution time.

Description

Explore the challenges and solutions of streaming content using content distribution networks (CDNs). This quiz highlights the issues with a single 'mega-server' approach and discusses scalable alternatives. Test your understanding of how CDNs support simultaneous users efficiently.