Networking Fundamentals: Caching and DNS

Caching

• Caching reduces response time by storing frequently requested data closer to the client, reducing traffic on access links.
• Caches are present throughout the internet, assisting even "poor" content providers to deliver content effectively.
• Servers inform caches about appropriate caching behavior through response headers.

DNS (Domain Name System)

• Resolves domain names to IP addresses
• DNSSEC (Domain Name System Security Extensions) adds security by authenticating name servers and ensuring message integrity.
• Top-Level Domain (TLD) servers handle .com, .org, .net, and country-specific domains (.cn, .uk, etc.).
• Authoritative DNS servers are specific to organizations, providing hostname to IP mappings for their hosts.
• Local DNS servers act as intermediaries between hosts and the DNS hierarchy, caching recent name-to-address translations, but might contain outdated information.
• When a host makes a DNS query, its local DNS server either resolves it from its cache or forwards the request through the DNS hierarchy.

DNS Resolution Processes

• Iterated query: The initial server contacts other servers in the hierarchy until the authoritative DNS server provides the IP address.
• Recursive query: The initial server takes on the responsibility to resolve the query, contacting other servers until the authoritative DNS server is reached. This puts a heavy load on servers at the top of the hierarchy.

Peer-to-Peer (P2P) File Distribution

• In P2P, peers contribute resources and act as both clients and servers, distributing files faster than traditional client-server approaches as the number of peers increases.
• P2P file distribution is typically faster than client-server for large file sizes.

Bittorrent

• Bittorrent protocol divides files into chunks and allows peers to exchange those chunks.
• Bittorrent uses a tracker to keep track of participating peers and their available chunks.
• When a peer joins a torrent, it gradually accumulates missing chunks and uploads chunks it already possesses to other peers, effectively contributing to the file distribution process.
• Peers might "churn" – join and leave the network, potentially affecting the distribution rate.

Multimedia: Video Compression

• Encoding reduces the number of bits required to represent images, improving storage and transmission efficiency.
• Spatial coding: Exploits redundancies within an image, such as repeating color values.
• Temporal coding: Leverages redundancies between consecutive frames, sending only differences in frame content.
• Constant Bit Rate (CBR): Maintains a fixed encoding rate, regardless of the complexity of the video content.
• Variable Bit Rate (VBR): Adjusts the encoding rate based on the complexity of the image, offering varying levels of compression.

Streaming Stored Video

• Streaming video presents challenges due to varying bandwidth and potential packet loss or delays.
• Techniques like buffering, adaptive streaming, and content delivery networks (CDNs) are employed to manage video quality and smooth playback.
• The text provides a simplified illustration of the video streaming process, highlighting the server’s role in sending the video content to a client.