2.2 The Web and HTTP part 2

Summary

The video discusses HTTP fundamentals and techniques to improve web performance, including web caching and conditional GET requests. It explains the benefits of web caching in reducing latency and load on servers, followed by a comparison of HTTP/2 and HTTP/3, highlighting their features that enhance user experience by minimizing delays. The video emphasizes the improvements in data transmission and packet handling in HTTP/2 and introduces the advancements expected in HTTP/3. It concludes with a focus on the evolution of HTTP as an application layer protocol and hints at upcoming discussions on email and SMTP.

Takeaways

• 🌐 HTTP connections can be either persistent or non-persistent, and the basic message types include request and get.
• 🍪 Cookies play a role in HTTP communication, with various methods for improving user-perceived performance.
• 📦 Web caching improves latency by storing copies of requested data closer to the user, reducing load on the origin server.
• 🎯 Caches serve dual roles: they act as clients when retrieving from origin servers and as servers when responding to user requests.
• 🚀 Caching reduces the response time for user requests and decreases network traffic, especially at the access link between networks.
• ⚙️ Web caching can significantly lower page load times and improve network efficiency by reducing the amount of data fetched from the origin server.
• 🔄 Conditional GET allows a client to avoid downloading unchanged objects, further reducing network traffic and improving performance.
• 🕓 HTTP/2 focuses on reducing delays in multi-object requests, utilizing features like prioritization and server push.
• 🔄 HTTP/2 can also split large objects into frames, reducing head-of-line blocking by interleaving the transmission of multiple objects.
• 🔒 HTTP/3, set for future release, aims to address issues like packet loss and security by improving upon HTTP/2’s foundation.

Q & A

What are the two main techniques discussed in the video for improving user perceived performance in HTTP?

The two main techniques are web caching and the conditional GET request, both of which aim to reduce latency and improve page load times.

How does web caching improve performance for the user and the server?

Web caching improves performance by storing frequently requested content locally, reducing the need to fetch it from the origin server repeatedly, which lowers the load on both the server and network access links, and speeds up the response time for users.

What role does the cache play in the client-server model in web caching?

In web caching, the cache acts as both a client and a server. It serves the client’s requests when the cached content is available and requests content from the origin server when it is not.

What are the performance benefits of web caching in terms of network load and page load times?

Web caching reduces the response time for client requests by serving content locally and reduces network traffic on the institutional access link by minimizing requests to the origin server. This leads to faster page load times and less network congestion.

How does the cache control header affect caching behavior?

The cache control header in an HTTP response message informs the cache about how long an object can be cached, or if it should not be cached at all, allowing the cache to respect content expiration or retrieval rules.

What is the main challenge with high access link utilization, and how can caching help alleviate this?

High access link utilization can cause queuing delays, especially if the network is nearly saturated. Caching helps by reducing the volume of traffic passing through the access link, lowering its utilization and thereby reducing queuing delays.

How can upgrading the access link solve network congestion, and why might this not always be the best solution?

Upgrading the access link increases the available bandwidth, reducing the utilization and queuing delays. However, this solution can be costly compared to installing a web cache, which also reduces network load but at a lower cost.

What is the purpose of the conditional GET request in HTTP, and how does it improve performance?

The conditional GET request allows the client to check if its cached copy of an object is up-to-date. If the object has not been modified, the server responds with a '304 Not Modified' status, saving network resources and avoiding unnecessary data transmission.

What improvements does HTTP/2 bring compared to HTTP/1.1 in terms of object transmission?

HTTP/2 allows for prioritizing the transmission of objects, server push for unrequested resources, and dividing large objects into frames, which helps mitigate 'head of line blocking' and improves overall performance by reducing delays.

How does HTTP/2 address 'head of line blocking,' and why is this beneficial for performance?

HTTP/2 mitigates 'head of line blocking' by allowing large objects to be divided into smaller frames and transmitting them alongside smaller objects, which prevents smaller requests from waiting behind larger ones, thus improving response times.