The first lik for leter L is: https://www.logicbig.com/quick-info/web/etag-header.html

The second link for letter L is: https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching

The third link for letter L is: https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching

The video link for letter L is: https://www.youtube.com/watch?v=XXiamIsYBos

The link on the letter M is: https://www.w3.org/2005/MWI/BPWG/techs/CachingWithETag.html

The second link on the letter M is: http://www.pocketsoap.com/weblog/stories/2002/05/0015.html

4. The HTTP RESPONSE message (Total 60 points) Consider the figure above, where the server is sending a HTTP RESPONSE message back the client Suppose the server-to-client HTTP RESPONSE message is the following HTTP/1.1 200 OK Date: Mon, 25 Feb 2018 18:00:00 +0000 Server: Apache/2.2.3 (CentoS) Last-Modified: Thu, 01 Feb 2018 18:00:00 +0000 ETag: "12345-abc-67890" Content-Length: 2635 Keep-Alive: timeout-23, max-10 Connection: Keep-alive Content-type: text/html