Estimate the energy required for an average person (see Fig.9.32) to run a mile in 4

Lecture 7  Web caches (proxy server) o Goal is to satisfy client requests withoug involving the origin server o Basically recently requested objects are housed in the cache. The browser sends HTTP requests to the cache and if it is there it returns right away, otherwise it requests the obj from the origin server and returns that o Cache can also rend a request to the origin server to check if the requested obect has been modified since it was stored in the cache. If it has been, the cache requests the new version and stores that, then returns the new obj to the server  Electronic mail o Three componenets  User agents  Outlook, gmail, etc.  Mail servers  Where the messages are atually stored  Message queue of outgoing mail messages  SMTP is used to send messgae between mail servers  SMTP: Simple Mail Transfer Protocol  Uses TCP on port 25  Transfers directly from one mail server to the recipient server  Three phase transfer  Handshake  Transfer of messages  Closure  Messages must be in 7-bit ASCII