topics = other half of web and http
Help!
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| are notion of multi-step exchanges of HTTP messages to complete a web transaction needed | no because HTTP "get" response interaction is stateless
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| what is not needed for a server or client to track in a multi-step exchange | the state
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| are all HTTP requests independent or dependent on each other | independent
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| what is not needed for client/server to do from a partially-completed-but-never-completely-completed transaction | recover
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| what do websites and client browsers use to maintain some state between transactions | cookies
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| what are the four main components of a cookie | cookie header line of HTTP response message / cookie header line in next HTTP request message / cookie file kept on users host managed by users browser / back-end database at website
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| what can cookies be used for | authorization / shopping carts / recommendations / user session state (web email)
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| how do you keep state | protocol endpoints, help in maintain state at sender and receiver over multiple transactions / cookies, HTTP messages carry state
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| how do cookies work with privacy | cookies permit sites to learn a lot about you on their site / third party persistent cookies allow common identity to be tracked across multiple websites
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| what is a web caches goals | satisfy client request without involving origin server
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| how does web caches work | user configures browser to point to a web cache / browser sends all HTTP requests to cache
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| what happens when an object is in cache | it returns object to the client
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| if object in cache isn't returned. what happens | cache requests the object from origin server, caches receive object then returns object to client
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| does web cache act as a client or a server | both
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| how does a web cache act as both client and server | server for original requesting client / client to origin server
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| how is web cache installed | by an ISP (uni, company, res ISP)
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| why is web cache an advantage to websites | reduced response time for client request (because cache is closer to client) / reduced traffic on an institutions access link / internet is dense with caches (enables poor content providers to more effectively deliver content)
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| examples on slides 38>41 on how to calc. access link utilization | practice it eventually
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| what is the main goal of a conditional "get" method | don't send object if cache has up to date cached version (no object transmission delay / lower link utilization)
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| what formula is used to specify date of cached copy in HTTP request | if-modified-since:<date>
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| what does a server do if cached copy is up to date | response contains no object
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| what is the main goal of HTTP/2 | decreased delay in multi-object HTTP requests
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| what did HTTP1.1 introduce | multiple, pipelined "gets" over a single TCP connection
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| how does the HTTP1.1 server work | works on a first come first served scheduling (FCFS) to "get" requests, small object may have to wait for transmission behind larger objects (head-of-line blocking)
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| what does HOL stand for regarding transmission | head-of-line
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| how does loss recovery work | it retransmits lost TCP which in turn stalls other object transmission
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| how does HTTP decrease delay in multi-object HTTP requests | increased flexibility at server in sending objects to client
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| are methods, status codes and header fields different from HTTP/2 and HTTP1.1 | no
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| what method is used to transmit requests in HTTP/2 | requested objects based on client-specified object priority, doesn't use FCFS
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| are unrequested objects pushed to clients in HTTP/2 | yes
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| how are objects mitigated in HTTP/2 for HOL blocking | divide objects into frames and schedule the frames into mitigate
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| what does HTTP/2 over single TCP connection mean | recovery from packet loss still stalls all object transmissions / opposite to HTTP1.1 browsers open multiple parallel TCP connections to reduce stalling and increase overall throughput
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| what type of security does HTTP/2 to HTTP/3 have | no security over vanilla TCP connection
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| what does HTTP/3 add to HTTP/2 | adds security, per object error and congestion control which means more pipelining over UDP
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| next section = email / SMTP / IMAP | slide 48
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