HTTP Web eb and d URLs Web page consists of objects Addressable - PowerPoint PPT Presentation

HTTP

Web eb and d URLs  Web page consists of objects  Addressable by a URL  Can be HTML file, JPEG image, Java applet, audio file,…  Bound to a host name and a path name within host www.someschool.edu/someDept/pic.gif path name host name Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP  Hypertext transfer protocol  Web’s application layer protocol  Send URL from client to server  Return content from server to PC running Explorer client  Client/server model  HTTP 1.0: RFC 1945 Server  HTTP 1.1: RFC 2068 running Apache Web server Mac running Navigator Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP over ervie view w (cont ntinued inued)  Uses TCP:  Client initiates bi-directional TCP connection (via socket) to server, port 80  Server accepts TCP connection from client  HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server)  Messages encoded in text  TCP connection closed Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP req equest uest me mess ssag age  Two types of HTTP messages: request, response  HTTP request message:  ASCII (human-readable format) request line (GET, POST, GET /somedir/page.html HTTP/1.1 HEAD commands) Host: www.someschool.edu User-agent: Mozilla/4.0 header Connection: close lines Accept-language:fr Carriage return, (extra carriage return, line feed) line feed indicates end of message http://www.someschool.edu/somedir/page.html Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP res espon ponse se me mess ssag age status line (protocol status code HTTP/1.1 200 OK status phrase) Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last- Modified: Mon, 22 Jun 1998 …... header Content-Length: 6821 lines Content-Type: text/html Connection: close data, e.g., data data data data data ... requested HTML file Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP hea eader ders  Contains a variety of headers for implementing  Caching  Session management (cookies)  Authentication  Tracking (referer)  Localization (language)  Content-encoding  Covered in 494/594 and 495/595 classes (Internetworking Protocols and Web Security)  Also contains headers for managing connection … Portland State University CS 430P/530 Internet, Web & Cloud Systems

Ser erial, ial, non-per persist sistent ent connect nnections ions  HTTP/1.0  One request/response per connection  simple to implement initiate TCP connection  server parses request, responds, RTT and closes connection request  RTT = round-trip time file total = 2RTT+transmit time RTT time to transmit file file receivedtime time Portland State University CS 430P/530 Internet, Web & Cloud Systems

Ser erial, ial, non-per persist sistent ent connect nnections ions Server Client 0 RTT SYN Client opens TCP connection SYN 1 RTT ACK DAT Client sends HTTP request for HTML Server reads from disk ACK DAT FIN 2 RTT Then delivers HTML before closing the connection ACK Client parses HTML FIN Client opens TCP connection ACK SYN SYN 3 RTT ACK Client sends HTTP request for image DAT Server reads from disk ACK 4 RTT DAT Image begins to arrive Portland State University CS 430P/530 Internet, Web & Cloud Systems

Iss ssue ue  Multiple embedded objects on page  Connection setup latency adds extra round trips per transfer (e.g. TCP’s three-way handshake)  Server and network overhead  Connection handling, extra packets  Short transfers hard on TCP  (e.g. slow-start, loss recovery algorithm) Portland State University CS 430P/530 Internet, Web & Cloud Systems

Pa Parall rallel el non-per persis sistent ent conn nnection ections  Netscape browser (1990s)  Improve latency by using multiple concurrent connections  Browsers often open up to 6-8 parallel TCP connections to fetch referenced objects  Different parts of Web page arrive independently on separate connections (object demux via connections)  Can grab more of the network bandwidth than other users  Doesn’t improve response time all the time  TCP connections contending with each other causing more packet losses and delay  OS overhead for each TCP connection Portland State University CS 430P/530 Internet, Web & Cloud Systems

Per ersis sisten ent t HTTP TP connection nnections  Default in HTTP/1.1  Server leaves connection open after sending response  Client sends additional requests on the same connection as soon as it encounters a referenced object  Subsequent HTTP messages between same client/server sent over open connection  On same TCP connection: server, parses request, responds, parses new request,..  As little as one RTT for all the referenced objects Portland State University CS 430P/530 Internet, Web & Cloud Systems

Per ersis sisten ent t HTTP TP ben enef efits its  Server overhead reduced  Less connection setup, more data transfer  TCP congestion control behavior improved  Longer connections with larger congestion windows  Response time improved  Avoids multiple, serial TCP handshakes  New HTTP request header for controlling  Connection: keep-alive  Connection: close Portland State University CS 430P/530 Internet, Web & Cloud Systems

Per ersis sisten ent t HTTP TP connection nnection exa xample ple Client Client Server 0 RTT DAT Client sends HTTP request for HTML ACK Server reads from disk DAT 1 RTT ACK Client parses HTML DAT Client sends HTTP request for image Server reads from disk ACK DAT 2 RTT Image begins to arrive Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP exa xample ple  Non-persistent HTTP/1.0 mashimaro <~> 9:11AM % nc -C chi-ni.com 80 GET / HTTP/1.0 Host: chi-ni.com HTTP/1.0 200 OK … Connection: close Content-Type: text/html <HTML> <HEAD> <TITLE>Jeannie's Web Site</TITLE> </HEAD> <BODY> <IMG SRC="./2007_06_11-09_31_40.jpg"> </BODY> </HTML> mashimaro <~> 9:21AM %

mashimaro <~> 9:20AM % nc -C chi-ni.com 80 GET / HTTP/1.1 Host: chi-ni.com Connection: keep-alive  Persistent HTTP/1.1 HTTP/1.1 200 OK … Keep-Alive: timeout=5, max=100 Connection: Keep-Alive Content-Type: text/html <HTML> <HEAD> <TITLE>Jeannie's Web Site</TITLE> </HEAD> <BODY> <IMG SRC="./2007_06_11-09_31_40.jpg"> </BODY> </HTML> GET /2007_06_11-09_31_40.jpg HTTP/1.1 Host: chi-ni.com Connection: close HTTP/1.1 200 OK Content-Length: 539 Connection: close Content-Type: image/jpeg ���� JFIFHH ���� C … mashimaro <~> 9:20AM %

Prob oblems lems wi with th HTTP/ TP/1.1  Serial delivery of objects  Head-of-line object blocking  Stall in one object prevents delivery of others  Most useful information in first few bytes (layout info)  Multiple connections allow incremental rendering of images Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP TP ope perat ration ion  Want the best of both worlds  Persistence  Single TCP connection  Parallel object delivery  Ability to simultaneously retrieve embedded objects over connection  Need application/object level demux within a single TCP connection to emulate multiple connections  Leads us to SPDY (2009) and HTTP/2, then QUIC and HTTP/3 Portland State University CS 430P/530 Internet, Web & Cloud Systems

HTTP/2

HTTP/ TP/2  Two main improvements  Multiplexed streams  Server-push

HTTP/ TP/2 2 mu multiple tiplexed ed st strea eams ms  HTTP/1.1 Pipelined, sequential operation • on each connection Must use multiple connections • HTTP/1.1 HTTP/2 to get parallel delivery of Sequential Multiplexed Client Server Client Server objects Typically, 4-8 outstanding • requests on 4-8 connections Still resource intensive on the • server  HTTP/2 One connection, many • pipelined, concurrent requests Normally limited to 100 •

HTTP/ TP/2 2 mu multiple tiplexed ed st strea eams ms  How?  HTTP stream identifiers combined with range requests/responses  Implemented as a framing protocol within HTTP  Server labels data with the object it is for and the range of bytes within it  Application-layer demultiplexing of object data  Allows one to support pipelining but avoid HOL blocking  Application specific solution to transport protocol problem.

De Demo mo  http://http2.golang.org/gophertiles  HTTP/1  Handshaking overhead, poor congestion control behavior, multiple RTT to request individual tiles  Exacerbated with lossy/wireless links and long RTTs  HTTP/2  One handshake, better congestion control behavior, tiles requested in single RTT

HTTP/ TP/2 2 se server er pu push sh  HTTP/1.1  Client fetches origin page HTTP/1.1  Must parse base page for embedded objects before initiate TCP submitting subsequent requests connection for them RTT request  Server often knows what client file will request next send RTT file parse and request embedded objects time time