From bfc45a025764587066501a0628d154f8d69730d5 Mon Sep 17 00:00:00 2001
From: Jet Hughes <jethughes0@gmail.com>
Date: Mon, 17 Oct 2022 11:58:03 +1300
Subject: [PATCH] vault backup: 2022-10-17 11:58:03

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 content/notes/17-app-layer.md | 77 +++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

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 - lecture
 ---
 
+# Client-server vs peer to peer
+- social network
+- email
+- multi player games
+- video streaming
+- P2P file sharing
+- voice over IP e.g., skype
+- remote ogin
 
+Principles
+- run of different end systems
+- communicate over network
+- no need to run application specific software on netwrk-core devices
+
+
+## client-server
+sercer
+- provide services to clients
+- always on
+- often in data centers, for scaling
+- needs to powerful
+	- multiple client requesting info at the same time
+	- have specialzed software
+
+client
+- request services by contacting and communicating with server
+- may be intermittently connected
+- do not communicate directly with each other
+
+## peer 2 peer
+- no alwasy on server
+- decentralize resource on a network
+- end systems are both client and servers
+- end systems communcatae directly
+- take advantage of distrivuted shared resources (bandwidth, CPU storage)
+- operate in dynamic environment with frequent join and leave
+- e.g., bitTorrent, blockchain
+
+
+## communication
+- process: network application running with a host
+	- client proces and server process
+	- processes in different hosts communicate by exhanging messages
+- process must have identifiers
+	- ip address to differentiate processes in different hosts
+		- IPv4: 10.96.35.21 • IPv6: fe80::44b:184c:7ebb:6524
+	- port number to differentiate processes in same host
+		- HTTP server (80), mail server (25)
+
+# functions of application protocols
+protocols define:
+- types of messages
+	- e.e.g, request, response
+- message syntax
+	- what fields in messages and how field are delineated
+- semantics
+	- meaning on information in fields
+- communcation rules
+	- when and how proceses send and response to messages
+
+
+## WEB http
+- client server model
+	- browser requests, recieves and displays web objects
+	- server sends objects in response to requests
+- HTTP
+	- communcation betwen browsers and servers
+- https
+	- extensioin of http that uses transport layer security for security
+
+methods
+- get, head, post, put (request to store a webpage), delete, link (connect two existing resources), unlink
+
+### exampl
+## Email
+## DNS
+
+# Socket programming