NetComms Chapter 2

timing, throughput, security, reliability (data integrity)

Network app development writes program that run on end system and communicate over the network, no need to write software for network core devices.

No always on server, end system communicate directly, peer request service from other peer and provide service in return, peers intermittently connected and change ip address.

Always on host, permanent ip address

Communicate with server directly, may intermittently connected, have dynamic ip address, do not communicate directly

house large number of host, create powerful virtual server, popular internet services employ one or more of this thing, can have hundreds thousands of server.

Program running within a host

inter-process communication (defined by os)

exchanging messages

process that initiates connection

process that waits to be connected

Process send/receives messages to/from its socket

Interface between application process and transport layer protocol

To receive process that includes ip address and port numbers associated with process on host

types of messages exchanges, message syntax, message semantic, rules, open protocols, proprietary protocols

reliable transport, flow control, congestion control, does not provide (timing, minimum throughput guarantee, security) , connection oriented

unreliable data transfer, does not provide:- reliability, flow control, congestion control, timing, throughput guarantee, security or connection setup.

provides encrypted TCP connection, data integrity, end point authentication, implimneted at application layer.

Operates on demand, everyone can be content publisher, hyperlink and search engines help find published contents, contents exhibited beautiful graphics, serves as a platform for many applications.

objects such as HTML, JPEG and audio files

a collection of items that can be called from a single URL

client that request, receives, displays web objects and server sends object in response to request.

TCP that sends request messages into its socket interface.

the server sends requested files to clients without storingany state information about the client, server maintains no information about past client requests, When client ask for the same object repeatedly ➔ theserver will resend

time for small packet to transfer between client to server and back.

each object requires 2 RTT delay, Operating System (OS)overhead for each TCPconnection – can burden theserver, browsers often open multipleparallel TCP connections tofetch referenced objects

one RTT to initiate TCP connection, one RTT for HTTP reuqest and first few bytes of HTTP response to return, response time = 2RTT+file transmission time

server leaves connection open after response, subsequent HTTP messages between same client/server sent over open connection, client send request as soon as it encounters referenced object, as little as one RTT for all the referenced object.

web page often includes from input, user input sent from client to server by post method

method to get specific object from server

only request header

uploads file to server, replace file at specified URL

request succeeded, requested object later in this message

requested object moved, new location specified later in this message (in the Location: field)

request message not understood by server

requested document not found on this server

able to maintain user/server state, help web servers handle thousand of simultaneous connections

authorization, shopping carts, recommendations, user session state

cookies header line of HTTP response message, cookie header line in next HTTP request message, cookies file kept o user's host thats managed by user's browser, back-end database at web site

satisfy client request without involving origin server

user configures browser topoint to (local) Web cache, browser sends all HTTPrequests to cache, If object in cache: cachereturns object to client, else cache requests objectfrom origin server, cachesreceived object, thenreturns object to client, acts as both client and server, typically installed by isp

reduce response time, reduce traffic on access link, effectively delivers content

don't send object if cache has up to date cached version thus no transmission delay and lower link utilization.

specify date of cached copy in HTT PrequestIf-modified-since: <date>

response contains no object if cached copy is up-to-date:HTTP/1.0 304 Not Modified

decreases delay in multi object http request

multiple pipelined Gets over single TCP connection, server responds in-order (FCFS: first-come-first-served scheduling) to GET requests. with FCFS, small object may have to wait for transmission (head-of- line (HOL) blocking) behind large object(s). loss recovery (retransmitting lost TCP segments) stalls object transmission

increased flexibility at server in sending objects to client. method, status code, most header files unchanged from HTTP 1.1. Transmission order of requested objects based on client-specified object priority. push unrequested objects to client. divide objects into frames, schedule frames to mitigate HOL blocking.

user transfer file to or from a remote host.

provide a form of authentication (Username n password)

client/server model

Runs on TCP, RFC 959 and server port 21

control connection to send control info and data connection for actual files transfer

server open 2nd TCP data connetion for file to client with port 20. After transferring exactly one file, server closes data connection.

client initiate TCP connection to server (port 80), server accept TCP connection from client, HTTP messages exchange between client and server, tcp connection closed