network systems - scsvmv - 30sep08 - modified vasan sanat tech pvt ltd

7/29/2019 Network Systems - SCSVMV - 30Sep08 - Modified Vasan Sanat Tech Pvt Ltd

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Discussion onNetwork Systems, Proxies andServers

inNational level Technical SymposiumSCSVMV, Kanchipuram

30-Sep-08Vasan V S([email protected])


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Agenda

Network System definition wrt Internet

Network Addressing

Network Proxy

Other network server applications

Questions?


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Whats the Internet: nuts and bolts view

millions of connectedcomputing devices: hosts= end systems

running network apps

communication links fiber, copper, radio,

satellite

transmission rate =bandwidth

routers:forward packets(chunks of data)

local ISP

companynetwork

regional ISP

router workstation

servermobile


4/49

Cool internet appliances

Worlds smallest web server

http://www-ccs.cs.umass.edu/~shri/iPic.html

IP picture frame

http://www.ceiva.com/

Web-enabled toaster +

weather forecaster

Internet phones


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Whats the Internet: nuts and bolts view

protocolscontrol sending,receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP

Internet:network of

networks loosely hierarchical

public Internet versusprivate intranet

Internet standards RFC: Request for comments

IETF: Internet EngineeringTask Force

local ISP

companynetwork

regional ISP

router workstation

servermobile


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A closer look at network structure:

network edge:applications andhosts

network core: routers

network ofnetworks

access networks,physical media:communication links


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The Network Core

mesh of interconnectedrouters

thefundamentalquestion: how is datatransferred through net?

circuit switching:dedicated circuit percall: telephone net

packet-switching: datasent thru net indiscrete chunks


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Access networks and physical media

Q: How to connect endsystems to edge router?

residential access nets

institutional access

networks (school,company)

mobile access networks

Keep in mind:

bandwidth (bits persecond) of accessnetwork?

shared or dedicated?


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Residential access: point to point access

Dialup via modem

up to 56Kbps direct access torouter (often less)

Cant surf and phone at sametime: cant be always on

ADSL: asymmetric digital subscriber line

up to 1 Mbps upstream (today typically < 256 kbps)

up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstream

4 kHz - 50 kHz for upstream

0 kHz - 4 kHz for ordinary telephone


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Company access: local area networks

company/univ local areanetwork (LAN) connectsend system to edge router

Ethernet:

shared or dedicated linkconnects end systemand router

10 Mbs, 100Mbps,

Gigabit Ethernet, 10 Gigabit Ethernet

(Coming soon)


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Wireless access networks

shared wirelessaccessnetwork connects end systemto router via base station aka access

point

wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps

wider-area wireless access provided by telco operator

3G ~ 384 kbps

Will it happen??

GPRS in Europe/US

basestation

mobilehosts

router


12/49

Home networks

Typical home network components: ADSL or cable modem

router/firewall/NAT

Ethernet

wireless accesspoint

wirelessaccesspoint

wirelesslaptops

router/firewallcablemodem

to/from

cableheadend

Ethernet


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Physical Media

Bit: propagates betweentransmitter/rcvr pairs

physical link: what liesbetween transmitter &receiver

guided media: signals propagate in solid

media: copper, fiber, coax

unguided media: signals propagate freely,

e.g., radio

Twisted Pair (TP) two insulated copper

wires Category 3: traditional

phone wires, 10 MbpsEthernet

Category 5:100Mbps Ethernet


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Internet structure: network of networks

roughly hierarchical at center: tier-1 ISPs (e.g., MCI, Sprint, AT&T, Cable

and Wireless), national/international coverage

treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1providersinterconnect

(peer)privately

NAP

Tier-1 providersalso interconnectat public networkaccess points(NAPs)


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Tier-1 ISP: e.g., Sprint

Sprint US backbone network

Seattle

Atlanta

Chicago

Roachdale

Stockton

San Jose

Anaheim

Fort Worth

Orlando

Kansas City

CheyenneNew York

PennsaukenRelayWash. DC

Tacoma

DS3 (45 Mbps)

OC3 (155 Mbps)

OC12 (622 Mbps)

OC48 (2.4 Gbps)

to/from customers

peering

to/from backbone

.

POP: point-of-presence


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Tier-2 ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP paystier-1 ISP forconnectivity torest of Internet tier-2 ISP iscustomeroftier-1 provider

Tier-2 ISPsalso peerprivately witheach other,interconnectat NAP


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Tier-3 ISPs and local ISPs last hop (access) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

local

ISPlocal

ISP

local

ISP

local

ISP

local

ISP Tier 3

ISP

local

ISP

local

ISP

local

ISP

Local and tier-3 ISPs arecustomersofhigher tierISPs

connectingthem to restof Internet


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a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

local

ISPlocal

ISP

local

ISP

local

ISP

local

ISP Tier 3

ISP

local

ISP

local

ISP

local

ISP


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How do loss and delay occur?

packets queuein router buffers packet arrival rate to link exceeds output link capacity

packets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets

dropped (loss) if no free buffers


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Four sources of packet delay

1. nodal processing: check bit errors

determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. queueing time waiting at output

link for transmission

depends on congestion

level of router


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Delay in packet-switched networks

3. Transmission delay: R=link bandwidth (bps)

L=packet length (bits)

time to send bits into

link = L/R

4. Propagation delay: d = length of physical link

s = propagation speed inmedium

propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing


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Real Internet delays and routes

What do real Internet delay & loss look like?

Traceroute program: provides delaymeasurement from source to router along end-endInternet path towards destination. For all i: sends three packets that will reach router ion path

towards destination

router iwill return packets to sender

sender times interval between transmission and reply.

3 probes

3 probes

3 probes


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Real Internet delays and routes

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms

5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms

13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *

19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136ms

traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements fromgaia.cs.umass.edu to cs-gw.cs.umass.edu

* means no response (probe lost, router not replying)

trans-oceaniclink


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Packet loss

queue (aka buffer) preceding link in bufferhas finite capacity

when packet arrives to full queue, packet is

dropped (aka lost) lost packet may be retransmitted by

previous node, by source end system, ornot retransmitted at all


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Internet protocol stack

application: supporting networkapplications FTP, SMTP, HTTP

transport: process-process data

transfer TCP, UDP

network: routing of datagrams fromsource to destination

IP, routing protocols link: data transfer between

neighboring network elements PPP, Ethernet

physical:bits on the wire

application

transport

network

link

physical


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sourceapplicationtransportnetwork

linkphysical

Ht

Hn

M

segment Ht

datagram

destination

applicationtransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht MM

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hnframe


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Agenda


Network Addressing

Network Proxy

Other network server applications

Questions?


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The Internet Network layer

forwardingtable

Host, router network layer functions:

Routing protocols

path selectionRIP, OSPF, BGP

IP protocoladdressing conventions

datagram formatpacket handling conventions

ICMP protocolerror reportingrouter signaling

Transport layer: TCP, UDP

Link layer

physical layer

Networklayer

IP d f


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IP datagram format

ver length

32 bits

data(variable length,typically a TCP

or UDP segment)

16-bit identifier

headerchecksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length(bytes)

max numberremaining hops

(decremented ateach router)

forfragmentation/reassembly

total datagram

length (bytes)

upper layer protocolto deliver payload to

head.len

type ofservice

type of dataflgs

fragmentoffset

upperlayer

32 bit destination IP address

Options (if any) E.g. timestamp,record routetaken, specifylist of routersto visit.

how much overheadwith TCP?

20 bytes of TCP

20 bytes of IP

= 40 bytes + app

layer overhead


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IP Addressing: introduction

IP address: 32-bitidentifier for host,router interface

interface:connection

between host/routerand physical link routers typically have

multiple interfaces

host typically has one

interface IP addresses

associated with eachinterface

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

223.1.1.1 = 11011111 00000001 00000001 00000001

223 1 11


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Subnets

IP address: subnet part (high

order bits)

host part (low orderbits)

Whats a subnet ? device interfaces with

same subnet part of IPaddress

can physically reacheach other withoutintervening router

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

223.1.3.2223.1.3.1

223.1.3.27

network consisting of 3 subnets

subnet


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Subnets 223.1.1.0/24 223.1.2.0/24

223.1.3.0/24

Recipe To determine the

subnets, detach eachinterface from its

host or router,creating islands ofisolated networks.Each isolated network

is called a subnet.Subnet mask: /24


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NAT: Network Address Translation

10.0.0.1

10.0.0.2

10.0.0.3

10.0.0.4

138.76.29.7

local network(e.g., home network)

10.0.0/24

rest ofInternet

Datagrams with source or

destination in this networkhave 10.0.0/24 address forsource, destination (as usual)

Alldatagrams leavinglocal

network have same single sourceNAT IP address: 138.76.29.7,different source port numbers


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Motivation: local network uses just one IP address asfar as outside world is concerned:

range of addresses not needed from ISP: just one IPaddress for all devices

can change addresses of devices in local networkwithout notifying outside world

can change ISP without changing addresses ofdevices in local network

devices inside local net not explicitly addressable,visible by outside world (a security plus).


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NAT: Network Address TranslationImplementation: NAT router must:

outgoing datagrams:replace(source IP address, port#) of every outgoing datagram to (NAT IP address,new port #). . . remote clients/servers will respond using (NAT

IP address, new port #) as destination addr.

remember (in NAT translation table)every (sourceIP address, port #) to (NAT IP address, new port #)translation pair

incoming datagrams:replace(NAT IP address, newport #) in dest fields of every incoming datagramwith corresponding (source IP address, port #)stored in NAT table


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10.0.0.1

10.0.0.2

10.0.0.3

S: 10.0.0.1, 3345

D: 128.119.40.186, 80

1

10.0.0.4

138.76.29.7

1: host 10.0.0.1sends datagram to128.119.40.186, 80

NAT translation tableWAN side addr LAN side addr

138.76.29.7, 5001 10.0.0.1, 3345

S: 128.119.40.186, 80D: 10.0.0.1, 3345 4

S: 138.76.29.7, 5001D: 128.119.40.186, 802

2: NAT routerchanges datagramsource addr from10.0.0.1, 3345 to138.76.29.7, 5001,

updates table

S: 128.119.40.186, 80D: 138.76.29.7, 5001 3

3: Reply arrivesdest. address:138.76.29.7, 5001

4: NAT routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345


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Agenda


Network Addressing

Network Proxy

Other network server applicationsQuestions?


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Web caches (proxy server)

user sets browser: Webaccesses via cache

browser sends all HTTP

requests to cache object in cache: cache

returns object

else cache requestsobject from origin

server, then returnsobject to client

Goal: satisfy client request without involving origin server

client

Proxy

server

clientoriginserver

originserver


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Conditional GET

Goal:dont send object ifcache has up-to-date cachedversion

cache: specify date ofcached copy in HTTP requestIf-modified-since:

server: response contains noobject if cached copy is up-to-date:HTTP/1.0 304 Not

Modified

cache server

HTTP request msgIf-modified-since:

HTTP responseHTTP/1.0

304 Not Modified

objectnot

modified

HTTP request msg

If-modified-since:

HTTP responseHTTP/1.0 200 OK

objectmodified


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Agenda


Network Addressing

Network Proxy

Other network server applications FTP

SMTP

Questions?


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FTP: the file transfer protocol

transfer file to/from remote host

client/server model

client:side that initiates transfer (either to/from

remote) server:remote host

ftp: RFC 959

ftp server: port 21

file transferFTP

server

FTPuser

interface

FTPclient

local file

system

remote file

system

userat host


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FTP: separate control, data connections

FTP client contacts FTPserver at port 21, specifyingTCP as transport protocol

Client obtains authorizationover control connection

Client browses remotedirectory by sendingcommands over controlconnection.

When server receives filetransfer command, serveropens 2ndTCP connection (forfile) to client

After transferring one file,server closes dataconnection.

FTPclient

FTPserver

TCP control connectionport 21

TCP data connectionport 20

Server opens another TCPdata connection to transferanother file.

Control connection: out of

band FTP server maintains state:

current directory, earlierauthentication


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FTP commands, responses

Sample commands: sent as ASCII text over

control channel

USERusername

PASS password LISTreturn list of file in

current directory

RETR filenameretrieves

(gets) file STOR filenamestores

(puts) file onto remotehost

Sample return codes status code and phrase (as

in HTTP)

331 Username OK,

password required 125 data connection

already open;

transfer starting

425 Cant open data

connection 452 Error writing

file


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Electronic Mail

Three major components: user agents

mail servers

simple mail transfer

protocol: SMTP

User Agent

a.k.a. mail reader

composing, editing, reading

mail messages e.g., Eudora, Outlook, elm,

Netscape Messenger

outgoing, incoming messagesstored on server

user mailbox

outgoingmessage queue

mail

server

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP


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Electronic Mail: mail servers

Mail Servers mailbox contains incoming

messages for user

messagequeue of outgoing

(to be sent) mail messages SMTP protocol between mail

servers to send emailmessages

client: sending mail

server server: receiving mail

server

mailserver

useragent

useragent

useragent

mail

server

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP


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Electronic Mail: SMTP [RFC 2821]

uses TCP to reliably transfer email message from clientto server, port 25

direct transfer: sending server to receiving server

three phases of transfer

handshaking (greeting) transfer of messages

closure

command/response interaction

commands: ASCII text

response: status code and phrase

messages must be in 7-bit ASCII

l d B b


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Scenario: Alice sends message to Bob

1) Alice uses UA to compose

message and [email protected]

2) Alices UA sends messageto her mail server; messageplaced in message queue

3) Client side of SMTP opensTCP connection with Bobsmail server

4) SMTP client sends Alices

message over the TCPconnection

5) Bobs mail server places themessage in Bobs mailbox

6) Bob invokes his user agent

to read message

useragent

mailserver

mailserver user

agent

1

2 3 4 56


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Questions?

Thank You

[email protected]

network systems - scsvmv - 30sep08 - modified vasan sanat tech pvt ltd

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