O N D EMAND L ECTURE P ART II By Dr. Nawaporn Wisitpongphan.

ON DEMAND LECTURE PART IIBy Dr. Nawaporn Wisitpongphan

ON DEMAND OUTLINE

Voice Over IP (VoIP)

Hyper Text Transfer Protocol (HTTP)

Domain Name Server (DNS)

INTRODUCTION TO VOIP Broadband Internet offers high-speed

connection Many applications become viable e.g.,

multimedia streaming, VoIP, etc. The technology for transmitting voice

conversation over the Internet has been available since early 1980s

VoIP allows two-way voice transmission over broadband connections

VoIP also carries telephony signals as digital audio Reduce data rate by using speech data

compression Encapsulating in a packet stream sent over IP

network

VOIP Not yet a big player with less than 5% of

market

Cost savings, enhanced voice services and new applications major advantages

VoIP gateways bridge circuit-switched PSTN and packet-switched Internet Gateways packetize, and compress voice, route

packets, authenticate users, and manage network of gateways

VOIP HARDWARE Enterprise gateway

Deployed between PBX and WAN device (router) for call set-up,routing, and conversion

VoIP routers Voice cards perform packetization and compression

functions in a router IP PBX

Distributed telephony servers that operat ein packt-switched mode

ISP VoIP gateways Aggregate incoming traffic and routing

VOIP INFRASTRUCTURE

VOIP ARCHITECTURE

IMPLEMENTING VOIP

VOIP STANDARDS H.323

Based on ISDN and limited to point-to-point applications

SIP Application layer (signaling) protocol Establishes temp sessions for multimedia

conferences, telephony, mobile phone-to-instant messaging

LDAP Standard directory server technology for Internet Enables retrieval of information from multi-vendor

directories Used for free phone and Internet phone number

hosting

THE PHONE WORKS – WHY BOTHER WITH VOIP

user perspective carrier perspective

variable compression: tin can to broadcast quality no need for dedicated lines

better codecs + silence suppression – packet header overhead = maybe reduced bandwidth

security through encryption shared facilities simplify management, redundancy

caller & talker identification advanced services

better user interface (more than 12 keys, visual feedback, semantic rather than stimulus)

cheaper bit switching

no local access fees (but dropping to 1c/min for PSTN)

transmit as data rather than voiceband data (14.4 kb/s)

adding video, application sharing is easy

VOIP VS PSTN (PUBLIC SWITCH TELEPHONE NETWORK) VoIP can transmit more than one phone call over the

same broadband connection

Conference call, call forwarding, auto redial, caller ID are free of charge

Secure calls using protocols such as (Secure Real-Time Transport Protocol)

Connection Independence. Can use VoIP anywhere there’s an Internet

Integration with other services available

Mobility

VOIP: DRAWBACK AND CHALLENGES Available Bandwidth

Network Latency

Packet Loss

Jitter

Echo

Security

Realiability

THE FIVE-PHASE "Technology Trigger" — The first phase of a hype cycle is the

"technology trigger" or breakthrough, product launch or other event that generates significant press and interest.

"Peak of Inflated Expectations" — In the next phase, a frenzy of publicity typically generates over-enthusiasm and unrealistic expectations. There may be some successful applications of a technology, but there are typically more failures.

"Trough of Disillusionment" — Technologies enter the "trough of disillusionment" because they fail to meet expectations and quickly become unfashionable. Consequently, the press usually abandons the topic and the technology.

"Slope of Enlightenment" — Although the press may have stopped covering the technology, some businesses continue through the "slope of enlightenment" and experiment to understand the benefits and practical application of the technology.

"Plateau of Productivity" — A technology reaches the "plateau of productivity" as the benefits of it become widely demonstrated and accepted. The technology becomes increasingly stable and evolves in second and third generations. The final height of the plateau varies according to whether the technology is broadly applicable or benefits only a niche market

HYPE CYCLE 2005

HYPE CYCLE 2006

HYPE CYCLE 2007

HYPE CYCLE 2008

HYPE CYCLE 2009

HTTP

ARCHITECTURAL OVERVIEW

Client with Web browser program Server with Web Server and pages (html) Other servers with Web Servers and pages Links between pages

BROWSER OPERATION WHEN USER CLICKS ON A LINK

B picks the URL from the clicked link B gets IP address of Web server from DNS B open TCP connection to the (IP, port 80) B sends a request for page (HTTP packet) W.S. sends the linked page (HTTP packet)

Page is in html language B. closes TCP connection B. interpret html, displays page to user B fetches & presents images linked to the file

THE CLIENT SIDE non html in page: PDF, GIF, JPEG, MP3, MPEG, ... Plug-ins: Code installed as an extension to the

browser Helper Applications, invoked by B as a separate

process

Plug-in Helper Application

SERVER SIDE

Accepts TCP connection Gets name of requested file (HTTP packet) Gets the file (local disk) Sends back the file (HTTP packets) Release TCP connection

To improve performance Maintain cache of files Multithreading

MULTI-THREADED WEB SERVER

Front-end thread accept request, build record Pass record to a Working Thread All threads share memory , including the cache If page not in cache, WT initiates disk read

TASKS OF A WORKING THREAD

Resolving name of the file Authenticating client (another lecture) Perform access control on client Check the cache Fetch file from disk Determine MIME type of file

This will be sent to the client Send reply to client

Construct HTTP packet(s) Write in the Web Server log What if the CPU can’t handle the load?

SERVER FARM ON A LAN

Problems Each Processing Node has its own cache

P.N. “specialize” with certain files Both requests and replies via the Front-end Solution?

TCP HANDOFF Front-end passes the TCP endpoint (IP, port) to

the Processing Node Processing Node send page to Client

Normal TCP Handoff

URLS – UNIFORM RESOURCE LOCATERS

URL provides answers to what? What is the name of the page? What is the location of the page? How to access the page (which protocol)?

?

?

STATELESSNESS AND COOKIES HTTP is request/reply; stateless But, server needs: to recognize users (registered?, adapt home page) to keep track of visited items (shopping cart) Cookies (small text files) keep that info.

Stored at Client C:\Documents and Settings\aviv\Cookies

Identified by domain name of the sending server

COOKIES: STRUCTUREdomain: where the cookie came fromPath: root of the file tree related to cookieContent: variableName=value pairs. AnythingExpires – if set it is kept (persistent cookie)Secure: If set cookie is sent only to secure server

Usages?

USING COOKIES

Casino server chooses which gambling option it presentsStore Server puts “items in cart” in the cookieWeb Portal server presents stock prices and Sport resultssneaky.com records visits of UserID in certain pages

pages include adds/banners/small picturesUser not aware its browser visited sneaky.comUser profile is built, maybe with name/password

USER-SERVER STATE: COOKIES

Many major Web sites use cookies

Four components:1) cookie header line in

the HTTP response message

2) cookie header line in HTTP request message

3) cookie file kept on user’s host and managed by user’s browser

4) back-end database at Web site

Example: Susan access Internet

always from same PC She visits a specific e-

commerce site for first time

When initial HTTP requests arrives at site, site creates a unique ID and creates an entry in backend database for ID

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COOKIES: KEEPING “STATE” (CONT.)

client server

usual http request msgusual http response

+Set-cookie: 1678

usual http request msg

cookie: 1678usual http response

msg

usual http request msg

cookie: 1678usual http response msg

cookie-specificaction

cookie-spectificaction

servercreates ID

1678 for user

entry in backend

database

access

acce

ss

Cookie file

amazon: 1678ebay: 8734

Cookie file

ebay: 8734

Cookie file

amazon: 1678ebay: 8734

one week later:

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WEB CACHES (PROXY SERVER)

user sets browser: Web accesses via cache

browser sends all HTTP requests to cache object in cache: cache

returns object else cache requests

object from origin server, then returns object to client

Goal: satisfy client request without involving origin server

client

Proxyserver

client

HTTP request

HTTP request

HTTP response

HTTP response

HTTP request

HTTP response

origin server

origin server

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MORE ABOUT WEB CACHING Cache acts as both

client and server Typically cache is

installed by ISP (university, company, residential ISP)

Why Web caching? Reduce response time

for client request. Reduce traffic on an

institution’s access link. Internet dense with

caches enables “poor” content providers to effectively deliver content (but so does P2P file sharing)

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CACHING EXAMPLE Assumptions average object size = 100,000

bits avg. request rate from

institution’s browsers to origin servers = 15/sec

delay from institutional router to any origin server and back to router = 2 sec

Consequences utilization on LAN = 15% utilization on access link = 100% total delay = Internet delay +

access delay + LAN delay = 2 sec + minutes + milliseconds

originservers

public Internet

institutionalnetwork 10 Mbps LAN

1.5 Mbps access link

institutionalcache

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CACHING EXAMPLE (CONT)Possible solution increase bandwidth of

access link to, say, 10 Mbps

Consequences utilization on LAN = 15% utilization on access link = 15% Total delay = Internet delay +

access delay + LAN delay

= 2 sec + msecs + msecs often a costly upgrade

originservers

public Internet

institutionalnetwork 10 Mbps LAN

10 Mbps access link

institutionalcache

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CACHING EXAMPLE (CONT)Install cache suppose hit rate is .4Consequence 40% requests will be

satisfied almost immediately

60% requests satisfied by origin server

utilization of access link reduced to 60%, resulting in negligible delays (say 10 msec)

total avg delay = Internet delay + access delay + LAN delay = .6*(2.01) secs + milliseconds < 1.4 secs

originservers

public Internet

institutionalnetwork 10 Mbps LAN

1.5 Mbps access link

institutionalcache

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DNS

DNS: DOMAIN NAME SYSTEMDomain Name System: distributed database

implemented in hierarchy of many name servers

application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation) note: core Internet

function, implemented as application-layer protocol

complexity at network’s “edge”

Why not centralize DNS? single point of failure traffic volume distant centralized database maintenance

doesn’t scale!

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Root DNS Servers

com DNS servers org DNS servers edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.comDNS servers

pbs.orgDNS servers

DISTRIBUTED, HIERARCHICAL DATABASE

Client wants IP for www.amazon.com; 1st approx: Client queries a root server to find com DNS

server Client queries com DNS server to get

amazon.com DNS server Client queries amazon.com DNS server to get

IP address for www.amazon.com

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DNS: ROOT NAME SERVERS contacted by local name server that can not resolve name root name server:

contacts authoritative name server if name mapping not known

gets mapping returns mapping to local name server

13 root name servers worldwideb USC-ISI Marina del Rey, CA

l ICANN Los Angeles, CA

e NASA Mt View, CAf Internet Software C. Palo Alto, CA (and 17 other locations)

i Autonomica, Stockholm (plus 3 other locations)

k RIPE London (also Amsterdam, Frankfurt)

m WIDE Tokyo

a Verisign, Dulles, VAc Cogent, Herndon, VA (also Los Angeles)d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MDj Verisign, ( 11 locations)

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TLD AND AUTHORITATIVE SERVERS Top-level domain (TLD) servers: responsible for

com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp. Network solutions maintains servers for com TLD Education for edu TLD

Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail). Can be maintained by organization or service provider

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LOCAL NAME SERVER

Does not strictly belong to hierarchy Each ISP (residential ISP, company,

university) has one. Also called “default name server”

When a host makes a DNS query, query is sent to its local DNS server Acts as a proxy, forwards query into hierarchy.

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requesting hostcis.poly.edu

gaia.cs.umass.edu

root DNS server

local DNS serverdns.poly.edu

1

23

4

5

6

authoritative DNS serverdns.cs.umass.edu

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TLD DNS server

ITERATED QUERIES

Host at cis.poly.edu wants IP address for gaia.cs.umass.edu

iterated query: contacted server replies

with name of server to contact

“I don’t know this name, but ask this server”

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requesting hostcis.poly.edu

gaia.cs.umass.edu

root DNS server

local DNS serverdns.poly.edu

1

2

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6

authoritative DNS serverdns.cs.umass.edu

7

8

TLD DNS server

3

RECURSIVE QUERIESrecursive query: puts burden of

name resolution on contacted name server

heavy load?

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