Transcript network protocols

Internet Development
What is the Internet anyway?
Colm O Suilleabhain
The Internet is short for:
• Interconnected Network
What is a network?
• From dictionary.com:
– An openwork fabric or structure in which cords,
threads, or wires cross at regular intervals.
– Something resembling an openwork fabric or
structure in form or concept, especially:
• A system of lines or channels that cross or interconnect: a
network of railroads.
• A complex, interconnected group or system: an espionage
network.
• An extended group of people with similar interests or
concerns who interact and remain in informal contact for
mutual assistance or support.
What is a network?
• From whatis.com
• A network is a series of points or nodes connected by
communication paths. Networks can interconnect with other
networks and contain subnetworks.
• Topology – Star, bus, ring
• Spatial distance as local area networks (LANs), metropolitan
area networks (MANs), and wide area networks (WANs).
• Type of data transmission technology in use on it (for example,
a TCP/IP or Systems Network Architecture network);
• Whether it carries voice, data, or both kinds of signals
• Who can use the network (public or private);
• Nature of its connections (dial-up or switched, dedicated or
nonswitched, or virtual connections);
• By the types of physical links (for example, optical fiber, coaxial
cable, and Unshielded Twisted Pair).
What’s the Internet NOT?
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“The web”
Google
Email-reachable users
Private networks
What can it do?
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Email
WWW, Hypertext, RSS, browsers
FTP, WebDav
Voice access (VXML, SALT)
Mobile phones (WAP)
IM, IRC
Online gaming
Video conferencing
Remote backups
Remote login/admin gotomypc.com
Streaming video & audio
Where did it come from?
• Advanced Research Projects Agency (ARPA) of the U.S.
government in 1969 and was first known as the
ARPANET.
• Original aim was to create a network that would allow
users of a research computer at one university to be able
to "talk to" research computers at other universities.
• A side benefit of ARPANet's design was that, because
messages could be routed or rerouted in more than one
direction, the network could continue to function even if
parts of it were destroyed in the event of a military attack
or other disaster.
How big is the Internet?
• Assessing the size of the Internet is a somewhat
difficult proposition, since it is a distributed body,
and no complete index of it exists
• Do we mean how many people use the Internet?
How many websites are on the Internet? How
many bytes of data are contained on the
Internet? How many distinct servers operate on
the Internet? How much traffic runs through the
Internet per second?
How big is the Internet?
• Just over a billion people used the Internet
in 2008
• Of these, about 500 million use the
Internet at least once a week
• There are thought to be some 155 million
websites on the Internet
• All these numbers are guestimates and
are nearly impossible to measure
accurately
Internet Software
• Clients
– A client is the requesting program or user in a
client/server relationship.
• Servers
– A program that awaits and fulfills requests from client
programs in the same or other computers.
• Peers
– A program may function as a client with requests for
services from other programs and also as a server of
requests from other programs.
Browser
• An application program that provides a way to
look at and interact with all the information on
the World Wide Web.
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Mosaic 1993
Opera
Firefox
Chrome
Internet Explorer
Web Server
• Using the client/server model and the World
Wide Web's Hypertext Transfer Protocol (HTTP),
serves the files that form Web pages to Web
users (whose computers contain HTTP clients
that forward their requests).
• Every computer on the Internet that contains a
Web site must have a Web server program.
• Apache
• Tomcat
• IIS
Other clients & servers?
• Mail server/client
– SendMail, Exchange, Lotus Domino
– Opera, Outlook, Mozilla
• FTP Server/Client
Peer to Peer
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Gnutella
Kazza
Bittorrent
Warez
eDonkey
Internet hardware
• Edge devices - Clients, servers, peers, PC’s
servers, phones, PDA’s
• Core devices – Hubs, switches, routers,
gateways
• Access devices – analogue modems, 802.11
base stations, ISDN modems, network cards,
cable modems, DSL modem
• Connection devices – POTS, wireless, fibre,
CAT5/CAT6
Hub
• The central part of a wheel where the spokes
come together.
• The term is familiar to frequent fliers who travel
through airport "hubs" to make connecting flights
from one point to another.
• In data communications, a hub is a place of
convergence where data arrives from one or
more directions and is forwarded out in one or
more other directions
Switch
• A device that channels incoming data from
any of multiple input ports to the specific
output port that will take the data toward
its intended destination.
Router
• A device or, in some cases, software in a computer,
that determines the next network point to which a
packet should be forwarded toward its destination.
• The router is connected to at least two networks and
decides which way to send each information packet
based on its current understanding of the state of the
networks it is connected to.
• May create or maintain a table of the available routes
and their conditions and use this information along
with distance and cost algorithms to determine the
best route for a given packet
Modem
• A modem modulates outgoing digital
signals from a computer or other digital
device to analog signals for a conventional
copper twisted pair telephone line and
demodulates the incoming analog signal
and converts it to a digital signal for the
digital device
Network card
• A network interface card (NIC) is a
computer circuit board or card that is
installed in a computer so that it can be
connected to a network.
• A dedicated full time connection
• Wired or wireless
Wireless
• 802.11 (a,b,g)
• GPRS
• 3G
ISDN
• Standards for digital transmission over ordinary
telephone copper wire as well as over other
media.
• Home and business users who install an ISDN
adapter (in place of a telephone modem) receive
Web pages at up to 128 Kbps compared with the
maximum 56 Kbps rate of a modem connection.
• Being replaced by ADSL where availible
ADSL
• Technology for transmitting digital information at a high
bandwidth on existing phone lines to homes and
businesses.
• Unlike regular dialup phone service, ADSL provides
continously-available, "always on" connection.
• ADSL is asymmetric in that it uses most of the channel to
transmit downstream to the user and only a small part to
receive information from the user. ADSL simultaneously
accommodates analog (voice) information on the same
line.
• ADSL is generally offered at downstream data rates from
512 Kbps to about 6 Mbps.
Question?
• How can such a diverse range of
hardware and software communicate?
• You can replace all the hardware with new
hardware and replace all the software with
new software, but its still the Internet!
• How come?
– Standard Protocols
What’s a protocol?
human protocols:
• “what’s the time?”
• “I have a question”
• introductions
… specific msgs sent
… specific actions
taken when msgs
received, or other
events
network protocols:
• machines rather
than humans
• all communication
activity in Internet
governed by
protocols
protocols define format, order of
msgs sent and received
among network entities, and
actions taken on msg
transmission, receipt
What’s a protocol?
a human protocol and a computer network
protocol:
Hi
TCP connection
req.
Hi
TCP connection
reply.
Got the
time?
Get http://gaia.cs.umass.edu/index.htm
2:00
<file>
time
Q: Other human protocol?
What do protocols look like?
• “Binary”
– Fixed-length fields, like C-structures
– Type-length-value (TLV)
• “Text”
– ftp: PUT foo
– GET index.html HTTP/1.1
Content-Length: 100
Connection-oriented service
Goal: data transfer
TCP service [RFC 793]
between end sys.
• reliable, in-order byte• handshaking: setup
stream data transfer
(prepare for) data transfer
– loss: acknowledgements and
retransmissions
ahead of time
– Hello, hello back human
• flow control:
protocol
– set up “state” in two
communicating hosts
• TCP - Transmission
Control Protocol
– Internet’s connectionoriented service
– sender won’t overwhelm
receiver
• congestion control:
– senders “slow down sending
rate” when network
congested
HTTP Protocol
Parameters
RFC’s:
1945
2068
2616
Web Browser
E.g. A user fills in a form,
which gets submitted to a
web server
Port Numbers (16 bit
numbers) identify the service
Web Server
Database (Optional)
http://www.ietf.org/rfc/rfc1945.txt?number=1945
SMTP Protocol
• Simple Mail Transfer Protocol
• Protocol for sending Email
• Originally designed for a secure network
RFC’s:
821
974
1869
2821
Mail Client
Mail Server Mail Server
Mail Server
Issues? Security & Non-repudiation
http://www.ietf.org/rfc/rfc0821.txt?number=821
Person
Shop
Farmer
Wholesalers
Co-op
Protocol Stacks
Internet Standardisation
• International Telecommunications Union (ITU)
– United Nations treaty organization
– Modem standards (V.90)
– Traditional telephone services, fax
• Internet Engineering Task Force (IETF)
– Core: Internet Protocol, transport (TCP)
– Applications: email, HTTP, ftp, NFS
– Not: HTML, APIs
• W3C
– HTML, XML, XSL, …
• IEEE
– WiFi
IETF
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Open membership
Meets three times a year, about 2,000+ people
Most work done on mailing lists (see www.ietf.org)
Working groups produce technology
No formal voting at WG level, but review by “area
directors”
• Emphasis on interoperability and deployment
• Internet drafts -> Proposed Standard (RFC)
• See www.normos.org for RFC directory
RFC’s
Network Working Group
Request for Comments: 1
Steve Crocker
UCLA
7 April 1969
Title: Host Software
Author: Steve Crocker
Installation: UCLA
Date: 7 April 1969
Network Working Group Request for Comment: 1
http://www.ietf.org/rfc.html
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Introduction
The software for the ARPA Network exists partly in the IMPs and
partly in the respective HOSTs. BB&N has specified the software of
the IMPs and it is the responsibility of the HOST groups to agree on
HOST software.
During the summer of 1968, representatives from the initial four
sites met several times to discuss the HOST software and initial
experiments on the network. There emerged from these meetings a
working group of three, Steve Carr from Utah, Jeff Rulifson from SRI,
and Steve Crocker of UCLA, who met during the fall and winter. The
most recent meeting was in the last week of March in Utah. Also
present was Bill Duvall of SRI who has recently started working with
Jeff Rulifson.
Somewhat independently, Gerard DeLoche of UCLA has been working on
the HOST-IMP interface.
I present here some of the tentative agreements reached and some of
the open questions encountered. Very little of what is here is firm
and reactions are expected.
What is Internet/Web
development?
• Creating software that:
– Runs on Internet hardware
– Runs on Internet software
– Uses Internet protocols