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Circuit Switched Networks vs. Packet-Switched NetworkThe Internet Emerges

https://www.photonics.com/Articles/Toward_Optical_Packet_Switching/a24582

A Supplement to Lecture 12

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What is the Internet?

• The Internet is a worldwide system of interconnected autonomous computer networks connecting hundreds of millions of digital “computing devices” together.

– “Computing devices” means desktop personal computers, workstations, servers, laptops, cell phones, VoIP phones, game consoles, IP-TV, GPS-enabled devices, environmental sensor devices, and home and office electrical and security systems.

– “Computing devices” connected to the Internet are sometimes called “hosts” or “end devices” or even “end systems.”

• The Internet is a vast network of packet-switched networks consisting of millions of private and public, academic, business, NGO and government networks of local to global scope.

http://deresinc.com/HomeNetworks.aspx

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https://dazeinfo.com/2016/06/13/number-internet-users-worldwide-2016-2020/

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Circuit-Switched Network

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

TelephoneSwitch

Many paths are possible, but only one is selected per

call.

Once a connection is established, this

connection is maintained until call

is terminated.

Caller

= Dedicated connection (point-to-point)

Subscriber lines(or local loops)

Trunks(links between

Exchanges)

Central Office

Central Office

Central Office

PSTN = public switched telephone network

Full Duplex

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Packet Switched Network

Internet

Many paths possible for a single message as packets are routed to

the destination.

Packets are routed according to the best path available at the

time.

Receiver(destination)

Sender(source)

Message broken into packets andeach addressed

Packets sequentiallyreassembled

to revealmessage

= Packet

Routeror Switch

(Data Packet or “Datagram”)

Large array of routers and data links.

Packet route

From: D. B. Estreich, Lecture from ES 101A in 2014

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Network Organization

Centralized Network Decentralized Network

(e.g., PSTN)

Distributed Network

(e.g., Internet)

In 1962, Paul Baran (RAND Corp.) envisioned a network of unmanned nodes using intelligent switches to route data node to node to their final destinations. Baran called this "hot-potato routing" or distributed communications. This was implemented in ARPANET which became the Internet.

Concept of hardened networks to deal with disasters.

A networkof routers

A highly vulnerablenetwork

7After Kurose & Ross, Computer Networking, 5th Edition, Addison-Wesley, New York, 2010.

National & Global ISPs

Local orRegional

ISP

MobileCellular

NetworkWireless

HomeNetwork

Corporate orUniversityNetwork

HomeNetwork

Example:

sonic.net

Example:

Keysight Technologies

Example:

Verizon

Example:

Sprint

ModemPacket Switch or Router

WirelessRouter

Cell Phone

Cellular

Base Station

VoIP Phone

Host

Mobile Laptop Server

Key:

A “representative” section of the Internet:

(ISP = Internet Service Provider)

Internet is a “Network of Networks”

8http://dafi1637.blogspot.com/2017/10/google-fiber-usa-map.html

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Brief History of the Internet – I

Year Event

1958 ARPA (Advanced Research Program Agency) is established by the U. S. Defense Department in response to the 1957 Sputnik launch.

1969 The ARPANET utilizes “packet switching” technology developed in part by Paul Baran of the RAND Corporation. The first four nodes in the network were UCLA, UCSB, Stanford and the Univ. of Utah.

1972-4 ARPANET expands to 15 nodes and standardization includes the TCP (Transmission Control Protocol) developed by Vinton Cerf of Stanford, thereby creating the TCP/IP network standard now used today.

https://www.internetsociety.org/internet/history-internet/brief-history-internet/

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Xerox PARC (and its Alto Computer in April 1973)

http://www.computerhistory.org/revolution/input-output/14/347

First workstation (personal computer)

Pulled together all the elements used inthe graphical user interface (GUI)

Features:(1) Bit-mapped display(2) Three-button mouse (D. Engelbart – SRI)(3) Use of graphical windows(4) Ethernet LAN (Robert Metcalf)(5) And more

Footnote: The IBM PC was introduced in 1981.

AltoComputer

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Beginning of the Internet Age

On August 27, 1976, scientists from SRI International celebrated the successful completion of tests by sending an electronic message from a computer set up at a picnictable behind the Alpine Inn. The message was sent via a radio network to SRI and on throughthe ARPANET to Boston. This event marked the beginning of the Internet Age.

Alpine Inn Beer Garden (Portola Valley)

Established 1852

California Historic Site

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Brief History of the Internet – II

Year Event

1990 The Internet goes private with a number of ISPs (Internet Service Providers) being created by businesses (most notably AOL – America Online).

1991 Tim Berners-Lee at CERN creates the World Wide Web (WWW), which uses Hypertext Markup Language (html), Hypertext Transport Protocol (http) and URLs (Uniform Resource Locator).

1993 First Web browser (MOSAIC) at the University of Illinois – soon becomes Netscape Navigator; later in 1995 Microsoft enters the market with Internet Explorer.

https://www.internetsociety.org/internet/history-internet/brief-history-internet/

How TCP/IP Works

STEP 1TCP protocolbreaks data intopackets andaddresses them.

STEP 2The packets travel fromrouter to router over the Internet according to IP protocol.

STEP 3TCP protocolreassembles thepackets into theoriginal whole.

To:From:

To:From:

router

routerrouter

router

router

router

SenderReceiver

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https://www.researchgate.net/figure/Classification-of-header-fields-in-the-IP-and-UDP-header_fig1_241622622

IP and UDP Headers

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https://www.w3.org/People/Frystyk/thesis/TcpIp.html

Reliable Packet Transmission (TCP Packets)

Lost Packet

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Feature Circuit Switching Packet Switching

Dedicated Path Yes

No

Path FormationPath dedicated for one conversation

Route is established on a per packet basis of the conversation using datagram (or per conversation with virtual circuit)

Delay Call setup delay Packet transmission delay (call setup delay for virtual circuit)

Bandwidth Type Fixed Bandwidth Dynamic bandwidth

Overload EffectsStops call establishment

Increases packet delay (can block call establishment and increase packet delay with virtual circuit)

Comparing Packet Switching to Circuit Switching

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Packet-Switched Network Operation

• Adaptive routing – routers chose the best path by examining traffic loading along available paths. Routers create a “routing table” for the packet travel.

• All users share the same network resources.

• Packet-switching is more efficient than circuit-switching in networks when data is bursty (i.e., variable delays interspersed with periods of data transmission). More “efficient” means a better utilization of the network resources.

This is an example of

“bursty” data

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An Internet Packet and its Headers

• In IPv4, each packet is restricted to 1,500 bytes of data (i.e., payload + headers)

• Each packet consists of the application data and headers

• The headers contain control and routing information such as:

– Source IP address and destination IP address

– Packet numbering for reconstruction at destination

• Every computer on the Internet has the TCP/IP program. The client/server model is used on the Internet.

• TCP (Transmission Control Protocol) puts the data or message into packets at the source and reassembles the data or message at the destination

• IP (Internet Protocol) does the packet addressing for the routing over the Internet

Application DataIP header TCP/UDP header

Internet Packet

The rules that govern communication – any form – are called “protocols.”

19https://computer.howstuffworks.com/question5251.htm

Internet Packets Have Header, Payload and Trailer

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Layer Pictorial View of Protocol Data Unit Entity

ApplicationData or

Message

Transport Segments

Internet or Network

Packets orDatagrams

Network Access

Frames

Data

DataTransport

Header

DataTransport

HeaderNetwork Header

DataTransport

HeaderNetwork Header

Frame Header

Frame Trailer

Protocol

SMTPHTTP, DNS

TCPUDP

IP

EthernetModem

FDDI

Number of segments 1

Bits transmitted over channel medium

TCP/IP Protocol Architecture Model

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TCP and IP Headers

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TCP versus UDP Transmission

TCP is “reliable” because it has flow & congestioncontrol, retransmission, &uses acknowledgements.

UDP does not use these because it is focused onlyupon sending packets. ItIs “best effort delivery.”

UDP

TCP and UDP Analogies:

Post OfficeVerifies deliveryRegistered

Letter

TCP

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Example of an IP Address (i.e., IPv4 format)

• Every Internet node must have an Internet address (some are “permanent” and others are “temporary”)

• When you connect to the Internet over a broadband access, an IP address is assigned to your computer by your Internet Service Provider (ISP)

• This IP address is “dynamic” – when you disconnect the network can allocate it to another user.

1 byte 1 byte

4 bytes = 32 bits in total

1 byte 1 byte

Decimal:

Binary:

EXAMPLE:

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IPv4 versus IPv6

How do you say 340,282,366,920,938,463,463,374,607,431,768,211,456?

It is 340 undecillion, 282 decillion, 366 nonillion, 920 octillion, 938

septillion, 463 sextillion, 463 quadrillion, 607 trillion, 431 billion,

768 million, 211 thousand, 456.

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▪ Uses computer-based technologies

▪ Highly interconnected but distributed in practice

▪ Networks interconnected thru gateways and access points (i.e., routers, link-layer switches, etc.)

▪ Each network stands on its own (TCP/IP protocols do not dictate internal changes to networks)

▪ TCP/IP is independent of the data type or the transport medium

▪ TCP/IP protocols are not proprietary (all can freely use it)

▪ Effectively little regulation applies to Internet (in fact, users of the Internet generally oppose regulation)

▪ There is NO direct global control of the Internet

Internet Attributes

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Computer History Museum (Mountain View, CA)

Open Wednesday through Sunday,1401 Shoreline Blvd (adjacent 101) in Mountain View, CA. 650-810-1010

After the coronavirus “shelter-in-place” ends, a great place to visit.

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Questions

https://www.colourbox.com/image/internet-concept-on-white-background-image-5798412