Overview of the Internet

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# 181U Spring 2020
## Introduction to the Internet

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# Agenda 
* What's the Internet ?
* What's a protocol ?
* Network Structure 
* "the Core "
* A bit of history
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# What's the Internet

![](images/buildingblocks.png# w-30pct)
![](images/nutsandbolts.png# w-60pct)

* Billions of connected computing devices
    - *hosts* = *end systems*
    - running *network apps*
* *Communication links*
    - fiber,copper,radio,satellite
    - transmission rate: **bandwidth**
* *Packet Switches* forward packets (chunks of data)
    - *routers* and *switches*

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# Internet-connected devices

![](images/images/space.png# w-2-12th)
![](images/connecteddevices.png# w-70pct)

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# What's the Internet: "nuts and bolts" view

![](images/nutsandbolts.png# w-33pct fr)

* **Internet**: "network of networks"
    - Interconnected ISPs
* **Protocols** control sending, receiving of messages
    - e.g. IP, TCP, HTTP, Skype
* **Internet standards**
    - RFC: Request for comments
    - IETF: Internet Engineering Task Force.

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# What's a protocol ?

**Human Protocols**
* "what's the time?"
* "I have a question"
* Introduction
<br>

**Network Protocols**
* Machines rather that humans
* all communication activity in Internet governed by protocols
<br>

**Protocols** 
define **format**, **order** of **messages** *sent and received* 
among network entities and **actions taken** on message transmission and receipt

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# What's a protocol ?

A Human protocol and a computer network protocol

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![](images/protocol1.png# w-70pct)

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# A closer look at network structure

![](images/nutsandbolts.png# w-33pct fr)

* **network edge**
    - hosts: clients and servers
    - servers often in data centers
* **access networks, physical media**
    - wired, wireless communicaiton links
* **network core**
    - interconnected routers
    - network of networks

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# Access networks and physical media

![](images/networkedge.png# w-33pct fr)

**Q: How to connect end systems to edge router ?**

* Residential access nets
* Institutional access networks (school, company)
* Mobile access networks

**Keep in mind**
* bandwidth (bits per second) of access network
* latency (end-to-end time) of messages
* shared or dedicated

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# Access network: digital subscriber line (DSL)

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* Use **existing** telephone line to central office DSLAM
    - data over DSL phone line goes to Internet
    - voice over DSL phone line goes to telephone network
* < 2.4 Mbps upstream transmission rate (typically < 1 Mbps)
* < 24 Mbps downstream transmission rate (typically < 10 Mbps)

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# Access network: cable network
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**frequency division multiplexing:** different channels transmitted on different frequency bands.
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# Access network: cable network

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* **HFC: hybrid fiber coax**
    - asymmetric: up to 30Mpbs downstream transmission rate, 2 Mbps upstream transmission rate
      (now much faster)
* **network** of cable, fiber attaches to ISP router
    - homes *share access network* to cable headend
    - unlike DSL, which has dedicated access to central office

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# Access network: home network
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![](images/homenetwork.png#  w-60pct)

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# Enterprise access networks (Ethernet)

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* Typically used in companies, universities, etc.
* 100 Mpbs, 1 Ggbs, 10 Gpbs transmission rates
* today, end system typically connect into Ethernet switch

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# Wireless access networks

Shared *wireless* access network connects end system to router veia base station (access point).

![](images/wirelessout.png#  w-30pct fr)

* **wireless LANS:**
   - within building (100ft)
   - 802.11 b/g/n (WiFi): 11,54,450 Mbps transmission rate

![](images/wirelesswide.png#  w-30pct fr)

* **wide-area wireless access**
    - provided by telco (cellular) operator, 10's km
    - between 1 and 10 Mbps
    - 3G, 4G:LTE

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# Host: sends *packets* of data

![](images/hostpacket.png# w-50pct fr)

Host sending function:
* Breaks application message into smaller chunks known as *packets* of length *L* bits.
* Transmits packets into access network at transmission rate *R*

\\[ \\text{transmission delay } = \\frac{L (bits)}{R (\\frac{bits}{sec})}\\]

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# Packet-switching: store-and-forward

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![](images/packetswitching.png# w-70pct )

* Takes L/R seconds to transmit L-bit packet into link at R pbs
* **store and forward**: entire packet must arrive at router before it can
be transmitted on next link
* For N hops, end-to-end delay is NL/R (assuming no propagation delay)

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# The network core

![](images/networkcore.png# w-30pct fr)

* Mesh of interconnected routers
* Packet-switching: hosts break application-layer messages
into *packets*
    - forward packets from one router to the next, across links on path from source to destination
    - each packet transmitted at full link capacity

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# Two key network-core functions

* **routing:** determines source-destination taken by packets (routing algorithms)
* **forwarding:** moves packets from router's input to appropriate router output

![](images/space.png# w-2-12th)
![](images/route-forward.png# maxw-70pct )

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# Internet structure: network of networks

* End systems connect to Internet via **access ISPs** (Internet Service Providers)
   * residential, company and university ISPs
* Access ISPs in turn must be interconnected
   * so that two hosts can send packets to each other 
* Resulting network of networks is very complex
   * evolution was driven by **economics** and **national policies**

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# Internet structure: network of networks

Competitors connnected through peering links and IXPs

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![](images/netofnets1.png# maxw-70pct)

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# Internet structure: network of networks

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![](images/netofnets2.png# maxw-50pct)

* At center a small number of well-connected large networks
   * **"tier-1"** commercial ISPs (e.g. Level 3, Sprint, AT&T,...) with national & international coverage
   * **content provider networks** (e.g. Google): private network that connects its data networks to Internet often bypassing tier-1 and regional ISPs.

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# Tier-1 ISP: Sprint

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# Protocol "Layers"

Networks are complex with many "pieces"
* hosts
* routers
* applications
* protocols
* hardware/software

Is there any hope of an *organizing* structure for the network ?

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# Internet protocol stack

![](images/ipstack.png# maxw-20pct fr)

* **application** : supports network applications
  * FTP, SMTP, HTTP
* **transport** : process-process data transfer
  * TCP, UDP
* **network** : routing of packets from source to destination
  * IP, routing protocol
* **link** : data transfer between neighboring network elements
  * Ethernet, Wifi, PPP
* **physical**: bits "on the wire"

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# Encapsulation

![](images/space.png# w-3-12th)
![](images/encapsulation.png# maxw-50pct)

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# Internet History (Early packet-switching principles)

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* **1961**: Kleinrock -- queuing theory shows effectiveness of packet-switching
* **1964**: Baran -- packet-switching in military nets
* **1967**: ARPAnet conceived by Advanced Research Projects Agency
* **1969**: First ARPAnet node operational
* **1972**:
   * ARPAnet public demo
   * NCP (Network Control Protocol) first host-host protocol
   * first e-mail program
   * ARPAnet has 15 nodes

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# Internet History

1972-1980: Internetworking, new and proprietary networks

![](images/cerfkahn.png# maxw-40pct fr)

* **1970**: ALOHAnet satellite network in Hawaii
* **1974**: Cerf and Kahn -- architecture for interconnecting networks
* **1976**: Ethernet at Xerox PARC
* **late 70's**: Proprietary architectures DECnet, SNA, XNA
* **1979**: ARPAnet has 200 nodes

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# Internet History

1980-1990: new protocols, application, proliferation of networks

* **1983**: deployment of TCP/IP
* **1982**: smtp e-mail protocol defined
* **1983**: DNS defined for name-to-IP-address translation
* **1985**: ftp protocol defined
* **1988**: TCP congestion control

<br>

* new national networks: CSnet, BITnet, NSFnet, Minitel
* 100,000 hosts connected in confederation of networks

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# Internet History

1990,2000's commercialization, the Web, new apps

* **early 1990's**: ARPAnet decomissioned
* **1991** : NSF lifts restricions on commerial use of NSFnet (decommisioned 1995)
* **early 1990s**: Web
  * hypertext (bush 1945, Nelson 1960's)
  * HTML, HTPP: Berners-lee
  * 1994: Mosaic (later Netscape)
  * late 1990's: commercialization of the web

**Late 1990's-2000's**

* New killer apps: instant messaging, P2P file sharing
* Network security becomes significant issue
* Backbone links running at Gpbs

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# Internet History

2005-present

* ~5 Billion devices attached to Internet (2016)
* Aggressive deployment of broadband access
* Increasing ubiquity of high-speed wireless acces
* Emergence of on-line social networks
* Service providers (Google, Microsoft,...) create their own networks
  * bypass Internet providing "instantaneous" access to search, content
* e-commerce, universities, enterprises running their services in the "cloud" (e.g. Amazon EC2)
  
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# Summary

![](images/kurosecover.jpg# w-33pct ba fr)

* Cover Image: The Opte Project [<a href="https://creativecommons.org/licenses/by/2.5">CC BY 2.5</a>], <a href="https://commons.wikimedia.org/wiki/File:Internet_map_1024_-_transparent,_inverted.png">via Wikimedia Commons</a>
* Source Material : Much of the content of these slides adapted from the slides provided for
 "Computer Networking: A Top Down 
Approach" 7th edition by Jim Kurose and Keith Ross.  That material is copyright 1996-2016 J.F Kurose and K.W. Ross.