Basics of Computing -- Chapter 4 An Introduction to ...bioinfolab.unl.edu/~cstrope/teaching/csce101s07/notes/chapter04/... · Cory L. Strope: Basics of Computing – Chapter 4 An

Network Fundamentals The Internet Network Protocols Review

Basics of Computing – Chapter 4An Introduction to Computer Networks

Cory L. Strope

Cory L. Strope: Basics of Computing – Chapter 4 An Introduction to Computer Networks


Network Fundamentals

The Internet

Network Protocols

Review



What is a Computer Network?

A computer network is a collection of computers that are connectedin order to communicate, exchange data, and share resources.

A network can be very large (the Internet) or very small (twocomputers connected at home).



Network Classification

Overview

I Size

I Topology

I Communication Models

I Transmission Media

I Recent & Future Trends




Network Size

According to geographical size, there are three “sizes” of networks:

LAN (Local Area Network): A network set up within a singlebuilding or campus. Generally, smaller than a few kilometersin size.

MAN (Metropolitan Area Network): A bigger version of a LAN,covering up to the size of a city.

WAN (Wide Area Network): Spans a large geographical area,often the size of a country or a continent.




Network Topology

The (physical) topology of a computer network is the pattern inwhich the machines are connected.

I There are 4 patterns of connection:

1. Ring2. Bus3. Star

Each pattern has advantages and disadvantages.I Choosing the correct topology depends on:

I Application of networkI How the network is usedI The communication modelI May depend on the nature of the area where the network is

physically deployed




Network TopologyRing




Network TopologyBus




Network TopologyStar




Communication ModelsThere are two models of interprocess communication,communication over the network between different computers.

I Client/server model – the process on the server communicateswith numerous clients

I Print server: A single printer in an office, available to allmachines on the network.

I File server: A high-capacity storage system containing all of anorganizations records.

I Napster

I Peer-to-peer model – two processes communicate as equalsI Instant MessagingI eDonkey, LimeWire, KaZaA

Note that a peer-to-peer network is like Santa Claus, theEaster Bunny, and the Tooth Fairy. It is a peer-to-peer model.




Transmission Media

So far, we have classified networks by size, topology, andcommunication model... Another method of classifying networks isthrough the transmission media used.

I When talking of topologies, the assumption was made that wewere using wires to connect computers... “wired networks”,in other words.

I If the medium of communication is the air, the network is saidto be a “wireless network”...




Transmission MediaAir




Connecting NetworksBridge

A bridge is a device that can be used to couple compatiblenetworks (two buses, for example).

I Does not pass all messages across the connection.

I Forwards message across connection only when the message isdestined for a computer on the other network.

I A switch is a bridge with more than 2 connections.




Connecting NetworksRouter

The end result of using bridges and switches is the creation of onelarge, single network.

I Each computer communicates over the system in the samemanner (protocol).

Not all networks have compatible characteristics. In thesenetworks, we build a “network of networks”, known as an internet.




Connecting NetworksRouter

To make an internet, a specialized computer must belong to bothnetworks.

I The router forwards messages in one network into othernetworks.

I Routers are complex, and may contain several other devices todo a specific task.




Recent and Future Trends in Networking

There is a great deal of research being done on new networkingtechniques:

I Optical Networks: The pro’s of optical networks is hugebandwidth.

I Many networks are desirable for military application:I Sensor Networks: A wireless, and possibly mobile, network

that connects sensors for a specific purpose.I ad hoc Networks: A wireless, self-configuring network of

mobile routers (and associated hosts) connected by wirelesslinks. What would the topology of this be?




The Internet

Network Protocols

Review



Basics

Asia PacificEurope / Middle East /Central Asia / AfricaNorth AmericaLatin American andCaribbean

Other: White & Cyan



Basics

The Internet– With a Capital ‘I’ !

The Internet does not have a specific topology; rather, the Internetcan be viewed as a collection of domains.

A domain is an autonomous system (AS) that is managedlocally.

I The Internet connects a collection of self-managed networks(locally administrated networks).

I For example, UNL campus network (an AS) is connected tothe Internet, but internally, it is managed by the campusnetwork administrators.



Basics

Domain EstablishmentICANN – Good Disc. Board Debate Topic!!!

To establish a domain, the entity desiring the domain must registerwith ICANN (Internet Corporation for Assigned Names andNumbers, a non-profit corporation.



Internet Addressing

Internet AddressingIP Address

For a computer to be allowed on the Internet, it must have an address.

Internet addresses are called the IP (Internet Protocol) addresses.

I Each IP address is 32 bits long (IPv4).I The next generation IP address is called IPv6, and contains

128 bits.

IP addresses have two main parts:I Network identifier: Used to identify the domain.

I Assigned by ICANN at the time the domain is established.I The registration process ensures the uniqueness of each

domain address.I Machine identifier: Also called the machine (host)

address, this identifies a particular machine within a domain.I Assigned by a network administrator working inside of the

domain.



Internet Addressing

IP AddressAn Example

Consider the Computer Science and Engineering department,which is part of the unl domain.

I The machine that hosts the web page of the CS departmenthas the IP address 129.93.165.2:

129.93.︸︷︷︸Network ID

165.2︸︷︷︸Mach. Addr.

I You can memorize this number (for a quiz) to access thedepartment web page.



Internet Addressing

IP AddressDomain Names

129.93.︸︷︷︸Network ID

165.2︸︷︷︸Mach. Addr.

I Or you can simply remember cse.unl.edu. Your choice.



Internet Addressing

IP AddressDomain Names

Because IP addresses are hard to memorize, each domain isassigned a unique address known as a domain name.

I The domain name for UNL? unl.edu

Domain names end with a top-level domain (TLD) identifier,e.g. .org, .com, .mil, .net, etc.1

I There are also two-letter TLDs for countries, calledcountry-code TLDs.

I .ca, .eg, .ws, .tv, .us, ...

1Interesting Discussion Board topic: Should there be a .xxx domain? Whywas this proposal turned down?



Internet Addressing

IP AddressMachine Name

After assigning a unique domain name, the local administrator isfree to extend it the domain name to include assigned names forindividual machines within its domain.

The Computer Science machine: cse.unl.edu



Internet Addressing

Internet ApplicationsEmail & HTTP

The Internet is dominated by two applications:

I Electronic mail (e-mail)2

I Hyper Text Transfer Protocol (HTTP)

Another rapidly expanding use of the Internet is Voice over IP(VoIP), which is simply transmitting telephone data over theInternet rather than the traditional phone lines.

2The word e-mail is outlawed in France. The word is “courrierelectronique”, or “Courriel” for short.



World Wide Web

World Wide Web

The terms “Internet” and “World Wide Web” are often usedsynonymously – but there is a difference.

I Internet: Physical world wide network of domains (i.e.networks).

I WWW: Collection of linked documents on the Internet,transferred via HTTP.



World Wide Web

World Wide WebURL

Documents on the Internet each have a unique address, called theUniform Resource Locator (URL).

I Contains the information needed by the browser (e.g. InternetExplorer, Mozilla Firefox) to contact the proper server andrequest the desired document.

http://www.cse.unl.edu/join us

Protocol required toaccess thedocument.As a note, https issecure http, used forbank websites, etc.

Name of the host(machine) holdingthe document.

The name of thedocument.Unnameddocuments arereferred to asindex.html.




The Internet

Network Protocols

Review



What is a Protocol?

In general, the rules that govern the communication betweendifferent components within the computer system are calledprotocols.

A protocol is an agreement between the communicating parties onhow communication should take place.

Rules that govern the communication of computers with eachother are computer network protocols.



Internet DeliveryMessages and Packets

Message: The data or information we wish to deliver over theInternet.

I A stream of 1s and 0s

The smallest unit of data that is transferred over the internet iscalled a “packet”. Each packet contains:

I Destination address (the address of the computer that shouldreceive the message).

I Data



Internet Software Layers

If the size of the message is larger than the packet size, themessage is divided into multiple packets, all with the samedestination address.

I Each packet is assigned a sequence number

I Packets are sent over the network, may stop at intermediatecomputers before arriving at the destination.

I At destination, packets are collected and concatenated in theiroriginal sequence.

Delivering packets over a network is complex, and is divided amongseveral entities (layers).

I Mail example: You, shipping company, airline.

Each entity (layer) is assigned a task in order to simplify the task.Layers are independent of each other.



Internet Software Layers





The Network Layer

Each router maintains a list of all other routers in the network,called the routing table.

I Updated frequently to reflect any changes in the topology ofthe network.

I A link going downI Router not accessibleI Discovery of a better path to another router

The network layer uses the IP address as an ID for the router tobuild the routing table.



The Link Layer

Also called the physical layer or the data link layer, the task ofthe link layer is to take care of the communication details on thephysical medium.

I Example: In the bus topology, all machines are connected tothe bus... How do the machines determine when they can usethe bus?



Layers in Action!

From:

http://ping.unl.edu

http://www.radb.net



The Australian National University



IP address Machine location Remarks129.93.1.253 Lincoln, NE, USA UNL campus network129.93.3.25 Lincoln, NE, USA UNL campus network129.93.4.237 Lincoln, NE, USA UNL campus network129.93.5.9 Lincoln, NE, USA UNL campus network164.113.234.134 Midwest, USA Great Plains Network, Internet 2164.113.238.149 Midwest, USA Great Plains Network, Internet 2164.113.238.193 Midwest, USA Great Plains Network, Internet 2198.32.8.13 Kansas City, MO, USA Abilene Network, Internet 2198.32.8.49 Denver, CO, USA Abilene Network, Internet 2198.32.171.32 Seattle, WA, USA Abilene Network, Internet 2202.158.194.93 Canberra, Australia AARNet202.158.201.226 Canberra, Australia AARNet202.158.201.234 Canberra, Australia AARNet150.203.99.8 Canberra, Australia



Link Layer Protocols




Link Layer Protocol-1Token Ring Protocol

Consider a ring network (LAN): The token ring protocal canmanage the physical transmission of data over the ring network.

I Developed by IBM in 1970, widely used today.

I Transmission in the ring is done in one direction (clockwise orcounter-clockwise)

I When the message reaches its destination, the destinationmachine keeps a copy of it and forwards a copy on around thering.

I When the forwarded copy reaches the origination machine, theoriginating machine removes the message from the ring.









The determination of which machine has the right to send amessage is determined by a unique bit pattern, called the token,which is passed around the ring.

I The machine that has the token has the right to send a singlemessage. Other machines may only forward messages.

I After the machine with the token sends its own message(successfully), the token is passed to the next machine.

I A machine that gets the token, but has no message to send,forwards the token to the next machine.




Link Layer Protocol-2CSMA/CD

The Carrier Sense, Multiple Access with Collision Detection(CSMA/CD) protocol is commonly used on a popular version ofthe bus network, Ethernet.

I Each machine broadcasts the message (all machines “hear”messages)

I Machines keep only the messages that are addressed to itself.

Machines can send messages only when the bus is not being used...What if two send at the same time? Packets collide

I Both machines will detect the collision, and wait for arandom amount of time before retransmitting.

I This process continues until each machine sends its messagesuccessfully.



Network classification:I Size

I LANI WANI MAN

I Communication ModelI Client/serverI Peer-to-peer

I Transmission MediumI Copper wire (electricity)I Wireless (radio waves)I Optical fiber (light)



Connecting Networks

I Bridges

I Routers

The Internet

I A collection of Domains (autonomous self-managed networks)

I ICANN assigns domains and addressesI Addressing:

I IPv4: 32 bitsI Network IdentifierI Machine Identifier

I Dotted decimal notation

I URL (Universal Resource Locator)I 3 parts: Transmission protocol, machine name, document

name.



Network Protocols

I Protocol: A set of rules thta governs communication betweentwo entities.

I Sending data over a network is a complex task, the approachused is a layered approach

I Each layer is responsible for a small part of the overall task.I A layer does not need to know the details of other layers

operation.

I Internet software layersI ApplicationI TransportI NetworkI Link

I Example link layer protocolsI Token RingI CSMA/CD



Questions on Chapter 4?
