1 Networks and Communications Demonstrations:. 2 What is a "network" anyway? A network is a collection of computers, communications channels, and

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Networks and CommunicationsNetworks and Communications

Demonstrations:Demonstrations:

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What is a "network" anyway?What is a "network" anyway? A network is a collection of computers, A network is a collection of computers,

communications channels, and appropriate communications channels, and appropriate software that allows the computers to software that allows the computers to communicate with each other in an communicate with each other in an organized way.organized way.

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Network ArchitectureNetwork Architecture Network ProtocolsNetwork Protocols Network ApplicationsNetwork Applications Home NetworksHome Networks

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Network ArchitectureNetwork Architecture

Local Area Networks (LAN)Local Area Networks (LAN) Wide Area Networks (WAN)Wide Area Networks (WAN) Personal Area Networks (PAN)Personal Area Networks (PAN) Wireless Personal Area Networks (WPAN)Wireless Personal Area Networks (WPAN)

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Local Area Networks (LAN)Local Area Networks (LAN)

A A local area networklocal area network is a collection of is a collection of computers located at a single location computers located at a single location (possibly large, such as an entire campus) (possibly large, such as an entire campus) connected together in such a way that they connected together in such a way that they can communicate with each other.can communicate with each other.

LAN's generally provide local file and printer LAN's generally provide local file and printer sharing, and electronic mail.sharing, and electronic mail.

Interconnection can be cables and/or wireless.Interconnection can be cables and/or wireless. ExamplesExamples: the Engineering College, the UH : the Engineering College, the UH

campus, a network in your homecampus, a network in your home

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Local Area Networks (LAN)Local Area Networks (LAN)

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Wide Area Networks (WAN)Wide Area Networks (WAN)

A A wide area networkwide area network consists of a diverse consists of a diverse collection of computers communicating with collection of computers communicating with each other over long distance, generally over each other over long distance, generally over common carrier lines.common carrier lines.

WAN's generally provide access to remote WAN's generally provide access to remote files and electronic mail.files and electronic mail.

ExampleExample: There’s really only one: Internet!: There’s really only one: Internet!

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Wide Area Networks (WAN)Wide Area Networks (WAN)

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Personal Area Networks (PAN)Personal Area Networks (PAN)

A personal area network (PAN) is the A personal area network (PAN) is the interconnection of information technology interconnection of information technology devices within the range of an individual devices within the range of an individual person, typically within a range of 10 meters.person, typically within a range of 10 meters.

For example, a person traveling with a For example, a person traveling with a laptop, a personal digital assistant (PDA), and laptop, a personal digital assistant (PDA), and a portable printera portable printer....

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Wireless Personal Area Wireless Personal Area Networks (WPAN)Networks (WPAN)

A WPAN (wireless personal area network) is a A WPAN (wireless personal area network) is a personal area network - a network for interconnecting personal area network - a network for interconnecting devices centered around an individual person's devices centered around an individual person's workspace - in which the connections are wirelessworkspace - in which the connections are wireless . .

Typically, a WPAN uses some technology that Typically, a WPAN uses some technology that permits communication within about 10 meters - in permits communication within about 10 meters - in other words, a very short range. One such other words, a very short range. One such technology is Bluetooth, which was used as the basis technology is Bluetooth, which was used as the basis for a new standard, IEEE 802.15.1for a new standard, IEEE 802.15.1

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WPAN WPAN (cont’d)(cont’d)

A key concept in WPAN technology is known as A key concept in WPAN technology is known as plugging inplugging in. In the ideal scenario, when any two . In the ideal scenario, when any two WPAN-equipped devices come into close proximity WPAN-equipped devices come into close proximity (within several meters of each other) or within a few (within several meters of each other) or within a few kilometers of a central server, they can communicate kilometers of a central server, they can communicate as if connected by a cable. as if connected by a cable.

The technology for WPANs is in its infancy and is The technology for WPANs is in its infancy and is undergoing rapid development . Every device in a undergoing rapid development . Every device in a WPAN will be able to plug in to any other device in WPAN will be able to plug in to any other device in the same WPAN, provided they are within physical the same WPAN, provided they are within physical range of one another. In addition, WPANs worldwide range of one another. In addition, WPANs worldwide will be interconnected. will be interconnected.

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Network ProtocolsNetwork Protocols Network Network protocolsprotocols provide the “language” for provide the “language” for

communications between devices.communications between devices. The Internet network model had 5 protocol The Internet network model had 5 protocol layerslayers::

1.1. Physical – bits & hardwarePhysical – bits & hardware

2.2. Datalink – frames & physical addressesDatalink – frames & physical addresses

3.3. Network – packets, path determination & logical Network – packets, path determination & logical addressingaddressing

4.4. Transport – end-to-end connections & reliabilityTransport – end-to-end connections & reliability

5.5. Application – network process to applicationApplication – network process to application

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Network Protocols Network Protocols SimplifiedSimplified

We’ll take a We’ll take a simplifiedsimplified view of these protocols: view of these protocols: Low-level ProtocolsLow-level Protocols (Layers 1 & 2) - These relate to (Layers 1 & 2) - These relate to

the the physicalphysical transmission of the data. transmission of the data. (Ethernet, Wi-(Ethernet, Wi-Fi, Bluetooth)Fi, Bluetooth)

High-level ProtocolsHigh-level Protocols (Layers 3 & 4) (Layers 3 & 4) - These provide - These provide the the generalgeneral rules for communicating between two rules for communicating between two computers over the low-level protocol. computers over the low-level protocol. (TCP/IP)(TCP/IP)

Client-server ProtocolsClient-server Protocols (Layer 5) - These specify how (Layer 5) - These specify how a specific a specific client applicationclient application will communicate with will communicate with its its server applicationserver application over the high-level protocol. over the high-level protocol. (Email, web, chat, instant messaging protocols)(Email, web, chat, instant messaging protocols)

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Low-level Protocols Low-level Protocols (Layers 1 & 2)(Layers 1 & 2)

Low-level protocols specify how basic Low-level protocols specify how basic packets of information are transmitted over a packets of information are transmitted over a single physical network, and generally also single physical network, and generally also include the hardware/electronics include the hardware/electronics specification.specification.

The computer must have a The computer must have a hardware hardware interfaceinterface corresponding to the low-level corresponding to the low-level protocol!protocol!

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Low-level Protocols Low-level Protocols (cont’d)(cont’d)

Analogy: Analogy: Highway traffic laws describe rules for the Highway traffic laws describe rules for the

use of highways to carry vehicles with various use of highways to carry vehicles with various contents from source to destination. Here we contents from source to destination. Here we are including the physical specification of the are including the physical specification of the highway and the vehicles, and the laws and highway and the vehicles, and the laws and procedures for using them. procedures for using them.

Similarly, there are laws and procedures for Similarly, there are laws and procedures for air traffic, train traffic, ocean traffic, etc.air traffic, train traffic, ocean traffic, etc.

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Low-level Protocols Low-level Protocols (cont’d)(cont’d)

EthernetEthernet IEEE 802.3, 100 Mbits/s on twisted pair wire. Use IEEE 802.3, 100 Mbits/s on twisted pair wire. Use

an an Ethernet network interface cardEthernet network interface card.. Wi-FiWi-Fi – wireless LAN standard – wireless LAN standard

802.11b (10 Mbps) and 802.11g (100 Mbps)802.11b (10 Mbps) and 802.11g (100 Mbps) All laptops, and newer PDA’s, have it built-in.All laptops, and newer PDA’s, have it built-in.

BluetoothBluetooth 802.15.1 (up to 2 Mbps) for short range 802.15.1 (up to 2 Mbps) for short range

networking (usually up to 10 meters)networking (usually up to 10 meters) Used for WPAN’s (PC to printer, PDA to PC, cell Used for WPAN’s (PC to printer, PDA to PC, cell

phone to car audio system or earpiece)phone to car audio system or earpiece)

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Network InterfaceNetwork Interface

There must be some sort of hardware connection There must be some sort of hardware connection between the computer and the network.between the computer and the network.

The The low-level protocollow-level protocol determines the hardware determines the hardware interface, not the high-level protocol. That is, you interface, not the high-level protocol. That is, you would purchase an Ethernet or Wi-Fi or Bluetooth, would purchase an Ethernet or Wi-Fi or Bluetooth, not a TCP/IP, interface for your PC (more on TCP/IP not a TCP/IP, interface for your PC (more on TCP/IP later).later).

Examples:Examples: Network interface cards.Network interface cards. Usually built-in on newer computers and PDAs.Usually built-in on newer computers and PDAs.

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MAC AddressesMAC Addresses

Each device has a unique Layer 2 Each device has a unique Layer 2 MAC addressMAC address (Media Access Control).(Media Access Control).

Ethernet & Wi-Fi MAC addresses are twelve hex Ethernet & Wi-Fi MAC addresses are twelve hex

digits. E.g., digits. E.g., 00-20-E0-6C-D8-2A00-20-E0-6C-D8-2A . . The address is built into the hardware and is not The address is built into the hardware and is not

changeable by the user.changeable by the user. Bluetooth MAC addresses are just 3 bits.Bluetooth MAC addresses are just 3 bits.

A Bluetooth network has at most 1 master device A Bluetooth network has at most 1 master device and 7 slave devices (called a and 7 slave devices (called a piconetpiconet).).

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High-level Protocols High-level Protocols (Layers 3 & 4)(Layers 3 & 4)

High-level protocols provide end-to-end High-level protocols provide end-to-end addressing and delivery of high-level packets addressing and delivery of high-level packets over any number of physical networks over any number of physical networks (internet) and low-level protocols. (internet) and low-level protocols.

The high-level packets are wrapped inside The high-level packets are wrapped inside the low-level packets as they traverse each the low-level packets as they traverse each physical network. physical network.

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High-level Protocols High-level Protocols (cont’d)(cont’d)

Analogy: Analogy: The postal service provides end-to-end The postal service provides end-to-end

delivery of mail packages properly delivery of mail packages properly addressed. addressed.

It uses a variety of transportation means It uses a variety of transportation means (highway, train, air). (highway, train, air).

The mail packages are carried inside the The mail packages are carried inside the vehicles, trains, planes of the physical carrier.vehicles, trains, planes of the physical carrier.

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High-level Protocols High-level Protocols (cont’d)(cont’d)

Biggest Example:Biggest Example:

TCP/IPTCP/IP (Unix , Windows, used on the (Unix , Windows, used on the InternetInternet). ).

TCP/IP runs over Ethernet, Wi-Fi, and TCP/IP runs over Ethernet, Wi-Fi, and many other low-level protocols.many other low-level protocols.

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Application Protocols Application Protocols (Layer 5)(Layer 5)

(Client-Server Protocols)(Client-Server Protocols) A network application is a program which A network application is a program which

transmits information over the LAN or WAN to transmits information over the LAN or WAN to another (similar?) application on a remote another (similar?) application on a remote computer. Frequently we say that a computer. Frequently we say that a clientclient program communicates with a program communicates with a serverserver program. program.

A A serverserver is an application (program) that is an application (program) that offers a service to some other application.offers a service to some other application.

A A clientclient is an application that requests the is an application that requests the service from the server.service from the server.

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Application Protocols Application Protocols (cont’d)(cont’d)

The service is provided using some agreed-The service is provided using some agreed-upon communication upon communication protocolprotocol that may be that may be specific to that kind of service.specific to that kind of service.

On the Internet, these protocols are On the Internet, these protocols are transported on top of the TCP/IP protocol.transported on top of the TCP/IP protocol.

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Application Protocols Application Protocols (cont’d)(cont’d)

Analogy:Analogy: As a customer (client) in this country you may As a customer (client) in this country you may

send an order for goods to a company send an order for goods to a company (server) in another country. (server) in another country.

The filled out order form conforms to a The filled out order form conforms to a specific procedure (protocol) for ordering from specific procedure (protocol) for ordering from that company, and you mail the form to them that company, and you mail the form to them in an envelope to be delivered by the postal in an envelope to be delivered by the postal system.system.

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Common Common Client-Server ProtocolsClient-Server Protocols HTTP (Hypertext Transfer Protocol) - used on WWW for HTTP (Hypertext Transfer Protocol) - used on WWW for

document transferdocument transfer SMTP (Simple Mail Transfer Protocol) - electronic mailSMTP (Simple Mail Transfer Protocol) - electronic mail POP (Post-Office Protocol) - email retrievalPOP (Post-Office Protocol) - email retrieval IMAP (Internet Message Access Protocol) – email IMAP (Internet Message Access Protocol) – email

retrieval and managementretrieval and management Telnet - remote terminal emulationTelnet - remote terminal emulation FTP (File Transfer Protocol) - file transferFTP (File Transfer Protocol) - file transfer DHCP (Dynamic Host Configuration Protocol) – dynamic DHCP (Dynamic Host Configuration Protocol) – dynamic

assignment of IP addressesassignment of IP addresses

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SummarySummary A client application uses a particular language – a set A client application uses a particular language – a set

of commands and responses -- to communicate with of commands and responses -- to communicate with a remote server application. a remote server application.

These commands and responses are delivered to the These commands and responses are delivered to the destination machine (specified by its IP address) by destination machine (specified by its IP address) by the TCP/IP protocol. the TCP/IP protocol.

The TCP/IP packets may be transported over The TCP/IP packets may be transported over multiple physical networks employing a variety of low-multiple physical networks employing a variety of low-level protocols.level protocols.

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TCP/IP on the InternetTCP/IP on the Internet

The TCP/IP suite has five protocol layers:The TCP/IP suite has five protocol layers:

Application

Transport

Network

Datalink

Physical

5: e.g., FTP, telnet, HTTP

4: TCP

3: IP

2: e.g., Ethernet frames

1: e.g., voltages

} "client-server protocols"

"high-level protocols"

"low-level protocols"

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TCP/IP TCP/IP (cont’d)(cont’d) From client to server:From client to server: Header information gets added to a packet at Header information gets added to a packet at

each protocol layer. For example:each protocol layer. For example:"GET /"HTTP request:

TCP header "GET /"TCP segment:

TCP header "GET /"IP headerIP datagram:

TCP header "GET /"IP headerEthernet headerEthernet frame:

Voltages:

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TCP/IP TCP/IP (cont’d)(cont’d)

The packet may traverse several devices on The packet may traverse several devices on its path between client and server.its path between client and server.

IP datagram

Ethernet frame

Voltage

Ethernet frame

Voltage

HTTP request

TCP segment

IP datagram

Ethernet frame

Voltage

HTTP request

TCP segment

IP datagram

Ethernet frame

Voltage

Client Server

Bridge

Router

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TCP/IP TCP/IP (cont’d)(cont’d)

To send a message on the network, a computer only To send a message on the network, a computer only has to put its data in an envelope, called an Internet has to put its data in an envelope, called an Internet Protocol (IP) packet, and "address" the packets Protocol (IP) packet, and "address" the packets correctly.correctly.

The communicating computers--not the network The communicating computers--not the network itself--are also given the responsibility to ensure that itself--are also given the responsibility to ensure that the communication is accomplished.the communication is accomplished.

The philosophy is that every computer on the network The philosophy is that every computer on the network can talk, as a peer, with any other computer.can talk, as a peer, with any other computer.

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Addresses, names, and Addresses, names, and domainsdomains

Each computer, or host, on the Internet has an Each computer, or host, on the Internet has an IP addressIP address consisting of four numbers consisting of four numbers separated by periods, or dots. E.g., separated by periods, or dots. E.g., 129.7.4.131129.7.4.131 is one of the computers in our is one of the computers in our network.network.

The The domain namedomain name system provides an easier- system provides an easier-to-remember name for an IP host on the net. to-remember name for an IP host on the net. E.g., E.g., violet.egr.uh.eduviolet.egr.uh.edu is the domain name for is the domain name for the IP address above.the IP address above.

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IP AddressesIP Addresses

IP addresses are assigned two ways:IP addresses are assigned two ways: Static addressesStatic addresses are sometimes assigned by are sometimes assigned by

IT personnel to corporate servers.IT personnel to corporate servers. Dynamic addressesDynamic addresses are assigned by a DHCP are assigned by a DHCP

server when a client is turned on and initiates server when a client is turned on and initiates the request over the network.the request over the network.

Dynamic addresses are used in all home Dynamic addresses are used in all home networks, and especially in all wireless networks, and especially in all wireless networks.networks.

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Addresses, names, and Addresses, names, and domains domains (cont’d)(cont’d)

Some top-level domain specifications are:Some top-level domain specifications are: edu educational institutionsedu educational institutions com commercial companiescom commercial companies org organizationsorg organizations gov government entitiesgov government entities net networksnet networks jp Japanjp Japan us United Statesus United States

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Addresses, names, and Addresses, names, and domains - Examplesdomains - Examples violet.egr.uh.edu a host in UH Engineeringviolet.egr.uh.edu a host in UH Engineering www.egr.uh.edu Engineering’s web serverwww.egr.uh.edu Engineering’s web server www.texas.gov Texas’ web serverwww.texas.gov Texas’ web server ftp.netscape.com Netscape’s FTP serverftp.netscape.com Netscape’s FTP server

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Network ApplicationsNetwork Applications

A network application is a program which A network application is a program which transmits information over the LAN or WAN to transmits information over the LAN or WAN to a complementary program on a remote a complementary program on a remote computer.computer.

These generally work in a “client/server” These generally work in a “client/server” configuration.configuration.

ExamplesExamples: : File and Print Services, World-Wide File and Print Services, World-Wide Web, Electronic Mail, Chat, Remote Terminal Web, Electronic Mail, Chat, Remote Terminal Emulation, File Transfer.Emulation, File Transfer.

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File ServicesFile Services

File service File service provides the ability to read and provides the ability to read and write files on a disk located on a remote write files on a disk located on a remote computer, the "file server", as if the disk were computer, the "file server", as if the disk were connected directly to the local computer.connected directly to the local computer. Demonstration: Look at server directories Demonstration: Look at server directories

in Windows Explorer.in Windows Explorer.

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Print ServicesPrint Services

Print servicePrint service provides the ability to print to a provides the ability to print to a printer located on a remote computer, the printer located on a remote computer, the "print server", as if the printer were directly "print server", as if the printer were directly connected to the local computer.connected to the local computer. Demonstration: Look at printers on the Demonstration: Look at printers on the

various servers.various servers.

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World-Wide WebWorld-Wide Web The WWW consists of The WWW consists of web serversweb servers which which

serve up documents that can be displayed in serve up documents that can be displayed in web clientweb client programs, which are usually called programs, which are usually called web web browsersbrowsers because of their use in because of their use in “browsing” the web.“browsing” the web.

Web documents provide Web documents provide hyperlinkshyperlinks to other to other web documents on the same or other servers.web documents on the same or other servers.

The web provides The web provides multimediamultimedia documents, documents, including text, sound, graphics, 3D, and more.including text, sound, graphics, 3D, and more.

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URLsURLs

Links to a document on the web are in the Links to a document on the web are in the form of a Uniform Resource Locator (URL).form of a Uniform Resource Locator (URL).

A URL expresses in a standard way both the A URL expresses in a standard way both the protocol and the network path to any protocol and the network path to any resource on the network.resource on the network.

Format (in its simplest form):Format (in its simplest form): protocol:host:port/path.../documentprotocol:host:port/path.../document

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URLs URLs (cont’d)(cont’d)

Some examples of URLs specifying various Some examples of URLs specifying various protocols:protocols:

http://www.egr.uh.edu:80/Welcome.htmlhttp://www.egr.uh.edu:80/Welcome.html ftp://ftp.egr.uh.edu/pub/ftp://ftp.egr.uh.edu/pub/ file://h:/notes/textdocs/html/demo.htmlfile://h:/notes/textdocs/html/demo.html

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Electronic Mail (email)Electronic Mail (email)

A A mail clientmail client uses the uses the SMTPSMTP protocol to protocol to sendsend a mail message to an SMTP server (“post a mail message to an SMTP server (“post office”), which then takes the responsibility for office”), which then takes the responsibility for sending the message to its destination SMTP sending the message to its destination SMTP server, retransmitting as necessary when server, retransmitting as necessary when errors are encountered. errors are encountered.

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Electronic Mail Electronic Mail (cont’d)(cont’d)

A client mail program A client mail program on the destination on the destination machinemachine can then read the message. (PC’s can then read the message. (PC’s are usually not SMTP servers.) are usually not SMTP servers.)

For example, if you receive mail on For example, if you receive mail on bayou.uh.edubayou.uh.edu, you can telnet to that machine , you can telnet to that machine and run the local mail program to read your and run the local mail program to read your mail.mail.

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POP Servers & ClientsPOP Servers & Clients IfIf the the destinationdestination SMTP server is SMTP server is alsoalso running a POP running a POP

service, an service, an alternativealternative way to read mail is to have a way to read mail is to have a mail client on some other machine, perhaps a PC, use mail client on some other machine, perhaps a PC, use the POP protocol to retrieve the mail from the POP the POP protocol to retrieve the mail from the POP server (which is the destination SMTP server). server (which is the destination SMTP server).

POP is only used for picking up mail that has already POP is only used for picking up mail that has already arrived at the SMTP/POP server. arrived at the SMTP/POP server.

For example, Thunderbird and Outlook Express are For example, Thunderbird and Outlook Express are POP clients you can use to retrieve and read mail from POP clients you can use to retrieve and read mail from multiple accounts.multiple accounts.

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IMAP Servers & ClientsIMAP Servers & Clients

Some mail servers support IMAP instead of POP (or Some mail servers support IMAP instead of POP (or perhaps in addition to it).perhaps in addition to it).

IMAP first retrieves just message headers, and IMAP first retrieves just message headers, and retrieves the message only when its header has been retrieves the message only when its header has been selected for reading.selected for reading.

Messages can be Messages can be managedmanaged onon the IMAP server the IMAP server (folders, etc.).(folders, etc.).

IMAP clients (e.g., Outlook Express, Thunderbird) IMAP clients (e.g., Outlook Express, Thunderbird) can connect to multiple IMAP servers and POP can connect to multiple IMAP servers and POP servers at the same time.servers at the same time.

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Configuring a Mail clientConfiguring a Mail client““Outgoing SMTP server” – the server that transmits Outgoing SMTP server” – the server that transmits

messages you write.messages you write. This server depends on This server depends on where the mail client where the mail client

accesses the Internetaccesses the Internet, for example, at UH or at home., for example, at UH or at home. Examples:Examples:

At UH, At UH, mail.uh.edumail.uh.edu.. At home, whatever your ISP specifies, e.g.,At home, whatever your ISP specifies, e.g.,

smtp-server.houston.rr.comsmtp-server.houston.rr.com for RoadRunner. for RoadRunner.

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Configuring a Mail client Configuring a Mail client (cont’d)(cont’d)

““Incoming POP or IMAP server” – the server where your Incoming POP or IMAP server” – the server where your incoming mail arrives.incoming mail arrives.

This server depends on This server depends on where you receive the mailwhere you receive the mail, , not where the client accesses the Internet.not where the client accesses the Internet.

Examples:Examples: mail.uh.edumail.uh.edu for your UH IMAP mail for your UH IMAP mail

(([email protected])[email protected]). At home, whatever your ISP specifies, e.g.,At home, whatever your ISP specifies, e.g.,

pop-server.houston.rr.compop-server.houston.rr.com for RoadRunner for RoadRunner (([email protected])[email protected]).

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Web-based MailWeb-based MailMost popular, however, is web-based mail:Most popular, however, is web-based mail: You simply connect to a web page and login to read and You simply connect to a web page and login to read and

send mail.send mail. Your mail and folders are stored on the server.Your mail and folders are stored on the server. Mail is accessed anywhere from a browser.Mail is accessed anywhere from a browser.

You don’t need to configure incoming and outgoing You don’t need to configure incoming and outgoing mail servers (for POP, SMTP, IMAP) – probably the mail servers (for POP, SMTP, IMAP) – probably the biggest advantage!biggest advantage!

Mail is not dependent on your ISP.Mail is not dependent on your ISP. At UH, At UH, mail.uh.edumail.uh.edu provides a web-based interface to the provides a web-based interface to the

IMAP folders.IMAP folders. HotmailHotmail and and GmailGmail are other popular examples. are other popular examples.

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Electronic Mail AddressesElectronic Mail Addresses

The standard Internet "domain-style" The standard Internet "domain-style" addressing is common.addressing is common.

Address format: Address format: [email protected]@computername.subdomain...domain

ExampleExample: : [email protected]@bayou.uh.edu . .

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Remote Terminal EmulationRemote Terminal Emulation

Remote terminal emulationRemote terminal emulation is the basic is the basic function of providing a command line function of providing a command line interface to a remote computer as if the user interface to a remote computer as if the user were connected locally to it via a terminal or were connected locally to it via a terminal or console.console.

telnettelnet: A popular program used on all Unix : A popular program used on all Unix systems and the Internet for remote terminal systems and the Internet for remote terminal emulation over TCP/IP.emulation over TCP/IP.

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File TransferFile Transfer

ftp: This is the standard Internet "file transfer ftp: This is the standard Internet "file transfer protocol“ used for file transfer long before the web protocol“ used for file transfer long before the web arrived.arrived.

File Transfer Modes:File Transfer Modes: Binary - byte-for-byte file image transfer.Binary - byte-for-byte file image transfer. Text (or ASCII) - In this mode, the assumption is Text (or ASCII) - In this mode, the assumption is

that the file is a standard ASCII text file. If the text that the file is a standard ASCII text file. If the text file format is different on the source and file format is different on the source and destination file systems, then ftp performs the destination file systems, then ftp performs the appropriate conversion during the transfer.appropriate conversion during the transfer.

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Anonymous FTP SitesAnonymous FTP Sites

Hundreds of sites around the country where Hundreds of sites around the country where anyone can login via FTP and pick up files anyone can login via FTP and pick up files (recently most have been replace by web (recently most have been replace by web sites).sites).

Sites usually have a "theme": Windows Sites usually have a "theme": Windows software, educational applications, music, software, educational applications, music, images, etc.images, etc.

Public files are in the Public files are in the pubpub directory and directory and below. Some have a below. Some have a submissionssubmissions directory directory where you can submit files.where you can submit files.

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Anonymous FTP Sites Anonymous FTP Sites (cont’d)(cont’d)

Login username: Login username: anonymousanonymous Password: your return email addressPassword: your return email address One list of sites:One list of sites:

http://www.ftp-sites.org/http://www.ftp-sites.org/

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FTP ProgramsFTP Programs

ftpftp is a command-line program available on is a command-line program available on both Windows and UNIX.both Windows and UNIX. Demo: Enter ftp at the DOS PromptDemo: Enter ftp at the DOS Prompt

There are also many programs that provide a There are also many programs that provide a GUI interface to ftp. GUI interface to ftp. Demo: WS_FTP LE, available free at UHDemo: WS_FTP LE, available free at UH

Most web browsers support the ftp protocol, so Most web browsers support the ftp protocol, so you can just browse the site. For example:you can just browse the site. For example:

ftp://ftp://ftp.egr.uh.eduftp.egr.uh.edu

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Home NetworksHome NetworksLet’s review and apply these ideas to a home network.Let’s review and apply these ideas to a home network. You’ll get to the Internet through an You’ll get to the Internet through an ISPISP (Internet (Internet

Service Provider).Service Provider). For high-speed/broadband service, you’ll use either For high-speed/broadband service, you’ll use either

cablecable (cable company) or (cable company) or DSLDSL (phone company). (phone company). You will be provided a You will be provided a cable modemcable modem or or DSL modemDSL modem..

On one side it connects to the provider.On one side it connects to the provider. On the other side it has Ethernet (twisted pair).On the other side it has Ethernet (twisted pair).

You should then connect a You should then connect a broadband routerbroadband router to the to the Ethernet.Ethernet. The router provides multiple Ethernet and/or Wi-Fi The router provides multiple Ethernet and/or Wi-Fi

connections to your home computers, printers, etc.connections to your home computers, printers, etc.

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Twisted pair

Ethernet

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Local IP AddressesLocal IP Addresses

The router uses DHCP to provide IP The router uses DHCP to provide IP addresses to devices connecting to it.addresses to devices connecting to it.

Home network IP addresses are usually: Home network IP addresses are usually: 192.168.xxx.yyy 192.168.xxx.yyy and are local to the home and are local to the home network, not seen on the Internet.network, not seen on the Internet. The router uses The router uses NATNAT (Network Address (Network Address

Translation) to allow multiple home Translation) to allow multiple home computers to share the router’s single IP computers to share the router’s single IP address (the only one assigned/allowed to address (the only one assigned/allowed to it by the ISP). it by the ISP).

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Wireless Router SecurityWireless Router Security

The router provides a form of “hardware firewall”, The router provides a form of “hardware firewall”, hiding your computers from Internet probes.hiding your computers from Internet probes.

However, the wireless link presents security risks, However, the wireless link presents security risks, and you should take these precautions:and you should take these precautions: Do not broadcast the router’s SSID (name).Do not broadcast the router’s SSID (name). Use WPA (Wi-Fi Protected Access) encryption.Use WPA (Wi-Fi Protected Access) encryption.

Most people do none of these, and their networks are Most people do none of these, and their networks are wide open to nearby hackers!wide open to nearby hackers!

Documents

1 Networks and Communications Demonstrations:. 2 What is a "network" anyway? A network is a collection of computers, communications channels, and