How the Internet How the Internet Works?Works?( TCP/IP, DNS( TCP/IP, DNS…… ) )

How computers send How computers send data?data?

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Channel

ProtocolConnection

method

Address

Communication Communication ChannelChannel

Telephone line (Twist pair, Optical fiber)Telephone line (Twist pair, Optical fiber) Modulator-Demodulator (Modulator-Demodulator (ModemModem)) Digital Subscriber Line (Digital Subscriber Line (DSLDSL))

Cable modemCable modem

Satellite, MicrowaveSatellite, Microwave

Wireless connection (IR, RF)Wireless connection (IR, RF)3

what kind of media?

Different mediumDifferent medium

Twisted pairTwisted pair

RJ45 connectorRJ45 connector

Coaxial cableCoaxial cable

BNC connectorBNC connector

Fiber optic cableFiber optic cable

Different cabling lengthDifferent cabling length Optic > coaxial > Twisted pairOptic > coaxial > Twisted pair

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Use ModemUse Modem

Modulation / De-modulationModulation / De-modulation

E.g. CU Dialup Pool (56kbps max.)E.g. CU Dialup Pool (56kbps max.)

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Telephone lineAnalog data

Digital data - 10101010101

Use Digital Subscriber Line Use Digital Subscriber Line (DSL)(DSL)

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Traditional phone line

ADSL modem

Why ADSL?

Why ADSL?Why ADSL?

AAsymmetric symmetric DSLDSLA slower upstream A slower upstream

(upload) can trade off a (upload) can trade off a faster downstream faster downstream (download) speed.(download) speed.

128 to 640 kbps 128 to 640 kbps (upstream)(upstream)

1.5M to 5M bps 1.5M to 5M bps (downstream)(downstream)

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Use Cable ModemsUse Cable Modems

Use coaxial cable to carry TV signal and High Use coaxial cable to carry TV signal and High speed Internet accessspeed Internet access

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Satellite & Satellite & MicrowaveMicrowave

Satellite systemsSatellite systems Use satellites orbiting above the Earth to relay Use satellites orbiting above the Earth to relay

signals from one part of a WAN to another, signals from one part of a WAN to another, cause 0.5 to 5 sec delays.cause 0.5 to 5 sec delays.

MicrowaveMicrowave Costly to install but cheaper than satellite.Costly to install but cheaper than satellite. It is very useful for connecting networks that It is very useful for connecting networks that

are separated by a barrier, such as a highway are separated by a barrier, such as a highway or a lake.or a lake. Requires line of sight.Requires line of sight.

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Using A Computer To Using A Computer To Interconnect NetworksInterconnect Networks

Special-purpose Special-purpose computers are used computers are used to interconnect to interconnect networks.networks.Using standard Using standard

hardware (CPU, hardware (CPU, memory, and network memory, and network interfaces)interfaces)

Running special-Running special-purpose softwarepurpose software

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Network Interface CardNetwork Interface CardNICNIC

Physically connects a computer to the Physically connects a computer to the transmission medium on a network.transmission medium on a network.

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Hardware/Physical/MAC (Media Hardware/Physical/MAC (Media Access Control) addressAccess Control) address

When a NIC is When a NIC is manufactured, manufactured, the card is given the card is given a unique a unique hardware hardware address.address.

It never changes.It never changes.

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RoutersRouters

Interconnecting computers are called routers Interconnecting computers are called routers by using the same protocol.by using the same protocol. Determining where to send packetsDetermining where to send packets

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Router

HubsHubs

A network cable connects a A network cable connects a computer via a network computer via a network card to a hub.card to a hub.

Provides a central location.Provides a central location.

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PortsPorts

A hub A hub contains contains sockets or sockets or ports.ports.

Some LED Some LED indicates indicates information information transferred transferred through through the port.the port.

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Ethernet RepeaterEthernet Repeater

A repeater is a device that strengthens and A repeater is a device that strengthens and retransmits signals on a network.retransmits signals on a network.

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Network ArchitectureNetwork Architecture

It refers how information transfers on networks.It refers how information transfers on networks.

Ethernet Ethernet It the most popular architecture used to build networks.It the most popular architecture used to build networks. Least expensive and easiest to setupLeast expensive and easiest to setup

Token-ring architectureToken-ring architecture It was developed by IBM in 1984.It was developed by IBM in 1984. They are popular found in large organizations, such as They are popular found in large organizations, such as

banks and insurance companies.banks and insurance companies.

Others: ARCnet, AppleTalk, Others: ARCnet, AppleTalk, ……

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Ethernet & Token RingEthernet & Token Ring

Ethernet, Fast Ethernet, Gigabit Ethernet Ethernet, Fast Ethernet, Gigabit Ethernet (transmit data at 1Gbps).(transmit data at 1Gbps).

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Postal ServicesPostal Services

You have to write a complete address You have to write a complete address on the envelope specifying the on the envelope specifying the countrycountry, , statestate, , citycity, , districtdistrict, , streetstreet, and so on., and so on.

After put the letter put into the After put the letter put into the mailbox, it will be delivered (routed) to mailbox, it will be delivered (routed) to its destination in a hierarchical way.its destination in a hierarchical way.

California Post Office knows the letter is California Post Office knows the letter is sent to NC, without concerning the sent to NC, without concerning the actual address to be routed within NC.actual address to be routed within NC.

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Basic Internet StructureBasic Internet Structure

The Internet works in a similar way as The Internet works in a similar way as postal services.postal services.

Roughly speaking, you may consider Roughly speaking, you may consider states within this country, as individual states within this country, as individual networks connecting to each other.networks connecting to each other.

The different pieces of the Internet are The different pieces of the Internet are connected by a set of computers connected by a set of computers (Gateways)(Gateways)Translates between protocolsTranslates between protocols

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Postage over the Postage over the InternetInternet

When delivering information via the When delivering information via the Internet, the information is split into small Internet, the information is split into small units called data packets (1500 byte each)units called data packets (1500 byte each)

When a packet is sent from California to a When a packet is sent from California to a particular host in UNC.particular host in UNC.

The packet is first delivered to NC,The packet is first delivered to NC, then is further transmitted to UNC,then is further transmitted to UNC, then is further transmitted to the appropriate then is further transmitted to the appropriate

department,department, finally arrived to the specific host.finally arrived to the specific host.

The data is reassembled at the destination.The data is reassembled at the destination.

The data packet is continuously being The data packet is continuously being switched from the source to destination.switched from the source to destination.

The Internet is said to be Packet Switching The Internet is said to be Packet Switching Network.Network.

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Packet Switching NetworkPacket Switching Network

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Packet switching Packet switching exampleexample

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Figure 16.1 An example internet with four networks connected by routers.

Figure 16.2 Cars from two roads merging onto another road are analogous to packets from two networks merging onto a third network.

IP addressIP address

Each host in the Internet is Each host in the Internet is assigned to a specific and unique assigned to a specific and unique number for identification.number for identification.

This number is called the IP This number is called the IP address of the specific host.address of the specific host.

This number is divided into 4 parts This number is divided into 4 parts for improving the readability.for improving the readability.

The range of each number is The range of each number is between 0 and 255.between 0 and 255. E.g. 0.0.0.0E.g. 0.0.0.0 255.255.255.255255.255.255.255

For example, the host For example, the host ““UNC.eduUNC.edu”” has its IP address of has its IP address of ““152.2.240.8152.2.240.8””

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Network Number / Network Number / Host NumberHost Number

IP addresses are split into 2 partsIP addresses are split into 2 partsA network number + a host numberA network number + a host number

For example, 152.2 is the network For example, 152.2 is the network number of UNC, 240.8 is the host number of UNC, 240.8 is the host number of the host number of the host ““UNC.eduUNC.edu””

Network numbers are assigned by a Network numbers are assigned by a central authority, the Internet central authority, the Internet Corporation for Assigned Names and Corporation for Assigned Names and Numbers (ICANN).Numbers (ICANN).

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Network ClassesNetwork Classes

There are 5 classes of IP addressThere are 5 classes of IP address

Class A comprises networks 1.0.0.0 to Class A comprises networks 1.0.0.0 to 127.255.255.255, the network address 127.255.255.255, the network address is in first quad. It allows roughly 16 is in first quad. It allows roughly 16 million hosts per network.million hosts per network.

Class B comprises network 128.0.0.0 to Class B comprises network 128.0.0.0 to 191.255.255.255, the network address 191.255.255.255, the network address is in the first two quads. It allows for is in the first two quads. It allows for 16,382 networks with up to 64K hosts.16,382 networks with up to 64K hosts.

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Network ClassesNetwork Classes

Class C comprises networks 192.0.0.0 to Class C comprises networks 192.0.0.0 to 223.255.255.255, with the network number 223.255.255.255, with the network number contained in the first three quads. It allows contained in the first three quads. It allows about 2 million networks with up to 254 hosts about 2 million networks with up to 254 hosts in each network.in each network.

Class D and E are falling into the range of Class D and E are falling into the range of 224.0.0.0 to 254.0.0.0 which are reserved for 224.0.0.0 to 254.0.0.0 which are reserved for multicast address and for special purpose multicast address and for special purpose use.use.

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SubnetSubnet

The Internet is structured hierarchically. UNC The Internet is structured hierarchically. UNC consists of many academic departments and consists of many academic departments and administrative bodies.administrative bodies.

IP allows you to subdivide a network into several IP allows you to subdivide a network into several subnets. E.g. SILS and Davis Library are two subnets. E.g. SILS and Davis Library are two subnets inside UNC.subnets inside UNC.

Each subnet is identified by a subnet number.Each subnet is identified by a subnet number.

E.g. we have a different way to interpret the IP E.g. we have a different way to interpret the IP address 152.2.62.223 (the ILS server)address 152.2.62.223 (the ILS server)

152.2 refers to the network number of UNC,152.2 refers to the network number of UNC, 62 refers to the subnet number of Davis Library,62 refers to the subnet number of Davis Library, 223 refers to the host number of 223 refers to the host number of ““aftonafton””..

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Dynamic Host Configuration Dynamic Host Configuration Protocol (DHCP)Protocol (DHCP)

A Protocol for assigning dynamic IP A Protocol for assigning dynamic IP address to devices on a network.address to devices on a network.

It is built on client and server models.It is built on client and server models.Server is the machine running DHCPD.Server is the machine running DHCPD.Client can be any network devices.Client can be any network devices.

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Advantage?Advantage?EliminatesEliminates manual manual configuration of network configuration of network parameters and parameters and utilizesutilizes the the use of IP addressuse of IP address

IP RoutingIP Routing

The process of transmitting a data packet The process of transmitting a data packet from the source to the destination via a from the source to the destination via a series of intermediate stations is called series of intermediate stations is called ““RoutingRouting””..

IP routing works as follow:IP routing works as follow: Each data packet is labeled with IP address of Each data packet is labeled with IP address of

the destination hostthe destination host

152.2.90.184152.2.90.184      1500 bytes Data here1500 bytes Data here

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IP PacketIP Packet

Includes Header, payload, dataIncludes Header, payload, data

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Packets Are Not The Same SizePackets Are Not The Same Size

Packets may be any size up to the maximum.Packets may be any size up to the maximum. Can be as small as a single keystrokeCan be as small as a single keystroke Can be larger, depending on applicationCan be larger, depending on application

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IP RoutingIP Routing

For example, when a packet is routing to For example, when a packet is routing to ““UNC.eduUNC.edu”” (152.2.62.223), the network (152.2.62.223), the network number is extracted as 152.2 which is number is extracted as 152.2 which is the network number of UNC. The packet the network number of UNC. The packet is then sent to NC and then to UNC.is then sent to NC and then to UNC.

Inside UNC, the subnet number is Inside UNC, the subnet number is examined and it is 62 which is the examined and it is 62 which is the subnet number of Davis. Then it is sent subnet number of Davis. Then it is sent to Afton.to Afton.

Inside Davis, the host number is Inside Davis, the host number is examined and it is 223 which is the host examined and it is 223 which is the host number of Afton. Finally, it is routed to number of Afton. Finally, it is routed to the destination.the destination.

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IP enough for routing?IP enough for routing?

A single packet is limited in length, usually 1-A single packet is limited in length, usually 1-1500 bytes.1500 bytes.

Network may lose packets, or damage the Network may lose packets, or damage the data in transit.data in transit.

Packets may arrive out of sequence (different Packets may arrive out of sequence (different routing path).routing path).

TCP is used to solve the problems.TCP is used to solve the problems.

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Protocol and AddressingProtocol and Addressing

To communicate over the Internet, the To communicate over the Internet, the computers must:computers must:use a use a common languagecommon language or a or a protocolprotocol to to

govern the exchange of messages.govern the exchange of messages.have a way to have a way to addressaddress one another. one another.

Protocol:Protocol:specifies exact format, order of messages specifies exact format, order of messages

sent and received among network entities, sent and received among network entities, and actions taken on message and actions taken on message transmission and receipt.transmission and receipt.

Addressing:Addressing:defines where to deliver the messages. defines where to deliver the messages.

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Protocol and AddressingProtocol and AddressingTCP/IP modelTCP/IP model

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Protocol and AddressingProtocol and Addressing

Internet has a large collections of Internet has a large collections of protocols organized in a layering model. protocols organized in a layering model. ApplicationApplication: enables the user, whether human : enables the user, whether human

or software, to access the network.or software, to access the network.TransportTransport: responsible for source-to-: responsible for source-to-

destination (end-to-end) data transfer.destination (end-to-end) data transfer.NetworkNetwork: responsible for routing packets from : responsible for routing packets from

source-to-dest across multiple networks. source-to-dest across multiple networks. Data linkData link: responsible for data transfer : responsible for data transfer

between neighboring network elements.between neighboring network elements.PhysicalPhysical: coordinates the functions required to : coordinates the functions required to

transmit a bit stream over a physical medium. transmit a bit stream over a physical medium.

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Protocol and AddressingProtocol and Addressing

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L5 data L5 data

Lower layer adds header to the data from upper Lower layer adds header to the data from upper layer. Header includes addressing and other layer. Header includes addressing and other fields.fields.

Protocol Stack - Open Systems Protocol Stack - Open Systems Interconnection (OSI) modelInterconnection (OSI) model

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Protocol and AddressingProtocol and Addressing

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TCP/IP Protocol Suite.TCP/IP Protocol Suite.

What is TCP/IP?What is TCP/IP?

““TCP would be in charge of the breaking TCP would be in charge of the breaking up the up the packetspackets and messages then and messages then reassembling them at the destination, reassembling them at the destination, and the IP would be responsible for and the IP would be responsible for transmitting the individual transmitting the individual packetspackets. For . For example: the TCP protocol would split up example: the TCP protocol would split up the letter and place it into multiple the letter and place it into multiple envelops, while the IP protocol would be envelops, while the IP protocol would be in charge of addressing the envelop and in charge of addressing the envelop and making sure it arrived at its proper making sure it arrived at its proper destination.destination.””

–– from from ““Where Wizards Stay Up LateWhere Wizards Stay Up Late””41

TCP/IPTCP/IP

A protocol is a collection of rules for A protocol is a collection of rules for formatting, ordering, and error-checking data formatting, ordering, and error-checking data sent across a network.sent across a network.

In 1974, Vincent Cerf and Robert Kahn In 1974, Vincent Cerf and Robert Kahn developed the Transmission Control Protocol developed the Transmission Control Protocol (TCP) which was further split into the Internet (TCP) which was further split into the Internet Protocol (IP) and TCP in 1978.Protocol (IP) and TCP in 1978.

In 1982, DoD adopted TCP/IP as the standard In 1982, DoD adopted TCP/IP as the standard protocol in the Internet.protocol in the Internet.

Because the significance of TCP/IP in the Because the significance of TCP/IP in the history of the Internet, Cerf and Kahn are history of the Internet, Cerf and Kahn are considered to be the Father of the Internet.considered to be the Father of the Internet.

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Transmission Control Transmission Control Protocol - TCPProtocol - TCP

Basic functionsBasic functions Decompose a lengthy data into multiple Decompose a lengthy data into multiple

packets for transmissionpackets for transmission Error detection, ensure validityError detection, ensure validity Packet loss? Packet loss?

No problem, packet retransmissionNo problem, packet retransmission

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Sequence NumbersSequence Numbers

TCP breaks the information into multiple TCP breaks the information into multiple packets.packets.

Each packet is associated with a Each packet is associated with a sequence number for identification.sequence number for identification.

152.2.90.184 Number 1152.2.90.184 Number 1      Data hereData here152.2.90.184 Number 2152.2.90.184 Number 2      Data hereData here 152.2.90.184 Number 3152.2.90.184 Number 3      Data hereData here

Each packet is individually routed in the Each packet is individually routed in the Internet, and arrive in random order.Internet, and arrive in random order.

The data is reassembled in the correct The data is reassembled in the correct order according to the sequence number.order according to the sequence number.

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Packet RetransmissionPacket Retransmission

A packet may be lost during the A packet may be lost during the transmission across the Internet (host transmission across the Internet (host down, link failure, down, link failure, …… ) )

When the destination host has been When the destination host has been waiting for a particular packet for a waiting for a particular packet for a certain time (timeout), it will request the certain time (timeout), it will request the source host to retransmit the packet.source host to retransmit the packet.

There is no need to retransmit all data There is no need to retransmit all data packets. Instead, only the missing packets. Instead, only the missing packet, which is identified by the packet, which is identified by the sequence number, needs to be sequence number, needs to be retransmitted.retransmitted.

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Error detection - Error detection - ChecksumsChecksums

Transmission errors occur even if a data Transmission errors occur even if a data packet is received by the destination packet is received by the destination successfully.successfully.

How to ensure the data is correctly How to ensure the data is correctly received?received?A method to detect possible transmission errors.A method to detect possible transmission errors.At the destination, checksum is recalculated At the destination, checksum is recalculated

based on the received data.based on the received data.The attached checksum and the newly The attached checksum and the newly

calculated checksum are compared. Mismatch calculated checksum are compared. Mismatch means there is transmission errors occurred.means there is transmission errors occurred.

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IPv6 (IP version 6)IPv6 (IP version 6)

Major changes:Major changes: More addressesMore addresses

IP address size from 32 IP address size from 32 bits to 128 bitsbits to 128 bits

Simplified IP headersSimplified IP headers Reduction of header Reduction of header

fields in IP packetfields in IP packet Added security Added security

featuresfeatures

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IPX/SPX ProtocolIPX/SPX Protocol

IPX/SPX makes up the IPX/SPX makes up the protocol suite that is used to protocol suite that is used to transfer information on transfer information on networks running the Novell networks running the Novell NetWare operating system.NetWare operating system.

Internetwork Packet Internetwork Packet Exchange (IPX) - Transfer Exchange (IPX) - Transfer information between information between devices.devices.

Sequenced Packet Exchange Sequenced Packet Exchange (SPX) - An extension of the (SPX) - An extension of the IPX protocol.IPX protocol.48

NetBEUI ProtocolNetBEUI Protocol

NetBNetBIOS IOS EExtended xtended UUser ser IInterfacenterface Is a network protocol used on small local area Is a network protocol used on small local area

networks.networks. A very small and efficient protocol, use little A very small and efficient protocol, use little

computer resources.computer resources.

NetBIOSNetBIOS NetNetwork work BBasic asic IInput/nput/OOutput utput SSystemystem Develop by IBM and allow computers to Develop by IBM and allow computers to

communicate with each other on a network.communicate with each other on a network.

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Why DNS?Why DNS?

What is DNS?What is DNS?Domain Name SystemDomain Name System

IP address is difficult to remember.IP address is difficult to remember.152.2.92.1 is which machine?152.2.92.1 is which machine?

Names are given to each computer on Names are given to each computer on the Internet for the convenience of the Internet for the convenience of human users.human users.

Besides IP addresses, all internet Besides IP addresses, all internet applications allow users to use applications allow users to use computer names.computer names.

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Computer names on the Computer names on the NETNET

How does it look like?How does it look like? DNS administrators is responsible to name DNS administrators is responsible to name

computers/group in their own subnet.computers/group in their own subnet. Each level of responsibility is called a domain.Each level of responsibility is called a domain.

Domains are separated by Domains are separated by ““dotsdots”” cse.UNC.edu.NCcse.UNC.edu.NC www.intel.comwww.intel.com

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Domain name and Host Domain name and Host namename

Each domain can create or change whatever Each domain can create or change whatever belongs to it.belongs to it. UNC can create any new domain, cseUNC can create any new domain, cse CSE can buy a new computer and name it as CSE can buy a new computer and name it as ––

robin, orchid, any other name.robin, orchid, any other name.

Two computers may have the same name if Two computers may have the same name if they are in different domains.they are in different domains. UNC.eduUNC.edu orchid.ie.UNC.edu.NCorchid.ie.UNC.edu.NC

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Domain Name System (DNS)Domain Name System (DNS)

Each node in the tree Each node in the tree hashas a a labellabel - a string with - a string with

a maximum of 63 a maximum of 63 characters.characters.

a a domain namedomain name - a - a sequence of labels sequence of labels separated by dots.separated by dots.

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How does DNS How does DNS work?work? DNS server = DNS service?DNS server = DNS service?

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IP vs Domain NameIP vs Domain Name

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Most Common Most Common hostnamehostname

Figure 18.1 The fifty most common names assigned to computers on the Internet in 2000.

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Top Level DomainsTop Level Domains

The Internet Corporation for Assigned Names The Internet Corporation for Assigned Names and Numbers (ICANN) define the and Numbers (ICANN) define the Top Level Top Level DomainsDomains..

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ISO 3166 Country ISO 3166 Country CodesCodes

Partial listPartial list Full listFull list

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Windows Internet Windows Internet Naming Service (WINS)Naming Service (WINS)Like DNS, WINS Like DNS, WINS

also resolves also resolves names and IP names and IP addresses except addresses except that the look up that the look up by WINS is by WINS is specific for specific for Windows Windows computers.computers.DynamicDynamicWin2k use DNS to Win2k use DNS to

replace WINSreplace WINS 59

SummarySummary

What should be considered if you install or What should be considered if you install or update a network?update a network? PlanPlan: the size, the budget: the size, the budget DetermineDetermine: the network design: the network design SelectSelect: the transmission media: the transmission media ChooseChoose: the network hardware, devices: the network hardware, devices InstallInstall: the network OS, drivers: the network OS, drivers ConfigureConfigure: server & client computers: server & client computers TestTest: the final network: the final network MaintainMaintain: the network reliability, admin: the network reliability, admin

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