network basics network basics

Network BasicsNetwork Basics

염익준

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What is a computer network?What is a computer network?

• a collection of computing nodes and links connecting the nodes

• why we need it?

– to transfer data to others

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What is the Internet?What is the Internet?

• originally means “Inter-network”• a network of networks

• now means a network using IP (Internet Protocol) for inter-networking

• equivalent to IP networks

• deployed in the whole world

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What is a network protocol?What is a network protocol?

• a pre-defined rule for data transfer

• examples: IP, TCP, UDP, HTTP, RTP

• why do we need it?

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What we learn in this classWhat we learn in this class

• architecture of the current networks

• basic operations of network protocols

• how they are implemented

• several well-known network applications

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Network LayeringNetwork Layering

• the current network protocols are implemented based on layering concept

• currently, there are five layers:

– physical, data-link, network, transport and application

• why ?

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Physical LayerPhysical Layer

Computer A Computer B

NICNetwork Interface CardEthernet CardLAN card

Wire

Physical Layer

Data

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Physical LayerPhysical Layer

• Twisted pair

• Coaxial Cable

• Fiber Optics

• RF

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Physical MediaPhysical Media

• physical link:transmitted data bit propagates across link

• guided media:

– signals propagate in solid media: copper, fiber

• unguided media:

– signals propagate freelye.eg., radio

Twisted Pair (TP)

• two insulated copper wires

– Category 3: traditional phone wires, 10 Mbps ethernet

– Category 5 TP: 100Mbps ethernet

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Physical Media: coax, fiberPhysical Media: coax, fiber

Coaxial cable:

• wire (signal carrier) within a wire (shield)

– baseband: single channel on cable

– broadband: multiple channel on cable

• bidirectional

• common use in 10Mbs Ethernet

Fiber optic cable:

• glass fiber carrying light pulses

• high-speed operation:

– 100Mbps Ethernet

– high-speed point-to-point transmission (e.g., 5 Gps)

• low error rate

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Physical media: radioPhysical media: radio

• signal carried in electromagnetic spectrum

• no physical “wire”• bidirectional

• propagation environment effects:

– reflection

– obstruction by objects

– interference

Radio link types:

• microwave

– e.g. up to 45 Mbps channels

• LAN (e.g., waveLAN)

– 2Mbps, 11Mbps

• wide-area (e.g., cellular)

– e.g. CDPD, 10’s Kbps• satellite

– up to 50Mbps channel (or multiple smaller channels)

– 270 msec end-end delay

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Hardware Building BlocksHardware Building Blocks

• General purpose computers such as PC, workstation, Laptop and PDA connected to a network.

• Either end-hosts or intermediate nodes (switch or router)

CPU

Cache

Memory I/O bus

Networkadaptor (To network)

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Hardware Building Blocks Hardware Building Blocks --

LinksLinks• Implemented on a variety of different physical media, including twisted pair, coaxial cable, optical fiber and space.

• Used to propagate signals.

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Wireless LinksWireless Links

• Global links – PCS, GSM

• Wireless LAN – IEEE 802.11a, b, g

• Piconet – Bluetooth (upto 1 Mbps)

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Data Link LayerData Link Layer

Computer A Computer B Computer C

Data

DataMACData link layer Data link layer

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Data Link LayerData Link Layer

• Unique ID

• Medium Access Control (MAC)

– CSMA/CD (Carrier Sense Multiple Access/Collision Detection)

– CSMA/CA (Collision Avoidance)

– Token Ring

– TDMA (Time Division Multiple Access)

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Network LayerNetwork Layer

Data link layer

Router

IP

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Network LayerNetwork Layer

• Routing

– RIP – Routing Information Protocol

– OSPF – Open Shortest Path First

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IP Packet FormatIP Packet Format

Version HLen TOS Length

Ident Flags Offset

TTL Protocol Checksum

SourceAddr

DestinationAddr

Options (variable) Pad(variable)

0 4 8 16 19 31

Data

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telnet

netscape

ftptelnet

netscape

ftp

Computer B

Data link layerIP

Computer A

Data link layerIPTCP TCP

Date

IP

MAC IPTCP

DateTCP

DateTCP

Date

Date

IP

MAC IPTCP

DateTCP

DateTCP

Date

Transport LayerTransport Layer

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Transport LayerTransport Layer

• End-to-end delivery

• Transmission Control Protocol (TCP)

– Flow control – Advertised Window

– Error control – Checksum

– Reliable delivery – Loss detection and

retransmission

• User Datagram Protocol (UDP)

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Typical Limitations of the Typical Limitations of the

NetworkNetwork• Drop messages

• Reorder messages

• Deliver duplicate copies of a given message

• Limit messages to some finite size

• Deliver messages after an arbitrarily long delay

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UDP (User Datagram Protocol)UDP (User Datagram Protocol)

• Extending the host-to-host deliver service of the underlying network into a process-to-process communication service.

• Port number

– Well-known port number

– Port mapper

• Checksum – pseudoheader

• Used for delay-sensitive applications

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UDP Header FormatUDP Header Format

SrcPort DstPort

Checksum Length

Data

0 16 31

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Source Port Destination Port

Sequence Number

Acknowledgement Number

Checksum Urgent Pointer

Options Padding

0 4 10 16 24 31

URG

ACK

PSH

RST

SYN

FIN

HeaderLength Reserved Window Size

Data

TCP SegmentTCP Segment

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Internet Protocol GraphInternet Protocol Graph

…

FTP HTTP NV TFTP

TCP UDP

IP

NET1 NET2 NETn

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Alternative View of the Alternative View of the

Internet ArchitectureInternet Architecture

TCP UDP

IP

Network

Application