computer network overview ikjun yeom. 2 what is a computer network? a collection of computing nodes...
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Computer Network OverviewComputer Network Overview
Ikjun Yeom
2
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
R1
H4
H5
H3H2H1
Network 2 (Ethernet)
Network 1 (Ethernet)
H6
Network 3 (FDDI)
H7 R3 H8
3
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
4
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?
5
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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Internet Protocol GraphInternet Protocol Graph
…
FTP HTTP NV TFTP
TCP UDP
IP
NET1 NET2 NETn
7
Physical LayerPhysical Layer
Computer A Computer B
NICNetwork Interface CardEthernet CardLAN card
Wire
Physical Layer
Data
Physical LayerPhysical Layer
• Computing nodes– PC, PDA, Cellular phone, and embedded
systems– create packets, send and receive them.
• Links– physical medium to propagate data (packets)
from a node to the other– wired or wireless
8
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Computing NodesComputing Nodes
• 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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Physical Media - WiredPhysical Media - Wired
Twisted Pair (TP)• two insulated copper
wires– Category 3: traditional
phone wires, 10 Mbps ethernet
– Category 5 TP: 100Mbps 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
11
Physical media - wirelessPhysical media - wireless
• no physical “wire”• categorized by transmission range:
– wide area links: CDMA and GSM– local area links: Wireless LAN– personal area links: Bluetooth, Zigbee
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Data Link LayerData Link Layer
Computer A Computer B Computer C
Data
DataDLLData link layer Data link layer
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Data Link LayerData Link Layer
• Framing• 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
22
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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