1. Computer Network Overview
Ikjun Yeom

2. What is a computer network?
a collection of computing nodes and links connecting the nodes
why we need it?
to transfer data to others H1 H2 H3
Network 1 (Ethernet)
Network 2 (Ethernet) H7 R3 H8 R1
Network 3 (FDDI) H4 H5 H6

3. 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?
a pre-defined rule for data transfer
examples: IP, TCP, UDP, HTTP, RTP
why do we need it?

5. Network Layering
the current network protocols are implemented based on layering concept
currently, there are five layers:
physical, data-link, network, transport and application
why ?

6. Internet Protocol Graph
FTP
HTTP NV
TFTP
TCP
UDP IP …
NET
NET
NET 1 2 n

7. Physical Layer NIC Network Interface Card Ethernet Card LAN card
Computer B
Computer A
Data
Physical Layer
Wire

8. Physical Layer Computing nodes Links
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

9. Computing 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
Network
adaptor (T
o network)

10. Physical 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 - wireless
no physical “wire”
categorized by transmission range:
wide area links: CDMA and GSM
local area links: Wireless LAN
personal area links: Bluetooth, Zigbee

12. Data Link Layer Computer A Computer B Computer C Data Data DLL

13. Data 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)

14. Network Layer
Data link layer
Router IP

15. Network Layer Routing RIP – Routing Information Protocol
OSPF – Open Shortest Path First

16. IP Packet Format 4 8 16 19 31 V ersion HLen TOS Length Ident Flags4 8 16 19 31 V
ersion
HLen
TOS
Length
Ident
Flags
Offset
TTL
Protocol
Checksum
SourceAddr
DestinationAddr
Pad
Options (variable)
(variable)
Data

17. Transport Layer Computer A Computer B TCP IP IP Data link layer
telnet
netscape
ftp
TCP
Date IP
MAC IP IP
Data link layer
Data link layer

18. Transport 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)

19. UDP Header Format

20. TCP Segment 0 4 10 16 24 31 Source Port Destination Port
Source Port Destination Port
Sequence Number
Acknowledgement Number U A P R S F
Header
Reserved R C S S Y I
Window Size
Length G K H T N N
Checksum Urgent Pointer
Options Padding
Data