Computer Network Overview Ikjun Yeom

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

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

What is a network protocol? a pre-defined rule for data transfer examples: IP, TCP, UDP, HTTP, RTP why do we need it?

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 ?

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

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

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

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)

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

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

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

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)

Network Layer Data link layer Router IP

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

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

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

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)

UDP Header Format

TCP Segment 0 4 10 16 24 31 Source Port Destination Port 0 4 10 16 24 31 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