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 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) H7R3H8

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 … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n

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

Physical 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

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 (To 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 AComputer BComputer C Data DLLData link layer

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 VersionHLen TOSLength IdentFlagsOffset TTLProtocolChecksum SourceAddr DestinationAddr Options (variable) Pad (variable) Data

17 telnet netscape ftp telnet netscape ftp Computer B Data link layer IP Computer A Data link layer IP TCP Date IP MACIPTC P DateTC P DateTC P Date IP MACIPTC P DateTC P DateTC P Date Transport 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 Typical Limitations of the Network Drop messages Reorder messages Deliver duplicate copies of a given message Limit messages to some finite size Deliver messages after an arbitrarily long delay

20 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

21 UDP Header Format

22 Source Port Destination Port Sequence Number Acknowledgement Number Checksum Urgent Pointer Options Padding U R G A C K P S H R S T S Y N F I N Header Length Reserved Window Size Data TCP Segment