1. ECE 526 – Network Processing Systems Design Networking: protocols and packet format Chapter 3: D. E. Comer Fall 2008

2. Ning WengECE 5262 Goals Review important protocols and packet formats Understand packet formats in different layers

3. Ning WengECE 5263 Outline Internet reference model Linker layer Network layer Transportation layer

4. Ning WengECE 5264 Internet Reference Model Five layer Internet reference model Multiple protocol can occur at each layer Question: example protocols in each layer?

5. Ning WengECE 5265 Example Network Protocols Linker layer: Ethernet Network layer: IP Transport layer: TCP, UDP We are not interested in physical layer: CSMA …

6. Ning WengECE 5266 Data Link Layer Providing communication between adjacent systems ─ Point-to-point or shared media communication ─ Specification of media access (e.g., CSMA) Three types of communication ─ Unicast: frame destined for single station ─ Multicast: frame destined for a subset of stations ─ Broadcast: frame destined for all stations in broadcast domain Two protocols are important ─ Ethernet ─ ATM We will concentrate on Ethernet

7. Ning WengECE 5267 Ethernet Frame Processing Machine access control address (MAC) ─ Hardware address ─ 48-bit ─ Globally unique ─ Not assigned to computer but Network Interface Card (NIC) 16-bit frame type: indicating the next layer protocol ─ 0800 (IP), 0806 (ARP) Additionally: 64-bit preamble, 32-bit CRC trailer

8. Ning WengECE 5268 Network Layer: Internet Protocol Internet Protocol (IP) functionality ─ Defines basic delivery service throughout the Internet ─ Provides end-to-end connectivity Processing by IP routers Internet packet header:

9. Ning WengECE 5269 IP Datagram Fields Which field changed between hops?

10. Ning WengECE 52610 IP Addressing 32-bit Internet address assigned to each computer Virtual, hardware independent value Prefix identifies network; suffix identifies host ─ Hosts within a subnet have same address prefix ─ Example: ECE 131.230.194.*, SIUC 131.230.* ─ Network address mask to specify boundary between prefix and suffix Who assigns the prefix? ─ Internet Assigned Numbers Authority (IANA) sign it to Regional Internet Registries (RIR) Are IP addresses globally unique? ─ No, network address translator allow private subnets ─ Private subnet address space: 192.168.0.0/16, 172.16.0.0/12 and 10.*

11. Ning WengECE 52611 Addressing Question What is the difference between Ethernet and IP address? ─ Software (reconfigurable) vs. hardware (hard coded) ─ Globally unique or not ─ IP: prefix and suffix Why need another address (IP), if Ethernet address is globally unique? ─ mobility moving the hosts or routers from one network to another ─ easiness to construct a subnet: prefix and suffix

12. Ning WengECE 52612 IP Forwarding Routing Table ─ Found in both hosts and routers ─ Stores destination, mask, next hop Example Routing Table network destinationnetmaskgateway/next hop 131.230.0.0255.255.0 131.230.193.66 131.230.194.0255.255.255.0 131.230.194.66 Default 131.230.195. Route lookup ─ Takes destination address as arguments ─ Finds next hop ─ Uses longest-prefix match

13. Ning WengECE 52613 IP Related Protocols Several other protocols support IP: We’ll cover routing tables with packet processing later

14. Ning WengECE 52614 Transport Layer End-to-end protocols for communication between applications ─ Transport layer is not changed inside the network How are applications identified? ─ Port number used for de-multiplexing Two transport layer protocols ─ UDP (user datagram protocol) ─ TCP (transport control protocol)

15. Ning WengECE 52615 UDP Datagram Format

16. Ning WengECE 52616 Transport Control Protocol UDP shortcomings ─ Unreliable (packet loss) ─ Packet reordering ─ No congestion control ─ No flow control TCP addresses these problems ─ Acknowledgements and retransmission timers ─ Sequence numbers ─ Congestion and flow control windows

17. Ning WengECE 52617 TCP Header Checksum, source and destination ports similar to UDP Sequence and Acknowledgement is byte count (not packet)

18. Ning WengECE 52618 TCP Questions How is a connection between two hosts established? ─ Three-way handshake How is reliability ensured when packet is lost? ─ Packet is not acknowledged, timeout occurs, retransmission. How is congestion control achieved? ─ Congestion window is continually increased to use available bandwidth ─ Congestion window is reduced when packet loss occurs

19. Ning WengECE 52619 Protocol Encapsulation Protocols are encapsulated when sent out Example

20. Ning WengECE 52620 Address Resolution Protocol Used to map IP address of a computer to an Ethernet address Used only within one network ARP header

21. Ning WengECE 52621 Questions Why not one protocol instead of many ones? ─ different applications need a different functionalities ─ different protocols solve different problems ─ easy to debug and design: concentrate one layer only ─ many protocols is connected by common protocol (IP) Any cons for layered structure?

22. Ning WengECE 52622 Summary Protocols standards ─ Defines semantics of computer communication ─ Specify packet formats ─ Addressing, forwarding Internet protocols are divided into fiver conceptual layers ─ Layer 2: ethernet, ARP ─ Layer 3: IP ─ Layer 4: TCP, UDP

23. Ning WengECE 52623 For Next Class Read Comer Chapter 4 ─ Computer Architecture: traditional network processing systems implementation