ECE 526 Network Processing Systems Design Networking protocols

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

Goals • Review important protocols and packet formats • Understand packet formats in different layers Ning Weng ECE 526 2

Outline • • Internet reference model Linker layer Network layer Transportation layer Ning Weng ECE 526 3

Internet Reference Model • Five layer Internet reference model • Multiple protocol can occur at each layer • Question: example protocols in each layer? Ning Weng ECE 526 4

Example Network Protocols • • Ning Weng Linker layer: Ethernet Network layer: IP Transport layer: TCP, UDP We are not interested in physical layer: CSMA … ECE 526 5

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 Ning Weng ECE 526 6

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 Ning Weng ECE 526 7

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: Ning Weng ECE 526 8

IP Datagram Fields • Which field changed between hops? Ning Weng ECE 526 9

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. * Ning Weng ECE 526 10

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 Ning Weng ECE 526 11

IP Forwarding • Routing Table ─ Found in both hosts and routers ─ Stores destination, mask, next hop • Example Routing Table network destination 131. 230. 0. 0 131. 230. 194. 0 Default netmask gateway/next hop 255. 0 131. 230. 193. 66 255. 0 131. 230. 194. 66 131. 230. 195. • Route lookup ─ Takes destination address as arguments ─ Finds next hop ─ Uses longest-prefix match Ning Weng ECE 526 12

IP Related Protocols • Several other protocols support IP: • We’ll cover routing tables with packet processing later Ning Weng ECE 526 13

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) Ning Weng ECE 526 14

UDP Datagram Format Ning Weng ECE 526 15

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 Ning Weng ECE 526 16

TCP Header • Checksum, source and destination ports similar to UDP • Sequence and Acknowledgement is byte count (not packet) Ning Weng ECE 526 17

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 Ning Weng ECE 526 18

Protocol Encapsulation • Protocols are encapsulated when sent out • Example Ning Weng ECE 526 19

Address Resolution Protocol • Used to map IP address of a computer to an Ethernet address • Used only within one network • ARP header Ning Weng ECE 526 20

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? Ning Weng ECE 526 21

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 Ning Weng ECE 526 22

For Next Class • Read Comer Chapter 4 ─ Computer Architecture: traditional network processing systems implementation Ning Weng ECE 526 23