1. Network Architecture IS250 Spring 2010 John Chuang chuang@ischool.berkeley.edu

2. John Chuang IS250 UC Berkeley2 Network Abstracted as Cloud  Network utility: ping client server Network

3. John Chuang IS250 UC Berkeley3 Network as Routers & Links Hosts Links or local networks A DE B C 1 2 5 4 3 6 Routers Network utility: traceroute/tracert Source: Coulouris, Dollimore and Kindberg

4. John Chuang IS250 UC Berkeley4 Local Exchange Carrier (LEC) Router Dial-Up ISP Backbone Provider 1 Router Client Tandem Switch Inter-exchange Carrier (IXC) Long- Distance Network Corporate LAN Firewall Analog Modem Content Provider Server Router Remote ISP Point of Presence xDSL Modem Cable Modem Packet Network Headend Cable Network Local Loop DNS Local Ingress Switch Exchange Point Router Internet Service ProvidersCustomer Premises Internet backbonesTelephone Network Local Egress Switch Backbone Provider 2 router Terminal Wireless ISP Interconnected Networks

5. John Chuang IS250 UC Berkeley5 A 2x2 Network Model EdgeCore Logical/ Service Internet Service Providers (ISPs) Internet Backbone Operators PhysicalLast-mile access networks Wide-area transit networks

6. John Chuang IS250 UC Berkeley6 Network Building Blocks  Transmission media -Copper (coax, twisted pair), optical fiber, free space (wireless)  Signals -Electrical currents, light, RF (radio-frequency), microwave  Hardware devices -End hosts, network interfaces -Routers, switches, hubs, bridges, repeaters  Software components -Communication protocol stack

7. John Chuang IS250 UC Berkeley7 Network Architecture  Networking can be quite complex and requires a high degree of cooperation between the involved parties.  Cooperation is achieved by forcing parties to adhere to a set of rules and conventions (protocol).  The complexity of the communication task is reduced by using multiple protocol layers: -Each layer is implemented independently. -Each layer is responsible for a specific subtask. -Layers are grouped in a hierarchy.  A structured set of protocols is called a network architecture, protocol architecture, or protocol suite.

8. John Chuang IS250 UC Berkeley8 Layering  Layering: a technique of organizing a network system into logically distinct entities such that the service provided by one entity is based on the service provided by a lower level entity  Service: what a layer does  Interface: how to access the service  Protocol: how the service is implemented -Set of rules and formats governing communication between two peers

9. John Chuang IS250 UC Berkeley9 What each layer does  Application (layer 7): specific to application need  Presentation (layer 6): conversion of data representation  Session (layer 5): access mgt, synchronization  Transport (layer 4): end-to-end delivery, congestion and flow control  Network (layer 3): addressing, routing  Data Link (layer 2): framing, error detection  Physical (layer 1): bits (0/1), voltages, frequencies, wires, pins, … Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer Layer 1 Layer 2 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 ISO/OSI Reference Model

10. John Chuang IS250 UC Berkeley10 Layered Protocol Architecture Application layer Transport layer Network layer Link layer TCP/IP Model Physical layer Layer 1 Layer 2 Layer 7 Layer 4 Layer 3 Software Operating System Hardware Application layer Presentation layer Session layer Transport layer Network layer Data link layer Physical layer Layer 1 Layer 2 Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 ISO/OSI Reference Model Socket API

11. John Chuang IS250 UC Berkeley11 Example: The “IP Hourglass” A single protocol

12. John Chuang IS250 UC Berkeley12 Why Layers?  Modularity -Divide and conquer: easier to design -Mix and match -Single network supports heterogeneous applications over heterogeneous networks -e.g., Voice-over-IP, IP-over-fiber, IP-over-wireless  Abstraction -Changes isolated -A layer can be changed without affecting upper/lower layers  Disadvantages of layering?

13. John Chuang IS250 UC Berkeley13 TCP/IP Model Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 end-to-end point-to-point end-to-end

14. John Chuang IS250 UC Berkeley14 TCP/IP Model Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 end-to-end point-to-point end-to-end

15. John Chuang IS250 UC Berkeley15 TCP/IP Model Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 end-to-end point-to-point end-to-end

16. John Chuang IS250 UC Berkeley16 Message Flow Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2

17. John Chuang IS250 UC Berkeley17 Encapsulation Example: Sending HTTP message using TCP/IP over Ethernet HTTP message TCP header IP header Ethernet header Ethernet frame port TCP IP IP datagram/packet TCP segment HTTP message Adapted from Coulouris, Dollimore and Kindberg

18. John Chuang IS250 UC Berkeley18 Encapsulation Appl Trans port Net work Link Net work Link Net work Link Appl Trans port Net work Link Host AHost BRouter 1Router 2 Data

19. John Chuang IS250 UC Berkeley19 Summary  Networking is a complex problem: geographic distribution; diverse ownership; heterogeneous technologies and applications  Abstraction helps in the analysis and design of networks  Layered architecture supports abstraction and modularity -Encapsulation: clear separation of layer-specific functionalities; isolation between layers -Hourglass: a single network layer protocol connects multiple networks; supports different applications over different underlying network technologies