TOBB ET Ü ELE46/ELE563 Com munications Networks Lecture 01 May 6, 2014

1. TOBB ETÜELE46/ELE563Communications NetworksLecture 01May 6, 2014 Fall 2011 Tuesday 10:30 – 12:20 (310) Thursday15:30 – 17:20 (372) İsrafil Bahçeci Office: 168 ibahceci@etu.edu.tr

2. Ders Bilgileri - I • Bu derste neler öğreneceğiz? • İnternet olgusu hayatımızın çok önemli bir parçasıdır. Her ne kadar bilgisayar ağı kavramı İnternetten ibaret olmasa da İnternet en önemli ve en yaygın bilgisayar ağlarının başında gelmektedir. Neden? • İnterneti olanaklı kılan teknolojiler ve yapı blokları nelerdir? • Bu yapı taşlarını kullanarak nasıl bir mimari oluşturulmuştur ki böylesi etkin ve yaygın bir iletişim sistemi ortaya çıkmıştır? • Bu sistemin eksikleri var mıdır? Varsa neledir?

3. Ders Bilgileri - II • Kaynak kitap • Computer Networks, Andrew Tanenbaum , 5th Edition, Prentice Hall 2011 • Yarımdcı kitap • Computer Networks: A Systems Approach, 5th Edition, Morgan Kaufmann (an Elsevier Company) by L. L. Peterson and B. S. Davie

4. Ders Bilgileri - III • Notlandırma • Arasınav: %30 • Sonsınav: %60 • Proje (seçmeli): %10

5. Objective of this Lecture • Requirements placed on the network • The idea of network architecture • Key elements in implementation of a network architecture • Key metrics to evaluate the performance of computer networks

6. An Example • URL (Uniform Resource Locator) • HTTP (Hyper Text Transfer Protocol) • Click in your browser “http://www.mkp.com/pd3e” • One click and as many as 17 messages are exchanged • Assuming the web page can be downloaded with a single message • Six messages to translate www.mkp.com into 213.38.165.180 • Three messages to set up TCP between the browser and the server • Four messages for the browser to send the HTTP “get” request and the server to reply with the requested page (+ ACKs) • Four messages to tear down the connection

7. (a) (b) Requirements: Connectivity:Links Nodes Point-to-point Multiple access • Scalability • Link • Node • Indirect connectivity → switching

8. Switched Network • Clouds • Switched network • Circuit switched (telephone system) • Packet switched (computer networks) • Packets, messages • Store-and-forward

9. Interconnection of Networks • internetwork (internet) • Router, gateway • address • routing • Unicasting, broadcasting, multicasting

10. Requirements: Cost-effective resource sharing • Efficient utilization of the links • Multiplexing • Analogy: CPU • TDM • FDM • More efficient multiplexing: statistical multiplexing

11. ■ ■ ■ Multiplexing over a link • How to service packets • FIFO • Round robin • Quality of Service (QoS) • Congestion

12. Support for Common Services • Application processes are communicating • Should each application perform all the complex functionality to communicate ? • Common services, hide complexity (abstraction) • Application level process communicate over logical channels • What functionality should the logical channel provide?

13. Common Communication Patterns • Client/Server • Request/reply channel • (small request message, large reply message) – a digital library • The opposite • Message stream channel – video on demand • Channel abstractions

14. Reliability • Networks can fail • Bit errors • Burst errors • Buffer overload • Software/OS errors • Routing errors • Human errors • Others (power failure)

15. Network Architecture:Example of A Layered Network System • Abstraction • Interface • Hide complexity • Decompose the problem • Monolithic software • Modularity

16. Protocols • Protocols • Service interface • Peer interface

17. Service and Peer Interface

18. Host 1 Host 2 Digital Digital Video Video File File library library application application application application application application Example of A Protocol Graph • RRP: Request Reply Protocol • MSP: Message Stream Protocol • HHP: Host-to-Host Protocol

19. Protocols • Protocol specification • Pseudo code • State transition diagram • Packet formats • Interoperability • Independent implementation • Standardization bodies • IETF (Internet Engineering Task Force) • ISO (International Standards Organization) • IEEE (Institute of Electrical & Electronics Engineers)

20. Host Host Application Application Application Application program program program program Data Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data Encapsulation • Header • Trailer • Body • Demultiplexing

21. OSI Reference Model • OSI (Open System Interconnection) • Reference model

22. Client-server model

23. REQUEST and REPLY

24. Applications • Business: Web, VoIP, e-commerce • Home: Connectivity, instant messaging, social network, wiki • Mobility

25. Peer-2-peer model

26. Network Scale and Hardware • Broadcast vs. Point-2-Point (unicast) • Scale of network Bluetooth, medical devices, RFID Enterprise, home, AP, wireless router, 802.11 (WiFi), 802.3 (Ethernet), Virtual LANs City coverage, cable TV + internet, Wireless MAN (802.16 WiMax) Large geographical area, country, continent

27. Network Scale and Hardware PAN LAN WAN MAN

28. Network Scale and Hardware WAN-ISP WAN-VPN • Transmission lines • Routers inter-communication: Routing, forwarding algorithms • Wireless WANs • Satellite • Cellular network

29. Network of Networks • ISP (Internet service provder) networks to connect many different types of networks • Subnet: collection of routers and communication lines • Hosts: connected to subnet • Gateway: interconnects different netwroks • Hardware and software translator

30. Network Software • Protocol: agreement between communicating parties • Protocol stack: Efficient simplified implementation by layers • Services to higher layers, similar to virtual machine

31. 5-layer protocol stack Physical communication Virtual communication • Clear, modular interface design, • Well-defined functions

32. Network Architecture • Set of protocol layers • Protocol stack: list of protocols used by a certain system

33. Network Architecture 2

34. Layer Design • Software design for higher levels, hardware/firmware design for lower layers • Design issues • Error detection, error correction • Path selection, routing • Network evolution: protocol layering • Packet aggregation/de-aggregation, addressing, ordering • Scalability • Resource allocation, scheduling, statistical multiplexing • Flow control, congestion control • Quality of service • Confidentiality, authentication

35. Connection Type • Connection-oriented service: circuit switch • Connectionless service: packet switch

36. Service vs. Protocol • Service: a set of operations that a layer provides to the layer above it • Protocol: set of rules for the formatting, packetization, message bit generation • Object operations vs. implementation

37. Network Architecture Examples • Open System Interconnection (OSI) • Generic model, although protocol layers are not directly used • TCP/IP • Not a generic model, but widely implemented protocol layers

38. Reference Model 1: OSI • Open Systems Interconnection (OSI) reference model • ISO (revised in 1995) • Principles • New layer for a different abstraction • Well-defined functionality • Internationally standardized protocols • Minimize information flow across interface • Distinct functions per layer

39. PHY:Raw bits over the air, cable, fiber • Data Link: Free of error transmission, ACK/NACK, • MAC: medium access control • Network: Routing, QoS, heterogonous network • Transport: Packets to arrive in order, independent of hardware or device, service type (e.g. error free connection, or unguaranteed connection) • True end-to-end layer • Session: Dialog control high-level communication sync • Presetation: Syntax and semantics

40. Reference Model 2: TCP/IP