1. CIS.IUPUI (from Leon-garcia)1 What is a protocol? A set of rules that governs how two parties are to interact. The purpose of a protocol is to provide a server to its users. Protocols stack/layers See a protocol example protocol Horizontal protocol Service to its user Vertical

2. CIS.IUPUI (from Leon-garcia)2 Computer networks & packet switching Internet Protocol (IP) provides a means of transferring information across multiple heterogeneous networks A message may divide into multiple packets, each of which may be transferred independently, therefore, packet switching Typical computer networks: terminal-oriented networks, computer-to-computer networks, the ARPANET, Ethernet local area networks, the Internet. (i.e., the evolution of computer networks)

3. CIS.IUPUI (from Leon-garcia)3 (a) Time-Shared Computers & Cables for Input Devices (b) Dial In C...... TT C...... T T T Modem Pool PSTN Modem T T = terminal Figure 1.12 Terminal-oriented networks Allow expensive host computers shared by a number of terminals What is the problem of this system?

4. CIS.IUPUI (from Leon-garcia)4 C TTTT Response from terminal Poll to terminal Figure 1.13 Terminal-oriented networks --Transmissions from terminals very bursty, so dedicated lines inefficient --Polling protocols for controlling the sharing of a transmission line were developed (Line sharing techniques)

5. CIS.IUPUI (from Leon-garcia)5 T T Host...... T Address Info Mux Figure 1.14 Terminal-oriented networks (Statistical Multiplexing Techniques) Statistical multiplexers developed to allow the sharing of a transmission line Messages from a terminal encapsulated in a frame that has a header that contains the terminal address A message must wait for line (buffer) to become available (FIFO) Framing technique to delineate the beginning and end of each message Error control techniques and check bits

6. CIS.IUPUI (from Leon-garcia)6 T T...... T.................. New York City San Francisco Chicago Atlanta Host Figure 1.15 Typical terminal-oriented networks High-speed lines Low-speed lines Tree- topology network connecting terminals to centralized shared computers, routing and forwarding is straightforward. What is the limitation of this kind of networks? Not flexible: could not handle proliferation of computers & applications

7. CIS.IUPUI (from Leon-garcia)7 Computer-to-Computer Networks The proliferation of computers led to a need to develop networks to interconnect computers Fundamentally different than connecting terminals to computers, because now both parties are intelligent Interactive applications require quick response – Implying that messages cannot be too long, because this will cause long delays Solution: Packet switching – variable-length messages (up to some maximum allowed) – longer messages are broken into several packets – connectionless transfer vs. connection-oriented transfer, i.e., IP datagram vs. ATM VC.

8. CIS.IUPUI (from Leon-garcia)8 UCLARANDTINKER USC NBS UCSB HARV SCD BBN STAN AMES McCLELLAN UTAHBOULDERGWCCASE CARN MITRE ETAC MIT ILL LINC RADC Figure 1.16 The ARPANET developed in 1960s by U.S. DoD Testbed for wide-area network packet switching research Interconnection of computers using a mesh networks There exist multiple paths between any pair of hosts Packet switches route packets from source to destination

9. CIS.IUPUI (from Leon-garcia)9 ARPANET Packet Switching Innovations Flexible interconnection of computers Connectionless transfer of packets Distributed synthesis of routes Adaptation to failures and traffic variations Layered architecture Investigation of complex network dynamics

10. CIS.IUPUI (from Leon-garcia)10 Figure 1.17 (a) (b) transceivers Bus topology Star topology Local Area Networks (LAN) Development of workstations led to LANs to allow sharing of resources (file servers, printers,...) LAN different than WAN – bandwidth is cheap, transmission relatively error-free – use broadcast packet transmissions, flat address space -- Frame structure to delineate individual transmission -- Media access control (MAC) to coordinate Star is better than bus in two ways: 1. twisted-pair is cheaper than coaxial wire. 2. fault tolerant.

11. CIS.IUPUI (from Leon-garcia)11 Internetworking (Internet) Different protocols were developed to transmit packets across different types of networks – packet switch networks, radio networks, satellite networks Problem: How to exchange information between computers attached to any of these networks? Internet Protocol (IP): creating a network of networks

12. CIS.IUPUI (from Leon-garcia)12 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway G Figure 1.18 Gateways provide interconnection across networks IP packets sent from gateway to gateway An internetwork H H H H

13. CIS.IUPUI (from Leon-garcia)13 Definition of the Internet “Internet”, the global information system that: is logically linked together by a globally unique address space based on the Internet Protocol (IP) –or its subsequent extensions/ follow-ons; is able to support communications using the TCP/ IP suite –or its subsequent extensions/follow-ons, or other IP-compatible protocols provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein

14. CIS.IUPUI (from Leon-garcia)14 Internet Innovations Keep gateways simple, put complexity at the edge Best-effort transfer of IP datagrams: –try best to deliver packets but no guarantee Route IP packets according to destination address Domain Name System –to map: host names  IP addresses – (people-friendly) (machine-friendly) Transmission Control Protocol (TCP) –to provide reliable connections over unreliable datagram transfer Any application that can run over TCP/ IP –Can immediately run over the entire Internet

15. CIS.IUPUI (from Leon-garcia)15 Discussion on switching approaches Telephone network Real-time voice Connection-oriented Resources allocated once set up and guaranteed All messages along the same route (circuit) Reliable Fast transfer Internet (IP) Good for various applications Connectionless No set up, no latency Each packet routed independently Robust around failure point No state information in routers, burden put on edge computers

16. CIS.IUPUI (from Leon-garcia)16 Discussion on switching approaches (cont.) Telephone network Not for other data transfer Latency at the beginning Poor utilization of bandwidth New set up when failure State information in switches Internet TCP not good for real-time applications Extra address overhead in each packet Overhead on routing for each packet Packets may lost, delay, out of order

17. CIS.IUPUI (from Leon-garcia)17 Technology Regulation Market Standards Figure 1.19 Key factors determining success of a new service Will it inter-operate? Can it be built? Will it sell? Is it allowed?