ENEE 426: Introduction

1. ENEE 426: Introduction Richard J. La Spring 2005

2. What is a Communication Network? • Communication network – a set of interconnected resources that support information transfer between geographically distributed users • Main function or service is “transfer of information” over shared communication resources • Examples • Telegraph networks (message) • Telephone networks (voice) • Computer networks (data)

3. History of Communication Networks – Telegraph 1. Telegraph network – transmission of text messages over long distances • 1837 Samuel B. Morse demonstrated a practical telegraph that provided the basis for telegram service (most successful version) • Morse code – long and short pulses e.g. A = , B = • Precursor of modern digital communication system • Led to development of codes (and information theory)

4. History of Communication Networks - Telegraph 1. Telegraph network (cont’d) • Routing of a message • Message or telegram arrives at a telegraph station • An operator makes a “routing” decision based on the destination “address” telegraph station telegraph station telegraph station Store-and- forward Message Switching

5. History of Communication Networks - Telephone 2. Telephone network • Telephone developed in 1876 by Alexander Graham Bell • Used analog transmission system • Requires setting up a connection before transfer of information can take place (called “circuit switching”) • “connection-oriented” • Reservation of resources • Dedicated end-to-end connection • Routing decision made when the path is set up

6. History of Communication Networks - Telephone 2. Telephone network (cont’d) • With transition to digital transmission and wide-spread user of computers for control, a separate “signaling network” is introduced • Enables new services • e.g., 800 number services, call forwarding, voicemail, etc.

7. History of Communication Networks – Computer Network 3. Evolution from telephone networks to data networks to the Internet • 1960s – expensive mainframes were time shared by many users • Tree-topology terminal-oriented networks • With emergence of more intelligent personal computers, dumb terminals were replaced by intelligent terminals and it became necessary to develop networks more flexible connecting many computers • More complex protocols and network topology

8. History of Communication Networks – Computer Network 3. ARPANET • Wanted to develop a resilient and robust communication network that can tolerate link/node failures (courtesy of Cold War!) • Kleinrock advocates the use of “packet-switching” over “circuit-switching” for reliability and efficiency (1961) • Leads to ARPANET project (1969) • Beginning of the Internet UTAH SRI UCSB UCLA – first Interface Message Processor (IMP)

9. History of Communication Networks – Computer Network 3. ARPANET (cont’d) Host Host-host protocol Host-IMP protocol Source IMP to destination IMP protocol Subnet IMP-IMP protocol IMP

10. History of Communication Networks – Computer Network 3. NSFNET (1986) • Created to provide access to NSF-sponsored supercomputing centers • Serve as a primary backbone linking together regional networks • Used to connect regional networks • Restriction on commercial use lifted in 1991 • Privatized and decommissioned in 1995 • Private service providers provide backbone service

11. History of Communication Networks – Computer Network Local ISP Regional ISP NSP B Private Peering NAP NAP NSP A Regional ISP Local ISP

12. History of Communication Networks – Computer Network • Current Internet • Hierarchical structure • End systems connected to local Internet service providers (ISPs) through access networks • e.g. local area network within a company or university, a dial telephone line with a modem, or a high-speed cable-based or phone-based access network • Local ISPs in turn connected to regional ISPs • Regional ISPs connected to national service providers (NSPs) • Can directly connect to network access points (NAPs) as well

13. History of Communication Networks – Computer Network • National Service Providers (NSPs) • Form independent backbone networks that span North American (and extend abroad as well) • internetMCI, SprintLink, etc. • Links ranging from 1.5 Mbps to tera bps • Provides hubs that interconnect its links and at which regional ISPs can tap into the NSP • NSPs interconnected at switching centers, called network access points (NAPs) • Many NAPs run by regional Bell operating companies (RBOCs)

14. Message switching, packet switching, & circuit-switching • Circuit-switched network • Resources needed along a path (buffers, link bandwidth) to provide for communication between the end systems reserved for the duration of the system at the set-up phase • E.g. telephone network • Message or packet-switched network • Resources not reserved • Messages or packets use the resource on demand • May need to wait due to lack of reservation • Queueing delay • E.g. telegraph network, computer networks

15. Telephone network 10 Regional Offices (fully connected) Sectional Offices Primary Offices Toll Offices End Offices

16. Resource Reserved on all links Telephone network

17. Message-switch vs. packet-switching • In packet-switching • Message may need to be segmented into smaller “packets” and reassembled at the edge nodes • Advantages: • Smaller end-to-end delay • Smaller probability of packet error • Disadvantage: • Larger overhead – source address, destination address, etc. need to padded to the packets

18. Message-switch vs. packet-switching 7.5 Mbits long message 1.5 Mbps 1.5 Mbps 1.5 Mbps 0 5 10 15

19. Message-switch vs. packet-switching 7.5 Mbits long message -> segmented into 5,000 1.5 kbits packets 1.5 Mbps 1.5 Mbps 1.5 Mbps 0 5 5.0002

20. Connection-oriented vs. Connectionless • Connection-oriented • Telephone network • A “circuit” must be established before a conversation can start • Connection-oriented data connection (TCP) • Three-way handshake • Connectionless • Connectionless data connection (UDP) • No set-up phase • Telegraph network