What is the Internet A worldwide computer network

What is the Internet? • • A world-wide computer network hosts or end systems network application program protocol communication link router packet switching

Service Description • The Internet allows distributed applications running on its end-systems to exchange data with each other • The Internet provides two services to its distributed applications: a connection-oriented service and a connectionless service. • Currently the Internet does not provide a service that makes promises about how long it will take to deliver the data from sender to receiver.

Soom Good Hyperlinks • • Internet Engineering Task Force (IETF): The World Wide Web Consortium (W 3 C): The Association for Computing Machinery (ACM) the Institute of Electrical and Electronics Engineers (IEEE): • Connected: An Internet Encyclopedia: • Media History Project:

What is a Protocol? • A Human Ananlogy : Fig 1. 2 • Network Protocols – a protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event

The Network Edge • End Systems, Clients and Servers • Figure 1. 3 • Connectionless and. Connection-Oriented Service – Connection-Oriented Services • • reliable data transfer Flow control congestion control TCP • Connectionless Service • UDP

The Network Core • Figure 1. 4 circuit switching • packet switching • Message Switching

Routing in Data Networks • Classes of packet-switched networks – datagram networks and virtual circuit networks – route according to host dest addr or to vc number – datagram net : Internet – vc network : X. 25, frame relay and ATM • VC network – a path – vc numbers, one # for each link along the path – entries in VC number translation table in each packet switch

• Why vc numbers are changed? – The length of the vc field is reduced – a network management function is simplified • Datagram network – ananlogous to postal services – do not maintain connection-state information in the switches

Access Networks and Physical Media • Access network - the physical link(s) that connect an end system to its edge router – residential access network – institutional – mobile • Residential access networks – use of a modem over POTS – twisted-pair phone line

– Narrowband ISDN • all digital transmission of data – ADSL and HFC • adsl uses frequency division multiplexing – a hig-speed downstream channel, 50 k. Hz-1 MHz – a medium-speed upstream channel, 4 k. Hz to 50 k. Hz – an ordinary POTS two-way telephone channel, 0 to 4 k. Hz • data rate : a function of the distance between the home modem and the ISP modem • HFC : extensions of the cable network – cable modem, 10 -Base T Ethernet port – the rates are shared among the homes

• Company access network – Lan is used to connect an end system to an edge router – twisted-apir copper wire or coxial cable – shared Ethernet and switched Ethernet • Mobile access networks – use radio spectrum to connect a mobile end system to a base station – cellular digital packet data

Physical Media • Guided media and unguided media • twisted pair copper wire – UTP : category 3 and 5 • coaxial cable : baseband broadband • fiber optics • terrestrial and satellite radio channels

Delay and Loss in Packet-Switched Networks • What can happen to a packet as it travels • suffers from several different types of delays at each node along the path • nodal processing delay, queing delay, transmission delay, propagation delay

Types of Delay • Processing delay : The time required to examine the packet’s header and determine where to direct the packet – the time needed to check for bit-level errors in the packet • Queuing delay : the time to wait to be trasmitted onto the link

• Transmission delay : the amount of time required to transmit all of the packet’s bits into the link • Propagation delay : the time required to propagate from the beginning of the link to the next router • traffic intensity : La/R – L : number of bits of packet – a : average rate at which packets arrive to the queue – R : transmission rate

• Packet loss : with no place to store packets, a router will drop that packet, lost.

Protocol layers and their service models • Layered architecture : protocol stack • see fig 1. 23 • layer functions : error control, flow control segmentation and reassembly, multiplexing connection setup

The Internet Protocol Stack • See fig 1. 24 : 5 layers • application layer : responsible for supporting network applications : http, smtp, ftp 등 • transport layer : responsible for transporting application-layer messages between the client and server sides of an application – TCP, UDP

• Network layer : responsible for routing datagrams from one host to another – a protocol that defines the fields in the IP datagrams as well as how the end systems and routers act on these field : IP protocol – routing protocols that determine the routes that datagrams take between sources and destinations : many routing protocols : RIP, OSPF, IDRP 등

• Link layer : responsible for moving a packet from one node to the next node in the route – ethernet, ppp, atm, frame relay • Physical layer : responsible for moving the individual bits within the frame from one node to the next

Network Entities and Layers • End systes and packet switches : network entities • two types of packet switches : routers and bridges • see fig 1. 25

Internet Backbones, NAPs and ISPs • Internet topology : complex, hierarchical • NBP : internet. MCI, Sprint. Link, PSINet, Uunet 등 - 1. 5 Mbps --- 622 Mbps and higher • each NBP : has hubs, regional ISP tap into it • NAP : NBP interconnect • local ISP -- regional ISP • new tiers and branches can be added to the Internet topology like Lego construction

A Brief History of Computer Networking and the Internet • Development and demonstration of early packet switching principles : 1961 -1972 – computer 등장 - time shared computers – need to share among geographically distibuted users – traffice was likely to be “bursty” – Kleinrock, Baran, Davies 등이 Packet switching 연구 – Robers : Advanced Research Projects Agency net – 4 nodes ; Interface Message Processor : switching – NCP : host-to-host protocol – e-mail : Ray Tomlinson at BBN in 1972

Internetworking and new and proprietary networks : 1972 -1980 • Additional packet-switching nework : – ALOHAnet, a satelliet network – Telenet : a BBN commercial net – Tymnet – Transpac : a French packet-switching net • Robert Metcalfe : 1973 Ethernet 연구 • Vinton Cerf and Robert Kahn : create a network of networks : open net architecture

• Open Network Architecture – Minimalism, autonomy – best effort service – stateless routers – decentralized control • proprietary network architectures : – DEC : DECnet 1975 – Xerox : XNS architecture – IBM : SNA architecture

A Proliferation of Networks : 1980 -1990 • • • Time of tremendous growth BITnet, CSNET 1986, NSFNET 1983 NCP ---> TCP/IP France : Minitel : based on X. 25 VC

Commercialization and the Web : The 1990 s • Continued evolution and the soon-to-arrive commercialization of the Internet • NSFnet : serve as a backbone network • Release of the WWW : CERN Time Berners -Lee : 1989 -1991 – based on hypertext concept from Bush(1940 s) and Ted Nelson(1960 s) • Marc Andreesen : Mosaic : Netscape Comm

Asynchronous Transfer Mode Networks • Goals of ATM : to transport real-time audio and video as well as text, e-mail, and image files. • ATM Forum and ITU : for BISDN • ATM standards – call for packet switching with virtual circuits – define how applications directly interface with ATM

• Deployed within telephone net and Intenet backbone • unsuccessful in extending itself all the way to PCs and W/S area • ATM이 성공하지 못할 것이라는 의견 – TCP/IP protocol suite was integrated into all of the popular operating systems – Companies began to transact commerce over the Internet – Residential Intenet access became very inexpensive – many wonderful application were developed for TCP/IP networks – low-cost high-speed LAN tech developed

Principle Characteristics of ATM • ATM standards defines protocols from transport layer to physical layer • uses packet switching with fixed-length packets of 53 bytes : cells – each cell : 5 bytes of header, 48 bytes of payload • uses VC : virtual channels – VCI : in the header • provides no retransmissions on a link-by-link basis • provides congestion control on an end-to-end basis • can run over just about any physical layer

Overview of the ATM Layers • Protocol stack – ATM adaptation layer(AAL) – ATM layer – ATM physical layer • ATM physical layer : deals with voltages, bit timings, and framing on the physical dedium • ATM layer : the core of the ATM standard, defines the structure of the ATM cell • AAL : roughly analogous to the transport layer in the Internet Protocol stack : support many different types of services – AAL 5 : allows tcp/ip to interface with atm