JAMES F. KUROSE AND KEITH W. ROSS

Transcription

1 JAMES F. KUROSE AND KEITH W. ROSS

2 What is the internet? There is no one definition. Two ways to try to describe it: Nuts and bolts i.e. the basic hardware and software components A networking infrastructure that provides services to distributed applications

3 The Nuts and Bolts Approach The internet is a worldwide computer network? Also includes PDAs, TVs, cell phones, and even toasters These devices are known as Hosts or End Systems

4 End Systems End systems are connected by Communication Links End systems do not directly connect but are indirectly connected through devices known as Packet Switches

5 Diagram showing End Systems, Packet Switches, and Communication Links

6 ISPs and TCP/IP End systems access the internet through Internet Service Providers (ISPs) AOL T mobile AT&T End systems, packet switches, and other pieces of the internet run Protocols that control the sending and receiving of information. Transmission Control Protocol (TCP) and Internet Protocol (IP) are the two most important Protocols on the public internet.

7 Service Description The Internet allows Distributed Applications running on its end systems to exchange data with each other Some distributed applications include: Web surfing IM Audio and video streaming Two services: Connection-orientated Reliable Service Connectionless Unreliable Service "The Web is not a separate network but one of many distributed applications that use the communication services provided by the internet. -Kurose and Ross p.5

8 Protocol A Protocol defines the format and 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

9 Clients and Servers End systems are also called Hosts because they host application programs Two categories: Clients and Servers Client/server is the most prevalent structure for internet applications, including: The Web Remote login

10 Online Toasters

11 Connection-Oriented Service In Connection-Oriented Service, the client program and the server program send control packets to each other before sending data This is called a handshake procedure Reliable Data Transfer an application can rely on the connection to deliver all of its data without error and in the proper order A connection in the Internet consists of nothing more than allocated buffers and state variables in the end systems; the intervening packet switches do not maintain any connection-state information. [emphasis added] p. 12

12 Connection-Oriented Cont. Flow Control - makes sure neither side overwhelms the other side by sending too many packets The Internet uses Congestion-Control to prevent the internet from entering into a state of gridlock Transmission Control Protocol (TCP) is the name of the Internet s connectionoriented service.

13 Connectionless Service No handshake procedure Faster but not as reliable User Datagram Protocol (UDP) is the name of the Internet s connectionless service.

14 Circuit Switching vs. Packet Switching Circuit switching The resources needed along a path to provide communication between end systems are reserved for the duration of the communication session Used by telephones Packet switching The resources are not reserved Used by internet

15 Circuit-Switching Two kind of circuit switching: Frequency division multiplexing (FDM) the frequency spectrum of a link is shared among the connections established across the link Time-division multiplexing (TDM) time is divided into frames, which are divided into slots. Each connection gets its own reserved slot within each frame.

16 FDMs vs. TDMs

17 Packet Switching Packets travel through communication links and packet switches Most packet switches use store-andforward transmission, which means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link

18 Packet Loss Output buffer stores packets that a router is about to send to a particular communication link Queuing delays arriving packet must wait in the output buffer when the link is busy transmitting another packet Packet Loss when the buffer is completely filled, either the arriving packet or one of the queuing packets will sometimes be dropped

19 Datagram Networks Datagram Networks Any network that forwards packets according to host destination The internet is a datagram network Example: Post office Virtual Circuit Networks A virtual connection between a source and a destination host End systems are not needed; destination is identified through VC ID

20 Benefit to Libraries Because the internet is so prevalent it is important to understand how it works (in general but especially for libraries!) Knowledge of various end systems can affect the way we make information accessible Could we print books on toast? (Many possibilities!)