E-Commerce. Infrastructure I: Computer Networks

Transcription

1 E-Commerce Infrastructure I: Computer Networks Almost all computers today are networked or part of a distributed system. I will provide an overview of networking and a basic description of network technology. Oct 8, Outline Technical foundations of E- commerce Distributed systems and Local area networks (LANs) Routing and addressing packets Intranets and extranets Connectivity Oct 8,

2 Learning outcomes Be able to: discuss about the Internet infrastructure explain the benefits of distributed systems and LANs distinguish between peer-to-peer and client server networks explain the concept and purpose of protocols explain what is meant by the Internet Oct 8, Technical Foundations of e- commerce-1/3 Computer networks and the Internet form the basic technology structure for electronic commerce. Computer Networks: LAN, WAN Internet includes: The hardware that connects the computers together and the hardware that connects the networks together Computing devices (clients and servers) running operating systems, database managers, web servers, application servers, encryption software, security software, multimedia creation and viewing software, and the graphical user interface Protocols Rapid change in these technologies requires businesses to be flexible. Oct 8,

3 Technical Foundations of e- commerce-2/3 The Internet: largest network in the world! enables sharing of resources/communication e.g. electronic mail, world wide web (WWW) local networks connected through gateways three levels backbone mid-level (regional) networks stub network Oct 8, Technical Foundations of e- commerce-3/3 The Internet: a distributed system system of computers autonomous heterogeneous interconnected by communication links......for exchange of information not: tightly coupled computers sharing central memory loosely coupled systems with little interaction Oct 8,

4 Distributed Systems and LANs- 1/10 Advantages of distributed systems reduced costs share expensive resources (h/w and s/w) e.g. printers, databases integrity can continue to function if failure occurs in the hardware or software Communication System sending and receiving messages detection and correction of errors message routing Oct 8, Distributed Systems and LANs- 2/10 networks can be classified into 2 categories Broadcast all stations connected to common transmission medium message transmitted by one station will reach all other stations Store and Forward message stored in a buffer of intermediate station before transmission to its destination Oct 8,

5 Distributed Systems and LANs- 3/10 N1 N6 N2 N5 disadvantages N stations: N(N-1)/2 links, (N-1) interfaces expensive broadcast messages have to be sent on (N-1) links N3 N4 Fully connected network each station connected by dedicated point-to-point link to every other station advantages parallel connections high throughput no intermediate nodes low density simpler communication software if redundant links used higher reliability Oct 8, Distributed Systems and LANs- 4/10 N1 N6 N2 N5 N3 N4 Partial network (mesh) it has point-to-point links between some, but not all, stations store and forward is therefore required between some stations it is required to connect each station to at least two others, just in case one link fails network delays can be high in a large network Oct 8,

6 Distributed Systems and LANs- 5/10 N1 N6 N2 N5 disadvantages poor reliability S N3 N4 Star all stations connected by single link to a central switching node advantages low expansion cost simple switching system small network delay a failure in a link isolates a station failure of the central switch stops all communication all communication via one switch: low throughput Oct 8, Distributed Systems and LANs- 6/10 Tree / Hierarchical variation of the star topology structure reflects the organisation of system R N1 N2 N3 N4 N5 N6 Oct 8,

7 Distributed Systems and LANs- 7/10 N1 N2 N3 N4 N5 disadvantages only one station can transmit at a time communication fails if the link is cut difficult to trace point of communication failure the overall length < 2 km unless repeaters used Serial Bus / Highway single transmission medium interconnects all stations advantages minimises interconnection costs no routing required communication software simple Oct 8, Distributed Systems and LANs- 8/10 LAN based on broadcast methods interconnect distributed, co-operative computer systems operated by a single organisation within a small geographical area (~1km radius) WAN based on store and forward methods interconnect autonomous computer systems operated by different types of organisations spread over large distances Oct 8,

8 Distributed Systems and LANs- 9/10 Services on networks Peer-to-peer: each PC is equal in importance; there are no special servers, although not all of the machine necessarily provide the same services. -PCs collaborate to share each other resources -Low cost and simplicity -Difficult to manage as services are spread all over the place -Program crash or switching off makes service unavailable Oct 8, Distributed Systems and LANs- 10/10 Services on networks Client-server: there is a dedicated computer, called server, that provides one or more of the important services and the users access whichever service the require. -Dedicated servers for data storage (file servers) -Dedicated servers for printing (print servers) -Gateways to exterior WANs -Much less risk of failure -Facilitate maintenance and file backup Oct 8,

9 Packets, Routing and Addressing -1/9 Four key rules have contributed to the success of the Internet. Independent networks should not require any internal changes to be connected to the network. Packets that do not arrive at their destinations must be retransmitted from their source network. Router computers act as receive-and-forward devices; they do not retain information about the packets that they handle. No global control exists over the network. Oct 8, Packets, Routing and Addressing -2/9 The Internet uses packet switching: Files are broken down into packets that are labeled with their origin, sequence, and destination addresses. This fact has very important consequences for both the performance and the security of e-commerce systems Oct 8,

10 Packets, Routing and Addressing -3/9 The programs on routers use routing algorithms that call upon their routing tables to determine the best path to send each packet. When packets leave a network to travel on the Internet, they are translated into a standard format by the router. These routers and the telecommunication lines connecting them are referred to as the Internet backbone. Between seller and customer there are several other actors who have a role to play Oct 8, Packets, Routing and Addressing -4/9 Oct 8,

11 Packets, Routing and Addressing -5/9 Protocols common language rules governing data exchange between two communicating entities layers in a station from station to station or network to network 3 key elements to consider syntax semantics timing Oct 8, Packets, Routing and Addressing -6/9 syntax includes data format signal levels semantics includes control information e.g. coordination and error handling timing includes speed matching sequencing Oct 8,

12 Packets, Routing and Addressing -7/9 TCP/IP protocol of internet Transmission Control Protocol / Internet Protocol simple and effective most types of network but does not include many security features OSI Reference Model Application Presentation Session Transport Network Data link Physical TCP, Transport Control Protocol IP, the Internet Protocol Logical link control Medium access control Physical TCP/IP IEEE 802 Reference Model Oct 8, Packets, Routing and Addressing -8/9 Hypertext Transfer Protocol (HTTP) is the set of rules for delivering Web pages over the Internet HTTP uses the client/server model The client opens an HTTP session and sends a request to a server The server returns an HTTP response message which contains data. After this, they forget about each other this has very significant implications for Web (and e- commerce) application development. Oct 8,

13 Packets, Routing and Addressing -9/9 IP addressing: 32-bit number to identify the computers connected to the internet (2 32 4billion) Domain names identify who you are (or else establishes your corporate identity).com.biz means you are a business.org means not for profit.uk means you are in the UK CNN.com displays your trade name Trademark law applies (Domain name wars) This has implications for e-commerce with regard to customer assumptions about you It costs! Oct 8, Intranets and Extranets -1/3 Intranet An intranet is an interconnected network (or internet small i intended) that does not extend beyond the organization that created it Intranets are an extremely popular and lowcost way to distribute corporate information An intranet uses Web browsers and Internetbased protocols (including TCP/IP, FTP, Telnet, HTML, and HTTP) and often includes a firewall Oct 8,

14 Intranets and Extranets -2/3 Extranet Extranets are intranets that have been extended to include specific entities outside the boundaries of the organization (business partners, suppliers, etc.) An extranet can be a public network, a secure (private) network, or a virtual private network (VPN). Oct 8, Intranets and Extranets -3/3 A public network is any computer or telecommunications network that is available to the public A private network is a private, leased-line connection between two companies that physically connects their intranets to one another A VPN extranet is a network that uses public networks and their protocols to send sensitive data to partners, customers, suppliers, and employees using a system called IP tunneling or encapsulation Oct 8,

15 Connectivity Large firms that provide Internet access to other businesses are called Internet Access Providers (IAPs) or Internet Service Providers (ISPs) The most common connection options that ISPs offer to the Internet are telephone, broadband, leased-line, and wireless Bandwidth is the amount of data that can travel through a communication line per unit of time Bandwidth can differ for data traveling to or from the ISP Oct 8, Summary The Internet infrastructure Distributed systems, LANs and WANs Peer-to-peer and client server networks Internet protocols Packet-switched networks IP addressing and domain names Oct 8,