DICT 301: Computer Networks Class 1: Networking Concepts

1. DICT 301: Computer NetworksClass 1: Networking Concepts Dr. Md. AminulHaqueAkhand

2. Network Concept

3. Network Concept • A network may be: • Traffic • Human • Social • Computers • Mobile • Neuronal • A network is a general term referring to a set of related elements or entities linked to each other. • The coexistence of these elements is defined by the communication or exchange processes performed within a structured environment.

4. Network Concept: Computer Networks • A computer network is a set of computers and devices interconnected to each other allowing the computers to communicate with each other and share resources and information. • Computers on a network can act as a client or a server. • A client is a computer that requests for resources. • A server is a computer that. controls and provides access to resources.

5. Wireless Access Point (WAP) KUET Network LAN Router Gateway Switch of admin. building Main Switch Firewall LAN Switch of CE Dept. Real IP Switch Lab Switch Switch of CSE Dept. Proxy Server Web Server Mail Server DNS Server Central Computer Center UTP Cable Teacher Student Optical Fiber Backbone

6. Four Elements of a Network • Rules or agreements to govern the messages are sent, directed, received and interpreted • The messages or units of information that travel from one device to another • A means of interconnecting these devices – a medium that can transport the messages from one device to another • Devices on the network that exchange messages with each other

7. Elements of a Network : Rules (Protocols) • Rules govern every step of the process, from the way cables are designed to the way the digital signals are sent. • These rules are called protocols, e.g. TCP/IP protocol stack

8. TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What is a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi Q: Other human protocols?

9. Elements of a Network: Messages (Data) • Message is a generic term that encompasses text, voice or video information • The message must be converted to bits, binary coded digital signals, before they are transmitted on the medium

10. wireless router UTP cables Wired connections Wireless connections Elements of a Network : Medium • Physically carries the message • Connects the devices • Can be wired or wireless

11. Elements of a Network : Networking Devices • End-user devices • desktop computer • server • notebook (or laptop) • IP phone • Networking devices • LAN switch • firewall • router • wireless router

12. Common Data Network Symbols

13. Non-Converged Networks • In the past, every one of the services required a different technology to carry its particular communication signal • Each service has its own set of rules and standards

14. Converged Networks • Convergence occurs when telephones, broadcasts (radio and TV), and computer communications all use the same rules, devices and media to transport messages

15. Circuit Switching vs Packet Switching

16. Circuit Switched Connection-Oriented Networks • A physical, dedicated path or circuit is temporary setup between the source and destination • The circuit is maintained for the duration of the call • Early circuit-switched networks do not dynamically recover from drop circuits

17. Packet Switched Connectionless Networks - base of Today's Internet • The entire message is broken into packets which are addressed and numbered • Any packets can be sent through the network using any available path

18. Sequence of A & B packets does not have fixed pattern  statistical multiplexing. D E resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • Node receives complete packet before forwarding Packet Switching: Statistical Multiplexing each end-end data stream divided into packets • user A, B packets share network resources • each packet uses full link bandwidth • resources used as needed 10 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link

19. Network Architecture

20. Network Architecture • Refers to the conceptual plans on which a physical network is built • Must support a wide range of applications and services • Four basic characteristics of the network architecture • fault tolerance • scalability • quality of service • security

21. Fault Tolerance • A fault tolerant network limits the impact of hardware or software failure • recover quickly when a failure occurs • depend on redundant links, or paths, between the source and destination of a message • redundant connections allow for alternate paths

22. Scalability • A scalable network can expand quickly to support new users and applications without impacting the performance of the service being delivered to existing users • Depends on a hierarchical layered design for the physical infrastructure and logical architecture

23. Internet Structure • The Internet is a hierarchical structure of interconnected networks ---- Internet: A Network of Networks • Many individual networks that provide Internet connectivity cooperate to follow accepted standards and protocols • new products can integrate with and enhance the existing infrastructure

24. Quality of Service (QoS) • QoS refers to the mechanism that manage congested network traffic • Congestion is caused when the demand on the network exceeds the available capacity • Some constraints on network resources cannot be avoided • technology limitations • cost • local availability of high-bandwidth services

25. Security • The Internet has become a widely accessible means of business and personal communications • the same environment that attracts legitimate business, however, also attracts scam artists and vandals • Tools and procedures are being implemented to combat inherent security flaws in the network architecture

26. Network Security Concerns • Network infrastructure security • physical securing of devices that provide network connectivity and preventing unauthorized access to the management software that resides on them • Content security • protecting the information contained within the packets being transmitted over the network and the information stored on network attached devices • tools to provide security for the content of individual messages must be implemented on top of the underlying protocols

27. Security Measures • Prevent unauthorized disclosure or theft of information • ensure confidentiality • Prevent unauthorized modification of information • maintain communication integrity • Prevent denial of service (DoS) • ensure availability

28. Confidentiality, Integrity and Availability (Optional) • Ensuring confidentiality • allowing only the intended and authorized users to read the data • a strong system for user authentication • encrypting the content • Maintaining communication integrity • data integrity is the assurance that the information has not been altered in transmission, from source to destination • source integrity is the assurance that the identity of the sender has been validated • using digital signatures and hashing algorithms • Ensuring availability • resources are available to authorized users • virus software and firewalls are used to combat virus and DoS attacks • building fully redundant network infrastructures

29. Trends in Networking (Optional) • Increasing number of mobile users • a demand for more mobile connectivity to data networks • New and more capable devices • functions performed by cell phones, personal digital assistants, organizers and pagers are converging into single handheld devices with continuous connectivity to providers of services and content • Increased availability of services • new services are introduced and older services are enhanced to meet user demands

30. Types of Networks

31. Types of Network/ Network Infrastructures • Network infrastructures can vary in terms of: • the size of the area covered • the number of users connected • the number and type of services available • Common types of network infrastructures • local area networks (LANs) • wide area networks (WANs) • Internet • Peer-to-Peer Networks • Client/Server Networks • LAN- Local Area Network • WAN- Wide Area Network • MAN- Metropolitan Area Network • Public Network • Private Network

32. Peer-to-Peer Networks • The simplest form of a network is a peer-to-peer network. In a peer-to-peer network, every computer can communicate directly with every other computer. • Each computer can be configured to share only some of its resources and prevent access to other resources. • Every computer is capable of sending and receiving information to and from every other computer.

33. Client/Server Networks • A network that uses a server to enable clients to share data, data storage space, and devices is known as a client/server network.

34. Local Area Networks (LANs) • A LAN usually spans a small geographical area • provides services and applications to people within a common organizational structure, such as a home, building or campus • usually administered by a single organization • security and access control policies are enforced on the network level

35. Wide Area Networks (WANs) • Telecommunications service provider (TSP) networks are used to interconnect an organization’s LANs that are located geographically far apart • TSPs operate large regional networks that span long distances • the TSP networks are referred to as wide area networks (WANs) • WANs use specifically designed network devices to make the interconnections between LANs

36. Metropolitan-Area Network (MANs)

37. Storage-Area Networks (SANS)

38. The Internet – A Network of Networks • A need to communicate with a resource on another network • sending an e-mail to a friend in another country • accessing news or products on a website • instant messaging with someone in another city • Internetwork • a global mesh of interconnected networks • owned by large public and private organizations • the Internet is an example of a publicly-accessible internetwork • Intranet • private connection of LANs and WANs that belongs to an organization • accessible only by the organization’s members, employees, or others with authorization

39. The Internet • LANs and WANs may be connected into internetworks

40. Networks Devices

41. Network Accessories • Computing Devices: Servers, Work Stations, Hosts • Server: Mail, Proxy, DNS, Web, Database etc. • Host/ Workstation: Computer, Mobile, PDA, Notebook etc. • Switching Devices: Router, Switch, Bridge, Hub, NIC Card, Modem, Getaway, Multiplexer, Repeater/ Signal Regenerator etc. • Connecting Medium: UTP, RJ 45 connector, Optical fiber, Wireless • Security Device: Firewall

42. hub switch switch router router Routers • Primary devices used to interconnect networks • each port on a router connects to a different network and routes packets between networks • Have the ability to break up broadcast domains (BD) and collision domains (CD) • Used to interconnect networks that use different technologies • LAN and WAN interfaces

43. Switches • A switch receives a frame and regenerates each bit of the frame on to the appropriate destination port • Used to segment a network into multiple collision domains • Each port on the switch creates a separate collision domain • creates a point-to-point logical topology to the device on each port • provides dedicated bandwidth on each port • Can be used to interconnect network segments of different speeds

44. Hubs • A hub receives a signal, regenerates it, and sends the signal over all ports • ports use a shared bandwidth approach • reduces the LAN performance due to collisions and recovery • maintains a single collision domain Used in a small LAN that requires low throughput requirements or when finances are limited Less expensive than a switch

45. Device Selection Factors • Cost • Speed and types of ports/interfaces • Expandability • Manageability • Additional features and services

46. Factors to Consider in Choosing a Switch • Cost • its capacity and features • network management capabilities, embedded security technologies and optional advanced switching technologies • Simple “cost per port” calculation • deploy one large switch at a central location • cost savings may be offset by the expense from the longer cables • Compare the cost of deploying a number of smaller switches connected by a few long cables to a central switch

47. Factors to Consider in Choosing a Switch (cont…) • Investing in redundancy • a secondary switch to operate concurrently with the primary central switch • additional cabling to allow the physical network to continue its operation even if one device fails

48. Purchasing decisions • just enough ports for today’s needs • mixture of UTP speeds • both UTP and fiber ports Speed and Type of Ports (Interfaces)

49. Factors to Consider in Choosing a Router • Expandability • modular devices have expansion slots that provide the flexibility to add new modules as requirement evolve • basic number of fixed ports as well as expansion slots • Media • additional modules for fiber optics can increase the cost • Operating system features • different versions of the operating system support certain features and services • security, quality of service, voice over IP, routing multiple Layer 3 protocols, NAT and DHCP

50. Bridge (Optional) • Bridges are used to divide larger networks into smaller sections. • They do this by sitting between two physical network segments and managing the flow of data between the two. • By looking at the MAC address of the devices connected to each segment, bridges can elect to forward the data (if they believe that the destination address is on another interface), or block it from crossing (if they can verify that it is on the interface from which it came).