est_320_Lect_4_Networking_2_28_08 - Lecture 4 Networking...

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Unformatted text preview: Lecture 4 Networking Wired Uses of Computer networks A network is a group of connected data communicating devices computers connected to in/out devices such as printer, fax, intranet, and internet. Networks exist so that data can flow form one point to another. Companies use Networks for: Resource sharing (hardware and software) High reliability Saving Money = Client/server Scalability Communication Medium People use Networks for: Access to remote information Person-to-person communication Interactive entertainment Network Architectures and Protocols Architectures: Systems need strategies International Standards Organization (ISO) for connecting devices within the network and to other networks. communication methods used to send data. Data Link Layer Protocols X.25 Protocol Protocols: Precisely define the Network Architecture == Layers For Example: Basic letter communication (US Postal service) Sender Higher == writes the letter Middle == picked up by carrier Lower == sorted by post office On the way == from one location to others Receiver Higher == carriers transport the letter to post office Middle == sorted and delivered to mail box Lower == pick up the letter and read Open Systems Interconnection Model, or OSI 7 layers 7 Application layer software that allows the user to interact with the network. 6 Presentation Layer - handles formatting issues 5 Session Layer Requests a connection, as per the end user, to a network. Also responsible for disconnecting from the network. 4 Transport Layer - Breaks the message into blocks and is also responsible for monitoring quality of the communication channel. 3 Network Layer creates routing messages and is concerned with the networks that will be used to send data 2 Data Link Layer gathers bits data bits into a block and sent to the physical layer 1 Physical Layer - sends a bit stream over a transmission medium FIGURE 7-1: LAYERS OF THE OPEN SYSTEMS INTERCONNECTION MODEL FIGURE 7-2: TRANSFERRING A FILE UNDER THE OSI MODEL FIGURE 7-3: MULTIPLE NODE COMMUNICATIONS UNDER OSI Protocols and Standards Key elements of a Protocols are: Syntax: structure or format of data. ie. First 8 bits of data represent the sender's address, the next 8 bits are the address of the receiver and the remaining bits represent the message. Semantics: meaning of each segment of bits. Does an address tell us the route to be taken or does it describe the final destination of the data. Timing When the data should be sent How fast it can be sent Standards "are essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes." (Data Communications and Networks, Forouzan 2004, pg19) X.25 Standard describes the functions necessary for communication with packet switching networks. Client/Server Computing Model/Architecture Users or clients wired to the network have access to programs on any server within the network. Allows companies to choose software applications and hardware with enough computational power to meet their needs. Generally, the client has the user interface on their desktop and the database management is handled by the server. Types of Network Connections Point-to-point: dedicated link between two devices. Communication is established via a wire, however, you can use infrared remote control, microwave or satellite links. Ex. A wire connecting printer to computer and/or your TV remote control device that uses infrared remote control to link to your TV. Multipoint (Multidrop): more than two specific devices share a single link. Ex. A mainframe computer connected to several work stations. Types of Connections (continued) Physical topology: the physical layout of a network how the connections connect. Voice and Data networks use Star and Mesh topologies. Star Topology - Users are connected to a central point and voice and data is routed thought this point Mesh Topology users connect via a cable to each device within the network. Bus: one long cable that acts as a backbone to link all the devices in a network. Data Transport Networks WAN - Wide Area Network Packet switching network - Frame Rely Networks, The Internet Public Packet Switching Networks Service providers own and operate network. LAN Local Area Network a data communications network that is privately owned. Ethernet Wide Area Wireless Networks wireless radio communications to a LAN beepers, pagers. Cellular networks divides areas into cells to send data Satellite Networks combination of satellites that provide point-to-point communication Proprietary Communications Architectures Systems Network Architecture (SNA) A SNA networks: each user on the network has access to programs on servers within the network. SNA architecture allows users to connect to many different devices with different capabilities. SNA architecture are expandable and can be linked to other SNA networks. SNA has sophisticated network-management functions. Wide Area Network Packet switching network Wide Area Networks span large geographical distances. Hierarchy International Service Providers connect nations National Service Providers Backbone network created and maintained by companies like MCI and SprintLink Regional Internet Service Providers connect to one or more National Service Providers Local Internet Service Provider connect and provide service to the end user. Optonline, AOL, Netzero Packet Switching Networks Main function send and deliver data over long distances. Based on the X.25 protocol. X.25 protocol provides standards for connecting to packet switching networks and functions at the lower levels of the OSI model (Physical Level, Frame Level and Packet Level). X.25 also provides for error checking and retransmission procedures of packets as they pass through the network. Data is divided into packets. Virtual circuit there is no continuous connection. Data is routed to it's destination upon demand. Each packet can take a different route as it travels through the network. Packets may or may not arrive at the same time. Once all the packets arrive they are resembled. If there is no data then the system remains inactive and no resources are used. Frame Relay Network Main function send and deliver data over vast distances. Wide Area network (WAN) Operates at the first two levels of the OSI model (physical and data Link layers) Virtual Circuits Network has the appearance of a permanent connection. Network recourses are used only when data is being transmitted. Frame relay networks have error detection only in the data link layer. Frame Relay networks do not have controlled data flow, error control and retransmission policies. Damaged frames are silently dropped from the transmission. Frame Relay networks were designed for more reliable media and provide the user with fast transmission capabilities. Fundamental Architecture of the Internet No single group owns the Internet. The Internet is managed by private organizations, Universities, and government agencies. Government many agencies such as the National Science Foundation (NSF), and NASA provide highspeed backbones for research and education. These agencies provide links to supercomputer centers. The United States government has also funded Internet 2, a super-fast network which has the ability to transfer information at 2.4 gigabits per second. Internet The Internet is a data network that uses Transmission Control Protocol/internet Protocols (TCP/IP). The Internet has a Global communications infrastructure TCP/IP Protocols The Internet uses higher level protocols making it an extremely efficient Global Network data is not only send but it can be used throughout the global network. It operates using 5 OSI layers (Layer 3 7) to provide uses with higher level services. Network Links to the Internet Dial- up dedicated telephone line sends data at 56Kbps (kilobits per second) T1 thru T3 - leased telephone lines with carrying speeds from 1.544 Mbps to 44.746 Mpbs Cable Modems up to 30 Mbps DSL connections up to 10 Mbps Modem data, voice and video is changed Terms in Computer Networks analog/digital and digital/analog Modulation/demodulation. Routers A device that forwards packets from one network to another. Works at the first 3 OSI layers. Access point Central base station in a Wireless LAN Gateway A device that connects separate networks and the separate networks use different protocols. Ports The port number of the server in a URL. Terms in Computer Networks (cont.) Repeaters A device that regenerates a signal thereby extending the distance a signal can travel. Bridge Operates at the first two levels of the OSI model. The device has filtering and forwarding capabilities. Nodes a computer or a router address on a network. Client work station (ie. your home computer) Server A program that provides clients with services. Wired Communication via the Public Telephone Network Public Telephone Network is a circuit switching network. Data and voice can be transferred using this network. Twisted-pair wire and fiber-optic cables provide end-to-end connections. Subscriber loop carriers (SLCs) connect home and business telephones. The area serviced by SLCs is called the local loop. Network Service Levels Availability uptime vs. downtime measures success of network Reliability data is able pass through the network with little errors Response Time importance depends on user Throughput "net bandwidth of a network" Network Management Approaches Nonautomated Network management Semiautomated Network Management Integrated Network Management Network Management Protocols Diagnostic methods Standards Organizations International Organization for Standardization (ISO) International Telecommunication Union Telecommunication Standards Sector (ITU-T) American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Discussion Questions Week one March 10 March 16 Briefly describe the history of the Internet. Tell us about its structure. In data communications, why is it important to have protocols and standards? Week two March 24 March 30 There are two main categories of data communication networks, LAN's and WANs. Each network has different characteristics and functionalities. What are they (a short explanation is fine)? How is a circuit switching network different from a packet switching network? ...
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