Center for Biotechnology Information,National Library of Me.ppt

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1、Chuong HuynhNational Center for Biotechnology Information, National Library of Medicine, National Institute of Health,May 21, 2001,Network Fundamentals: Intro to Network Structure and Protocol LAN, WAN, TCP/IP,Outline,Basic concepts in communications Understanding Networking. Understanding Transmiss

2、ion Medium (Network Cables) Understanding Network Hardware WAN and LAN Understanding Network Protocols,Basic Concepts in Communication,Basic Concepts,Communications activity associated with distributing or exchanging information Telecommunications technology of communications at a distance that perm

3、its information to be created any where and used everywhere with little delay Today it, involves Data: digital and analog Voice: spoken word Video: telelcommunication imaging,Essentials for Communications,Must have a message Message must have a transmitter Message must have a medium Message must be

4、understood Message must have some level of security,Source Transmitter Transmission Receiver Destination,Source System,Destination System,Workstation/PC,Workstation/PC,Medium,1,2,3,4,5,6,Essentials for Communications,Source Transmitter Transmission Receiver Destination,Source System,Destination Syst

5、em,Workstation/PC,Workstation/PC,Medium,1,2,3,4,Text input information Input data digital bit stream Transmitted analog signal Received analog signal Output data digital bit stream Text output information,5,6,Data Communication Tasks,Understanding Networking,Big Picture,What do you see here for a ty

6、pical network?,Key Network Terminology Explained (1),Networks needs to interconnect at a distance by a form of point to point or point to multiple point connected media A network is a group of computers connected together in such a way as to allow Networks that are interconnected have proven to be l

7、ow cost, reliable, and efficient means of communicating at a distance,Key Network Terminology Explained (2),Node: anything connected to the network, usually a computer, but it could be a printer or a scanner Segment: any portion of a network that is separated by a switch, bridge or a router from ano

8、ther part of a network. Backbone: the main cabling of a network that all of the segment connect to. Usually, the backbone is capable of carrying more information than the individual segments. Topology: The way each node is physically connected to the network,Network architecture ,Common Topologies -

9、 Bus,Bus: each node is daisy-chained (connected one right after the other) along the same backbone. Information sent from a node travels along the backbone until it reaches its destination node. Each end of a bus network must be terminated with a resistor to keep the,Common Topologies - Ring,Ring: S

10、imilar to a bus network, rings have nodes daisy chained, but the end of the network in a ring topology comes back around to the first node, creating a complete circuit. Each node takes a turn sending and receiving information through the use of a token. The token along with any data is sent from the

11、 first node to the second node which extracts the data addressed to it and adds any data it wishes to send. Then second node passes the token and data to the third node, etc. until it comes back around to the first node again. Only the node with the token is allowed to send data . All other nodes mu

12、st wait for the token to come to them.,Common Topologies - Star,In a star network, each node is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network.,A hub does not perform any type of filtering or routi

13、ng of the data. A hub is a junction that joins all the different nodes together.,Common Topologies - Star,In a star network, each node is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network.,Common Topo

14、logies Star Bus,Prob. Most common topology used today. Combines elements of the star and bus topologies to create a versatile network environment. Nodes in particular areas are connected to hubs (and create star topology), and hubs are connected together along the network backbone (like a bus networ

15、k). Often you have stars nested within stars.,Other network topologies (architecture),Some basic network topologies not previously mentioned: One-to-one Hierarchical Hybrid Client-server Multiple nodes,Key Network Terminology Explained (3),Simplex: information flows in only one direction Half-duplex

16、: information flows in two directions, but only in one direction at a time. Full-duplex: information flows in two directions at the same time,Basic Signal Terminologies,Bit: binary digit, either 0 or 1 Baud (dont really use anymore; not accurate) = one electronic state change per second Bit rate a m

17、ethod for measuring data transmission speed bits per second Mbps millions of bits per second (data speed; measure of bandwidth = total information flow over a given time) on a telecommunication medium 8 bits = 1 byte Mb million bits (quantity of data) MB million bytes (quantity of data) Gbps Billion

18、 bits per second (data speed) Teraflops trillion operations per second,Kilo K 210 Mega M 220 Giga G 230 Tera T 240 Peta P 250 Exa E 260 Zetta Z 270 Yotta Y 280,Data Transmission,Successful transmission of data depends on: The quality of the signal being transmitted Characteristics of the transmissio

19、n medium Data rate bits per second in data communications Bandwidth bandwidth or signal is constrained by the transmitter and the nature of the transmission in cycles per second or hertz Noise Average level of noise over the communication path. Error rate rate at which errors occur where error in 1

20、or 0 bit occurs,Understanding Transmission Medium,Basic transmission medium concepts,Medium is the physical path between transmitter and receiver in a data transmission system Guided Medium: waves are guided along a solid medium path (twisted pair, coaxial cable, and optical fiber). Unguided medium:

21、 waves are propagated through the atmosphere and inner/outerspace (satellite, laser, and wireless transmissions).,Medium examples by type,Conductive: twisted pairs and coaxial cables Electromagnetic: microwave Light: lasers and optical fibers (need clear line of sight) Wireless inner/outerspace; sat

22、ellite (omnidirectional security issues),Coaxial cable (1),Widely installed for use in business and corporation ethernet and other types of LANs. Consists of inter copper insulator covered by cladding material, and then covered by an outer jacket Physical Descriptions:, Covered by sheath material, O

23、uter conductor is braided shielded (ground), Separated by insulating material, Inner conductor is solid copper metal,Coaxial cable (2),Applications: TV distribution (cable tv); long distance telephone transmission; short run computer system links Local area networksTransmission characteristics: Can

24、transmit analog and digital signals Usable spectrum for analog signaling is about 400 Mhz Amplifier needed for analog signals for less than 1 Km and less distance for higher frequency Repeater needed for digital signals every Km or less distance for higher data rates Operation of 100s Mb/s over 1 Km

25、.,Twisted Pair Cables,Physical description: Each wire with copper conductor Separately insulated wires Twisted together to reduce cross talk Often bundled into cables of two or four twisted pairs If enclosed in a sheath then is shielded twisted pair (STP) otherwise often for home usage unshielded tw

26、isted pair (UTP). Must be shield from voltage lines Application: Common in building for digital signaling used at speed of 10s Mb/s (CAT3) and 100Mb/s (CAT5) over 100s meters. Common for telephone interconnection at home and office buildings Less expensive medium; limited in distance, bandwidth, and

27、 data rate.,Categories of Twisted Pairs Cabling System,Specs describe cable Material, type of Connectors, and Junction blocks to Conform to a category,Optical Fibers (1),Physical Description: Glass or plastic core of optical fiber = 2to125 m Cladding is an insulating material Jacket is a protective

28、cover Laser or light emitting diode provides transmission light source Applications: Long distance telecommunication Greater capacity; 2 Gb/s over 10s of Km Smaller size and lighter weight Lower attenuation (reduction in strength of signal) Electromagnetic isolation not effected by external electrom

29、agnetic environment. Aka more privacy Greater repeater spacing fewer repeaters, reduces line regeneration cost,Repeaters ,Optical Fibers (2),multimode fiber is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the

30、optical fiber core. used for relatively short distances because the modes tend to disperse over longer lengths (this is called modal dispersion) . For longer distances, single mode fiber (sometimes called monomode) fiber is used. In single mode fiber a single ray or mode of light act as a carrier,Wi

31、reless Transmission (1),Frequency range (line of sight): 26 GHz to 40 GHz: for microwave with highly directional beam as possible 30 MHz to 1 GHz: for omnidirectional applications 300MHz to 20000 GHz: for infrared spectrum; used for point to point and multiple point application (line of sight) Physi

32、cal applications: Terrestrial microwave long haul telecommunication service (alternative to coaxial or optical fiber) Few amplifier and repeaters Propagation via towers located without blockage from trees, etc (towers less than 60 miles apart),Wireless Transmission (2),Satellite is a microwave relay

33、 station Geostationary orbit (22,000 miles) and low orbit (12000 miles) Satellite ground stations are aligned to the space satellite, establishes a link, broadcast at a specified frequency. Ground station normally operate at a number of frequencies full duplex Satellite space antenna is aligned to t

34、he ground station establishes a link and transmits at the specified frequency. Satellite are capable of transmitting at multiple frequencies simultaneously, full duplex. To avoid satellites from interfering with each other, a 4 degree separation is required for 4/6 GHz band and 3 degree for 12/14 GH

35、z band. Limited to 90 satellites. Disadv: not satellite repair capability; greater delay and attenuation problems.,Wireless LAN,Wireless LAN HiperLAN (European standard; allow communication at up to 20 Mbps in 5 GHz range of the radio frquency (RF) spectrum. HiperLAN/2 operate at about 54 Mbps in th

36、e same RF band.,Network Hardware,Hubs,A hub is the place where data converges from one or more directions and is forwarded out in one or more directions. Seen in local area networks,Reference to equipment,Gateways,A gateway is a network point that acts as an entrance to another network. On the inter

37、net, in terms of routing, the network consists of gateway nodes and host nodes. Host nodes are computer of network users and the computers that serve contents (such as Web pages). Gateway nodes are computers that control traffic within your companys network or at your local internet service provider

38、 (ISP),Routers,A router is a device or a software in a computer that determines the next network point to which a packet should be forwarded toward its destination. Allow different networks to communicate with each other A router creates and maintain a table of the available routes and their conditi

39、ons and uses this information along with distance and cost algorithms to determine the best route for a given packet. A packet will travel through a number of network points with routers before arriving at its destination.,Bridge,a bridge is a product that connects a local area network (LAN) to anot

40、her local area network that uses the same protocol (for example, Ethernet or token ring). A bridge examines each message on a LAN, “passing“ those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).,What is the difference between?,Bridge: devi

41、ce to interconnect two LANs that use the SAME logical link control protocol but may use different medium access control protocols. Router: device to interconnect SIMILAR networks, e.g. similar protocols and workstations and servers Gateway: device to interconnect DISSIMILAR protocols and servers, an

42、d Macintosh and IBM LANs and equipment,Switches,Allow different nodes of a network to communicate directly with each other. Allow several users to send information over a network at the same time without slowing each other down.,WANs and LANs,Major Categories of Networks,Local Area Networks (LAN) A

43、network of computers that are in the same general physical location, within a building or a campus. Metropolitan Area Networks (MAN) Wide Area Networks (WAN)Issues of size and breadth.,Data Communications Through WANs (1),WANs were developed to communicate over a large geographical area (e.g. lab-to

44、-lab; city-to-city; east coast-to-west coast; North America-to-South America etc) WANs require the crossing of public right of ways (under control and regulations of the interstate commerce and institute of telephone and data communications established by the govt and international treaties). WANs a

45、round the world relies on the infrastructure established by the telephone companies (“common carrier”) or public switched telephone network (PSTN). WANs consists of a number of interconnected switching nodes (today = computers). Transmission signals are routed across the network automatically by sof

46、tware control to the specified destination. The purpose of these nodes are to route messages through switching facilities to move data from node to node to its destination.,Data Communications Through WANs (2),WANs originally implemented circuit switching and packet switching technologies. Recently,

47、 frame relay and asynchronous transfer mode (ATM) networks have been implemented to achieve higher operating and processing speeds for the message. WAN transmission speeds are _ WAN are owned by the common carrier in the U.S. and governement in most foreign countries. Interconnected devices, I.e. LA

48、Ns or Personal Computers (PC) or Workstation or Servers can be (usually are) privately owned by companies.,Circuit Switching Technologies,Circuit switching is a dedicated communications path established between two stations or multiple end points through nodes of the WAN Transmission path is a conne

49、cted sequence of physical link between nodes. On each link, a logical channel is dedicated to the connection. Data generated by the source station are transmitted along dedicated path as rapidly as possible. At each node, incoming data are routed or switched to the appropriate outgoing channel witho

50、ut excessive delay. However, if data processing is required, some delay is experienced. Example of circuit switching above is the telephone networks.,Packet Switching Technologies,It is not necessasry (as in circuit switching) to dedicate transmission capacity along a path through the WAN rather dat

51、a are sent out in a sequence of small chucks, called packets. Each packet, consisting of several bits is passed through the network from node to node along some path leading from the source to the destination At each node along the path, the entire packet is received, stored briefly, and then transm

52、itted to the next node. At destination all individual packets are assembled together to form the complete text and message from the source. Each packet is identified as to its place in the overall text for reassembly. Packet switching networks are commonly used for terminal-to-computer and computer-to-computer communications. If packet errors occur, the packet is retransmitted.,