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Transcript
Introduction and Networking Fundamental Data networks • Businesses needed a solution that would successfully address the following three problems: – How to avoid duplication of equipment and resources – How to communicate efficiently – How to set up and manage a network Network history • In the 1980s users with stand-alone computers started to share files using modems to connect to other computers. This was referred to as point-topoint, or dial-up communication • Bulletin boards became the central point of communication in a dial-up connection. Drawbacks to this type of system were: – That there was very little direct communication – Availability was limited to only with those who knew about the location of the bulletin board – Required one modem per connection. If five people connected simultaneously it would require five modems connected to five separate phone lines • From the 1960s-1990s, the DoD (Department of Defense, USA) developed large, reliable, WANs (Wide Area Networks) for military and scientific reasons. • In 1990, the DoDs WAN eventually became the Internet In Our Highway Analogy... • What is flowing? – Traffic • What different forms flow? – Cars, Trucks, Buses, etc. • What rules govern flow? – Traffic Laws & Rules of Courtesy • Where does the flow occur? – Streets In Computer Networks... • What is flowing? – Data • What different forms flow? – Text, Video, Audio • What rules govern flow? – Standards & Protocols • Where does the flow occur? – Wires, Fiber, Atmosphere Physical Topologies Physical topology is the actual layout of the wire or media Logical Topology Logical topology defines how media is accessed by hosts 1. Broadcast means that each host sends its data to all other hosts on the network medium. Non-deterministic - there is no order that the stations must follow to use the network. First come, first served. Example: Ethernet 2. Token Passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Examples: Token Ring, FDDI ( where Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. ) Networking Terminology End-user devices provide users with a connection to the network. Also referred to as hosts. Allow users to share, create, and obtain information. Note: The Macintosh or Mac, is a line of personal computers (PCs) designed, developed, and marketed by Apple Inc. Network devices provide transport for data between end-user devices. Provide cable connections, extensions, concentration. Conversion of data formats, and management of data transfers. Networking Terminology Repeater: A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise, and regenerates it. The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart. OR In telecommunication, the term repeater has the following standardized meanings: – An analog device that amplifies an input signal regardless of its nature (analog or digital). – A digital device that amplifies, reshapes, retimes, or performs a combination of any of these functions on a digital input signal for retransmission. A repeater that includes the retiming function is also known as a regenerator. Repeater • Extend the physical length • No network function has been changed • Location is matter Function of repeater Repeater is not exactly as same as Amplifier Networking Terminology (Continued..) Hub: A repeater with multiple ports is known as a hub. Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance. As a result, many network architectures limit the number of repeaters that can be used in a row, e.g., the Ethernet 5-4-3 rule. Hubs have been mostly obsoleted by modern switches; but repeaters are used for long distance links, notably undersea cabling. Ethernet: Ethernet is a family of computer networking technologies for local area (LAN) and larger networks. It was commercially introduced in 1980 while it was first standardized in 1983 as IEEE 802.3 The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced with twisted pair and fiber optic links in conjunction with hubs or switches. Data rates were periodically increased from the original 10 megabits per second to 100 gigabits per second. Hub • Actually is a multiport repeater • Star / Tree Topology Networking Terminology (Continued..) An Ethernet hub, active hub, network hub, repeater hub, multiport repeater or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC and/or Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. 10BASE2 (also known as cheapernet, thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable (RG-58A/U or similar, as opposed to the thicker RG-8 cable used in 10BASE5 networks), terminated with BNC connectors. During the mid to late 1980s this was the dominant 10 Mbit/s Ethernet standard, but due to the immense demand for high speed networking, the low cost of Category 5 Ethernet cable, and the popularity of 802.11 wireless networks, both 10BASE2 and 10BASE5 have become increasingly obsolete, though they still exist in some locations. Where BNC (Bayonet Neill–Concelman or Baby N Connector) connector is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. Networking Terminology (Continued..) Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Early Ethernet cabling had generally been based on various grades of coaxial cable, but in 1984, StarLAN showed the potential of simple unshielded twisted pair by using Cat3 cable—the same simple cable used for telephone systems. This led to the development of 10BASE-T and its successors 100BASE-TX and 1000BASE-T, supporting speeds of 10, 100 and 1000 Mbit/s respectively. Often the higher-speed implementations support the lower-speed standards making it possible to mix different generations of equipment; with the inclusive capability designated 10/100 or 10/100/1000 for connections that support such combinations. All these three standards support both full-duplex and half-duplex communication. All these standards use 8P8C connectors, and the cables from Cat3 to Cat7 have four pairs of wires; though 10BASE-T and 100BASE-TX only require two of the pairs. Networking Terminology (Continued..) Bridge: A network bridge connects and filters traffic between two network segments at the data link layer (layer 2) of the OSI model to form a single network. This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks. Bridges come in three basic types: – Local bridges: Directly connect LANs – Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers. – Wireless bridges: Can be used to join LANs or connect remote devices to LANs. Bridge Bridge • Divide a large network into smaller segment • Isolating and controlling the link problems (e.g. congestion) • Regenerate signal + Checking Physical Address and forward only to the specified segment Function of a bridge Multiport bridge Networking Terminology (Continued..) Switches: A network switch is a device that forwards and filters OSI layer 2 datagrams between ports based on the MAC addresses in the packets. A switch is distinct from a hub in that it only forwards the frames to the physical ports involved in the communication rather than all ports connected. It can be thought of as a multi-port bridge. It learns to associate physical ports to MAC addresses by examining the source addresses of received frames. If an unknown destination is targeted, the switch broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star topology for devices, and cascading additional switches. Multi-layer switches are capable of routing based on layer 3 addressing or additional logical levels. The term switch is often used loosely to include devices such as routers and bridges, as well as devices that may distribute traffic based on load or based on application content (e.g., a Web URL identifier). Routers: A router is an internetworking device that forwards packets between networks by processing the routing information included in the packet or datagram (Internet protocol information from layer 3). The routing information is often processed in conjunction with the routing table (or forwarding table). A router uses its routing table to determine where to forward packets. (A destination in a routing table can include a "null" interface, also known as the "black hole" interface because data can go into it, however, no further processing is done for said data.) Routers Routers in an internet Routers • Act like stations on a network • Multi-home • Definition (Goal) – “Learning how to get from here to there." – “Process of discovering, selecting, and employing paths from one place to another (or to many others) in a network” [from David M. Piscitello, Bellcore and A. Lyman Chapin, BBN] Routing Principle • Goal: Arriving at the destination • Considerations: – Direct route (shortest) – Reliable route – Cheap route – Safe route – Scenic (Attractive) route Network protocols • Protocol suites are collections of protocols that enable network communication from one host through the network to another host. • Protocols control all aspects of data communication such as: – – – – – How the physical network is built How computers connect to the network How the data is formatted for transmission How that data is sent How to deal with errors LAN Operate within limited geographical area Allow multi-access to high bandwidth media Control network privately under local administration Provide full-time connectivity to local services Connect physically adjacent devices MAN Spans a metropolitan area such as a city or suburban area Usually consists of LANs in a common geographic area Example: a bank with multiple branches may utilize a MAN WAN Operate over a large geographical area Allow access over serial interfaces operating at lower speeds Provide full-time and part-time connectivity Connect devices separated over wide areas SAN High-performance network to move data to/from storage areas Separate, dedicated network avoids traffic conflict VPN Private network constructed within public network such as Internet Access VPNs, Intranet VPNs, Extranet VPNs Metropolitan-area networks (MANs) • A MAN is a network that spans a metropolitan area such as a city or suburban area. • Usually consists of 2 or more LANs in a common geographic area. • Ex: a bank with multiple branches may utilize a MAN. • Typically, a service provider is used to connect two or more LAN sites using private communication lines or optical services. Storage-area networks (SANs) • A SAN is a dedicated, high-performance network used to move data between servers and storage resources. • Separate, dedicated network, that avoids any traffic conflict between clients and servers • SANs offer the following features: – Performance – allows concurrent access of disk or tape arrays by two or more servers at high speeds – Availability – have disaster tolerance built in, because data can be mirrored using a SAN up to 10km or 6.2 miles away. – Scalability – Like a LAN/WAN, it can use a variety of technologies. This allows easy relocation of backup data, operations, file migration, and data replication between systems. SAN Virtual private network (VPN) • A VPN is a private network that is constructed within a public network such as the Internet. • It offers secure, reliable connectivity over a shared public network infrastructure such as the Internet. Benefits of VPNs • Three main types of VPNs: – Access VPNs – provide remote access to a mobile worker and a small office/home office (SOHO) to the hq of the Intranet or Extranet over a shared infrastructure. Access VPNs use analog, dialup, ISDN, DSL, cable technologies – Intranet VPNs – link regional and remote offices to the hq of the internal network over a shared infrastructure using dedicated connections. They allow access only to the employees of the enterprise. – Extranet VPNs – link business partners to the hq of the network over a shared infrastructure using dedicated connections. They allow access to users outside the enterprise VPNs Bandwidth • • • • Bandwidth is limited by physics and technology Bandwidth is not free Bandwidth requirements are growing at a rapid rate Bandwidth is critical to network performance Throughput Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network. Often far less than the maximum possible digital bandwidth. Factors that determine throughput: Internetworking devices Type of data being transferred T = Time S = Size Network topology BW = Bandwidth Number of users on the network P = Throughput User computer Server computer Power conditions Using layers to analyze problems in a flow of materials • The concept of layers is used to describe communication from one computer to another • The information that travels on a network is generally referred to as data or a packet • A packet is a logically grouped unit of information that moves between computer systems. • As the data passes between layers, each layer adds additional information that enables effective communication with the corresponding layer on the other computer. Networking Models • The historical and technical standard of the Internet is the TCP/IP model • The U.S. Department of Defence created the TCP/IP reference model, to design a network that could survive any conditions, including a nuclear war Application layer handles issues of representation, encoding, and dialog control. Transport layer deals with the quality of service issues of reliability, flow control, and error correction Internet layer is to divide TCP segments into packets and send them from any network. Best path determination and packet switching occur at this layer Network Access layer (aka host-to-network layer) concerned with all components, both physical and logical, that are required to make a physical link Application layer • • • • • • Trivial File Transfer Protocol (TFTP) File Transfer Protocol (FTP) Network File System (NFS) Simple Mail Transfer Protocol (SMTP) Simple Network Management Protocol (SNMP) Domain Name System (DNS) Transport layer TCP and UDP • Segmenting upper-layer application data • Sending segments from one end device to another end device TCP only • Establishing end-to-end operations • Flow control provided by sliding windows • Reliability provided by sequence numbers and acknowledge me Internet layer • The purpose of the Internet layer is to select the best path through the network for packets to travel • IP provides connectionless, best-effort delivery routing of packets. • Internet Control Message Protocol (ICMP) provides control and messaging capabilities. • ARP resolves MAC address, for known IP addresses. • Reverse Address Resolution Protocol (RARP) determines IP addresses when the MAC address is known Network access layer The network access layer defines the procedures for interfacing with the network hardware and accessing the transmission medium. Drivers for software applications, modem cards and other devices operate at the network access layer OSI Model • Reduces complexity • Standardizes interfaces • Facilitates modular engineering • Ensures interoperable technology • Accelerates evolution • Simplifies teaching and learning • The OSI reference model was released in 1984 to help network builders implement networks that could communicate (interoperability) • The OSI reference model is the primary model for network communications • The process of moving information between computers is divided into seven smaller and more manageable steps Presentation Session Transport Network Data-Link Physical DATA SEGMENT PACKET FRAME BITS 0101010101010101010 DECAPSULATION Application Destination ENCAPSULATION Source Application Presentation Session Transport Network Data-Link Physical OSI Top 3 Layers – Application issues Application provides network services to the user's applications file, print, message, database and application services HTTP, SMTP, FTP Presentation responsible for manipulating data’s appearance as needed by the Application layer Data encryption, compression and translation services JPEG, MIDI, QuickTime, EBCDIC to ASCII Session establish and maintain communication between two hosts Dialogue control NFS, SQL, RPC 5/3/2017 NESCOT CATC 46 OSI Lower 4 Layers – Data Transport issues Transport PDU (protocol data unit ) – Segment the transport layer establishes, maintains, and tears down virtual circuits Windowing TCP and UDP Network PDU - Packet Routing Data packets and route update packets connectivity and path selection between two hosts Data-Link PDU - Frame physical addressing, network topology, network access, error notification, ordered delivery of frames, and flow control Ethernet LCC and MAC layers Physical PDU – bits Cabling, standards TCP/IP Vs OSI Similarities of the OSI and TCP/IP models: • • • • • NOTE: Both have layers Both have application layers, though they include very different services Both have comparable transport and network layers Packet-switched, not circuit-switched, technology is assumed Networking professionals need to know both models Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit. Differences of the OSI and TCP/IP models: • TCP/IP combines the presentation and session layer into its application layer • TCP/IP combines the OSI data link and physical layers into one layer • TCP/IP appears simpler because it has fewer layers • TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does Connecting Devices Networking Devices Repeaters Bridges Internetworking Devices Routers Gateways Connecting Devices Hub Gateways (protocol converter) A gateway SNA network (IBM) Netware network (Novell) Connecting Devices Networking Devices Repeaters Bridges Internetworking Devices Routers Gateways Other devices • Multiprotocol routers • Brouters (Bridge Router) • Switches Single VS. Multiprotocol router Brouter Backbone Network Bus Backbone Star Backbone Virtual LAN (VLAN) VLANs create broadcast domains VLAN with backbone switch Copper Media Cable specifications Coaxial cable Shielded twisted pair (STP) • Costs more and harder to install than UTP • Must be grounded at both ends • Reduces both internal and external sources of interference Unshielded twisted pair (UTP) • • Relies on cancellation effect produced by the twisting to limit signal degradation caused by EMI and RFI Easier to install, thinner and less expensive Straight-Through, Rollover and Crossover Cables Straight-Through Used for up-links Crossover Used for linking devices at the same level Rollover Used for connecting a terminal to the console port Cross 1 with 3 and 2 with 6 Optical Media • • • lRadio, microwaves, radar, visible light, x-rays, and gamma rays are all types of electromagnetic waves The wavelength of the light in optical fiber is either 850 nm, 1310 nm, or 1550 nm In a vacuum light travels at 300,000 kps - light travels at slower speeds through air, water, and glass Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Refraction is the change in direction of a wave due to a change in its transmission medium. Due to change of medium, the phase velocity of the wave is changed but its frequency remains constant. Two conditions must be met to prevent loss due to refraction and achieve Total Internal Reflection: 1. The core of the optical fiber has to have a larger index of refraction than the cladding. 2. The angle of incidence must be greater than the critical angle for the core and its cladding. The numerical aperture of a core is the range of angles of incident light rays entering the fiber that will be completely reflected . Index of refraction (refractive index ) “n” of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as , where c is the speed of light in vacuum and v is the speed of light in the substance. Orange jacket Kevlar Plastic buffer Cladding Core Other Optical Components There are two types of light sources: 1. Light Emitting Diode (LED) producing infrared light with wavelengths of either 850nm or 1310 nm Used with multimode fiber in LANs. 2. LASER producing a thin beam of intense infrared light with wavelengths of 1310nm or 1550 nm Used with single-mode fiber over longer distance Extra care should be exercised to prevent eye injury Fibre-optic receivers are called PIN photodiodes (p-intrinsic-n diodes) On single-mode fiber, the ST (Straight Tip) connector is frequently used. With multimode fiber the SC (Subscriber Connector ) connector is used EM Spectrum ISM band 902 – 928 Mhz 2.4 – 2.4835 Ghz 5.725 – 5.785 Ghz LF 30kHz 10km MF 300kHz 1km VHF HF 3MHz 30MHz 100m 10m UHF 300MHz 1m SHF 3GHz EHF 30GHz 300GHz 1cm 100mm 10cm X rays infrared visible UV 1 kHz 1 MHz 1 GHz 1 THz 1 PHz Gamma rays 1 EHz Propagation characteristics are different in each frequency band 20 Hz to ~14 kHz, acoustic — normal range of adult human hearing (most children and some animals perceive sounds outside this range, most teens and children can hear frequencies from 14 kHz up to ~16 kHz where most adults can't) 530 kHz to 1.710 MHz, electromagnetic — AM radio broadcasts EM Spectrum 42 MHz to 260 MHz, electromagnetic — VHF terrestrial TV broadcast channels 88 MHz to 108 MHz, electromagnetic — FM radio broadcasts 902 MHz to 928 MHz, common cordless telephone frequency in the US 0.8 to 2.3 GHz, (electromagnetic) - mobile phone conversation channels. 2.4 GHz, (electromagnetic) - microwave ovens, Wireless LANs and cordless phones (starting in 1998). 5.8 GHz, cordless phone frequency introduced in 2003 428 THz to 750 THz, electromagnetic — visible light, from red to violet 30 Petahertz (PHz), electromagnetic — x-rays 300 Exahertz (EHz) and above - gamma rays Designation Frequency Wavelength ELF extremely low frequency 3Hz to 30Hz 100'000km to 10'000 km SLF superlow frequency 30Hz to 300Hz 10'000km to 1'000km ULF VLF LF ultralow frequency very low frequency low frequency 300Hz to 3000Hz 3kHz to 30kHz 30kHz to 300kHz 1'000km to 100km 100km to 10km 10km to 1km MF medium frequency 300kHz to 3000kHz 1km to 100m HF high frequency 3MHz to 30MHz 100m to 10m VHF very high frequency 30MHz to 300MHz 10m to 1m UHF ultrahigh frequency 300MHz to 3000MHz 1m to 10cm SHF superhigh frequency 3GHz to 30GHz 10cm to 1cm EHF extremely high frequency 30GHz to 300GHz 1cm to 1mm EM Spectrum 42 MHz to 260 MHz, electromagnetic — VHF terrestrial TV broadcast channels 88 MHz to 108 MHz, electromagnetic — FM radio broadcasts 902 MHz to 928 MHz, common cordless telephone frequency in the US 0.8 to 2.3 GHz, (electromagnetic) - mobile phone conversation channels. 2.4 GHz, (electromagnetic) - microwave ovens, Wireless LANs and cordless phones (starting in 1998). 5.8 GHz, cordless phone frequency introduced in 2003 428 THz to 750 THz, electromagnetic — visible light, from red to violet 30 Petahertz (PHz), electromagnetic — x-rays 300 Exahertz (EHz) and above - gamma rays Designation Frequency Wavelength ELF extremely low frequency 3Hz to 30Hz 100'000km to 10'000 km SLF superlow frequency 30Hz to 300Hz 10'000km to 1'000km ULF VLF LF ultralow frequency very low frequency low frequency 300Hz to 3000Hz 3kHz to 30kHz 30kHz to 300kHz 1'000km to 100km 100km to 10km 10km to 1km MF medium frequency 300kHz to 3000kHz 1km to 100m HF high frequency 3MHz to 30MHz 100m to 10m VHF very high frequency 30MHz to 300MHz 10m to 1m UHF ultrahigh frequency 300MHz to 3000MHz 1m to 10cm SHF superhigh frequency 3GHz to 30GHz 10cm to 1cm EHF extremely high frequency 30GHz to 300GHz 1cm to 1mm IEEE Standards for Wireless Wireless Media 802.11 802.11b 802.11a 802.11g Includes Direct Sequence Spread Spectrum (DSSS) applies to wireless devices operating within a 1 to 2 Mbps range Wi-Fi™ - Increased transmission capabilities to 11 Mbps Typically speeds 2 to 4 Mbps All 802.11b systems are backward compliant Operate within 2.4 GHZ transmission band Operate within 5 GHZ transmission band No interoperability with 802.11b Capable of throughput of 54 Mbps (typically 20-26 Mbps) Same throughout as 802.11a Backwards compatibility for 802.11b Uses Othogonal Frequency Division Multiplexing (OFDM) Wireless Devices and Topologies Wireless network may consist of as few as two devices equipped with wireless network interface controllers (NICs) Access Point (AP) are installed to act as central hubs for the WLAN and to solve NIC compatibility issues APs are equipped with antennae and provide wireless connectivity over a specified area referred to as a cell • Three types of frames are used in wireless communication: control, management, and data • WLANs use CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) • WLAN authentication authenticates the device, not the user • Authentication and Association types 1. Unauthenticated and unassociated 2. Authenticated and unassociated - The node has been authenticated on the network but has not yet associated with the access point 3. Authenticated and associated • Wireless security can be difficult to achieve. Tools include: EAP-MD5 Challenge, LEAP (Cisco), User authentication, Encryption, Data authentication • VPN technology effectively closes the wireless network