Network Architecture #3 Networking - OSI & Ethernet PDF

INTERNATIONAL & ACCESS FOUNDATION PROGRAMMES COMPUTER SCIENCE MODULE Semester I Part 4 Networks: OSI Model and Ethernet Nevan Bermingham The OSI Model The Open Systems Interconnection (OSI) model is a product of the Open Systems Interconnec...

INTERNATIONAL & ACCESS FOUNDATION PROGRAMMES COMPUTER SCIENCE MODULE Semester I Part 4 Networks: OSI Model and Ethernet Nevan Bermingham The OSI Model The Open Systems Interconnection (OSI) model is a product of the Open Systems Interconnection effort at the International Organisation for Standardisation. It attempts to standardise the functions of a communications system in terms of abstraction layers.  Similar communication functions are grouped into logical layers. A layer serves the layer above it and is served by the layer below it. The OSI Model Most of the network 7 communication Application Set Application 6 Presentation protocols used today have a structure based 5 Session on the OSI model. 4 Transport In this lecture, we will Transport Set 3 Network see where Ethernet and IP belongs in the 2 Link OSI Model. 1 Physical We will also look at the Modern GSM Mobile Network Layers of the OSI Layer architecture simplifies the network design. It is easy to debug network applications in a layered architecture network. The network management is easier due to the layered architecture. Network layers follow a set of rules, called protocol. The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers. Layers of the OSI The Upper Layers: This deals with Application issues and generally are implemented only in software. The highest layer is closest to the end user. This layer is where communication from one end user to another begins through the interaction between the application layer processes and the end user. The Lower layers: This handles Data transport. The physical layer and Data link layers are implemented in hardware and software. The OSI Model The OSI Model The OSI Model OSI in Networks Application Application 7 Presentation Presentation 6 Session Session 5 Transport TCP (UDP) 4 Network IP 3 Link Ethernet/MAC Layer 2 Physical V.35/RJ45/RS-232 1  PART 2 – ETHERNET Nevan Bermingham - 2015 Networking Networking allows one computer to send information to and receive information from another. The Internet is the most conspicuous example of computer networking, linking millions of computers around the world, but smaller networks play a role in information access on a daily basis. E.g Many public libraries have replaced their card catalogs with computer terminals that allow patrons to search for books far more quickly and easily. Networking allows many different devices in LAN’s & WAN’s  We can classify network technologies as belonging to one of two basic groups 1. Local area network (LAN) technologies connect many devices that are relatively close to each other, usually in the same building. 2. Wide area network (WAN) technologies connect a smaller number of devices that can be many kilometres apart. For example, if two libraries at the opposite ends of a city wanted to share their book catalog information, they would most likely make use of a wide area network technology.  WAN’s use dedicated line leased from the local telephone company, intended solely to carry their data.  In comparison to WANs, LANs are faster and more reliable.  Fiber optic cables have allowed LAN technologies to connect devices tens of kilometers apart, while at the same time greatly improving the speed and reliability of WANs. Ethernet (IEEE 802.x) The original Ethernet was developed as an experimental coaxial cable network in the 1970s by Xerox Corporation Original Data rate of 3 Mbps using a carrier sense multiple access collision detect (CSMA/CD) protocol for LANs with sporadic but occasionally heavy traffic requirements. Success with that project attracted early attention and led to the 1985 joint development of the 10-Mbps Ethernet Version 1.0 specification, IEEE 802.3, by the three-company consortium: Digital Equipment Corporation (DEC), Ethernet  Ethernet has since become the most popular and most widely deployed network technology in the world.  The Ethernet standard has grown to encompass new technologies as computer networking has matured, but the mechanics of operation for every Ethernet network today stem from the original design.  The original Ethernet described communication over a single cable shared by all devices on the network.  Once a device attached to this cable, it had the ability to communicate with any other attached device. This allows the network to expand to accommodate new devices without requiring any modification to those devices already on the network.  These days, Ethernet utilises Fibre Optics, Satellite and Microwave point to points communications. Ethernet Terminology Protocols:- In networking, the term protocol refers to a set of rules that govern communications. Protocols is analogous to language in humans. For two devices on a network to successfully communicate, they must both understand the same protocols. Terminology  Medium - Ethernet devices attach to a common medium that provides a path along which the electronic signals will travel. Historically, this medium has been coaxial copper cable, but today it is more commonly a twisted pair or fibre optic cabling.  Segment - We refer to a single shared medium as an Ethernet segment.  Node - Devices that attach to that segment are stations or nodes.  Frame - The nodes communicate in short messages called frames, which are variably sized chunks of information. The Ethernet protocol specifies a set of rules for constructing frames:-  destination address and a source address,  explicit minimum and maximum lengths for frames,  Mandatory Information that must appear in the frame. Motivations for Local Area Networking  Local area networks are usually privately owned with limited coverage, this means that the underlying network technologies and network services may be freely selected.  The growing demand for local area networks is due to technical, economic and organizational factors:  Cost reductions through sharing of information and databases, resources and network services.  Increased information exchange between different departments in an organization, or between individuals.  Automation of communication and manufacturing process.  Improve the organisations security.  Increasing number and variety of intelligent data terminals, PCs and workstations. LAN designs  Peer-to-Peer Networking  It offers a quick way to tie all your resources and people together.  Users can access information from and share it directly with others in the network.  Users can easily share files and directories in a peer-to-peer network.  Client/Server Networking  Clients are connected to a centralized server.  The server provides centralized security, backup, and recover capability and controls access to sensitive files and expensive peripherals.  A dedicated server improves data integrity, because the most current version of a document will be saved in one location.  This type of network requires a network operating system. Servers Traditional Ethernet Bus (Including Tree) – All the stations are attached to a common medium, so there may be collision if two or more stations try to transmit at the same time. Traditional Ethernet uses bus topology. Bus Extender CSMA/CD Carrier-Sense Multiple Access with Collision Detection If the stations hear their own When one transmission Ethernet Before a station transmits, it returning in a station garbled form, as transmits, all "listens" to the medium to would happen if the stations some other station on the determine if another station had begun to medium hear transmit its own the is transmitting, before sending. message at the transmission same time, then they know that a collision occurred. Disadvantages of Ethernet  There are practical limits to the size of our Ethernet network, for example, the length of the shared cable:-  A network cable must be short enough that devices at opposite ends can receive each other's signals clearly and with minimal delay. This places a distance limitation on the maximum separation between two devices (called the network diameter) on an Ethernet network.  Electrical signals weaken as they propagate (attenuation)  Electrical interference from neighbouring devices (fluorescent lights, electrical motors, solar flares, etc) can scramble the signal.  With CSMA/CD only a single device can transmit at a given time, there are practical limits to the number of devices that can coexist in a single network. Attach too many devices to one shared segment and contention for the medium will increase. Ring Topology Each station attaches to the network via a repeater. Data are transmitted in packets which contains : : source address and Repeater destination address. The station will copy the Token data destined to itself, Frame Data 1 and the source is responsible for removing the data from the ring. : : No contention Station Media can be twisted pair, coaxial cable, or optical fibre An example is Token Ring Networks Ring Topology The data transmission process goes as follows: 1. Empty information frames are continuously circulated on the ring. 2. When a computer has a message to send, it seizes the token – sets the token to 1 and inserts data. 3. The frame is then examined by each successive workstation or PC. The workstation that identifies itself to be the destination for the message copies it from the frame and changes the token back to 0. 4. When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame. 5. The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send. Star Topology Uses a Digital Switch : Digital : Seen in Digital PBX Switch (Private Branch eXchange) : : Switched Ethernet Passive - Optical fibre, baseband coaxial Active - Twisted pair : : Station/Client 27 Mesh Topology A type of networking where each node must not only capture and disseminate its own : : : data, but also serve as a relay for other nodes It must collaborate to propagate the data in the network. Self-healing (the network is typically quite : reliable, as there is often more than one path : between a source and a destination in the network) Mostly used in wireless scenarios. 28 Wireless Network Topology Fixed-wire replacement 10-20 m Ad hoc Server 50-100 m Portable-to-fixed Network 29 Linking Networks Linking Networks To link network segments, Ethernet networks implemented bridges. Bridges connect two or more network segments, increasing the network diameter Bridges also help regulate traffic. The bridge does not originate any traffic of its own, it only echoes what it hears from other stations. Segmentation of Networks Repeaters Some network devices With physical media can also serve as like Ethernet or Wi-Fi, repeaters, but usually data transmissions can have some other name. only span a limited Active hubs, for distance before the example, are repeaters. quality of the signal For example, in Wi-Fi, degrades. access points function Repeaters attempt to as repeaters only when preserve signal operating in “repeater integrity and extend mode”. the distance over which All repeaters are data can safely travel. technically OSI physical layer devices.  Switched Ethernet  Modern Ethernet implementations are very different form the original historical Ethernet.  Legacy Ethernet networks transmitted data at 10 megabits per second (Mbps), modern networks can operate at 100 or even 1,000 Mbps (Gigabits Networks)  Switched networks replace the shared medium of legacy Ethernet with a dedicated segment for each station (essentially dividing the network into many small networks)  Full-duplex is a data communications term that refers to the ability to send and receive data at the same time.  These segments connect to a switch, which acts much like an Ethernet bridge, but can connect many of these single station segments. Þ Switches allow us to create a "dedicated road" between individual users. Ethernet Switches Transmission Mediums Transmission Mediums The term Transmission media refer to the technical device which contains the material substance to transmit or guide the waves. Transmission media are the physical pathways that connect computers, other devices, and people on a network An apology is the Motorways (large capacity) and back roads (local networks) that comprise the information superhighway Transmission Mediums Bound Media: Twisted pair Un Bound Media: Microwave Co-axial Infrared cable Satellite Fibre optic The Electromagnetic Spectrum Frequency Usage Modulation Modulation Digital Modulation Digital Modulation (Phase Shift Keying) Digital Modulation (Frequency Shift Keying) Radio Frequencies  A type of wiring in which two Twisted Pair conductors of a single circuit are twisted together for the purposes of cancelling out electromagnetic interference (EMI) from external sources (e.g. Cross talk on old telephone systems,) Twisting changes the relative position of the cables. Can transmit both analogue and digital. Less expensive than coaxial cable, and fibre. “CAT 5” 100Mz 10/100BASE-T Most commonly used medium in telephone network. Two types: UNSHIELDED TWISTED PAIR (UTP) CABLE SHIELDED TWISTED PAIR (STP) CABLE Twisted Pair UNSHIELDED TWISTED PAIR SHIELDED TWISTED PAIR (STP) CABLE (UTP) CABLE Set of twisted It offers protective pairs of cable sheathing around within a plastic the copper wire. sheet Provides better Transmission rate performance at of 10-100Mbps Least expensive lower data rates. Not commonly Maximum cable used segment is Installation is 100meters Very flexible and easy Distance is only easy to work Uses RJ-45 100-500 meters Special connector Most susceptible connecters are required. to electrical Also suffers from inference or cross outside talk interference. Twisted Pair Less expensive than coaxial cable, and fibre. Easy to Install & Maintain. Most widely used. Low Bandwidth Noisy (interference). Easy to install. Covers less distance. Co-Axial Cable It is an electrical cable invented by Oliver Heaviside in 1880 The cable consists of two conductors:- 1. The inner conductor is encased in insulation 2. The outer conductor is a mesh that acts as a shield that blocks electrical interference. The distance between the two conductors and the insulation material used greatly affects the properties of the cable, referred to as “impedance”. Co-Axial Cable Applications:- 1950’s Used for Submarine cables Late 1960s Use in Data Processing 1980-1987 LANs Used for both analogue and digital data transmission Common in Cable television networks Co-Axial Cable Low circuitry cost Simple circuitry Higher security High noise immunity Speed is good, but not for large data traffic Light weather sensitive Short range only Fibre Optic Cables It is a light pipe which is used to carry a light beam from one place to another. They may be single, but often they are bundled together in centre of cable Fibre Optic Cables Communications systems that carry information through a guided fibre cable are called fibre optic systems. Use of optical fibres to replace conventional transmission lines and microwave wave-guide in telecommunication systems. Light is effectively the same as RF (Radio Frequency) radiation but at a much higher frequency, theoretically the information-carrying capacity of a fibre is much greater than that of microwave radio systems. They are not electrically conductive:- very suitable for use in areas where electrical isolation Fibre Optic Cable Design  The core and cladding act as an optical wave-guide.  Core - it is a transmission area of fibre.  typical core diameters range from 50 to 500 nm  Cladding:  it surrounds the core and has a different index of refraction than the core.  it defines the optical boundary of the core and makes sure that total internal reflection occurs at the core outer skin. Fibre Optic Transmission Fibre Optic Construction Best fibre optic cable use Glass, or Silica - Silicon Dioxide (SiO2) – which is very pure ÞAttenuation is low Attenuations is caused by absorption (impurities in the material) and absorption of material at certain frequencies. If light travelled over 10km of cable 10% of the signal would arrive at the following end (90% attenuation) By contrast, if light travelled over regular window glass, it would attenuate by 90% in as little as under 50 meters. Fibre Optic Modes Multi Mode Multimode use multiple light paths Causes modal dispersion Single Mode Single mode use single light path Shorter distances Greater bandwidth Modal Dispersion (Multimode) Single Mode (Monomode) Fibre Optics Advantages: Disadvantages: Thinner Expensive to Higher Carrying maintain. Capacity (≈ The termination of a 100Mbps) fibre optic cable is Less Signal complex and Degradation requires special Non-Flammable tools. Light Weight Need Repeaters No electromagnetic over long distances (every 2km) interference They are more High Security Fibre Optic Transmission Typical Uses: Long Distance Telecommunications (High Bandwidth) Local Area Networks (typically Token Ring Networks) Cable TV & Broadband to the History of Fibre Optics: home The “Light Fountain” or “Light Pipe:- CCTV First demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s Unbound Mediums Unbound mediums use the Electromagnetic Spectrum Radio Microwaves Infrared (IR) Light X-Rays In general, the greater the frequency the more data can be transmitted per second (throughput) Microwave Point2Point Line of Sight transmission (Point to Point) High Frequencies => More Data Microwave links are commonly used by television broadcasters to transmit programmes across a country, for instance, or from an outside broadcast back to a studio. Affected greatly by environmental constraints, including rain fade. Have very limited penetration capabilities through obstacles such as hills, buildings and trees (Line of Sight) Infrared (IR) Point2Point Line of Sight transmission (Point to Point) High Frequencies => More Data Used for short range communication. Have very limited penetration capabilities through obstacles such as hills, buildings and trees (Line of Sight) => Used normally for indoor. Low cost simple circuitry High noise immunity Light sensitive Short range only Less common with the advent of WiFi Satellite In a geostationary or geosynchronous (the satellite always appears at the same position above the Earth) orbit 35,000km above the earth’s surface. Used for a large collection of interconnected, high-capacity, commercial, government, and academic data routes and core routers that carry data. Connecting with other countries and continents around the world. Comparisons Evaluation Factors... What are the factors that determine which medium to use? Evaluation Factors... What are the factors that determine which medium to use? Cost Bandwidth required? Delay (Latency) – important for real-time critical data. Ease of installation Ease of Maintenance Life expectancy