Presentation on theme: "Train IT – Computer Networks University of Debrecen"— Presentation transcript:
1Train IT – Computer Networks University of Debrecen Train IT - Networks1Debrecen, 2012.
2I. – Basics of Computer Networks Train IT - Networks2Debrecen, 2012.
3Computer Networks Computer Networks : Two or more computers linked together with some software and hardware tools for an information transmission related purpose.Objectives:Sharing resources.Increasing reliability.Increasing speed.Human communication.Train IT - Networks3Debrecen, 2012.
4Classification of Computer Networks Based on their Sizes Range< 1m1 km10 km100 km <NameMulticomputerLocal Area Network (LAN)Metropolitan Area Network (MAN)Wide Area Network (WAN)Train IT - Networks4Debrecen, 2012.
5Components of LANs Computers Network cards Peripherals Network transmission linesNetwork devicesTrain IT - Networks5Debrecen, 2012.
6Functions of WANs Covering large geographical area Providing (real-time) communication between usersNonstop access to remote resources that can be connected to local servicesProviding , internet, file transfer, and e-commerce servicesTrain IT - Networks6Debrecen, 2012.
7Accessibility of Networks Public Network: A network that is accessible for everyone (eg. Internet).Private Network: A network that is accessible only for the owner organization (expensive for large networks).Virtual Private Network(VPN): A private network that provides private type access and data transfer via public infrastructure (eg. Internet).Train IT - Networks7Debrecen, 2012.
8Computer Network Node Node: Device with own network address. It can communicate independently (eg. computer, printer, router).In a communication a node can act either as a transmitter (sender, source) or as a receiver (destination).Categories of network devices and tools:End user node: computer, printer, scanner, and any other devices that provide services directly to the userNetwork linking/connecting tools: devices that enable communication between end user nodes by connecting them to each otherTrain IT - Networks8Debrecen, 2012.
9Signal, Signal Coding, Modulation Signal: Physical quantities, depending on place and time, and carrying information. Information carrier on the communication chanel, it could be analog or digital.Signal Coding: Mapping the (digital) information onto the (digital) carrier signal (eg. voltage levels, changing of voltage levels).Modulation: Mapping onto analog carrier signal. The process of creating the (modulated) signal to be transmitted through the chanel from the modulating signal coming from the source and the analog carrier signal. The inverse process is the demodulation. A modem performs modulation and demodulation, as well.Train IT - Networks9Debrecen, 2012.
10Transmission Media, Chanel, Collision Device or material on which the transmission of information (signal) is performed. (Eg. twisted-pair cable, coaxial cable, fiber-optic cable, or air).Transmission chanel:Data path, frequency band for transmitting signals. Usually, in a transmission media multiple chanels (data path) are formed.Collision:A collision occurs when two (or more) nodes transmit information at the same time on a common transmission chanel.Train IT - Networks10Debrecen, 2012.
11Transmission SpeedTransmission speed (network speed, bandwidth, bit rate):Amount of information transmitted during a time unit. Measure of unit: bit/sec, b/s, bps.The throughput measured in applications is always lower than the physical bandwidth.Larger units:1 Kbps = 1000 bps1 Mbps = 1000 Kbps1 Gbps = 1000 MbpsTrain IT - Networks11Debrecen, 2012.
12Connections of Data Transmission Peer-to-peer (Point-To-Point) connection:The propagation of information performed between two points (a transmitter and a receiver) is called a peer-to-peer connection.Multipoint connection, broadcasting:A transmitter provided information to multiple receivers is called a multiple nodes connection. Broadcasting is a multiple nodes connection, where all receivers get the information inside a given range (eg. radio broadcasting).Train IT - Networks12Debrecen, 2012.
13Directions of Information Transmission One way (simplex) connection:The transmission of information allowed only one way is called a one way (simplex) connection (eg. radio broadcasting).Alternate way (half duplex) connection:The transmission allowed both directions, but only one direction at a time is called a half duplex connection (eg. CB radio).Two way (full duplex) connection:The traffic allowed in both directions simultaneously is called a full duplex connection (eg. telephone).Train IT - Networks13Debrecen, 2012.
14Basics of Addressing Unicast (Unique) address: An identifier, assigned to a network interface of a node.Broadcast address:An address, identifying all nodes (and interfaces of nodes) in a so called broadcast domain.Train IT - Networks14Debrecen, 2012.
15Computer Network Protocol The formal description of all rules and conventions which determines the communication of the network devices (nodes) (set of communication rules).Train IT - Networks15Debrecen, 2012.
16Server-Client Architecture Server: A network node (and software) which provides services for other nodes. The service of a server is ensured by a server-software (eg. a web-server).Client: A network node (and software) which has some kind of network service demand. For recourse to the service the client uses a client-software (eg. web browser).The communication between the server and the client is described by a high level protocol (eg. http) .Train IT - Networks16Debrecen, 2012.
17Layered Network Architecture Train IT - Networks17Debrecen, 2012.
19Layered Network Architecture - Concepts Layer N protocol:A protocol which describes the specifications of layer (level) N.Peers:Entities which located on the same level of the two communication endpoints (nodes). In some logical way the peers communicate each other by the help of the corresponding layer protocol.Layer N/N+1 interface:Connection of boundary surface of layers N and N+1.Service of Layer N:Set of actions (services) which are provided to layer N+1 by layer N (through the interface).Train IT - Networks19Debrecen, 2012.
21Network Communication - Concepts Encapsulation:Packaging the information arrived from a higher level with a header of a specific protocol (it is similar when a surface mail letter is put in an envelope and the envelope is addressed).Protocol Data Unit (PDU):Entity (contains header and data) handled by the considered protocol. (It is frequently mentioned as packet.)Train IT - Networks21Debrecen, 2012.
22Encapsulation - Example Pictures and text are transformed into data.Data are packaged into segments.The data segment is encapsulated into a packet containing the addresses (IP addreses) of the source and destination nodes.The packet is encapsulated into a frame containing the physical address (Ethernet address) of the next device connected directly.The frame is transformed into series of bits (ones and zeros) which can be transferred through the transmission media.Train IT - Networks22Debrecen, 2012.
23OSI Reference Model Layer Name of PDU 7 Application Layer APDU 6 Presentation LayerPPDU5Session LayerSPDU4Transport LayerTPDU, Segment3Network LayerPacket2Data Link LayerFrame1Physical LayerBitTrain IT - Networks23Debrecen, 2012.
24Mapping of TCP/IP - OSI Model OSI LayersTCP/IP Layer7Application LayerApplication Layer6Presentation LayerNot present in theTCP/IP model5Session Layer4Transport LayerTransport Layer3Network LayerNetwork Layer2Data Link LayerHost-to-Network Layer1Physical LayerTrain IT - Networks24Debrecen, 2012.
25Hybrid Reference Model 5Application Layer4Transport Layer3Network Layer2Data Link Layer1Physical LayerTrain IT - Networks25Debrecen, 2012.
26Network Interconnection Devices Train IT - Networks26Debrecen, 2012.
27Network Interconnection Devices - Basics Collision domain; Bandwidth domain:Part of a network , where collisions can be detected (a common communication channel that is shared by multiple nodes).In a collision domain only one information transmission can be performed at a time.Broadcast domain:Part of a network, where information transmitted with a broadcast destination address can be detected.Train IT - Networks27Debrecen, 2012.
28Network Interconnection Devices Subnetworks – based on the functionality of network interconnection devices – can be connected in different OSI Layers:OSI layerConnector itemAbove Transport LayerGatewayNetwork LayerRouterData Link LayerBridgePhysical LayerRepeaterTrain IT - Networks28Debrecen, 2012.
29Network Interconnection Devices Repeater:Amplifies and repeats the signals sent on transmission media.Does not separate the connected subnetworks.Repeater with multiple ports is called a HUB.Bridge:Working in Data Link Layer it performs selective connection.The interconnected subnets form separate collision domains.Usually transmits the broadcast messages towards all interconnected subnets.Train IT - Networks29Debrecen, 2012.
30Network Interconnection Devices Switch:A multiple port device with bridge functionality between any two ports.Router:Working in Network Layer it performs selective connection, routing, and traffic control.The interconnected subnets form separate collision domains and separate broadcast domains.It is a node with own IP address.It is also called a gateway in the Network Layer (default gateway).Train IT - Networks30Debrecen, 2012.
32Topologies Physical topology: Investigates the placement of nodes and their connection possibilities. (Cable topologies, Physical topologies).Logical topology:Investigates the logical sequence and order of nodes.Train IT - Networks32Debrecen, 2012.
33Physical Topologies Star (extended star) Ring Host (workstation or server)CenterRingTrain IT - Networks33Debrecen, 2012.
34Physical Topologies Bus Repeater Train IT - Networks 34 Debrecen, 2012.
35Physical TopologiesTreeTrain IT - Networks35Debrecen, 2012.
36II. – Physical LayerTrain IT - Networks36Debrecen, 2012.
37Electricity - Basics Electricity is the free flow of electrons. Materials highly restraining the flow of electrons are called insulators. Materials slightly restraining the flow of electrons (free of resistance) are called conductors.Semiconductors are able to control accurately the conducted electricity.The resistance is denoted by R, the measure of unit is ohm, (Ω)The current is the quantity of electric charge through a circuit in a second. It is denoted by I, the measure of unit is ampere (A)The voltage is an electronic force or pressure which arises at separation of electrons and protons. It is denoted by U, the measure of unit is volt (V)Ohm’s Law: U=I*RTrain IT - Networks37Debrecen, 2012.
38AttenuationThe amplitude of a signal is decreasing during its way in a transmission media.The length of a transmission media is determined such a way that the signal should be interpreted securely by the receiver.If large distance has to be covered, the signal has to be restored by the help of amplifiers (repeaters).The attenuation depends on frequency, thus the amplifiers have to compensate this with frequency dependent amplification.The quantity of attenuation and amplification is expressed in decibels (dB) on a logarithmic scale.Train IT - Networks38Debrecen, 2012.
39Attenuation of Guided Media Twisted pair303/8” coaxialcable10Attenuation (dB/km)3Opticalfiber10,31 kHz1 MHz1 GHz1 THz1000 THzFrequencyTrain IT - Networks39Debrecen, 2012.
40Twisted Pair Four pairs are typically grouped in a plastic sheath. The grouped pairs can be shielded (Shielded Twisted Pair, STP) or unshielded (UTP).Train IT - Networks40Debrecen, 2012.
41Twisted Pair– Physical Characteristics The cheapest and most commonly used transmission media.Two insulated copper conductors are twisted according to a regular pattern.Usually several pairs are grouped (UTP has 4 pairs) and protected with a plastic sheath.Number of twists decreases crosstalk between pairs and ensures noise protection.The length of twists might be different in pairs in order to decrease crosstalk.The diameter of conductor is mm .It is the cheapest media, easy to use but the data transmission speed and the distance to be covered are highly limitated.Train IT - Networks41Debrecen, 2012.
42Twisted Pair– Transmission Characteristics The attenuation of twisted pairs is highly dependent on frequency.It is sensitive to interference and noise. For example easily takes the 50Hz energy from the parallel AC network.A shield can be used against disturbance (STP, FTP).Crosstalk between neighbour pairs can be decreased by variable twist length.With a point-point analog signals a frequency bandwidth of cca. 100KHz can be obtained (transmission of multiple voice channels).For short distance over 100 Mbps speed can be achieved.Train IT - Networks42Debrecen, 2012.
43Types of Twisted PairsCategory 5. UTP cable and connector for 100 MHz transmission.For limited distance (100 meters) it provides 100 Mbps speed transmission. Cabling of new buildings usually is done with this cable.New standards: Cat5e – enables simultaneous use of the 4 pairs,Cat6: ~250MHz; Cat7 STP: ~600MHz.)STP: Twisted pairs are shielded separately.FTP: Twisted pairs has a common shield cover (foil) . (It is cheaper than STP, and better than UTP.)Train IT - Networks43Debrecen, 2012.
44Twisted Pair with RJ-45 Connector Train IT - Networks44Debrecen, 2012.
45Assignment of Contacts of RJ-45 Connectors Straight RJ-45 female (PC, Router):Tx+ Tx- Rv+ Rv-Cross RJ-45 female (Switch, Hub):Rv+ Rv- Tx+ Tx-RJ-45 females with same assignment (eg. pc-pc, hub-hub) are connected with a crossover cable (568A – 568B).The different RJ-45 females (eg. pc-hub, pc-switch, router-switch) are connected with a straight-through cable (568A – 568A or 568B – 568B).Certain devices can detect the assignment of RJ-45 female on the other side, and are able to handle it automatically (auto sense).Train IT - Networks45Debrecen, 2012.
46Coaxial Cable– Physical Characteristics Cross section of a coaxial cableInner conductorOuter coverInsulationOuter conductorDiameter of the cable: mm.Due to the concentric structure, it is less sensitive for interference and crosstalk, than the twisted pair.It can be used for larger distance and in multipoint application supports more stations, than the twisted pair.Train IT - Networks46Debrecen, 2012.
47Coaxial Cable Applications Transmission of television broadcasting. Large distant telephone transmission.Connection of computersLocal networks.Transmission characteristicsIn case of analog transmission, amplifiers are required in every several km. It can be used up to 400 MHz.In case of digital transmission amplifiers are required in every km.Train IT - Networks47Debrecen, 2012.
49Optical Fiber– Physical Characteristics CladdingCoreProtecting coverAngle ofincidencereflectionA light ray incidentbelow the critical angleis absorbed in thecladdingTrain IT - Networks49Debrecen, 2012.
50Optical Fiber– Physical Characteristics A floppy optical fiber with μm of diameter is able to transmit light ray.Optical fiber is made of glass or plastic.The cladding is also made of glass or plastic, but it has different optical characteristics than the core.The outer plastic cover protects against impurities, wearing, and other outer effects.Train IT - Networks50Debrecen, 2012.
51Optical fiber- Advantages Applications (benefits):Larger capacityHigh transmission speed can be achieved (2 Gbps in10x km).Smaller size and weightSmaller attenuationThe attenuation is smaller, and it is constant at a wide frequency range.Electromagnetic isolationNot sensitive for outer electromagnetic effects, there is no crosstalk. Does not emit energy, thus it can not be intercepted. It is difficult to tap an optical fiber.Larger repeating distanceSmaller the number of repeaters is, smaller the possibilities of errors and the costs are.Technology keeps developing. Eg. 3.5 Gbps transmission speed over 318 km without any amplifier (AT&T, 1990).Train IT - Networks51Debrecen, 2012.
52Optical Fiber Applications Big city trunks Long-haul country trunks Telephone center trunksSubscriber loopsLocal area networksTransmission characteristicsWorks in Hz (infrared) domain.3 versions are used:multi modesingle modemulti mode graded indexPossible light sources:LEDLaser diode.Train IT - Networks52Debrecen, 2012.
53Types of Optical Fibers Transmission characteristicsMulti mode fiberLight rays coming with different angles from light source are reflecting in different angles at the boundary of the two materials, thus they travels different distances during different time. So light impulses will be distorted. Consequently, the data transmission speed is decreasing.Single mode fiberDecreasing the diameter of core, only rays paralell with fiber axis will pass through the fiber. Light impulses will not be distorted, higher data transmission speed can be achieved.Multi mode graded index fiberThe refractive index of core material is increasing when the radial distance from the fiber axis become larger. Due to this property the light rays will be focused. The characteristics of this type can be placed between the two other types.Train IT - Networks53Debrecen, 2012.
54Types of Optical Fibers Optical sourceOptical detectorMulti modeMulti mode graded index fiberWavelength and diameter of fiber 3 – 10 μmSingle modeTrain IT - Networks54Debrecen, 2012.
55Wireless Transmission Propagation and detection of electromagnetic signals are performed by antennas.The two ways of broadcasting:DirectedOmnidirectional (not directed)In directed case the antenna radiates a focused electromagnetic ray. The receiver antenna should be positioned very precisely.The omnidirectional radiation can be received with multiple antennas.Signals with higher frequency can be focused better.Three frequency ranges can be used for wireless transmission:GHz (microwave transmission) (directed)30 MHz - 1 GHz (radio frequency) (omnidirectional)Hz (infrared)Train IT - Networks55Debrecen, 2012.
56WAN TechnologiesTrain IT - Networks56Debrecen, 2012.
57WAN Cabling Technologies Serial connections: provide reliable, long-distance communicationsISDN: For dial-based on demand services or spare connectionsDSL: For achieving a T1/E1 (1, ,048 Mbit/s) speed via telephone lineCable modem connection: Cable providers use the coaxial TV-cables. The coaxial cables are appropriate for achieving high-speed connections. These speeds can even be higher, than the speed of the DSL-accessesThese technologies require specific transmission media and connectors.Train IT - Networks57Debrecen, 2012.
58Technical Structure of ADSL Subscriber sideNetwork sideDSLAMCPEFilterDatanetworkATM BackboneADSL NTTelephone centerPhone network PTSNPOTS or ISDN PhoneComputerTrain IT - Networks58Debrecen, 2012.
59WAN Technologies WAN connection ISDN concepts, equipements Serial or smart-serial ports of router can be used.Connection based on clock signal:Data Communication Equipment (DCE, provides clock signal eg. modem, CSU/DSU).Data Terminal Equipment (DTE, eg. router)ISDN concepts, equipementsTE1 Terminal Equipment 1ISDN compatible device, connecting to NT1 or NT2.TE2 Non ISDN compatible device, connecting to TA.TA Terminal AdapterConnects a non ISDN device to an ISDN network.NT1 Connects a 4-wire ISDN to a 2-wire ISDN (2-wire connects to CO).NT2 Connects different „subscriber devices” to NT1 (switching and connectivity)Train IT - Networks59Debrecen, 2012.
60III. – Data Link Layer LAN Data Link Layer Solutions Train IT - Networks60Debrecen, 2012.
61The IEEE 802 protocol family IEEE LAN StandardsIEEE802Logical Link ControlMedium Access ControlPhysical802.3802.4802.5802.2Network LayerTransmission mediaPhysical LayerData link LayerISOreferencemodel802.2 = Logical Link Control Protocol802.3 = CSMA/CD802.4 = Token bus802.5 = Token ringMedia accessprotocolsThe IEEE 802 protocol familyTrain IT - Networks61Debrecen, 2012.
62Ethernet (CSMA/CD)Train IT - Networks62Debrecen, 2012.
63Ethernet – Physical Technologies 10BASE-T: transmission speed 10 Mbit/s, type of transmission is digital, T refers to using a twisted pair). Maximum cable length is 100m.10BASE-2: transmission speed 10 Mbit/s, type of transmission is digital, no. 2 refers to the maximum 200 of segment size. A 10BASE2 segment contains up to 30 station.10BASE-5: transmission speed 10 Mbit/s, type of transmission is digital, no. 5 refers to the 500 meters maximum distance of signals transmitted to.rule:Five segments of transmission media (max meter).Four repeater or hub.Three segments for connecting stations.Two connector segment without any station.One large collision domain.Train IT - Networks63Debrecen, 2012.
64Ethernet Frame Format 7 bytes: 7 x ‘10101010’ (Synchronization) Preamble7 bytes: 7 x ‘ ’ (Synchronization)Start of Frame1 byte: ‘ ’Direction oftransmissionDestination address6 bytes: 1-3 bytes ID of manufacturer,4-6 bytes offsetSource address6 bytes: 1-3 oktet ID of manufacturer,4-6 offsetLength/Type2 bytesDatabytesbytes: minimum frame length is 64 bytesPad (if necessary)CRC4 bytesIEEE / Ethernet frame formatTrain IT - Networks64Debrecen, 2012.
65Ethernet Parameters of functionality Transmission speed 10 Mbps (Manchester kódolás)Slot time bit-timeGap time 9,6 sMax. no. of transmission frames 16Jam size 32 bitsMaximum frame lenght byteMinimum frame length 512 bits (64 bytes)Destination address can beExact address of a stationAll bits are ‘1’ : broadcast, message is sent for all stations.Source address must not be a multiple address!Train IT - Networks65Debrecen, 2012.
66Ethernet Frame Transmission (CSMA/CD) Waiting for frame to be transmitted.Formatting the frame.Is the chanel busy?INWaiting the gap time.Starting transmissionIIs there a collision?NSending JAM signals.Increasing the number of trials.Complete transmission..IMax. number of trialsis reached (16)?Indicating of reachingthe maximum numbers of trialsNComputing the delay andwaiting a random time period.Functionality of MAC sublayer: transmitting framesTrain IT - Networks66Debrecen, 2012.
67Ethernet Frame Transmission Determining the time of repeated transmission of a frame:The slot time or round-trip delay is twice the time it takes for the first bit of frame to travel the length of the maximum distance between two nodes. During this time tne nodes detect the collisions almost surely. (Cable delay: ~5μs/1000m.)Slot time = 2 * (cable delay + repeaters delay)+ reserve timeSlot time = 51.2 μs (2 * (2.5 km + delay of 4 repeaters), transmission time of 512 bits)Waiting time is the multiplication of slot time with a random integer, which depends on the number of transmission trials:1 collision 1 Waiting randomly 0 or 1 slot time2 collisions Waiting randomly 0, 1, 2 or 3 slot times3 collisions Waiting randomly 0, 1, 2 …7 slot times.10 collisions Waiting randomly 0 – (210-1) slot times11 collisions - ” -. - “ -15 collisions - “ -After 16 collisions the interface card does not try any more time. It indicates that the transmission failed.Train IT - Networks67Debrecen, 2012.
68Receiving an Ethernet Frame Is there any incoming signal?NIIndicating the busy state of chanel.Bit synchronization, waiting for theframe delimiter.Reading the frame.NCRC and frame lengt are OK?IDest. addr = own addr.or a broadcast addr.?NIForwarding the frame to a higherprotocol layer for processingDiscarding the frame.Functionality of MAC sublayer: receiving framesTrain IT - Networks68Debrecen, 2012.
69Fast Ethernet (802.3u) Goal of developement: For 10 Base T Ethernet(IEEE 802.3) 10 times transmission speed,Preserve the cabling system,Keep the MAC method and the frame format.Major part of 10 Base T networks were connetcted to repeater with cables less than 100m. So the distance between two stations is at most 200m. In case of 100 Mbps transmission speed the outermost stations can detect collision, too during the time of 512 bits data transmission.Thus, shortening the maximum lenghts the method of CSMA/CD MAC can be retained.The standard:100BASE-TX can reach 100 Mbit/s transmission speed in half-duplex mode, and 200 Mbit/s in full-duplex mode.100BASE-FX separate transmit (Tx) and receive (Rx) lines together ensure 200 Mbit/s transmission speed.Train IT - Networks69Debrecen, 2012.
70Fast Ethernet (802.3u) 100 Base X (100BaseTX, 100BaseFX) It was designed for divverent media (X):Category 5 unshielded (UTP) cable,Category 5 shielded (STP) cable,Optical fiberThe 4B5B (4B/5B) binary coding developed for FDDI networks was adapted for 100 Base X.Every 4 bits of data (nibble) is coded on 5 bits. Only those 5-bit symbols are used, where exist at most two adjacent ‘0’ bits.The guaranteed 2 bit signal transmit ensures a good bit synchronizing.The 100BASE-TX version performs first 4B/5B coding, then performs shuffling and multi-level transmit, (MLT-3) coding.Train IT - Networks70Debrecen, 2012.
714B/5B binary coding 4B5B codes Data symbols Control symbols 0000 11110 IDLE 11111J 11000K 10001T 01101R 00111S 11001QUIET 00000HALT 001004-bitdata group5-bitsymbol4B5B codesTrain IT - Networks71Debrecen, 2012.
72Gigabit Ethernet (802.3ab, 802.3z) 1000BASE-TX: – for Cat5e UTP cable(802.3ab).A Cat5e cables can reliably reach up to 125 Mbit/s transmission speed.For Gigabit bandwidth all of 4 wires is used .Hybrid cirtuits are required, which enable duplex transmission on a single pair. Thus the bandwidth increased up to 250 Mbit/s.The required 1000 Mbit/s speed can be achieved by applying the four pairs.1000BASE-SX: 850 nm laser or LED sources on a multi mode optical fiber. It is not so expensive and suitable for short distances.1000BASE-LX: 1310 nm laser sources on a single or multi mode optical fiber. Using laser on a single mode optical fiber the signals can be transferred even a distance of 5000 m.Separate optical fibers are set for transmitting (transmit, Tx) and for receiving (receive, Rx). The connection originally has duplex characteristics.Train IT - Networks72Debrecen, 2012.
73Ethernet - TimingAt Ethernet transmisson, each transmission has to be at least the length of slot time.The slot times can be calculated by the largest regular network architecture and the longest allowed cable parts.For a 10 and 100 Mbit/s speed Ethernet the slot time is 512 bit ie. 64 byteFor a 1000 Mbit/s speed Ethernet the slot time is 4096 bit, ie.512 byteIn case of collision detection a32 bit congestion signal has to be usedThe minimum gap between two non-colliding frames is called Frame gapOn a10 Mbit/s speed Ethernet network after sending a frame each node has to be wait at least the time of 96 bits (9.6 microsecundum)In case of collision, each node – waiting the time of frame gap– leaves the cable idleTrain IT - Networks73Debrecen, 2012.
74Ethernet SwitchingTrain IT - Networks74Debrecen, 2012.
75Ethernet - Segmentation A collision domain occurs when multiple computers are connected to the single, shared transmisson media (line).Devices in second layer divide the collision domains. These devices control the transmission of frames by Mac-addresses assigned to the Ethernet devices. Second layer devices are the bridges and switches.The devices in second and third layers do not transmit collisions. The collision domains are divided smaller domains by the third level devices, as well.Train IT - Networks75Debrecen, 2012.
76Ethernet – SwitchesA switch is essentially a fast speed bridge (in 2. layer) with multiple ports.Each port forms a separate collision domain. (Eg. A 24-port switch forms 24 separate collision domains.).Switches for each port stores the Ethernet addresses (Mac addresses) of the accessible devices from that port in a table (switching table).Switches upload and maintain their switching tables dynamically (based on the source addresses of incomingframes).The switching table is stored in a content-addressable memory (CAM).A CAM memory works reverse way compared to a common memory: if you enter a data (Ethernet address), the output will be the corresponding memory address. By the help of CAM, switches are able to find the port corresponding to a given MAC address without using any search algorythm.Train IT - Networks76Debrecen, 2012.
77Ethernet SwitchingThe switch looks for the destination address of the incoming Ethernet frames in its switching table:If the destination address is a broadcast address (48 times ‘1’ bit value), then the frame will be transmitted on each port (except the incoming port).If the destination address can not be found in the switching table, then the frame will be transmitted on each port (except the incoming port).If the destination address can be found in the switching table, then the frame will be transmitted on the corresponding port (assuming, that this port is not identical with the incoming port of the frame).Train IT - Networks77Debrecen, 2012.
78Ethernet Switching Switching methods: Store-and-forward: Transmission of the frame will start after the whole frame has been arrived. The switch recomputes the frame checksum (FCS). If the frame is corrupted, it is discarded.Cut-through switching: After arriving the destination address (6 bytes), the transmission of frame starts immediately on the outgoing port.Fragment free switching: After arriving a minimum frame length (64 bytes), the transmission of frame starts on the outgoing port. (Collided frames will not be transmitted.)Train IT - Networks78Debrecen, 2012.
79IV. – Network LayerTrain IT - Networks79Debrecen, 2012.
80The IP Network Protocol IP (Internet Protocol) RFC 791The network layer protocol of TCP/IP reference model.Widely used, it is the basic element of Internet.Most important characteristics:Structure of IP header.Consists of 32-bit words.Length: Minimum 5, maximum 15 words.IP addressing, address classes.Fragment supporting.Datagram services towards Transport Layer.Ethernet frame type value: 0x0800.Train IT - Networks80Debrecen, 2012.
81Structure of Internet Protocol Type of serviceVersionIHLWhole lengthDFMFIdentifierFragment offsetUpper LayerprotocolTTLHeader checksumSender (Source) IP addressReceiver (Destination) IP addressOptional field(s)Train IT - Networks81Debrecen, 2012.
82IP Addresses Identifies the node in Network Layer. Dotted decimal notation egManaging identifiers – InterNIC, IANA.For organisations not unique addresses but address domains (network identifiers) are assigned.The first part on an IP address identifies the network, the second part identifies the node (inside the network).The IP routing based on the network identifiers.How many bits should be in network IDs?If too small, the large domains will be unused.Il too large, only small subnetworks can be handled.Train IT - Networks82Debrecen, 2012.
83Classes of IP Addresses Bit#1724Class ANetwork #Host #Bit#111416Class B1Network #Host #Bit#111218Class C11Network #Host #Train IT - Networks83Debrecen, 2012.
84The Rule of the first byte Leading bit(s)Value of 1st byteClassA10B110CTrain IT - Networks84Debrecen, 2012.
85Network mask Network mask (netmask): A 32 bit mask, which contains bits with values of 1 in place of network and subnetwork identifiers, and bits with values of 0 in place of host identifiers.By the help of netmask the boundary of network-machine can be modified, which boundary originally was determined (static way) by the classes.Prefix length:The number of value 1 in the netmask (number of network identifier bits in the netmask).Train IT - Networks85Debrecen, 2012.
86Default Network Masks Network masks belonging to each classes: Class A :Network mask: Prefix lenght: 8.Class B :Network mask : Prefix lenght: 16.Class C:Network mask : Prefix lenght: 24.Train IT - Networks86Debrecen, 2012.
87Special IP addressesNon specificated hostBroadcast on actual networkNetwork …ID of the specific networkNetwork …Broadcast on the specific networkAnythingLoopbackTrain IT - Networks87Debrecen, 2012.
88Data Link and Network Addressing Problems Train IT - Networks88Debrecen, 2012.
89Problems of Dual Address Classes In Network and Data Link Layers two independent address classes (IP addresses and Ethernet addresses) are considered.For encapsulation of Data Link Layer (forming an Ethernet frame) the physical address (MAC address) belonging to the IP address has to be determined.In certain cases (eg. Network boot, central IP address assignment) it could be necessary to determine the IP address by the help of Ethernet address.Train IT - Networks89Debrecen, 2012.
90Network Address -> Physical Address (ARP) ARP (Address Resolution Protocol) RFC 826Each node records physical addresses belonging to the network addresses in a table (ARP table).How get a new data (pair of addresses) into the table?1. Broadcasted ARP question: Who knows the physical address of the network address X?2. Each node of of subnet receives and processes the frame of the question by a broadcast message.3. If a node ‘identifies itself’ with network address X, sends an answer to the ARP question with own physical address.Train IT - Networks90Debrecen, 2012.
91Structure of ARP Frame Type of hardware Type of protocol Length of ph. add.Lenght of net. add.Action codePhysical address of senderPhysical address of senderIP address of senderIP address of destinationIP address of destinationPhysical address of destinationPhysical address of destinationWords 1 - 2: General ARP header.Words : IPv4/Ethernet-specific data segment.Ethernet frame type value: 0x0806Train IT - Networks91Debrecen, 2012.
92Physical Address -> Network Address (RARP) RARP (Reverse Address Resolution Protocol) RFC 903It is needed only in special cases (eg. network boot).The RARP server(s) records the network addresses belongig to physical addresses in a table (RARP table).The table is maintained by the system administrator.The assignment of physical address – network address is static.In case of more RARP servers, the same network address has to be assigned to a physical address on each RARP server (the assignment must not depend on servers).Train IT - Networks92Debrecen, 2012.
93Physical Address -> Network Address (RARP) RARP (Reverse Address Resolution Protocol) RFC 903Scheme of functioning:1. RARP question: Who knows the network address of the physical address X?2. Each node of of subnet receives the frame of the question by a broadcast message.3. The RARP servers process the question: If the physical address X is found in their tables, send an answer for RARP question with the network address found in tables.Train IT - Networks93Debrecen, 2012.
94Physical Address -> Network Address (BOOTP) BOOTP (BOOTstrap Protocol) RFC 951The RARP works within only one broadcast domain.The BOOTP is an IP/UDP-based protocol, where the client and the server could be in different broadcast domain.Phases of boot based on BOOTP:Determine IP address.Download Boot file (not investigated).Working scheme is the same as RARP.BOOTP agent – boot support through a router.Train IT - Networks94Debrecen, 2012.
95Physical Address -> Network Address (DHCP) DHCP (Dynamic Host Configuration Protocol) RFC 1531Allows assignment of IP address domain.In case of more DHCP servers, the handled address domains should not overlep (in default).Packet structure similar to BOOTP.Clients get the IP address for a (renewable) time period.Train IT - Networks95Debrecen, 2012.
96Physical Address -> Network Address (DHCP) DHCP (Dynamic Host Configuration Protocol) scheme of functioning :1. DHCP question: Who can give me an IP address? (DHCPDISCOVER)2. Each node of of subnet receives the frame of the question by a broadcast message (DHCP relay agent).3. A DHCP servers process the question: If there is a free IP address in the handled address domain, then send an answer to DHCP question with that IP address. (DHCPOFFER)4. The client chooses one from the received DHCP answers, and sends a feedback of its choice to the corresponding DHCP server. (DHCPREQUEST)5. The DHCP server „books” the choice of address (the address became occupied), and confirms client on booking. (DHCPACK/DHCPNAK)DHCPDECLINE: The assigned IP address by the server is invalid (in use).DHCPRELEASE: The client does not need for an IP address any more.Train IT - Networks96Debrecen, 2012.
98IP Subnets Why is it necessary to create subnets? The logical functionality of the institute can be a reason.On an IP network more than one broadcast domains (usually with the same size) have to be created.How can we create a subnet?Some of the higher position bits of the host ID of the IP address will be used identifying the subnet.The new network-node boundary is denoted with the network mask (longer prefix is used).Train IT - Networks98Debrecen, 2012.
99Subnets - Example Example: IP address of network: 184.108.40.206 Default subnet mask:3 bits are used identifying the subnet.Network mask:8 subnets can be created.Train IT - Networks99Debrecen, 2012.
100Subnets - Example Addresses of the subnets: No. Network ID Host Addresses220.127.116.11.18.104.22.168.Train IT - Networks100Debrecen, 2012.
101Subnet RoutingE2E0E1Destination IP address:Routing table:Destination Netmask Int. Next hop MetricEEETrain IT - Networks101Debrecen, 2012.
102Subnet RoutingDestination IP address :&Network mask:Train IT - Networks102Debrecen, 2012.
103IP Network Problems in ‘90s Train IT - Networks103Debrecen, 2012.
104The growth of Internet 90 January 90 April 90 July 90 October 92715251727206323382622308635564526Routing table sizes of IP backbonesTrain IT - Networks104Debrecen, 2012.
105Depletion of Internet Addresses Assignment status of classful addresses in 1992 (RFC 1466):Total Assigned Assigned (%)Class A %Class B %Class C %Train IT - Networks105Debrecen, 2012.
106Short Time solution: CIDR Train IT - Networks106Debrecen, 2012.
107Problems of Classful IP Addressing- CIDR The solution: CIDR (Classless Inter-Domain Routing) RFC 1519.Assigning continuous class C addresses (instead of class B).By the help of a network mask with a variable length the network-machine boundary can be shifted with arbitrary number of bits (supernetting) or right (subnetting).Forming address domain zones based on locations.Joined routing informations by the help of network masks.Giving the mask representation of network addresses is mandatory:<Network IP address, Network mask>Train IT - Networks107Debrecen, 2012.
108IP Address Domains of Continents The class C IP addresses are assigned based on the continents (sizes of routing tables can be reduced significantly) RFC 1366,1466:ContinentAddress domainEuropeNorth AmericaMiddle & South AmericaAsia, AustraliaTrain IT - Networks108Debrecen, 2012.
109Long Time solution: NAT Train IT - Networks109Debrecen, 2012.
110NATThe major part of nodes take part „only” as clients in communication.It is sufficient to provide for clients possibilities of access to services for clients.Application dependent solutions: Proxy, ALG.Non application dependent solutions : NAT, PATRFC , 2766, 3022.Train IT - Networks110Debrecen, 2012.
111NAT BasicsAddress realm: Part of a network, where the uniqueness of IP addresses has to be ensured.Public/Global/External Network: Address realm with address domain managed by IANA.Private/Local Network: Address realm with local, organizational addressing./ / /16Train IT - Networks111Debrecen, 2012.
112NAT, Address Realms – Principle of Function Local (private)address realmGlobal address realmPrivate IP addresses:/16/12/8AddressinginformationsLocal (private)address realmTrain IT - Networks112Debrecen, 2012.
115NAT Resources NAT solutions require resources (processor). Searching address transformation tables.Address exchange (port number exchange).Recompute checksums.There is no need to perform the computations for the whole PDU:„Substracting” the old addresses from the old checksums.„Adding” new addresses to the obtained result.Train IT - Networks115Debrecen, 2012.
116IP - RoutingTrain IT - Networks116Debrecen, 2012.
117Routing Basics Routing: Make decisions on the directions of transmitting packets (IP datagrams).Routing table:A table containing necessary informations for routing. Typical (most important) fields:Destination net Netmask Outgoing int. Next hop MetricTrain IT - Networks117Debrecen, 2012.
118Routing Basics Routed protocol: A general data transmission protocol belonging to Network Layer, which can be controlled by the router (eg. IP).Routing protocol:A protocol describing the propagation of necessary informations (exchange between routers) for building up routing table(s) (eg. RIP, OSPF, BGP).Train IT - Networks118Debrecen, 2012.
119Routing Basics Autonomous System (AS): The routing administration unit of a network, where a common routing strategy (routing protocol) works.Metric:Measuring method of the quality of a path resulted by a given routing process. Basically there are two categories (can be transformed into each other):Metric based on distance (cost).Metric based on goodness.Train IT - Networks119Debrecen, 2012.
120Basic Operations of Routers – Fitting IP Addresses 1./ The rows of the routing table is ordered descending by prefix length. N=1.This ensures, that in case of more than one matching lines the one with the longest prefix will be the result.2./ If the line N does not exist in the table, then there is no matching line.The router discards the packet. The algorythm is terminated.3./ A Bitwise AND operation is performed on every bit of the destination address of the packet and the network mask of line N.4./ If the result of this AND operation is identical with the address of destination network in line N, then the address matches line N.The router transmits the packet towards the direction in line N. End of algorythm.5./ N=N+1, continue with Step 2.Train IT - Networks120Debrecen, 2012.
121Classification of Routing Configurations Minimal routing:Fully isolated (without router) network configuration (eg. giving IP address and network mask).Static routing:The routing table is maintained by the system administrator (eg. giving default gateway).Dynamic routing:The routing tables are maintained by some routing protocol.Interior routing protocols (IGP - eg. RIP, OSPF).The main principle is to determine the „best path” with a method of distance vector or link state.Exterior routing protocols(EGP - eg. EGP, BGP).The aim is not necessarily to determine the best path (policy based routing - BGP).Train IT - Networks121Debrecen, 2012.
122Distance Vector Routing Train IT - Networks122Debrecen, 2012.
123Distance Vector Routing Basic principle of operation:The routers keep records for all accessible destinations (machine or network) how can a given destination be reached on the best path (direction and distance – distance vector).The routers exchange these information in a certain time period.Concerning the new information, the routers check whether there is any necessary modification regarding the previously known best path.Train IT - Networks123Debrecen, 2012.
124Distance Vector – Routing Table Problems Problem of too small initial value:If the optimal path is„corrupted” a path with larger cost (longer) can not replace it.Solution: Larger cost from the direction of optimal path overrides the (lower) cost.Problem of counting to infinity:In certain cases the procedure responds very slow to changing of topology.Train IT - Networks124Debrecen, 2012.
125Count to Infinity- Example 1101AD11BConsider the routing towards D.Starting routing entries (optimal paths to D):A: B,2B: D,1C: B,2Train IT - Networks125Debrecen, 2012.
126Count to Infinity- Example 1101AD1BConsider changing of routing tables in case of corruption of link B-D:A B,2 C,3 C,4 C,5 … C,10 C,11 C,11B --- C,3 C,4 C,5 … C,10 C,11 C,11C B,2 A,3 A,4 A,5 … A,10 D,10 D,10Train IT - Networks126Debrecen, 2012.
127Routing Information Protocol - RFC 1058 Characteristics of Routing Information Protocol (RIP):Distance vector based IGP protocol.Old, but continuously developed and enhanced.Metric: Number of hops (16=infinite distance).It can be used in cases of optimal paths with maximum length of 15 routers.Propagate routing informations in every 30 seconds.„Triggered update” for reducing the time of count to infinity.RIP V2 (RFC 1723) CIDR compatible.Train IT - Networks127Debrecen, 2012.
128Enhanced Interior Gateway Routing Protocol (EIGRP) It is the own distance vector based routing protocol of Cisco.Multiple goals, flexible, scaleable.Metric: compound (computed from 5 variables, can be weighted):bandwidthdelayloadreliabilityMTUTrain IT - Networks128Debrecen, 2012.
129Enhanced Interior Gateway Routing Protocol (EIGRP) Most important characteristics:CIDR compatible.The metric based on „Bandwith” in default.Mechanism of exploring neighbours (avoid broadcast).Handling count to infinity:Split Horizon, Holddown Timer, Triggered update.Recording potential substitute paths.Propagating updates (not the whole table).Integrated routing (can be used for multiple directed protocol).Train IT - Networks129Debrecen, 2012.
130Link State RoutingTrain IT - Networks130Debrecen, 2012.
131Link State Routing Scheme of functioning of Link State Routing: 1./ Exploring neighbours2./ Measuring the costs (length) of the link to the neighbours.3./ Creating packets containing the measurement results.4./ Propagate the packets to all routers of the network unit.5./ All routers know the topology of the network and can compute (eg. with Dijkstra algorythm) the optimal paths (spanning tree) to the other routers.Train IT - Networks131Debrecen, 2012.
132Link State Routing– Processes (IS-IS) Train IT - Networks132Debrecen, 2012.
133Open Shortest Path First - RFC 1131 Characteristics of Open Shortest Path First (OSPF):Link State Routng IGP protocol.New, recommended as default protocol since 90er years.Using smaller network unit (area) than AS.(Non disjunct) classification of routers:Routers working inside the area.Routers working on boundaries of areas.Routers working on backbones.Routers working on AS boundary.Able to perform equal cost, multiple paths routing.Using the „Service type” field of IP header.Recent version: OSPF V2 (RFC 2328).Train IT - Networks133Debrecen, 2012.
134OSPF AreasThe base of the decision process (Dijkstra algorythm) is the area.The areas form a „star pattern” with a special area – the backbone – in the center connecting the areas.Tasks of routers on area boundaries are complex:Separate decision process for all areas.Summarizing informations get from areas.Propagating the summarized informations to other areas.Inter area routing:Routing in source area as far as the boundary router.Routing on backbone as far as the boundary router of the destination area.Routing in destination area to destination network.Train IT - Networks134Debrecen, 2012.
135Administration of OSPF Data Most important items of an OSPF router table:Type of destination (network, area boundary router, AS boundary router).Id. of destination (IP address).Type of service.Giving the path/paths towards destination:Type of path (intra-area, inter-area, AS-external).Cost of path.Next router (IP address, interface of access).Train IT - Networks135Debrecen, 2012.
136Transport LayerTrain IT - Networks136Debrecen, 2012.
137Transport Layer Protocols UDP - User Datagram Protocol RFC 768Connection free, non-reliable Transport Layer protocol.TCP - Transmisson Control Protocol RFC 793Connection based, Összeköttetés alapú, reliable Transport Layer protocol.Train IT - Networks137Debrecen, 2012.
138UDPThe UDP (User Datagram Protocol) is the connection free transport protocol of the TCP/IP protocol set.Transmission of datagrams without any guarantee (without confirmation).Failure management is to higher level (applications) protocols.The UDP protocol is suitable applications which do not need to concatenate sequences of segments. Eg. TFTP, SNMP, DHCP, DNS .Train IT - Networks138Debrecen, 2012.
139Structure of UDP header Source port numberDestination port numberLength (byte)ChecksumTrain IT - Networks139Debrecen, 2012.
140PORT Numbers- Protocols (RFC 1700) echo 7/tcp echoecho 7/udp echoftp-data /tcp # File Transfer [Default D]ftp-data /udp # File Transfer [Default D]ftp /tcp # File Transfer [Control]telnet /tcp telnettelnet /udp telnetsmtp /tcp mail # Simple Mail Transsmtp /udp mail # Simple Mail Transhttp /tcp # World Wide Web HTTPhttp /udp # World Wide Web HTTPTrain IT - Networks140Debrecen, 2012.
141TCPThe TCP (Transmission Control Protocol) is the connection based transfer protocol of the TCP/IP protocol set. It provides a reliable (receipted) bit stream for applications.Before starting data transmission, the two nodes build up a TCP connection (TCP session) by the help of the so called three-way handshake.Information to be submitted is divided into segments (64KB).Before transmission each segment gets a number. The sender keeps record on each transmitted TCP segments, and requires a receipt.The destination node reverts the original message from the segments, and receipts the segment(s).If a segment is missing, the TCP protocol ensures re-transmission of the missing segment.Train IT - Networks141Debrecen, 2012.
142Structure of TCP Header Source port numberDestination port numberNo. of sequence (SEQ No.)No. of acknowledgement(ACK No.)URGACKPSHRSTSYNFINDataOffsetBusyWindow sizeChecksumURG pointerOptionsFillingTrain IT - Networks142Debrecen, 2012.
143TCP – Three-Way Handshake TCP Client TCP Server0. CLOSED LISTEN1. SYN-SENT --> <SEQ=100><CTL=SYN> > SYN-RECEIVED2. ESTABLISHED <-- <SEQ=300><ACK=101><CTL=SYN,ACK> <-- SYN-RECEIVED3. ESTABLISHED --> <SEQ=101><ACK=301><CTL=ACK> > ESTABLISHED4. ESTABLISHED <-- <SEQ=301><ACK=102><CTL=ACK><DATA> <-- ESTABLISHEDTrain IT - Networks143Debrecen, 2012.
144Application LayerTrain IT - Networks144Debrecen, 2012.
145Application Layer Protocol The highest level protocol which ensures the communication required by the users via applications typically with client-server architecture).The most common protocols:Name-IP address assignment – dnsWeb, www – httpFile transfer – ftp, sftpRemote login – telnet, ssh– smtp; pop3, imap4Train IT - Networks145Debrecen, 2012.
146HTTP ProtocolThe HTTP (HyperText Transfer Protocol) is the protocol of web, which is the most quickly spreading and most widely used part of internet.It provides easy information accessWe can navigate on World Wide Web by the help of hyperlinks. (A hyperlink is an object on a web page pointing to an other web page.)The URL address (Uniform Resource Locator) necessary for this is contained by the web page, usually embedded in the HTML code.Train IT - Networks146Debrecen, 2012.
147HTTP ProtocolThe HTTP protocol is based on a client-server architecture.The web browser is a client application. A web browser requires components with client and server functionality, as well.At first the web browser examines the protocol, from which it determines whether an other program should be called or launched.It determines the IP address of web server via DNS.It builds up a session with web server via TCP.The data sent to HTTP server give the name of the folder (and the HTML file) containing the web page.The server responds the request by sending to client the text, voices, clips, and graphics defined on the HTML page.The client-side browser composes files, displays the web page, and closes the session.Train IT - Networks147Debrecen, 2012.
148Traffic Filtering – Access Control Lists Without filtering the whole traffic is enabled.With traffic filtering you can control the traffic on a specified interface of the firewall (router): what kind of traffic is enabled or disabled.The control is described with a list (ACL):Condition1 specification / enableCondition2 specification / disable…In the control list conditions can be stated for IP addresses, protocols (TCP/UDP), and port numbers (80=http, 25=smtp).If a packet does not match any list items, the packet is discarded (implicit deny).The traffic filtering works independently of routing.Train IT - Networks148Debrecen, 2012.
149Wireless Network Technologies Train IT - Networks149Debrecen, 2012.
150Wireless Network Technologies Local network technologies (WLAN, Wi-Fi):Wireless extension of an organizational LAN.Free frequencies for use (2.4 GHz, 5 GHz).Spreading as the light.2.4 GHz is near to resonance frequency of water!Ensures mobility on the organizational data communication network.Provides long distance connection (GPRS, EDGE, UMTS).Enables global network access.Extension of mobile phone technology to data transmission.Data (transmission) charges.Train IT - Networks150Debrecen, 2012.
151Bases of Wireless Communication Wave: A kind of changing, which results point-to-point (cyclic) energy transfer.Amplitude: Distance between the zero and the maximum signal height.Frequency (F): Number of cycles in one second.Time of period (T): The time of one cycle T = 1/F.Wave length (l): Distance between two identical signal height values.C = Fl = km/s (light speed)Train IT - Networks151Debrecen, 2012.
152WLAN DevicesAccess Point, AP: Provides the access to a wired network (Internet) for clients (mobile devices).Bridge: A device for connecting two wired LAN. The connection can be done in Data Link Layer.Client adapter: Network card for wireless networks.RF devices: antennas, cables, connectors.Wi-Fi Certification!Train IT - Networks152Debrecen, 2012.
153AntennasAntenna: A device developed for transmitting and receiving RF signals. The strength of signal transmission of an antenna can be controlled or uncontrolled.Antenna gain: Changing the strength of signal (power) compared to isotropic antenna (theoretical point source of waves). The gain measures how efficiently the antenna focuses the radiated RF energy. (measure of unit: dBi)Train IT - Networks153Debrecen, 2012.
154Omnidirectional Antennas Isotropic antenna: A theoretical point source of waves (0 dBi).Dipol antenna: Rod shaped circle source of waves (2.2 dBi).Train IT - Networks154Debrecen, 2012.
155Directional Antennas Yagi antenna: An antenna equipped with RF Mirrors and elements providing direction for waves (12 dBi).Train IT - Networks155Debrecen, 2012.
156Directional Antennas Yagi antenna: An antenna equipped with RF Mirrors and elements providing direction for waves (12 dBi).Parabolic antenna: An antenna equipped with a parabolic mirror and a head positioned in the point of focus (22 dBi).Train IT - Networks156Debrecen, 2012.
157WLAN ModesInfrastructure: The mobile devices are connected to the (wired) organizational network via a radio access point (AP).The mobile devices do not perform direct radio communication.Ad-hoc: The mobile devices are connected directly each other via their own radio interface. In case of large numbers of machines it is not efficient.Train IT - Networks157Debrecen, 2012.
158WLAN Logical Architectures BSS (Basic Service Set): Network environment working within a coverage of a radio interface (AP). Identifying the network environment a text identifier (SSID) is used.IBSS (Independent BSS): Several independent BSS. It is used typically in Ad-hoc networks.DS (Distributed Systam): Several BSS connected via radio or wired infrastructure.ESS (Extended Service Set): Several BSS (with DS connection). The transit between BSSs is possible without any loss of network connections (Roaming).Train IT - Networks158Debrecen, 2012.
159Scheme of WLAN Transmission Client AP> <Request to Send> ><-- <Clear to Send> <--> <DATA> ><-- <ACK> <--The measured throughput is significantly less, than the theoretical bandwidth!Train IT - Networks159Debrecen, 2012.
160802.11b13 (overlapping) channels (EU) with 5 MHz bandwidth on 2.4 GHz.Four different data transmission speeds with four different coding and modulating technologies:11 Mbps (least coverage)5.5 Mbps2 Mbps1 Mbps (largest coverage)Train IT - Networks160Debrecen, 2012.
161802.11g and a802.11g:New coding and modulating technology on 2.4 GHz (PBCC, OFDM).54 Mbps data transmission speed.Retain frequency (2.4 GHz) provides a backward compatibility for b systems.802.11a:Technology working on 5 GHz (light-like propagation).Requires a separate RF unit (5 GHz).Train IT - Networks161Debrecen, 2012.
162Wireless SecuritySSID: Not a protective factor (it is only an identifier, can be intercepted).WEP (Wired Equivalent Privacy): RC4 encryption, tha standard specifies a 64-bit key, or in some manufacturer implementation a 128-bit key. Nowdays it is not safe, using free softwares for analyzing the trafic the key (even the 128-bit key) can be „obtained”.MAC address filtering: Based on the MAC addresses of clients the connection can be enabled or disabled. Not specified inWPA (Wi-Fi Protected Access): A system, (partly) containing the (second generation) security elements of i (Extensible Authentication Protocol, EAP; Temporary Key Integrity Protocol, TKIP).Train IT - Networks162Debrecen, 2012.
163XP – The Most Important Network Commands Train IT - Networks163Debrecen, 2012.
164Writing and Renewing the IP Configuration ipconfig – Writes the IP address, netmask, and the default gateway (for all network cards).ipconfig /all – Writes the whole configuration (MAC address, address of DNS server, expiration dates).ipconfig /release – „Releases” the IP address (previously assigned by DHCP).ipconfig /renew – Renew (asking again) the IP address assigned by DHCP. Before this one submitting an ipconfig /release command is recommended.Train IT - Networks164Debrecen, 2012.
165Testing the Accessibility of a Node ping machine – Tests the accessibility of the given (by name or IP address) machine with 4 packets.ping –t machine – Tests the accessibility of the given machine with continuous packet sending (until pressing Ctrl+C).ping –a IP address – Beside testing it writes the DNS name belongigng to the IP address (Fully Qualified Domain Name).Train IT - Networks165Debrecen, 2012.
166Testing the Accessibility of a Node ping –l size machine – Tests the accessibility of the machine with packets containing bytes given with parameter of size.ping –i ttl machine – Adjust the TTL field of IP packets to ttl during testing. (Investigates, wheter the machine can be accessed through routers max. number of ttl.)Train IT - Networks166Debrecen, 2012.
167Exploring a Path to a Destination tracert machine – Writes the sequence of routers (hops) on a path leading to the machine (given with name or IP address). The DNS names of routers are displayed in the list (DNS names are backtracked from IP addresses).tracert –d machine – The IP addresses of routers are displayed in the list (faster, because DNS names are not backtracked from IP addresses).Train IT - Networks167Debrecen, 2012.
168Displaying and Modifying the Routing Table route print – Displays the routing table: destination network, netmask, gateway, connection (interface), metric.netstat -nr – Identical with the route print command.route ADD destination MASK mask gateway METRIC metric – Inserts a new row into the routing table for the given destination network with the specified parameters (mask, gateway, metric). Despite of the occasionally displayed „Network database can not be open” error message the command can be executed normally (can be verified with the route print command).route DELETE destination MASK maszk – Deletes the given row (specified with the destination, mask parameters) of the routing table. Despite of the occasionally displayed „Network database can not be open” error message the command can be executed normally (can be verified with the route print command).Train IT - Networks168Debrecen, 2012.
169Displaying and Modifying the ARP Table arp –a – Displays the ARP table (a table, containing the IP address – MAC address assignment).arp –s IP address Eth. address – Assigns the given IP address with the Eth. Address inserting a new entry in the ARP table (creates a static ARP entry).arp –d IP address – Deletes the row belonging to the given IP address from the ARP table.Train IT - Networks169Debrecen, 2012.
170Writing NetBIOS Network Configuration nbtstat -n – Writes NetBIOS names of local machine.nbtstat –a machine – Lists the NetBIOS nametable of remote machine. Displays the Mac address of the given machine, as well.nbtstat –A IP address – Lists the NetBIOS nametable of remote machine with IP address. Displays the Mac address of the given IP address.nbtstat -r – Lists the names resolved by broadcasting or WINS.nbtstat -R – Deletes the list of resolved names by broadcasting.Train IT - Networks170Debrecen, 2012.
171BibliographyAndrew S. Tanenbaum, David J. Wetherall: Computer Networks, 5th edition, , Prentice Hall, Fred Halsall: Computer Networking and the Internet, 5th edition, , Addison Wesley, William Stallings: Data and Computer Communications, 8th edition, , Prentice Hall, RFC Documents:Train IT - Networks171Debrecen, 2012.