Networking Concepts

Networking Concepts

LANConceptsAttenuation, NoiseHardwareRepeater, AmplifierBridge, Router, Gateway, Switch, HubTwisted pair, Coaxial cable, Fiber opticsServer, WorkstationWireless access pointTopologyBus, Tree, Star, Ring

LANStandardOSI (Open Systems Interconnection)IEEE (Institute of Electrical and Electronic Engineers)ITU-T (Intl Telephone Union Telecom. Sector)ISO (International Standards Organization)EIA (Electronic Industries Association)ETS (European Telecom. Standard)

Communications HardwareRepeaterExtends distance limitation on networks (both voice and data)Filters noiseRegenerates signalsFor twisted pair wire, repeaters are placed every 100 metersAmplifierExtends distance limitation on networks (both voice and data)Amplifies both signal and noise

Communications HardwareBridgeConnects two LANs using same protocolSingle path between LANsMinimal sophisticationRouterConnects multiple LANs using same protocolChoice of paths between LANsMainstay of internetworking

Communications HardwareGatewayConnects multiple LANs using any protocolVery sophisticatedSupports todays internet by providing access points to several networksHubConnects nodes to a networkSometimes acts as repeater

Communications HardwareSwitchConnects multiple LAN segments using the same protocolConnections may use twisted pair, coaxial cable, or fiber optics wiringFaster than bridgesEnables simultaneous communication between multiple network segments

EthernetEthernet was developed jointly by Xerox, Intel, and DEC in 1980DEC (Digital Equipment Corporation) a computer company that specialized in mini-computers in the 1970s. It was acquired by Compaq and Compaq merged with HP.This was the first commercial LAN systemEthernet is a simple protocol to implementEthernet addresses the layers 1 and 2 functionality for the OSI modelEthernet standard is very close to IEEE 802.3 standard, but has some minor differences

EthernetEthernet uses bus topology (which we will discuss next)Ethernet transmits a baseband signal at 10 MbpsBaseband signals are digital and bidirectionalEthernet allows the user data to have a variable length up to 1500 bytesUnlike HDLC and SDLC protocols, ethernet uses a length field in the header to identify the length of the user data in bytes. Because of this, no special bit pattern is needed to recognize the start and end of the user data.

Ethernet frame format

Ethernet diagram

Bus topologyIt is a contention-based topology, which means that each node on the network must contend for accessEach node listens to traffic on the networkWhen a node has packets to transfer and the bus is not busy, then the packets are put on the bus in both directions, with the destination address marked on the packetsAll nodes listen to traffic on the network and the node that has packets addressed to it, receives the packetsNo routing or switching is involved in data transfer

Bus topology diagram

Tree topologyTree topology is a variation on bus topologyA special node is designated as rootThe primary reason for this topology is to segment nodes so that not all nodes need to listen to packets broadcast on a segmentThis adds a layer of security in the form of unwanted nodes not listening to the network trafficSpeeds up data transfer since there will be fewer nodes on each segment

Tree topology diagram

Star topologyThis is another variation on bus topologyThis has a central hub, a passive deviceStar is a logical bus and a physical ringHub has ports in multiples of 8. Multiple hubs can be connected in a daisy chain formatEasy to add nodes to the network and remove nodes from the networkCentral node does switching between nodesMultiple nodes can communicate simultaneously without collisionPotential problem is the single point of failure for the network when the central node fails

Star topology diagram

Ring topologyThe nodes are connected in a ring patternUnlike bus topology, each node on the ring acts as a repeater on the networkNodes access the network using a token, which eliminates the need for contention as in bus topologyToken is a series of bits that identifies the node that has the right to transmit at any given timeExample of a token: Assume that there are 6 nodes on the network. The nodes are labeled 1 through 6 and the token would consist of 3 bits. The token 100 will indicate that node 4 has the token.Tokens circulate in a single direction from a node to its neighbor

Ring topology diagram

OSI 7-layer model

IEEE 802802.1General LAN management of OSIlayers 3 through 7802.2LLC sublayer802.3Ethernet802.4Token bus802.5Token ring802.6MAN802.7Broadband, in general

IEEE 802802.10Network Security802.11Wireless LAN802.12100VG-AnyLAN (Voice Grade)802.13unused802.14Cable Modem

WANConceptsGateway, Frame Relay, ATM, DSL, T1, T3, STS (Synchronous Transport Signal)StandardTCP/IP (Transmission Control Protocol /Internet Protocol)IETF (Internet Engineering Task Force)ATM Forum (Asynchronous Transfer Mode)

STS, STM, OC equivalencies

ATM VPI and VCI

TCP/IP functionsEstablish a connection between nodesManage data flow on the networkHandle transmission errorsTerminate connection at the endTCP is a connection-oriented protocol, meaning that a packet sent to the next node is monitored for proper receiptIP is a connection-less protocol, meaning that a packet sent to the next node is not monitored for proper deliverySince TCP and IP work together, the packet delivery is reliableConnection-less mode is known as User Datagram Protocol (UDP)

TCP/IP 5-layer modelTCP/IP protocol is divided into 5 layersApplication layerTransport layerNetwork layerData link layerPhysical layer

IP AddressingIP address consists of 4 octets: n.n.n.n where n is in the range 0 to 255This form of IP address is known as IPv4, denoting IP address Version 4A new form of IP address known as IPv6, denoting IP address Version 6, has been proposed. It uses 128-bit addressing instead of 32-bit addressing.

IP Address HierarchyThere are 3 main classes of IP addresses in use and two additional classes of IP addresses available for multicast and testingClass A First octet range: 1 126IBM, AT&T, HP, Merck, Stanford UniversityClass B First octet range: 128 191U of L and most other universitiesClass C First octet range: 192 223IGLOU, Louisvilles first ISP

UDPUser Datagram Protocol is a best effort protocolbest effort means no guarantee of deliveryThis is a connection-less protocolUDP does not provide reliabilityUDP sends out packets without first establishing a connectionRFC 768 describes UDPUDP header consists of source port, destination port, length, checksumExample of UDP: TFTP (Trivial File Transfer Protocol). TFTP is used when bootsrapping diskless systemTFTP is on UDP port 69