Hands-on Networking FundamentalsX.25X.25 and the OSI ModelSlide 4X.25 Transmission ModesSlide 6X.25 DeploymentFrame RelaySlide 9Frame Relay Layered CommunicationsVendor ServicesIntegrated Services Digital Network (ISDN)1.200 Services for NetworkingDigital Communication ServicesSlide 15Broadband ISDNSlide 17ISDN ConsiderationsAsynchronous Transfer ModeSlide 20How ATM WorksSlide 22Digital Subscriber Line (DSL)DSL Service TypesDSL Service Types (continued)SONETCommunications Media and CharacteristicsSlide 28Slide 29Ethernet-Based MANs And WANs (Optical Ethernet)Slide 31Hands-on Networking Fundamentals Chapter 9Understanding WAN Connection ChoicesHands-on Networking Fundamentals 2X.25•WAN protocol that uses packet-switching techniques•Used in public data networks (PDNs) from 1976–PDN: provides data communication services to public•Current specifications–Defines data transfer from DTE to DCE, then into PDN•DTE (Data terminal equipment) may be a computer•DCE (Data circuit equipment) may be a packet switch–Point-to-point connection-oriented communications–Includes transmission speeds up to 2.048 Mbps•Globally accepted due to reliability and adaptability–Links older LANs, mainframes, minicomputers to WANsHands-on Networking Fundamentals 3X.25 and the OSI Model•ITU-T (Telecommunications Standardized Sector of the International Telecommunications Union)–Defines X.25 in layers like first three of OSI model•X.25 Physical Protocol layer (Layer 1)–Governs physical connectivity to adapters and cables•X.25 Link Access layer (Layer 2) –Equivalent to OSI Data Link layer's Mac sublayer–Handles data transfer, flow control, frame composition•X.25 Packet Protocol layer (Layer 3)–Like the OSI Network layer–Manages orderly exchange, reliability of connectionHands-on Networking Fundamentals 4Hands-on Networking Fundamentals 5X.25 Transmission Modes•Three modes for transmitting data packets–Switched virtual circuit (SVC) •Two-way channel between nodes based on X.25 switch•Logical connection maintained for transmission only•Example of packet switching–Permanent virtual circuit (PVC)•Logical channel remains connected at all times•Another example of packet switching–Datagrams•Packaged data sent without establishing channel•Reach destination using form of message switchingHands-on Networking Fundamentals 6Hands-on Networking Fundamentals 7X.25 Deployment•Reasons for popularity of X.25 networks–Provide worldwide connectivity between LANs–Release unused bandwidth from nodes not communicating•New technologies replacing X.25 networks–Frame relay–SMDS–SONET–Optical EthernetHands-on Networking Fundamentals 8Frame Relay•Meets demand of high-volume, high-bandwidth LANs–Current speeds up to 45 Mbps over DS-3 links•Defined via ITU-T I.451/Q.931 and Q.922 standards•Some transported protocols: IP, IPX, AppleTalk, PPP•Elements in common with X.25–Both use packet switching over virtual circuits–Connections are switched (SVC) or permanent (PVC)•Frame relay specific elements–Uses frame relay assembler disassembler (FRAD) –Provides connectionless-oriented service•Does not perform extensive error checkingHands-on Networking Fundamentals 9Hands-on Networking Fundamentals 10Frame Relay Layered Communications•Differ from X.25 in number and some functionality •Two communication layers–Physical layer: corresponds to OSI Physical layer•Consists of interfaces similar to those in X.25•Adapters connect to frame relay network•Telecommunication lines used for wire communications •Includes optional sublayer for reliability–Link Access Protocol for Frame Mode Bearer Services (LAPF): corresponds to OSI Data Link layer•Formats and validates frames•Performs switching•Checks for transmission errors and line congestionHands-on Networking Fundamentals 11Vendor Services•Three types offered by frame relay service providers–Committed information rate (CIR)•Provides pledged minimum transmission rate•Problems: lines not monitored well, rate difficult to verify–Permanent virtual connection (PVC)•A continuous dedicated connection to a specific location•Appropriate for linking mission critical nodes –Port•Based on purchasing access to set of ports•Ports located on vendor’s telecommunications switchHands-on Networking Fundamentals 12Integrated Services Digital Network (ISDN)•Digital-based standard with multiple applications–LAN-to-LAN connectivity–Home offices and telecommuting–Off-site backup and disaster recovery –Connecting private telephone system to a public telco–LAN-to-LAN video and multimedia applications•Benefits of ISDN–Provides voice, data, video services over one network–Layered protocol structure compatible with OSI model–Channels in multiples of 64 Kbps, 384 Kbps, 1536 Kbps–Has switched and non-switched connection services–Broadband ISDN capabilities of 155 Mbps and higherHands-on Networking Fundamentals 131.200 Services for Networking•Divided into three parts–Bearer services •Circuit-mode: ISDN communication delivers service •Packet-mode: virtual call/permanent virtual call circuits–Teleservices•Provides for 3.1-KHz speech communications•Includes telex for interactive telecommunications, fax•Includes videotex to retrieve mailbox information–Supplementary services•Primarily for voice communications•Caller ID and conference callingHands-on Networking Fundamentals 14Digital Communication Services•Two N-ISDN interfaces: basic rate and primary rate•Basic Rate Interface (BRI) ISDN–Uses form of time division multiple access (TDMA)–Has aggregate data transmission rate of 144 Kbps•Two 64-Kbps Bearer (B) channels: data, voice, graphics •One 16-Kbps Delta (D) channel: call setup and teardown –Multiple BRI channels can be "bonded" together•Many systems support bonding using Multilink PPP•Example: Bond two B channels for 128-Kbps throughput–Some telcos allow D channel to be used for downloads•Four-wire twisted pair connects BRI ISDN to customerHands-on Networking Fundamentals 15Hands-on Networking Fundamentals 16Broadband ISDN•Supports transfer rates of 155 Mbps to 1 Gbps (fiber)•Uses cells instead of packets–Cell has three parts: header, control data, data payload•Compatible with two other technologies–Asynchronous Transfer Mode (ATM)–Synchronous optical network (SONET)•Has not yet gained widespread acceptanceHands-on