Transcript Hands-on Networking Fundamentals

Hands-on Networking
Fundamentals
Chapter 9
Understanding WAN Connection
Choices
X.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 WANs
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X.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 connection
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X.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 switching
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X.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
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Frame relay
SMDS
SONET
Optical Ethernet
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Frame 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 checking
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Frame Relay Layered
Communications
• Differ from X.25 in number and some functionality
• Two communication layers
– Physical layer: corresponds to OSI Physical layer
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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 congestion
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Vendor 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 switch
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Integrated Services Digital Network
(ISDN)
• Digital-based standard with multiple applications
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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
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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 higher
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1.200 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 calling
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Digital 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 customer
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Broadband 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 acceptance
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ISDN Considerations
• Two reasons to choose ISDN
– Faster WAN solutions not available
– Need to operate multiple devices over connection
• Local availability depends on two factors
– Whether service is offered by telco
– Whether city infrastructure supports ISDN
• Most commonly used protocols
– National ISDN-1 (NI-1): RBOCs, long distance carriers
– National ISDN-2 (NI-2): later version of NI-1
• Cabling: twisted-pair copper wire or fiber-optic cable
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Asynchronous Transfer Mode
• High-speed network transport used in WANs or LANs
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Carries data, voice, video, and multimedia applications
Many possible transmission speeds (up to 40 Gbps)
Easily scalable: as traffic grows, add more switches
Physical links operate over many cable types
• Cell switching for communications over ATM channel
– Adds virtual channel identifier to front of TDM time slot
• Enables device to place bit onto channel asynchronously
– Gives Quality of Service (QoS) for time-sensitive traffic
• Supported by ANSI, the IETF, the ETSI, and the ITU-T
• Compatible with B-ISDN, DSL, FDDI, and others
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How ATM Works
• Sets up virtual circuits as pathway between nodes
• Three types of virtual circuits employed
– ATM permanent virtual circuit (ATM PVC)
• Dedicated circuit with preassigned path
• Eliminates delays caused by circuit setup and teardown
– ATM switched virtual circuit (ATM SVC)
• Set up and tear down as needed (transparent to user)
• Temporary connection active during communication only
– ATM smart permanent virtual circuit (ATM SPVC)
• Manually configured like PVCs (but only at end devices)
• Provides a dedicated bandwidth like a PVC
• Defined path to switch and fault tolerance similar to SVC
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Digital Subscriber Line (DSL)
• High-speed networking between subscriber and telco
• Transmits data, voice, and video communications
• Useful applications of DSL
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Internet access, especially file downloads and uploads
Residential lines for home use and telecommuting
Office and small business WAN access
Accessing multimedia over a network
Quickly transmitting a large image file
Taking an interactive class or seminar
Implementing a distributed client/server application
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DSL Service Types
• Asymmetric Digital Subscriber Line (ADSL)
– Supports traditional data, multimedia, distance learning
– Allows simultaneous transfer of voice and data
• G.lite Asymmetric Digital Subscriber Line (G.lite ADSL)
– Variation of ADSL compatible with Plug and Play (PnP)
• Integrated Services Digital Network Digital Subscriber
Line (IDSL)
– Enables DSL in networks with Digital Loop Carrier
• Rate Adaptive Asymmetric Digital Subscriber Line
(RADSL)
– Transmission rate adapted to data, multimedia, or voice
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DSL Service Types (continued)
• High Bit-Rate Digital Subscriber Line (HDSL)
– Full-duplex communications at fixed transfer rates
– Does not support voice as well as ADSL and RADSL
• Symmetric High Bit-Rate Digital Subscriber Line
(SHDSL)
– Can be used over one or two wires
– Use of two wires improves range over other DSL types
• Digital Subscriber Line (VDSL)
– High-bandwidth alternative to coaxial or fiber-optic
based networks
• Symmetric Digital Subscriber Line (SDSL)
– Symmetrical bandwidth useful with interactive media
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SONET
• Synchronous optical network
– Open, affordable fiber-optic transmission standard
– Connects to interfaces for ATM, ISDN, and routers
– Transmits data faster than 1 Gbps (up to 9.953 Gbps)
• Five applications for SONET
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Very high-speed data connectivity over long distances
Video conferencing between distant sites
Long-distance teaching
High-quality sound and video reproduction
High-speed transmission of complex graphics
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Communications Media and
Characteristics
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Uses single-mode fiber-optic cable, T-carrier lines
Main transport method occurs at Physical layer
Compatible with technologies using fixed cell lengths
SONET transmission speeds: 51.84 to 9953.28 Mbps
– Designated by optical carrier (OC) and Synchronous
Transport Signal Level (STS)
– Common options: OC-3, OC-12, OC-48, and OC-192
• Synchronous Digital Hierarchy (SDH)
– SONET-like standard developed by ITU-T
– Synchronous Transport Model Level (STM)
• Designation for various speeds
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Ethernet-Based MANs And WANs
(Optical Ethernet)
• High-speed alternative to SONET and frame relay
• Networks consist of three basic elements
– Gigabit or 10 Gigabit Ethernet MAN or WAN backbone
– Multimode fiber-optic cable connections up to six miles
– Single-mode fiber-optic cable connections up to 43.4
miles
• Ethernet backbone links three types of LANs
– Fast Ethernet
– Gigabit Ethernet
– 10 Gigabit Ethernet
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