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Computer Network
Module 8
| Question | Answer |
|---|---|
| Committed Information Rate (CIR) | The guaranteed minimum amount of bandwidth selected when leaseing a frame relay circuit. |
| DSL Access Multiplexer(DSLAM) | A connectivity device located at a telecommunications carrier's office that aggregates multiple DSL subscriber lines and connects them to a larger carrier or to the internet backbone |
| Hybrid fiber-coax (HFC) | A link that consists of fiber cable connecting the cable company's offices to a node location near the customer and coaxial cable connecting the node to the customer's house. |
| Permanent Virtual Circuit (PVC) | A point-to-point connection over which data may follow any number of different paths, as opposed to a dedicated line that follows a predefined path, x.25, frame relay, and some forms of ATM use PVC's. |
| Switched virtual circuit (SVC) | A logical, poin-to-point connection that relies on switches to determine the optimal path between sender and receiver. |
| Wide Area Networks | •Provide the exchange of data between two or more supported LANs •Span a relatively large geographical area •Often connected through public networks, such as the telephone system •Can also be connected through leased lines or satellites |
| Largest WAN in existence is the | Internet |
| WAN Essentials Typically described as two types: | Non-dedicated and Dedicated |
| Non-dedicated | connection is established, may be a point-to-point connection |
| Dedicated | oContinuously available (for data transfer) and often point-to-point oDistinguished by capacity and transmission characteristics |
| A continuously available channel is called a: | dedicated lines |
| Bus Topology | oTypically uses a single communication channel oEach site connects to one or two other sites oGood option for a low number of sites and the capability to use dedicated circuits |
| Bus Topology Advantage | lowest cost |
| Bus Topology Disadvantage | low scalability and single failure disables some communication |
| Ring Topology | oTypically uses parallel communication channels oEach site connects two other sites oGood option for a low number of sites and the capability to use dedicated circuits |
| Ring Advantage | single failure does not disable all communication, moderate cost |
| Ring Disadavantage | suitable for smaller WANs and low scalability |
| Generally, which WAN topology is less costly to extend and provides shorter data paths? | Star |
| Star | oMay use a single or parallel communication channel oSingle site acts as a central connection point oNo two sites have the same data path oGood option for a larger number of sites and the capability to use dedicated circuits |
| Star Advantage | higher scalability, moderate cost and shorter traffic paths, |
| Star Disadvantage | high central site traffic affects all communication |
| Mesh Topology | oMay use a single or parallel communication channel oEach site often connects to numerous other sites oMultiple data paths for any two sites oGood for entities with low down-time tolerance that can use dedicated circuits |
| Full mesh | all sites are interconnected |
| Mesh Advantage | highly fault tolerant and shortest data path |
| Mesh Disadvantage | low scalability and highest cost |
| Tiered Topology | oCombination of other technologies in a layered approach Typically one topology type creates a backbone between regions Another topology type connects sites within each region oPerhaps the most common topology |
| Tiered Advantage | allows focused dedication of resources, high scalability |
| Tiered Disadvantage | moderate to high cost |
| WAN Protocols Operate | at the Lowest Levels of the OSI model |
| A Data Link Layer | encapsulation type (protocol) to frame a packet |
| A Physical Layer | signaling method to transmit the data (Fiber-light, copper-voltage, wireless-radio frequency) |
| Timing schemes for data transmissions may be | synchronous or asynchronous |
| Dialup over PSTN/POTS | •Point-to-point technology to access remote servers •Modems perform A/D-D/A conversions, some of the link is usually analog •Uses circuit switching or (newer) packet switching |
| Conversion process limits throughput to 56Kbps, | FCC further limits throughput to 53Kbps |
| Dialup over PSTN/POTS Advantage | low-cost, availability, ease of use and it is a mature technology |
| Dialup over PSTN/POTS Disadvantage | low quality/reliability, low throughput levels and phone circuit tie-up |
| Describe the term Local Loop as it relates to the PSTN. | The portion of the PSTN that connects any residence or business to the nearest CO |
| Frame Relay | •Describes a protocol and service (evolved from the older X.25 technology) •Older and mature packet-switched, multi-path technology |
| Switched Data Link layer protocol | oServices multiple virtual circuits oUses HDLC encapsulation between connected devices |
| Frame Relay Advantage | lower cost, easy upgrade to T-carrier and Frame Relay is a mature technology |
| Frame Relay Disadvantages | variable bandwidth availability and lower privacy and security |
| ISDN | •Older and mature technology, may be dedicated or dial-on-demand •Uses both circuit switching and packet switching techniques •Connections are based on 64Kbps bearer (B) and 16 or 64Kbps data (D) channels |
| ISDN Advantage | one connection/multiple signals and ISDN is a mature technology |
| ISDN Disadvantage | cost and distance limitations |
| T-Carriers (Trunk)Broadband technology | Circuit-switched and point-to-point |
| One T1 line consists of: | o24 multiplexed (with TDM) 64Kbps channels: Two wire pairs each capable of simultaneous transmit and receive Each channel may contain data, voice, or video signals 1.544Mbps throughput |
| T lines require | CSU/DSU and usually multiplexer devices |
| T-Carriers (Trunk)Common installations | include fractional T1s, T1s, multiple T1s, and T3s |
| How do T-carrier wire pairs terminate at the customer’s building? (Identify the device) | At the customers demarc (demarcation point) either inside or outside the building, T-Carrier wire pairs terminated with a smart jack |
| What is the function of a T-carrier multiplexer? | Incoming T-Carrier line separate its combined channels into individual signals that can be interpreted on the LAN. Separate at the receiver end or combined at the trnasceiver |
| The CSU/DSU and multiplexer device are often contained | within a single unit |
| LAN side is the | DSU side |
| The Internet side is the | CSU side |
| T-Carriers (Trunk) Advantage | higher reliability and throughput levels |
| T-Carriers (Trunk) Disadavantage | higher cost and the technical expertise to administer |
| DSL | •Dedicated technology that directly competes with ISDN, T-carrier and Cable •Suited for businesses and consumers with two categories of service |
| A technology that offers more throughput in one direction than the other is called: | Asymmetrical |
| DSL Uses the PSTN network but is limited on distance from the carriers POP | oDSL operates in the unused portion of the PSTN bandwidth oEmploys advanced modulation techniques oSplitters or filters must be used to prevent the signal from affecting non-DSL devices |
| DSL Advantages | lower cost and DSL uses the PSTN infrastructure |
| DSL Disadvantages | lower reliability than T-carrier |
| Cable | • Dedicated, shared access technology that directly competes with T-carrier, ISDN and DSL • Existing cable TV technology is easily adapted to Internet use, requires a cable MODEM |
| Is broadband cable symmetrical or asymmetrical? | Asymmetrical |
| Cable Advantages | existing infrastructure capable of carrying digital signals with a wide bandwidth |
| Cable Disadvantages | shared access, bandwidth competition and less infrastructure than PSTN |
| Which type of dedicated connection is considered more secure, DSL or Broadband Cable? | DSL |
| ATM (Asynchronous Transfer Mode) | •ITU standard, used primarily by telecomm carriers •Employs virtual circuits that allows many configurable options, is highly efficient with available bandwidth, and offers the benefits of circuit-switching technology without wasted bandwidth |
| ATM Includes layer two protocols and layer one signaling technologies | Packet-switching technology |
| Runs over fiber or copper with a fixed packet size: | 48B Data + 5B Header = 53B Packets |
| ATM Compatible with leading LAN technologies | Supports TCP/IP and is easily integrated with Ethernet LANs |
| What converts incoming Ethernet frames into ATM cells? | LANE (LAN Emulation) |
| SONET/SDH (Synchronous Optical Network/ Synchronous Digital Hierarchy) | •Specifies framing and multiplexing techniques at the physical layer •Often used as a backbone to aggregate other WAN technologies •Commonly used to connect telecom Central Offices and remote switching facilities |
| SONET/SDH Four key strengths | Seamlessly integrates different WAN technologies, Fast data transfer rates, Highly scalable and Fault tolerant |
| SONET/SDH Features two independent rings that run over fiber optic cable | • One ring is primary, secondary is backup – if primary fails, data is rerouted to secondary ring |
| SONET/SDH Data rates are indicated by the | OC level |
| What SONET device combines the individual SONET signals on the transmitting end? | Multiplexer |
| Remote users may connect to a LAN via Remote access | Many remote access methods exist that differ by various characteristics |
| Dialup Networking | oDialing directly to a Remote access server oServer authenticates the Remote user for network logon |
| Remote Access Servers | oMany types exist from special purpose to general purpose oMicrosoft provides RRAS (Routing and Remote Access Service) oRRAS accepts multiple connections over various transmission paths oOffers security to the remote access client in the form on a VPN |
| Remote Access Protocols | oSLIP (older) and PPP (newer) enable serial (MODEM) connections between devices oSLIP only carried IP datagrams, PPP offers many features lacking from SLIP oPPP is used over many DSL and Cable broadband connections (PPoE) |
| Remote Virtual Computing | oAllows a user on one PC to control one or more remote PCs oOften simple to configure and runs over many types of connections oMicrosoft provides the service as “Remote Desktop” |
| VPN (Virtual Private Networks) | oEstablishes a link between two points that appears as a private WAN link oUses the public infrastructure with special VPN protocols oThe protocols create the virtual connections called tunnels |
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