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UNFORMATTED ATTACHMENT PREVIEW
QUESTION 1 1. What best describes “broadband access”? a. broadband access is a specific term used to describe the delivery of one-way television programming to subscribers b. broadband access describes any digital network that supports 1 Gbps or greater bit rates c. broadband access describes technical methods that enable users to connect to high speed networks d. broadband access is a term only applicable to analog television programming 10 points QUESTION 2 1. What are some ways to accomplish full-duplex (FDX) digital communications on guided medium at the physical layer (OSI Layer 1)? a. separate receive and transmit paths using separate physical mediums b. separate digital signals by using separate time slots – does not work for analog signals c. separate receive and transmit paths by modulating each at different carrier frequencies d. all of the above are ways to accomplish FDX 10 points QUESTION 3 1. ____________ is a broadband access method that depends upon fiber optic cables. a. PONS b. CATV c. ADSL d. WLL 10 points QUESTION 4 1. ____________ is a broadband access method based upon a shared medium, which initially experienced security and privacy issues. a. PONS b. CATV c. ADSL d. WLL 10 points QUESTION 5 1. Which technologies are used with ADSL? a. OFDM, TDD (time division duplexing) b. OFDM, M’ary modulation c. M’ary modulation, WDM d. WDM, WLL 10 points QUESTION 6 1. Which technology is used with asymmetric DSL (ADSL)? a. time division multiplexing (TDM) b. frequency division multiplexing (FDM) c. orthogonal frequency division multiplexing (OFDM) d. direst sequence spread spectrum (DSSS) 10 points QUESTION 7 1. Since attenuation over UTP lines are a major concern, ADSL near-end crosstalk (NEXT) is of greater concern than far-end crosstalk (FEXT). True False 10 points QUESTION 8 1. What statement(s) are correct regarding Discrete MultiTone (DMT)? a. DMT describes a technique used to enable wireless BWA b. DMT is a modulation method used for broadband access over coaxial cable networks c. DMT describes the use of OFDM to enable ADSL d. all statements are correct 10 points QUESTION 9 1. ADSL supports both analog voice calls and digital communications simultaneously. True False 10 points QUESTION 10 1. What is true about dynamic rate adaptive modems used in ADSL. a. these modems can sense line conditions and adjust “M” as required b. these modems can sense line conditions and move communications away from noise impacted subcarrier channels c. these types of modems are used on ADSL links d. all of the above are true 10 points QUESTION 11 1. Why was DOCSIS important for the CATV industry? a. it helped to standardize the industry b. it allowed several large CATV corporations to operate as a regulated monopoly c. it merged the CATV and telephone industries d. all of the above 10 points QUESTION 12 1. Because CATV DOCSIS uses OFDM, there is no need to use modulation methods such as QPSK or QAM. True False 10 points QUESTION 13 1. The Passive Optical Network (PON) standard does not require active components such as repeaters or amplifiers to be used between the subscriber to service provider network. True False 10 points QUESTION 14 1. Select the correct statement(s) regarding Passive Optical Networks (PONs). a. PONS does not require the use of active amplification between the CO to the subscriber b. PONS operates over SMF optical cables c. PONS uses passive splitters to distribute signals to subscribers d. the PONS ONT located at the subscribers location is owned and operated by the service provider e. all statements are correct 10 points QUESTION 15 1. Select the correct statement(s) regarding PONS. a. only MMF cables can be used, since MMF enables greater data capacities compared to SMF b. PONS systems require active amplifiers, since high frequency signals attenuate quickly over distance c. PONS systems use passive devices between OLT and ONT d. all are correct statements 10 points QUESTION 16 1. IEEE 802.16 WiMAX BWA, also known as fixed wireless access, is an alternative to the guided local loop. In many cases, BWA can be implemented more quickly than its guided medium counterparts. However, frequency licensing through regulatory agencies and signal interference can be major challenges. True False 10 points QUESTION 17 1. Select the correct statement(s) regarding IEEE 802.16 WiMAX BWA. a. WiMAX BWA describes both 4G Mobile WiMAX and fixed WiMax b. DSSS and CDMA are fundamental technologies used with WiMAX BWA c. OFDM is implemented to increase spectral efficiency and to improve noise performance d. all of the statements are correct 10 points QUESTION 18 1. Free space optics (FSO) are considered a wireless local loop (WLL) capability. True False 10 points QUESTION 19 1. What standard enables broadband access over traditional PSTN local loop lines? a. ADSL b. WLL c. PONs d. CATV 10 points QUESTION 20 1. What standard enables broadband access over SMF? a. ADSL b. WLL c. PONs d. CATV IT 300 Modern Telecommunications Dr. Riki Y. Morikawa 1 Lecture 7 Networks 2 Networks Public Switched Telephone Network Public Switched Telephone Network (PSTN) – aka Plain Old Telephone Network (POTS): Started as an all analog telephone voice network Today the PSTN infrastructure is mostly digital In most cases, provides the infrastructure to support WANs and MANs, Internet Provides user digital access to networks such as the Internet (..other access methods through satellite, CATV, cellular, etc.) Wide Area Networks (WAN): 3 Extends telecommunications over a large geographic area Connects smaller networks such as several Local Area Networks (LANs) and Metropolitan Area Networks (MANs) together Digital network Networks Public Switched Telephone Network – A bit of History 1876 –Alexander Graham Bell demonstrates the first telephone 1877 – The Bell Telephone Company created 1885 – American Telegraph and Telephone (AT&T) – subsidiary of the Bell System, long distance telephone network 1913 – The Kingsbury Agreement The Wilson administration considers anti-trust proceedings Mr. Kingsbury (AT&T vice president) agrees to stop acquisition of other telcos Interpreted as an agreement to allow AT&T to function as a regulated monopoly from 1913 to 1984. March 3, 1847 – August 2, 1922 4 Networks Public Switched Telephone Network – A bit of History Congress passed the Communications Act of 1934, Federal Communications Commission (FCC) was established 1956 Hush-a-Phone decision Challenged by AT&T, reaffirmed by the FCC U.S. Court of Appeals in DC reversed decision – allowed devices not manufactured by AT&T to be attached mechanically to telephones. The restriction against interconnecting to AT&T’s network challenged in 1965 and lifted in 1968 through the Carterfone decision 5 1968, the FCC “Carterfone” decision http://www.textually.org/textually/ar chives/images/set2/hush-a-phonead.gif Networks Public Switched Telephone Network – A bit of History In 1969, Microwave Communications International (MCI) began carrying business phone calls over microwave links. 1973: MCI begins to meet with DOJ to discuss AT&T Nov 20, 1974 DOJ files antitrust suit against AT&T 1982 – The Modified Final Judgment (MFJ) – The Justice Department’s primary goal for breaking up AT&T was to spur innovation and competition 6 1984, Jan 1 Divestiture took place 22 former Bell Operating Companies (BOCs) were reorganized into seven Regional Bell Operating Companies (RBOCs). (aka Regional Holding Companies (RHCs)) Networks Public Switched Telephone Network – A bit of History FCC Telecommunications Act of 1996 – convergence of data networking 7 Allowed new entrants into the telecommunications market (i.e., dot.com era) Bells were allowed to offer long-distance and Internet access Bells would have to sell access to their existing landline networks at a fair price Entrepreneurs began building massive fiber networks Many failed “start-up” companies Frenzy of mergers and acquisitions in the telecomm. industry Networks Public Switched Telephone Network – Regulation and Standards National regulatory organizations such as the FCC exist in every country Regulation is heavily influenced by the ITU-T International Telecommunication Union – chartered by the United Nations (UN) ISO – International Organization for Standardization Non-governmental organization (NGO) Comprises national-level standards organizations from 156 countries (United States rep. is ANSI – American National Standards Institute) ISO has great influence over a wide range of international standards (e.g., OSI – Open Systems Interconnection Reference Model) 8 Networks Public Switched Telephone Network – NPA Numbering Plan Administration (NPA) enables connectivity to other telephones ITU-T is responsible for NPA at the international level, each nation or region has similar responsibility within their domains ITU-T E.164 recommendation specifies NPA convention Maximum of 15 digits Figure 7.1. ITU-T E.164 International Telephone Numbering Plan. 9 Networks Public Switched Telephone Network – Infrastructure Today’s PSTN is a collection of mostly digital equipment such as switches connected by a variety of communications links (UTP, fiber optic, microwave, satellite, cellular, etc.) Central Office – facility where local loops connect to the PSTN infrastructure International Gateway Facilities (IGF) – provide connectivity between international carriers Carriers now provide the Public Data Network (PDN) to users 10 PDN protocols map to Layers 1 & 2 of the OSI RM (T-1, SONET, WDM/DWDM, ATM, FR, Carrier Ethernet, etc.) PDN is part of the PSTN PDN ex.: WAN (private and public), Internet Networks Public Switched Telephone Network – Infrastructure – PDN Voice Support: Traditional PSTN provided 4kHz analog voice PDN supports digitized voice using PCM techniques – uncompressed 64kbps voice grade channel (Layers 1 & 2) Today analog local loop still exist Many techniques use data compression techniques VoIP is a digitized voice stream using Real Time Protocol (RTP) Layers 5 to 7 over UDP/IP Layers 3 & 4 – supported via ISP Dedicated Circuit– physical circuit leased for exclusive by user Circuit Switched – physical circuit exclusively assigned for duration of call, then released Virtual Circuit – physical circuit shared by other users, but transparent to the user Permanent Virtual Circuit – physical routing always the same Switched Virtual Circuit – similar to circuit switched only virtual 11 Networks Public Switched Telephone Network – Infrastructure Customer Premises Equipment (CPE) – e.g., telephones, PBXs, computers, facsimile, etc. Demarcation Point (demarc) – point of delineation between CPE and the carrier network PBX (Private Branch Exchange) is a switch owned by a user Network Interface Unit (NIU) – a.k.a. Network Interface Device (NID) – includes high voltage/current spike protection Local Loop (UTP, fiber optic, coaxial, WLL, etc.) Switches are located within the Central Office (CO) Trunks connect network switches together which form the network 12 Trunks can be wired, fiber optic, microwave, satellite, etc. Networks Public Switched Telephone Network – Control and Signaling Common Channel Signaling (CCS) is a robust sub-network that supports signaling and control In-Band Signaling & Control functions take place over the same physical path as the conversation Signaling System 7 – current ITU-T version Disruptive and intrusive Seldom employed except on analog local loops Out-of-Band Signaling & Control takes places outside of conversation channel 13 No interference between signaling/control and conversation Networks Public Switched Telephone Network – Dedicated Circuits T-1 T-carrier is a dedicated digital, leased-line service offering that employs TDM to multiplex channels T-carrier is physical medium independent OSI Layer 1 T-1 = 1.544 Mbps Initially developed to support only voice transmission but now supports data, image and video Channelized T-1 supports 24 DS0 64kbps voice grade channels Unchannelized T1 supports data applications that do not lend themselves to 64 kbps channelization 14 Networks Public Switched Telephone Network – Dedicated Circuits T-1 F DS0 1 DS0 2 Each Byte supports 1 voice channel DS0 3 DS0 4 DS0 5 … DS0 24 T-1 Frame 24 Bytes (supporting 24 DS0 channels) + 1 framing bit = 193 bits Therefore, if we want to support (24) 64 kbps voice grade circuit, we need to have a frame rate of 8000 frames per second, or 8000 frames/sec * 193 bits/frame = 1.544 Mbps DS-0 (Digital Signal Level Zero) Voice grade channel BWfreq = 4kHz Nyquist Rate fs ≥ 2xBWfreq = 8000 sps 8000(sps)=64kbps 15 7.4.2 Channelized T1 16 17 Networks Public Switched Telephone Network – SONET Synchronous Optical Network (SONET) is a North American standard for broadband communications over Single Mode Fiber (SMF) OSI Physical layer (Layer 1) Use of a central timing source that generates and distributes clock signals (high costs) Synchronous Digital Hierarchy (SDH) is the international version specified by ITU-T Atomic clock minimizes buffering (PRS Stratum 1 primary reference source – 72 days between slips) SONET continues to compete – Ethernet over SONET 18 Networks Public Switched Telephone Network – SONET SONET an SDH are based on the Optical Carrier (OC) concept On the optical side, the minimum OC level is OC-1 at 51.84 Mbps OC levels can go as high as OC-768, 40 Gbps STS (Synchronous Transport Signal) is the electrical equivalent of the SONET optical signal (OC-1) Known as Synchronous Transport Module (STM) in SDH OC-3 = STS-3 = STM-1 = 155.52 Mbps 19 Networks Public Switched Telephone Network – SONET 20 Networks Public Switched Telephone Network – SONET SONET Frame: 9 rows x 90 Bytes = 810 Bytes Each SONET Frame is 125×10-6seconds per frame, or 1/ 125×10-6seconds = 8000 frames per second STS-1 = 810 Bytes/fr x 8 bits/Byte x 8000 fr/sec = 51.84 Mbps Support 672 DS-0s (64 kbps each) 21 Networks Public Switched Telephone Network – WDM/DWDM Wavelength Division Multiplexing (WDM) – multiplexing of different “colors” of light (i.e., prism) to enable multiple channels on a single fiber (four wavelengths separated by 10nm each) Dense WDM (DWDM) – Increased the number of wavelengths up to 32, and even 160 Requires more stable laser sources WDM is more cost effective than SONET – simply add more wavelengths vice upgrading equipment SMF required although MMF can be used for short ranges (i.e., within a building) Physical Layer SONET over DWDM hybrid systems have been used 22 Networks Public Switched Telephone Network – ATM ATM (Asynchronous Transfer Mode) is a fast cellswitched technology for broadband signals (ITU-T) OSI Layer 1 & 2 Still offered by service providers 53 octets fixed cell length Connection-Oriented Use of small fixed cell size advantage: Predictable latency, offers QoS Supports numerous forms of information (voice, images, video, data, etc.) ATM switches are use to switch cells from one switch to another SONET/SDH preferred physical medium 23 Networks Public Switched Telephone Network – ATM ATM Physical Layer – Manages the physical medium ATM Layer – •Provides cell multiplexing of virtual circuits over the physical link •Congestion control •Cell header generation /address translation •Sequential delivery – connection-oriented ATM Adaptation Layer – AAL isolates higherlevel protocols •Prepares/Segregates user data into 48 bytes information payloads 24 Networks Public Switched Telephone Network – FRAME RELAY Frame Relay (FR) is a “Fast Packet Technology” that became very popular in the 1990s FR transmits variable sized frames (i.e. packets up to 4096 octets) In 2014 IP-enabled FR; AT&T offers frame relay services to business and gov’t customers (2015) Cheaper alternative to dedicated leased lines (T-1 and T-3) Designed to support “bursty” traffic (ex., LAN-to-LAN) variable length frames can lead to unpredictable levels of congestion FR standards address OSI Layers 1 and 2 Connection-oriented at the Data Link Layer 25 Networks Public Switched Telephone Network – Carrier Ethernet Shared Ethernet (traditional LAN) – data collisions possible Switched Ethernet – reduces data collisions (HDX), eliminates data collisions (FDX) Carrier Ethernet – native Ethernet supported; considered a viable Layer 2 protocol for MAN and WAN connectivity CE 1.0 Services (CE 2.0 from MEF, Metropolitan Ethernet Forum, is newest generation): E-Line E-LAN E-Tree E-Access E-Transit Ethernet over SONET/SDH 26 Figure 7.12. E-Line service (UNI to UNI). Figure 7.13. E-LAN service (multiple UNI interconnected over the MEN). Figure 7.14. E-Tree service (root and leaf EVC). Figure 7.15. E-Access service (EVC between UNIs located on different MENs). 27 Figure 7.16. E-Transit service (E-NNI to E-NNI connection). Networks Network Devices – PBX (Private Branch Exchange) User-owned and operated switch vice service switch 28 Large organizations Requires user to have technical expertise Networks Network Devices – CENTREX Service provider owned switch offered to users 29 Provides similar functionality as a PBX for a monthly fee Users do not have to have technical expertise Networks Network Devices – ACD Automatic Call Distributors (ACDs) 30 PBXs that switch incoming calls to a call center Employs Interactive Voice Response (IVRs)
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