School of Business Eastern Illinois University Telecommunications systems (Part 2) Abdou Illia, Spring 2007 (Week 12, Thursday 3/29/2007) T-1 Digital Subscriber Line (DSL) Cellular Telephone System Integrated Services Digital Network (ISDN) Learning Objectives 2 Describe and compare types of connections offered by telephone companies Explain Cellular Telephone System T-1 Leased lines 1
Trunk lines 4 Trunk lines = Transmission lines that connect telephone switches Trunk lines operate at speed from 56 kbps to 40 Gbps Synchronous Optical Network T-1 1.544 Mbps T-3 45 Mbps SONET768 40 Gbps Trunk lines T-1 Lines 5 Access Line T-1 Trunk Line (1.544 Mbps) Trunk Line Computer Telephone Switch Telephone Switch Telephone Switch Server T-1 Leased Line (1.544 Mbps) End-to-End Circuit with Trunk Line Speed T-1 Leased lines 6 T-1 Leased lines: Extend T-1 trunk line speeds to end-to-end circuits between two locations (e.g. 2 customer offices) Require fiber optic or at least a special data-grade twisted Pair (Note: fiber optic is used for T-3 and SONET) Data-Grade Twisted Pair Q: What is the difference between T-1 Trunk line and T-1 Leased line? Q: In T-1 Leased lines, what kind of TP is used to connect a customer to the 1 st telephone switch? 2
T-1 Lines 7 The customer can request Fractional T-1 lines that offer low-speed choices, typically: 128 bps 256 kbps 384 kbps 512 kbps 768 kbps T-1 Costs depend on distance: ~$350-400/mo for local connection (non long-distance) ~$1200/mo plus 2.50/mile for long-distance connection Digital Subscriber Line - DSL Digital Subscriber Line (DSL) 9 Standard telephone line (Cat 1 UTP) Capable of handling more than 3.1 Khz bandwidth DSL exploits Standard telephone line s extra capacity to transmit data without disturbing the line s ability to transmit voice Bandwidth usage for some Asymmetric DSL (ADSL) service: 0-4 Khz band for Voice conversation Upstream transmission in 25 160 Khz band Downstream transmission in 240 1500 Khz band DSL uses Filters (splitters) to separate voice and data signals Typically a filter is needed for each analog device (telephone, fax, etc.) 3
Digital Subscriber Line (DSL) 10 User End Telephone Company End Office Switch Data WAN PC DSL Modem Standard telephone line Telephone Splitter DSLAM* PSTN * DSL Access Multiplexer: (1) mixes data from many customers and (2) forwards mixed packets Digital Subscriber Line (DSL) 11 User End Telephone Company End Office Switch Data WAN PC DSL Modem Telephone Splitter DSLAM PSTN Q: On the user end, what elements are needed to establish a DSL connection? Digital Subscriber Line (DSL) 12 DSL speed: 256 kbps 24000 kbps Digital Subscriber Lines (DSLs) Asymmetric DSL (ADSL) Standard ADSL Downstream (to customer): 256 kbps to over 1.5 Mbps Upstream (from customer): 64 kbps or higher ADSL2 Downstream (to customer): 5 Mbps to aver 12 Mbps Upstream (from customer): 1 Mbps to 3.5 Mbps Q: How can a 3.5 Mbps upstream speed be achieved with Cat 1 UTP? 4
Digital Subscriber Line (DSL) 13 Digital Subscriber Lines (DSLs) HDSL (High-rate DSL) Needed in business. (ADSL primarily for home and small business access.) Maximum range: 3 kilometers Symmetric speed over voice-grade twisted pair HDSL: symmetric 768 kbps HDSL2: symmetric 1.544 Mbps or symmetric 2.3 Mbps Summary Questions 1. What is the difference between a T-1 Trunk line and T-1 Leased line? Answer: A T-1 trunk line only runs between two switches within the telephone network. T-1 Leased lines extend T-1 trunk line speeds to end-to-end circuits between 2 locations. 14 2. In T-1 Leased lines, what kind of twisted pair wire is used to connect a customer to the 1st telephone switch? Answer: Data-grade TP which is a category 2 TP. Summary Questions 3) On the user end, what elements are needed to establish a DSL connection? A DSL modem and splitter(s) to separate regular analog channel from the DSL data channels. 4) ADSL provides for higher downstream speeds than upstream speeds. (a) Is this good for web service? (b) Is it good for videoconferencing? a) Asymmetric speeds are good for web service because http requests tend to be small but downloaded material are large. (b) It is not good for videoconferencing, which needs high speed in both directions. 15 5
Twisted Pair wires 16 Cellular Telephone System Cells, Cellsites, MTSO 18 PSTN Mobile Telephone Switching Office Cellsite G D K Metropolitan service area is divided B into cells. H N Cellsite in each cell A communicates E with cellphones. C I L O P MTSO controls all cellsites, links cellular system to PSTN. F J M 6
PSTN Cellular Telephone: The big picture Mobile Telephone Switching Office Cellsite 19 G D K B H N A C E I L O P Cellsite main components: - Transceiver - Devices for supervising cellphones operation (initiating calls, terminating calls, etc.) F J M Why cells? 20 PSTN Mobile Telephone Switching Office Channel 47 A Why cells? F So channels can be reused in different cells. Channel reuse allows more customers J to be supported. B C D E G H I K L M Cellsite N P O Mobility 21 Handoff Switching service from one cellsite to another when users move from cells to cell in a system (city) Roaming Switching service from one MTSO to another when users move from one system (city) to another. N L O Handoff P 7
Generations of Cellular Technology 22 Generation 1G 2nd 3G Year 1980 1990 2002 Signaling Analog Digital Digital Data Transfer Rate Technology Data transfer is difficult; ~5 kbps Frequency Division Multiplexing FDM 10 kbps 30 kbps to 500 kbps Code Code Division Division Multiplexing Multiplexing CDM CDM Summary Questions 23 1) In cellular technology, what is: a) A cell? b) A cellsite? 2) What is the benefit of using cells instead of a large geographical area? 3) What are the main functions of a Mobile Telephone Switching Office (MTSO)? 4) Distinguish between handoff and roaming. Integrated Services Digital Network- ISDN 8
Integrated Services Digital Network 25 Personal Computer Original idea: one voice channel, one data channel 2. 64 kbps B Channel Analog Voice Signal On Telephone Wires 1. 64 kbps B Channel Digital Signal On Serial Cable (1010) ISDN Wall Jack (RJ-45) Desktop Telephone Integrated Services Digital Network 26 Personal Computer 64 kbps B Channel Digital Signal On Serial Cable (1010) ISDN Modem Internal DSU Converts Serial Port Signal to Digital B Channel Signal at 64 kbps (1010) All-digital Service (1101001..) ISDN Wall Jack (RJ-45) Desktop Telephone The Data Channel Uses 232 Serial Cable Integrated Services Digital Network 27 Personal Computer The Voice Channel Uses Home Telephone Cord ISDN Wall Jack (RJ-45) ISDN Modem 64 kbps B Channel All-digital Internal Codec Analog Voice Signal Service Converts On Telephone Wires (1101001..) Analog Voice Signal to Digital B Channel Signal at 64 kbps (000010000)) Desktop Telephone 9
Integrated Services Digital Network 28 Personal Computer 64 kbps B Channel Digital Signal On Serial Cable (1010) Internal DSU Converts Serial Port Signal to Digital B Channel Signal at 64 kbps (1010) ISDN Wall Jack (RJ-45) ISDN Modem All-digital Service (1101001..) Desktop Telephone Bonding Use Both B Channels for Data Send and Receive at 128 kbps Integrated Services Digital Network 29 Dial Up: Not always connected Do not have to pay for full-time use Good if usage is small per day, say to upload sales data from retail once per night ISDN Costs 30 Must install an ISDN line Will cost more than telephone line Actually, could use your existing phone line But then would need one B channel for telephony 10
ISDN Costs 31 Need ISDN modem (expensive) Costs for standard ISDN service $40/mo plus $1.00/minute for usage ISDN tend to be used as a backup service. Example: Most banks communicate with headquarters using T-1, SONET, etc. If these services fails, they activate the ISDN connection. Summary Questions 5. (a) What is the highest speed you can have to and from an ISP using ISDN? (b) Is ISDN an alwaysactive service? (c) How is it likely to be used in corporations? Why? (a) With bonding, ISDN can provide 128 kbps Internet access. (b) ISDN is NOT an always-on service. It is a dialup service like ordinary telephone service. (c) It is likely to be a backup service because ISDN payments are modest except when the service is being actively used 32 11