Telecommunications systems
(Part 2)
School of Business Eastern Illinois University
© Abdou Illia, Spring 2007
(Week 12, Thursday 3/29/2007)
T-1
Digital Subscriber Line (DSL) Cellular Telephone System Integrated Services Digital Network (ISDN)
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Learning Objectives
Describe and compare types of connections offered by telephone companies
Explain Cellular Telephone System
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Trunk lines
Trunk lines = Transmission lines that connect telephone switches Trunk lines operate at speed from 56 kbps to 40 Gbps
Trunk lines
T-1 1.544 Mbps
T-3 45 Mbps
SONET768 40 Gbps Synchronous Optical Network
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T-1 Lines
Computer Telephone Switch Telephone Switch Telephone Switch Server Access Line T-1 Trunk Line (1.544 Mbps) T-1 Leased Line (1.544 Mbps) End-to-End Circuit with Trunk Line SpeedTrunk Line
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T-1 Leased lines
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?
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T-1 Lines
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
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Digital Subscriber Line (DSL)
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
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Digital Subscriber Line (DSL)
Data WAN PSTN DSLAM* DSL Modem Splitter Telephone Telephone Company End Office Switch
Standard telephone line PC
* DSL Access Multiplexer: (1) mixes data from many customers and (2) forwards mixed packets
User End
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Digital Subscriber Line (DSL)
Data WAN PSTN DSLAM DSL Modem Splitter Telephone User End Telephone Company End Office Switch
PC
Q: On the user end, what elements are needed to establish a DSL connection?
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Digital Subscriber Line (DSL)
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
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Digital Subscriber Line (DSL)
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
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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.
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.
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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.
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Twisted Pair wires
Cellular Telephone System
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Cells, Cellsites, MTSO
B E H D I G L K F C M A J N P O PSTN Mobile Telephone Switching Office Cellsite
Metropolitan service area is divided into cells. Cellsite in each cell communicates
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Cellular Telephone: The big picture
B E H D I G L K C M A J N P O PSTN Mobile Telephone Switching Office Cellsite
Cellsite main components: - Transceiver
- Devices for supervising cellphones’ operation (initiating calls, terminating calls, etc.)
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Why cells?
B E H D I G L K F C M A J N P O PSTN Mobile Telephone Switching Office Cellsite Why cells?So channels can be reused in different cells. Channel reuse allows more customers
to be supported. Channel 47 21
Mobility
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.
L N
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Generations of Cellular Technology
Generation 1G 2nd 3G
Year 1980 1990 2002
Signaling Analog Digital Digital
Data Transfer Rate
Data transfer is difficult; ~5 kbps 10 kbps 30 kbps to500 kbps Technology Frequency Division Multiplexing FDM Code Division Multiplexing CDM Code Division Multiplexing CDM 23
Summary Questions
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.
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Integrated Services Digital Network
Personal Computer
Desktop Telephone 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)
Original idea: one voice channel, one data channel
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Integrated Services Digital Network
Personal Computer Desktop Telephone “ISDN Modem” 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) All-digital Service (1101001..) ISDN Wall Jack (RJ-45)
The Data Channel
Uses 232 Serial Cable
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Integrated Services Digital Network
Personal Computer
Desktop Telephone 64 kbps B Channel Analog Voice Signal On Telephone Wires “ISDN Modem” Internal Codec Converts Analog Voice Signal to Digital B Channel Signal at 64 kbps (000010000)) All-digital Service (1101001..) ISDN Wall Jack (RJ-45)
The Voice Channel
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Integrated Services Digital Network
Personal Computer Desktop Telephone “ISDN Modem” 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) All-digital Service (1101001..) ISDN Wall Jack (RJ-45) Bonding
Use Both B Channels for Data Send and Receive at 128 kbps
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Integrated Services Digital Network
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
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ISDN Costs
Must install an ISDN line
– Will cost more than telephone line
Actually, could use your existing phone line
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ISDN Costs
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.
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Summary Questions
5. (a) What is the highest speed you can have to and from an ISP using ISDN? (b) Is ISDN an always-active service? (c) How is it likely to be used in corporations? Why?
(a) With bonding, ISDN can provide 128 kbps Internet access.
