Transcript N6C06-PPT r1 for Instructors.PPT
Telecommunications
Chapter 6 Updated January 2007 Panko’s
Business Data Networks and Telecommunications, 6th edition
Copyright 2007 Prentice-Hall May only be used by adopters of the book
Telecommunications
• From Chapter 1: – Data communications – Telecommunications: Voice and Video Communications 6-2
Technical Elements of the Public Switched Telephone Network
Figure 6-1: Elements of the Public Switched Telephone Network (PSTN)
1. Customer Premises Equipment 1. Customer Premises Equipment 6-4
Figure 6-2: Customer Premises Equipment
Site Handset PBX 4-Pair UTP Telephone Wiring PSTN A typical business site.
The private branch exchange is an internal switch for the site.
4-pair UTP was created for business premises telephone wiring Company is essentially its own telephone company that connects to the outside PSTN 6-5
Figure 6-1: Elements of the Public Switched Telephone Network (PSTN)
2.
Access Line (Local Loop) The Access System consists of the access line to the customer (called the local loop) and termination equipment at the end office (nearest telephone office switch).
2.
Access Line (Local Loop) 2. & 3. End Office Switch (Class 5) 6-6
Figure 6-1: Elements of the Public Switched Telephone Network (PSTN)
3. Transport Core 3.
Switch 3. Trunk Line The Transport Core connects end office switches and core switches.
Trunk lines connect switches.
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Figure 6-1: Elements of the PSTN
• Telephone Company Switch 6-8
Figure 6-1: Elements of the Public Switched Telephone Network (PSTN)
4. Signaling System Transport is the actual transmission of voice.
Signaling is the control of calling (setup, teardown, billing, etc.).
SS7 in the United States C7 in Europe 6-9
Figure 6-3: Points of Presence (POPs)
Local Access and Transport Area (LATA) Local Carrier 1 Sw itch POP Long-Distance Carrier A Other Local Area POP Local Carrier 1 Customer Local Carrier 2 Sw itch Local Carrier 2 Customer International Carrier X Other Country In the U.S., competing carriers connect at points of presence (POPs).
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Figure 6-4: Circuit Switching
The PSTN has traditionally used circuit sw itching.
A circuit is an end-to-end connection betw een tw o subscribers.
Capacity is reserved on all trunk lines and sw itches along the w ay.
Capacity must be paid f or even if it is not used.
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Figure 6-5: Voice and Data Traffic
Full-Duplex (Two-Way) Circuit Voice Traffic: Fairly Constant Use; Circuit Switching Is Fairly Efficient Full-Duplex (Two-Way) Circuit Data Traffic: Short Bursts, Long Silences; Circuit Switching Is Inefficient The reserved capacity of circuit switching is OK for voice, but not for bursty data transmission.
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Figure 6-6: Dial-Up Circuits Versus Leased Line Circuits
Operation Speed for Carrying Data Number of Voice Calls Multiplexed Dial-Up Circuits Dial-Up. Separate circuit for each call.
Up to 56 kbps Residence can only Send up to 33.6 kbps One Leased Line Circuits Permanent circuit, always on.
56 kbps to gigabit speeds Several due to multiplexing There are two types of circuits between customer premises: ordinary dial-up circuits and leased line circuits.
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Figure 6-7: Local Loop Technologies
Technology 1-Pair Voice-Grade UTP 2-Pair Data-Grade UTP Optical Fiber Use Residences Businesses for Lowest-speed access lines Businesses for higher-speed access lines Status Already installed Must be pulled to the customer premises (this is expensive) Must be pulled to the customer premises (this is expensive) Residential 1-pair voice-grade UTP is already installed.
This makes it inexpensive to use Business 2-pair data-grade UTP and fiber for leased lines must be installed; this is expensive.
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Figure 6-8: Analog Telephone Transmission
Analog (Analogous) Electrical Signal Sound Wave Analog signals rise and fall in intensity with the human voice.
No resistance to errors as there is in digital transmission.
Initially, the entire PSTN was analog.
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Figure 6-9: The PSTN: Mostly Digital with Analog Local Loops
Today's Telephone Network: Predominantly Digital Residential Telephone (Analog) Local Loop (Analog) Switch (Digital) Switch (Digital) Trunk Line (Digital) Switch (Digital) Local Loop (Digital) PBX (Digital) Today, everything is digital except for the local loop access line and residential telephones.
The actual local loop line can carry either analog or digital signals, but the equipment at both ends is analog.
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Figure 6-10: Codec at the End Office Switch
Analog Signal ADC Digital Signal Telephone Home Local Loop Codec DAC Digital Switch End Office A codec at the end office translates between residential analog and PSTN digital signaling.
ADC = analog to digital conversion DAC = digital to analog conversion 6-17
Figure 6-11: Frequency Division Multiplexing (FDM) in Microwave Transmission
Box: Codec Operation Microwave uses radio transmission for PSTN trunk lines Channel 1 / Circuit A Channel 2 / Circuit D Channel 3 / Circuit C Channel 4 / Unused Channel 5 / Circuit E Each circuit is sent in a separate channel.
If channel bandwidth is large, there will be fewer channels.
Voice uses 4 kHz-wide channels to allow more channels.
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Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Step 1: Bandpass Filtering Box: Codec Operation Analog Voice Signal Analog Electrical Signal Subscriber Filter at End Office Switch At the end office, the voice signal is bandpass-filtered to limit its bandwidth to 4 MHz.
This permits more calls to be multiplexed on trunk lines 6-19
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box: Codec Operation Step 1: Bandpass Filtering Signal Energy Distribution of Human Speech Along the Frequency Spectrum 0 Hz 300 Hz 3,400 Hz (3.4 kHz) 20 kHz Frequency Bandwidth (3.1 kHz) Actually, to provide a safety margin, the signal is filtered to between about 300 Hz and 3.4 kHz instead of from 0 Hz to 4 kHz.
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Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling 255 (maximum) Analog Signal Signal Amplitude Duration of Sample (1/8000 sec.) Box: Codec Operation 0 Nyquist found that signals must be Sample For a top frequency of 4 kHz, there must be 8,000 samples per second.
Each sample is 1/8000 second.
Time 6-21
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling 255 (maximum) Analog Signal Signal Amplitude Box: Codec Operation Duration of Sample (1/8000 sec.) 0 Intensity of Sample (125/255 or 01111101) Sample In each sampling period, the intensity of the signal is measured.
In pulse code modulation, the signal is measured as one of 256 intensity levels.
Time One byte stores one sample.
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Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling 255 (maximum) Signal Amplitude 0 Analog Signal Duration of Sample (1/8000 sec.) Intensity of Sample (125/255 or 01111101) Sample Pulse Code Modulation (PCM) produces 8,000 one-byte samples per second.
This is 64 kbps of data.
Time Box: Codec Operation 6-23
ADC Recap
Box: Codec Operation • First, Bandpass-Filter the Incoming Signal to 4 kHz – Really about 300 Hz to 3.4 kHz – To reduce transmission requirements • The Codec then Uses PCM for the Conversion – Samples at twice the highest frequency (4 kHz so 8,000 samples/second) – Loudness is recorded with 8 bits per sample (to give 256 loudness levels) – Generates 64 kbps of traffic (8 bits/sample times 8,000 samples per second) 6-24
Figure 6-13: Digital-to-Analog Conversion (DAC)
One 8-Bit Sample Box: Codec Operation One 8-Bit Sample 00000100 00000011 00000111 To Customer: Generated “analog” signal (Sounds smooth because the sampling rate is very high) DAC at End Office Switch From digital PSTN network: Arriving digital signal from the PSTN Core (8,000 Samples/Second) 6-25
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Office PSTN G D Channel 47 B H A E C In cellular technology, the region F is divided into smaller cells.
I J In each cell, a cellsite serves cellphones in the cell.
M K L Cellsite N P O Handoff 6-26
Figure 6-14: Cellular Telephony
• Cellsites 6-27
Figure 6-14: Cellular Telephony
PSTN Channel 47 A Channel reuse supports more customers.
This is the reason for using cells.
G D K B H N E L P C I O F M Handoff J 6-28
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Office PSTN Channel 47 D cell to another in a cellular system, A When a subscriber moves from E one city to another, this is roaming.
F (In WLANs, handoffs and roaming mean the same thing.) G H I J M K L Cellsite N P O Handoff 6-29
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Office PSTN D Channel 47 A coordinates the cellsites and E The MTSO also connects cellphones to the PSTN (called the wireline network).
F Cellsite G H I K L M N P O Handoff J 6-30
Cellular Technologies
• GSM is the worldwide standard for cellular voice – Uses time division multiplexing (TDM) – Uses 200 kHz channels – Divides each second into many frame periods – Divides each frame into 8 slots – Gives same slot in each frame to a conversation Time Frame 1 Frame 2 Slot 1 Conversation A Slot 2 Conversation B …… Slot 8 Conversation H Slot 1 Conversation A 6-31
Cellular Technologies
• Cannot use the same channel in adjacent cells – So can only reuse a channel about every 7 cells – For example, suppose there are 50 cells • Channel can be reused 50 / 7 times • This is 7 (not precise, so round things off) • So each channel can support 7 simultaneous customers in these 7 cells 6-32
Cellular Technologies
• Code Division Multiple Access (CDMA) – Also used in the United States – A form of spread spectrum transmission – Unlike traditional spread spectrum technology, multiple users can transmit simultaneously – 1.25 MHz channels – Can support many users per channel • Can use the same channel in adjacent cells – So can only reuse a channel in every cell 6-33
Figure 6-15: Voice over IP (VoIP)
PC with Multimedia Hardware and VoIP Software VoIP carries telephone calls over LANs and the Internet With IP, there is no wasted capacity as there is with circuit switching.
This reduces cost.
Internet Media Gateway IP Telephone with Codec and TCP/IP Functionality PSTN 6-34
Figure 6-15: Voice over IP (VoIP)
Stations can be special IP telephones with IP functionality Or a PC with multimedia hardware and VoIP software PC with Multimedia Hardware and VoIP Software IP phones need a codec to convert voice analog signals from the microphone into digital IP signals Media Gateway IP Telephone with Codec and TCP/IP Functionality PSTN 6-35
Figure 6-15: Voice over IP (VoIP)
PC with Multimedia Hardware and VoIP Software A media gateway connects a VoIP network to the PSTN Handles transport and signaling differences Internet Media Gateway IP Telephone with Codec and TCP/IP Functionality PSTN 6-36
Figure 6-16: Speech Codes
Codec
G.711
G.721
G.722
G.722.1
G.723.1A
Transmission Rate
64 kbps (pulse code modulation) 32 kbps (adaptive PCM) 46, 56, or 64 kbps 24, 32 kbps 5.3, 6.3 kbps There are several codec standards.
They differ in transmission rate, sound quality, and latency.
Both sides must use the same codec standard.
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Figure 6-17: VoIP Protocols
Signaling: SIP or H.323
(Call setup, breakdow n, accounting, and other supervisory tasks) VoIP Transport Packet Codec Data Stream RTP Hdr UDP Hdr IP Hdr PC w ith Multimedia and VoIP Sof tw are Transport (Voice transmission) Transport is the transmission of voice (carries codec data).
Signaling is call supervision.
IP Telephone 6-38
Figure 6-17: VoIP Protocols
1. VoIP transport packets use UDP at the transport layer.
Signaling: SIP or H.323
(There is no time for retransmissions to repair errors.) The receiver puts in fill sounds for lost packets.
3.
The application message is a codec data stream PC w ith Multimedia and VoIP Sof tw are VoIP Transport Packet Codec Data Stream RTP Hdr UDP Hdr IP Hdr Transport (Voice transmission) IP Telephone 2. The UDP header is followed by a Real Time Protocol (RTP) header, which contains a sequence number and timing information.
Receiver uses timing information to smooth out sound playback.
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Figure 6-17: VoIP Protocols
Signaling: SIP or H.323
(Call setup, breakdow n, accounting, and other supervisory tasks) VoIP Transport Packet Codec Data Stream RTP Hdr UDP Hdr IP Hdr PC w ith Multimedia and Transport Signaling is call supervision.
IP Telephone The H.323 signaling standard came first for VoIP signaling.
SIP is simpler and now dominates VoIP signaling 6-40
Video over IP
• The Other VoIP – It’s not just voice over IP – Video Telephones – Video Conferencing • PC to PC • Multiparty • Sometimes room-to-room – Video Downloads on Demand 6-41
Figure 6-18: Residential Internet Access Services
• Telephone Modems Note: Speeds and Prices Change Rapidly • Broadband Internet Access • Asymmetric Digital Subscriber Line (ADSL) • Cable Modem Service • 3G Cellular Data Service • WiMAX (802.16d and 802.16e) • Broadband over Power Lines • Fiber to the Home (FTTH) 6-42
Figure 6-19: Telephone Modem Connection to an ISP
Telephone modems convert digital computer signals to analog telephone signals.
PSTN (Digital) Analog Client A Digital 33.6 kbps Analog Access Line Telephone Modem Telephone 56 kbps 6-43
Figure 6-19: Telephone Modem Connection to an ISP
PSTN (Digital) Digital Leased Line (No Modem) Digital 56 kbps ISP does not have a modem.
It has a digital leased line so can send at 56 kbps.
(There is no bandpass filtering on digital leased lines.) 33.6 kbps ISP 6-44
Figure 6-19: Telephone Modem Connection to an ISP
Client A PSTN (Digital) Analog Digital 33.6 kbps Analog Access Line Telephone Modem Telephone 56 kbps Digital Access Line (No Modem) Digital 56 kbps 33.6 kbps Circuit ISP Dial-up circuits connect the client with the ISP.
56 kbps downstream, 33.6 kbps upstream 6-45
Telephone Modem Limitations
• Very low transmission speeds – Long delays in downloading webpages • Subscriber cannot simultaneously use the telephone line for voice calls • Still used by 30% to 40% of Internet users.
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Figure 6-20: Amplitude Modulation
Binary Data Modulated Analog Signal PSTN Client A Serial Cable Modem Telephone Cable Telephone Amplitude Modulation Modulation is the conversion of binary computer signals into analog signals that can travel over an ordinary access line.
Demodulation, at the other ends, converts the modulated 1 signals back to digital computer signals.
1 6-47
Client A
Figure 6-20: Amplitude Modulation
Modulated Analog Signal Serial Cable two amplitude (loudness levels) — one for 1 and one for 0 Modem Telephone Cable Telephone Amplitude Modulation PSTN 1 0 1 1011 is loud-soft-loud-loud 1 6-48
Figure 6-21: Asymmetric Digital Subscriber Line (ADSL)
Subscriber Premises Telephone Company End Office Switch PC ADSL Modem Single Pair of Voice-Grade UTP Wires Data WAN Splitter DSLAM PSTN Telephone ADSL
ALSO
uses the existing residential local loop technology.
Inexpensive because no need to pull new wires, but 1-pair voice-grade UTP is not designed for high-speed transmission.
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Figure 6-21: Asymmetric Digital Subscriber Line (ADSL)
1.
Subscriber needs an ADSL modem.
End Office Switch telephone wall outlet.
PC ADSL Modem Single Pair of Voice-Grade UTP Wires Data WAN Splitter DSLAM Telephone 2.
Telephone carrier needs a digital subscriber line access multiplexer (DSLAM) to separate the two signals.
PSTN 6-50
Figure 6-21: Asymmetric Digital Subscriber Line (ADSL)
Subscriber Premises Downstream Data Up to 3 Mbps Telephone Company End Office Switch PC Telephone ADSL Modem Upstream Data Up to 512 kbps Single Pair of Voice-Grade UTP Wires Data WAN Splitter DSLAM PSTN Ordinary Telephone Service Unlike telephone modems, ADSL service provides simultaneous voice and data transmission.
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Figure 6-21: Asymmetric Digital Subscriber Line (ADSL)
Subscriber Premises Downstream Data Up to 3 Mbps Telephone Company End Office Switch PC Telephone Upstream Data Up to 512 kbps ADSL Modem Single Pair of Voice-Grade UTP Wires Splitter DSLAM Speed is
asymmetric
Faster downstream than upstream (Up to 3 Mbps versus up to 512 kbps) Ideal for Web access Acceptable for e-mail Good for residential use Data WAN PSTN 6-52
Figure 6-22: Cable Modem Service
Coaxial Cable in Neighborhood (Shared Throughput) Maximum dow nload throughput is about 5 Mbps ISP Coaxial Cable Drop Cable PC UTP or USB Cable Modem Neighborhood Splitter Optical Fiber to Neighborhoods Cable Television Head End Subscriber Premises Cable modem service brings high-speed optical fiber lines to the neighborhood.
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Figure 6-22: Cable Modem Service
Thick Coaxial Cable in Neighborhood (Shared Throughput) Thin Coaxial Cable Drop Cable PC UTP or USB Cable Modem Neighborhood Splitter Subscriber Premises In the neighborhood, thick coaxial cable brings service to Fiber to shared by everyone in the neighborhood.
A thin coax line goes to each home’s cable modem.
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Figure 6-22: Cable Modem Service
Thick Coaxial Cable in Neighborhood (Shared Throughput) Thin Coaxial Cable Drop Cable PC UTP or USB Cable Modem Subscriber Premises Maximum dow nload throughput is about 5 Mbps Neighborhood Splitter Optical Fiber to Neighborhoods ISP Cable Television Head End Downstream speeds up to 5 Mbps.
Upstream speeds up to about 1 Mbps.
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ADSL versus Cable Modem Service
• Do Not Over-Stress the Importance of Sharing – Cable modem service usually is still faster than ADSL service – DSLAM sharing can slow ADSL service too • The Bottom Line Today: – Cable modem service usually is faster – ADSL service usually is cheaper • ADSL offers more speed-price options • Both are improving rapidly in terms of speed and (sometimes) price 6-56
Figure 6-23: Third-Generation (3G) Cellular Data Services
• Cellphone connects to computer via a cellphone modem or USB • Traditional GSM and CDMA – Limited to only about 10 kbps – Far too slow for usability 6-57
Figure 6-23: Third-Generation (3G) Cellular Data Services
• Both GSM and CDMA are evolving • Second Generation (now dominant) – Only 10 kbps data transmission • Third Generation – Low end: comparable to telephone modem service – High end: comparable to low-speed DSL service • Future – Speeds comparable to high-end DSL or cable modem service – 100 Mbps or more (fast enough for good video) 6-58
Figure 6-18: Residential Internet Access Services
• WiMax (802.16) – Wireless Internet access for metropolitan areas – Basic 802.16d standard: ADSL speeds to fixed locations • Will use dish antennas • Just reaching the market – 802.16e will extend the service to mobile users • Will use omnidirectional antennas 6-59
Figure 6-18: Residential Internet Access Services
New • Satellite Internet Access – Very expensive – Often needed to serve rural areas 6-60
Figure 6-18: Residential Internet Access Services
• Broadband over Power Lines – Broadband data from your electrical company – It already has transmission wires and access to residences and businesses – It can modulates data signals over electrical power lines – It works, but has very limited availability and is slow – Especially promising for rural areas 6-61
Figure 6-18: Residential Internet Access Services
• Fiber to the Home (FTTH) – Carrier runs fiber to the home – Provides speeds of tens of megabits per second for high speed video, etc.
• Less if fiber only goes to the curb (FTTC) • Or to the neighborhood (FTTN) – Much faster than other residential internet access services – Could dominate residential (and business) Internet access in the future 6-62
Internet Access and VoIP
• Most ISPs are Planning to or Already Provide VoIP Telephone Service – An alternative to the local telephone company service – Media gateways will interconnect with the PSTN – Should be less expensive that traditional phone service – Questions remain • Voice quality and reliability • 911 and 911 location discovery • Regulation and taxation • Laws that require wiretapping with warrants 6-63
Topics Covered
Telecommunications
• Data Communications versus Telecommunications • The PSTN’s Technical Elements – Customer premises equipment (PBX and 4-pair UTP) – Access system (local loop) – Transport core – Signaling (call setup and management) • POP to interconnect carriers 6-65
Telecommunications
• Access Lines – For residences, 1-pair voice-grade UTP • DSL uses existing residential access lines to carry data by changing the electronics at each end (DSL modem in the home and DSLAM at the end office switch) • DSL is cheap because 1-p VG UTP is already in place – For businesses, • 2-pair data-grade UTP for speeds up to a few Mbps • Optical fiber for faster speeds • Usually must be pulled into place, so expensive – Eventually, fiber to the home (FTTH), FTTC, FTTN 6-66
PSTN Transmission
• Circuit Switching – Reserved capacity end-to-end – Acceptable for voice, but not for bursty data transmission – Dial-up and leased line circuits • Analog and Digital Transmission – Analog signals on the local loop – ADC and DAC at the end office switch – ADC: bandpass filtering and sampling for 64 kbps – DAC: sample values are converted to sound levels 6-67
Cellular Telephony
• Cells Allow Channel Reuse – Channel reuse allows more customers to be served with a limited number of channels • GSM: most widely used technology for cellular telephony • CDMA for greater channel reuse • Handoffs and Roaming 6-68
VoIP
• To allow voice to be carried over data networks • Converge voice and data networks • Phone needs a codec • Transport: UDP header followed by RTP header • Signaling: H.323 and SIP • Video over IP 6-69
Residential Internet Access Services
• Telephone Modems • Asymmetric Digital Subscriber Line (ADSL) • Cable Modem Service • 3G Cellular Data Service • WiMAX (802.16 and 802.16e) • Broadband Over Power Lines • Fiber to the Home (FTTH) 6-70