Diversity A Technique to Mitigate the Effects of Fading and Dispersion
18.4.2.1 Scope. We discuss diversity to reduce the effects of fading and to mitigate dispersion. Diversity was briefly covered in Section 9.2.5 where we dealt with LOS microwave. In that section we discussed frequency and space diversity. In principle, such techniques can be employed either at the base station and or at the mobile unit, although different problems have to be solved for each. The basic concept behind diversity is that two or more radio paths carrying the same information are...
Numbering Plan For International Signaling Point Codes
The number plan described in ITU-T Rec. Q.708 Ref. 12 has no direct relationship with telephone, data, or ISDN numbering. A 14-bit binary code is used for identification of signaling points. An international signaling point code ISPC is assigned to each signaling point in the international signaling network. The breakdown of these 14 bits into fields is shown in Figure 14.8. The assignment of signaling network codes is administered by the ITU Telecommunication Standardization Sector previously...
The Human Voice
Human voice communication depends on the voice-generating mechanism of mouth and throat being the initial transmitter, with the acuity of the ear being the receiver. Frequency components of the human voice extend down to some 20 Hz and as high as 32,000 Hz. The lower frequency components carry the voice energy and the higher frequency components carry emotion. Figure 5.1 shows a distribution of energy and emotion of the typical human voice. The human ear and many devices and components of the...
Coding
Older PCM systems used a 7-bit code, and modern systems use an 8-bit code with its improved quantizing distortion performance. The companding and coding are carried out together, simultaneously. The compression and later expansion functions are logarithmic. A pseudologarithmic curve made up of linear segments imparts finer granularity to low-level signals and less granularity to the higher-level signals. The logarithmic curve follows one of two laws, the A-law and the -law pronounced mu-law ....
Channel Capacity
A leased or switched voice channel represents a financial investment. Therefore one goal of the system engineer is to derive as much benefit as possible from the money invested. For the case of digital transmission, this is done by maximizing the information transfer across the system. This section discusses how much information in bits can be transmitted, relating information to bandwidth, signal-to-noise ratio, and error rate. These matters are discussed empirically in Section 10.9.5. First,...
An Overview of the MPEG2 Compression Technique
This section is based on the ATSC Advanced Television System Committee version of MPEG-2, which is used primarily for terrestrial broadcasting and cable TV. The objective of the ATSC standard Refs. 16, 17 is to specify a system for the transmission of high-quality video, audio, and ancillary services over a single 6-MHz channel.8 The ATSC system delivers 19 Mbps of throughput on a 6-MHz broadcasting channel and 38 Mbps on a 6-MHz CATV channel. The video source, which is encoded, can have a...
Approaches to PCM Switching
6.11.2.1 General. A digital switch's architecture is made up of two elements, called T and S, for time-division switching T and space-division switching S , and can be made up of sequences of T and S. For example, the AT amp T No. 4 ESS is a TSSSST switch No. 3 EAX is an SSTSS and the classic Northern Telecom DMS-100 is TSTS-folded. Many of these switches e.g., DMS-100 are still available. One thing these switches have in common is that they had multiple space S stages. This has now changed....
References Rvb
1. IEEE Standard Dictionary of Electrical and Electronic Terms, 6th ed., IEEE Std 100-1996, IEEE, New York, 1996. 2. R. L. Freeman, Telecommunication Transmission Handbook, 4th ed., Wiley, New York, 1998. 3. National Networks for the Automatic Service, CCITT-ITU Geneva, 1968. 4. Specifications of Signaling Systems 4 and 5, CCITT Recommendations, Fascicle VI.4, IXth Plenary Assembly, Melbourne, 1988. 5. Signaling from Telecommunications Planning Documents, ITT Laboratories, Madrid, November,...
Fades Fading and Fade Margins
In Section 9.2.3.4.2 we showed how path loss can be calculated. This was a fixed loss that can be simulated in the laboratory with an attenuator. On very short radio paths below about 10 GHz, the signal level impinging on the distant-end receiving antenna, assuming full LOS conditions, can be calculated to less than 1 dB. If the transmitter continues to give the same output, the RSL will remain uniformly the same over long periods of time, for years. As the path is extended, the measured RSL...
Definitions
Synchronous Transport Module STM . An STM is the information structure used to support section layer connections in the SDH. It is analogous to STS in the SONET regime. STM consists of information payload and section overhead SOH information fields organized in a block frame structure that repeats every 125 sec. The information is suitably conditioned for serial transmission on selected media at a rate that is synchronized to the network. A basic STM STM-1 is defined at 155,520 kbps....
IEEE 80216 MAC Requirements
The 802.16 MAC design addresses network access in the wireless environment affording very efficient use of the spectrum. Its broadband services support high bit rates and a n PS Symbol Rate x Frame Length 4 n PS Symbol Rate x Frame Length 4 Figure 13.7 Atypical IEEE 802.16 TDD frame, 10-66 GHz. Figure 13.7 Atypical IEEE 802.16 TDD frame, 10-66 GHz. Figure 13.8 TDD downlink subframe. DIUC, downlink interval usage code. broad range of QoS requirements. Its broadband services include IPV4, IPV6,...
CSMA and CSMACD Access Techniques
Carrier sense multiple access CSMA is an early LAN access technical, which some simplistically call listen before transmit. This listen before transmit idea gives insight into the control mechanism. Essentially, if user No. 2 is transmitting, user No. 1 and all others hear that the medium is occupied and refrain from using it. The technique was prone to collisions due to propagation and processing delays to detect that the line is busy. In that open period before carrier detection, user No. 1,...
Discussion of the Erlang and Poisson Traffic Formulas
When dimensioning a route, we want to find the optimum number of circuits to serve the route. There are several formulas at our disposal to determine that number of circuits based on the BH traffic load. In Section 4.2.1.2, four factors were discussed that will help us to determine which traffic formula to use given a particular set of circumstances. These factors primarily dealt with 1 call arrivals and holding-time distributions, 2 number of traffic sources, 3 availability full or limited ,...
Setup and Release of VCCs
The setup and release of VCCs at the user-network interface UNI can be performed in various ways Without using signaling procedures. Circuits are set up at subscription with permanent or semipermanent connections. By meta-signaling procedures, where a special VCC is used to establish or release a VCC used for signaling. Meta-signaling is a simple protocol used to establish and remove signaling channels. All information interchanges in meta-signaling are carried out via single cell messages....
The Virtual Path Level
The virtual path VP is a generic term for a bundle of virtual channel links all the links in a bundle have the same endpoints. A VPI identifies a group of VC links, at a given reference point, that share the same VPC. A specific value of VPI is assigned each time a VP is switched in the network. A VP link is a unidirectional capability for the transport Figure 20.13 Relationship between VC and VP, and the transmission path. 11 VC cross-connect A network element which connects VC links. It...
LAN Bridges
Whereas repeaters have no intelligence, bridges do. Bridges can connect two LANs, at the data-link or MAC protocol level. There are several varieties of bridges, depending on the intelligence incorporated. There is the transparent bridge that builds a list of nodes the bridge sees transmitting on either side. It isolates traffic and will not forward traffic that it knows is destined to another station on the same side of the bridge as the sending station. The bridge is able to isolate traffic...
In the DS3 Frame
One of the most popular high-speed digital transmission systems in North America is DS3 operating at a nominal transmission rate of 45 Mbps. It is also being widely implemented for transport of SMDS. The system used to map ATM cells into the DS3 format is the same that is used for SMDS. To map ATM cells into a DS3 bit stream, the physical layer convergence protocol PLCP is employed. A DS3 PLCP frame is shown in Figure 20.16. Figure 20.16 Format of DS3 PLCP frame. From Ref 1, courtesy of...
Telecommunication Will Touch Everybody
In industrialized nations, the telephone is accepted as a way of life. The telephone is connected to the public switched telecommunications network PSTN for local, national, and international voice communications. These same telephone connections may also 'The source for the data in this paragraph is the US FCC Study on Telephone Trends 2004. Fundamentals of Telecommunications, Second Edition, by Roger L. Freeman ISBN 0-471-71045-8 Copyright 2005 by Roger L. Freeman carry data and image...
BINARY TRANSMISSION AND THE CONCEPT OF TIME 1071 Introduction
As emphasized in Chapter 6, time and timing are most important factors in digital transmission. For this discussion consider a binary end instrument e.g., a PC sending out in series a continuous run of marks and spaces. Those readers who have some familiarity with the Morse code will recall that the spaces between dots and dashes told the operator where letters ended and where words ended. The sending device or transmitter delivers a continuous series of characters to the line, each consisting...
Introduction to the Busy Hour and Grade of Service
The PSTN is very inefficient. This inefficiency stems from the number of circuits and the revenue received per circuit. The PSTN would approach 100 efficiency if all the circuits were used all the time. The facts are that the PSTN approaches total capacity utilization for only several hours during the working day. After 10 P.M. and before 7 A.M., capacity utilization may be 2 or 3 . The network is dimensioned sized to meet the period of maximum usage demand. This period is called the busy hour...
The Electrical Telegraph An Early Form of LongDistance Communications
Let's connect a battery terminal or electrode with a length of copper wire looping it back to the other electrode. A buzzer or other sound-generating device is inserted into that loop at the farthest end of the wire before looping back we now have the essentials of a telegraph circuit. This concept is shown in Figure 2.2. The loop has a certain resistance, which is a function of its length and the diameter of the wire. The longer we make the loop, the greater the resistance. As the length...
Equalization
Of the critical circuit parameters mentioned in Section 10.9.3, two that have severely deleterious effects on data transmission can be reduced to tolerable limits by equalization. These two are amplitude-frequency response amplitude distortion and EDD delay distortion . The most common method of performing equalization is the use of several networks in tandem. Such networks tend to flatten response and, in the case of amplitude response, add attenuation increasingly toward channel center and...
VoIP Gateway
Gateways are defined in different ways by different people. In our context here a gateway is a server it may also be called a media gateway. Figure 15.4 illustrates a typical gateway. It sits on the edge of the network and carries out a switching function of a local, tandem, or toll-connecting PSTN switch described in Chapters 3 and 6. Media gateways are part Figure 15.4 A media gateway from one perspective. API, application programs interface. From IEC on-line Jan. 2003 . of the physical...
Site Selection and Preparation of a Path Profile
9.2.3.3.1 Site Selection. In this step we will select operational site where we will install and operate radio equipment. After site selection, we will prepare a path profile of each link to determine the heights of radio towers to achieve line of sight. Sites are selected using large topographical maps. If we are dealing with a long system crossing a distance of hundreds of miles or kilometers, we should minimize the number of sites involved. There will be two terminal sites, where the system...
Correlation Key Concept in Direct Sequence Spread Spectrum In
direct sequence DS spread spectrum systems, the chip rate is equivalent to the code generator clock rate. Simplistically, a chip can be considered an element of RF energy with a certain recognizable binary phase characteristic. A chip or chips is are a result of direct sequence spreading by biphase modulating an RF carrier. Being that each chip has a biphase modulated characteristic, we can identify each one with a binary 1 or binary 0. These chips derive from biphase PSK modulating a carrier...
Overview Of Ss No 7 Architecture
The SS No. 7 network model consists of network nodes, termed signaling points SPs , interconnected by point-to-point signaling links, with all the links between two SPs called a link set. When the model is applied to a physical network, most commonly there is a one-to-one correspondence between physical nodes and logical entities. But when there is a need e.g., a physical gateway node needs to be a member of more than one network , a physical network node may be logically divided into more than...
Modem Selection Considerations
The critical parameters that affect data transmission have been discussed these are amplitude-frequency response sometimes called amplitude distortion , envelope delay distortion, and noise. Now we relate these parameters to the design of data modems to Figure 10.13 Pulse response through a Gaussian band-limited channel GBLC . Gaussian refers to a channel limited by thermal noise that has a Gaussian distribution. See Ref. 1. Figure 10.13 Pulse response through a Gaussian band-limited channel...
References Vyr
1. Telecommunications Transmission Engineering, 3rd ed., Bellcore, Piscataway, NJ, 1989. 2. Raymond Steele, ed., Mobile Radio Communications, IEEE Press, New York, and Pentech Press, London, 1992. 3. Y. Okumura et al., Field Strength and Its Variability in VHF and UHF Land Mobile Service, Rec. Electr. Commun. Lab., 16, Tokyo, 1968. 4. M. Hata, Empirical Formula for Propagation Loss in Land-Mobile Radio Services, IEEE Trans. Vehicular Technology, VT-20, 1980. 5. F. C. Owen and C. D. Pudney,...
Frequency Reuse
Because of the limited bandwidth allocated in the 800-MHz band for cellular radio communications, frequency reuse is crucial for its successful operation. A certain level of interference has to be tolerated. The major source of interference is cochannel interference from a nearby cell using the same frequency group as the cell of interest. For the 30-kHz bandwidth AMPS system, Ref. 5 suggests that C I be at least 18 dB. The primary isolation derives from the distance between the two cells with...
THE ATM CELL KEY TO OPERATION 2041 ATM Cell Structure
As we mentioned earlier, the ATM cell consists of 53 octets, 5 of which make up the header and 48 make up the payload or info portion of the cell.5 Figure 20.4 shows an ATM cell stream, delineating the 5-octet header and 48-octet information field of each cell. Figure 20.5 shows the detailed structure of cell headers at the user-network interface UNI Figure 20.5a and at the network-node interface NNI 6 Figure 20.5b . We digress a moment to discuss why a cell was standardized at 53 octets. The...
Call Progress AudibleVisual
This type of signaling we categorize in the forward direction and in the backward direction. In the forward direction there is alerting. This provides some sort of audible-visual means of informing the called subscriber that there is a telephone call waiting. This is often done by ringing a telephone's bell. A buzzer, chime, or light may also be used for alerting. The remainder of the techniques we will discuss are used in the backward direction. Among these are audible tones or voice...
Voice Transmission
3.2.2.1 Loudness Rating and Its Predecessors. Historically, on telephone connections, the complaint has been that at the receiving telephone the distant talker's voice was not loud enough. Hearing sufficiently well on a telephone connection is a subjective matter. This is a major element of quality of service QoS . Various methods have been derived over the years to rate telephone connections regarding customer satisfaction. The underlying cause of low signal level is loss across the network....
The Essential Functions of a Local Switch
As we mentioned above, means are provided in a local switch to connect each subscriber line to any other in the same exchange. In addition, any incoming trunk must be able to connect to any subscriber line and any subscriber to any outgoing trunk.7 These switching functions are remotely controlled by the calling subscriber, whether she he is a local subscriber or long-distance subscriber. These remote instructions are transmitted to the switch exchange by off-hook, on-hook,8 and dial...
Cable Characteristics
When employed in the long-distance telecommunication plant, standard coaxial cable sizes are as follows The fractions express the outside diameter of the inner conductor over the inside diameter of the outer conductor. For instance, for the large bore cable, the outside diameter of the inner conductor is 0.104 in. and the inside diameter of the outer conductor is 0.375 in. This is illustrated in Figure 9.35. As can be seen from Eq. 9.27 in Figure 9.35, the ratio of the diameters of the inner...
Subscriber Loop Length Limits
It is desirable from an economic standpoint to permit subscriber loop lengths to be as long as possible. Thus the subscriber serving area could become very large. This, in turn, would reduce the number of serving switches required per unit area affording greater centralization, less land to buy, fewer buildings, simpler maintenance, and so forth. Unfortunately, there are other tradeoffs forcing the urban suburban telecommunication system designer to smaller serving areas and more switches. The...
Review Exercises Ywl
1. For very-high-capacity transmission systems e.g., gt 20,000 equivalent voice channel , what transmission medium should be selected 2. What are the advantages of using the RF bands from 2 GHz to 10 GHz for trunk telephony data Name at least two. 3. Discuss the problem of delay in speech telephone circuits traversing a geostationary satellite. Will there be any problem with data and signaling circuits 4. Give four of the five basic procedure steps in designing an LOS microwave link. 5. Where...
Megaco or ITUT Rec H248 Ref 13
Megaco is a call-control protocol that communicates between a gateway controller and a gateway. It evolved from and replaces SGCP simple gateway control protocol and MGCP media gateway control protocol . Megaco addresses the relationship between a media gateway MG and a media gateway controller MGC . An MGC is sometimes called a softswitch or call agent. Both Megaco and MGCP are relatively low-level devices that instruct MGs to connect streams coming from outside the cell or packet data network...
Noise
3.3.3.1 General. Noise, in its broadest definition, consists of any undesired signal in a communication circuit. The subject of noise and noise reduction is probably the most important single consideration in transmission engineering. It is the major limiting factor in overall system performance. For our discussion in this text, noise is broken down into four categories 3.3.3.2 Thermal Noise. Thermal noise occurs in all transmission media and all communication equipment, including passive...
Design of the FiberOptic Portion of an HFC System
Before proceeding with this section, it is recommended that the reader turn back to Chapter 9 for a review of the principles of fiber-optic transmission. There are two approaches to fiber-optic transmission of analog CATV signals. Both approaches take advantage of the intensity modulation characteristics of the fiber-optic source. Instead of digital modulation of the source, amplitude modulation analog is employed. The most common method takes the entire CATV spectrum as it would appear Figure...
Structure of the SCCP
The basic structure of the SCCP is illustrated in Figure 14.9. It consists of four functional 1. SCCP Connection-Oriented Control. This controls the establishment and release of signaling connections for data transfer on signaling connections. 2. SCCP Connectionless Control. This provides the connectionless transfer of data units. 3. SCCP Management. This functional block provides the capability, in addition to the signal route management and lower control functions of the MTP, to handle the...
What Is Frequency
To understand more advanced telecommunication concepts, we need a firm knowledge of frequency and related parameters such as band and bandwidth, wavelength, period, and phase. Let us first define frequency and relate it to everyday life. The IEEE defines frequency as the number of complete cycles of sinusoidal variation per unit time. The time unit we will use is the second. For those readers with a mathematical bent, if we plot y sin x, where x is expressed in radians, a sine wave is developed...
Multiple Access to a Communication Satellite
Multiple access is defined as the ability of a number of earth stations to interconnect their respective communication links through a common satellite. Satellite access is classified 1 by assignment, whether quasi-permanent or temporary, namely, a preassigned multiple access or b demand-assigned multiple access DAMA and 2 according to whether the assignment is in the frequency domain or the time domain, namely, a frequency-division multiple access FDMA or b time-division multiple access TDMA ....
QUALITY OF SERVICE VOICE DATA AND IMAGE 321 SignaltoNoise Ratio
Signal-to-noise ratio S N or SNR is the most widely used parameter for measurement of signal quality in the field of transmission. Signal-to-noise ratio expresses in decibels the amount that signal level exceeds the noise level in a specified bandwidth. As we review the several types of material to be transmitted on a network, each will require a minimum S N to satisfy the user or to make a receiving instrument function within certain specified criteria. The following are S N guidelines at the...
Review Exercises Qst
1. Define switching in light of transmission. 3. Define calling rate and holding time. 4. Define lost calls using the terms offered traffic and carried traffic. 5. Why are call attempts so important in the design of modern SPC switches 6. Suppose the average holding time of a call is 3.1 minutes and the calling rate in the busy hour is 465 on a particular work day. What is the traffic flow 7. Under normal operating conditions, when can we expect blockage of calls 16Duty cycle refers to how long...
Phase Distortion
We can look at a voice channel as a bandpass filter. A signal takes a finite time to pass through the telecommunication network. This time is a function of the velocity of Figure 3.3 Typical attenuation distortion across a voice channel bandpass filter. Crosshatched areas are response specifications, whereas the wavy line is the measured response. Figure 3.3 Typical attenuation distortion across a voice channel bandpass filter. Crosshatched areas are response specifications, whereas the wavy...
Cookbook Design Methods for Subscriber Loops
5.4.5.1 Resistance Design Concept. Resistance design RD dates back to the 1960s and has since been revised. It was basic North American practice. Our inclusion of resistance design helps understand the cookbook design concept. At the time of its inception, nearly all local serving area switches could handle loops up to 1300 Q resistance. In virtually every case, if the RD rules were followed, the attenuation limit of 8 dB would be complied with. The maximum resistance limit defines a perimeter...
Telephone Numbering and Routing
Every subscriber in the world is identified by a number, which is geographically tied to a physical location.4 This is the telephone number. The telephone number, as we used it 4This wiH change. At least in North America, we expect to have telephone number portability. Thus, whenever one moves to a new location, she he takes their telephone number with them. Will we see a day when telephone numbers are issued at birth, much like social security numbers above, is seven digits long. For example...
Critical Impairments to the Transmission of Data
The effect of various telephone circuit parameters on the capability of a circuit to transmit data is a most important consideration. The following discussion is intended to familiarize the reader with problems most likely to be encountered in the transmission of data over analog or mixed analog-digital circuits. We make certain generalizations in some cases, which can be used to facilitate planning the implementation of data systems. 10.9.3.1 Phase Distortion. Phase distortion constitutes the...
Baseband Lan Transmission Considerations
A baseband LAN is a point-to-point or point-to-multipoint network. Two transmission problems arise as a result. The first deals with signal level and signal-to-noise S N ratio, and the second deals with standing waves. Each access on a common medium must have sufficient signal level and S N such that copied signals have a BER in the range of 1 x 10 8 to 1 x 10 12. If the medium is fairly long in extension and there are many accesses, the signal level must be high for a transmitting access to...
SignaltoNoise Ratio SN Versus CarriertoNoise Ratio CN in CATV Systems
We have been using S N and C N many times in previous chapters. In CATV systems S N has a slightly different definition as follows Ref. 2 This relationship is expressed by the signal-to-noise ratio, which is the difference between the signal level measured in dBmV, and the noise level, also measured in dBmV, both levels being measured at the same point in the system. S N can be related to C N on CATV systems as This is based on Carson Ref. 4 , where the premise is noise just perceptible by a...