PPT ON GSM ADVANCE TRAINING

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1.INTRODUCTION TO GSM

2.INTRODUCTION The Global System for Mobile Communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operation across international boundaries. GSM networks are digital and can cater for high system capacities. They are consistent with the world-wide digitization of the telephone network, and are an extension of the Integrated Services Digital Network (ISDN), using a digital radio interface between the cellular network and the mobile subscriber equipment.

3.CELLULAR TELEPHONY A cellular telephone system links mobile subscribers into the public telephone system or to another cellular subscriber. Information between the mobile unit and the cellular network uses radio communication. Hence the subscriber is able to move around and become fully mobile. The service area in which mobile communication is to be provided is divided into regions called cells. Each cell has the equipment to transmit and receive calls from any subscriber located within the borders of its radio coverage area.

4.GSM FREQUENCIES GSM systems use radio frequencies between 890-915 MHz for receive and between 935-960 MHz for transmit. RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for use. An RF carrier is a pair of radio frequencies, one used in each direction. Transmit and receive frequencies are always separated by 45 MHz.

5.Extended GSM (EGSM) EGSM has 10MHz of bandwidth on both transmit and receive. Receive bandwidth is from 880 MHz to 890 MHz. Transmit bandwidth is from 925 MHz to 935 MHz. Total RF carriers in EGSM is 50.

6.DCS1800 FREQUENCIES DCS1800 systems use radio frequencies between 1710-1785 MHz for receive and between 1805-1880 MHz for transmit. RF carriers are spaced every 200 kHz, allowing a total of 373 carriers. There is a 100 kHz guard band between 1710.0 MHz and 1710.1 MHz and between 1784.9 MHz and 1785.0 MHz for receive, and between 1805.0 MHz and 1805.1 MHz and between 1879.9 MHz and 1880.0 MHz for transmit. Transmit and receive frequencies are always separated by 95 MHz.

7.FEATURES OF GSM

8.FEATURES OF GSM INCREASED CAPACITY The GSM system provides a greater subscriber capacity than analogue systems. GSM allows 25 kHz per user, that is, eight conversations per 200 kHz channel pair (a pair comprising one transmit channel and one receive channel). Digital channel coding and the modulation used makes the signal resistant to interference from cells where the same frequencies are re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular. This allows increased geographic reuse by permitting a reduction in the number of cells in the reuse pattern.

9.AUDIO QUALITY Digital transmission of speech and high performance digital signal processors provide good quality speech transmission. Since GSM is a digital technology, the signals passed over a digital air interface can be protected against errors by using better error detection and correction techniques. In regions of interference or noise-limited operation the speech quality is noticeably better than analogue. USE OF STANDARDISED OPEN INTERFACES Standard interfaces such as C7 and X25 are used throughout the system. Hence different manufacturers can be selected for different parts of the PLMN. There is a high flexibilty in where the Network components are situated.

10.IMPROVED SECURITY AND CONFIDENTIALITY GSM offers high speech and data confidentiality. Subscriber authentication can be performed by the system to check if a subscriber is a valid subscriber or not. The GSM system provides for high degree of confidentiality for the subscriber. Calls are encoded and ciphered when sent over air. The mobile equipment can be identified independently from the mobile subscriber. The mobile has a identity number hard coded into it when it is manufactured. This number is stored in a standard database and whenever a call is made the equipment can be checked to see if it has been reported stolen.

11.CLEANER HANDOVERS GSM uses Mobile assisted handover techique. The mobile itself carries out the signal strength and quality measurement of its server and signal strength measurement of its neighbors. This data is passed on the Network which then uses sophisticated algorithms to determine the need of handover. SUBSCRIBER IDENTIFICATION In a GSM system the mobile station and the subscriber are identified separately. The subscriber is identified by means of a smart card known as a SIM. This enables the subscriber to use different mobile equipment while retaining the same subscriber number.

12.ENHANCED RANGE OF SERVICES Speech services for normal telephony. Short Message Service for point ot point transmission of text message. Cell broadcast for transmission of text message from the cell to all MS in its coverage area. Message like traffic information or advertising can be transmitted. Fax and data services are provided. Data rates available are 2.4 Kb/s, 4.8 Kb/s and 9.6 Kb/s. Supplementary services like number identification , call barring, call forwarding, charging display etc can be provided.

13.FREQUENCY REUSE

14.NETWORK COMPONENTS

15.NETWORK COMPONENTS

16.Mobile Switching Centre (MSC)

17.Mobile Switching Centre (MSC) – Lucent MSC

18.Mobile Station (MS) Mobile Equipment

19.SIM

20.Mobile Station International Subscribers Dialling Number ( MSISDN ) :

21.International Mobile Subscribers Identity ( IMSI ) :

22.Temporary Mobile Subscribers Identity ( TMSI ) :

23.Equipment Identity Register ( EIR )

24.EIR

25.International Mobile Equipment Identity ( IMEI ) :

26.HOME LOCATION REGISTER( HLR )

27.VISITOR LOCATION REGISTER ( VLR )

28.Authentication Centre ( AUC )

29.AUTHENTICATION PROCESS

30.Base Station Sub-System ( BSS ) :

31.Transcoder( XCDR )

32.TRANSCODER(XCDR) - Siemens

33.TRANSCODING

34.Base Station Controller (BSC)

35.Base Station Controller (BSC) – Siemens BSC

36.Base Transceiver Station (BTS)

37.Base Transceiver Station (BTS)

38.BTS Connectivity

39.Operation And Maintenance Centre For Radio (OMC-R)

40.Operation And Maintenance Centre For Radio (OMC-R)

41.Base Station Identity Code

42.MS Class Mark

43.MOBILE MAXIMUM RANGE

44.MULTIPLE ACCESS TECHNIQUES

45.TERRESTERIAL INTERFACE

46.INTERFACE NAMES

47.2 Mbits/s Trunk 30- channel PCM

48.BSS CONNECTIONS

49.Cell Global Identity ( CGI ) :

50.CHANNEL CONCEPT

51.GSM Traffic Channels

52.GSM Control Channels

53.BCH Channels

54.CCCH Channels

55.DCCH Channels

56.NORMAL BURST

57.NORMAL BURST

58.FREQUENCY CORRECTION BURST

59.SYNCHRONISATION BURST

60.DUMMY BURST

61.ACCESS BURST

62.NEED FOR TIMESLOT OFFSET

63.NEED FOR TIMESLOT OFFSET

64.26 FRAME MULTIFRAME STRUCTURE

65.BCCH/CCCH NON-COMBINED MULTIFRAME

66.BCCH/CCCH COMBINED MULTIFRAME

67.DCCH/8 MULTIFRAME

68.CHANNEL CONCEPT

69.CODING, INTERLEAVING CIPHERING

70.SPEECH CODING

71.SPEECH CODING

72.CHANNEL CODING

73.CHANNEL CODING

74.CHANNEL CODING FOR GSM SPEECH CHANNELS

75.Speech Channel Coding

76.CHANNEL CODING FOR CONTROL CHANNELS

77.CHANNEL CODING FOR DATA CHANNELS

78.INTERLEAVING

79.GSM SPEECH CHANNEL INTERLEAVING

80.GSM SPEECH CHANNEL INTERLEAVING ( Diagram )

81.CONTROL CHANNEL INTERLEAVING

82.DATA INTERLEAVING

83.CIPHERING

84.SIGNALLING

85.SIGNALLING SYSTEM

86.SIGNALLING SYSTEM C7

87.GENERAL INTRODUCTION

88.SIGNALING IN TELECOMMUNICATION NETWORK

89.Access Signaling

90.Digital Subscriber Signaling System No. 1 (DSS1) is the standard access signaling system used in ISDN. It is also called a D-channel signaling system D-channel signaling is defined for digital access lines only.

91.Trunk Signaling

92.CHANNEL ASSOCIATED SIGNALING (CAS)

93.COMMON CHANNEL SIGNALING (CCS)

94.OSI REFERENCE MODEL

95.OSI MODEL REFERENCE DIAGRAM

96.COMMUNICATION PROCESS

97.DESCRIPTION OF LAYERS Application Layer

98.Presentation Layer

99.Transport Layer

100.Network Layer Data Link Layer

101.Physical Layer

102.SIGNALING SYSTEM NO. 7 INTRODUCTION

103.Thus, there is a need for a generic system that is able to support a wide variety of applications in telecommunication.

104.USER PARTS

105.MTP user parts

106.SCCP

107.Transaction Capabilities (TC) Operation and Maintenance Application Part (OMAP)

108.OSI Model

109.CALL FLOW

110.Mobile originated call

111.Mobile terminated call

112.POWER CONTROL

113.RF POWER CONTROL

114.POWER CONTROL IN THE MS

115.POWER CONTROL MS

116.TIMING OF POWER CHANGE BY MS

117.BSS POWER CONTROL

118.RADIO LINK FAILURE

119.RADIO LINK FAILURE

120.CELL SELECTION AND RE-SELECTION

121.CELL SELECTION AND RE-SELECTION

122.CELL SELECTION - NO BCCH DATA AVAILABLE

123.CELL SELECTION - NO BCCH DATA AVAILABLE

124.The MS stores the BCCH carriers in use by the PLMN selected when it was last active in the GSM network. A MS may also store BCCH carriers for more than one PLMN which it has selected previously (e.g. at national borders or when more than one PLMN serves a country).

125.PATH LOSS CRITEREON( C1)

126.PATH LOSS CRITEREON( C1)

127.Monitoring of Received Level and BCCH data

128.The MS has to decode the full BCCH data of the serving cell at least every 30 seconds. The MS attempts to decode the BCCH data block that contains the parameters affecting cell reselection for each of the 6 strongest non-serving cell BCCH carriers at least every 5 minutes.

129.CALL RE-ESTABLISHMENT

130.bs_ag_blk_res

131.Bs_pa_mfrms

132.PAGING

133.max_retran

134.tx_intege

r 135.AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP

136.CALCULATION OF CCCH AND PAGING GROUP NO

137.HANDOVER

138.HANDOVER

139.MS END

140.BTS END

141.MS IDLE TIME REPORTING

142.MEASUREMENT IN ACTIVE MODE

143.NUMBER OF NEIGHBORS

144.NUMBER OF NEIGHBORS

145.INTERFERENCE ON IDLE CHANNEL

146.The BSS keeps on measuring the interference on the idle timeslots.

147.HANDOVER

148.HANDOVER CONDITIONS

149.HANDOVER TYPES Intra-Cell Handover

150.HANDOVER TYPES Intra-BSC Handover

151.HANDOVER TYPES Inter-BSC Handover

152.HANDOVER TYPES Inter-MSC Handover

153.LOCATION UPDATE

154.LOCATION UPDATE

155.LOCATION UPDATE TYPES

156.LOCATION UPDATE

157.IMSI ATTACH

158.DISCONTINOUS TRANSMISSION

159.IMPLEMENTATION OF DTX Voice Activity Detector ( VAD )

160.SYSTEM INFORMATIONMESSAGES

161.BROADCAST MESSAGES

162.BROADCAST MESSAGES

163.SYSTEM INFORMATION

1 64.SYSTEM INFORMATION 1

165.RACH Control Parameters

166.SYSTEM INFORMATION 2 

167.SYSTEM INFORMATION 3

168.Control Channel Description

169.SYSTEM INFORMATION 3

170.SYSTEM INFORMATION 4

171.SYSTEM INFORMATION 4

172.SYSTEM INFORMATION 5

173.SYSTEM INFORMATION 6

174.PAGING

175.CALCULATION OF PAGING GROUP

176.CALCULATION OF PAGING GROUP

177.AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP

178.CALCULATION OF PAGING GROUP

179.CALCULATION OF PAGING GROUP Total number of paging groups on 1 CCCH_GROUP(N)

180.AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP

181.CALCULATION OF CCCH AND PAGING GROUP NO

182.SOME KEY DATABASE PARAMETERS

183.TIMER T3101

184.TIMER T3101

185.Wait_indication parameter & Timer T3122

186.Wait_indication parameter & Timer T3122

187.CALL QUEING

188.TCH RESOURCE REPORTING

189.TCH RESOURCE REPORTING

190.T3109

191.T3109 LADDER DIAGRAM

192.T3110 AND T3111 - Normal Release

193.T3110 AND T3111 - Normal Release

194.FREQUENCY HOPPING

195.INTRODUCTION TO FREQUENCY HOPPING

196.Introduction to Frequency Hopping

197.Introduction to Frequency Hopping

198.Increased Immunity to fading

199.Increased Immunity to fading

200.Considering a non hopping system, the set of calls on the interferer cells which can interfere with the wanted call is fixed for the duration of those calls and some calls will be found with very good quality (no interference problems) whereas some others with very bad quality (permanent interference problems).

201.TYPES OF HOPPING Base Band Hopping (BBH)

202.TYPES OF HOPPING Synthesiser Frequency Hopping (SFH)

203.Hopping Parameters

204.INTRODUCTION TO RF PLANNING

205.INTRODUCTION TO RF PLANNING

206.RF planning plays a critical role in the Cellular design process. By doing a proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we may encounter in the future and also reduce substantially the cost of optimization.

207.TOOLS USED FOR RF PLANNING Network Planning Tool CW Propagation Tool Traffic Modeling Tool Project Management Tool

208.Network Planning Tool

209.Network Planning Tool (PLANET)

210.Propagaton Test Kit

211.Propagaton Test Kit

212.Traffic Modeling Tool

213.Project Management Tool

214.RF PLANNINGPROCEDURES

215.PRELIMINARY WORK

216.PRELIMINARY WORK This is done using Project management or site management databases.

217.Marketing Analysis and GOS determination

218.Set Initial Link Budget

219.Initial cell radius calculation

220.INITIAL SURVEY

221.Morphology Drive Test

222.Propagation Tool Adjustment

223.INITIAL DESIGN

224.Reset Cell Placement( Ideal Sites) According to the predictions change the cell placements to design the network for contigious coverage and appropriate traffic.

225.Design Review With The Client Initial design review has to be carried out with the client so that he agrees to the basic design of the network. During design review, first put only the background map which is on paper. Then step by step put the site layout and coverage prediction. Display may show some coverage holes in phase 1 which should get solved in phase 2 .

226.Prepare Initial Search Ring Note the latitude and longitude from planning tool. Get the address of the area from mapping software. Release the search ring with details like radius of search ring, height of antenna etc.

227.Select Initial Anchor Sites Initial anchor sites are the sites which are very important for the network buildup, Eg - Sites that will also work as a BSC.

228.Reset / Review Search Rings If the prediction shows a coverage hole ( as the actual site may be shifted from the designed site), the surrounding search rings can be resetted and reviewed.

229.Drive Test And Review Best Candidate In order to verify that a candidate site, selected based on its predicted coverage area, is actually covering all objective areas, drive test has to be performed. Drive test also points to potential interference problems or handover problems for the site.

230.Drive Test Integration The data obtained from the drive test has to be loaded on the planning tool and overlapped with the prediction. This gives a idea of how close the prediction and actual drive test data match. If they do not match ( say 80 to 90 %) then for that site the model may need tuning. Visit Site With All Disciplines( SA, Power, Civil etc ) A meeting at the selected site takes place in which all concerned departments like RF Engineering, Site acquisition, Power, Civil Engineer, Civil contractor and the site owner is present. Any objections are taken care off at this point itself.

231.Select Equipment Type For Site Select equipment for the cell depending on channel requirements Selection of antenna type and accessories. Locate Equipment On Site For Construction Drawing Plan of the building ( if site located on the building) to be made showing equipment placement, cable runs, battery backup placement and antenna mounting positions. Antenna mounting positions to be shown separately and clearly. Drawings to be checked and signed by the Planner, site acquisition, power planner and project manager.

232.Perform Link Balance Calculations Link balance calculation per cell to be done to balance the uplink and the downlink path. Basically link balance calculation is the same as power budget calculation. The only difference is that on a per cell basis the transmit power of the BTS may be increased or decreased depending on the pathloss on uplink and downlink. EMI Studies Study of RF Radiation exposure to ensure that it is within limits and control of hazardous areas. Data sheet to be prepared per cell signed by RF Planner and project manager to be submitted to the appropriate authority.

233.Radio Frequency Plan/ PN Plan Frequency planning has to be carried out on the planning tool based on required C/I and C/A and interference probabilities. System Interference Plots C/I, C/A, Best server plots etc has to be plotted. These plots have to be reviewed with the customer to get the frequency plan passed. Final Coverage Plot This presentation should be the same as design review presentation. This plot is with exact locations of the site in the network.

234.Identification of coverage holes Coverage holes can be identified from the plots and subsequent action can be taken(like putting a new site) to solve the problem.

235.RADIO WAVE PROPAGATION

236.Isotropic RF Source A point source that radiates RF energy uniformly in all directions (I.e.: in the shape of a sphere) Theoretical only: does not physically exist. Has a power gain of unity I.e. 0dBi. Effective Radiated Power (ERP) Has a power gain of unity i.e. 0dBi The radiated power from a half-wave dipole. A lossless half-wave dipole antenna has a power gain of 0dBd or 2.15dBi. Effective Isotropic Radiated Power (EIRP) The radiated power from an isotropic source EIRP = ERP + 2.15 dB

237.BASIC DEFINITIONS

238.dB is a a relative unit of measurement used to describe power gain or loss.

239.The most common "defined reference" use of the decibel is the dBm, or decibel relative to one milliwatt.

240.dBm

241.dBm = 10 log (P) (1000 mW/watt) where dBm = Power in dB referenced to 1 milliwatt P = Power in watts

242.dBm = 10 log (P) (1000 mW/watt) The dBm can also be negative value. If power level is 1 microwatt Power in dBm = 10 log (1 x 10E-6 watt) (1000 mW/watt) = -30 dBm Since the dBm has a defined reference it can be converted back to watts if desired. Since it is in logarithmic form it may also be conveniently combined with other dB terms.

243.To convert field strength in db?v/m to received power in dBm with a 50? optimum terminal impedance and effective length of a half wave dipole ?/? 0dBu = 10 log[(10-6)2(1000)(?/?)2/(4*50)] dBm At 850MHZ 0dBu = -132 dBm 39dBu = -93 dBm

244.FREE SPACE PROPAGATION

245.PROPAGATION MECHANISMS

246.MULTIPATH

247.Multipath Propagation Multipath propagation causes large and rapid fluctuations in a signal These fluctuations are not the same as the propagation path loss.

248.WHAT IS FADING ?

249.WHAT IS FADING ?

250.LONG TERM FADING

251.RAYLEIGH FADING

252.RICEAN FADING

253.DIVERSITY ANTENNA SYSTEMS

254.Diversity Antenna Systems

255.NEED OF DIVERSITY

256.Multipath Propagation Multipath propagation causes large and rapid fluctuations in a signal These fluctuations are not the same as the propagation path loss.

257.DIVERSITY TECHNIQUE

258.CONCEPT OF DIVERSITY ANTENNA SYSTEMS

259.CONCEPT OF DIVERSITY ANTENNA SYSTEMS

260.Diversity Antenna Systems

261.SPATIAL DIVERSITY ANTENNA SYSTEMS

262.TYPICAL SPATIAL ANTENNA DIVERSITY CONFIGURATIONS

263.THREE ANTENNA SPATIAL CONFIGURATION

264.TWO ANTENNA SPATIAL CONFIGURATION

265.POLARISATION DIVERSITY ANTENNA SYSTEMS

266.DUAL POLARISED ANTENNAS

267.ADVANTAGES OF DUAL POLARISED ANTENNAS

268.DUAL POLARISED ANTENNA CONFIGURATIONS

269.INTERFERENCE

270.WHAT IS INTERFERNCE ?

271.EFFECTS OF INTERFERENCE

272.SOURCES OF INTERFERENCE

273.TYPES OF INTERFERENCE

274.Co-Channel Interference

275.Co-Channel Interference

276.Co-Channel Interference Q = D / R = ?3N By increasing the ratio of D/R, the spatial seperation between the co-channel cells relative to the coverage distance of a cell is increased. In this way interference is reduced from improved isolation of RF energy from the co-channel cell. The parameter Q , called the co-channel reuse ratio, is related to the cluster size. A small value of Q provides larger capacity since the cluster size N is small whereas a large value of Q improves the transmission quality.

277.Adjacent-Channel Interference Interference resulting from signals which are adjacent in frequency to the desired signal is called adjacent channel interference. Adjacent channel interference results from imperfect receiver filters which allow nearby frequencies to leak into the passband. Adjacent channel interference can be minimized through careful filtering and channel assignments. By keeping the frequency separation between each channel in a given cell as large as possible , the adjacent interference may be reduced considerably.

278.Adjacent-Channel Interference

279.POWER CONTROL

280.ECTORIZATION

281.REPEATERS

282.REPEATERS

283.INTRODUCTION There are two types of repeater band selective and channel selective. Band selective repeater amplifies a band of frequency. Hence it amplifies any frequency that falls within its band. Channel selective repeater allows selection of a number of individual channels to amplify and rebroadcast. Typically a channel selective repeater allows selection of 2 to 4 channels. If the GSM900 or DCS1800 network incorporates frequency hopping, then only band selective repeaters should be used.

284.TRANSMISSION SYSTEMS

285.Introduction To Transmission Systems Transmission systems form the backbone of any networks. Normally transmission systems include SDH, PDH, ATM, Microwaves, leased lines. In GSM normally the core network is located in the same premises and are mostly interconnected by fixed wireline. In huge network consisting of many MSC located at different places the interconnection may be through any of the transmission systems mentioned above. The Access network consists of BSC’s with many BTS’s connected to them in various transmission topologies. Normal practice is to connect various BSC’c to the MSC via fiber and different BTS’s connected to BSC via microwave in Daisy chain, star or any other topology. However there can be many different ways of implementation.

286.E1

287.Typical implementation of a E1

288.The 2.048 Mbps Framing Format

289.Framing Format

290.E1

291.TS 16 Multiframe Format

292.E1 If there are voice channels on the 2.048 Mbps signal, it is necessary to take up additional bandwidth to transmit the signalling information. ITU-T Recommendation G.704 allocates time slot 16 for the transmission of the channel-associated signalling information. The 2.048 Mbps can carry up to thirty 64 kbps voice channels in time slot 1-15 and 17-31. Voice channels are numbered 1-30; voice channels 16-30 are carried in time slot 17-31. However, the 8 bits in time slot 16 are not sufficient for all 30 channels to signal in one frame. Therefore, a multiframe structure is required where channels can take turns using time slot 16.

293.Since two channels can send their ABCD signalling bits in each frame, a total of 15 frames are required to cycle through all of the 30 voice channels. One additional frame is required to transmit the multiframe alignment signal (MFAS) pattern, which allows receiving equipment to align the appropriate ABCD signalling bits with their corresponding voice channels. This results in the TS-16 multiframe structure where each multiframe contains a total of 16 2.048 Mbps, numbered 0-15. Figure on the previous slide shows the TS-16 multiframe format for the 2.048 Mbps signal as defined by the ITU-T Recommendation G.704.

294.As can be seen in Figure , time slot 16 of frame 0 contains the 4-bit long multiframe alignment signal (MFAS) pattern (0000) in bits 1-4. The “Y” bit is reserved for the remote alarm (MFAS Distant Alarm) which indicates loss of multiframe alignment when it is set to 1. Time slot 16 of frames 1-15 contains the ABCD signalling bits of the voice channels. Time slot 16 of the nth frame carries the signalling bits of the nth and (n+15)th voice channels. For example, frame 1 carries the signalling bits of voice channels 1 and 16, frame 2 carries the signalling bits of channels 2 and 17 etc. It is also important to note that the frame alignment signal (FAS) is transmitted in time slot 0 of the even numbered frames.

295.T1 Introduction T1 is a digital communications link that enables the transmission of voice, data, and video signals at the rate of 1.544 million bit per second (Mb/s). Introduced in the 1960s, it was initially used by telephone companies who wished to reduce the number of telephone cables in large metropolitan areas. T1 simplifies the task of networking different types of communications equipment since it can carrz both voice and data on the same link.

296.T1 Introduction To illustrate, Figure 1 on the next page shows what a company’s communications network might look like without T1 Figure 1 shows that telephone, facsimile, and computer applications would all require separate lines. Typically, voice and low-speed data applications are serviced by analog lines, while high-speed data applications are serviced by digital facilities. Figure 2 on the next page depicts the same network with a T1 link installed.

297.T1

298.T1

299.PDH Overview Long-established analog transmission systems that proved inadequate were gradually replaced by digital communications networks. In many countries, digital transmission networks were developed based upon standards collectively known today as the Plesiochronous Digital Hierarchy (PDH). Although it has numerous advantages over analog, PDH has some shortcomings: provisioning circuits can be labor-intensive and time-consuming, automation and centralized control capabilities of telecommunication networks are limited, and upgrading to emerging services can be cumbersome. A major disadvantage is that standards exist for electrical line interfaces at PDH rates, but there is no standard for optical line equipment at any PDH rate, which is specific to each manufacturer.

300.This means that fiber optic transmission equipment from one manufacturer may not be able to interface with other manufacturers’ equipment. As a result, service providers are often required to select a single vendor for deployment in areas of the network, and are locked into using the network control and monitoring capabilities of that vendor. Reconfiguring PDH networks can be difficult and labor-intensive - resulting in costly, time-consuming modifications to the network whenever new services are introduced or when more bandwidth is required.

301.SDH Overview Bellcore (the research affiliate of the Bell operating companies in the United States) proposed a new transmission hierarchy in 1985. Bellcore’s major goal was to create a synchronous system with an optical interface compatible with multiple vendors, but the standardization also included a flexible frame structure capable of handling either existing or new signals and also numerous facilities built into the signal overhead for embedded operations, administration, maintenance and provisioning (OAM&P) purposes. The new transmission hierarchy was named Synchronous Optical Network (SONET). The International Telecommunication Union (ITU) established an international standard based on the SONET specifications, known as the Synchronous Digital Hierarchy (SDH), in 1988.

302.The SDH specifications define optical interfaces that allow transmission of lower-rate (e.g., PDH) signals at a common synchronous rate. A benefit of SDH is that it allows multiple vendors’ optical transmission equipment to be compatible in the same span. SDH also enables dynamic drop-and-insert capabilities on the payload; PDH operators would have to demultiplex and remultiplex the higher-rate signal, causing delays and requiring additional hardware. Since the overhead is relatively independent of the payload, SDH easily integrates new services, such as Asynchronous Transfer Mode (ATM) and Fiber Distributed Data Interface (FDDI), along with existing European 2, 34, and 140 Mbit/s PDH signals, and North American 1.5, 6.3, and 45 Mbit/s signals.

303.SDH Overview STM1 data rate calculation SDH multiplexing combines low-speed digital signals such as 2, 34, and 140 Mbit/s signals with required overhead to form a frame called Synchronous Transport Module at level one (STM-1). Figure 1 shows the STM-1 frame, which is created by 9 segments of 270 bytes each. The first 9 bytes of each segment carry overhead information; the remaining 261 bytes carry payload. When visualized as a block, the STM-1 frame appears as 9 rows by 270 columns of bytes. The STM-1 frame is transmitted row #1 first, with the most significant bit (MSB) of each byte transmitted first. 

304.This formula calculates the bit rate of a framed digital signal: bit rate = frame rate x frame capacity In order for SDH to easily integrate existing digital services into its hierarchy, it operates at the basic rate of 8 kHz, or 125 microseconds per frame, so the frame rate is 8,000 frames per second. The frame capacity of a signal is the number of bits contained within a single frame. Figure 2 shows: frame capacity = 270 bytes/row x 9 rows/frame x 8 bits/byte = 19,440 bits/frame The bit rate of the STM-1 signal is calculated as follows: bit rate = 8,000 frames/second x 19,440 bits/frame = 155.52 Mbit/s

305.SDH Overview

306.SDH Overview

307.SDH Overview Multiplexing of STM frames As the Figure coming on the next slide shows, the ITU has specified that an STM-4 signal should be created by byte interleaving four STM-1 signals. The basic frame rate remains 8,000 frames per second, but the capacity is quadrupled, resulting in a bit rate of 4 x 155.52 Mbit/s, or 622.08 Mbit/s. The STM-4 signal can then be further multiplexed with three additional STM-4s to form an STM-16 signal. Table 1 lists the defined SDH frame formats, their bit rates, and the maximum number of 64 kbit/s telephony channels that can be carried at each rate.

308.SDH Overview Multiplexing of STM frames

309.SDH Overview Multiplexing of STM frames

310.Microwave Overview Normally used for point to point transmission Used mainly in the GHz range. Normally distance between radios is less than 50Kms.