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Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
Fiber Optic Transmission Networks
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Fiber Optic Transmission Networks


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  • In this presentation transmission technology and is explained right from from the lowest order bit rates of 2.048 Mbps to STM-16 level (2.5Gbps) . The PDH/SDH hierarchy, frame format, multiplexing are discussed in depth. The functional description of 140Mbps Fiber Optic Transmission System of NEC is described in detail. The focus will primarily be on the ETSI/ITU-world ( i.e. European rates).However the differences with North American (ANSI) standards will be briefly discussed.
  • The topics to be discussed will include the issues related to the Network installation practice, Fiber connectivity to the Telecom sites, PDH hierarchies (up to 140Mbps), STS-1 signal envelope, pointer concepts, SDH Network elements and their functionality.
  • Network Planning is an important aspect of the Transmission. The OFC network planning typically involves Route Surveying and charting out the issues related to the Right of Way.
  • The Network Implementation involves installing OF cable, its termination at the REG,ADM,BTS sites. The fiber chosen for long-haul networks typically is 48-fiber central core armoured cable. The optical characteristics of the fiber are critical for backbone networks. The Polarization Mode Dispersion (PMD) of the fiber would will make its effect at bit rates at 2Gbps. Dispersion tailored fibers like Dispersion Compensated Fiber, Non-Zero Dispersion Shifted Fiber (ITU-T G.655) are being deployed for Dense Wavelength Division Multiplexing networks.
  • Typically fiber connectivity to the sites is done as follows: Regenrator (REG ) sites : All fibers of both the cables coming from the opposite sides is to be brought in REG sites and terminated at Termination Box/ Fiber Distribution Management System. Add Drop Multiplexer (ADM) sites: a) In case of single Point of Interconnect (POI) or Launch site in the town/city where ADM site exists, the fiber connectivity to ADMs is done by laying two 24-fiber cable, one un-armoured di-electric for active deployment and other armoured cable for redundancy. b) Incase there is any FSP/ISP or Cellular Service Provider in the town the OFC route shall be taken from the closest point to above sites so as to give on demand connectivity in future. It is expected that ADM site shall be close to POI at an approx distance of 6Km.
  • ADM sites with Multiple POI: In case of multiple POI (BSNL,FSP,ISP,Cellular etc) route shall be selected in such a way that it passes through the closest point to all the existing service providers and make a ring with ADM and all POIs. ADM sites co-located with BTS/Launch sites. Launch site is connected electrically in case site is co-located with Tx ADM or located at a distance of 250m. BTS/launch sites not co-located with ADM sites but within 6Km radius: In this case the ADM site is to be connected through a 24 fiber armoured cable either by Making a spur route from the nearest joint pit and tapping 2 fibers from the 48-fiber armoured cable or By tapping out 2 fibers from the two adjacent joint pits of Tx 48 fiber cable making path diversity. BTS sites not co-located with ADM but falling alomg the Tx route beyond 6Km. In this case fiber connectivity to such sites is made by tapping 2 fibers from either sides of the nearest joint pit of 48 fiber Tx cable. A separate 24F cable shall be laid between BTS/Launch site and nearest joint pit. Two fibers out of 24F is to be used for linking one side and another two fibers for linking other side of BTS sites. All 4 fibers shall belong to the same 24 fiber cable laid between BTS and nearest joint pit
  • Originally the telecom network was analogue where telephone calls were carried over a physical wire, forming an electrical circuit connecting the two ends.However,in 1962 AT&T introduced digital switching in the public telecom network in order to use newly available digital technologies which allowed more telephone calls to be carried over fewer wires. To do this required the analogue voice to be represented digitally with Pulse Code Modulation (PCM). Reeves invented PCM in 1937, but it was only in 1962 when it was used in the network. A telephone quality voice signal has a bandwidth of 3.1kHz. According to Nyquist’s theorem, to recreate the digital signal accurately you must sample at twice the maximum frequency. This would mean our voice channel must be sampled at 6200 times per second in order to recreate the information of the analogue signal. In fact a sampling frequency of 8kHz is used. This is then converted in a binary value. Here we use an 8-bit word (128 levels) to represent the analogue signal. So this gives a voice channel with a bit rate of 64kb/s. Table above shows the A-law compressed quantized encoded values of analogue signal. 64kb/s PCM stands the fundamental building block which most transmission systems are designed to carry. PDH and SONET/SDH are just built round this 64kb/s channel and higher speeds like 2.5Gbps are just multiple of 64kb/s. The analogue sample is shown above is encoded as 8 bits according to A-law in the format ‘PABCWXYZ’. Where P is meant for +/- polarity of signal. ABC for segment number, WXYZ for quantization code
  • Multiplexing is how we transmit voice channels on links running faster than 64kb/s The two common methods of multiplexing are Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM). TDM is what we use in PDH and SDH systems. It combines the voice channels together by devoting small periods of time to serving each of the different voice channels ( or tributaries). It is also known as ‘sequential byte interleaving’. FDM is used in wireless applications, amongst others. Basically the different channels are transmitted on different frequency, and can be separated by tuning to a particular frequency. FDM is used in radio and television broadcasts. The primary rates for transmission are 2Mb/s in ETSI/ITU-T world which gives 30 voice channels and 1.544 Mb/s in North America with 24 channels.
  • Each voice channel or time slot comes in, the multiplexer takes each time slot in turn and concatenates them to the output signal running at a faster speed. The reverse process is simply demultiplexing. Now this is known as synchronous multiplexing because all the tributary voice channels are perfectly synchronized to a common clock. However as you might guess, in real world the different voice channels coming in on different circuits are not perfectly synchronized. Because they come in at slightly different bit rates, the multiplexer must compensate to transmit them at a higher rate. This is done by adding dummy bits or ‘justification bits’.
  • In order to recreate our higher-order signal we bit-stuff (also known as positive justification). This means we add redundant (non-data carrying) bits to the tributary input stream to make up the expected input stream. The way we can tell that justification bits have been added is through the use of Justification Control Bits (C1-C4) covered later. Justification occur at 8Mb/s and above in the PDH hierarchy. 2Mb/s multiplexing is synchronous, hence there is no need of justification when multiplexing 64kb/s.
  • So pleisochronous is ‘almost Synchronous’ The major drawback of PDH is the fact it is not synchronous. If a Telecom operator wants to provide a 2Mb/s service to a customer, it will be carried on the operators high speed network at , for e.g.. 140Mb/s. However, because of the use of justification bits it is impossible for a network element to identify the exact location of required 2Mb/s stream. So, to access the customers 2Mb/s service the entire 140Mb/s signal must be de-multiplexed and then reformed back up to 140Mb/s. Secondly, PDH does not provide much in the way of network management information. Both these issues are alleviated with SONET/SDH as see forward through this discussion.
  • The PDH hierarchy is as shown above. The main rates are 2Mb/s (primary rate also known as E1), 8Mb/s (E2), 34Mb/s & 140Mb/s. These are the international rates covered by ETSI/ITU-T Standards and are used in most countries with exception of North America and Japan. The North American hierarchy differs in that the primary rate is 1.544Mb/s. This allow 24 Voice channels to be carried and is referred to as DS1(T1). A DS2 is 6.3Mb/s and a DS3 is 45Mb/s. DS3 are commonly used and are sometimes used in place of ITU 34Mb/s rate.
  • Two line codes are used in PDH. The first is Alternate Mark Inversion. Binary Values of 1 are represented by a pulse an the line, whereas a zero is by absence of a pulse. By using positive and negative pulses( bipolar), the net current on the line is 0 Amps. This allows the signal to travel twice as far on the copper wire pair. A second advantage is its built-in error detection. If the two pulses are detected with same polarity, Bipolar Violation (BPV). When a BPV is encountered, it is obvious that the signal has been disrupted by defective equipment or environmental conditions (e.g...lightening strikes). However there is an inherent problem with AMI. When the data being transmitted contains a lot of 0 bits, the network elements have a no pulse edges to synchronize with. This can lead to timing problems. Therefore, another scheme called High Density Bipolar (HDB3) ensures that there is adequate ‘1’son the line.
  • In this Scheme, for every four consecutive 0s a special pattern replaces the group of zeros. This pattern includes an intentional Bipolar Violation. This ensures that there are enough pulses on the line to maintain synchronization. The receiving terminal can extract the pattern reconstructing the original signal. The pattern inserted is governed by the polarity of the last inserted bit as well as the number of pulses following the previous violation bit. For an odd number of pulses : 000V is inserted. For even number of pulses: B00V is substituted, where B is the opposite polarity of the bit immediately preceding it and V is the same as B.
  • Shown above is the basic 2Mb/s frame structure, which is the fundamental building block of PDH. Each 2Mb/s frame contains 256 bits at a repetition rate of 8kHz. The first timeslot is reserved for framing, error checking and alarm signals. In PCM31 framed signals, the remaining 31 time slots are available to carry voice traffic. However, PCM30 is commonly used and this reserves another timeslot for network signaling information. This is called channel associated signaling as the signaling information is carried in the same link as the data.(in contrast to SS7).
  • The Frame Alignment signal is used to synchronize the transmit and receive ends of the transmission path (FAS =Si 0011011). This is transmitted every second frame in the timeslot 0 of the 2Mb/s frame. The ‘Non-Frame Alignment Signal’(NFAS) is transmitted in timeslot 0 every second frame. If the network detects3 bad frames in 4, a Loss of Frame alarm (LOF) will be generated. Frame Synchronization will be recovered with a correct FAS-NFAS-FAS sequence. When bit Si is 1, this signifies that the 2Mb/s structure is an international path. This bit is present in both FAS & NFAS. The A bit is used to flag when a remote network element has detected am alarm and informs the receiving network element that there is a problem elsewhere in the network. Bits Sa4-Sa8 are used in specific point-to-point applications. These may be specified to individual operators, but are often used for synchronization status messages. TS16 is used for signaling information .The signaling information for 30 Voice channels is carried over 16 frames. The beginning of this multi-frame indicated by a multi-frame alignment signal (MFAS). The network searches for the pattern 0000 in TS16,as this marks the beginning of 16 frames. The next 15 frames carry pairs of ‘abcd’ signaling information, with one set for every voice channel. In the MFAS, x is for international use and y flags a remote multi-frame alarm.
  • Above the primary rate, the PDH multiplex structure is complicated by the need to include positive justification for synchronizing the tributaries. For 8Mb/s, the multiplexer aggregates four 2Mb/s tributaries together. The start of the frame is signified by the frame alignment signal 111010000. The frame also contains 12 justification control bits with 4 optional justification bits (one per tributary). If all control bits C1 are set t o1, then the justification bit J1 is present. The same applies to the other control bits. The control bits are repeated three times in a frame. However,a majority vote is used to determine whether the justification bit has been used. This means that justification process is robust to errors. If there was an error in the justification process, frame alignment would be lost along with a considerable amount of data. If a PDH multiplexer loses the input signal or frame alignment, an ‘all ones’ Alarm Indication Signal (AIS) is sent out, which is picked up down streams to set network alarms.
  • The 34Mb/s frame structure is very similar to that of 8Mb/s, however with longer FAS and for the 140 Mb/s, 5 sets of justification control bits.
  • The Output of the 140Mux is fed to the L-SW which has a provision for switching the regular system to protection system in case of fault. The L-SW receives 140Mbps CMI signals from a number of 140M multiplexers. Normally the signals are fed to their respective OLTs. Incase of fault that particular 140Mux is routed to protection system, through L-SW. After the L-SW, the signal is fed to OLTE where it converts 140M CMI to optical signal. In addition to 140Mbps traffic signal, system has alarm control unit (ACU) as well as Service Data Interface (SDF). This unit is used for supervisory functions. The Portable Control Terminal (PCT) can be connected to ACU for monitor & control functions. In addition to PCT, optionally L-SV (Line Supervisory system ) can also be implemented. The SD Interface is used for supervisory functions such as Order wire facility for L-Sw and for central supervisory arrangement. The Order wire provides 64kbps data to OLTE and accepts 64kbps data from it through this SD interface of OLTE. These signals are also combined with traffic of 140Mbps signal. Traffic plus supervisory signal together is converted to Optical signal which is fed to the Transmission fiber through Fiber Distribution panel. Incase the operating fiber goes faulty, then the cable pair can be changed at FTP. The arrangements at the Transmission station are similar at Repeater.
  • The function of OLTE is to convert the digital multiplexed electrical stream into an optical signal in the trans direction. In the receive direction it recovers back the electrical signal from the optical signal. Transmit circuit: A 139264 Kbps CMI coded digital multiplexed signal is fed to CMI-to- Unipolar Converter, where the signal is amplified and equalized to compensate for station cable loss and distortion. The signal is converted into unipolar (NRZ) form and fed to a S/P as a 140M NRZ data signal. The timing information is also extracted from the incoming CMI signal and applied to the S.P as a 140M CLK signal. If the loss of the incoming 13926kbps is detected, a monitor circuit generates the S IN DOWN alarm and sends it to AC &RSD INTF. In the S/P , the 140M NRZ data is converted into 5-bit parallel data, which is stored in elastic memory in the speed converter by a write clock. This write clock is produced from 140M CLK signal. The 5-bit parallel data is read out by a read clock which is derived from the 168M CLK by a counter & timing generator. The 168M CLK is generated by a Phase Locked Oscillator., which keeps the phase difference between the 140M CLK and 168M CLK signals constant. This speed conversion prepares the 6 th bit position for 5B6B conversion and the time slots for the frame synchronization bits and Overhead bits. The Speed Converted 5-bit parallel data is scrambled. Each 5-bit parallel data applied to the address lines of a ROM chip which contains data organized according to 5B6B coding law. An Overhead bit controller receives the serial data and remote service data from SD Interface and alarm control and remote data interface at a rate of 276kbps and 55kbps respectively. The overhead bit controller scans and aligns the data as overhead bits and feed them to the combiner. In the combiner ,the frame synchronization bits (111000110011) and overhead bits are inserted into the 6-bit parallel data.The Overhead bits comprise twelve bits in total: five bits of service data, one bit for remote service data and six complementary bits for adjusting the disparity of the Overhead bits to zero to prevent the state transition of 5B6B code. The complete 6-bit parallel data is converted into a 168443kbps serial data in a P/S converter and the 168M data is sent to the E-O converter together with the 168443kHz clock signal (168M CLK).
  • In continuation with OLTE, in the Receive Code converter the incoming 168443kbps from the O-E Converter is applied to the 168M DATA IN terminals. A synchronizer & S/P converter establishes sync with the incoming signal when the frame sync bits (110001100011) are detected properly and converts the serial data to 6-bit parallel data. If the sync is not established, the SYNC LOSS alarm is sent to the AC &RD Interface. A separator extracts the overhead bits from the bit-controller, where the bits are reconstructed as the 276 kbps service data. The service data is sent to SD Interface along with the clock signal ( 550K CLK). The remote service data is fed to the AC & RD interface with RSD CLK signal. The 6-bit parallel data from the separator is converted into 5-bit parallel data by a 5B6B decoder using P-ROMs which contain data according to 6B to5B decoding law. The 5-bit data from the 5B6B decoder is de-scrambled and stored in the elastic memory of the speed converter by a write clock which is derived from the 168M CLK by a frame counter & timing generator. The stored 5-bit parallel data is read out by a read clock which is derived from the 139,264 kHz clock (140M CLK). The 140M CLK is generated by a Phase –Locked Oscillator, which keeps the phase difference between the 168M CLK and 140M CLK signals constant. As a result , the data rate is decreased from 168443kbps to 139264kbps. A P/S converter converts the 5-bit parallel data into a serial signal which is further converted into a CMI coded signal by a Unipolar- to –CMI converter. This CMI signal is sent out from the 140M CMI OUT terminal .If the output signal is lost a monitor circuit generates the R OUT DOWN alarm and sends the alarm to AC & RD Interface.
  • The 168Mb/s data signal is applied to the input interface with 168MHz clock signal and is converted from NRZ to RZ. The Laser diode (LD) is activated by the driver circuit and the modulated output is sent down the fiber via an optical adapter at the front of the unit. The output level of the LD is stabilized by APC circuit , using monitor photodiode (PIN) output current and controls the bias current to the LD to keep the optical level constant. This compensates for the tolerance of the LD to variance in the temperature If the backward beam is lost (indicating loss of optical o/p) the APC generates the S CUT DOWN alarm and sends to ACU &RD Interface unit. If the bias current to the LD exceeds the threshold, the APC generates LD BIAS ALM and sends to ACU &RD Interface unit. The LD bias current can be calculated by measuring the LD BIAS MON voltage at the check terminals {LD bias current (am) = check terminal voltage (mV) / 10 (ohms) }.When the ground signal is applied to the LD CUT terminal, it sets the LD bias current to 0 am, thus cutting off LD optical output. E-O converter works off –9V dc from power unit. This –9V dc is converted into –6V stabilized supply for use in the E-O conversion unit.
  • The Avalanche Photodiode(APD) converts the incoming optical pulses, which are applied to optical adapter, into a weak electrical signal is amplified and reshaped by a pre-amplifier, automatic gain control(AGC) amplifier and main amplifier to obtain maximum SNR and minimize inter-symbol interference. The resultant signal is fed to a DC clamper, peak level detector and timing extractor. The output of the main amplifier is kept a constant value of feedback circuit. This compensates for receive level variations due to cable length differences, optical output power variation at the remote station etc.The peak level detector detects the peak level of the main amplifier output and informs a gain controller and bias controller of the peak level. The gain controller controls the gain of the AGC amplifier and the bias controller controls the multiplication factor of the APD to keep the optimum operation of the circuit. The timing extractor extracts the timing signal from the main amplifier output. Since the level of the extracted signal varies with the pattern of the input signal, a limiter produces a stable clock signal by amplifying and limiting the extracted signal. A distributor supplies this clock signal to a decision circuit and interface circuit. The DC clamper restores the DC component to the main amplifier output. The decision circuit then determines whether the output is ‘1’ or ‘0’ at the timing of the clock signal. The resultant signal is in NRZ form and fed with the clock signal to the Interface circuit, which converts both signals to an ECL level and sends out the signals from the DATA OUT and CLK OUT terminals. An alarm interface circuit monitors the clock signal and generates the R IN DOWN alarm if loss of the clock signal ( i.e. loss of incoming optical signal) is detected. Two power supply circuits generate stabilized +6V and –5.2V dc from +9V &-9V dc respectively and supply these voltages to each part of the unit.
  • The SDH standards are based on the principles of direct synchronous multiplexing which is the key to cost effective and flexible telecommunication networking. In essence, it means that the individual tributary signals may be multiplexed directly into higher rate SDH signals without intermediate stages of multiplexing. SDH network Elements can then be interconnected directly with obvious cost and equipment savings over the existing network. Advanced network management and maintenance capabilities are required to effectively manage the flexibility provided by SDH. Approximately 5% of the SDH signal structure is allocated to supporting advanced network management procedures and practices. The SDH signal is capable of transporting all common tributary signals found in today’s telecom networks. This means that SDH can be deployed as an overlay to the existing signal types. In addition, SDH has the flexibility to readily accommodate new types of customer service signals that Network Operators will wish to support in future. SDH can be used in all three traditional telecom application areas namely, Long Haul,local network, and Access network.SDH therefore makes it possible for a unified telecom network infrastructure to evolve. In fact that SDH provides a single common standard for this telecom network means that equipment supplied by different manufacturers may be interconnected directly.
  • SONET (Synchronous Optical Network) is an optical transmission interface proposed by Bellcore and standardized by ANSI. A compatible version referred as Synchronous Digital Hierarchy (SDH) has been published by ITU-T in recommendation G.707,G.708 & G.709. SONET is intended to provide a specification for taking advantage of the high speed digital transmission capability of optical fiber. Signal hierarchy: The SONET specification defines a hierarchy of standardized digital data rates. The lowest level referred to as STS-1(Synchronous Transport Signal level –1) or OC-1 (optical carrier level –1) is 51.84 Mbps. This data rate can be used to carry a single DS-3 signal or a group of lower rate signals such as DS1,DS1C,DS2 plus ITU-T rates (e.g... 2.048 Mbps) As seen from the slide above , multiple STS-1 signals can be combined to form an STS-N signal. The signal is created by interleaving bytes from N STS-1 signals that are mutually synchronized. For the ITU-T SDH , the lowest rate is 155.52 Mbps which is designated as STM-1 (Synchronous Transport Module level 1). This corresponds to SONET STS-3. The reason for the discrepancy is that STM-1 is the lowest rate signal that can accommodate an ITU-T level 4 signal (139.264 Mbps).
  • An ingenious feature of SDH is the way that data is carried in the frame payload. This involves the use of pointers. The combination of a pointer in a fixed location of STM frame, and a floating ‘Virtual Container’ in the payload , to which it points , is called in the CCITT recommendations as an ‘Administrative Unit’ (AU). So AU = pointer + VC.A Virtual Container consists of an Overhead and a container payload. Individual VCs may be smaller than STM-1 payload in which case there may be more than one per STM payload, with each having its own pointer. In general, however, VCs constitute an integer number of 9-row columns (i.e. they consist of 9 x k bytes where k is an integer) and the first column contains the path overhead. Various sizes of VCs are available to carry the many different PDH rates. For e.g. a single AU per STM-1 frame, taking up the whole payload capacity can carry one 139264kbps channel. This type of AU is referred to as AU-4 , because the 139264kbps signal which it carries is level-4 in PDH hierarchy. Likewise VC associated with AU-4 is itself designated as VC-4. There also exists AU-3s corresponding to level –3 in PDH. Because of this lower data rate, there is sufficient capacity in an STM-1 for 4 level-3 signals from European hierarchy and 3 level-3 signals from US hierarchy. The signals from lower levels of PDH (level1,2) are also carried in the VC-1,VC-2 respectively. But these containers are not put directly into the STM-1 payload, rather they are ‘nested’ with in higher level VC payloads. At each level in the nesting, the VC has an associated pointer which is in a fixed position with respect to the VC at the next level. A pointer plus its VC levels 1 or 2 is known as a ‘Tributary Unit (TU)’. The characteristic difference between AU & TU is that an AU is at the top of the hierarchy, directly in an STM frame, while TU is in a higher level VC.
  • The signal bits are transmitted in a raster scanned sequence, similar to lines on a video signal.
  • A comparison of the STS-1 & STM-1 signals will best exemplify the byte interleaved multiplexing in SONET/SDH. STS-1 has a signaling rate of 51.840Mbps and is chosen so as to carry one of the US PDH level-3 signals(DS3,44.736Mbps). The STS-1 frame structure is described by a rectangle of 90 columns and 9 rows, with first three columns containing overhead. Synchronously multiplexing, by byte interleaving, three STS-1 signals gives the STS-3 which is same as CCITT STM-1 signal.
  • The basic SONET building block is the STS-1 frame consists of 810 octets and is transmitted in 125us for an overall data rate of 51.84Mbps. The frame can logically be viewed as a matrix of 9 rows of 90 octets each with transmission of one row at a time, from left to right and top to bottom. The first three columns(3 octets x 9 rows =27 octets) of the frame are devoted to overhead bytes. Nine octets are devoted to section-related overhead and 18 octets for line overhead. The remainder of the frame is payload, which is provided by the path layer. The payload includes a column of path overhead, which is not necessarily in the first available column position; the line overhead contains a pointer that indicates where the path overhead starts.
  • From the transmission point of view, the SONET/SDH network can be described in terms of four network segment : 1)The lower order path which allows network performance to be maintained end-to-end for a Tributary Unit mapped service 2)The Higher order path which allows network performance to be maintained end –end at the VC-4 level . 3)The multiplexer section (line) which allows network performance to be maintained between transport nodes and provides the majority of network management reporting. 4)The Regenerator section span allows network performance to be maintained between regenerators or between REG and an SDH network element allowing fault localization.
  • Section Overhead: A1,A2: Framing bits= F6,26hex;used to synchronize the beginning of frame. C1: STS-1 ID identifies the STS-1 number (1to N) for each STS-1 within an STS-N multiplex. B1: Bit Interleaved parity byte providing even parity over previous STS-N frame after scrambling; the i th bit of this octet contains the even parity value calculated from the i th bit position of all octets in the previous frame. E1: Section level 64kbps PCM Order wire ;optional 64kbps voice channel to be used between section terminating equipment, hubs and remote terminals. F1: 64kbps channel set aside for user purposes. D1- D3: 192kbps data communication channel for alarms, maintenance, control and administration between sections. Line Overhead: H1-H3: pointer bytes used in frame alignment and frequency adjustment of payload data B2: Bit interleaved parity for line level error monitoring. K1-K2: two bytes allocated for signaling between line level automatic protection switching eqpt; uses a bit-oriented protocol that provides for error protection management of SONET optical link. D4-D12: 576Kbps data communication channel for alarms, maintenance, control monitoring and administration at the line level. Z1,Z2: Reserved for future use. E2: 64kbps PCM voice channel for line level order wire. Path Overhead: J1: 64kbps used to repetitively send a 64-octet fixed length string so that a receiving terminal can continuously verify the integrity of the path; B3: Bit interleaved parity at the path level, calculated over all bits of the previous SPE. C2: STS Path signal label to designate equipped versus un-equipped signals. Unequipped signals means the line connection is complete but there is no path data to send. G1: Status byte sent from the path terminating equipment to path originating equipment to convey status of terminating equipment and path error performance. F2: 64Kbps channel for path user. H4 : Multi frame indicator for payloads needing frames that are longer than the single STS frame; multi frame indicators are used when packing lower rate channels into SPE. Z3-Z5: Reserved for future use.
  • When there is a difference in phase or frequency, the pointer value is adjusted. To accomplish this, a process known as byte stuffing is used. In other words, the SPE payload pointer indicates where in the container capacity a VT starts, and the byte-stuffing process allows dynamic alignment of the SPE in case it slips in time. Positive Stuffing When the frame rate of the SPE is too slow in relation to the rate of the STS–1, bits 7, 9, 11 , 13, and 15 of the pointer word are inverted in one frame, thus allowing 5-bit majority voting at the receiver. These bits are known as the I-bits or increment bits. Periodically, when the SPE is about one byte off, these bits are inverted, indicating that positive stuffing must occur. An additional byte is stuffed in, allowing the alignment of the container to slip back in time. This is known as positive stuffing, and the stuff byte is made up of non information bits. The actual positive stuff byte immediately follows the H3 byte (that is, the stuff byte is within the SPE portion). The pointer is incremented by one in the next frame, and the subsequent pointers contain the new value. Simply put, if the SPE frame is traveling more slowly than the STS–1 frame, every now and then stuffing an extra byte in the flow gives the SPE a one-byte delay Negative Stuffing Conversely, when the frame rate of the SPE frame is too fast in relation to the rate of the STS–1 frame, bits 8, 10, 12, 14, and 16 of the pointer word are inverted, thus allowing 5-bit majority voting at the receiver. These bits are known as the D-bits or decrement bits. Periodically, when the SPE frame is about one byte off, these bits are inverted, indicating that negative stuffing must occur. Because the alignment of the container advances in time, the envelope capacity must be moved forward. Thus, actual data is written in the H3 byte, the negative stuff opportunity (within the overhead); this is known as negative stuffing. The pointer is decremented by one in the next frame, and the subsequent pointers contain the new value. Simply put, if the SPE frame is traveling more quickly than the STS–1 frame, every now and then pulling an extra byte from the flow and stuffing it into the overhead capacity (the H3 byte) gives the SPE a one-byte advance. In either case, there must be at least three frames in which the pointer remains constant before another stuffing operation (and therefore a pointer value change) can occur
  • Transport for lower rate tributary signals such as 2Mbps is provided by a Tributary Unit (TU) frame structure.TU s are specifically meant to support the transport and switching of payload capacity which is less than that provided by the STS-1 VC-4.By design, the TU frame structure fits neatly into the VC-4 in order for TU multiplexing. A fixed number of whole TU s may be assembled within the C-4 container of VC-4 of STS-1. The same also holds for VC-4 of STM-1. Different sizes of Tributary unit frames: the notation for the respective VC is given as C x +POH =VC x TU 11: each TU-11 frame consists of 27 bytes, structured as 3 columns of 9 bytes. At a frame rate of 8000 Hz, these bytes provide a transport capacity of 1.728Mb/s and will accommodate the mapping of a 1.544Mb/s DS1 signal. 84 TU-11 can be multiplexed into VC-4 of STM-1. TU-12: Each TU-12 frame contains 36 bytes, structured as 4 columns of 9 bytes. At a frame rate of 8000Hz, these bytes provide a transport capacity of 2.304Mb/s and will accommodate the mapping of a 2.048Mb/s signal. 63 TU-12 may be multiplexed into VC-4 of STM-1. TU-2: Each TU-2 frame consists of 108 bytes, structured as 12 columns of 9 bytes. At a frame rate of 8000Hz, these bytes provide a transport capacity of 6.912Mb/s and will accommodate the mapping of a ANSI DS2 signal. 21 TU-2 may be multiplexed into STM-1 VC-4. TU-3: Each TU-3 frame consists of 774 bytes, structured as 86 columns of 9 bytes. At a frame rate of 8000Hz, these bytes provide a transport capacity of 49.54Mb/s and can accommodate 34Mb/s or DS3.3 TU-3 may be put in VC-4of STM-1
  • REG Section Overhead functions: There are 3 A1 & 3 A2 bytes which form STM-1 frame word. The pattern used is Hex F6F6F6282828.Every STM-1signal within STM-N has this framing pattern. The first thing a network element does is to search for the frame. J0 byte is REG section trace message. This byte is used to transmit respectively a Section Access Point Identifier so that the section receiver can verify its continued connection to the intended transmitter. B1 holds the result of BIP-8 calculation and is used for performance monitoring at the REG level. The computation is made over all bytes of previous STM-N frame after scrambling. The result is placed in B1 of the current frame before scrambling. B1 is only defined for the STM-1 in an STM-N. The E1 bytes provide an order wire at REG level. F1 User Channel byte is used for user purposes to provide temporary data/voice connections for special maintenance purposes. Mutiplexer Section Overhead functions: Here 3 B2 bytes available which makes a BIP-24 check for monitoring error performance. Multiplexer Section Overhead cares about the errors between multiplexers so it calculates BIP-24 over the bytes in VC and the multiplexer section overhead of the previous frame. It leaves the REG section overhead out of the calculation so that the REG can do the BIP over the whole STM-N signal. The whole point of this is that, we can sectionalize faults using the results of different overhead calculations. In an STM-N signal, B2 s are provided for all STM-1 s. The K1/K2 bytes are used by multiplexers to control protection switching. Standard messages can be sent to ,for example, force a line onto protection. The Multiplex section Remote Defect Indication is used to return an indication to the transmit end that the received end has detected an incoming section defect or is receiving MS-AIS. MS-RDI is generated by inserting ‘110’ code in positions 6,7,8 of the K2 byte before scrambling. D4-D12 bytes provide a data communication channel for multiplexers to exchange management information. These bytes are defined for the first STM-1 in an STM-N. S1 carries level of quality of synchronization defined by G.811,G.812,G.813. M1 is allocated for use as a Multiplex section Remote Error Indication. The byte shall be set to convey the count of interleaved bit blocks that have been detected in error by the BIP-24. E2 byte provides order wire voice channel to let crew coordinate work. It is defined for first STM-1 of STM-N.
  • VC-4 assembly process: The process of assembling the tributary into a VC is referred as ‘mapping’. To provide uniformity across all SDH transport capabilities, the payload capacity provided for each individual tributary signal is always slightly greater than that required by the tributary signal. Thus, the essence of the mapping process is to synchronize the tributary signal with payload capacity provided for transport. This is achieved by adding extra stuffing bits to the signal stream as a part of mapping process. For e.g. a 140Mbps tributary signal needs to be synchronized with a payload capacity of 149.76Mbps provided by the C-4. Addition of the Path Overhead completes the assembly of the VC-4 and increases the bit rate of the composite signal to 150.34Mbps. VC-4Disaasembly process: At the point of exit from the synchronous network, the tributary signal must be recovered from the VC. This process is referred as ‘de-mapping’. The VC comprises of Path Overhead, the tributary signal and additional stuffing bits that have been added to synchronize the signal rate of the tributary signal to the payload capacity available for transportation. Thus, the essence of the de-mapping process is to de-synchronize the tributary signal form the composite VC signal. This recovered tributary signal must then be output, as near as is possible , in its original form. So for e.g. a VC-4 carrying a mapped 140Mbps signal arrives at the tributary disassembly location with signal rate of 150.34Mbps. Stripping the Path Overhead and stuffing bits from VC-4 results in a discontinuous signal representing the transported 140Mbps signal. These timing discontinuities are reduced by means of de-synchronizing PLL in order to produce a continuous 140Mbps tributary signal.
  • The multiplexing principles of SONET are as follows: mapping —used when tributaries are adapted into VTs by adding justification bits and POH information aligning —takes place when a pointer is included in the STS path or VT POH, to allow the first byte of the VT to be located multiplexing —used when multiple lower order path-layer signals are adapted into a higher-order path signal, or when the higher-order path signals are adapted into the line overhead stuffing —SONET has the ability to handle various input tributary rates from asynchronous signals; as the tributary signals are multiplexed and aligned, some spare capacity has been designed into the SONET frame to provide enough space for all these various tributary rates; therefore, at certain points in the multiplexing hierarchy, this space capacity is filled with fixed stuffing bits that carry no information but are required to fill up the particular frame One of the benefits of SONET is that it can carry large payloads (above 50 Mbps). However, the existing digital hierarchy signals can be accommodated as well, thus protecting investments in current equipment. To achieve this capability, the STS SPE can be sub-divided into smaller components or structures, known as VTs, for the purpose of transporting and switching payloads smaller than the STS–1 rate. All services below DS–3 rate are transported in the VT structure. Slide illustrates the basic multiplexing structure of SONET. Any type of service, ranging from voice to high-speed data and video, can be accepted by various types of service adapters. A service adapter maps the signal into the payload envelope of the STS–1 or VT. New services and signals can be transported by adding new service adapters at the edge of the SONET network.
  • Terminal Multiplexer: The path terminating element (PTE), an entry-level path-terminating terminal multiplexer, acts as a concentrator of DS–1s as well as other tributary signals. Its simplest deployment would involve two terminal multiplexers linked by fiber with or without a regenerator in the link. This implementation represents the simplest SONET link (a section, line, and path all in one link; Regenerator: A regenerator is needed when, due to the long distance between multiplexers, the signal level in the fiber becomes too low. The regenerator clocks itself off of the received signal and replaces the section overhead bytes before re-transmitting the signal. The line overhead, payload, and POH are not altered Add/Drop Multiplexer (ADM) Although network elements (NEs) are compatible at the OC–N level, they may differ in features from vendor to vendor. SONET does not restrict manufacturers to providing a single type of product, nor require them to provide all types. For example, one vendor might offer an add/drop multiplexer with access at DS–1 only, whereas another might offer simultaneous access at DS–1 and DS–3 rates A single-stage multiplexer/demultiplexer can multiplex various inputs into an OC–N signal. At an add/drop site, only those signals that need to be accessed are dropped or inserted. The remaining traffic continues through the network element without requiring special pass-through units or other signal processing. The add/drop multiplexer provides interfaces between the different network signals and SONET signals. Single-stage multiplexing can multiplex/demultiplex one or more tributary (DS–1) signals into/from an STS–N signal. It can be used in terminal sites, intermediate (add/drop) sites, or hub configurations. At an add/drop site, it can drop lower-rate signals to be transported on different facilities, or it can add lower-rate signals into the higher-rate STS–N signal. The rest of the traffic simply continues straight through digital cross-connect interfaces various SONET signals and DS–3s. It accesses the STS–1 signals, and switches at this level. It is the synchronous equivalent of the DS–3 digital cross-connect, except that the broadband digital cross-connect accepts optical signals and allows overhead to be maintained for integrated OAM&P (asynchronous systems prevent overhead from being passed from optical signal to signal). The broadband digital cross-connect can make two-way cross-connections at the DS–3, STS–1, and STS–Nc levels. It is best used as a SONET hub, where it can be used for grooming STS–1s, for broadband restoration purposes, or for routing traffic.
  • Digital Loop Carrier The digital loop carrier (DLC) may be considered a concentrator of low-speed services before they are brought into the local central office (CO) for distribution. If this concentration were not done, the number of subscribers (or lines) that a CO could serve would be limited by the number of lines served by the CO. The DLC itself is actually a system of multiplexers and switches designed to perform concentration from the remote terminals to the community dial office and, from there, to the CO. Whereas a SONET multiplexer may be deployed at the customer premises, a DLC is intended for service in the CO or a controlled environment vault (CEV) that belongs to the carrier. Bellcore document TR–TSY–000303 describes a generic integrated digital loop carrier (IDLC), which consists of intelligent remote digital terminals (RDTs) and digital switch elements called integrated digital terminals (IDTs), which are connected by a digital line. The IDLCs are designed to more efficiently integrate DLC systems with existing digital switches
  • Point-to-Point: The SONET multiplexer, an entry-level path-terminating terminal multiplexer, acts as a concentrator of DS–1s as well as other tributaries. Its simplest deployment involves two terminal multiplexers linked by fiber with or without a regenerator in the link. This implementation represents the simplest SONET configuration. In this configuration the SONET path and the service path (DS–1 or DS–3 links end-to-end) are identical, and this synchronous island can exist within an asynchronous network world. In the future, point-to-point service path connections will span across the whole network and will always originate and terminate in a multiplexer. Point-to-Multipoint :A point-to-multipoint (linear add/drop) architecture includes adding and dropping circuits along the way. The SONET ADM (add/drop multiplexer) is a unique network element specifically designed for this task. It avoids the current cumbersome network architecture of demultiplexing, cross-connecting, adding and dropping channels, and then remultiplexing. The ADM is typically placed along a SONET link to facilitate adding and dropping tributary channels at intermediate points in the network Hub Network: The hub network architecture accommodates unexpected growth and change more easily than simple point-to-point networks. A hub concentrates traffic at a central site and allows easy reprovisioning of the circuits The following are two possible implementations of this type of network: using two or more ADMs, and a wideband cross-connect switch, which allows cross-connecting the tributary services at the tributary level using a broadband digital cross-connect switch, which allows cross-connecting at both the SONET level and the tributary level
  • Ring Architecture :The SONET/SDH building block for a ring architecture is the ADM. Multiple ADMs can be put into a ring configuration for either bidirectional or unidirectional traffic. The main advantage of the ring topology is its survivability; if a fiber cable is cut, the multiplexers have the intelligence to send the services affected via an alternate path through the ring without interruption. The demand for survivable services, diverse routing of fiber facilities, flexibility to rearrange services to alternate serving nodes, as well as automatic restoration within seconds, have made rings a popular SONET/SDH topology
  • When a Node receives a bridge request it sends identical traffic on both the service and protection fibers When a node executes a switch it selects traffic from the protection fiber rather than the service fiber.
  • Following development of the SONET standard by ANSI, the CCITT undertook to define a synchronization standard that would address interworking between the CCITT and ANSI transmission hierarchies. That effort culminated in 1989 with CCITT's publication of the synchronous digital hierarchy (SDH) standards. SDH is a world standard, and, as such, SONET can be considered a subset of SDH . Transmission standards in the United States, Canada, Korea, Taiwan, and Hong Kong (ANSI) and the rest of the world (ITU–T, formerly CCITT) evolved from different basic-rate signals in the non-synchronous hierarchy. ANSI time division multiplexing (TDM) combines twenty-four 64–kbps channels (DS–0s) into one 1.54–Mbps DS–1 signal. ITU TDM multiplexes thirty-two 64–kbps channels (E0s) into one 2.048–Mbps E1 signal. The issues between ITU–T and ANSI standards-makers involved how to accommodate both the 1.5–Mbps and the 2–Mbps non-synchronous hierarchies efficiently in a single synchronization standard. The agreement reached specifies a basic transmission rate of 52 Mbps for SONET and a basic rate of 155 Mbps for SDH. Synchronous and non-synchronous line rates and the relationships between each are shown in above slide Convergence of SONET and SDH Hierarchies: SONET and SDH converge at SONET's 52–Mbps base level, defined as synchronous transport module–0 (STM–0). The base level for SDH is STM–1, which is equivalent to SONET's STS–3 (3 x 51.84 Mbps = 155.5 Mbps). Higher SDH rates are STM–4 (622 Mbps) and STM–16 (2.5 Gbps). STM–64 (10 Gbps) has also been defined. Multiplexing is accomplished by combining or interleaving multiple lower-order signals (1.5 Mbps, 2 Mbps, etc.) into higher-speed circuits (52 Mbps, 155 Mbps, etc.). By changing the SONET standard from bit interleaving to byte interleaving, it became possible for SDH to accommodate both transmission hierarchies.
  • Both Optical & Electrical Physical interfaces are defined for SDH. Optical Interfaces: Specifications are defined at each rate for 3 different application scenario. Intra-Office optical Interfaces: (denoted I-n where n= STM hierarchical level).Covers applications requiring transmission up to approximately 2Km, having system loss budgets in the range 0 to 7 dB with single-mode fiber. I-n optical transmitters may be either LEDs or low power Multi-longitudinal mode lasers(MLM) at 1310 wavelength. Short Haul optical interfaces:(denoted S-n. 1or2, where n=STM level; 1= 1310nm wavelength on G.652 fiber; 2= 1550 nm wavelength on G.652 fiber.) Covers applications up to 15Km, having system loss budgets in the range 0 to 12 dB with SM fiber. Single Longitudinal mode (SLM) or MLM laser transmitters are used at either 1310 or 1550 nm wavelengths. Long Haul optical interfaces: (denoted L-n.1,2 or 3 where n= STM level;1= 1310 nm wavelength on G.652 fiber; 2=1550 nm wavelength on G.652 or G.654 fiber, 3 = 1550nm wavelength on G.653 fiber).Covers application up to 40 Km, having system loss budgets in the range 0 to –35 dB with SM fiber.
  • A typical STM-1 ring is in metro networks where service providers need flexibility to reliably transport and manage a wide variety of different applications including private lines, PBX, primary rate ISDN, LAN-WAN, mobile base station links, etc.   For e.g.. a TN-1X of Nortel Networks can be configured as a head end Mux in a ring comprising other TN-1X and TN1C/1P elements or to provide 2Mb/s access to a TN-16X (STM-16) based network. It functions as an Add/Drop multiplexer providing access to an STM-1 transport aggregate at VC-12 and VC-3 levels. It supports a 2,34,45 Mb/s PDH and STM-1 SDH tributaries (optical and electrical) with in-service upgrade of up to 4 tributary cards by a flexible combination of VC-12 and VC-3 tributaries to fully fill payload capacity. The tributary cards are (a) 16 x 2 Mb/s (with 75 or 120 ohm interface option) (b) 34/45 Mb/s tributary card to VC-3 (c) 34Mb/s tributary card (G.742, G.751 channelization to 16 x 2 Mb/s and VC-12) (d) STM-1 tributary card (G.703 electrical or G.957 optical- L1.1 1310nm long haul or S1.1 1310 nm short haul, hardware selectable) STM-1 aggregate and tributary interfaces can be configured with 1+1 Multiplex Section Protection. 2Mb/s tributary cards are protected at 1:N (N is 4 max) and 1+1 protection levels for 34/45 Mb/s tributary cards. Thus the VC path protection is ensured. The network management communication to the SDH network elements use an integral Data Communication Network (DCN) that minimizes the use of external data communication equipment. This type of DCN routing is self-configuring and self-healing- adapting dynamically and automatically to changes in the network. This allows remote download of the Network Element’s operational and configuration software versions and upload of configuration data, without impacting live traffic. This allows in-service upgrades to be efficiently carried out from a central location. This significantly minimizes the field engineering errors. In a TN-1X this is typically performed with the F interface (RS-232) for local craft access terminal and Command line Q3 interface via Embedded communication channel to Element Controller and service enabling software center.
  • STM-4 ring: A STM-4 system is applicable in local and regional SDH networks, where service providers need to efficiently deliver and / or aggregate a significant number of 2Mb/s services. For e.g. TN-4T of Nortel Networks can be configured to feed into an STM-4 or STM-16 ring as shown in slide. This setup allows add/drop or through VC-12 connections to be configured at other network elements around the ring. It provides access to a STM-4 transport aggregate delivers up to 252 x 2 protected 2Mb/s service interfaces per shelf supporting VC-12 connectivity. Up to 8 x electrical interface cards, 32 x 2 Mb/s asynchronous tributaries per card (PDH G.703 with 75 ohm and 120 ohm interface options) Dual STM-4 G.957 S.4.1 Short-haul optical aggregate interfaces with automatic laser shutdown. 1+1 Multiplexer Section Protection of STM-4 optical interfaces; 1:N protection of tributary cards (N=4 max); F interface (RS-232) for local craft access terminal; Q3 interface via Embedded Communication Channel to Element controller and service software enable center. A TN-4T can also be configured to feed into an STM-16 ring using TN-16X (STM-16 equipment). In this setup, the connection is linear point- to –point connection since a TN-16X manages signals at VC-4 level. Any TN-16X network elements must be configured with a through STM-4 connection.
  • STM-16 ring: This high capacity telecom networks, at a bit rate of 2.488 Gbps, forms a backbone for the service provider for delivering broadband services to metropolitan urban core areas.   For e.g. TN-16X of Nortel Networks is a SDH Add/drop Multiplexer at STM-16 level used for providing point-to-point, repeater and unique shared protection facilities. It supports a wide range of tributaries and aggregate ports including 34Mb/s, 140Mb/s, STM-1 electrical, STM-1 & STM-4 optical. It provides a full complement of network survivability features including; revertive (1:1 or 1:N; N=1 to14) or non-revertive (1+1) automatic protection switching schemes and 1:N, 1+1 full STM16 protected. Tributary protection is available for tributary types and matched nodes provide inter-ring connection protection. TN-16X multiplexer has bi-directional self-healing ring topologies (MS-SP rings), allowing protection capacity resulting in a higher utilization of ring capacity when compared with path switched dedicated protection rings. Ring Switch times less than 50 ms is available ensuring service reliability during a cable break. It is also possible to connect the customer via two geographically diverse fibers onto the network, thus increasing survivability. The system facilitates remote operation and configuration software download through Network Management Interface and also features Q3 interface for vendor independent network level manager. Apart from this it supports 32  integrated DWDM enabling up to 80Gbps on a fiber pair making it future proof system. TN-16X DWDM allows service provider to grow in economic 2.5 Gbps incremental steps.  
  • Optical Amplifiers are categorized in terms of function and perform. Three basic types are (1) Boosters (2)in-line amplifiers (3) and pre-amplifiers. A booster is a power amplifier that magnifies a transmitter signal before sending down the fiber. A booster raises the power of the optical signal to the highest level, which maximizes the transmission distance. The main requirement of this amplifier is to produce maximum output power, not maximum gain, because the input signal here is relatively large; it comes almost immediately after Tx. An additional benefit of using a booster is that it relieves the Tx of the necessity of producing maximum optical power, enabling Tx designers to concentrate on improving a broad range of transmitter characteristics. An in-line amplifier operates with a signal in the middle of the fiber optic link. Its primary function is to compensate for power losses caused by fiber attenuation, connections and signal distribution in networks. A preamplifier magnifies the signal immediately before it reaches the receiver. This type of optical amplifier operates with weak signal. Hence, good receiver sensitivity, high gain, and low noise are major requirements here. Using a preamplifier lessens the stringent demand otherwise would be made on receiver’s sensitivity and eventually allows a network to operate at a higher bit rate. The power budget for a STM-16 equipment above presents the feasibility of obtaining significant power margin by using optical amplification which is otherwise not possible without it. Thus Optical Amplification leaves a broad scope for evolving high bit rate next generation networks.
  • Transcript

    • 1. Fiber Optic Transmission Networks Raghunath Kummaraguntla
    • 2. Fiber Optic Transmission Networks
    • 3. Topics
      • Network Planning (Route Survey , RoW issues, roll-out)
      • Network Implementation (cable Installation & Termination, Fiber management)
      • PDH hierarchy & systems
      • Introduction to SDH/SONET Transmission
      • Format for STS-1 (OC-1) stream
      • Format for STM-1,STM-4,STM-16 streams,
      • Network Elements in an SDH Network.
      • Overheads in STM-1 signal
      • Mapping the Virtual Containers VC-1,2,3 and Tributaries into VC-4 of STM-1
      • In Service Testing
      • SDH Optical Networks(Linear, Ring)
      • Protection Switching Implemented in SDH.
      • Typical SDH Equipment Planning (TN-16X, TN-4XE, REG16,ADM16,REG4,ADM1)
      • Typical Power Budgeting for STM-16 Equipment
    • 4. Network planning OFC Network Planning   Ist Step: Route Survey.   Objective: To Asses the feasibility of alternative routes connecting rollout cities. Tools: Tourist Map, State map, District PWD map, Revenue map, Local Guidance. Points of Observation: Route name Brief about route (different sections of route i.e. towns, diversions, turning enroute Start and last point of route. Route length (measured with milometer or Km stones) Major Town/ commercial establishment on the route( Jurisdiction-MC/PWD) Villages & Towns with length Rivers/nallahs with details (Name,length,possible methods of crossing over/under/clamping etc) Bridges/culverts(Total no, Max width, total appox.length in each section & crossing methods) Railway crossings Road details (NH/SH/MCD/NHAI/Development agencies/panchayat/ Defense/) Road levels w.r.t ground (hilly terrain, embankment) Forest details Waterlogged area HT Lines details Details of existing OFC/Coax cables Gas pipeline , water pipe line crossings Future expansion plan of road Industrial Units Visible Rodent affected area Recommended location of ADM/Regenerators
    • 5. Network Implementation Fiber Packaging : The fibers shall be bundled in –groups of 6,8, 12 fibers. Two bundling threads or tapes helically wrapped on the fiber groups shall be colour coded in the order: Group#1 Blue, Group#2 Orange Group#3 Green Group#4 Brown Group#5 slate Group#6 White Group#7 Red Group#8 Black All the fibers in the bundle of 12 fiber shall be color coded with UV curable ink as : Fiber#1 Blue , Fiber#2 Orange, Fiber#3 Green, Fiber#4 Brown, Fiber#5 Slate, Fiber#6 White, Fiber#7 Red, Fiber#8 Black, Fiber#9 Yellow, Fiber#10 Violet, Fiber#11 Pink, Fiber#12 Natural, Optical Characteristics :
    • 6.  
    • 7.  
    • 8.  
    • 9. PCM Sampling Speech Bandwidth 300 Hz to 3400 KHz Nyquist Theorem - 2 X to represent Signal Use 8KHz 128 Analogue levels, 8bit word 8000 Hz X 8 bits = 64 kb/s = 1 Voice Channel
    • 10. Multiplexing
      • Mutiplexing allows multiple voice channels on one physical circuit
      • Two common methods in electrical domain
      • a) Time Division Multiplexing
      • b) Frequency Division Multiplexing
      • TDM Primary rates:
      • -2Mbps in Europe
      • - 1.544 Mbps in US, North America
    • 11. Synchronous Multiplexing
    • 12.  
    • 13. Plesiochronous Digital Hierarchy
      • Plesiochronous is derived from the Greek meaning 'almost synchronous’.
      • Drawbacks of PDH
      • Complete de-multiplex required to access any particular channel.
      • Lack of Network Management information.
    • 14.  
    • 15. Line coding used in PDH systems
    • 16. HDB3 Line coding
    • 17. 2.048 Mbps Frame structure 3.9 μ sec 1 Frame alignment word Network Signaling All time slots contain 8 bit words (PCM, Data, sub rate, n x 64 kbps 0 2 3..14 15 16 17..30 31 0 … .
    • 18. Frame Alignment (PCM 31)
    • 19. 8Mb/s Frame Structure
    • 20. 34 Mb/s Frame Structure
    • 21. Typical 140Mbps FOT System
    • 22. Typical 140 M OLTE MUX & DMUX : Multiplexer & De Multiplexer SD CH: Service Data Channel SYNC & S/P : Synchronizer and Serial-to-Parallel Converter UART: Universal Asynchronous Receiver/ Transmitter CC : Code Converter RSD INTF: Remote Service Data Interface.
    • 23. 140Mb/s Frame Structure
    • 24. Typical E-O Converter in 140 Mbps FOTS
    • 25. Typical O-E Conversion in 140Mb FOTS
    • 26. PDH Versus SDH
      • SDH
      • Synchronization between payload and Frame
      • Pointers allow Direct Access to Payload
      • Standardized from 155 Mb/s upwards.
      • Bandwidth Allocation easy
      • Simpler equipment
      • Can carry existing & Future services
      • Protected Networks
      • PDH
      • No Synchronization between Payload & Frame
      • Demultiplexing required to access Payload
      • Standardized up to 140 Mb/s
    • 27. Introduction to SDH/Sonet Optical Level Electrical Level Line Rate (Mbps) Payload Rate (Mbps) Overhead Rate (Mbps) SDH Equivalent OC-1 STS-1 51.840 50.112 1.728 - OC-3 STS-3 155.520 150.336 5.184 STM-1 OC-9 STS-9 466.560 451.008 15.552 STM-3 OC-12 STS-12 622.080 601.344 20.736 STM-4 OC-18 STS-18 933.120 902.016 31.104 STM-6 OC-24 STS-24 1244.160 1202.688 41.472 STM-8 OC-36 STS-36 1866.240 1804.032 62.208 STM-13 OC-48 STS-48 2488.320 2405.376 82.944 STM-16 OC-96 STS-96 4976.640 4810.752 165.888 STM-32 OC-192 STS-192 9953.280 9621.504 331.776 STM-64
    • 28. Outline of Payload Structure in STM signal
    • 29. Serial Stream of STS-1 Signal
    • 30. STS-1, STM-1Frame comparison
    • 31. STS-1 Envelope
    • 32. Overhead layers
    • 33. Section &Line Overheads
    • 34. Pointers for Frame synchronization & bit stuffing
    • 35. Virtual Tributary into STS-1 signal     VT Type Bit Rate (Mbps) Size of VT VT 1.5 1.728 9 rows, 3 columns   VT 2 2.304 9 rows, 4 columns   VT 3 3.456 9 rows, 6 columns   VT 6 6.912 9 rows, 12 columns  
    • 36. Section Overheads in STM-1
    • 37. Putting 140 Mb/s into VC-4 of STM-1
    • 38. Multiplexing Hierarchy in Sonet/SDH
    • 39. Sonet/SDH Network Elements (Terminal Mux,REG,ADM,DXC
    • 40. Digital Loop Carrier
    • 41. Network Configuration(point-point,multipoint)
    • 42. Ring Network Configuration (BLSR (4-fiber) with diversity routing)
    • 43. Protection Switching in SDH
      • Bridge: The action of transmitting identical traffic on both working &protection channels.
      • Switch: The action of selecting traffic from the protection channels rather than the working channels
      service protection service protection
    • 44. Sonet/SDH Capacity     SONET Signal Bit Rate (Mbps) SDH Signal SONET Capacity SDH Capacity STS–1, OC–1 51.840 STM–0 28 DS–1s or 1 DS–3 21 E1s STS–3, OC–3 155.520 STM–1 84 DS–1s or 3 DS–3s 63 E1s or 1 E4 STS–12, OC–12 622.080 STM–4 336 DS–1s or 12 DS–3s 252 E1s or 4 E4s STS–48, OC–48 2,488.320 STM–16 1,344 DS–1s or 48 DS–3s 1,008 E1s or 16 E4s STS–192, OC–192 9,953.280 STM–64 5,376 DS–1s or 192 DS–3s 4,032 E1s or 64 E4s Note: Although an SDH STM–1 has the same bit rate as the SONET STS–3, the two signals contain different frame structures. STM = synchronous transport module (ITU–T) STS = synchronous transfer signal (ANSI) OC = optical carrier (ANSI) ANSI Rate ITU–T Rate Signal           Bit Rate Channels Signal Digital Bit Rate Channels   DS–0 64 kbps 1 DS–0 64–kbps 64 kbps 1 64–kbps DS–1 1.544 Mbps 24 DS–0s E1 2.048 Mbps 1 E1 DS–2 6.312 Mbps 96 DS–0s E2 8.45 Mbps 4 E1s DS–3 44.7 Mbps 28 DS–1s E3 34 Mbps 16 E1s   not defined   E4 144 Mbps 64 E1s
    • 45. ITU-T G.Series key recommendations ITU-T G.series Description comment G.703 Physical/ Electrical characteristics of Hierarchical Digital Interfaces Electrical Interfaces coding, Output level, Mask G.707 Network Node Interface for SDH SDH mapping, Alarms, Overhead byte description G.783 Characteristics of SDH equipment functional blocks Automatic protection switching protocol linear networks & switching times. G.841 Types and characteristics of SDH network protection architectures Automatic protection switching protocol ring networks & switching times. G.957 Optical interfaces for equipment and systems relating to SDH Optical interfaces, optical receiver sensitivity, optical o/p power
    • 46. Typical System level Technical specifications of SDH Network Elements
      • Aggregate Interfaces :
      • STM-1 Electrical G.703
      • STM-1/4/16 Optical G.957
      • Tributary interfaces :
      • 2.048/34.368/139.264/155.52/Mb/s (G.703)
      • 155Mb/s(G.957)
      • Synchronization Interfaces:
      • I/p: 2.048 MHz network clock
      • 2.048 Mb/s data signal (G.703)
      • STM-1 tributary port
      • STM-N aggregate signal
      • O/p : 2.048 MHz clock
      • 2.048 Mb/s data signal (G.703)
      • Network Management Interfaces
      • Local Terminal interface: V.24 serial propriety (F Interface)
      • NMS Interface : Q3,X.25,Ethernet for lower layer
    • 47. Typical SDH ring at STM-1 Level
    • 48. STM-4 Ring
    • 49. STM-16 ring
    • 50. Optera LH1600
    • 51. Power Budget of STM-16 equipment
    • 52. References
      • ‘ Fundamentals of SDH’ courses on Telecommunication by Agilent Technologies India Pvt Ltd, New Delhi.
      • ‘ NEC 140Mbps Fiber Optic Transmission System’ of Regional Telecom Training Center.
      • ‘ SONET/SDH online course’ of International Engineering Consortium
      • SDH Transmission Equipment Technical Documentation of Nortel Networks
      • ‘ Fiber Optic Communication Technology’-D.K. Mynabaev and L.L. Scheiner, Pearson Education Asia ,2001
    • 53. Thank you for Your Attention