Information in this SDH primer is based on the latest information available from Use this primer as an introduction to the technology of SDH. Consult the actual. Information in this SONET primer is based on the latest information available from the. Bellcore and ITU-T .. Convergence of SONET and SDH Hierarchies. Synchronous digital hierarchy (SDH) and synchronous optical network (SONET) SDH has provided transmission networks with a vendor-independent and.
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Information in this SDH primer is based on the latest information available from the ITU-T standardisation organization. Also included is a Technical Note on a. The STM-1 frame is the basic transmission format for SDH. The frame lasts for microseconds, therefore, there are frames per second. The STM-1 frame. Information in this SDH primer is based on the latest information available from the ITU-T standardisation organization. Use this primer as an introduction to the.
When trans- accesses the STM-1 signals, traffic and send them sepa- porting video, for example, and connects payloads, for rately to the high-bandwidth each programming channel is example, at a TU level see for example video switch delivered dropped at the Figure One major differ- and a low-bandwidth voice node and repeated for delivery ence between a cross-connect switch. It supports hubbed to the next and subsequent and an add-drop multiplexer network architectures. Not all bandwidth This type of cross-connect is similar to the broadband cross-connect except that the TU Switch Matrix switching is done at TU level.
Broadband Digital Cross-connect Figure Wideband digital cross-connect example. Broadband digital cross-connect example. Flexible multiplexer example. The SDH point-to-point networks. It avoids the current re-provisioning of the circuits synchronous island can exist cumbersome network archi- see Figure In the future, cross-connecting, adding and mentations of this type of point-to-point service path dropping channels, and then network function: The ADM 1.
Cross-connection at the whole network and will typically is placed in an SDH higher-order path levels, always originate and termi- link to facilitate adding and for example, using AU-4 nate in a multiplexer. Cross-connection at lower- order path levels, for example, using TU granularity in the switching matrix.
Mesh architecture. Multiple send the services affected via automatic restoration within ADMs can be put into a ring an alternate path through the seconds, have made rings a configuration for either Bi- ring without a lengthy inter- popular SDH topology. Ring architecture. The current stan- different locations onto one SDH provides much more dards also fully define the facility, while segregation is powerful networking capabil- frame structure, overhead, the separation of traffic.
Grooming eliminates ineffi- chronous systems. The key Enhancements are being cient techniques such as benefits provided by SDH are: By contrast, to align the data streams makes the equipment.
The an SDH system can segregate using non-deterministic bit- network provider can traffic at either an STM-1 or stuffing is unnecessary. For demultiplexing is not needed locations or customer example, at an interconnect to access the bitstreams. Users may now point, an incoming SDH line For those situations in which obtain the STM-N equipment may contain different types of synchronisation reference of their choice and meet with traffic, such as switched frequency and phase may their network provider of voice, leased circuits for data, vary, SDH uses pointers to choice at that STM-N level.
Pointers the switched and non- are the key to synchronous Most existing asynchronous switched traffic. In other Multiplexing The cross-connect allows words, one connection can In the asynchronous PDH many nodes or sites to reach all network elements systems, care must be taken communicate as a single within a given architecture; when routing circuits in order network instead of as separate separate links are not to avoid multiplexing and systems.
Cross-connecting required for each network demultiplexing too many reduces requirements for element. Remote provisioning times since electronics and back-to-back multiplexing provides centralized mainte- their associated capital cost and demultiplexing, and nance and reduced travel for are required every time an E1 helps realize the benefits of maintenance personnel — signal is processed.
With traffic grooming. Because of synchronisation, need to own and maintain Note: OAM is sometimes an entire optical signal customer-located equipment. Convergence is the trend ical level.
Each ATM cell is supply high-speed transporta- short, fixed-length packets made up of 53 octets, or bytes tion over any medium to any called cells. Asynchronous see Figure Of these, 48 location. Tektronix is Transfer Mode multiplexes a octets make up the user-infor- pursuing new opportunities service into cells that may be mation field and five octets to lead the market by combined and routed as make up the header. The cell providing test and measure- necessary.
The virtual path defines the over high-speed networks. In principle, ATM is quite connections through which Many of the new broadband similar to other packet- the cell is routed to reach its services may use switching techniques; destination see Figure The rate at which cells can be 48 bytes Payload USER transmitted through the INFO network is dependent upon the physical layer of the network used for transport of the cells. The interface rate VCI: Generic Flow Control maximum rate, which ensures a much more effi- Figure ATM cell structure.
ANSI network standard. Multiplexing is accomplished by combining — or interleaving — multiple lower-order signals Table Table Copies can DS2 6. A stan- carrying capacity of a tion carried in a transmission dards-setting, non-govern- communication channel.
The Asynchronous — A network network. Bi-directional plexer without additional nised and each network APS allows protection processing. N Administrative Unit AU — an identification header field is typically 3, 6, or 8. An Administrative Unit is the and an information field. The BIP-8 Bit Interleaved information structure which transfer mode is asyn- Parity-8 — A method of error provides adaptation between chronous in the sense that the checking in SDH which the Higher-Order path layer use of the cells depends on allows in-service perfor- and the Multiplex Section the required or instantaneous mance monitoring.
For layer. The Virtual Container bit rate. The line-coding spare protection line. N of data. Demultiplex terms are not equivalent; each additional processing.
DEMUX is the process of sepa- has a distinct meaning: Bit Error rate BER is transmitted line code and that rate channels in higher-rate calculated with the formula: In SDH, a number discrete steps. A block is a set of consecutive size of the TU. Fixed stuff locations, some- plexing.
The to perform a required func- tion. Persistence of a defect Floating Mode — A tributary transmission rate for digital can cause a failure. Circuit Switching — Basic capacity of fibre-optic data Grooming — Consolidating or switching process whereby a transmission systems through segregating traffic for effi- circuit between two users is the multiplexing of multiple ciency.
A bipolar coding for the duration of the trans- DWDM systems support the method that does not allow mission. MS-AIS Provisioning — Provides the harmonization of national maintains operation of the facilities and personnel policies.
It functions through downstream regenerators, required to manage a international committees of and therefore prevents gener- network.
Orderwire — A dedicated starting location of the VC. Multiplex Section Overhead voice channel used by Locked mode has less pointer MSOH — 18 bytes of over- installers to expedite the processing than floating head accessed, generated, and provisioning of lines.
This overhead Sophisticated applications multiplexing, implying more supports functions such as software that manages opera- visibility inside the resultant locating the payload in the tion of the entire network. Layers Mapping — The process of define hardware and software maintenance.
For over a single channel. The seven layers example, mapping an E1 Multiplexer — A device for from lowest to highest are: Multiframe — Any structure Narrowband — Services Overhead — Extra bits in a made up of multiple frames. Orderwire, for level and at the VC-N level.
A network elements are: Section Overhead — Nine parity bit an even number. Remote Alarm Indication columns of SDH overhead For odd parity, the parity bit RAI — A code sent upstream accessed, generated, and is set to make the total on an En circuit as a notifica- processed by section termi- number of ones in the block tion that a failure condition has nating equipment. This over- an odd number. STE Overhead accessed, gener- receiving Terminating interprets and modifies or ated, and processed by path- Equipment detects a Loss of creates the Section Overhead.
REI defines optical carrier levels E3. The contents of a VC. RFI — A failure is a defect multi-vendor environment that persists beyond the and positions the network for Payload Capacity — The maximum time allocated to transport of new services, number of bytes the payload the transmission system synchronous networking, and of a single frame can carry.
Status Messages. For further overhead that locates a Regenerator — Device that details on the assignment of floating payload structure. TU-M pointers sion; also called a repeater. Multiplex Section Overhead.
SDH standards were point in the U. Lower-Order path layer and implies that these variations the Higher-Order path layer. Container VC plus a tribu- tary unit pointer. Worldwide Web: For the most up-to-date product information, visit our web site at www. From other areas, contact: Tektronix, Inc. Export Sales, P.
Tektronix products are covered by U. Information in this publication supersedes that in all previously published material. Specification and price change privileges reserved. The first column is for Path Overhead, it is followed by the payload container.
Virtual Containers can have any phase alignment within the Administrative Unit, and this alignment is indicated by the Pointer in row four, as will be described later in Pointers and Dynamic Alignment.
Within the Section Overhead, the first three rows are used for the Regenerator Section Overhead, and the last 5 rows are used for the Multiplexer Section Overhead. Figure 2. As the tributary signals are multiplexed and aligned, some spare capacity has been designed into the SDH 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.
The notations in the boxes, such as C-1, VC-3, and AU-4, are explained in the table after the figure. At the lowest level, containers C are input to virtual containers VC. SDH network layers. STM-1 Regenerator section overhead. Byte by byte, the Multiplex Section Overhead is shown in Table 5.
Table 4. The A1, A2 bytes are unscrambled. J0 Regenerator Section RS Trace message It s used to transmit a Section Access Point Identifier so that a section receiver can verify its continued connection to the intended transmitter. The coding of the J0 byte is the same as for J1 and J2 bytes. RS bit interleaved parity code BIP-8 byte This is a parity code even parity , used to check for transmission errors over a regenerator section.
RS orderwire byte This byte is allocated to be used as a local orderwire channel for voice communication between regenerators. The channel can be used from a central location for control, monitoring, administration, and other communication needs.
STM-1 Multiplex section overhead. The value is placed in the three B2 bytes of the MS Overhead before scrambling. MS-RDI is generated by inserting a code in positions 6, 7, and 8 of the K2 byte before scrambling. Following is the assignment of bit patterns to the four synchronisation levels agreed to within ITU-T other values are reserved : Bits Quality unknown existing sync. This message may be emulated by equipment failures and will be emulated by a Multiplex Section AIS signal.
Bits 2 to 8 of the M1 byte are used to carry the error count of the interleaved bit blocks that the MS BIPxN has detected to be in error at the far end of the section. It s a voice channel for use by craftspersons and can be accessed at multiplex section terminations.
Table 6. A byte free-format string is also permitted for this Access Point Identifier. This allows the receiving terminal in a path to verify its continued connection to the intended transmitting terminal. Path bit interleaved parity code Path BIP-8 byte This is a parity code even , used to determine if a transmission error has occurred over a path. Its value is calculated over all the bits of the previous virtual container before scrambling and placed in the B3 byte of the current frame.
Path signal label byte This byte specifies the mapping type in the VC-N. Therefore the bi-directional path in its entirety can be monitored, from either end of the path.
For the E-RDI codes, bit 7 is set to the inverse of bit 6.
Equipment conforming to an earlier version of this standard may include PLM as a trigger condition. Path user channel byte This byte is used for user communication between path elements. In the latter case, the content is payload specific e. The slot offset indicator contains a binary number indicating the offset in octets between the H4 octet and the first slot boundary following the H4 octet. The valid range of the slot offset indicator value is 0 to A received value of 53 to 63 corresponds to an error condition.
Path user channel byte This byte is allocated for communication purposes between path elements and is payload dependent. K3 bits are allocated for future use. These bits have no defined value. The receiver is required to ignore their content. In this manner, it is possible for the Tandem Connection sink at the tail end of the Tandem Connection link to use the IEC code field to distinguish between unequipped conditions started within or before the Tandem Connection.
Reserved capacity for future standardization. Table 7. This bit is set to one if a failure is declared, otherwise it is set to zero. A failure is a defect that persists beyond the maximum time allocated to the transmission system protection mechanisms. The Virtual Container path Signal Label coding is: Unequipped or supervisory-unequipped Equipped non-specific Asynchronous Bit synchronous Byte synchronous Reserved for future use Test signal, O. Used to repetitively transmit a Lower-Order Access Path Identifier so that a path receiving terminal can verify its continued connection to the intended transmitter.
A byte frame is defined for the transmission of Path Access Point Identifiers. This byte frame is identical to the byte frame of the J1 and J0 bytes.
Fixed to 1. This guarantees that the contents of N2 is not all zeroes at the TC-source. This enables the detection of an unequipped or supervisory unequipped signal at the Tandem Connection sink without the need of monitoring further OH-bytes. Operates as an incoming AIS indicator. Bits are reserved for optional use.
Bit 8 is reserved for future use and has no defined value. Table 8 and Figure 9, that follow the definitions, list the criteria for errors and the performance monitoring for errors. Anomaly The smallest discrepancy which can be observed between the actual and desired characteristics of an item. The occurrence of a single anomaly does not constitute an interruption in the ability to perform a required function.