STANDARD T1.PP Pre-published American National Standard for Telecommunications -

Transcription

1 PE E-PUBLISHED STANDAD T1.PP Pre-published American National Standard for Telecommunications - Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, ates and Formats Prepared by T1X1.5 Working Group on Optical Hierarchical Interfaces NOTICE This document is a pre-published American National Standard of Committee T1. The document has been approved by Committee T1 and the American National Standards Institute (ANSI). The document, however, has not completed the editing and publication cycles. As such, this document is subject to further change. ATIS and Committee T1 expressly advise that any use of or reliance upon the material in this document is at your risk and neither ATIS nor Committee T1 shall be liable for any damage or injury, of whatever nature, incurred by any person arising out of any utilization of the material. The final version of this document will be published as T Copyright 2001 by Alliance for Telecommunications Industry Solutions All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. For information, contact ATIS at or NOTE - The user s attention is called to the possibility that compliance with this standard may require use of an invention covered by patent rights. By publication of this standard, no position is taken with respect to the validity of this claim or any patent rights in connection therewith. The patent holder has, however, filed a statement of willingness to grant license under these rights on reasonable and nondiscriminatory terms and conditions to applicants desiring to obtain such a license. Details may be obtained from the publisher.

2 CONTIBUTION TO T1 STANDADS POJECT ***************************************************************************** TITLE: evised Draft T105 SONET Base Standard ***************************************************************************** AUTHO: Steven Gorshe SOUCE: CONTACT: Steven Gorshe NEC Eluminant Technologies, Inc N.E. Shute oad Hillsboro, O steveg@tdd.hbo.nec.com ***************************************************************************** DATE: October 20, 2000 ***************************************************************************** DISTIBUTION: T1X1.5 (ates and Formats) Working Group ***************************************************************************** ABSTACT: This contribution contains the final version of T1.105 with the inclusion of the addendum information approved for Letter Ballot. ***************************************************************************** NOTICE This document has been prepared to assist Standards Committee T1- Telecommunications. This document is offered as a basis for discussion and isn t binding for NEC America, Inc. NEC America, Inc. specifically reserves the right to add to, or amend the statements in this contribution at any time.

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4 ANSI T x T1X1.5/ (Draft ANSI T x Contents of LB809 with addendum information from T1X1.5/ ) American National Standard for Telecommunications Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, ates and Formats Secretariat: Alliance for Telecommunications Industry Solutions Approved <date> American National Standards Institute, Inc. Abstract The purpose of this standard is to specify the multiplexing format and basic overhead definitions for the Synchronous Optical Network (SONET) signal. Other standards in the T1.105 series build upon this base document by providing additional detailed information about other, specific aspects of SONET.

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6 Contents Page Foreword... iii 1. Scope Normative eferences Definitions Abbreviations General ates Transport formats Layered overhead and transport functions Payload pointers Multiplex procedure...36 Tables 1 - Standard OC rates VT1.5 Locations VT2 Locations VT3 Locations VT6 Locations Overhead usage byte frame structure for trace messages SONET Synchronization Status Messages Path signal label - Byte C DI-P defects eserved SAPI values for the Path Layer Data Channel VT signal label - Byte V5 (5-7) VT sizes DI-V defects Triggers for PDI-P VT Multiframe Indicator Byte (H4)...51 Figures 1 - Layered model representation of AIS, DI and FI Indications Simplified diagram depicting Section, Line, Tandem Connection and Path Diagram Illustrating Section, Line, Tandem Connection and Path Definitions Bit Position Numbering STS-1 Frame STS-1 Synchronous Payload Envelope (SPE) STS-1 Synchronous Payload Envelope with STS-1 POH and STS-1 Payload Capacity Illustrated...58 i

7 8 - STS-1 SPE in Interior of STS-1 Frame VT Sizes Example of VT Structured STS-1 SPE Three-Dimensional epresentation of Example VT-Structured STS-1 SPE VT-Structured STS-1: All VT VT-Structured STS-1: All VT2...Error! Bookmark not defined VT-Structured STS-1: All VT VT-Structured STS-1: All VT VT Superframe VT-Synchronous Payload Envelope STS-N Frame STS-3c Synchronous Payload Envelope STS-Nc (N 3X where X=1, 4, or 16) Synchronous Payload Envelope Interface Layers Overhead Byte Locations in an STS-1 Frame Transport Overhead Byte Locations in an STS-3 Frame Transport Overhead Byte Locations in an STS-12 Frame STS Path Status Byte (G1) V5 Overhead Byte VT Overhead Byte Z PDI-P Triggers Equipment Examples of AIS, DI and FI...97 x Equipment example of TEST-P STS-1 Payload Pointer (H1, H2, H3) Coding STS-1 Pointer Offset Numbering Positive STS-1 Pointer Adjustment Operation Negative STS-1 Pointer Adjustment Operation VT Payload Pointer Coding VT Pointer Offsets Example of Byte Interleaving...Error! Bookmark not defined Frame Synchronous Scrambler (Functional Diagram An Example of STS-1 Frame and OC-N Line Signal Composition Annexes A LAPD usage for path data channel to pass security information B Bibliography ii

8 Foreword (This foreword is not part of American National Standard T x.) This standard is the baseline of a set of standards which were created when ANSI T1.105 was broken up into its constituent parts. This document describes a base rate and format along with a multiplex scheme. This revision of T1.105 includes clarifications or revisions to the J0, DI, J1, J2, AIS-P, and AIS-V; new signal labels; definition of virtual concatenation; and definition of STS-768. Other documents included in the T1.105 series (at the time that this document was approved) are listed below. Some of these documents are not included in the normative reference since these documents were not approved standards at the time that this document was approved. T Synchronous Optical Network (SONET) Automatic Protection Switching T x Synchronous Optical Network (SONET) Payload Mappings T Synchronous Optical Network (SONET) Jitter at Network Interfaces T Synchronous Optical Network (SONET) Data Communication Channel Protocols and Architectures T Synchronous Optical Network (SONET) Tandem Connection Maintenance T Synchronous Optical Network (SONET) Physical Layer Specifications T Synchronous Optical Network (SONET) Sub STS-1 Interface ates and Formats Specifications T x Synchronous Optical Network (SONET) In-band Forward Error Correcting Code Specification T x Synchronous Optical Network (SONET) - Timing and Synchronization ANSI guidelines specify two categories of requirements: mandatory and advisory. The mandatory requirements are designated by the word "shall" and the advisory criteria by the word "should". Mandatory requirements generally apply to signaling and compatibility by specifying absolute, acceptable limits in these areas: advisory requirements generally refer to optional features. This standard has 2 annexes. One is normative and is part of the standard; that is this annex includes requirements that are a part of the specifications of this standard. One is informative and is not considered part of this standard; that is, this annex does not include requirements for the interface, but provides information about the interface specified. This standard is technically consistent with work in ITU-T on the Network Node Interface (NNI) using synchronous multiplexing techniques, and is compatible with ITU-T ecommendations G.707, G.708, G.709, G.783 and G.784 Synchronous Digital Hierarchy (SDH). iii

9 Suggestions for improvement of this standard will be welcome. They should be sent to the Alliance for Telecommunications Industry Solutions, 1200 G Street, N.W., Suite 500, Washington, D.C This standard was processed and approved for submittal to ANSI by Accredited Standards Committee on Telecommunications, T1. Committee approval of this standard does not necessarily imply that all committee members voted for its approval. At the time it approved this standard, the T1 Committee had the following members: iv

10 AMEICAN NATIONAL STANDAD ANSI T x American National Standard for Telecommunications (Draft) Synchronous Optical Network (SONET) - Basic Description including Multiplex Structure, ates and Formats 1. Scope This document is the baseline of a series of standards that define a modular family of rates and formats available for use in interfaces generally referred to as SONET. This series of documents is identified by the T1.105 prefix. This document (T x) describes a base rate and format along with a multiplexing scheme. Other characteristics described in this standard are: layering of overhead, definitions of function and position of overhead, frequency justification, scrambling, conditions for setting overhead values, and a standardized set of payload carrying envelopes. As an aid to the reader, a mapping is provided between SONET and SDH terminology. Any differences between the SDH and SONET specifications at the time of approval of this standard which affect interworking are highlighted. The differences are relative to the SDH ecommendations under review in SG 15 at that time. Other T1.105.xx standards are listed in clause 2 and describe such items as payload mappings, protection switching, data communications interfaces, tandem connection and physical layer specifications. NOTE - The user's attention is called to the possibility that compliance with this standard may require use of inventions covered by patent rights. By publication of this standard, no position is taken with respect to the validity of these claims or of any patent rights in connection therewith. The patent holders have, however, filed statements of willingness to grant licenses under these rights on reasonable and nondiscriminatory terms and conditions to applicants desiring to obtain such licenses. Details may be obtained from the publisher. No representation or warranty is made or implied that these are the only licenses that may be required to avoid infringement in the use of this standard. 2. Normative eferences The following standards contain provisions which, through reference in this text, constitute provisions of this American National Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this American National Standard 1

11 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. T , Telecommunications Synchronization Interface Standards for Digital Networks T (1999), Telecommunications Digital Hierarchy Electrical Interfaces T , Telecommunications Synchronous Optical Network (SONET) Automatic Protection Switching T x, Telecommunications Synchronous Optical Network (SONET) Payload Mappings T , Telecommunications Synchronous Optical Network (SONET) Jitter at Network Interfaces T , Telecommunications Synchronous Optical Network (SONET) Data Communication Channel Protocols and Architectures T , Telecommunications Synchronous Optical Network (SONET) Tandem Connection Maintenance T Telecommunications Synchronous Optical Network (SONET) Physical Layer Specification T , Telecommunications Digital Hierarchy - Formats Specifications T , Telecommunications Digital Hierarchy - In-Service Digital Transmission Performance Monitoring T , Telecommunications Information Interchange Structure and epresentation of Trace Message formats for the North American Telecommunications System ITU-T ecommendation G.707 (1996), Synchronous Digital Hierarchy Bit ates 1) 3. Definitions 3.1. administrative unit (AU): An SDH-specific information structure, consisting of an STS SPE and its associated set of STS pointer/pointer action bytes. An AU-3 includes an STS-1 SPE and bytes H1, H2, and H3. An AU-4 includes an STS-3c SPE and three sets of bytes H1, H2, and H3. An AU-4-Xc includes an STS-Nc (N=3X) SPE and N sets of bytes H1, H2, and H alarm indication signal (AIS): A code sent downstream in a digital network as an indication that an upstream defect has been detected. It is associated with multiple transport layers as shown in figure 1. 1) ITU-T has replaced CCITT. ITU-T publications are available from the American National Standards Institute, 11 West 42nd Street, New York, NY

12 3.3. asynchronous transfer mode (ATM): A multiplexing/switching technique in which information is organized into fixed-length cells with each cell consisting of an identification header field and an information field; the transfer mode is asynchronous in the sense that the recurrence of cells depends on the required or instantaneous bit rate bit interleaved parity N (BIP-N): A method of error monitoring. If even parity is used, an N-bit code is generated by the transmitting equipment over a specified portion of the signal in such a manner that the first bit of the code provides even parity over the first bit of all N-bit sequences in the covered portion of the signal, the second bit provides even parity over the second bits of all N-bit sequences within the specified portion, and so on. Even parity is generated by setting the BIP-N bits so that there are an even number of 1s in each of all N-bit sequences including the BIP-N concatenated synchronous transport signal level N (STS-Nc): A signal constructed by concatenating the envelope capacities of N STS-1s to carry an STS-Nc SPE which transports a super-rate signal. These STS-1s shall be transported as a single entity. The equivalent SDH term for an STS-3c SPE is a VC-4. The equivalent SDH term for an STS-Nc (N>3) SPE is a VC-4-Xc, where X=N/3. The closest equivalent SDH term for an STS-Nc signal is an AU-4-Xc structured STM-M, where M=X=N/3. There are equivalent SDH signals only for values of N that are multiples of container: An SDH term that is equivalent to the payload capacity of a synchronous payload envelope distributed queue dual bus (DQDB): A family of standards developed by the IEEE Metropolitan Area Network (MAN) Standards Committee and approved by ANSI and ISO. This series defines the protocols, formats, and characteristics for public Metropolitan Area Networks designed to operate on various common carrier media drop side signal: A signal with reduced overhead functionality suitable for intraoffice interconnection DS0 path terminating equipment (DS0 PTE): Network elements that originate and/or terminate DS0 channels. DS0 PTEs can originate, access, modify, or terminate the DS0 signaling information necessary to transport the DS0 channels, or can perform any combination of these actions electrical carrier level 1 (EC-1): The signal that results from an electrical conversion of an STS-1 signal. There is no SDH equivalent electrical carrier level 3 (EC-3): The signal that results from an electrical conversion of an STS-3 signal. The equivalent SDH term is electrical STM embedded operations channel (EOC): Dedicated overhead channel within a SONET or DSn signal that is used to transport operations, administration, maintenance and provisioning information far end block error (FEBE): See remote error indication (EI) far-end receive failure (FEF): See remote defect indication fiber distributed data interface (FDDI): A family of American National Standards and International Standards developed by Working Group X3T9.5 of Accredited Standards Committee (ASC) X3. This series defines the protocol, formats, and characteristics of a 100-Mbit/s Token ing Local Area Network designed to operate on fiber optic media. (See T for references to these standards.) fixed stuff ( bits and bytes): Fixed stuff ( bits and bytes) are used to compensate for the differences between the bandwidth available in the STS-1 and VT Synchronous Payload Envelopes and the bandwidth required for the actual payload mappings (i.e., DS1, DS1C, DS2, DS3, and so on). bits and bytes have no defined value. The receiver is required to ignore the value of these bits and bytes. 3

13 3.17. higher order path: The SDH term for an STS level path high order virtual concatenation: Virtual concatenation of STS-1/3c SPEs line: A transmission medium, together with the associated equipment, required to provide the means of transporting information between two consecutive Network Elements (NEs), one of which originates the line signal and the other terminates the line signal (see figures 2 and 3). The equivalent SDH term is multiplex section line alarm indication signal (AIS-L) code: An AIS-L code is generated by a Section Terminating Equipment upon loss of input signal or loss of frame. The AIS-L signal will maintain operation of the downstream Section Terminating Equipments and therefore prevent generation of unnecessary alarms. At the same time, data and orderwire communication is retained between the Section Terminating Equipments and the downstream Line Terminating Equipment (LTE). The equivalent SDH term is multiplex section alarm indication signal (MS AIS) line remote defect indication (DI-L): A signal returned to a transmitting Line Terminating Equipment (LTE) upon receipt of an AIS-L code or detection of an incoming line defect at the receiving LTE. For a detailed definition, refer to T line side signal: A signal with full overhead functionality suitable for inter-office interconnection line terminating equipment (LTE): Network elements that originate and/or terminate line (OC-N) signals (see figures 2 and 3). LTEs shall originate, access, and terminate the transport overhead (Section and Line) Link Capacity Adjustment Scheme (LCAS): LCAS in the virtual concatenation source and sink adaptation functions provides a control mechanism to hitlessly increase or decrease the capacity of a link to meet the bandwidth needs of the application. It also provides a means of removing member links that have experienced failure. The LCAS assumes that in cases of capacity initiation, increases or decreases, the construction or destruction of the end-to-end path is the responsibility of the Network and Element Management Systems loss of cell delineation (LCD): LCD is an ATM term used to signal inability to maintain the ATM cell alignment boundary in an octet stream. LCD is declared when the current cell boundary in the extracted payload does not allow the ATM header error check polynomial G(x), C(x) rule to be obeyed. An LCD condition exists when the ATM cell alignment process is not in the "Sync" state loss of frame (LOF): Defect that is raised by a network element when the network element is unable to frame align on an incoming signal. For a detailed definition, refer to T loss of pointer (LOP): Defect that is raised by a SONET network element when a LTE or PTE is unable to locate a valid pointer on an incoming signal. For a detailed definition, refer to T loss of signal (LOS): Defect that is raised by a network element when no signal is present on an incoming signal. An LOS is typically defined as an all zeros pattern. For a detailed definition, refer to T lower order path: The SDH term for a VT level path low order virtual concatenation: Virtual concatenation of VTn (n=1.5,2,3 or 6) SPEs most significant bit: The left most bit position. See bit 1 as illustrated in figure multiplex section: The SDH term for a SONET line network element (NE): Entities defined by the functionality of the functional groups they contain and by their interfaces. 4

14 3.34. optical carrier level 1 (OC-1): The optical signal that results from an optical conversion of an STS- 1 signal. SDH does not make the distinction between a logical signal (e.g. STS-1 in SONET) and a physical signal (e.g. OC-1 in SONET) optical carrier level N (OC-N): The optical signal that results from an optical conversion of an STS- N signal. SDH does not make the distinction between a logical signal (e.g., STS-N in SONET) and a physical signal (e.g., OC-N in SONET). The equivalent SDH term for both logical and physical signals is synchronous transport module level M (STM-M), where M=(N/3). There are equivalent STM-M signals only for values of N=3, 12, 48, 192, and path: A logical connection between the point at which a standard frame format for the signal at the given rate is assembled, and the point at which the standard frame format for the signal is disassembled (see figures 2 and 3). The equivalent SDH term is also path path overhead (POH): Overhead assigned to and transported with the payload until the payload is demultiplexed. It is used for functions that are necessary to transport the payload. The equivalent SDH term is virtual container path overhead (VC POH) payload defect indication (PDI): A code in the STS Path Signal Label which is transmitted downstream to indicate a defect of one or more directly mapped embedded payloads, such as VT-x or DS3 for an STS-1 signal. For ring interworking applications PDI can be used to detect defects in embedded payloads and as a protection switching criterion payload label mismatch (PLM): A defect that is raised by a STS or VT PTE when the incoming signal label does not match the expected signal label payload pointer: The pointer that indicates the location of the beginning of the Synchronous Payload Envelope. The equivalent SDH term is pointer regenerator section: The SDH term for a SONET section remote defect indication (DI): A signal returned at the first opportunity to a transmitting equipment when a terminal detects specific defects in the incoming signal. The equivalent SDH term is also remote defect indication. This signal was formerly known as far-end receive failure (FEF) remote error indication (EI): An indication returned to a transmitting node (source) that an errored block has been detected at the receiving node (sink). The equivalent SDH term is also remote error indication. This indication was formerly known as far end block error (FEBE) remote failure indication (FI): A signal returned to a transmitting equipment when a terminal determines that specific defects have persisted long enough to declare a received signal failure. The equivalent SDH term is also remote failure indication sequence indicator (SQ): The sequence identifier identifies the sequence/order in which the individual SPEs of a virtual concatenation are combined to form the integral super-container synchronous digital hierarchy (SDH): A family of ITU-T standards whose technical contents closely resemble that found for the SONET family of ANSI standards section: The portion of a transmission facility, including terminating points, between (i) a line terminating equipment (LTE) and a Section Terminating Equipment or (ii) two Section Terminating Equipments. A terminating point is the point after signal regeneration at which performance monitoring is (or may be) done (see figures 2 and 3). The equivalent SDH term for section is regenerator section section terminating equipment (STE): Network elements that originate and terminate section (OC-N) signals (see figures 2 and 3). STEs shall originate, access, and terminate the section overhead. 5

15 3.49. SONET: An acronym of Synchronous Optical NETwork. SONET is a term in general usage that refers to the rates and formats specified in this standard STS envelope capacity: Bandwidth within, and aligned to, the STS Frame that carries the STS Synchronous Payload Envelope (SPE). This bandwidth can be combined from N STS-1s in order to carry an STS-Nc SPE. The equivalent SDH term is STM-M payload (M=N/3) STS path overhead (STS POH): Nine evenly distributed Path Overhead bytes per 125 µs starting at the first byte of the STS SPE. STS Path Overhead provides for communication between the point of creation of an STS SPE, and its point of disassembly. The equivalent SDH term is VC-3/4 path overhead (VC-3/4 POH) STS path terminating equipment (STS PTE): Network Elements that multiplex/demultiplex the STS payload. STS PTEs shall originate, access, and terminate the STS Path Overhead necessary to transport the STS payload STS payload capacity: The maximum bandwidth within the STS Synchronous Payload Envelope that is available for payload. The equivalent SDH term for STS-1 payload capacity is container level 3 (C- 3). The equivalent SDH term for STS-3c payload capacity is container level 4 (C-4). The equivalent SDH term for STS-Nc (N>3) capacity is container level 4-Xc (C-4-Xc), where X=(N/3). There are equivalent C- 4-Xc signals only for values of N that are multiples of STS synchronous payload envelope (STS SPE): A 125-microsecond frame structure composed of STS Path Overhead and bandwidth for payload. The term generically refers to STS-1 SPEs and STS- Nc SPEs. The equivalent SDH term for STS-1 SPE is virtual container level 3 (VC-3), with the exception that a VC-3 does not contain the fixed stuff bytes found in columns 30 and 59 of an STS-1 SPE. The equivalent SDH term for STS-3c SPE is virtual container level 4 (VC-4). The equivalent SDH term for STS-Nc SPE (N>3) is virtual container level 4-Xc (VC-4-Xc), where X=(N/3) super-rate signal: A signal that has to be carried by a Concatenated Synchronous Transport Signal level Nc (STS-Nc). There is no equivalent SDH term synchronous: The essential characteristic of time-scales or signals such that their corresponding significant instants occur at precisely the same average rate synchronous network: The synchronization of synchronous transmission systems with synchronous payloads to a master (network) clock that can be traced to a reference clock synchronous payloads: Payloads derivable from a network transmission signal by removing integral numbers of bits in every frame, i.e., there are no variable bit stuffing rate adjustments required to fit the payload in the transmission signal synchronous transport module level 1 (STM-1): The lowest bit-rate signal for the Synchronous Digital Hierarchy (SDH). At Mbit/s, this signal is equivalent in rate and format to a SONET OC-3 signal synchronous transport module level M (STM-M): These are the defined transport signals for the Synchronous Digital Hierarchy (SDH). Defined signals exist at rates of M times Mbit/s, where M=1, 4, 16, or 64. These are equivalent to SONET OC-N signals, where N=3M synchronous transport signal level 1 (STS-1): The basic logical building block signal with a rate of Mbit/s. SDH does not make the distinction between a logical signal (e.g., STS-1 in SONET) and a physical signal (e.g., OC-1 in SONET). 6

16 3.62. synchronous transport signal level N (STS-N): This signal is obtained by byte interleaving N STS-1 signals together. The rate of the STS-N is N times Mbit/s. SDH does not make the distinction between a logical signal (e.g. STS-N in SONET) and a physical signal (e.g., OC-N in SONET). The equivalent SDH term for both logical and physical signals is synchronous transport module level M (STM-M), where M=(N/3). There are equivalent STM-M signals only for values of N=3, 12, 48, 192, and tandem connection: A high-order tandem connection is defined as a group of STS-1s or STS-Ncs which are transported and managed together through one or more tandem line systems, with the constituent SPE payload capacities unaltered. Note that in support of the layered overhead approach used in SONET, the high-order tandem connection sub-layer falls between the STS line and path overhead layers (see figures 1 and 2). A lower-order tandem connection is defined as a group of VTs which are transported and managed together through one or more tandem line systems, with constituent SPE payload capacity unaltered. The equivalent SDH term is also tandem connection trace identifier mismatch (TIM): A defect that is raised by a STS PTE when the incoming path trace does not match the expected path trace. For a detailed definition, refer to ANSI T1.231, transport: Facilities associated with the carriage of OC-1 or higher-level signals transport overhead: The overhead added to the STS SPE for transport purposes. Transport Overhead consists of Line and Section Overhead. The equivalent SDH term is section overhead tributary unit (TU): The SDH term for SONET virtual tributaries. A TU-11 is equivalent to a SONET VT1.5. A TU-12 is equivalent to a SONET VT2. A TU-2 is equivalent to a SONET VT6. SDH also includes a TU-3, which has no SONET equivalent unassigned (X) bits/bytes: Those locations within the signal that have not had a function or value assigned to them at this time. The receiver is required to ignore the value of these bytes unequipped channel: A portion of an STS-N such as an STS-1 SPE or VT SPE that is intentionally unoccupied unequipped indication: A code placed in unequipped channels by originating equipment to indicate to Path Terminating Equipment that the channel is intentionally unoccupied so that alarms can be inhibited user channel: This is allocated to the user for input of information such as data communication for use in maintenance activities and remoting of alarms external to the span equipment in a proprietary fashion Virtual concatenation: Virtual concatenation breaks the integral payload into individual SPEs, separately transports each SPE and then recombines them into a contiguous bandwidth at the end point of the transmission. This type of concatenation requires concatenation functionality only at the path termination equipment virtual container (VC): An SDH term for either an STS or VT SPE. Lower order VCs (LO VCs) correspond to VT SPEs. Specifically, a VC-11 is equivalent to a VT1.5 SPE, a VC-12 is equivalent to a VT2 SPE, and a VC-2 is equivalent to a VT6 SPE. Higher order VCs (HO VCs) correspond to STS SPEs. Specifically, a VC-3 is equivalent to an STS-1 SPE, with the exclusion of the fixed stuff bytes of columns 30 and 59 of the STS-1 SPE. A VC-4 is equivalent to an STS-3c SPE, and a VC-4-Xc is equivalent to an STS-Nc (N=3X) SPE virtual tributary (VT): A structure designed for transport and switching of sub-sts-1 payloads. There are currently four sizes of VT: VT1.5, VT2, VT3 and VT6. The equivalent SDH term is tributary unit (TU). 7

17 3.75. VT envelope capacity: Bandwidth within, and aligned to, the VT Superframe that is available for the VT Synchronous Payload Envelope. There is no equivalent SDH term VT group: A 9-row by 12-column structure (108 bytes) that carries one or more VTs of the same size. Seven VT groups (756 bytes) are byte-interleaved within the VT-organized SPE. The equivalent SDH term is tributary unit group level 2 (TUG-2) VT path overhead (V5, J2, Z6, Z7): Four Path Overhead bytes per 500 µs. VT Path Overhead provides for communication between the point of creation of a VT SPE and its point of disassembly. The equivalent SDH term is VC-1/2 path overhead (VC-1/2 POH) VT path terminating equipment (VT PTE): Network elements that multiplex/demultiplex the VT payload. PTEs shall originate, access, and terminate the VT Path Overhead necessary to transport the VT payload VT payload capacity: The maximum bandwidth within the VT Synchronous Payload Envelope that is available for payload. The equivalent SDH term is lower order container. Specifically, the equivalent SDH term for VT1.5 payload capacity is container level 11 (C-11). The equivalent SDH term for VT2 payload capacity is container level 12 (C-12). The equivalent SDH term for VT6 payload capacity is container level 2 (C-2). There is no SDH equivalent to a VT3 payload capacity VT superframe: The VT is organized into a 500 µs superframe structure overlaid on and aligned to the 125 µs STS-1 Synchronous Payload Envelope (SPE). Contained within this structure is the VT Payload Pointer and the VT SPE. The equivalent SDH term is tributary unit (TU) multiframe VT synchronous payload envelope (VT SPE): A 500 µs frame structure carried by the VT composed of VT Path Overhead (POH) and bandwidth for payload. The envelope is contained within, and can have any alignment with respect to the VT Envelope Capacity. The term generically refers to VT1.5, VT2, VT3 and VT6 SPEs. The general equivalent SDH term is lower order virtual container (LO VC). Specifically, the SDH equivalent of a VT1.5 SPE is a VC-11. The SDH equivalent of a VT2 SPE is a VC- 12. The SDH equivalent of a VT6 SPE is a VC-2. There is no SDH equivalent to a VT3 SPE VTx: A VT of size x (currently x = 1.5, 2, 3, or 6). The general equivalent SDH term is tributary unit (TU). Specifically, the SDH equivalent of a VT1.5 is a TU-11. The SDH equivalent of a VT2 is a TU-12. The SDH equivalent of a VT6 is a TU-2. There is no SDH equivalent to a VT3. 4. Abbreviations ASC AIS AIS-L AIS-P AIS-V APS ANSI ATM AU - Accredited Standards Committee - Alarm Indication Signal - Line AIS - STS Path AIS - VT Path AIS - Automatic Protection Switching - American National Standards Institute - Asynchronous Transfer Mode - Administrative Unit 8

18 BIP-N B-ISDN C DCC DQDB EOC EDI FDDI FEBE FEC FEF HO HP IAO ISDN ISO ITU-T LAPD LCAS LCD LCD-P LO LOF LOP LOP-P LOP-V LOS - Bit Interleaved Parity N - Broadband Integrated Services Digital Network - Container - Data Communications Channels - Distributed Queue Dual Bus - Embedded Operations Channel - Enhanced DI [Editor s note: This terminology was used in some of the new text. Should it be adopted as an official abbreviation in the standard? Do we need a definition in clause 3?] - Fiber Distributed Data Interface - Far End Block Error - Forward Error Correction - Far End eceive Failure - Higher Order - Higher order Path - Intraoffice Signal - Integrated Services Digital Network - International Standards Organization - International Telecommunication Union - Telecommunication Standardization Sector - Link Access Protocol for the D Channel - Link Capacity Adjustment Scheme - Loss of Cell Delineation - STS Path LCD - Lower Order - Loss of Frame - Loss of Pointer - STS Path LOP - VT Path LOP - Loss of Signal 9

19 LP LTE MAN MFAS MS NDF NE NNI - Lower order Path - Line Terminating Equipment - Metropolitan Area Network Multiframe Alignment Signal - Multiplex Section - New Data Flag - Network Element - Network Node Interface OAM&P - Operations, Administration, Maintenance & Provisioning OC-1 - Optical Carrier level 1 OC-N PDI PDI-P PLM PLM-P PLM-V POH PTE AI DI DI-L DI-P DI-V EI FI FI-V SAPI SDH - Optical Carrier level N - Payload Defect Indication - STS Path PDI - Payload Label Mismatch - STS Path PLM - VT Path PLM - Path Overhead - Path Terminating Equipment - emote Alarm Indication - emote Defect Indication - Line DI - STS Path DI - VT Path DI - emote Error Indication - emote Failure Indication - VT Path FI - Service Access Point Identifier - Synchronous Digital Hierarchy 10

20 SONET SPE STE STM-M STS - Synchronous Optical Network - Synchronous Payload Envelope - Section Terminating Equipment - Synchronous Transport Module level M - Synchronous Transport Signal STS-1 - Synchronous Transport Signal level 1 STS-1-Xv SPE STS-3c-Xv SPE Virtual concatenation of X STS-1 SPEs Virtual concatenation ot X STS-3c SPEs STS-N - Synchronous Transport Signal level N STS-Nc - Contiguous concatenated Synchronous Transport Signal level N TC TCTE TEI - Tandem Connection - Tandem Connection Terminating Equipment - Terminal Endpoint Identifier TEST-P - STS SPE Supervisory-unequipped signal TIM TIM-P TU UNEQ - Trace Identifier Mismatch - STS Path TIM - Tributary Unit - Unequipped UNEQ-P - STS Path UNEQ UNEQ-V - VT Path UNEQ UNI VC VT - User Network Interface - Virtual Container - Virtual Tributary VTn-Xv SPE Virtual concatenation of X VTn SPEs VTx - VT of size x (currently x = 1.5, 2, 3, or 6) 11

21 5. General A primary goal in creating this standard for the rates and formats is to define a synchronous optical hierarchy with sufficient flexibility to carry many different capacity signals. This has been accomplished by defining a basic signal of Mbit/s and a byte interleaved multiplex scheme that results in a family of standard rates and formats defined at a rate of N times Mbit/s, where N is an integer. Since some signals that need to be transported are greater than the basic rate (such as the broadband ISDN and the Mbit/s signals), a technique of linking several basic signals together to build a transport signal of varying capacity has also been defined in this standard. Note that the lowest bit-rate signal for SDH is Mbit/s, which is equivalent in rate and format to a SONET OC-3 signal. The basic signal can be divided into a portion that is assigned for Transport Overhead and a portion that contains the payload. This payload can be used to transport DS3 signals or to transport a variety of sub- DS3 signals. To maintain a consistent payload structure while providing for transport of a variety of lower rate services (such as DS1, DS1C, DS2, or Mbit/s signals), a structure called a Virtual Tributary (VT) [TU] is defined in this standard. This structure is designed to facilitate consistent transport and switching of various payloads uniformly by handling only VTs. All services below the DS3 rate are transported within a VT structure. Many different types of overhead are defined in this standard, including overhead for maintenance, user channels, frequency justification, orderwire, channel identification, and growth channels. A layered approach to overhead has been established whereby overhead bandwidth has been allocated to a layer based on the function addressed by that particular channel. This layered approach, detailed in clause 8, allows creation of equipment that need not access all layers of overhead, thereby allowing the creation of equipment to meet different needs. Growth channels have been identified to allow for future uses not defined or conceived at this time. The rest of the document concentrates on the actual specification of the rates and formats for optical interfaces. Clause 6 describes the rates. Clause 7 covers the frame formats for the base signal as well as higher rate signals. Overhead functions as well as layering of the overhead are described in clause 8. Payload Pointers for STS-1 and Virtual Tributary processing are described in clause 9. Multiplexing procedures are outlined in clause 10. Payload mappings defined thus far are detailed in T Automatic Protection Switching functions are described in T and Data Communications Channel requirements are provided in T It is anticipated that these documents will be revised as new signals and capabilities are defined that need to be supported. 6. ates 6.1 STS-1/OC-1 rate The basic modular signal is called the Synchronous Transport Signal level 1 (STS-1). The rate is Mbit/s. The optical counterpart of the STS-1 is the Optical Carrier level 1 signal (OC-1), which is the result of a direct optical conversion of the STS-1 after frame synchronous scrambling (see 10.3) [Note that SDH does not make the distinction between a logical signal (e.g., STS-N in SONET) and a physical signal (e.g., OC-N in SONET). The equivalent SDH term for both logical and physical signals is synchronous transport module level M (STM-M), where M=(N/3)]. 6.2 Synchronous hierarchical rates The definition of the first level (STS-1, OC-1) defines the entire hierarchy of synchronous optical signals, since the higher-level signals are obtained by synchronously multiplexing lower-level signals. The higherlevel signals are denoted by STS-N and OC-N where N is an integer. 12

22 There is an integer multiple relationship between the rates of the basic module OC-1 and the multiplexed signal OC-N, i.e., the rate of OC-N is equal to N times the rate of OC-1. The SDH STM-M is equal to M times the rate of the STM-1 signal, which is equivalent to SONET OC-N signals, where N=3M. In the range from 1 to 768, this standard recognizes only certain values of N. These values of N are: 1, 3, 12, 24, 48, 192, and 768. Table 1 lists standard Optical Carrier (OC) rates from Mbit/s through Mbit/s, with the equivalent SDH signal indicated. Values of N greater than 768 may be addressed in future revisions of this standard. 7. Transport formats 7.1 Frame structure of the STS-1 The STS-1 frame depicted in figure 5 consists of 90 columns and 9 rows of 8-bit bytes, for a total of 810 bytes (6480 bits). 2) With a frame length of 125 microseconds (i.e., 8000 frames per second), the STS-1 has a bit rate of Mbit/s. The order of transmission of bytes is row by row, from left to right. In each byte, the most significant bit is transmitted first (see figure 4). An SDH STM-1 frame consists of 270 columns and 9 rows of 8-bit bytes, for a total of 2430 bytes Transport overhead eferring to figure 5, the first three columns are the Transport Overhead, which contains overhead bytes for Section and Line layers. Twenty-seven bytes have been assigned, with nine bytes for Section Overhead and eighteen bytes for Line Overhead. Details of these overhead allocations are described in clause 8. In SDH, the first nine columns of rows 1-3 and 5-9 are the Section Overhead for an STM-1, which contains overhead bytes for the egenerator and Multiplex Sections respectively STS-1 synchronous payload envelope The STS-1 Synchronous Payload Envelope (SPE) is depicted in figures 6, 7, and 8. [VC-3 plus 2 columns of fixed stuff.] It consists of 87 columns and 9 rows of bytes, for a total of 783 bytes as illustrated in figure 6. Column 1 contains the STS Path Overhead (9 bytes) and the remainder (774 bytes) is available for payload as illustrated in figure 7. The STS-1 SPE may begin anywhere in the STS Envelope Capacity illustrated in figure 8. Typically it begins in one frame and ends in the next (although it may be wholly contained in one frame). The payload pointer contained in the Transport Overhead designates the location of the byte where the STS-1 SPE begins. STS-1 Payload Pointers are discussed in 9.1. STS Path Overhead is defined in each payload and is to be used to communicate functions from the point where a service is mapped into the STS SPE to the point where it is delivered. STS Path Overhead is discussed in detail in clause 8. All current mappings for the STS-1 SPE have fixed stuff bytes in columns 30 and 59. The bytes in each row in these columns shall be the same. This is to ensure even parity that will permit interworking with SDH AU-3 based equipment Virtual tributary (VT) structure The Virtual Tributary [TU] is a structure designed for transport and switching of sub-sts-1 payloads. There are four sizes of VT: the VT1.5 [TU-11] (1.728 Mbit/s), the VT2 [TU-12] (2.304 Mbit/s), the VT3 2) Byte and octet are synonymous in this standard. 13

23 (3.456 Mbit/s), and the VT6 [TU-2] (6.912 Mbit/s). These are illustrated in figure 9. In the nine-row structure of the STS-1 Synchronous Payload Envelope, these VTs occupy three columns, four columns, six columns, and twelve columns, respectively. In order to accommodate mixes of these VTs in an efficient manner, the VT-structured STS-1 SPE is divided into seven VT Groups [TUG-2s] as illustrated in figure 10. Each VT Group occupies twelve columns of the nine-row structure and may contain four VT1.5s, three VT2s, two VT3s, or one VT6. Note that a VT Group shall contain only one size of VT; however, each VT Group within an STS-1 may be a different VT size. Figure 11 is a three-dimensional representation of the STS-1 SPE, which further illustrates this point. In figures 12 through 15, the entire STS-1 SPE is shown containing one of the four VT sizes. Tables 2 through 5 define the relationship between the VT number, VT Group number, and column number in the STS-1 SPE from figures 12 through 15, respectively. The Byte 1 references in these figures refer to the first byte of the VT as defined in figure 9. In the floating VT mode, four consecutive 125 µs frames of the STS-1 SPE are organized into a 500 µs superframe, the phase of which is indicated by the Multiframe Indicator byte (H4) in the STS Path Overhead. This defines a 500 µs structure for each of the VTs, called the VT Superframe. The VT Superframe [TU multiframe] contains the VT Payload Pointer and the VT Synchronous Payload Envelope as shown in figure 16. The VT Pointer occupies 4 bytes: V1, V2, V3, and V4, and the remaining bytes define the VT Envelope Capacity [lower order container], which is different for each VT size. The placement of the V1-V4 bytes is such that they will appear in byte 1 of each frame of the four frame superframe, regardless of the VT size. Figure 17 illustrates the four VT SPEs corresponding to the four VT sizes. Each VT SPE contains four bytes of VT Path Overhead (V5, J2, Z6 and Z7). The remaining bytes define the VT Payload Capacity [lower order container], which is different for each VT size. The VT Payload Pointer provides for flexible and dynamic alignment of the VT SPE within the VT Envelope Capacity, independent of other VT SPEs. VT Payload Pointers are further described in Frame structure of the STS-N The STS-N signal is formed by byte interleaving N STS-1 signals. The STS-N frame structure is depicted in figure 18. The transport overhead channels of the individual STS-1 signals must be frame aligned before interleaving. The associated STS SPEs are not required to be aligned because each STS-1 will have a unique payload pointer to indicate the location of the SPE. When forming the STS-N frame, as noted in clauses and 8.2.2, certain Section and Line Layer Overhead bytes in the STS-1 number 2 through number N are unspecified at this time. The receiver shall ignore the value of these bytes (except for BIP calculation purposes). 7.3 Concatenated structures For the transport of payloads that exceed the payload capacity of the standard set of synchronous payload envelops (STS-1 SPE, VT1.5/2/3/6 SPEs) SPE concatenation can be used. Two methods for concatenation are defined; contiguous and virtual concatenation. Both methods provide concatenated bandwidth of X times the SPE payload capacity at the path termination. The difference between these two approaches is the transport between the path termination. Contiguous concatenation maintains the contiguous bandwidth through out the whole transport, while virtual concatenation breaks the contiguous bandwidth into individual SPEs, transports the individual SPEs and recombines these SPEs to a contiguous bandwidth at the end point of the transmission. Virtual concatenation requires concatenation functionality only at the path termination equipment, while contiguous concatenation requires concatenation functionality at each network element Contiguous concatenated STS-1s Concatenated STS-1s are used to transport super-rate services that require more payload carrying capacity than that which is available in a single STS-1, (e.g., transport of broadband ISDN payloads). Super-rate services are mapped into and transported as an STS-Nc SPE [N=3X there X=1, 4 16, 64, or 14

24 256 or SDH VC-4 or VC-4-Xc, where X=N/3] whose constituent STS-1s are phased aligned. The STS-Nc is carried in an STS-M line signal where M N. The STS-Nc [N=3X there X=1, 4 16, 64, or 256 or SDH AU-4-Xc structured STM-M where X=M=N/3] shall be multiplexed, switched, and transported through the network as a single entity. A concatenation indication is used in the STS-1 pointer (STS-1 #2-N) to show that the signal is part of an STS-Nc. Details of the STS-1 concatenation indication are provided in 9.1.4, the mapping of super-rate services is covered in T , and general concatenation levels are covered in Figure 19 shows the SPE for an STS-3c. It consists of 261 byte columns (3 x 87) by 9 rows. The order of byte transmission is by row beginning with row 1 from left to right and ending with row 9. Only one set of STS Path Overhead is defined for an STS-3c SPE. The STS-3c SPE is carried within the STS-3 such that the STS Path Overhead always appears in the first STS-1 of the 3 STS-1s which make up the STS-3c. Figure 20 shows the SPE for a generic STS-Nc (N=3X, where X = 1, 2, 3,...). This STS-Nc SPE consists of N x 87 byte columns by 9 rows. The order of byte transmission is by row beginning with row 1 from left to right and ending with row 9. Only one set of STS Path Overhead is defined for an STS-Nc (N 3) SPE (e.g., the BIP-8 covers the full N x 87 columns of the STS-Nc). The STS-Nc Path Overhead is carried in the first column of the SPE. The next (N/3-1) columns consist of fixed stuff bytes. The remaining (N x 87 - N/3) columns are available for payload mapping Virtual concatenation of X STS-1/STS-3c SPEs (STS-1/3c-Xv SPE, X = ) For the transport of payloads that do not fit efficiently into the standard set of synchronous payload envelops (STS-1 and STS-Nc SPEs) virtual concatenation can be used. An STS-1/3c-Xv SPE provides a contiguous payload area of X STS-1/3c SPE with a payload capacity of X*48384/ kbit/s as shown in figures 21 and 22. The payload capacity is mapped into X individual STS-/3c1 SPEs which form the STS-1/3c-Xv SPE. Each STS-1/3c SPE has its own POH as specified in The H4 POH byte is used for the virtual concatenation specific sequence and multi-frame indication as defined below. In figure 21, note that for ease of inter-working with SDH VC-3 signals, columns 30 and 59 of the STS-1 SPE contain fixed stuff. Each STS-1/3c SPE of the STS-1/3c-Xv SPE is transported individually through the network. Due to different propagation delay of the STS-1/3c SPEs a differential delay will occur between the individual STS-1/3c SPEs. This differential delay has to be compensated and the individual STS-1/3c SPEs have to be realigned for access to the contiguous payload area. The realignment process has to cover at least a differential delay of 125 µs. Each STS-1/3c SPE of the STS-1/3c-Xv SPE is transported individually through the network. Due to different propagation delay of the STS-1/3c SPEs a differential delay will occur between the individual STS-1/3c SPEs. This differential delay has to be compensated and the individual STS-1/3c SPEs have to be realigned for access to the contiguous payload area. The realignment process has to cover at least a differential delay of 125 µs. The sequence indicator SQ identifies the sequence/order in which the individual STS-1/3c SPEs of the STS-1/3c-Xv SPE are combined to form the contiguous STS-1/3c-Xc SPE payload capacities shown in figure 23. Each STS-1/3c SPE of a STS-1(3c-Xv SPE has a fixed unique sequence number in the range of 0 to (X-1). The STS-1/3c SPE transporting the first time slot of the STS-1/3c-Xc SPE has the sequence number 0, the STS-1/3c SPE transporting the second time slot the sequence number 1 and so on up to the STS-1/3c SPE transporting time slot X of the STS-1/3c-Xc SPE with the sequence number (X-1). The sequence number is fixed assigned and not configurable. It allows the service provider to check the correct constitution of the STS-1/3c-Xv SPE without using the trace. The 8-bit sequence number (which supports values of X up to 256) is transported in bits 1 to 4 of the H4 bytes, using frame 14 (SQ bits 1-4) and 15 (SQ bits 5-8) of the first multi-frame stage as shown in figure