It has been suggested that this article be split into articles entitled Synchronous optical networking, SONET and Synchronous digital hierarchy. (Discuss)

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Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH), are two closely related multiplexing protocols for transferring multiple digital bit streams using lasers or light-emitting diodes (LEDs) over the same optical fiber. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting larger amounts of telephone calls and data traffic over the same fiber wire without synchronization problems. In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol that is currently under development in the IETF. Applications that might make use of DCCP include those with timingconstraints on the delivery of data such that reliable in-order delivery, when combined with congestion control, is likely... In the field of computer networking, the IETF Signaling Transport (SIGTRAN) working group defined the Stream Control Transmission Protocol (SCTP) as a transport layer protocol in 2000. ... The Resource ReSerVation Protocol (RSVP), described in RFC 2205, is a Transport layer protocol designed to reserve resources across a network for an integrated services Internet. ... Network congestion avoidance is a process used in computer networks to avoid congestion. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Internet Protocol version 4 (IPv4) is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ... Internet Protocol version 6 (IPv6) is a network layer for packet-switched internetworks. ... The Open Shortest Path First (OSPF) protocol is a hierarchical interior gateway protocol (IGP) for routing in Internet Protocol, using a link-state in the individual areas that make up the hierarchy. ... Is Is is Yeah Yeah Yeahs third EP, to be released on July 24, 2007. ... IPsec (IP security) is a suite of protocols for securing Internet Protocol (IP) communications by authenticating and/or encrypting each IP packet in a data stream. ... In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a hosts hardware address when only its network layer address is known. ... Reverse Address Resolution Protocol (RARP) is a network layer protocol used to obtain an IP address for a given hardware address (such as an Ethernet address). ... This article is chiefly about the Routing Information Protocol (RIP) for the Internet Protocol, but also discusses some other routing information protocols. ... The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. ... The ICMP for IPv6 (Internet Control Message Protocol Version 6) is an integral part of the IPv6 architecture and must be completely supported by all IPv6 implementations. ... The Internet Group Management Protocol (IGMP) is a communications protocol used to manage the membership of Internet Protocol multicast groups. ... The data link layer is layer two of the seven-layer OSI model as well as of the five-layer TCP/IP reference model. ... IEEE 802. ... The IEEE 802. ... Wi-Fi (IPA: ) is the common name for a popular wireless technology used in home networks, mobile phones, video games and more. ... Official WiMax logo WiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... Dynamic synchronous Transfer Mode , or DTM for short, is a network protocol. ... Token-Ring local area network (LAN) technology was developed and promoted by IBM in the early 1980s and standardised as IEEE 802. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... In computer networking, fiber-distributed data interface (FDDI) is a standard for data transmission in a local area network that can extend in range up to 200 km (124 miles). ... In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. ... Evolution-Data Optimized or Evolution-Data only, abbreviated as EV-DO or EVDO and often EV, is one telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. ... High-Speed Packet Access (HSPA) is a collection of mobile telephony protocols that extend and improve the performance of existing UMTS protocols. ... High-Level Data Link Control (HDLC) is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... The Point-to-Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. ... In computer networking, the Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs). ... ISDN redirects here. ... ARCNET (also CamelCased as ARCnet, an acronym from Attached Resource Computer NETwork) is a local area network (LAN) protocol, similar in purpose to Ethernet or Token Ring. ... Link Layer Topology Discovery (LLTD) is a licensed data link layer protocol for network topology discovery and quality of service diagnostics, developed by Microsoft as part of their Windows Rally set of technologies. ... This article does not cite any references or sources. ... The Ethernet physical layer is the physical layer component of the Ethernet standard. ... RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... There are very few or no other articles that link to this one. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... Coaxial Cable For the weapon, see coaxial weapon. ... 25 Pair Color Code Chart 10BASE-T UTP Cable Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of cancelling out electromagnetic interference known as crosstalk. ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... For other uses, see Digital (disambiguation). ... For other uses, see Laser (disambiguation). ... LED redirects here. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... The Plesiochronous Digital Hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems. ... For other uses, see Telephone (disambiguation). ... For other uses, see Data (disambiguation). ...

SONET and SDH are based on circuit mode communication, meaning that each connection achieves a constant bit rate and delay. For example, SDH or SONET may be utilized to allow several Internet Service Providers to share the same optical fiber, without being affected by each others traffic load, and without being able to temporarily borrow free capacity from each other. Only certain integer multiples of 64 kbit/s are possible bit rates. To meet Wikipedias quality standards, this article or section may require cleanup. ... “ISP” redirects here. ...

Since SONET and SDH are characterized as pure time division multiplexing (TDM) protocols (not to be confused with TDMA), offering permanent connections, and do not involve packet mode communication, they are considered as physical layer protocols. Time-division multiplexing (TDM) is a type of digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i. ... Time Division Multiple Access (TDMA) is a technology for shared medium (usually radio) networks. ... This article does not cite any references or sources. ...

Both SDH and SONET are widely used today: SONET in the U.S. and Canada and SDH in the rest of the world. Although the SONET standards were developed before SDH, their relative penetrations in the worldwide market dictate that SONET now is considered the variation. For other uses of terms redirecting here, see US (disambiguation), USA (disambiguation), and United States (disambiguation) Motto In God We Trust(since 1956) (From Many, One; Latin, traditional) Anthem The Star-Spangled Banner Capital Washington, D.C. Largest city New York City National language English (de facto)1 Demonym American...

The two protocols are standardized according to the following:

• SDH or Synchronous Digital Hierarchy standard developed by the International Telecommunication Union (ITU), documented in standard G.707 and its extension G.708
• SONET or Synchronous Optical Networking standard as defined by GR-253-CORE from Telcordia and T1.105 from American National Standards Institute

The International Telecommunication Union (ITU; French: Union internationale des télécommunications, Spanish: Unión Internacional de Telecomunicaciones) is an international organization established to standardize and regulate international radio and telecommunications. ... ... The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ...

Difference from PDH

Synchronous networking differs from PDH in that the exact rates that are used to transport the data are tightly synchronized across the entire network, made possible by atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network. The Plesiochronous Digital Hierarchy (PDH) is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems. ... Synchronization is coordination with respect to time. ... “Nuclear Clock” redirects here. ... This article or section is in need of attention from an expert on the subject. ...

Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or used directly to support either ATM or so-called Packet over SONET/SDH (POS) networking. As such, it is inaccurate to think of SDH or SONET as communications protocols in and of themselves, but rather as generic and all-purpose transport containers for moving both voice and data. The basic format of an SDH signal allows it to carry many different services in its Virtual Container (VC) because it is bandwidth-flexible. Encapsulation may refer to: information hiding and separation of concerns, in software engineering, the process of enclosing programming elements inside larger, more abstract entities integrated circuit encapsulation, in electronics the design and manufacture of protective packages micro-encapsulation, means to confine material molecular encapsulation, means to confine molecules encapsulation (pharmacology... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... Packet over SONET/SDH, abbreviated POS, is communications protocol for transmitting packets over SDH or SONET, which are both circuit switched protocols. ...

Structure of SONET/SDH signals

SONET and SDH often use different terms to describe identical features or functions, sometimes leading to confusion that exaggerates their differences. With a few exceptions, SDH can be thought of as a superset of SONET. The two main differences between the two:

• SONET can use either of two basic units for framing while SDH has one
• SDH has additional mapping options which are not available in SONET.

Protocol overview

The protocol is an extremely heavily multiplexed structure, with the header interleaved between the data in a complex way. This is intended to permit the encapsulated data to have its own frame rate and to be able to float around relative to the SDH/SONET frame structure and rate. This interleaving permits a very low latency for the encapsulated data- data passing through equipment can be delayed by at most 32 microseconds, compared to a frame rate of 125 microseconds; many competing protocols buffer the data for at least one frame or packet before sending it on. Extra padding is allowed for the multiplexed data to move within the overall framing due to it being on a different clock to the frame rate, and the decision to allow this at most of the levels of the multiplexing structure makes the protocol complex, but gives high all-round performance. Latency is the time a message takes to traverse a system. ...

The basic unit of transmission

The basic unit of framing in SDH is an STM-1 (Synchronous Transport Module level - 1), which operates at 155.52 Mbit/s. SONET refers to this basic unit as an STS-3c (Synchronous Transport Signal - 3, concatenated), but its high-level functionality, frame size, and bit-rate are the same as STM-1. STM is the INFORMATION STRUCTURE, used to support information pay load and overhead information field, organized in a block frame structure which repeats every 125 micro seconds. ... This article or section does not cite any references or sources. ...

SONET offers an additional basic unit of transmission, the STS-1 (Synchronous Transport Signal - 1), operating at 51.84 Mbit/s - exactly one third of an STM-1/STS-3c. This article or section does not cite any references or sources. ...

Framing

In packet oriented data transmission such as Ethernet, a packet frame usually consists of a header and a payload, with the header of the frame being transmitted first, followed by the payload (and possibly a trailer, such as a CRC). In synchronous optical networking, this is modified slightly. The header is termed the overhead and the payload still exists, but instead of the overhead being transmitted before the payload, it is interleaved, with part of the overhead being transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted. In the case of an STS-1, the frame is 810 octets in size while the STM-1/STS-3c frame is 2430 octets in size. For STS-1, the frame is transmitted as 3 octets of overhead, followed by 87 octets of payload. This is repeated nine times over until 810 octets have been transmitted, taking 125 microseconds. In the case of an STS-3c/STM-1 which operates three times faster than STS-1, 9 octets of overhead are transmitted, followed by 261 octets of payload. This is also nine times over until 2,430 octets have been transmitted, also taking 125 microseconds. For both SONET and SDH, this is normally represented by the frame being displayed graphically as a block: of 90 columns and 9 rows for STS-1; and 270 columns and 9 rows for SDH/STS-3c. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload. Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... A cyclic redundancy check (CRC) is a type of function that takes an input of data stream of any length and produces as output a value of a certain fixed size. ...

The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. However, the standards are extremely similar in implementation, such that it is easy to interoperate between SDH and SONET at particular bandwidths.

It is worth noting that the choice of a 125 microsecond interval is not an arbitrary one. What it means is that the same octet position in each frame comes past every 125 microseconds. If one octet is extracted from the bitstream every 125 microseconds, this gives a data rate of 8 bits per 125 microseconds - or 64 kbit/s, the basic DS0 telecommunications rate. This relation allows an extremely useful behaviour of synchronous optical networking, which is that low data rate channels or streams of data can be extracted from high data rate streams by simply extracting octets at regular time intervals - there is no need to understand or decode the entire frame. This is not possible in PDH networking. Furthermore, it shows that a relatively simple device is all that is needed to extract a datastream from an SDH framed connection and insert it into a SONET framed connection and vice versa. In T-carrier systems Digital signal 0 (DS0) is a basic digital signaling rate of 64 kb/s, corresponding to the capacity of one voice-frequency-equivalent channel. ...

In practice, the terms STS-1 and OC-1 are sometimes used interchangeably, though the OC-N format refers to the signal in its optical form. It is therefore incorrect to say that an OC-3 contains 3 OC-1s: an OC-3 can be said to contain 3 STS-1s.

SDH Frame

A STM-1 Frame. The first 9 columns contain the overhead and the pointers. For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and 9 rows, but the protocol does not transmit the bytes in this order in practice

For the sake of simplicity, the frame is shown as a rectangular structure of 270 columns and 9 rows. The first 3 rows and 9 columns contain Regenerator Section Overhead (RSOH) and the last 5 rows and 9 columns contain Multiplex Section Overhead (MSOH. The 4th row from the top contains pointers

The STM-1 (Synchronous Transport Module level - 1) frame is the basic transmission format for SDH or the fundamental frame or the first level of the synchronous digital hierarchy. The STS-1 frame is transmitted in exactly 125 microseconds, therefore there are 8000 frames per second on a fiber-optic circuit designated OC-1 (optical carrier one). The STM-1 frame consists of overhead plus a virtual container capacity. The first 9 columns of each frame make up the Section Overhead, and the last 261 columns make up the Virtual Container (VC) capacity. The VC plus the pointers (H1, H2, H3 bytes) is called the AU (Administrative Unit). STM is the INFORMATION STRUCTURE, used to support information pay load and overhead information field, organized in a block frame structure which repeats every 125 micro seconds. ... STM is the INFORMATION STRUCTURE, used to support information pay load and overhead information field, organized in a block frame structure which repeats every 125 micro seconds. ...

Carried within the VC capacity, which has its own frame structure of nine rows and 261 columns, is the Path Overhead and the Container . The first column is for Path Overhead; it’s followed by the payload container, which can itself carry other containers. Virtual Containers can have any phase alignment within the Administrative Unit, and this alignment is indicated by the Pointer in row four,

The Section overhead of an STM-1 signal (SOH) is divided into two parts: the Regenerator Section Overhead (RSOH) and the Multiplex Section Overhead (MSOH). The overheads contain information from the system itself, which is used for a wide range of management functions, such as monitoring transmission quality, detecting failures, managing alarms, data communication channels, service channels, etc.

The STM frame is continuous and is transmitted in a serial fashion, byte-by-byte, row-by-row.

STM–1 frame contains

• Total content : 9 x 270 bytes = 2430 bytes

• overhead : 9 rows x 9 bytes
• payload : 9 rows x 261 bytes

• Period : 125 μsec
• Bitrate : 155,520 Mbit/s (2430 x 8 bits x 8000 frame/s )

• payload capacity : 150,336 Mbit/s (2349 x 8 bits x 8000 frame/s)

The transmission of the frame is done row by row, from the top left corner

Framing Structure

The frame consists of two parts, the transport overhead and the path virtual envelope.

Transport overhead

The transport overhead is used for signaling and measuring transmission error rates, and is composed as follows:

• Section overhead - called RSOH (Regenerator Section Overhead) in SDH terminology: 27 octets containing information about the frame structure required by the terminal equipment.
• Line overhead - called MSOH (Multiplex Section Overhead) in SDH: 45 octets containing information about alarms, maintenance and error correction as may be required within the network.
• Pointer – It points to the location of the J1 byte in the payload.

To meet Wikipedias quality standards, this article or section may require cleanup. ...

Path virtual envelope

Data transmitted from end to end is referred to as path data. It is composed of two components:

• Payload overhead (POH): 9 bytes used for end to end signaling and error measurement.
• Payload: user data (774 bytes for STS-1, or 2349 bytes for STM-1/STS-3c)

For STS-1, the payload is referred to as the synchronous payload envelope (SPE), which in turn has 18 stuffing bytes, leading to the STS-1 payload capacity of 756 bytes.^[1]

The STS-1 payload is designed to carry a full PDH DS3 frame. When the DS3 enters a SONET network, path overhead is added, and that SONET network element (NE) is said to be a path generator and terminator. The SONET NE is said to be line terminating if it processes the line overhead. Note that wherever the line or path is terminated, the section is terminated also. SONET Regenerators terminate the section but not the paths or line. Two Network Interface Units, one with a single card, the other with two In telecommunications, T-carrier is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan. ... A network element (NE) is telecommunications hardware equipment that is addressable and manageable. ... Synchronous Optical Networking, commonly known as SONET, is a standard for communicating digital information over optical fiber. ...

An STS-1 payload can also be subdivided into 7 VTGs, or Virtual Tributary Groups. Each VTG can then be subdivided into 4 VT1.5 signals, each of which can carry a PDH DS1 signal. A VTG may instead be subdivided into 3 VT2 signals, each of which can carry a PDH E1 signal. The SDH equivalent of a VTG is a TUG2; VT1.5 is equivalent to VC11, and VT2 is equivalent to VC12. Digital signal 1 (DS1, also known as a T1) is a T-carrier signaling scheme devised by Bell Labs. ... E1 or E-1 may be: E1 elimination reaction, in organic chemistry E-1 Tracer, an airborne early warning aircraft used by the United States Navy from 1954 to the early 1970s. ...

Three STS-1 signals may be multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s. The multiplexing is performed by interleaving the bytes of the three STS-1 frames to form the STS-3 frame, containing 2,430 bytes and transmitted in 125 microseconds. In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... Time-Division Multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but physically are taking turns on the channel. ... Optical Carrier levels are used for the categories of bandwidth in a SONET fiber optic network. ...

Higher speed circuits are formed by successively aggregating multiples of slower circuits, their speed always being immediately apparent from their designation. For example, four STS-3 or AU4 signals can be aggregated to form a 622.08 Mbit/s signal designated as OC-12 or STM-4. OC-12 (Optical Carrier 12) is a fiber optic network line with a SONET rate of 621. ...

The highest rate that is commonly deployed is the OC-192 or STM-64 circuit, which operates at rate of just under 10 Gbit/s. Speeds beyond 10 Gbit/s are technically viable and are under evaluation. [Few vendors are offering STM-256 rates now, with speeds of nearly 40Gbit/s]. Where fiber exhaust is a concern, multiple SONET signals can be transported over multiple wavelengths over a single fiber pair by means of Wavelength division multiplexing, including Dense Wave Division Multiplexing (DWDM) and Coarse Wave Division Multiplexing (CWDM). DWDM circuits are the basis for all modern transatlantic cable systems and other long-haul circuits. OC-192 (Optical Carrier 192) is a fiber optic network line with a SONET rate of 9953. ... In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ...

SONET/SDH and relationship to 10 Gigabit Ethernet

Another circuit type amongst data networking equipment is 10 Gigabit Ethernet (10GbE). This is similar to the line rate of OC-192/STM-64 (9.953 Gbit/s). The Gigabit Ethernet Alliance created two 10 Gigabit Ethernet variants: a local area variant (LAN PHY), with a line rate of exactly 10,000,000 kbit/s and a wide area variant (WAN PHY), with the same line rate as OC-192/STM-64 (9,953,280 kbit/s). The Ethernet wide area variant encapsulates its data using a light-weight SDH/SONET frame so as to be compatible at low level with equipment designed to carry those signals. 10 Gigabit Ethernet or 10GbE or 10 GigE is the most recent (as of 2006) and fastest of the Ethernet standards. ...

However, 10 Gigabit Ethernet does not explicitly provide any interoperability at the bitstream level with other SDH/SONET systems. This differs from WDM System Transponders, including both Coarse- and Dense-WDM systems (CWDM, DWDM) that currently support OC-192 SONET Signals, which can normally support thin-SONET framed 10 Gigabit Ethernet. In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colours) of laser light to carry different signals. ... The original version of this article was based on FOLDOC, with permission In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ... The original version of this article was based on FOLDOC, with permission In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ...

SONET/SDH data rates

In the above table, Payload bandwidth is the line rate less the bandwidth of the line and section overheads. User throughput must also deduct path overhead from this, but path overhead bandwidth is variable based on the types of cross-connects built across the optical system. OC-1 (optical carrier one) is a SONET line with transmission speed of 51. ... Optical Carrier levels are used for the categories of bandwidth in a SONET fiber optic network. ... STM is the INFORMATION STRUCTURE, used to support information pay load and overhead information field, organized in a block frame structure which repeats every 125 micro seconds. ... OC-12 (Optical Carrier 12) is a fiber optic network line with a SONET rate of 621. ... OC-24 is a SONET line with transmission speed of 1. ... OC-48 (Optical Carrier 48) is a fiber optic network line with a SONET rate of 2488. ... (Optical Carrier 96) is a fiber optic network line with a SONET rate of 4976. ... OC-192 (Optical Carrier 192) is a fiber optic network line with a SONET rate of 9953. ... OC-768 is a fiber optic network line with a SONET rate of 39,813. ... OC-1536 is a SONET line with transmission speed of about 80 Gbit/s using optical fiber. ... OC-3072 is a SONET line with transmission speed of about 160 Gbit/s using for instance an optical fiber. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Note that the typical data rate progression starts at OC-3 and increases by multiples of 4. As such, while OC-24 and OC-1536, along with other rates such as OC-9, OC-18, OC-36, and OC-96 may be defined in some standards documents, they are not available on a wide-range of equipment.

As of 2007, OC-3072 is still a work in progress.

SONET physical layer

The physical layer in SONET actually comprises a large number of layers within it, only one of which is the optical/transmission layer (which includes bitrates, jitter specifications, optical signal specifications and so on). The SONET and SDH standards come with a host of features for isolating and identifying signal defects and their origins. This article does not cite any references or sources. ...

SONET/SDH Network Management Protocols

SONET equipment is often managed with the TL1 protocol. TL1 is a traditional telecom language for managing and reconfiguring SONET network elements. TL1 (or whatever command language a SONET Network Element utilizes) must be carried by other management protocols, including SNMP, CORBA and XML. Transaction Language 1 Transaction Language 1 (TL1) is a widely used, legacy, management protocol in telecommunications. ... The Simple Network Management Protocol (SNMP) forms part of the internet protocol suite as defined by the Internet Engineering Task Force (IETF). ... In computing, Common Object Request Broker Architecture (CORBA) is a standard for software componentry, created and controlled by the Object Management Group (OMG). ... The Extensible Markup Language (XML) is a general-purpose markup language. ...

There are some features that are fairly universal in SONET Network Management. First of all, most SONET NEs have a limited number of management interfaces defined. These are: A network element (NE) is telecommunications hardware equipment that is addressable and manageable. ...

• Electrical Interface. The electrical interface (often 50 Ω) sends SONET TL1 commands from a local management network physically housed in the Central Office where the SONET NE is located. This is for "local management" of that NE and, possibly, remote management of other SONET NEs.

• Craft Interface. Local "craftspersons" can access a SONET NE on a "craft port" and issue commands through a dumb terminal or terminal emulation program running on a laptop. This interface can also be hooked-up to a console server, allowing for remote out-of-band management and logging.

• SONET and SDH have dedicated Data Communication Channels (DCC)s within the section and line overhead for management traffic. Generally, section overhead (regenerator section in SDH) is used. According to ITU-T G.7712, there are three modes used for management:

• IP-only stack, using PPP as data-link
• OSI-only stack, using LAP-D as data-link
• Dual (IP+OSI) stack using PPP or LAP-D with tunneling functions to communicate between stacks.

An interesting fact about modern SONET NEs is that, to handle all of the possible management channels and signals, most NEs actually contain a router for routing the network commands and underlying (data) protocols. In the field of telecommunications, a central office or telephone exchange houses equipment that is commonly known as simply a switch, which is a piece of equipment that connects phone calls. ... A console server (also console access server or console management server or serial console server) is a device or service that provides access to the system console of a computing device via networking technologies. ... Out-of-band management is the use of a dedicated management channel for device maintenance. ... Data logging is the practice of recording sequential data, often chronologically. ... The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... This article or section does not adequately cite its references or sources. ... Link Access Procedures on the D channel (LAPD), specified in ITU-T Q.920 and ITU-T Q.921, is the second layer protocol on the ISDN protocol stack in the D channel. ...

The main functions of SONET Network Management include:

• SONET Network and NE Provisioning. In order to allocate bandwidth throughout a SONET Network, each SONET NE must be configured. Although this can be done locally, through a craft interface, it is normally done through a Network Management System (sitting at a higher layer) that in turn operates through the SONET/SDH Network Management Network.

• Software Upgrade. SONET NE Software Upgrade is in modern NEs done mostly through the SONET/SDH Management network.

• Performance Management. SONET NEs have a very large set of standards for Performance Management. The PM criteria allow for monitoring not only the health of individual NEs, but for the isolation and identification of most network defects or outages. Higher-layer Network monitoring and management software allows for the proper filtering and troubleshooting of network-wide PM so that defects and outages can be quickly identified and responded to.

SONET equipment

With recent advances in SONET and SDH chipsets, the traditional categories of SONET NEs are breaking down. Nevertheless, as SONET Network architectures have remained relatively constant, even newer SONET Equipment (including "Multiservice Provisioning Platforms") can be examined in light of the architectures they will support. Thus, there is value in viewing new (as well as traditional) SONET Equipment in terms of the older categories.

SONET regenerator

Traditional SONET Regenerators terminate the SONET Section overhead, but not the line or path. SONET Regens extend long haul routes in a way similar to most regenerators, by converting an optical signal that has already traveled a long distance into electrical format and then retransmitting a regenerated high-power signal.

Since the late 1990s, SONET regenerators have been largely replaced by Optical Amplifiers. Also, some of the functionality of SONET Regens has been absorbed by the Transponders of Wavelength Division Multiplexing systems. An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. ... In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ...

SONET add-drop multiplexer (ADM)

SONET ADMs are the most common type of SONET Equipment. Traditional SONET ADMs were designed to support one of the SONET Network Architectures, though new generation SONET systems can often support several architectures, sometimes simultaneously. SONET ADMs traditionally have a "high speed side" (where the full line rate signal is supported), and a "low speed side", which can consist of electrical as well as optical interfaces. The low speed side takes in low speed signals which are multiplexed by the SONET NE and sent out from the high speed side, or vice versa. A main element of optical fiber networks. ...

SONET Digital Cross Connect system

Recent SONET Digital Cross Connect systems (DCSs or DXCs) support numerous high-speed signals, and allow for cross connection of DS1s, DS3s and even STS-3s/12c and so on, from any input to any output. Advanced SONET DCSs can support numerous subtending rings simultaneously. A digital cross-connect system (DCS) is a piece of circuit-switched network equipment, typically used in telephone networks, that allows lower-level TDM bit streams, such as DS0 bit steams, to be rearranged and interconnected among higher-level TDM signals, such as DS1 bit streams. ...

SONET Network Architectures

Currently, SONET (and SDH) have a limited number of architectures defined. These architectures allow for efficient bandwidth usage as well as protection (i.e. the ability to transmit traffic even when part of the network has failed), and are key in understanding the almost worldwide usage of SONET and SDH for moving digital traffic. The three main architectures are:

• Linear APS (Automatic Protection Switching), also known as 1+1: This involves 4 fibers: 2 working fibers in each direction, and two protection fibers. Switching is based on the line state, and may be unidirectional, with each direction switching independently, or bidirectional, where the NEs at each end negotiate so that both directions are generally carried on the same pair of fibers.
• UPSR (Unidirectional Path Switched Ring): In a UPSR, two redundant (path-level) copies of protected traffic are sent in either direction around a ring. A selector at the egress node determines the higher-quality copy and decides to use the best copy, thus coping if deterioration in one copy occurs due to a broken fiber or other failure. UPSRs tend to sit nearer to the edge of a SONET network and, as such, are sometimes called "collector rings". Because the same data is sent around the ring in both directions, the total capacity of a UPSR is equal to the line rate N of the OC-N ring. For example if we had an OC-3 ring with 3 STS-1s used to transport 3 DS-3s from ingress node A to the egress node D, then 100% of the ring bandwidth (N=3) would be consumed by nodes A and D. Any other nodes on the ring, say B and C could only act as pass through nodes. The SDH analog of UPSR is Subnetwork Connection Protection (SNCP); however, SNCP does not impose a ring topology, but may also be used in mesh topologies.

• BLSR (Bidirectional Line Switched Ring): BLSR comes in two varieties, 2-fiber BLSR and 4-fiber BLSR. BLSRs switch at the line layer. Unlike UPSR, BLSR does not send redundant copies from ingress to egress. Rather, the ring nodes adjacent to the failure reroute the traffic "the long way" around the ring. BLSRs trade cost and complexity for bandwdith efficiency as well as the ability to support "extra traffic", which can be pre-empted when a protection switching event occurs. BLSRs can operate within a metropolitan region or, often, will move traffic between municipalities. Because a BLSR does not send redundant copies from ingress to egress the total bandwidth that a BLSR can support is not limited to the line rate N of the OC-N ring and can actually be larger than N depending upon the traffic pattern on the ring. The best case of this is that all traffic is between adjacent nodes. The worst case is when all traffic on the ring egresses from a single node, i.e. the BLSR is serving as a collector ring. In this case the bandwidth that the ring can support is equal to the line rate N of the OC-N ring. This is why BLSRs are seldom if ever deployed in collector rings but often deployed in inter-office rings. The SDH equivalent of BLSR is called Multiplex Section-Shared Protection Ring (MS-SPRING).

SONET synchronization

Synchronization of SONET and SDH networks is a difficult and arcane subject. Remember that a SONET NE will transport and/or multiplex traffic that has originated from a variety of different clock sources. In addition, a SONET NE may have a number of different synchronization options to choose from, which in some cases it will do so dynamically based on Synch Status Messages and other indicators.

As for Synchronization sources available to a SONET NE, these are:

• Local External Timing. This is generated by an atomic Caesium clock or a satellite-derived clock by a device located in the same central office as the SONET NE. The interface is often a DS1, with Sync Status Messages supplied by the clock and placed into the DS1 overhead.
• Line-derived timing. A SONET NE can choose (or be configured) to derive its timing from the line-level, by monitoring the S1 sync status bytes to ensure quality.
• Holdover. As a last resort, in the absence of higher quality timing, a SONET NE can go into "holdover" until higher quality external timing becomes available again. In this mode, a SONET NE uses its own timing circuits to time the SONET signal.

An interesting and hard-to-troubleshoot issue in SONET Networks is the existence of "timing loops". With a timing loop, SONET NEs in a network are each deriving their timing from another NE, and back again to initial NE, like a snake biting its own tail. This network loop will eventually see its own timing "float away" from any external SONET networks, causing mysterious bit errors, the source of which can be hard to find (unless the presence of the timing loop is detected). In general, a SONET Network that has been properly configured will never find itself in a timing loop, but it is sometimes hard to avoid this without sophisticated network management tools.

Next-generation SONET/SDH

SONET/SDH development was originally driven by the need to transport multiple PDH signals like DS1, E1, DS3 and E3 along with other groups of multiplexed 64 kbit/s pulse-code modulated voice traffic. The ability to transport ATM traffic was another early application. In order to support large ATM bandwidths, the technique of concatenation was developed, whereby smaller SONET multiplexing containers (eg, STS-1) are inversely multiplexed to build up a larger container (eg, STS-3c) to support large data-oriented pipes. Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ...

One problem with traditional concatenation, however, is inflexibility. Depending on the data and voice traffic mix that must be carried, there can be a large amount of unused bandwidth left over, due to the fixed sizes of concatenated containers. For example, fitting a 100 Mbit/s Fast Ethernet connection inside a 155 Mbit/s STS-3c container leads to considerable waste. In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. ...

Virtual Concatenation (VCAT) allows for a more arbitrary assembly of lower order multiplexing containers, building larger containers of fairly arbitrary size (e.g. 100 Mbit/s) without the need for intermediate SONET NEs to support this particular form of concatenation. Virtual Concatenation increasingly leverages X.86 or Generic Framing Procedure (GFP) protocols in order to map payloads of arbitrary bandwidth into the virtually concatenated container. Virtual concatenation is an inverse multiplexing technique used to split SONET/SDH bandwidth into logical groups, which may be transported or routed independently. ... Generic Framing Procedure (GFP) is defined by ITU-T G.7041. ...

Link Capacity Adjustment Scheme (LCAS) allows for dynamically changing the bandwidth via dynamic virtual concatenation, multiplexing containers based on the short-term bandwidth needs in the network. Link Capacity Adjustment Scheme or LCAS is a method to dynamically increase or decrease the bandwidth of virtual concatenated containers. ...

The set of next generation SONET/SDH protocols to enable Ethernet transport is referred to as Ethernet over SONET/SDH (EoS). Ethernet Over SDH (EoS) or Ethernet over SONET refers to a set of protocols which allow Ethernet traffic to be carried over synchronous digital hierarchy networks in an efficient and flexible way. ...

See also

• Routing Wavelength Assignment (RWA)
• List of device bandwidths

The problem of routing and wavelength assignment (RWA) is critically important for increasing the efficiency of wavelength-routed all-optical networks. ... This is a list of device bandwidths: the channel capacity (or, more informally, bandwidth) of some computer devices employing methods of data transport is quantified in units of kilobits per second (kbit/s), megabits per second (Mbit/s), or gigabits per second (Gbit/s) as appropriate. ...

References

1. ^ International Engineering Consortium SONET Tutorial, undated, URL retrieved on 21 April 2007

is the 111th day of the year (112th in leap years) in the Gregorian calendar. ...

External links

• Understanding SONET/SDH
• The Queen's University of Belfast SDH/SONET Primer
• SDH Pocket Handbook from Acterna/JDSU
• SONET Pocket Handbook from Acterna/JDSU
• The Sonet Homepage
• SONET Interoperability Form (SIF)
• Network Connection Speeds Reference
• Next-generation SDH and MSPP
• The Future of SONET/SDH (pdf)

Standards

• Telcordia GR 253 CORE: SONET Transport Systems: Common Generic Criteria
• ANSI T1.105: SONET - Basic Description including Multiplex Structure, Rates and Formats
• ANSI T1.119/ATIS PP 0900119.01.2006: SONET - Operations, Administration, Maintenance, and Provisioning (OAM&P) - Communications
• ITU-T recommendation G.707: Network Node Interface for the Synchronous Digital Hierarchy (SDH)
• ITU-T recommendation G.783: Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks
• ITU-T recommendation G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)