Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. The method was developed to replace the plesiochronous digital hierarchy (PDH) system for transporting large amounts of telephone calls and data traffic over the same fiber without the problems of synchronization.
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time according to agreed rules, e.g. with each transmitter working in turn. It can be used when the bit rate of the transmission medium exceeds that of the signal to be transmitted. This form of signal multiplexing was developed in telecommunications for telegraphy systems in the late 19th century but found its most common application in digital telephony in the second half of the 20th century.
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over a single strand of fiber as well as multiplication of capacity.
In computer networking and telecommunications, a pseudowire is an emulation of a point-to-point connection over a packet-switched network (PSN).
A passive optical network (PON) is a fiber-optic telecommunications network that uses only unpowered devices to carry signals, as opposed to electronic equipment. In practice, PONs are typically used for the last mile between Internet service providers (ISP) and their customers. In this use, a PON has a point-to-multipoint topology in which an ISP uses a single device to serve many end-user sites using a system such as 10G-PON or GPON. In this one-to-many topology, a single fiber serving many sites branches into multiple fibers through a passive splitter, and those fibers can each serve multiple sites through further splitters. The light from the ISP is divided through the splitters to reach all the customer sites, and light from the customer sites is combined into the single fiber. Many fiber ISPs prefer this system.
An add-drop multiplexer (ADM) is an important element of an optical fiber network. A multiplexer combines, or multiplexes, several lower-bandwidth streams of data into a single beam of light. An add-drop multiplexer also has the capability to add one or more lower-bandwidth signals to an existing high-bandwidth data stream, and at the same time can extract or drop other low-bandwidth signals, removing them from the stream and redirecting them to some other network path. This is used as a local "on-ramp" and "off-ramp" to the high-speed network.
In fiber optics, a reconfigurable optical add-drop multiplexer (ROADM) is a form of optical add-drop multiplexer that adds the ability to remotely switch traffic from a wavelength-division multiplexing (WDM) system at the wavelength layer. This is achieved through the use of a wavelength selective switching module. This allows individual or multiple wavelengths carrying data channels to be added and/or dropped from a transport fiber without the need to convert the signals on all of the WDM channels to electronic signals and back again to optical signals.
Generic Framing Procedure (GFP) is a multiplexing technique defined by ITU-T G.7041. This allows mapping of variable length, higher-layer client signals over a circuit switched transport network like OTN, SDH/SONET or PDH. The client signals can be protocol data unit (PDU) oriented or can be block-code oriented.
Virtual concatenation (VCAT) is an inverse multiplexing technique creating a large capacity payload container distributed over multiple smaller capacity TDM signals. These signals may be transported or routed independently. Virtual concatenation has been defined for SONET/SDH, OTN and PDH path signals.
Automatically Switched Optical Network (ASON) is a concept for the evolution of transport networks which allows for dynamic policy-driven control of an optical or SDH network based on signaling between a user and components of the network. Its aim is to automate the resource and connection management within the network. The IETF defines ASON as an alternative/supplement to NMS based connection management.
ITU-T Recommendation G.709Interfaces for the Optical Transport Network (OTN) describes a means of communicating data over an optical network. It is a standardized method for transparent transport of services over optical wavelengths in DWDM systems. It is also known as Optical Transport Hierarchy (OTH) standard. The first edition of this protocol was approved in 2001.
Ethernet over PDH or EoPDH is one of many techniques that provided Ethernet connectivity over non-Ethernet networks. Specifically, EoPDH is a standardized methodology for transporting native Ethernet frames over the existing telecommunications copper infrastructure by leveraging the established PDH transport technology. EoPDH is one of several Ethernet transport technologies that enables Telecommunication Service Providers to offer "Carrier Ethernet" services. Also commonly used as a means of connecting businesses to a Metro Ethernet network.
Connection-oriented Ethernet refers to the transformation of Ethernet, a connectionless communication system by design, into a connection-oriented system. The aim of connection-oriented Ethernet is to create a networking technology that combines the flexibility and cost-efficiency of Ethernet with the reliability of connection-oriented protocols. Connection-oriented Ethernet is used in commercial carrier grade networks.
TFI-5 in computer networking is a standardized TDM Fabric to Framer Interface by the Optical Internetworking Forum (OIF) that allow both framer components and switch components from multiple vendors to inter-operate facilitating the development of add/drop multiplexers, TDM cross connect and grooming switches. The TFI-5 standard includes link integrity monitoring, connection management and mapping mechanisms for both SONET/SDH and non-SONET/SDH clients such as Ethernet and Fibre Channel.
Ethernet over PDH over SONET/SDH (EoPoS) is one of many techniques that provided Ethernet connectivity over non-Ethernet networks. EoPoS is a standardized method for transporting native Ethernet frames over the existing telecommunications optical infrastructure use both the established Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SONET/SDH) transport technologies.
The general communication channel (GCC) was defined by G.709 is an in-band side channel used to carry transmission management and signaling information within optical transport network elements.
IP over DWDM (IPoDWDM) is a technology used in telecommunications networks to integrate IP routers and network switches in the OTN . A true IPoDWDM solution is implemented only when the IP Routers and Switches support ITU-T G.709. In this way IP devices can monitor the optical path and implement the transport functionality as FEC specified by ITU-T G.709/Y.1331 or Super FEC functionality defined in ITU-T G.975.1.
An optical mesh network is a type of optical telecommunications network employing wired fiber-optic communication or wireless free-space optical communication in a mesh network architecture.
Link protection is designed to safeguard networks from failure. Failures in high-speed networks have always been a concern of utmost importance. A single fiber cut can lead to heavy losses of traffic and protection-switching techniques have been used as the key source to ensure survivability in networks. Survivability can be addressed in many layers in a network and protection can be performed at the physical layer, Layer 2 and Layer 3 (IP).
Path protection in telecommunications is an end-to-end protection scheme used in connection oriented circuits in different network architectures to protect against inevitable failures on service providers’ network that might affect the services offered to end customers. Any failure occurred at any point along the path of a circuit will cause the end nodes to move/pick the traffic to/from a new route. Finding paths with protection, especially in elastic optical networks, was considered a difficult problem, but an efficient and optimal algorithm was proposed.
