Optical WDM in Fiber Optic Network

Optical WDM networks are networks that deploy optical wdm fiber links where each fiber link carries multiple wavelength channels.

An exciting Optical Network (AON) is definitely an optical wdm network which supplies end-to-end optical paths by using all optical nodes that allow optical signal in which to stay optical domain without conversion to electrical signal. AONs are often optical circuit-switched networks where circuits are switched by intermediate nodes in the granularity of the wavelength channel. Hence a circuit-switched AON can also be called a wavelength routing network where optical circuits are equal to wavelength channels.

A wavelength routing network includes optical cross-connect (OXC) and optical add-drop multiplexer (OADM) interconnected by WDM fibers. Transmission of information over this optical network is performed using optical circuit-switching connections, referred to as lightpaths. An OXC is definitely an N * N optical switch with N input fibers and N output fibers with every fiber carries wavelengths. The OXC can optically switch all the incoming wavelengths of its input fibers to the outgoing wavelengths of its output fibers. An OADM can terminate the signals on a quantity of wavelengths and inserts new signals in to these wavelengths. The rest of the wavelengths pass through the OADM transparently.

For a user to deliver data to some destination user, a circuit-switching connection is made by using a wavelength on each hop along the connection path. This unidirectional optical path is known as lightpath and also the node in between each hop is either an OXC or an OADM. These units are utilized within the 100G DWDM networks. A separate lightpath has to be established using different fibers to setup transmission within the opposite direction. To fulfill the wavelength continuity constraint, the same wavelength can be used on every hop along the lightpath. If a lightpath is blocked since the required wavelength is unavailable, a converter in an OXC can transform the optical signal transmitted in one wavelength to another wavelength.

Because the bandwidth of a wavelength is usually much larger than that requires by a single client, traffic glooming is used to allow the bandwidth of the lightpath to be shared by many people clients. The bandwidth of the lightpath is split into subrate units; clients can request one or more subrate units to carry traffic streams at lower rates. For instance, information is transmitted over an optical network using SONET (Synchronous Optical Network) framing with a transmission rate of OC-48 (2.488 Gbps). A lightpath is established from OXC1 to OXC3 through OXC2 using wavelength w, the subrate unit available on this lightpath is OC-3 (155 Mbps). A user on OXC1 can request any integer number of OC-3 subrate units up to a total of 16 to transmit data to another user on OXC3. A network operator can use traffic-groomed lightpaths to provide subrate transport services to the users with the addition of an online network towards the fiber optic network.

Information on a lightpath is typically transmitted using SONET framing. In the future, the data transmitted over optical network uses the brand new ITU-T G.709 standard, referred to as digital wrapper. In ITU-T, an optical network is referred to as the optical transport network (OTN). Listed here are some of the options that come with G.709 standard: 1) The conventional permits transmission of various kinds of traffic: IP packets and gigabit Ethernet frames using Generic Framing Procedure (GFP), ATM cells and SONET/SDH synchronous data. 2) It supports three bit rate granularities: 2.488 Gbps, 9.95 Gbps and 39.81 Gbps. 3) It offers capabilities to monitor an association on an end-to-end basis over several carriers, in addition to over a single carrier. 4) G.709 uses Forward Error Correction (FEC) to detect and correct bit errors brought on by physical impairments in the transmission links.

Lightpath may either be static or dynamic. Static lightpaths are in place using network management procedures and may remain up for a long time. Virtual Private Networks (VPN) could be set up using static lightpaths. Dynamic lightpaths are established instantly using signaling protocols, such as GMPLS (Generalized Multi-Protocol Label Switching) and UNI (User Network Interface) proposed by OIF (Optical Internetworking Forum). GMPLS is definitely an extension of MPLS and is built to apply MPLS label switching techniques to Time Division Multiplexing (TDM) networks and wavelength routing networks, in addition to packet switching networks. The OIF UNI specifies signaling procedures for clients to automatically create, delete and query an association over wavelength routing network. The UNI signaling is implemented by extending the label distribution protocols, LDP and RSVP-TE.

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