The ITU standard G.709, Interface for the Optical Transport Network, provides an industry-wide frame structure and overhead definition for the photonic layer. This standard defines a hierarchy among optical network elements and provides for performance management of complex Dense Wavelength Division Multiplexing (DWDM) networks.
One of the key benefits of single-channel SONET systems was their extensive performance monitoring and error detection capabilities, provided by the SONET Section, Line, and Path overhead bytes. As networks grew from single-channel SONET systems to multi-wavelength DWDM networks, there was a need to provide a similar frame structure; performance monitoring, error correction, and management function at the optical (i.e. wavelength) layer so that carriers could manage their DWDM networks.
The ITU standard G.709 “Interface for the Optical Transport Network” provides this industry-wide frame structure and overhead definition for the photonic layer; G.709 is sometimes referred to as the “digital wrapper.”
The G.709 OTN standards define:
- An optical transport hierarchy among optical network elements
- A frame structure for mapping client signals
- A definition of the overhead bytes for optical layer performance management and FEC
In a similar manner to SONET definitions, the optical network hierarchy is divided into Optical Path, Optical Transport, and Optical Multiplex layers, as shown below.
|Signal||Approximate data rate (Gbit/s)||Applications|
|OTU1||2.66||Transports SONET OC-48 signal|
|OTU2||10.70||Transports an OC-192 or wide area network (WAN) physical layer (PHY) for 10 Gigabit Ethernet (10GBASE-W)|
|OTU2e||11.09||Transports a 10 Gigabit Ethernet local area network (LAN) PHY coming from IP/Ethernet switches and routers at full line rate (10.3 Gbit/s). This is specified in G.Sup43.|
|OTU2f||11.32||Transports a 10 Fibre Channel.|
|OTU3||43.01||Transports an OC-768 signal or a 40 Gigabit Ethernet signal.|
|OTU3e2||44.58||Transports up to four OTU2e signals|
|OTU4||112||Transports a 100 Gigabit Ethernet signal|
A client signal is mapped into an OPU payload along with OPU overhead bytes, and this entire package gets mapped into an OTU frame along with additional ODU/OTU overhead information and FEC data.
|Signal||Data Rate (Gbit/s)||Typical Applications|
Transport of a timing transparent transcoded (compressed) 1000BASE-X signal[or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure
Transport of two ODU0 signals or a STS-48 signal or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure.
|ODU2||10.0372739240506||Transport of up to eight ODU0 signals or up to four ODU1 signals or a STS-192 signal or a WAN PHY (10GBASE-W) or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure|
Transport of a 10 Gigabit Ethernet signal or a timing transparent transcoded (compressed) Fibre Channel 10GFC signal
Transport of up to 32 ODU0 signals or up to 16 ODU1 signals or up to four ODU2 signals or a STS-768 signal or a timing transparent transcoded 40 Gigabit Ethernet signal or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure
Transport of up to four ODU2e signals
Transport of up to 80 ODU0 signals or up to 40 ODU1 signals or up to ten ODU2 signals or up to two ODU3 signals or a 100 Gigabit Ethernet signal
|ODUflex (CBR)||239⁄238 x client bit rate||
Transport of a constant bitrate signal such as Fibre Channel 8GFC, InfiniBand or Common Public Radio Interface
|ODUflex (GFP)||any configured rate||
Transport of a stream of packets (such as Ethernet, MPLS or IP
Next Generation OTN Platforms
Legacy OTN Platforms
SONET provides an excellent network infrastructure for all types of mission-critical traffic.
Since the late 1980s, SONET has been the workhorse of the telecommunications industry. Over the last 20 years, line rates and capacities have gone up, types of interfaces have increased and manufacturers continue to improve their products with new features and lower costs. Whether your network is carrying a single-voice call or a 10 Gbps data pipe, SONET provides the same transport dependability that the industry has come to rely on.
Although with much reduced revenues in recent years on new deployments, there exists a huge installed base of equipment still operating flawlessly, and significant need for growth and support as SONET still provides an excellent network infrastructure for all types of mission-critical traffic.
- Standards-Based – ensures compatibility across spans and between vendors
- Deterministic and Predictable – robust, voice-centric heritage extends high quality of service to all traffic
- Multi-service Capable – equally effective at carrying TDM and packet-based traffic including ATM, Ethernet and MPLS
- Fault Tolerant – protected rings provide 50 msec recovery from node and span failures
- Mature Technology – well-known technology and provisioning model
- Price/Performance – one of the most cost-effective architectures up to 10 Gbps
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