Optical Transport Network
ITU-T defines an Optical Transport Network (OTN) as a set of Optical Network Elements (ONE) connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals.[1] An ONE may Re-time, Re-Amplify, Re-shape (3R) but it does not have to be 3R – it can be purely photonic.
Standards
OTN was designed to provide support for optical networking using wavelength-division multiplexing (WDM) unlike its predecessor SONET/SDH.
ITU-T Recommendation G.709 is commonly called Optical Transport Network (OTN) (also called digital wrapper technology or optical channel wrapper). As of December 2009, OTN has standardized the following line rates.
| Signal | Approximate data rate (Gbit/s) | Applications |
|---|---|---|
| OTU1 | 2.66 | Transports SONET OC-48 or synchronous digital hierarchy (SDH) STM-16 signal |
| OTU2 | 10.70 | Transports an OC-192, STM-64 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 or STM-256 signal or a 40 Gigabit Ethernet signal.[2] |
| OTU3e2 | 44.58 | Transports up to four OTU2e signals |
| OTU4 | 112 | Transports a 100 Gigabit Ethernet signal |
The OTUk (k=1/2/2e/3/3e2/4) is an information structure into which another information structure called ODUk (k=1/2/2e/3/3e2/4) is mapped. The ODUk signal is the server layer signal for client signals. The following ODUk information structures are defined in ITU-T Recommendation G.709
| Signal | Data Rate (Gbit/s) | Typical Applications |
|---|---|---|
| ODU0 | 1.24416 | Transport of a timing transparent transcoded (compressed) 1000BASE-X signal[3] or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure |
| ODU1 | 2.49877512605042 | Transport of two ODU0 signals or a STS-48/STM-16 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/STM-64 signal or a WAN PHY (10GBASE-W) or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure |
| ODU2e | 10.3995253164557 | Transport of a 10 Gigabit Ethernet signal or a timing transparent transcoded (compressed) Fibre Channel 10GFC signal |
| ODU3 | 40.3192189830509 | Transport of up to 32 ODU0 signals or up to 16 ODU1 signals or up to four ODU2 signals or a STS-768/STM-256 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 |
| ODU3e2 | 41.7859685595012 | Transport of up to four ODU2e signals |
| ODU4 | 104.794445814978 | 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[3] | Transport of a constant bitrate signal such as Fibre Channel 8GFC, InfiniBand or Common Public Radio Interface |
| ODUflex (GFP) | any configured rate[3] | Transport of a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure |
Equipment
At a very high level the typical signals that OTN equipment at the Optical Channel layer processes are:
- OTN
- SONET/SDH
- Ethernet/FibreChannel
- Packets
A few of the key functions performed on these signals are:
- Protocol processing of all the signals . Some of the more complex processes are:
- Forward error correction (FEC) on OTN signals
- Multiplexing and de-multiplexing of OTN signals
- Mapping and de-mapping of non-OTN signals into and out of OTN signals
- Packet processing in conjunction with mapping/de-mapping of packet into and out of OTN signals
Switch fabric
The OTN signals at all data-rates have the same frame structure but the frame period reduces as the data-rate increases. As a result, the Time-Slot Interchange (TSI) technique of implementing SONET/SDH switch fabrics is not directly applicable to OTN switch fabrics. OTN switch fabrics are typically implemented using Packet Switch Fabrics.
FEC Latency
On a point-to-point OTN link there is latency due to forward error correction (FEC) processing.
See also
References
- ↑ ITU-T OTN definitions
- ↑ OTN offers transparent service delivery, Retrieved June 2, 2007
- 1 2 3 "ODU0 and ODUflex — A Future-Proof Solution for OTN Client Mapping" (PDF). TPACK A/S. February 2010. Archived from the original (PDF) on 12 March 2012.
External links
- Anritsu Poster - Details of all OTN areas including breakdown of the full frame
- Optical Transport Network (OTN) Tutorial, ITU-T, only covers G.709 (2003/03)
- OTN – Transporting Ethernet and SDH/SONET - JDSU Poster
