Thursday, August 1, 2019

ODUk container


The ODUk container consists of 15240 bytes from the OPUk container plus 3 x 14 bytes of the ODUk OH. The total container capacity is therefore:  

•15240 bytes + (14bytes x 3 row) = 15282 bytes 


The information in the ODU OH, just to recap, consists of information related to the signal path. One of the functionalities this enables is to perform a signal trace. The user can assign a signal trace of the path, which the user can then have verified at the end of path. 

Saturday, July 27, 2019

Optical Transport Module (OTM-n.m, OTM-nr.m)


The OTM-n is the output from the OMS layer and is actually the signal that will be output onto the fiber. The OTM-m signal is the result of multiplexing all of the OCh payloads with the OSC signal (OOS). 

The OSC signal contains information related to:  
•The state of the clients' signals 
•Maintenance and operation functions of the OMS 
•Maintenance and operation functions of the OTS 
•General management communication between network equipment  

Putting it all together we have the visual representation below

The OTM also has a reduced version represented as OTM-nr.m where r represents reduced functionality. The primary difference between the two OTM-n.m and OTM-nr.m is that the reduced functionality version has no OSC. 

Tuesday, July 23, 2019

Optical Channel (OCh, OChr)


Now that the system has created all the information required and prepared it in a container of appropriate size for it to cross an OTH network and if necessary, for it to be regenerated, it is a requirement to provide an additional transparent network connection. The requirement for this transparent connection is due to the fact that to be able to direct and process client information - which is inside an OTUk remember – the system must be able to access the individual wavelength state without performing a full optical to electrical conversion. 



The way the OTH standard handles this is to use the OCh OH but instead of inserting it into the client carrier wavelength they utilize another wavelength channel altogether and this is the purpose of the OSC (optical supervisor channel) that has been mentioned in passing on several occasions. 

The OSC is carried on a frequency out with the carrier wavelength spectrum so that it does not interfere with the carrier wavelengths. Furthermore all vendor active network equipment has electrical access to this OSC channel. The OSC is the only signal, which all OTH compliant equipment can access.
Consequently if any piece of equipment on the optical path detects a client signal failure (loss of signal) it will process the corresponding OCh OH to inform the other system equipment about the state of the client wavelength. 

Note: There are two versions of the optical channel OCh & OChr.  The non-standard version is called OChr, where 'r' represents the reduced version that does not insert an OCh OH into the OSC wavelength.


Friday, July 19, 2019

Optical Channel Transport Unit (OTUk, OTUkV)


With the introduction of an overhead into each client signal as is representative of that signal only, it becomes necessary to introduce a further OH that will provide information to equipment handling regeneration. The information the equipment uses to perform this task is inserted into the OTU overhead (OTU OH). This information relates to the maintenance and operation functions to support the optical channel section. 

These functions include:  
•Functionalities of section monitoring 
•General communication channel 
•Reserved bits 


This unit also contains information that defines the use of a FEC (forward error control) as a way to improve signal quality and reliability. This unit is represented as follows: 
ODUk 
OTUk 
ODU1 
OTU1 
ODU2 
OTU2 
ODU3 
OTU3 
ODU4 
OTU4 

The OTU terminates at the point of assembly/disassembly and this is identical to the regeneration overhead in SDH. Note: The standard defines that the use of several types of FEC is possible though the only one standardized at the time was RS (255,239) the type of FEC used now though is based on Reed-Solomon and it is used to define the OTUk. Other possibilities of FEC are inserted into the OTUkV.