Monday, January 28, 2013


Ok, let's talk about IP over DWDM.

This post includes:

  1. Optical channel payload unit (OPU)
  2. Optical channel data unit (ODU)
  3. Optical channel transport unit (OTU)
  4. Optical channel (OCh)
  5. Shared Risk Link Group (SRLG)
  6. Virtual Transponder (VTXP)
  7. FEC-FRR Triggering
  8. Optical Parameters - Rx-los-threshold, Wavelength and Transmit-power
  9. G.709 Parameters

Long story short:
  • integration of DWDM technology into the router
  • GMPLS-UNI interface from the router to the DWDM network
  • Advanced DWDM control plane - GMPLS/WSON
Supported platforms:
  • CRS-1/3
  • ASR9K
  • 12K
  • 7600
  • or any platform with tunable WDM optics support
  1. IPoDWDM and IP NGN Core Design - deep dive
  2. Cisco Live 2010 (Las Vegas) - IPoDWDM: 40G 100G and Beyond (BRKOPT-2115).
  3. Cisco Live 2012 (London) - Converged Architecture for IP + Optical, multi-Terabit Routing, Control Plane (BRKSPG-2606) - this one is really good overview
  4. White Paper: Converge IP and DWDM Layers in the Core Network
  5. ITU-T G.709: Interfaces for the optical transport network
  6. Wikipedia: G.709
  7. Cisco 7600 ES+ line cards: Configuring IPoDWDM
  8. Configuring Dense Wavelength Division Multiplexing Controllers on Cisco IOS XR Software
  9. Configuring Dense Wavelength Division Multiplexing Controllers on the Cisco ASR 9000 Series Router
  10. Dense Wavelength Division Multiplexing Commands on the Cisco IOS XR Software

Optical Transport Network


From Cisco Config Guide[8]:

DWDM support in Cisco IOS XR software is based on the Optical Transport Network (OTN) protocol that is specified in ITU-T G.709. This standard combines the benefits of SONET/SDH technology with the multiwavelength networks of DWDM. It also provides for forward error correction (FEC) that can allow a reduction in network costs by reducing the number of regenerators used.
To enable multiservice transport, OTN uses the concept of a wrapped overhead (OH). To illustrate this structure:
  • Optical channel payload unit (OPU) OH information is added to the information payload to form the OPU. The OPU OH includes information to support the adaptation of client signals.
  • Optical channel data unit (ODU) OH is added to the OPU to create the ODU. The ODU OH includes information for maintenance and operational functions to support optical channels.
  • Optical channel transport unit (OTU) OH together with the FEC is added to form the OTU. The OTU OH includes information for operational functions to support the transport by way of one or more optical channel connections.
  • Optical channel (OCh) OH is added to form the OCh. The OCh provides the OTN management functionality and contains four subparts: the OPU, ODU, OTU, and frame alignment signal (FAS). 

Basically, all IPoDWDM topics are described in Configuring Dense Wavelength Division Multiplexing Controllers on the Cisco ASR 9000 Series Router document.

Shared Risk Link Group (SRLG)

From Cisco white paper:
The Shared Risk Link Group (SRLG) feature on the Cisco ONS 15454 allows the sharing of DWDM risk information between the optical layer and the IP layer. Typically the IP part of a network is not aware of existing DWDM physical connectivity when performing routing decisions. The advent of multi-degree ROADM technology and IPoDWDM makes SRLG a valuable feature for planning routes that help ensure survivability against all DWDM signal faults and for increasing utilization.
Configuring the SRLG and Optical Layer DWDM Ports
IOS XR Example - The following example shows how to configure a Shared Risk Link Group (SRLG) and Optical Layer DWDM ports:
RP/0/RP0/CPU0:Router# configure
RP/0/RP0/CPU0:Router(config)# controller dwdm 0/1/0/1
RP/0/RP0/CPU0:Router(config-dwdm)# network srlg value1 value2 value3
RP/0/RP0/CPU0:Router(config-dwdm)# network port id 1/0/1/1
RP/0/RP0/CPU0:Router(config-dwdm)# network connection id 1/1/1/1  

Virtual Transponder (VTXP)

From Cisco manual:
Virtual transponder feature allows you to configure the L1 parameters of a Cisco 7600 IPoDWDM line card from an ONS 15454 MSTP Network Craft Terminal (CTC). Using this feature, you can monitor port status, and retrieve monitoring points such as Optical Power, Q Factor, BER, Alarm Status, and so on.
Basically, it is a "feature"to hide IPoDWDM functionality of the router and represent it as a standard old good transponder. The reason for doing this - old network management software.

FEC-FRR Triggering

See [8].

Found interesting note regarding FEC support here:
The enhanced FEC mode supported on the Cisco CRS Router (ITU-T G.975.1 I.7) and the Cisco ASR 9000 Series Router (ITU-T G.975.1 I.4) are different and therefore, incompatible. To support interoperability of DWDM between these routers, standard FEC must be configured. The OC-768c/STM-256c DWDM PLIM on the Cisco CRS Router supports enhanced FEC mode only. Disabling FEC or enabling standard FEC is not supported.
IOS XR Example: 
RP/0/RP0/CPU0:Router# configure
RP/0/RP0/CPU0:Router(config)# controller dwdm 0/1/0/1
RP/0/RP0/CPU0:Router(config-dwdm)# proactive
RP/0/RP0/CPU0:Router(config-dwdm)# logging signal LogFile1
RP/0/RP0/CPU0:Router(config-dwdm)# proactive trigger threshold 1 9
RP/0/RP0/CPU0:Router(config-dwdm)# proactive trigger window 10000
RP/0/RP0/CPU0:Router(config-dwdm)# proactive revert threshold 1 9
RP/0/RP0/CPU0:Router(config-dwdm)# proactive revert window 600000 

G.709 Parameters 

See [8].

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