question about RFC 3946

["Richard Rabbat" <richard.rabbat@us.fujitsu.com>]

Title: Message

Hi Dimitri, Eric, Jonathan,

I have a question about RFC 3946.

 

I'm trying to figure out how to understand text about setting NCC and RCC 
values for STS-3c and VC-4. Here's the context:

 

Quoting from RFC 3946:

 

   Note 1: when requesting a SONET STS-Nc SPE with N=3*X, the
      Elementary Signal to use must always be an STS-3c_SPE signal type
      and the value of NCC must always be equal to X.  This allows also
      facilitating the interworking between SONET and SDH.  In
      particular, it means that the contiguous concatenation of three
      STS-1 SPEs can not be requested because according to this
      specification, this type of signal must be coded using the STS-3c
      SPE signal type.

 

Note 1 implies that for SONET STS-3c SPE, NCC =1

 

   Note 2: when requesting a transparent STS-N/STM-N signal
      limited to a single contiguously concatenated STS-Nc_SPE/VC-4-Nc,
      the signal type must be STS-N/STM-N, RCC with flag 1 and NCC set
      to 1.

 

Note 2 seems to imply that for STS-3c_SPE/VC-4-1c, RCC = NCC = 1

 

Then later on:

 

   The NCC value must be consistent with the type of contiguous
   concatenation being requested in the RCC field.  In particular, this
   field is irrelevant if no contiguous concatenation is requested (RCC
   = 0), in that case it must be set to zero when sent, and should be
   ignored when received.  A RCC value different from 0 must imply a
   number of contiguous components greater than 1.

 

Given that RCC must be different from 0, the last sentence literally

says that an RCC value of 1 (thus different from 0) must imply that NCC > 1.

 

Going on to the examples of Annex 1:
   1.   A VC-4 signal is formed by the application of RCC with value 0,
        NCC with value 0, NVC with value 0, MT with value 1 and T with
        value 0 to a VC-4 Elementary Signal.
...
   8.   An STS-3c SPE signal is formed by the application of RCC with
        value 1 (standard contiguous concatenation), NCC with value 1,
        NVC with value 0, MT with value 1 and T with value 0 to an STS-
        3c SPE Elementary Signal.

 

So, what values of NCC and RCC should one use for STS-3c/VC-4?

--

Option 1-a:
Set NCC = RCC = 1 for STS-3c and VC-4. Example 1 of the annex is not the
RFC text and should not be followed.

 

Option 1-b:
Set NCC = RCC = 0 for STS-3c and VC-4. Example 8 of the annex is not the
RFC text and should not be followed.

 

Option 2:
Set NCC = RCC = 0 for VC-4 and NCC = RCC = 1 for STS-3c AND convert these
values when moving between SDH and SONET domains

 

Option 3:
Find some NCC-RCC combination that satisfies:
"  A RCC value different from 0 must imply a
   number of contiguous components greater than 1."

 

I sent email to Greg Bernstein, and he is of the opinion that options 1-a or 1-b are best.

If you also agree, we may need an errata along the lines:

 

Those would be the suggested changes.

 

FROM:
   The NCC value must be consistent with the type of contiguous
   concatenation being requested in the RCC field.  In particular, this
   field is irrelevant if no contiguous concatenation is requested (RCC
   = 0), in that case it must be set to zero when sent, and should be
   ignored when received.  A RCC value different from 0 must imply a
   number of contiguous components greater than 1.
TO:
   The NCC value must be consistent with the type of contiguous
   concatenation being requested in the RCC field.  In particular, this
   field is irrelevant if no contiguous concatenation is requested (RCC
   = 0), in that case it must be set to zero when sent, and should be
   ignored when received.  A RCC value different from 0 must imply a
   number of contiguous components greater than or equal to 1.
                                                ^^^^^^^^^^^^<- for option 1.a
FROM:
   1.   A VC-4 signal is formed by the application of RCC with value 0,
        NCC with value 0, NVC with value 0, MT with value 1 and T with
        value 0 to a VC-4 Elementary Signal.

 

   8.   An STS-3c SPE signal is formed by the application of RCC with
        value 1 (standard contiguous concatenation), NCC with value 1,
        NVC with value 0, MT with value 1 and T with value 0 to an STS-
        3c SPE Elementary Signal.
TO:
   1.   A VC-4 signal and an STS-3c SPE signal are formed by the
        application of RCC with value i, NCC with value i, NVC with
        value 0, MT with value 1 and T with value 0 to a VC-4 Elementary
        Signal and an STS-3c SPE Elementary Signal respectively.

        (RR: To replace i with 0 if we choose option 1a and 1 for option 1b)

 

   8.   An STS-3c SPE signal is formed as shown in example 1. RFC 3946's
        example 8 is now deprecated.
        In order to support earlier versions of the standard, a node
        should accept RFC 3946-compliant values of NCC = RCC = !i when
        receiving them until all known implementations have updated
        their code to the Errata.

        (RR: make sure we accept the other value)

Looking forward to your answer.

Richard.