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SDH/SONET label
All,
let me start a final attempt on the label issue, even so we already spent a lot of time on it with out progress.
Juergen
1. The proposal is to use the same SUKLM coding for SDH and SONET. The reason is that SDH and SONET have the same multiplex structure with the exception that SONET doesn't support sub-structured STS-3c-SPEs and SDH doesn't support VT-3. A SDH VC-4 and a SONET STS-3c-SPE are identical signals, the same applies to SDH VC-11 in a higher order VC-3 and SONET VT-1.5 in a STS-1-SPE. So why should we use different SUKLM coding for identical signals as it is the case with the current definition.
Using different codings means that we always have to check and test both codings when we introduce new features. It might even happen that we can use a new feature only for one coding and not for the other due to the differences in coding. We should learn from the interwroking problems in the passt due to differences in SONET and SDH and try to avoid such differences.
So the proposal has technical benefits in my view. It saves implementation and test efforts and problems in the future.
2. My concrete proposal was to use the SDH coding also for SONET by introducing a STS-3 group.
T1.105 already defines this in section 10.1.1
"From the Standard OC-N Rates (table 1), it is observed that the rates above OC-1 are multiples of the OC-3 rate. Three STS-1 input signals shall be interleaved one byte at a time to form the STS-3 signal.....
To form a higher level signal STS-N (N = 3M; M = 1,4,8,16,64), M STS-3s shall be interleaved one byte at a time....."
Eric mentioned that he sees problems with the proposal in case of STS-X SPE forwarding adjacencies that are not multiples of 3 (X<>3N, e.g. STS-5 SPE) as they don't fill full STS-3 groups. However if this is the case the same problem already applies to the currently defined SDH higher order VC-3 coding. Eric mentioned further that it is not a big problem as it is possible to work with partial filled STS-3 groups. So not an issue in my view.
3. Eric mentioned that the existing definition is validate and he doesn't want to introduce late changes that force vendors to change their implementation. My proposal is not a new definition it uses the already defined and validated SDH coding for SONET. So if the SDH coding is validated my proposal works. Vendors just can take the SDH implementation and use if also for SONET. Furthermore what is the purpose of a last call if no changes can be introduced. The proposal to use the same coding is already on the table for over half a year. It was rejected/ignored without any reasonable arguments in my view.
4. Looking further on the current label definition I found two inconsistencies.
First the STS-3c-SPE signal type is not considered. In the signal type definition it is state
"A dedicated signal type is assigned to a SONET STS-3c SPE instead
of coding it as a contiguous concatenation of three STS-1 SPEs.
This is done in order to provide easy interworking between SONET
and SDH signaling."
The label definition mentions contiguous concatenation, but it is not clear about STS-3c-SPE as it is not coded as contiguous concatenation.
The introduction of the STS-3 group now also indicates that if a STS-3 group is already occupied by one or more STS-1 SPE it can no longer be used by a STS-3c-SPE. This is in according to the T1.105 defnitions for a STS-3c
"When STS-3c signals are multiplexed to a higher rate, each STS-3c shall be wholly contained within an STS-3 as shown in figure 40, Two-stage interleaving (i.e., occur only on tributary input boundaries 1-3, 4-6, 7-9, etc.)."
Second the definition of the L value has a problem. It says
" 4. L indicates a specific branch of a TUG-3, VC-3 or STS-1 SPE.
It is not significant for an unstructured VC-4 or STS-1 SPE. L=1
indicates that the TUG-3/VC-3/STS-1 SPE is not further
subdivided and contains a VC-3/C-3 in SDH or the equivalent in
SONET. L=2->8 indicates a specific TUG-2/VT Group inside the
corresponding higher order signal. "
The second sentence says that it is not significant for unstructured STS-1 SPE while the third sentence says that L=1 has to be used for a unstructured STS-1 SPE.
I repeat my proposal below with slight modifications due to the inconsistencies indicated above:
The format of the label for SDH and/or SONET TDM-LSR link is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S | U | K | L | M |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For SDH, this is an extension of the numbering scheme defined in
G.707 section 7.3, i.e. the (K, L, M) numbering. For SONET, the same
signaling scheme is used in order to provide easy interworkign between
SDH and SONET signaling. For the S field a STS-3 group,which
corresponds with the SDH AUG-1 level is introduce. The U field indicates
the position of the STS-3c-SPE or STS-1-SPE within the STS-3 group.
Each letter indicates a possible branch number starting at the
parent node in the multiplex structure. Branches are considered as
numbered in increasing order, starting from the top of the
multiplexing structure. The numbering starts at 1, zero is used to
indicate a non-significant field.
When a field is not significant in a particular context it MUST be
set to zero when transmitted, and MUST be ignored when received.
When hierarchical SDH/SONET LSPs are used, an LSP with a given
bandwidth can be used to tunnel lower order LSPs. The higher
order SDH/SONET LSP behaves as a virtual link with a given
bandwidth (e.g. VC-3), it may also be used as a Forwarding
Adjacency. A lower order SDH/SONET LSP can be established through
that higher order LSP. Since a label is local to a (virtual) link,
the highest part of that label is non-significant and is set to
zero.
For instance, a VC-3 LSP can be advertised as a forwarding
adjacency. In that case the labels allocated between the two ends
of that LSP (i.e. for that "link") will have S, U and K set to
zero, i.e., non-significant, while L and M will be used to
indicate the signal allocated in that VC-3.
1. S is the index of a particular AUG-1/STS-3 group. S=1->N
indicates a specific AUG-1/STS-3 group inside an STM-N/STS-3xN
multiplex. For example, S=1 indicates the first AUG-1/STS-3 group,
and S=N indicates the last AUG-1/STS-3 group of this multiplex.
S is not significant for STM-0/STS-1.
2. U indicates a specific VC/STS-SPE inside a given AUG-1/STS-3
group or STM-0/STS-1. U=1 indicates a single VC-4/STS-3c-SPE in a
AUG-1/STS-3 group or the single VC-3/STS-1-SPE in a STM-0/STS-1, while U=2->4
indicates a specific VC-3/STS-1-SPE inside the given AUG-1/STS-3
group.
3. K is only significant for VC-4/STS-3c and must be ignored for
higher order VC-3/STS-1-SPE. For SDH it indicates a specific branch of a VC-4.
K=1 indicates that the VC-4 is not further subdivided and
contains a C-4. K=2->4 indicates a specific TUG-3 inside the VC-4.
For a SONET STS-3c-SPE it is fixed to K=1 as SONET doesn't support
substructured STS-3c-SPE.
4. L indicates a specific branch of a TUG-3, VC-3 or STS-1 SPE.
It is not significant for an unstructured VC-4/STS-3c-SPE. L=1
indicates that the TUG-3/VC-3/STS-1 SPE is not further
subdivided and contains a VC-3/C-3 in SDH or the equivalent in
SONET. L=2->8 indicates a specific TUG-2/VT Group inside the
corresponding higher order signal.
5. M indicates a specific branch of a TUG-2/VT Group. It is not
significant for an unstructured VC-4, STS-3c-SPE, TUG-3, VC-3 or STS-1 SPE.
M=1 indicates that the TUG-2/VT Group is not further subdivided
and contains a VC-2/VT-6 SPE. M=2->3 indicates a specific VT-3
inside the corresponding VT Group, these values MUST NOT be used
for SDH since there is no equivalent of VT-3 with SDH. M=4->6
indicates a specific VC-12/VT-2 SPE inside the corresponding
TUG-2/VT Group. M=7->10 indicates a specific VC-11/VT-1.5 SPE
inside the corresponding TUG-2/VT Group. Note that M=0 denotes
an unstructured VC-4, VC-3 or STS-1 SPE (easy for debugging).
The M encoding is summarized in the following table:
M SDH SONET
----------------------------------------------------------
0 unstructured VC-4/VC-3 unstructured STS-1 SPE
1 VC-2 VT-6
2 - 1st VT-3
3 - 2nd VT-3
4 1st VC-12 1st VT-2
5 2nd VC-12 2nd VT-2
6 3rd VC-12 3rd VT-2
7 1st VC-11 1st VT-1.5
8 2nd VC-11 2nd VT-1.5
9 3rd VC-11 3rd VT-1.5
10 4th VC-11 4th VT-1.5
In case of contiguous concatenation, the label that is used is the
lowest label of the contiguously concatenated signal as explained
before. The higher part of the label indicates where the signal
starts and the lowest part is not significant. For instance, when
requesting an VC-4-16c the label is S>0, U=0, K=0, L=0, M=0.
Examples of labels:
Example 1: S>0, U=1, K=1, L=0, M=0
Denotes the unstructured VC-4/STS-3c-SPE of the Sth AUG-1/STS-3 group.
Example 2: S>0, U=1, K>1, L=1, M=0
Denotes the unstructured VC-3 of the Kth-1 TUG-3 of the Sth AUG-1.
Example 3: S>0, U>1, K=0, L=1, M=0
Denotes the Uth unstructured VC-3/STS-1 SPE of the Sth AUG-1/STS-3 group.
Example 4: S>0, U>1, K=0, L>1, M=1
Denotes the VC-2/VT-6 in the Lth-1 TUG2/VT Group in the Uth VC-3/STS-1 SPE of the Sth AUG-1/STS-3 group.
Example 5: S>0, U>1, K=0, L>1, M=9
Denotes the 3rd VC-11/VT-1.5 in the Lth-1 TUG2/VT Group in the Uth VC-3/STS-1 SPE of the Sth AUG-1/STS-3 group.
Example 6: S>0, U=1, K>1, L>1, M=5
Denotes the 2nd VC-12 in the Lth-1 TUG2 in the Kth TUG3 in the VC-4 of the Sth AUG-1.