[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: comments on draft-shiba-ccamp-gmpls-lambda-labels-00.txt

shiba

Shiba, Sidney wrote:

[snip]


Another question might be:

 If I want to signal a path with wavelength constraints what
 information do I need to include in the signaling message?

shouldn't you ask the question, what's not workable with 
the present solution we have at hand in RFC3473 ?

I'd suggest that when we started on GMPLS, we were 
enthusiastic about transparent optical networks, but we were  
not properly focusing wavelength constraints because lambda-
switching PXCs didn't take off. 

Therefore we didn't examine the requirements for wavelength 
constraints in routing and signaling. The authors of this I-D 
are claiming new hardware requirements for the same function.

adrian, i am not sure to understand ... hence, i would like 
to know from authors how the following cornerstone problem has 
been solved

1. either the network is pre-engineered and you don't need to 
take care about any spectral routing specifics for traffic 
engineering purposes

[Sidney] In most of the cases, the network is pre-engineered using
spectral data, which will require a mapping effort. Of course, this
is feasable but we are proposing an approach that does not require
mapping effort when possible.

would it be possible that you provide with a real estimate of 
the effort required for such mapping - i did it and it just 
requires to have a single/common profile per wavelength/color 
that you can use based on the received label value index (in 
the pre-engineered case there properties are known)

[Sidney] An equipment that integrates an optical switch and mux/demux

can't use port mapping as the optical signal transmitted/received is 
a waveband. As an analogy, the optical signal transmitted/received by

a SONET equipment is OCn and it is mux/demux internally to individual
STS-nC facilities.

For the case of these new technology, the wavelength/frequency (nominal)
value is used to identify the facilities.

but then we are in agreement there is no added value in this specific 
case for having such LSC value space - is my deduction from your reply 
correct ?

2. or the network is not pre-engineered and i would like to 
know if the specifics of analog transmission/switching have been 
addressed such as to be compatible with the constraint-based routing 
mechanisms used today while keeping a low blocking probability

[Sidney] As I said previously, we might need to increase the scope 
of the draft to include wavelength availability information for the 
routing in order to keep low the blocking probability.

yes but this is where all complexity lies, as you don't know 
about the routing/selection of the wavelenght you are creating a 
closed loop such that your network will convergence problems; the 
major issue with lambda switching is that locality principle is not 
preserved, setting up a path in a non pre-engineered network implies 
that a reservation on a link can have impact on other link along the 
path but even on links that are not followed by that -

[Sidney] You touched a very important point. What I propose is to
extend the scope of this discussion to include the wavelength availability
as LSA routing information in order to allow path computation to take
into account wavelength continuity constraint. For scalability the following
structure could be used:

the issue here is the coupling between the spectral information to the 
TE routing advertisement, as the former does not respect any locality 
principle a given event may create instability in your TEDB (in fact it 
may never converge again)

the reason is that lighting up a certain path is not only disabling the 
lambda on the link where used but may also disable usage of certain 
frequencies on links that are not traversed by this LSC LSP; the latter 
can subsequently enable other wavelength(s) that were previously not 
possible ... hence, you can reach state where you would be oscillating 
when there is no appropriate pre-engineering of the network

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Start Frequency                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       Frequency spacing               | Number of Frequencies |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Frequency Availability Bitmap             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Frequency Availability Bitmap (cont)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


	- Start Frequency (32-bit) - this attribute indicates the first 
        frequency identified by the least significant bit in the Frequency 
        Availability bitmap field. IEEE Floating point value.
      - Frequency Spacing (20-bit) - this attribute indicates the spacing 
        (in MHz) between adjacent frequencies.
      - Number of Frequencies (12-bit) - this attribute indicates the number 
        of frequencies that is encoded in the Frequency Availability Bitmap 
        field.
      - Frequency Availability Bitmap (variable) - This variable length 
        attribute is a bitmap structure where each bit indicates if a frequency 
        is available or not. When set to 0, the frequency is available and when 
        set to 1 it indicates that the frequency is already in use. The least 
        significant bit (LSB) identifies the start frequency. The remaining bits 
        indicate the subsequent frequencies in decrement of spacing. For example,
        if bit0 = 195.70, bit1 = 195.60, bit2 = 195.50, and so on for a spacing 
        of 100 GHz. Each 32-bit word can encode the availability of 32 wavelengths.
        As an example, a 40 wavelength capable system, 2 x 32-bit data structure 
        is necessary, where bit40 - bit63 are padding bits.

the issue is not (only) about the representation (note that there are 
representation that are more efficient (it terms of encoding) than 
others) the issue is about feasibility,

there is another specific issue about the amount of information that 
would need to be flooded but more importantly - the homogeneity - you 
seem to assume that spacing/and other properties are homogeneously 
distributed but this is not necessarily the case; hence how a given 
system would be able to process information of other systems for which 
it is not capable to process the specifics