Re: [Sigtran] Number of links towards a DPC (ITU)

["David Laight" <[e-mail]>]

> ITU has a 4-bit SLS and a 4 bit SLC.  The SLS and SLC is shared under
> ITU and ITU does not do SLS rotation.  Therefore, because 1 bit is used
> for link-set selection, there can only be 8 links in a linkset (16 links
> in a combined linkset).

In ITU each linkset can have 16 links.
Brian is right in that MTP3 only has a 4 bit SLS value to select the
destination link, so traffic to a specific destination will only use
a maximum of 16 links even if there are routes by 2 adjacents and there
are 16 links in the linkset to each.

If you have two linksets with 16 links each, the routing rules for
different destinations could be arranged to use different links
in order to utilise all 32 links.

> ANSI has an 8-bit SLS and a 5-bit SLC.  The SLS and SLC are not shared
> and ANSI does SLS rotation.  Therefore, it is possible to have 32 links
> in a linkset (64 links in a combined linkset).  Using the old 5-bit SLS
> it was only possible to have 16 links in a linkset and 32 links in a
> combined linkset because 1 of the 5 bits was used for linkset selection
> within a combined linkset.

ANSI only has 4 bits for the SLC (not 5), so a linkset is limited to 16 links.
However the larger SLS value (8 bits, 5 in some earlier versions)
means that MTP3 can loadshare between more links.

It also isn't quite right to say that one of the bits is used for
linkset selection. If some of the links are down, the sls that
would be assigned to the 'down' links are evenly spread across
all of the working links, not just assigned to the working links
in their original linkset (this might be a config option since
the ANSI and ITU specs differ here.)

An endsystem ITU MTP3 may have more SLS bits available, so could
loadshare between more than 16 links.

	David