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Hi,
Since SLS parameter is not available in SUA layer, and Sequence Control
has a one to one mapping with SLS, is Sequence control used for
"loadsharing based on SLS" in SUA.
>From RFC Q.714
In protocol class 1, the features of class 0 are complemented by an
additional feature (i.e. the
sequence control parameter contained in the N-UNITDATA request
primitive) which allows the
higher layer to indicate to the SCCP that a given stream of NSDUs shall
be delivered in-sequence.
The Signalling Link Selection (SLS) parameter in the MTP-TRANSFER
request primitive is chosen
by the originating SCCP based on the value of the sequence control
parameter. The SLS shall be
identical for a stream of NSDUs with the same sequence control
parameter. The MTP then encodes
the Signalling Link Selection (SLS) field in the routing label of MTP
messages relating to such
NSDUs, so that their sequence is, under normal conditions, maintained by
the MTP and SCCP. With
the above constraints, the SCCP and MTP together ensure in-sequence
delivery to the user. Thus,
this protocol class corresponds to an enhanced connectionless service,
where an additional
in-sequence delivery feature is included.
>From RFC 3868
The field is coded with the value of the sequence control parameter
associated with a group of messages and are chosen so as to ensure
proper loadsharing of message groups over SLS values while ensuring
that sequence control values within message groups have the sequence
control value coded with the same value as the initial message of the
message group.
Regards
Amrita Garg
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