Re: Question related with DAUD Message

Oscar,

Some implementations of SCCP provide local management primitives
that permit the SCCP-User to query the local SCCP-provider to
determine the state of subsystems and SCCP for associated point
codes.  For SUA ASP-SG operation, the SCCP-provider is at the SG
and the SCCP-User at the ASP.  DAUD provides a mechanism that
can be used by SCCP-Users at the ASP using legacy management
interfaces to peform a like function.

Other implementation of SCCP use the normal responsive method
described by ITU specifications.  Under the method when the
SCCP-User requests transfer of traffic (N-DATA-Request,
N-UNITDATA-Request) to unavailable subsystems, it is informed on
a responsive basis (N-INFORM-Indication) every 8 or 10 requests.
In this way the SCCP-User does not have to maintain state but
can blindly send messages.

Some SUA implementations might prefer to maintain SCCP-Provider
management state at the ASP.  Others might leave it at the SCCP
layer in the SG (where I think it belongs).  The DUNA procedures
provide a protocol mechanism to accomplish this.  An SUA
implementation that choses to maintain SCCP-Provider management
state at the ASP can use the explicit and periodic DAUD
procedures to keep that management state synchronized with the
SCCP-Provider at the SG.  An SUA implementation that chooses to
leave SCCP-Provider management state at the SG has little need
for periodic DAUD procedures.

As to whether multiple responses should be grouped into one
message or not, it is pretty much up to the SGP.  The form of
the response is usable.

At any point in time in the SS7 network, subsystems and remote
SCCPs are mostly available.  The easiest way to reduce the size
of SNMM messages sent in response to DAUD is to send SCON for
listing congested subsystems, then DAVA(*) indicating all
subsystems are available,  immediately followed by DUNA listing
only the unavailable subsystems/point codes (all sent ordered on
SCTP stream 0).  This should result in only two or three really
small messages.  Note also that subsystems are only informed of
the N-STATE and N-PCSTATE of subsystems and point codes for
which they are concerned (as indicated by the RC in the DAUD
message), which is also a short list.  SGs do not need to limit
the size of responses as management messages are rare compated
to traffic.  An ASP might want to somehow limit the rate at which
it sends DAUD(*) to better utilize the SCTP association, however,
it is up to the ASP how it wishes to utilize its available
bandwidth and the SG simply responds to any request.

IMO is not not up to the SG to limit sending the responses
either in size or frequency.  The ASP that wishes to avoid
inefficient use of the available bandwidth is welcome to send
fewer DAUD messages, or to send DAUD messages with a narrower
response (i.e. DAUD(5-5-5) instead of DAUD(*)).

I hope that addresses your questions with regard to DAUD.

--brian


Colmenares, Oscar (Oscar) wrote:             (Wed, 31 Jan 2007 08:43:55)
> 
> Sigtran Experts
> 
> 	I was looking for some help related with how to set the DAUD
> message, I was reading some message from HS Jang related when the ASP need
> to use the DAUD message, explain as follow
> 
> Let me summarize about DAUD in SUA ASP with your postings and my
> understanding. first of all,
>  1) ASP does not need to send DAUD in normal situation. because SCCP in SG
> cares it with its mechanism and inform the ASP of the changes in DPC/SSN
> with SSNM message. i.e. the state information about destinations are
> synchronized all the time.
>  2) the only time ASP needs to send DAUD is when the ASP is recovered from
> isolation because ASP has no state information about destinations now. ( but
> this is also not necessary for normal operation of data transfer. it is only
> necessary when ASP really wants to know the state information of
> destinations for example, in the respect of OAM or something ) 
> 3) there are mentions about sending DAUD periodically in RFC but it is
> somewhat wrong. 
> 	
> 	Now base on these explanation and related with point 2, send DAUD
> message when the ASP is recovered from isolation, my question is there is
> any rules in other to how to send these point codes?? do we have or must
> send multiple messages with one point code information per message, or send
> just one message with all the point codes information???
> 
> 	The main idea here is understand if I have a system with multiple
> point codes, for example 25 point codes, how the standard said we need to
> send the DAUD message, just one message with all the point codes inside or
> 25 single messages with just one point code per message.
> 
> I really appreciate your help on this question
> 
> Best regards
> 
> Oscar
> 
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-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/