RE: RFC 4666 on Signaling System 7(SS7)Message TransferPart 3 (MTP3) - User Adaptation Layer (M3UA)

Tolga,

It would be possible to implement SCTP in an embedded on a NIC card with
dual ports for supporting multihoming and the UA layers running on the
host.  If the NIC card failed (OR if a Tier 4 support engineering
accidently unplugged a few power cables disabled a couple routers), we
could loose some associations while still keeping others.

Some type of "OPTIONAL" retrieval mechanism would go towards the 0%
message loss that SS7 is striving towards.  I'm not sure why you would
oppose such a mechanism if it is optional.  

Regards,
Lincoln

-----Original Message-----
From: Tolga Asveren [mailto:[email protected]] 
Sent: Thursday, September 21, 2006 9:33 AM
To: [email protected]
Cc: [email protected]
Subject: RE: [Sigtran] RFC 4666 on Signaling System 7(SS7)Message
TransferPart 3 (MTP3) - User Adaptation Layer (M3UA)

Satya,

If SCTP association to ASP11 is lost, this implies that ASP11 host is
down, because network redundancy is provided with SCTP multihoming and
proper IP network engineering. When ASP11 is down, there is no way to
retrieve anyhting. The possibility of loosing SCTP association without a
host failure should be guranateed to be below some acceptable threshold
value, i.e.
really really low.

BTW, your assumption of SCTP not being able to failover between paths
with no message loss is not correct. SCTP does this without message loss
and missequencing.

     Thanks,
     Tolga
-----Original Message-----
From: Satya Prasad Nemana
[mailto:[email protected]]
Sent: Thursday, September 21, 2006 9:27 AM
To: Tolga Asveren
Cc: [email protected]
Subject: Re: [Sigtran] RFC 4666 on Signaling System 7 (SS7)Message
TransferPart 3 (MTP3) - User Adaptation Layer (M3UA)


Tolga,

Consider the situation

SP1 is routing  ISUP messages to  AS1 (which has ASP11, ASP12) via SG-
SG1 in loadshared...
SG1 has sent 1000 msgs to AS1 via SCTP assoc of ASP11..
When SCTP assoc of ASP11 fails and AS1 has acked via SACK 940 msgs..
The current implementations do not have the capacity to retransmit the
remaining 60 msgs...
They are lost although we have ASP12 for redundancy purposes.

Considering the case of Multi Homing also...
even if ASP11 is multi homed and loses one path with a similar
situation, there is still no chance of retransmitting the msgs as M3UA
does not define any such method for retrieval ....

Regards,
Satya Prasad



Tolga Asveren wrote:

Satya,

In M3UA network redundancy is provided by SCTP multihoming and host
redundancy by using multiple ASPs for an AS.

For the configuration you are mentioning, if the ASP host is down, there
is no message retrieval possible in SS7 as well for the similar case. If
the SCTP association is lost to an ASP, this shouldn't happen due to
network problems (this property be guaranteed with SCTP multihoming and
proper IP network configuration) and should indicate a host failure.

     Thanks,
     Tolga


-----Original Message-----
From: Satya Prasad Nemana
[mailto:[email protected]]
Sent: Thursday, September 21, 2006 5:05 AM
To: [email protected]
Cc: [email protected]; [email protected]; [email protected]
Subject: Re: [Sigtran] RFC 4666 on Signaling System 7 (SS7) Message
TransferPart 3 (MTP3) - User Adaptation Layer (M3UA)



A general comment on ASP failover cases, M3UA does not have any method
of doing retrieval /retranamission Although SCTP does have the
capability through multi homing, the ULP should have the request in
place to do the retrieval/retransmission In the case of a single AS
having only a single ASP configured, there is no chance of retrieval
(but this is the most rare configuration as networks are configured  not
to go down with a single point of failure) In case the AS is configured
with two ASPs and each having a different SCTP assoc with a single path
in  each of the assoc..
there is no chance of message retrieval... as per the current rfc.

No idea if this was not felt important in a telecom network!!

[email protected] wrote:


A new Request for Comments is now available in online RFC libraries.


       RFC 4666

       Title:      Signaling System 7 (SS7) Message
                   Transfer Part 3 (MTP3) - User
                   Adaptation Layer (M3UA)
       Author:     K. Morneault, Ed.,
                   J. Pastor-Balbas, Ed.
       Status:     Standards Track
       Date:       September 2006
       Mailbox:    [email protected],
                   [email protected]
       Pages:      124
       Characters: 292991
       Obsoletes:  RFC3332
       See-Also:

       I-D Tag:    draft-ietf-sigtran-rfc3332bis-06.txt

       URL:        http://www.rfc-editor.org/rfc/rfc4666.txt

This memo defines a protocol for supporting the transport of any SS7
MTP3-User signalling (e.g., ISUP and SCCP messages) over IP using the
services of the Stream Control Transmission Protocol.  Also, provision
is made for protocol elements that enable a seamless operation of the
MTP3-User peers in the SS7 and IP domains.  This protocol would be used
between a Signalling Gateway (SG) and a Media Gateway Controller (MGC)
or IP-resident Database, or between two IP-based applications.  It is
assumed that the SG receives SS7 signalling over a standard SS7
interface using the SS7 Message Transfer Part (MTP) to provide
transport.  This document obsoletes RFC 3332.  [STANDARDS TRACK]

This document is a product of the Signaling Transport Working Group of
the IETF.

This is now a Proposed Standard Protocol.

STANDARDS TRACK: This document specifies an Internet standards track
protocol for the Internet community,and requests discussion and
suggestions for improvements.Please refer to the current edition of the
Internet Official Protocol Standards (STD 1) for the standardization
state and status of this protocol.  Distribution of this memo is
unlimited.

This announcement is sent to the IETF list and the RFC-DIST list.
Requests to be added to or deleted from the IETF distribution list
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Joyce K. Reynolds and Sandy Ginoza
USC/Information Sciences Institute

...



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