RE: Client-server relation between two IPSPs

Ilie,

There are currently two modes of operation defined for IPSP:

a)Single-Exchange mode (SE-IPSP)
This is a true peer-to-peer relationship. AS defines traffic at both ends. A
single ASPAC/ASPAC-ACK exchange is sufficient to open the path for traffic.
the path is used  bidirectionally.

b)Double-Exchange mode (DE-IPSP)
This, you can think as two SGP/ASP relationships coupled where each path is
used unidirectionally. For each path ASPAC/ASPAC-ACK exchange is performed.

I know the above is a very short description and the existing text in the
documents is not the best to prevent confusion, but just hold on a few days
more for a more complete answer.

    Thanks,
    Tolga

> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Ilie Glib
> Sent: Monday, December 05, 2005 10:19 AM
> To: [email protected]
> Subject: [Sigtran] Client-server relation between two IPSPs
>
>
> Hello Folks,
>
> could you, please, clarify how the client-server relation is
> established between two IPSPs in all IP architecture (IPSP to IPSP).
> Is there any difference between SUA and M3UA?
>
> It seems most up-to-date description is for M3UA.
>
> I've found tree alternative answers.
>
> 1) Are client / server roles provisioned per IPSP to IPSP relation? So
> that one IPSP acts always as a client (for SCTP association
> establishment and subsequent SUA signalling) while the other acts as a
> server.
> This follows the old M3UAbis "
> - 1- IPSP Single Exchange (SE) model. One IPSP takes the role of the
> - client and the other the role of the server. The behavior then is
> - the same as the ASP-SGP scenario. An IPSP node following this
> - model will be named as C-IPSP (client node) or S-IPSP (server
> - node). The same node may act as a client with one peer IPSP and
> - server with another peer IPSP. Also upon common agreement the role
> - (client/server) of the IPSPs can be changed in different dialogs
> - between two IPSPs."
>
> 2) Alternatively, are both IPSPs trying to establish SCTP association
> and depending on what IPSP is first, it acts further as a client
> according to the following quote from the RFC 3868
> "5.2.1.  Establishment of SUA connectivity
> ...
> The endpoint that establishes SCTP
>    connectivity MUST also establish UA connectivity (see RFC 2960,
>    section 5.2.1 for handling collisions) [2960].
>
>    IP SEP A                                                  IP SEP B
>    AS A                                                          AS B
>    ASP-a1     ASP-a2                                 ASP-b2    ASP-b1
>
>    [All ASPs are in the ASP-DOWN state]
>
>    +-------------------------------ASP Up-------------------------->
>    <-----------------------------ASP Up Ack------------------------+
>
>                  +--------------ASP Up--------------->
>                  <------------ASP Up Ack-------------+
>
>    +---------------------------ACTIVE------------------------------->
>    <-------------------------ACTIVE Ack-----------------------------+
> "
>
> 3) new M3UAbis proposal
> " + 1- IPSP Single Exchange (SE) model. Only a single exchange of ASPTM
> + or ASPSM messages is needed to change the IPSP state. This means
> + that a set of request from one end and acknowledge from the other
> + will be enough.
> "
>
> Items 2) and 3) mean that an IPSP has to have provisioned as many ASes
> as there are remote SCCP/MTP entities, while item 1) reduces
> considerably the amount of required configuration.
> Item 3) improves network management and makes it possible to
> decativate a signalling relation from both sides, which was not
> possible before.
>
> Any opinions?
>
> Thank you in advance
>
> Ilie
>
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