1. M3UA (MTP3-User Adaptation Layer)
<draft-ietf-sigtran-m3ua-02.txt>
******* SS7 ****** IP *******
* SP * * SG * *IP SEP*
******* ****** *******
| ISUP | < > | ISUP |
| MTP | <----> | MTP | M3UA | <----> | M3UA |
| L3 | <----> | L <---->
| L2 | <----> | L2 | SCTP | <----> | SCTP |
| L1 | <----> | L <---->
| | | | UDP | <----> | UDP |
SP - SS7 Signaling Point (SS7 SEP or STP)
IP SEP - IP-based Node (e.g., MGC, IP SCP, …)
User - MTP3-User Protocol (e.g., ISUP, SCCP, TUP, ..)
SCTP - Simple Common Transmission Protocol
Example

2. M3UA Principles
Supports MTP3-User Interface and Services (Transparent to MTP3-User)
Open/Closes SCTP Transport Associations
Starts/Stops Traffic across an open SCTP Association
Allows Flexible Message Distribution (e.g., SS7 OPC/DPC/SLS/CIC) to ASPs
ASP Fail-over support within AS list
N+k Redundancy Support
Load-balancing Support
Allows ASP signalling through redundant SGs to SS7 Network
Does not re-encode MTP-3 Routing Label / SIO in MTP-Transfer primitive
SCTP Stream Mapping

3. Changes in M3UA Issue 2
Removed explicit SCN Protocol Identifier & Protocol Identifier Parameters. Now use MTP3 SIO and/or Network Appearance (if required) 
Cleaned up SG configuration terminology (i.e., Routing Key, AS, ASP, Routing Context, SPMC, Network Appearance)
Expanded to include n+k redundancy, load-sharing
Better description of fail-over operation
Added Ability for ASP to route SS7 traffic across redundant SGs
Added Point Code Lists in SSNM Messaging (DUNA, DAVA, SCON…)
Made SSNM DAUD (Audit) more flexible

4. Changes - Continued
Added State Change Notification SG-ASPs in AS to allow better coordination
Use Cases Expanded
Added Optional M3UA-level Heartbeat

5. Current Issues
Impact of a future registration protocol component [M3UA, M2UA, IUA]  
Implementation-dependent Parameters or Messages [M3UA, M2UA, IUA] (Agreed but not added yet)  
New SS7 Network Unavailable message? [M3UA] (Agreed but not added yet)  
Nodal inter-working function still confusing? [M3UA]
More Use cases required in Section (Agreed but not added yet)
Timer provisional values required. [M3UA, M2UA, IUA]

6. Current Issues
ASP "graceful shutdown" case required? [M3UA, M2UA, IUA] Provide consistent use of MUST, SHALL, MAY etc as in rfc – see SCTP.
New Items from List:
Add possible case of SG sending UPU message into SS7 network when it determines that all ASPs in SPMC is no longer available, at least for a particular User Part.
TCP text proposal. Sentence or two in introduction of Adaptation layer docs and later Section/Annex with more info as agreed on Design Team call?  
IP to IP M3UA? Section possible to describe M3UA operation where two communicating points are in IP network with no need for an SG. Probably start with the idea that DUNA/DAVA/SCON/UPU and related procedures are omitted. Basis for BICC STC?

7. Current Issues
Specify explicitly Data recovery from a failed SCTP Association (e.g., to ASP1) to new SCTP Association (e.g., to to ASP2) – do we attempt this. Smells like SS7 Normal Change-over – is this appropriate? Recover Unsent (Tx Buffer) only or also Sent/Unacked.(RTx Buffer). Stringent requirements for duplicated MSUs may impact choice.   Other Ideas:
 SCON from ASP to SG to indicate ASP nodal congestion?

8. Status & Work Plan
<draft-ietf-sigtran-m3ua-02.txt> currently available
Issues List substantially reduced at the Washington Design Team Meeting
Draft 03 addressing above issues end-of-April at latest
Possible Last Call