RFC 4129
Digital Private Network Signaling System (DPNSS)/Digital Access Signaling System 2 (DASS 2) Extensions to the IUA Protocol
RFC 4129: Digital Private Network Signaling System (DPNSS)/Digital Access Signaling System 2 (DASS 2) Extensions to the IUA Protocol 🎀
okay bestie, the title block is giving everything 📋✨
- Network Working Group 🌸
- RFC 4129, category Standards Track 🦋
- Dated August 2005 📅
- Written by R. Mukundan (Wipro Technologies), K. Morneault (Cisco Systems), and N. Mangalpally (Nortel Networks) 👑
- The title block doesn't list anything this one obsoletes or updates 💅
Status of This Memo 💅
okay so this doc is an Internet standards track protocol for the Internet community 🌈 it's asking everyone to talk about it and send ideas for making it better. for the official standardization status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1) 📖. and yes, distribution of this memo is unlimited 🫶
Copyright Notice 🌸
Copyright (C) The Internet Society (2005). 💖
Abstract ✨
so this doc is all about backhauling DPNSS 1 and DASS 2 messages over IP 🌐 it does that by extending the ISDN User Adaptation (IUA) Layer Protocol from RFC 3057 🎀 DPNSS 1 is specified in ND1301:2001/03 (formerly BTNR 188) and it's what connects PBXs inside a private network 🏢 DASS 2 is in BTNR 190 and it connects PBXs to the PSTN 📞 the goal is for this to become an Appendix to IUA and to be the base for a DPNSS 1/DASS 2 User Adaptation (DUA) implementation. main character energy 👑🔥
Table of Contents 🧚
1. Introduction ................................................. 2
1.1. Scope .................................................. 2
1.2. Terminology ............................................ 3
1.3. DPNSS Overview ......................................... 4
1.4. Proposed DPNSS Backhaul Architecture ................... 5
2. Changes from IUA ............................................. 5
2.1. New Message Class for DUA .............................. 5
2.2. Message Header ......................................... 6
2.3. Unit Data Message ...................................... 7
2.4. DLC Status Message ..................................... 7
2.5. Management (MGMT) Messages ............................. 9
3. IANA Considerations .......................................... 10
4. Use of SCTP Payload Protocol ID .............................. 10
5. Message Sequence in DUA ...................................... 11
5.1. Resetting of single DLC ................................ 11
5.2. Resetting all DLCs in a Link ........................... 11
5.3. Information Transfer on a DLC .......................... 12
5.4. Link Takedown (Single DLC) ............................. 12
5.5. Link Takedown (All DLCs) ............................... 12
5.6. Getting Link Status .................................... 12
5.7. Error Conditions ....................................... 12
6. Security Considerations ...................................... 13
7. References ................................................... 13
7.1. Normative References ................................... 13
8. Acknowledgements ............................................. 131. Introduction ✨
okay so this section explains how to do DPNSS 1 [2] (just "DPNSS" from here on) and DASS 2 [3] backhaul messaging over IP 🌐 it uses a modified version of the ISDN User Adaptation Protocol (IUAP) [1]. the DPNSS/DASS 2 User Adaptation (DUA) builds on top of IUA 🎀 by defining the extensions IUA needs for a DPNSS/DASS2 implementation. it's giving layered cake 🍰
1.1. Scope 🦋
there's a need to deliver Switched Circuit Network (SCN) signaling from a DPNSS Signaling Gateway (SG) to a Media Gateway Controller (MGC) 📦 the delivery mechanism should support these protocols:
- DPNSS (Digital Private Network Signaling System) [2]
- DASS 2 (Digital Access Signaling System Number 2) [3]
unless it's specifically mentioned, everything in this doc applies to both DPNSS and DASS 2 💅
1.2. Terminology 📖
okay the vocab list, bestie 🧠
Data channel (D-channel): a 64 kbit/s time slot that works as a common signaling channel on a 2048 kbits/s interface or a 1544 kbits/s interface that's provisioned to carry DPNSS signaling 📡
DPNSS channel: time slots 1 to 15 and 17 to 31 on a 2048 kbits/s interface, or time slots 1 to 23 on a 1544 kbits/s interface, are called DPNSS channels 🎀 these are the traffic channels that carry voice or data.
- DPNSS supports 60 Channels (30 Real and 30 Virtual)
- DASS2 supports 30 Channels (All Real)
Data Link Connection(DLC): a DLC is the level 2 process that controls the transfer of level 3 messages on behalf of one DPNSS channel 💖 each DLC uniquely identifies one DPNSS channel 🫶
- DPNSS supports 60 DLCs (30 Real and 30 Virtual)
- DASSII supports 30 DLCs (All Real)
DPNSS Link: a logical collection of the D-channel and the associated DPNSS channels on a 2048 kbits/s interface or a 1544 kbits/s interface is called a "DPNSS Link" 🔗
Real channel: a signalling channel with an associated traffic channel (TS) ✨
Virtual channel: a signalling channel with no associated traffic channel 🌙
NT1: the DPNSS minimum retransmission period ⏱️
NT2: the DPNSS minimum post retransmission acknowledgement delay ⏳
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [5]. these are the official BCP 14 power words, so they're the ones with the real force 💪
1.3. DPNSS Overview 🌈
so DPNSS is an industry standard interface (ref. ND1301:2001/03) [2] that's defined between a PBX and an Access Network (AN) 🏢 it extends the features that normally only work between extensions on one PBX so they work across all extensions on PBXs connected in a private network 🤝 DPNSS was originally derived from BT's Digital Access Signaling System I (DASS I) and was enhanced where needed for private networks. some of those enhancements made it into DASS 2 [3] 💅 DPNSS runs on a 2048 kbits/s or 1544 kbits/s Digital Transmission System Interface, as shown in Figure 1 below 📊
---------- ---------- o--o
| | 2048 kbits/s | |------- /\
| |--------------| | --
| PBX | 1544 kbits/s | AN |
| |--------------| | o--o
| | | |------- /\
---------- ---------- --
Figure 1channel 16 is on the 2048 kbits/s (E1) interface, and channel 24 is on the 1544 kbits/s (T1) interface 🎀 both are reserved for data communication between LE and AN. the reserved data channels are called "Data Channels" or "D-Channels" 💖
the D-Channels are the physical media used to swap data between the DPNSS protocol peer entities 🔄 a logical collection of the D-channel and the associated DPNSS channels is called a "DPNSS Link" 🔗
1.4. Proposed DPNSS Backhaul Architecture 🦋
here's the proposed picture, bestie 🖼️
****** DPNSS ****** IP *******
*PBX *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|DPNSS| (NIF) |DPNSS|
| L3 | | L3 |
+-----+ +----------+ +-----+
| | | | DUA| | DUA |
|DPNSS| |DPNSS+----+ +-----+
| L2 | | L2 |SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP + | IP |
+-----+ +-----+----+ +-----+the abbreviations, in case you forgot 📝
- NIF: Nodal Interworking function
- SCTP: Stream Control Transmission Protocol
- DUA: DPNSS User Adaptation Layer Protocol
2. Changes from IUA 💅
this section lays out how DUA is different from IUA 🌸
2.1. New Message Class for DUA 🎀
so the DPNSS/DASS2 Layer 2 to Layer 3 primitives [2] [3] need to be easy to tell apart from IUA boundary primitive transport messages and from the boundary primitive transport messages of other IUA extensions (for example V5 or GR-303) 🔍 that's why DUA messages need a different message class parameter.
for all DPNSS/DASS2 interface boundary primitives, a new Message Class gets introduced:
13 DPNSS/DASS2 Boundary Primitives Transport Messages
(DPTM)just like IUA, the other valid message classes for DUA are:
0 Management (MGMT) Message
3 ASP State Maintenance (ASPSM) Messages
4 ASP Traffic Maintenance (ASPTM) Messages2.2. Message Header 🧚
the IUA Message Header [1] MUST be used with the DPTM messages 💖 the one difference is that the DLCI field in the DLCI parameter is formatted differently 🦋 here's the IUA Message Header with an integer-based Interface Identifier:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Identifier (integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x5) | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DLCI | Spare |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 IUA Message Header (integer-based Interface Identifier)in DUA, the DLCI field has its own format, following ND1301:2001/03 (formerly BTNR 188) [2] ✨
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |V|0|Channel No.|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Reserved: 7 bits. Should be set to all '0's and ignored by the receiver. 🙈
V-bit: 1 bit. the V-bit tells you whether the message is for one particular DLC or for all the DLCs in the carrier 🔥 these are the possible values:
Value Description
0 Action is to be performed on all DLCs;
Channel number parameter is ignored.
1 Action is to be performed on a single
DLC specified by channel number.this V-bit value is only used by the Establish and Release messages 🫶 data messages should ignore it. the indicator exists so one single command can establish or release all the DLCs in one DPNSS Link, which is honestly iconic 👑
for Channel Number (Channel No.), the valid values are 0 to 63 for DPNSS and 0 to 31 for DASS 2 🌸 that's because DASS 2 doesn't support virtual DLCs, so it only has 32 DLCs. not me being like "wait, that's the whole reason" 💀
Part 1 of 3 is a wrap, bestie 🦋 part 2 is coming up next, so stay tuned 💜✨
2.3. Unit Data Message 🎀
okay so DPNSS layer 2 doesn't have a unit data primitive 🙅♀️, which means the Unit Data Messages (Request, Indication) are invalid for a DUA application 💀. instead, DUA uses the Data Request and Indication messages (message types 1 and 2, respectively) 🦋
2.4. DLC Status Message 💅
bestie, DUA needs a brand new message to carry the status of the DLCs ✨. this one is a Management message, so its message class is 0 for Management 🌸. these are the message types for it:
5 DLC Status Request
6 DLC Status Confirm
7 DLC Status Indicationthe DLC Status messages get swapped between DUA layer peers to request, confirm, and indicate the status of the DLCs 🫶. they start with the common message header, followed by the IUA message header, as described in section 2.2 💖
the DLC Status Confirm and Indication messages also carry the brand new DLC Status parameter 🧚. for an E1 interface, the parameter looks like this:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x12) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA| D1| D2| D3| D4| D5| D6| D7| D8| D9|D10|D11|D12|D13|D14|D15|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA|D17|D18|D19|D20|D21|D22|D23|D24|D25|D26|D27|D28|D29|D30|D31|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA|D33|D34|D35|D36|D37|D38|D39|D40|D41|D42|D43|D44|D45|D46|D47|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA|D49|D50|D51|D52|D53|D54|D55|D56|D57|D58|D59|D60|D61|D62|D63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+NA means Not Applicable 🙈. D0 and D16 are N/A on E1 because timeslot 0 handles E1 framing and synchronization bits, and timeslot 16 handles signaling 📡. for DPNSS you get a max of 60 DLCs (30 real + 30 virtual) 🔥, and for DASS2 you get 30 DLCs (no virtuals) 💜
for a T1 interface, the parameter looks like this:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (0x12) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D0| D1| D2| D3| D4| D5| D6| D7| D8| D9|D10|D11|D12|D13|D14|D15|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D16|D17|D18|D19|D20|D21|D22| NA|D24|D25|D26|D27|D28|D29|D30|D31|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA|D33|D34|D35|D36|D37|D38|D39|D40|D41|D42|D43|D44|D45|D46| NA|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+D23 is N/A on T1 because timeslot 23 is used for signaling 🙃. for DPNSS that's a max of 46 DLCs (23 real + 23 virtual), and DASS2 gets 23 DLCs (no virtuals) ✨
the parameter tracks DLC status with two bits per DLC 🎀. here's what the possible values mean:
Value Description
00 Out Of Service
01 Reset Attempted
10 Reset Completed
11 Information Transferfor DASS 2, the value 00 (Out Of Service) is invalid, because DASS 2 DLCs don't have that state 💀. also, the Idle state is a transient state local to the DLC, so it doesn't get a value allocated 🙅♀️
DASS 2 has no virtual DLCs, so only 32 DLCs' worth of info needs to be carried 🌈. that's why the status message has a length of 12 for a DASS 2 DLC Status message 🦋
2.5. Management (MGMT) Messages 🫧
only the Notify and Error messages are valid for DUA 💅. the TEI Status messages aren't used at all 🙈
2.5.1. Error Message 🚨
the ERR message gets sent when an invalid value or an unrecognized message shows up in an incoming message 😭
the Error Code parameter tells you the reason for the Error Message 🔍. these are the values IUA supports:
Invalid Version 0x01
Invalid Interface Identifier 0x02
Unsupported Message Class 0x03
Unsupported Message Type 0x04
Unsupported Traffic Handling Mode 0x05
Unexpected Message 0x06
Protocol Error 0x07
Unsupported Interface Identifier Type 0x08
Invalid Stream Identifier 0x09
Unassigned TEI 0x0a
Unrecognized SAPI 0x0b
Invalid TEI, SAPI combination 0x0c
Refused - Management Blocking 0x0d
ASP Identifier Required 0x0e
Invalid ASP Identifier 0x0fin DUA, error codes 0x0a, 0x0b, and 0x0c are invalid, since they're ISDN-specific 🚫
DUA also supports these extra error codes 💖:
Channel Number out of range 0x1c
Channel Number not configured 0x1dthe "Channel Number out of range" error gets sent if a message comes in with a channel number greater than 63 for DPNSS or 31 for DASS 2 🔢
the "Channel Number not configured" error gets sent if a message comes in with a channel number that isn't configured 🙅♀️
3. IANA Considerations 📋
IANA assigned a DUA value for the SCTP Payload Protocol Identifier field, the one used in SCTP Payload Data chunks 🧾. the following value SHOULD be used for DUA in that field:
SCTP Payload Protocol ID = "10"4. Use of SCTP Payload Protocol ID 🎀
okay so, as an option, the IUA value for SCTP Payload Protocol ID MAY also be used for DUA 🌸. for example, you might want to backhaul ISDN and DPNSS over the same SCTP association 🫶. however, using separate SCTP Payload Protocol IDs (10 for DUA and 1 for IUA) is recommended as the primary option, even when ISDN and DPNSS are backhauled over the same SCTP association ✨
an SCTP Payload Protocol ID of "10" SHOULD be used for DUA if only DPNSS is backhauled over an SCTP association 💜. that's the case where you're not required to backhaul ISDN and DPNSS at the same time over the same association, so it's NOT required 🙃
the SCTP Payload Protocol Identifier rides along in every SCTP Data chunk to show which protocol SCTP is carrying 🧚. SCTP doesn't use it directly, but certain network entities MAY use it to figure out what kind of information a Data chunk is carrying 👀
5. Message Sequence in DUA 🦋
here's an example of the message flows for setting up a data link on a signaling channel, passing PDUs, and releasing a data link on a DPNSS channel 💫. an active association between MGC and SG gets set up before any of these flows happen 🫧
5.1. Resetting of single DLC 🔄
i) Successful
PBX SG MGC
<----------- SABMR <----------- Est Req(Ind=1)
UA -----------> Est Cfm -----------> (DLC in RC State)
Ind=1)
ii) Unsuccessful(Link Failure)
PBX SG MGC
<----------- SABMR <----------- Est Req(Ind=1)
Retransmissions over
NT1 and NT2 expired
Rel Ind -----------> (DLC in RA state)
(RELEASE_OTHER,Ind=1)5.2. Resetting all DLCs in a Link 🌷
PBX SG MGC
<----------- SABMR(1) <----------- Est Req(Ind=0)
<----------- SABMR(2)
<----------- SABMR(3)
.............
<----------- SABMR(N)
In each DLC either
UA is received or
NT1/NT2 is expired
Est Cfm -----------> (Status of DLCs
(Ind=0) are not updated)
<----------- Status Req
Status cfm ----------> (Mark DLC status
based on
status bits)if one or more DLCs stay out-of-service after this procedure (for example, because of layer 2 management) 🛠️, the MGC can either retry that DLC with an Est Req(Ind=1) that names the specific DLC, or send an Est Req(Ind=0) and let the SG retry the appropriate out-of-service DLC 🔁
5.3. Information Transfer on a DLC 📨
PBX SG MGC
<----------- UI(C) <----------- Data Req
UI(R)-----------> Data Ind ----------->5.4. Link Takedown (Single DLC) 🪦
PBX SG MGC
(For DPNSS, mark DLC as OOS) <----------- Rel Req
(For DASSII, mark DLC as RA) (RELEASE_MGMT,
Ind=1)
Rel Cfm ---------->
(Ind=1)5.5. Link Takedown (All DLCs) 🧹
PBX SG MGC
(For DPNSS, mark all DLCs as OOS) <-------- Rel Req
(For DASSII, mark DLC as RA) (RELEASE_MGMT,
Ind=0)
Rel Cfm ---------->
(Ind=0)5.6. Getting Link Status 👀
PBX SG MGC
<----------- Stat Req
Stat Cfm -----------> (Mark DLC status
based on
status bits)5.7. Error Conditions 🚨
PBX SG MGC
Invalid Message <-----------Est/Rel/Data/-
Error Ind ----------->
(Error Code) Stat Req6. Security Considerations 🔐
⚠️ the security considerations for the ISDN User Adaptation Protocol (IUAP) [1] (Section 6) and the security considerations for SIGTRAN Protocols document [4] apply to this document as well. please don't skip these, bestie, they're load-bearing 😭
7. References 📚
7.1. Normative References 💜
[1] Morneault, K., Rengasami, S., Kalla, M., and G. Sidebottom, "ISDN Q.921-User Adaptation Layer", RFC 3057, February 2001.
[2] Ofcom/NICC ND1301:2001/03, DPNSS [188], Digital Private Signalling System No 1 (DPNSS 1) (Formerly BTNR 188).
[3] BTNR (British Telecom Network Requirements) 190 Issue 2 Digital Access Signaling System No 2.
[4] Loughney, J., Tuexen, M., and J. Pastor-Balbas, "Security Considerations for Signaling Transport (SIGTRAN) Protocols", RFC 3788, June 2004.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
8. Acknowledgements ✨
okay bestie, the authors wanna shout out Shashi Kumar and Venkatesh Seshasayee of Wipro Technologies 🫶 for their useful suggestions and comments. literally the best support squad 💖
Authors' Addresses
okay so, if you need to reach the authors about this doc, here are their deets 📮 (copied exactly, no typos 🙈)
Ranjith Mukundan
Wipro Technologies
72, Electronics City
Hosur Main Road
Bangalore 560100
India
Phone: +91-80-51195893
EMail: ranjith.mukundan@wipro.com
Ken Morneault
Cisco Systems Inc.
13615 Dulles Technology Drive
Herndon, VA. 20171
USA
Phone: +1-703-484-3323
EMail: kmorneau@cisco.com
Narsimuloo Mangalpally
Nortel Networks
250 Sidney Street
Belleville, Ontario K8P 3Z3
Canada
Phone: +1-613-967-5034
EMail: narsim@nortelnetworks.comFull Copyright Statement
okay the legal bit, but make it cute 🎀 The Internet Society owns the copyright here, so it's Copyright (C) The Internet Society (2005). ✨
This doc is governed by the rights, licenses and restrictions in BCP 78 💅, and outside of what BCP 78 says, the authors keep all their rights. Mine, not yours, bestie 🙃
Heads up, this next part is all caps for a reason 🚨 It's a legal disclaimer, so don't skim it: This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Acknowledgement
last but not least, the RFC Editor function is funded by the Internet Society 🌸 ily, thanks for the support 💜
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