Internet Engineering Task Force Anil Vydyam Ranjith Mukundan Narsimuloo Mangalpally Nortel Networks Expires in 6 months November 2000 DPNSS/DASS 2 extensions to the IUA protocol Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document defines a mechanism for backhauling of DPNSS/DASS2 messages over IP by extending the ISDN User Adaptation Layer Protocol Version 9 (). The document aims to become an Appendix to IUA and to be the base for a DUA implementation. Table of Contents 1.0 Introduction ......................................... 3 1.1 Scope ............................................. 3 1.2 Terminology ....................................... 3 1.3 DPNSS Overview .................................... 3 1.4 Proposed DPNSS Backhaul Architecture .............. 4 2.0 Changes from IUA...................................... 4 2.1 Message Header..................................... 4 Vydyam/Mukundan/Mangalpally 1 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 2.2 Adaptation Layer Identifier........................ 5 2.3 Unit Data Message.................................. 5 2.4 Status Message..................................... 5 2.5 Error Message...................................... 6 3.0 IANA Considerations................................... 6 4.0 Message Sequence in DUA............................... 6 4.1 Resetting of single DLC............................ 6 4.2 Resetting all DLCs in a link....................... 7 4.3 Information Transfer on a DLC...................... 7 4.4 Link Takedown(Single DLC).......................... 7 4.5 Link Takedown(All DLCs)............................ 7 4.6 Getting link Status................................ 7 4.7 Error conditions................................... 7 5.0 References ........................................... 8 6.0 Author's Addresses.................................... 8 1.0 Introduction This document describes a method of implementing DPNSS/DASS 2 back- haul messaging over IP using a modified version of the ISDN User Adaptation Protocol (IUAP). The document aims to become an Appendix to IUA and to be the base for the "appli- cation guide". 1.1 Scope There is a need for Switched Circuit Network (SCN) signaling protocol delivery from a DPNSS Signaling Gateway (SG) to a Media Gateway Controller (MGC). The delivery mechanism should support the following protocols: - DPNSS(Digital Private Network Signaling System) - DASS 2 (Digital Access Signaling System No 2) Unless specifically mentioned the details in this document are applicable to both DPNSS and DASS2. 1.2 Terminology Data channel (D-channel) - A 64 kbit/s time slot which functions as a common signaling channel on a 2048 kbits/s interface or a 1544 kbits/s interface which is 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 termed as DPNSS channels. These are the traffic channels which carry voice or data traffic. - 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 Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 controls the transfer of level 3 messages on behalf of one DPNSS channel. A 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 in a 2048 kbits/s interface or a 1544 kbits/s interface is called a "DPNSS Link". 1.3 DPNSS Overview DPNSS is an industry standard interface (reference BTNR 188) defined between a PBX and an Access Network (AN). DPNSS extends facilities normally only available between extensions on a single PBX to all extensions on PBXs that are connected together in a private network. DPNSS was originally derived from BT's Digital Access Signaling System I (DASS I) enhanced where necessary to meet the private network requirements. Some of these enhancements were incorporated in DASS 2. DPNSS uses 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 1 Channels 16 on a 2048 kbits/s interface and channel 24 on a 1544 kbits/s interface is reserved for data communication between LE and AN. The channels reserved for data are called "Data Channels" or "D-Channels." The D-Channels are the physical media to exchange 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 ****** DPNSS ****** IP ******* *PBX *---------------* SG *--------------* MGC * ****** ****** ******* +-----+ +-----+ |DPNSS| (NIF) |DPNSS| | L3 | | L3 | +-----+ +----------+ +-----+ Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 | | | | DUA| | DUA | |DPNSS| |DPNSS+----+ +-----+ | L2 | | L2 |SCTP| |SCTP | | | | +----+ +-----+ | | | | IP + | IP | +-----+ +-----+----+ +-----+ NIF - Nodal Interworking function SCTP - Stream Control Transmission Protocol DUA - DPNSS User Adaptation Layer Protocol 2.0 Changes from IUA The following section outlines the differences between DUA and IUA 2.1 Message Header IUA Message header has the format as shown in Figure 2 below. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DLCI | Spare | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 IUA Message Header In DUA header DLCI field has a different format in accordance with the BTNR 188. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Indicator |0|Channel No.|1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The indicator field is used to determine whether the message is for a particular DLC or it is applicable for all the DLCs in the carrier. The possible values of the indicator is mentioned below. Value Description 0 Action is to be performed on all DLCs Channel number parameter is ignored. Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 1 Action is to be performed on a single DLC specified by channel number. This indicator value is used only by the Est and Rel messages. Data messages should ignore this value. This indicator is provided so that a single command can be issued to establish or release all the DLCs in one DPNSS Link. For channel number the valid values are 0 to 63 for DPNSS and 0 to 31 for DASS 2. This is because DASS 2 does not support virtual DLCs and hence has only 32 DLCs. 2.2 Adaptation Layer Identifier Adaptation Layer Identifier string must be set to "DUA" for the DUA applications. 2.3 Unit Data Message DPNSS layer 2 does not have a unit data primitive and hence the Unit Data Messages (Request, Indication) are invalid for a DUA application. 2.4 Status Message IUA MIUA-TEI STATUS Message has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In DUA this will be known as the Status message and will have the following format. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+ DLC 1 | | | | | | | | | | | | | | | | | DLC 16 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+ DLC 17 | | | | | | | | | | | | | | | | | DLC 32 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+ DLC 33 | | | | | | | | | | | | | | | | | DLC 48 Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+ DLC 49 | | | | | | | | | | | | | | | | | DLC 64 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +-+-+ These 4 words carry the status of DLCs using two bits for each DLC. These are the possible values for these two bits. Value Description 00 Out Of Service 01 Reset Attempted 10 Reset Completed 11 Information Transfer For DASS 2 there are no virtual DLCs and hence information about only 32 DLCs need to be carried. Therefore the status message will have only 2 words instead of 4 for DPNSS. For DASS 2 the value 00 (Out Of Service) is invalid since the DASS 2 DLC does not have this state. 2.5 Error Message The ERR message is sent when an invalid value is found in an incoming message. The Error Code parameter indicates the reason for the Error Message. These are the supported values in IUA. Invalid Version 0x1 Invalid Interface Identifier 0x2 Invalid Adaptation Layer Identifier 0x3 Invalid Message Type 0x4 Invalid Stream Identifier 0x5 Unassigned TEI 0x6 Unrecognized SAPI 0x7 Invalid TEI, SAPI combination 0x8 Invalid AS Mode Type 0x9 In DUA the error codes 0x6 to 0x8 are invalid as they are specific to ISDN. The following additional error codes are supported in DUA. Channel Number out of range 0xA Channel Not configured 0xB 3.0 IANA Considerations A request will be made to IANA to assign a DUA value for the Payload Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 Protocol Identifier in SCTP Payload Data chunk. The following SCTP Payload Protocol Identifier will be registered: The SCTP Payload Protocol Identifier is included in each SCTP Data chunk, to indicate which protocol the SCTP is carrying. This Payload Protocol Identifier is not directly used by SCTP but may be used by certain network entities to identify the type of information being carried in a Data chunk. The User Adaptation peer may use the Payload Protocol Identifier as a way of determining whether the message is for IUA or DUA. 4.0 Message Sequence in DUA An example of the message flows for establishing a data link on a signaling channel, passing PDUs and releasing a data link on a DPNSS channel is shown below. An active association between MGC and SG is established prior to the following message flows. 4.1 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_PHYS,Ind=1) 4.2 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 Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 (Ind=0) are not updated ) <----------- Stat Req Stat Res -----------> (Mark DLC status based on status bits) 4.3 Information Transfer on a DLC PBX SG MGC <----------- UI(C) <----------- Data Req UI(C)-----------> Data Ind -----------> 4.4 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) 4.5 Link Takedown(All DLCs) PBX SG MGC (For DPNSS, mark all DLCs as OOS) <----------- Rel Req (For DASSII, mark all DLCs as RA) (RELEASE_MGMT,Ind=0) Rel Cfm ----------> (Ind=0) 4.6 Getting link Status PBX SG MGC <----------- Stat Req Stat Res -----------> (Mark DLC status based on status bits) 4.7 Error conditions PBX SG MGC Invalid Message ----------- Est/Rel/Data/Stat Req Error Ind -----------> (Error Code) 5.0 Glossary of terms Vydyam/Mukundan/Mangalpally 9 Internet Draft draft-anil-sigtran-dua-00.txt November 2000 Real channel : The signalling channel with associated traffic channel (TS). Virtual channel: The signalling channel with no associated traffic channel. NT1 : Retransmission period of 500msec. NT2 : Recommended value is 64. 6.0 References [1] ISDN Q.921-User Adaptation Layer [2] BTNR (British Telecom Network Requirements) 188 Issue 6 Digital Private Network Signaling System 1 [3] BTNR (British Telecom Network Requirements) 190 Issue 2 Digital Access Signaling System No 2 [4] ETS 300 167 (08/1993) : Transmission and Multiplexing; Functional characteristic of 2048 kbits/s interfaces (Standard is based on G.704, G.706). 7.0. Acknowledgments The authors would like to thank Sudarsan Naganathan, Subhas Mondal and Sivaram Subramanian of Nortel Networks for their useful suggestions/comments. 8.0 Author's Addresses Authors : Anil Vydyam, Ranjith Mukundan and Narsimuloo Mangalpally All correspondence regarding this draft should be sent to the following address : Mick Dragon Tel. +44 (0)1628434388 Nortel Networks plc Email. mdragon@nortelnetworks.com Concorde Road Maidenhead Berkshire SL6 4AG United Kingdom Vydyam/Mukundan/Mangalpally 9