Network Working Group M. Suzuki Request for Comments: 2383 NTT Category: Informational August 1998 ST2+ over ATM Protocol Specification - UNI 3.1 Version Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. Abstract This document specifies an ATM-based protocol for communication between ST2+ agents. The ST2+ over ATM protocol supports the matching of one hop in an ST2+ tree-structure stream with one ATM connection. In this document, ATM is a subnet technology for the ST2+ stream. The ST2+ over ATM protocol is designed to achieve resource- reservation communications across ATM and non-ATM networks, to extend the UNI 3.1/4.0 signaling functions, and to reduce the UNI 4.0 LIJ signaling limitations. The specifications of the ST2+ over ATM protocol consist of a revision of RFC 1819 ST2+ and specifications of protocol interaction between ST2+ and ATM on the user plane, management plane, and control plane which correspond to the three planes of the B-ISDN protocol reference model. 1. Introduction 1.1 Purpose of Document The purpose of this document is to specify an ATM-based protocol for communication between ST2+ agents. The ST2+ over ATM protocol is designed to support the matching of one hop in an ST2+ tree-structure stream with one ATM connection; it is not designed to support an entire ST2+ tree-structure stream with a point-to-multipoint ATM connection only. Suzuki Informational [Page 1] RFC 2383 ST2+ over ATM August 1998 Therefore, in this document, ATM is only a subnet technology for the ST2+ stream. This specification is designed to enable resource- reservation communications across ATM and non-ATM networks. 1.2 Features of ST2+ over ATM Protocol o Enables resource-reservation communications across ATM and non-ATM networks. ATM native API supports resource-reservation communications only within an ATM network; it cannot support interworking with non-ATM networks. This is because - ATM native API cannot connect terminals without an ATM interface. - ATM native API does not support IP addressing and SAP (port) addressing systems. o Extends UNI 3.1/4.0 signaling functions. ST2+ SCMP supports MTU-size negotiation at all hops in an ST2+ tree-structure stream. UNI 3.1/4.0 supports only max CPCS_SDU (i.e., MTU) negotiation with the called party of a point-to-point call or with the first leaf of a point-to-multipoint call. o Reduces UNI 4.0 LIJ signaling limitations. The ST2+ over ATM protocol supports UNI 4.0 LIJ Call Identifier notification from the root to the leaf by using an ST2+ SCMP extension. LIJ Call Identifier discovery at the leaf is one of the major unsolved problems of UNI 4.0, and the ST2+ over ATM protocol provides a solution. Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support the above feature. It will be supported by the UNI 3.1/4.0 version. 1.3 Goals and Non-goals of ST2+ over ATM Protocol The ST2+ over ATM protocol is designed to achieve the following goals. o Specify protocol interaction between ST2+ [4] and ATM on the ATM Forum Private UNI 3.1/4.0 (Sb point) [10, 11]. Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support UNI 4.0. It will be supported by the UNI 3.1/4.0 version. Suzuki Informational [Page 2] RFC 2383 ST2+ over ATM August 1998 o Support ST2+ stream across ATM and non-ATM networks. o Define one VC on the UNI corresponding to one ST2+ hop; this VC is not shared with other ST2+ hops, and also this ST2+ hop is not divided into multiple VCs. o Support both SVC and PVC. o Not require any ATM specification changes. o Coexist with RFC 1483 [16] IPv4 encapsulation. o Coexist with RFC 1577 [17] ATMarp. o Coexist with RFC 1755 [18] ATM signaling for IPv4. o Coexist with NHRP [19]. Because ST2+ is independent of both routing and IP address resolution protocols, the ST2+ over ATM protocol does not specify the following protocols. o IP-ATM address resolution protocol o Routing protocol Because the ST2+ over ATM protocol is specified for the UNI, it is independent of: o NNI protocol o Router/switch architecture Suzuki Informational [Page 3] RFC 2383 ST2+ over ATM August 1998 2. Protocol Architecture The ST2+ over ATM protocol specifies the interaction between ST2+ and ATM on the user, management, and control planes, which correspond to the three planes in ITU-T Recommendation I.321 B-ISDN Protocol Reference Model [14]. 2.1 User Plane Architecture The user plane specifies the rules for encapsulating the ST2+ Data PDU into the AAL5 [15] PDU. An user plane protocol stack is shown in Fig. 2.1. +---------------------------------+ | RFC 1819 ST2+ | | (ST2+ Data) | +---------------------------------+ Point of ST2+ over ATM |/////////////////////////////////| <--- protocol specification of +---------------------------------+ user plane | | | | | I.363.5 | | | | AAL5 | | | | | +---------------------------------+ | I.361 ATM | +---------------------------------+ | PHY | +----------------+----------------+ | UNI +--------||------- Fig. 2.1: User plane protocol stack. Suzuki Informational [Page 4] RFC 2383 ST2+ over ATM August 1998 An example of interworking from an ATM network to an IEEE 802.X LAN is shown in Fig. 2.2. ST2+ ST2+ ST2+ Origin ATM Cloud Intermediate Agent Target +---------+ +---------+ | AP |--------------------------------------------->| AP | +---------+ +-------------------+ +---------+ |ST2+ Data|------------------>| RFC 1819 ST2+ Data|----->|ST2+ Data| +---------+ +---------+---------+ +---------+ |I.363 AAL|------------------>|I.363 AAL| SNAP |----->| SNAP | +---------+ +---------+ +---------+---------+ +---------+ |I.361 ATM|--->|I.361 ATM|--->|I.361 ATM| LLC |----->| LLC | +---------+ +---------+ +---------+---------+ +---------+ | | | | | |IEEE802.X| |IEEE802.X| | PHY |--->| PHY |--->| PHY | & 802.1p|----->| & 802.1p| +---------+ +---------+ +---------+---------+ +---------+ Fig. 2.2: Example of interworking from an ATM network to an IEEE 802.X LAN. The ATM cell supports priority indication using the CLP field; indication is also supported by the ST2+ Data PDU by using the Pri field. It may be feasible to map these fields to each other. The ST2+ over ATM protocol specifies an optional function that maps the Pri field in the ST header to the CLP field in the ATM cell. However, implementors should note that current ATM standardization tends not to support tagging. Suzuki Informational [Page 5] RFC 2383 ST2+ over ATM August 1998 2.2 Management Plane Architecture The management plane specifies the Null FlowSpec, the Controlled-Load Service [5] FlowSpec, and the Guaranteed Service [6] FlowSpec mapping rules [8] for UNI 3.1 traffic management. A management plane protocol stack is shown in Fig. 2.3. +---------------------------------+ | Null FlowSpec | |Controlled-Load Service FlowSpec | | Guaranteed Service FlowSpec | +---------------------------------+ Point of ST2+ over ATM |/////////////////////////////////| <--- protocol specification of +---------------------------------+ management plane | | | UNI 3.1 | | | | | | Traffic Management | | | | | | VBR/UBR | | | +---------------------------------+ Fig. 2.3: Management plane protocol stack. Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support Guaranteed Services. It will be supported by the UNI 3.1/4.0 version. The ST2+ over ATM protocol specifies the ST FlowSpec format for the Integrated Services. Basically, FlowSpec parameter negotiation, except for the MTU, is not supported. This is because, in the ST2+ environment, negotiated FlowSpec parameters are not always unique to each target. The current ATM standard does not support heterogeneous QoS to receivers. The ST2+ over ATM protocol supports FlowSpec changes by using the CHANGE message (RFC 1819, Section 4.6.5) if the I-bit in the CHANGE message is set to one and if the CHANGE message affects all targets in the stream. This is because the UNI 3.1 does not support QoS changes. The ST2+ over ATM protocol supports FlowSpec changes by releasing old ATM connections and establishing new ones. The ST2+ over ATM protocol does not support stream preemption (RFC 1819, Section 6.3). This is because the Integrated Services FlowSpec does not support the concept of precedence. Suzuki Informational [Page 6] RFC 2383 ST2+ over ATM August 1998 It does not support the ST2+ FlowSpec (RFC 1819, Section 9.2). ST2+ FlowSpec specifies useful services, but requires a datalink layer to support heterogeneous QoS to receivers. The current ATM standard does not support heterogeneous QoS to receivers. 2.3 Control Plane Architecture The control plane specifies the rules for encapsulating the ST2+ SCMP PDU into the AAL5 [15] PDU, the relationship between ST2+ SCMP and PVC management for ST2+ data, and the protocol interaction between ST2+ SCMP and UNI 3.1 signaling [10]. A control plane protocol stack is shown in Fig. 2.4. +---------------------------------+ | RFC 1819 ST2+ | | (ST2+ SCMP) | +---------------------------------+ Point of ST2+ over ATM |/////////////////////////////////| <--- protocol specification of +------------+---+----------------+ control plane | IEEE 802 | |UNI3.1 Signaling| | SNAP | +----------------+ +------------+ | Q.2130 SSCF | | ISO 8802-2 | +----------------+ | LLC Type1 | | Q.2110 SSCOP | +------------+ +----------------+ | I.363.5 AAL5 | +---------------------------------+ | I.361 ATM | +---------------------------------+ | PHY | +----------------+----------------+ | UNI +--------||------- Fig. 2.4: Control plane protocol stack. The ST2+ over ATM protocol does not cover a VC (SVC/PVC) that transfers ST2+ SCMP. VCs for IPv4 transfer may be used for ST2+ SCMP transfer, and implementations may provide particular VCs for ST2+ SCMP transfer. Selection of these VCs depends on the implementation. Implementors should note that when ST2+ data and SCMP belong to a stream, the routing directions on the ST2+ layer must be the same. Implementors should also note that ST2+ and IPv4 directions for routing to the same IP destination address are not always the same. Suzuki Informational [Page 7] RFC 2383 ST2+ over ATM August 1998 The ST2+ over ATM protocol supports both SVC and PVC for ST2+ Data PDU transfer. If SVC is used, the ST2+ and ATM layers establish a connection sequentially by using respectively ST2+ SCMP and UNI 3.1 signaling. An example of ST2+ SCMP and UNI 3.1 signaling message flows for establishing and releasing of ST2+ data connections is shown in Fig. 2.5, where (S) means an ST2+ entity and (Q) means a UNI 3.1 signaling entity. ATM SW ATM SW +------------+ UNI +----+ NNI +----+ UNI +------------+ ____|Intermediate|--||--| \/ |______| \/ |--||--|Intermediate|____ | (Upstream) | | /\ | | /\ | |(Downstream)| +------------+ +----+ +----+ +------------+ SCMP ------->(S)<------------------------------------------>(S)<------- \ UNI Sig. UNI Sig. / CONNECT | (Q)<--------->(Q)<-------->(Q)<--------->(Q) | -------->| | ACK <----|--------------------CONNECT------------------>| CONNECT |<---------------------ACK---------------------|--------> | |<--- ACK | | ACCEPT | |<-------- |<-------------------ACCEPT--------------------|---> ACK |----------------------ACK-------------------->| | | |->|----SETUP--->| | | | | |<-CALL PROC--|----------->|----SETUP--->|->| | | | |<----CONN----|<-| ACCEPT | |<----CONN----|<-----------|--CONN ACK-->|->| <--------|<-|--CONN ACK-->| | | | ACK ---->| | | | -------\ |--------------------------------------------\ |-------\ >| ST2+ Data >| > -------/ |--------------------------------------------/ |-------/ | | DISCONN | | -------->| | ACK <----|-------------------DISCONNECT---------------->| |<---------------------ACK---------------------| | | |->|---RELEASE-->| | | | |<-|<--REL COMP--|----------->|---RELEASE-->|->| DISCONN | | | |<--REL COMP--|<-|--------> | |<--- ACK Fig. 2.5: Example of ST2+ SCMP and UNI 3.1 signaling message flows. Suzuki Informational [Page 8] RFC 2383 ST2+ over ATM August 1998 UNI 3.1/4.0 specifies PVC, point-to-point SVC, and point-to- multipoint SVC as VC styles. However, in actual ATM network environments, especially public ATM WANs, only PVC and bi-directional point-to-point SVC may be supported. To support the diverse VC styles, the ST2+ over ATM protocol supports the following VC styles for ST2+ Data PDU transfer. o PVC o Reuse of reverse channel of bi-directional point-to-point SVC that is used by existing stream. o Point-to-point SVC initiated from upstream side. o Point-to-multipoint SVC initiated from upstream side. o Point-to-point SVC initiated from downstream side. o Point-to-multipoint SVC initiated from downstream side (LIJ). Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support LIJ. LIJ will be supported by the UNI 3.1/4.0 version. The second style is needed in environments supporting bi-directional point-to-point SVC only. The selection of PVC and SVC styles in the ST2+ agent is based on preconfigured implementation-dependent rules. SVC supports both upstream and downstream call initiation styles. Implementors should note that this is independent of the sender- oriented and receiver-oriented ST2+ stream-building process (RFC 1819, Section 4.1.1). This is because the ST2+ over ATM protocol specifies the process for establishing ST2+ data hops on the UNI, and because the ST2+ stream building process belongs to another layer. The SVC initiation side should be determined based on the operational and billing policies between ST2+ agents; this is basically independent of the sender-oriented and receiver-oriented ST2+ stream-building process. Suzuki Informational [Page 9] RFC 2383 ST2+ over ATM August 1998 An example of ST2+ SCMP interworking is shown in Fig. 2.6. _____ / \ (Origin ) \ / A ~~|~~ A | = | UNI Signaling | | | | +-+-+ V | | X | ATM SW | +-+-+ A SCMP | | | NNI Signaling | +-+-+ V | | X | ATM SW | +-+-+ A | | | | = | UNI Signaling V | V +-----+------+ IEEE 802.X & 802.1p | |<---------------------+ |Intermediate|--------------------+ | | |<-----------------+ | | +------------+ L2 Signaling| | | A | A | | | | = | UNI Signaling | | | SCMP | | | | | | | +-+-+ V | | | | | X | ATM SW V | | | +-+-+ A +---+-|-+ SCMP | | | NNI Signaling | \ /| | | +-+-+ V | X | |LAN SW | | X | ATM SW | / \| | | +-+-+ A +---+-|-+ | | | A | | | = | UNI Signaling | | | V __|__ V V_|_V / \ / \ (Target ) (Target ) \ / \ / ~~~~~ ~~~~~ Fig. 2.6: Example of ST2+ SCMP interworking. Suzuki Informational [Page 10] RFC 2383 ST2+ over ATM August 1998 3. Revision of RFC 1819 ST2+ To specify the ST2+ over ATM protocol, the functions in RFC 1819 ST2+ must be extended to support ATM. However, it is difficult for the current ATM standard to support part of the specifications in RFC 1819 ST2+. This section specifies the extended, restricted, unsupported, and modified functions in RFC 1819 ST2+. Errata for RFC 1819 appears in Appendix A. 3.1 Extended Functions of RFC 1819 ST2+ 3.1.1 ST FlowSpec for Controlled-Load Service The ST2+ over ATM protocol specifies the ST FlowSpec format for the Integrated Services. Basically, FlowSpec parameter negotiation, except for the MTU, is not supported. The ST2+ intermediate agent and the target decide whether to accept or refuse the FlowSpec parameters, except for the MTU. Therefore, each of the FlowSpec parameter values other than MTU is the same at each target in the stream. The format of the ST FlowSpec for the Controlled-Load Service is shown in Fig. 3.1. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PCode = 1 | PBytes = 36 | ST FS Ver = 8 | 0(unused) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver=0 | 0(reserved) | Overall Length = 7 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SVC Number |0| 0(reserved) | SVC Length = 6 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Param Num = 127| Flags = 0 | Param Length = 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token Bucket Rate [r] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token Bucket Size [b] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Peak Data Rate [p] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Minimum Policed Unit [m] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Maximum Packet Size [M] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig. 3.1: Format of ST FlowSpec for Controlled-Load Service. Suzuki Informational [Page 11] RFC 2383 ST2+ over ATM August 1998 The PCode field identifies common SCMP elements. The PCode value for the ST2+ FlowSpec is 1. The PBytes field for the Controlled-Load Service is 36 bytes. The ST FS Ver (ST FlowSpec Version) field identifies the ST FlowSpec version. The ST FlowSpec version number for the Integrated Services is 8. The Ver (Message Format Version) field identifies the Integrated Services FlowSpec message format version. The current version is zero. The Overall Length field for the Controlled-Load Service is 7 words. The SVC Number (Service ID Number) field identifies the Integrated Services. If the Integrated Services FlowSpec appears in the CONNECT or CHANGE message, the value of the SVC Number field is 1. If it appears in the ACCEPT, NOTIFY, or STATUS-RESPONSE message, the value of the SVC Number field is 5. The SVC Length (Service-specific Data Length) field for the Controlled-Load Service is 6 words. The Param Num (Parameter Number) field is 127. The Flags (Per-parameter Flags) field is zero. The Param Length (Length of Per-parameter Data) field is 5 words. Definitions of the Token Bucket Rate [r], the Token Bucket Size [b], the Peak Data Rate [p], the Minimum Policed Unit [m], and the Maximum Packet Size [M] fields are given in [5]. See section 5 of [5] for details. The ST2+ agent, that creates the FlowSpec element in the SCMP message, must assign valid values to all fields. The other agents must not modify any values in the element. The MaxMsgSize field in the CONNECT message is assigned by the origin or the intermediate agent acting as origin, and updated by each agent based on the MTU value of the datalink layer. The negotiated value of MaxMsgSize is set back to the origin or the intermediate agent acting as origin using the [M] field and the MaxMsgSize field in the ACCEPT message that corresponds to the CONNECT message. Suzuki Informational [Page 12] RFC 2383 ST2+ over ATM August 1998 In the original definition of the Controlled-Load Service, the value of the [m] field must be less than or equal to the value of the [M] field. However, in the ST FlowSpec for the Controlled-Load Service, if the value of the [m] field is more than that of the [M] field, the value of the [m] field is regarded as the same value as the [M] field, and must not generate an error. This is because there is a possibility that the value of the [M] field in the ACCEPT message may be decreased by negotiation. In the ST2+ SCMP messages, the value of the [M] field must be equal to or less than 65,535. In the ACCEPT message that responds to CONNECT, or the NOTIFY message that contains the FlowSpec field, the value of the [M] field must be equal to the MaxMsgSize field in the message. If these values are not the same, FlowSpec is regarded as an error. If the ST2+ agent receives the CONNECT message that contains unacceptable FlowSpec, the agent must generate a REFUSE message. 3.1.2 ST FlowSpec for Guaranteed Service Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support Guaranteed Services. It will be supported by the UNI 3.1/4.0 version. 3.1.3 VC-type common SCMP element The ST2+ over ATM protocol specifies an additional common SCMP element that designates the VC type used to support the diverse VC styles. The CONNECT and CHANGE messages that establish a hop with a VC must contain a VC-type common SCMP element. This element is valid between neighboring ST2+ agents, but must not propagate beyond the previous-hop or next-hop ST2+ agent. Suzuki Informational [Page 13] RFC 2383 ST2+ over ATM August 1998 The format of the VC-type common SCMP element is shown in Fig. 3.2. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PCode = 8 | PBytes = 20 | VCType | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PVCIdentifer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0(unused) | UniqueID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OriginIPAddress | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LIJCallIdentifer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig. 3.2: Format of VC-type common SCMP element. The PCode field identifies the common SCMP elements. The PCode value for the VC type is 8. The PBytes field for the VC type is 20 bytes. The VCType field identifies the VC type. The correspondence between the value in this field and the meaning is as follows: 0: ST2+ data stream uses a PVC. 1: ST2+ data stream uses the reverse channel of the bi- directional point-to-point SVC used by the existing stream. 2: ST2+ data stream is established by a point-to-point SVC initiated from the upstream side. 3: ST2+ data stream is established by a point-to-multipoint SVC initiated from the upstream side. 4: ST2+ data stream is established by a point-to-point SVC initiated from the downstream side. 5: ST2+ data stream is established by a point-to-multipoint SVC initiated from the downstream side. Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support VCType 5. It will be supported by the UNI 3.1/4.0 version. Suzuki Informational [Page 14] RFC 2383 ST2+ over ATM August 1998 The PVCIdentifer field identifies the PVC identifier uniquely assigned between neighboring ST2+ agents. This field is valid only when the VCType field is zero. The UniqueID and OriginIPAddress fields identify the reverse channel of the bi-directional point-to-point SVC that is used by this SID. These fields are valid only when the VCType field is 1. The LIJCallIdentifer field identifies the LIJ Call Identifier for point-to-multipoint SVC. This field is valid only when the VCType field is 5. 3.1.4 Reason Code The extension of the Reason Code (RFC 1819, Section 10.5.3) to the ST2+ over ATM protocol is shown below. 57 CantChange Partial changes not supported. 58 NoRecover Stream recovery not supported. 3.2 Restricted Functions of RFC 1819 ST2+ 3.2.1 FlowSpec changes In the following case, the ST2+ over ATM protocol supports stream FlowSpec changes by using the CHANGE message. o The I-bit is set to 1 and the G-bit is set to 1. In the following case, the CHANGE fails and a REFUSE message, with the E and N-bits set to 1 and the ReasonCode set to CantChange, is propagated upstream. o The I and/or G-bits are set to zero. 3.3 Unsupported Functions of RFC 1819 ST2+ 3.3.1 ST2+ FlowSpec The ST2+ over ATM protocol does not support the ST2+ FlowSpec (RFC 1819, Section 9.2). The ST2+ FlowSpec specifies useful services, but requires the datalink layer to support heterogeneous QoS to receivers. The current ATM standard does not support heterogeneous QoS to receivers. Suzuki Informational [Page 15] RFC 2383 ST2+ over ATM August 1998 3.3.2 Stream preemption The ST2+ over ATM protocol does not support stream preemption (RFC 1819, Section 6.3). This is because the Integrated Services FlowSpec does not support the concept of precedence. 3.3.3 HELLO message Implementations may not support the HELLO message (RFC 1819, Section 10.4.7) and thus ST2+ agent failure detection using the HELLO message (RFC 1819, Section 6.1.2). This is because ATM has an adequate failure detection mechanism, and the HELLO message is not sufficient for detecting link failure in the ST2+ over ATM protocol, because the ST2+ data and the ST2+ SCMP are forwarded through another VC. 3.3.4 Stream recovery Implementors must select the NoRecover option of the CONNECT message (RFC 1819, Section 4.4.1) with the S-bit set to 1. This is because the descriptions of the stream recovery process in RFC 1819 (Sections 5.3.2, 6.2, and 6.2.1) are unclear and incomplete. It is thus possible that if a link failure occurs and several ST2+ agents detect it simultaneously, the recovery process may encounter problems. The ST2+ over ATM protocol does not support stream recovery. If recovery is needed, the application should support it. A CONNECT message in which the NoRecover option is not selected will fail; a REFUSE message in which the N-bit is set to 1 and the ReaseonCode is set to NoRecover is then propagated upstream. 3.3.5 Subnet Resources Sharing The ST2+ over ATM protocol does not support subnet resources sharing (RFC 1819, Section 7.1.4). This is because ATM does not support the concept of the MAC layer. 3.3.6 IP encapsulation of ST The ST2+ over ATM protocol does not support IP encapsulation of ST (RFC 1819, Section 8.7), because there is no need to implement IP encapsulation in this protocol. 3.3.7 IP Multicasting The ST2+ over ATM protocol does not support IP multicasting (RFC 1819, Section 8.8), because this protocol does not support IP encapsulation of ST. Suzuki Informational [Page 16] RFC 2383 ST2+ over ATM August 1998 3.4 Modified Functions of RFC 1819 ST2+ The ST2+ receiver-oriented stream creation procedure has some fatal problems: the value of the LnkReferecnce field in the CONNECT message that is a response to a JOIN message is not valid, ST2+ agent cannot update the LnkReference field in the JOIN-REJECT message, and ST2+ agent cannot deliver the JOIN-REJECT message to the target because the JOIN-REJECT message does not contain a TargetList field. To solve these problems, the ST2+ over ATM protocol modifies the ST2+ protocol processing rules. 3.4.1 Modifications of Message Processing Rules Modifications of the CONNECT, JOIN, and JOIN-REJECT message processing rules in the ST2+ over ATM protocol are described in the following. o The target that creates a JOIN message assigns the same value as in the Reference field to the LnkReference field. o The agent that creates a CONNECT message as a response to a JOIN message assigns the same value as in the LnkReference field in the JOIN message to the LnkReference field. In other cases, the value of the LnkReference field in a CONNECT message is zero. o The agent that creates a JOIN-REJECT message assigns the same value as in the LnkReference field in the JOIN message to the LnkReference field. o An intermediate agent must not modify the value of the LnkReference field in the CONNECT, JOIN, or JOIN-REJECT message. Note that this rule differs from the LnkReference field processing rule in the ACCEPT and REFUSE messages. Suzuki Informational [Page 17] RFC 2383 ST2+ over ATM August 1998 3.4.2 Modified JOIN-REJECT Control Message The modified JOIN-REJECT control message in the ST2+ over ATM protocol is shown in Fig. 3.3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OpCode = 9 | 0 | TotalBytes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reference | LnkReference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SenderIPAddress | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | ReasonCode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GeneratorIPAddress | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : TargetList : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fig. 3.3: JOIN-REJECT Control Message. The TargetList is assigned the same TargetList in the JOIN message as the one that corresponds to the JOIN-REJECT message. 4. Protocol Specification of the User Plane This section specifies the AAL5 PDU encapusulation for the ST2+ Data PDU. 4.1 Service Primitives Provided by User Plane 4.1.1 Overview of interactions The ST2+ data layer entity on the user plane of the ST2+ over ATM protocol provides the following services to the upper layer. o st2p_unitdata.req o st2p_unitdata.ind 4.1.1.1 St2p_unitdata.req The st2p_unitdata.req primitive sends a request for an ST2+ Data PDU transfer to the ST2+ data layer entity. The semantics of the primitive are as follows: Suzuki Informational [Page 18] RFC 2383 ST2+ over ATM August 1998 st2p_unitdata.req ( pri, sid, data ) The pri parameter specifies priority of ST2+ Data PDU. The sid parameter specifies SID of ST2+ Data PDU. The data parameter specifies ST2+ data to be transferred. 4.1.1.2 St2p_unitdata.ind The st2p_unitdata.ind primitive indicates an ST2+ Data PDU delivery from the ST2+ data layer entity. The semantics of the primitive are as follows: st2p_unitdata.ind ( pri [optional], sid, data, status [optional] ) The pri parameter indicates priority of ST2+ Data PDU, if AAL5 is used for encapsulating the ST2+ Data PDU. The sid parameter indicates SID of ST2+ Data PDU. The data parameter indicates delivered ST2+ data. The status is an optional parameter that indicates whether the delivered ST2+ data is corrupt or not. 4.2 Service Primitives Provided by AAL5 4.2.1 Requirements for AAL5 The requirements for the AAL5 layer on the ST2+ over ATM user plane are as follows: o The SSCS must be null. o Implementations must use message-mode service. Note: Selection of the corrupted SDU delivery option on the receiver side depends on the implementation, so the receiver may or may not be able to select this option. 4.2.2 Overview of Interactions The AAL5 layer entity on the ST2+ over ATM user plane provides the following services to the ST2+ data layer. Suzuki Informational [Page 19] RFC 2383 ST2+ over ATM August 1998 o AAL5_UNITDATA.req o AAL5_UNITDATA.ind 4.2.2.1 AAL5_UNITDATA.req The AAL5_UNITDATA.req primitive sends a request for an AAL5 data (AAL5 CPCS_SDU) transfer from the ST2+ data layer entity to the AAL5 layer entity. The semantics of the primitive are as follows: AAL5_UNITDATA.req ( DATA, CPCS_LP, CPCS_UU ) The DATA parameter specifies the AAL5 data to be transferred. The CPCS_LP parameter specifies the value of the CLP field in the ATM cell. The CPCS_UU parameter specifies the user-to-user data to be transferred. 4.2.2.2 AAL5_UNITDATA.ind The AAL5_UNITDATA.ind indicates an AAL5 data (AAL5 CPCS_SDU) delivery from the AAL5 layer entity to the ST2+ data layer entity. The semantics of the primitive are as follows: AAL5_UNITDATA.ind ( DATA, CPCS_LP, CPCS_UU, STATUS [optional] ) The DATA parameter indicates the delivered AAL5 data. The CPCS_LP parameter indicates the value of the CLP field in the ATM cell. The CPCS_UU parameter indicates the delivered user-to-user data. The STATUS parameter indicates whether the delivered AAL5 data is corrupt or not. The STATUS parameter is an optional parameter, and valid only when the corrupted SDU delivery option is selected. 4.3 AAL5 Encapsulation for ST2+ Data PDU 4.3.1 Mapping from st2_unitdata.req to AAL5_UNITDATA.req The ST2+ Data PDU is directly assigned to the DATA parameter in AAL5_UNITDATA.req. That is, as shown in Fig. 4.1, the ST2+ Data PDU is mapped to the payload of AAL5 CPCS_PDU. Suzuki Informational [Page 20] RFC 2383 ST2+ over ATM August 1998 +-------+---------------------------+ | ST | ST2+ data | ST2+ | header| | Data PDU +-------+---------------------------+ : : : : +---------------------------------------+--------+ | CPCS_PDU |PAD|CPCS_PDU| AAL5 | payload | |trailer | CPCS_PDU +---------------------------------------+--------+ Fig. 4.1: Mapping of ST2+ data to AAL5 CPCS_PDU payload. The value of CPCS_LP in AAL5_UNITDATA.req depends on the implementation: 1 (low priority) or zero (high priority) may be assigned permanently, or they may be assigned depending on the value of pri in st2_unitdata.req. The value of the CPCS_UU indication field in AAL5_UNITDATA.req is set to zero. 4.3.2 Mapping from AAL5_UNITDATA.ind to st2p_unitdata.ind The DATA parameter in AL5_UNITDATA.ind is directly assigned to the ST2+ Data PDU. That is, the payload in AAL5 CPCS_PDU is mapped to the ST2+ Data PDU. If the value of STATUS in AAL5_UNITDATA.ind is valid, it is assigned to the status in st2p_unitdata.ind. 4.3.3 Value of MTU The value of MTU is Maximum CPCS_SDU size. 5. Protocol Specification of the Management Plane The management plane specifies the Null FlowSpec, the Controlled-Load Service FlowSpec, and the Guaranteed Service FlowSpec mapping rules for UNI 3.1 traffic management. 5.1 Mapping of the Null FlowSpec The Null FlowSpec is mapped to the UBR (VBR with the Best Effort Indicator). The value of the PCR (CLP=0+1) is shown in section 6.7.2. Suzuki Informational [Page 21] RFC 2383 ST2+ over ATM August 1998 5.2 Mapping of the Controlled-Load Service FlowSpec The Controlled-Load FlowSpec is mapped to the VBR whose PCR (CLP=0+1), SCR (CLP=0+1), and MBS (CLP=0+1) are specified. The value of the PCR (CLP=0+1) is shown in section 6.7.2. Let scr be the calculated value of the SCR (CLP=0+1). Based on the value of the [r] field in the Controlled-Load FlowSpec, it is given by: scr = ([r] / 48) * S, where S is the coefficient of segmentation, and in an implementation, it must be configurable to any value between 1.0 and 56.0. The recommended default value is 1.2. The value of the SCR (CLP=0+1) is a minimum integer equal to or more than the calculated value of the scr. Let mbs be the calculated value of the MBS (CLP=0+1). Based on the value of the [b] field in the Controlled-Load FlowSpec, it is given by: mbs = ([b] / 48) * S. The value of the MBS (CLP=0+1) is a minimum integer equal to or more than the calculated value of the mbs. The values of the [p] and [m] fields in the Controlled-Load FlowSpec are ignored. 5.3 Mapping of the Guaranteed Service FlowSpec Note: The UNI 3.1 version of the ST2+ over ATM protocol does not support Guaranteed Services. It will be supported by the UNI 3.1/4.0 version. 6. Protocol Specification of the Control Plane This section specifies the rules for encapsulating the ST2+ SCMP PDU into the AAL5 PDU, the relationship between ST2+ SCMP and PVC management for ST2+ data, and the protocol interaction between ST2+ SCMP and UNI 3.1 signaling. 6.1 AAL5 Encapsulation for ST2+ SCMP PDU This subsection describes AAL5 PDU encapsulation for the ST2+ SCMP PDU. ST2+ Data PDU compatible encapsulation, AAL5 encapsulation based on RFC 1483, and on the RFC 1483 extension are specified. Selection of which one to use depends on the implementation. Suzuki Informational [Page 22] RFC 2383 ST2+ over ATM August 1998 The ST2+ over ATM protocol does not cover a VC (SVC/PVC) that transfers ST2+ SCMP. VCs for IPv4 transfer may be used for ST2+ SCMP transfer, and implementations may provide particular VCs for ST2+ SCMP transfer. Selection of these VCs depends on the implementation. 6.1.1 ST2+ Data PDU compatible encapsulation The ST2+ Data PDU compatible encapsulation is shown in Fig. 6.1: the ST2+ SCMP PDU is mapped to the payload of AAL5 CPCS_PDU. Implementors should note that this encapsulation is not applicable when the ST2+ SCMP PDU is multiplexed with other protocols. +-------+---------------------------+ | ST | ST2+ SCMP | ST2+ | header| | SCMP PDU +-------+---------------------------+ : : : : +---------------------------------------+--------+ | CPCS_PDU |PAD|CPCS_PDU| AAL5 | payload | |trailer | CPCS_PDU +---------------------------------------+--------+ Fig. 6.1: ST2+ Data PDU conpatible encapsulation. 6.1.2 RFC 1483 base encapsulation The RFC 1483 base encapsulation is shown in Fig. 6.2: the ST2+ SCMP PDU with the RFC 1483 LLC encapsulation for routed protocol format is mapped to the payload in AAL5 CPCS_PDU. +------+----------------+ | ST | ST2+ SCMP | ST2+ |header| | SCMP PDU +------+----------------+ : : +---+---+---+-----------------------+ |LLC|OUI|PID| Information | IEEE 802 SNAP | | | | | ISO 8802-2 LLC +---+---+---+-----------------------+ : : +---------------------------------------+--------+ | CPCS_PDU |PAD|CPCS_PDU| AAL5 | payload | |trailer | CPCS_PDU +---------------------------------------+--------+ Fig. 6.2: RFC 1483 base encapsulation. Suzuki Informational [Page 23] RFC 2383 ST2+ over ATM August 1998 The value of the LLC is 0xAA-AA-03, the value of the OUI is 0x00-00- 00, and the value of the PID is 0x08-00. The classification of the IPv4 and the ST2+ SCMP is determined by the IP version number, which is located in the first four bits of the IPv4 or ST headers. 6.1.3 RFC 1483 extension base encapsulation The RFC 1483 extension base encapsulation is the same as for RFC 1483 base encapsulation, except that the value of the OUI is 0x00-00-5E (IANA) and the value of the PID is 0xXX-XX (TBD). The RFC 1483 base encapsulation for the SCMP is ideal, but requires modifying the IPv4 processing in the driver software of the WS or PC. Therefore, the RFC 1483 base encapsulation may be difficult to implement. This encapsulation is designed to solve this problem. 6.2 Service Primitives Provided by Control Plane RFC 1819 ST2+ does not specify SCMP state machines. And the ST2+ over ATM protocol does not correspond to SCMP state machines. Therefore, the control plane specification assumes the following. o The ST2+ agent has ST2+ SCMP layer entities that correspond to the next hops and the previous hop in the stream. o The SCMP layer entity terminates ACK, ERROR, and timeout processing and provides reliable SCMP delivery. o The origin consists of an upper layer entity, ST2+ SCMP layer entities for next hops, and a routing machine that delivers SCMP messages between these entities. o The intermediate agent consists of ST2+ SCMP layer entities for a previous hop and for next hops and a routing machine that delivers SCMP messages between these entities. o The target consists of an upper layer entity, an ST2+ SCMP layer entity for a previous hop, and a routing machine that delivers SCMP messages between these entities. At least, the ST2+ SCMP layer entity for the next hop provides the following services to the routing machine. o connect.req This primitive sends a request for a CONNECT message transfer to the ST2+ SCMP layer entity. Suzuki Informational [Page 24] RFC 2383 ST2+ over ATM August 1998 o change.req This primitive sends a request for a CHANGE message transfer to the ST2+ SCMP layer entity. o accept.ind This primitive indicates an ACCEPT message delivery from the ST2+ SCMP layer entity. o disconnect.req This primitive sends a request for a DISCONNECT message transf