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INTERNET-DRAFT Mark W. Garrett, Bellcore Expires 26 September 1997 Marty Borden, New Oak Communications 26 March 1997 Interoperation of Controlled-Load and Guaranteed Services with ATM <draft-ietf-issll-atm-mapping-02.txt> Status of this Memo This document is an Internet-Draft. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract Service mappings are an important aspect of effective interoperation between Internet Integrated Services and ATM networks. This document provides guidelines for ATM virtual connection features and parameters to be used in support of the IP integrated services protocols. The specifications include IP Guaranteed Service, Controlled-Load Service and ATM Forum UNI specification, versions 3.0, 3.1 and 4.0. These service mappings are intended to facilitate effective end-to- end Quality of Service for IP networks containing ATM subnetworks. We discuss the various features of the IP and ATM protocols, and identify solutions and difficult issues of compatibility and interoperation. Garrett, Borden Expires September 1997 [Page 1] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 Table of Contents 0.0 What's New in This Version ......................................... 3 1.0 Introduction ....................................................... x 1.1 General System Architecture .................................... x 1.2 Related Documents .............................................. x 2.0 Discussion of ATM Protocol Features ................................ x 2.1 Service Category and Bearer Capability ......................... x 2.1.1 Service Categories for Guaranteed Service ................ x 2.1.2 Service Categories for Controlled Load ................... x 2.1.3 Service Categories for Best Effort ....................... x 2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions .... x 2.3 ATM Adaptation Layer ........................................... x 2.4 Broadband Low Layer Information ................................ x 2.5 Traffic Descriptors ............................................ x 2.5.1 Translating Traffic Descriptors for Guaranteed Service ... x 2.5.2 Translating Traffic Descriptors for Controlled Load Service x 2.5.3 Translating Traffic Descriptors for Best Effort Service .... x 2.6 QoS Classes and Parameters ..................................... x 2.7 Additional Parameters -- Frame Discard Mode .................... x 3.0 Discussion of IP-IS Protocol Features .............................. x 3.1 Handling of Excess Traffic ..................................... x 3.2 Use of AdSpec in Guaranteed Service with ATM ................... x 4.0 Discussion of Miscellaneous Items .................................. x 4.1 Units Conversion ............................................... x 5.0 Summary of ATM VC Setup Parameters for Guaranteed Service .......... x 5.1 Encoding GS Using Real-Time VBR ................................ x 5.2 Encoding GS Using CBR .......................................... x 5.3 Encoding GS Using Non-Real-Time VBR ............................ x 5.4 Encoding GS Using ABR .......................................... x 5.5 Encoding GS Using UBR .......................................... x 5.6 Encoding GS Using UNI 3.0 and UNI 3.1. ......................... x 6.0 Summary of ATM VC Setup Parameters for Controlled Load Service ..... x 6.1 Encoding CLS Using ABR ......................................... x 6.2 Encoding CLS Using Non-Real-Time VBR ........................... x 6.3 Encoding CLS Using Real-Time VBR ............................... x 6.4 Encoding CLS Using CBR ......................................... x 6.5 Encoding CLS Using UBR ......................................... x 6.6 Encoding CLS Using UNI 3.0 and UNI 3.1. ........................ x 7.0 Summary of ATM VC Setup Parameters for Best Effort Service ......... x 7.1 Encoding Best Effort Service Using UBR ......................... x Garrett, Borden Expires September 1997 [Page 2] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 7.2 Encoding Best Effort Service Using Other ATM Service Categories x 8.0 Acknowledgements ................................................... x Appendix 1 Abbreviations .............................................. x REFERENCES ............................................................. x AUTHORS' ADDRESSES ..................................................... x 0.0 What's New in This Version Corrections to VC setup parameter tables. Deleted specific QoS parameter values in tables. Section 3.1 on handling of excess traffic. 1.0 Introduction We consider the problem of providing IP Integrated Services [1] with an ATM subnetwork. This document is intended to be consistent with the rsvp protocol [2] for IP-level resource reservation (although it is, strictly speaking, independent of rsvp, since GS and CLS services can be supported through other mechanisms). In the ATM network, we consider ATM Forum UNI Signaling, versions 3.0, 3.1 and 4.0 [3, 4, 5]. The latter uses the more complete service model of The ATM Forum's TM 4.0 specification [6, 7]. This is a complex problem with many facets. In this document, we focus on the service types, parameters and signalling elements needed for service interoperation. The resulting service mappings can be used to provide effective end-to-end Quality of Service (QoS) for IP traffic that traverses ATM networks. The IP services considered are Guaranteed Service (GS) [8] and Controlled Load Service (CLS) [9]. We also treat the default Best Effort Service (BE) in parallel with these. Our recommendations for BE are intended to be consistent with RFC 1755 [10], and its revision (in progress) [11], which defines how ATM VCs can be used in support of normal BE IP service. The ATM services we consider are: CBR Constant Bit Rate rtVBR Real-time Variable Bit Rate nrtVBR Non-real-time Variable Bit Rate UBR Unspecified Bit Rate ABR Available Bit Rate Garrett, Borden Expires September 1997 [Page 3] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 (Note, Appendix 1 provides definitions for all abbreviations.) In the case of UNI 3.0 and 3.1 signaling, where these service are not all clearly distinguishable, we identify the appropriate available services. The service mappings which follow most naturally from the service definitions are as follows: Guaranteed Service -> CBR or rtVBR Controlled Load -> nrtVBR or ABR (with a minimum cell rate) Best Effort -> UBR or ABR For completeness we provide detailed mappings for all service combinations and identify how each meets or fails to meet the requirements of the higher level IP services. The reason for not restricting mappings to the most obvious or natural ones is that we cannot assume now that these services will always be ubiquitously available. A number of details, such as treatment of packets in excess of the flow traffic descriptor, make service mapping a complicated subject, which cannot be expressed briefly and accurately at the same time. The remainder of this introduction provides a general discussion of the system configuration and other assumptions. Section 2 considers the relevant ATM protocol elements and their effects as related to Guaranteed, Controlled Load and Best Effort services (the latter being the default "service"). Section 3 discusses a number of important features of the IP services and how they can be handled on an ATM subnetwork. Section 4 addresses a few miscellaneous problems which are neither distinctly IP nor ATM. Section 5 gives detailed VC setup parameters for Guaranteed Service, and considers the effect of using each of the ATM service categories. Section 6 provides a similar treatment for Controlled Load Service. Section 7 considers Best Effort service. This document is only a part of the total solution to providing the interworking of IP integrated services with ATM subnetworks. The important issue of VC management, including flow aggregation, is considered in [12]. We do not consider how routing -- QoS sensitive or not -- interacts with the use of VCs, especially in the case of multicast (or point-to-multipoint) flows. We expect that a considerable degree of implementation latitude will exist, even within the guidelines presented here. Many aspects of interworking between IP and ATM will depend on economic factors, and will not be subject to standardization. Garrett, Borden Expires September 1997 [Page 4] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 1.1 General System Architecture We assume that the reader has a general working knowledge of IP, rsvp and ATM protocols. The network architecture we consider is illustrated in Figure 1, below. An IP-attached host may send unicast datagrams to another host, or may use an IP multicast address to send packets to all of the hosts which have "joined" the multicast "tree". In either case, a destination host may then use RSVP to establish resource reservation in routers along the internet path for the data flow. An ATM network lies in the path (chosen by the IP routing), and consists of one or many ATM switches. It uses VCs to provide both resources and QoS within the ATM cloud. These connections are set up, added to (in the case of multipoint trees), torn down, and controlled by the edge devices, which act as both IP routers and ATM interfaces, capable of initiating and managing VCs across the ATM user-to-network (UNI) interface. The edge devices are assumed to be fully functional in both the IP int-serv/RSVP protocols and the ATM UNI protocols, as well as translating between them. ATM Cloud ------------------ H ----\ ( ) /------- H H ---- R -- R -- E --( ATM Sw -- ATM Sw ) -- E -- R -- R -- H H ----/ | ( ) \ | ------------------ \------ H H ----------R Figure 1: Network Architecture with hosts (H), Routers (R) and Edge Devices (E). The edge devices may be considered part of the IP internet or part of the ATM cloud, or both. This is not an issue since they must provide capabilities of both environments. The edge devices have normal RSVP capability to process RSVP messages, reserve resources, and maintain soft state (in the control path), and to classify and schedule packets (in the data path). They also have the normal ATM capabilities to initiate connections by signaling, and to accept or refuse connections signaled to them. They police and schedule cells going into the ATM cloud. An IP-level reservation (RESV message) triggers the edge device to translate the RSVP service requirements into ATM VC (UNI) semantics. A range of VC management policies are possible, which determine whether a flow should initiate a new VC or join an existing one. VCs Garrett, Borden Expires September 1997 [Page 5] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 are managed according to a combination of standards and local policy rules, which are specific to either the implementation (equipment) or the operator (network service provider). Point-to-multipoint connections within the ATM cloud can be used to support general IP multicast flows. In ATM, a point to multipoint connection can be controlled by the source (or root) node, or a leaf initiated join (LIJ) feature in ATM may be used. Note, the topic of VC management and mapping of flows onto VCs is considered at length in another issll working group draft [12]. Figure 2 shows the functions of an edge device, summarizing the work not part of IP or ATM abstractly as an InterWorking Function (IWF), and segregating the control and data planes. (Note: for expositional convenience, policy control and other control functions are included as part of the admission control in the diagram.) IP ATM ____________________ | IWF | | | admission <--> | service mapping | <--> ATM control | VC management | signalling & | address resolution | admission |....................| control | | classification/ |ATM Adaptation Layer| cell policing & <--> | Segmentation and | <--> scheduling/ scheduling | Reassembly | shaping | Buffering | ____________________ Figure 2: Edge Device Functions showing the IWF In the logical view of Figure 2, some functions, such as scheduling, are shown separately, since these functions are required of both the IP and ATM sides. However it may be possible in an integrated implementation to combine such functions. It is not possible to completely separate the service mapping and VC management functions. Several illustrative examples come to mind: (i) Multiple integrated-services flows may be aggregated to use one point-to-multipoint VC. In this case, we assume the IP flows are of the same service type and their parameters have been merged appropriately. (ii) The VC management function may choose to allocate extra resources in anticipation of further reservations or Garrett, Borden Expires September 1997 [Page 6] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 based on an empiric of changing TSpecs. (iii) There must exist a path for best effort flows and for sending the rsvp control messages. How this interacts with the establishment of VCs for QoS traffic may alter the characteristics required of those VCs. See [12] for further details on VC management. Therefore, in discussing the service-mapping problem, we will assume that the VC management function of the IWF can always express its result in terms of an IP-level service with some QoS and TSpec. The service mapping algorithm, which is the subject of this document, can then identify the appropriate VC parameters, whether the resulting action is initiation of a new VC, the addition/deletion of a leaf to an existing multipoint tree, or the modification of an existing VC to one of another description. 1.2 Related Documents Earlier ATM Forum documents were called UNI 3.0 and UNI 3.1. The 3.1 release was used to correct errors and fix alignment with the ITU. Unfortunately UNI 3.0 and 3.1 are incompatible. However this is in terms of actual codepoints, not semantics. Therefore, descriptions of parameter values can generally be used for both. After 3.1, the ATM Forum decided to release documents separately for each technical working group. The Traffic Management and Signalling 4.0 documents are available publically at ftp.atmforum.com/pub. We refer to the combination of traffic management and signalling as TM/UNI 4.0, although specific references may be made to the TM 4.0 specification or the UNI SIG 4.0 specification. Within the IETF area, related material includes the work of the rsvp [2], int-serv [1, 8, 9, 13, 14] and ion working groups [10, 11] of the IETF. Rsvp defines the resource reservation protocol (which is analogous to signaling in ATM). Int-serv defines the behavior and semantics of particular services (analogous e.g., to the Traffic Management working group in the ATM Forum). Ion defines interworking of IP and ATM for traditional Best Effort service, and covers all issues related to routing and addressing. A large number of ATM signaling details are covered in RFC 1755 [10], e.g., differences between UNI 3.0 and UNI 3.1, encapsulation, frame- relay interworking, etc. These considerations generally extend to IP over ATM with QoS as well. Any description given in this document of IP Best Effort service (i.e. the default behavior) over ATM is intended to be consistent with RFC 1755 and it's extension for UNI 4.0 [11], and those documents are to be considered definitive. In some instances with non-best-effort services, certain IP/ATM features will diverge from the following RFC 1755. The authors have attempted Garrett, Borden Expires September 1997 [Page 7] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 to note such differences explicitly. (For example, best effort VCs are taken down on timeout by either edge device, while QoS VCs are only removed by the upstream edge device when the corresponding rsvp reservation is deleted.) RFC 1821 [15], represents an early discussions of issues involved with interoperating IP and ATM protocols for integrated services and QoS. 2.0 Discussion of ATM Protocol Features In this section, we discuss each of the items that must be specified in the setup of an ATM VC. For each of these we discuss which specified items and values may be most appropriate for each of the three integrated services. The ATM Call Setup is sent by the edge device to the ATM network to establish end-to-end (ATM) service. This setup contains the following information. Service Category/Broadband Bearer Capability AAL Parameters Broadband Low Layer Information Calling and Called Party Addressing Information Traffic Descriptors QoS Parameters Additional Parameters of TM/UNI 4.0 We will discuss each of these, except addressing information, as they relate to the translation of GS and CLS to ATM services. Following the discussion of the service categories, we discuss the tagging and conformance definitions for IP and ATM, since the policing method is implicit in the call setup. We then continue with mappings of the other parameters and information elements. 2.1 Service Category and Bearer Capability The highest level of abstraction distinguishing features of ATM VCs is in the service category or bearer capability. Service categories were introduced in TM/UNI 4.0; previously the bearer capability was used to discriminate at this level. In each version of the ATM specifications, these indicate the general properties required of a VC: whether there is a real-time delay Garrett, Borden Expires September 1997 [Page 8] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 constraint, whether the traffic is constant or variable rate, the applicable traffic and QoS description parameters and (implicitly) the complexity of some supporting switch mechanisms. For UNI 3.0 and UNI 3.1, there are only two distinct options for bearer capabilities (in our context): BCOB-A: constant rate, timing required, unicast/multipoint; BCOB-C: variable rate, timing not required, unicast/multipoint. There is a third capability, BCOB-X, but in the case of AAL5 (which we require -- see below) it can be used interchangeably and consistently with the above two capabilities. In TM/UNI 4.0 the service categories are: Constant Bit Rate (CBR) Real-time Variable Bit Rate (rtVBR) Non-real-time Variable Bit Rate (nrtVBR) Unspecified Bit Rate (UBR) Available Bit Rate (ABR) The first two of these are real-time services, so that rtVBR is new to TM/UNI 4.0. The ABR service is also new to TM/UNI 4.0. UBR exists in all specifications, except perhaps in name, through the ``best effort'' indication flag and/or the QoS Class 0. The encoding used in 4.0 is consistent with the earlier versions. For example, the Service Category is indicated solely by the combination of the Bearer Capability and the Best Effort indication flag. In principle, it is possible to support any foreseeable service through the use of BCOB-A/CBR. This is because the CBR service is equivalent to having a ``pipe'' with specified bandwidth/timing. However, it may be desirable to make better use of the ATM network's resources by using other, less demanding, services when available. (See RFC 1821 for a discussion of this [15].) 2.1.1 Service Categories for Guaranteed Service There are two possible mappings for GS: CBR (BCOB-A) rtVBR GS requires real-time support, that is, timing is required. Thus in Garrett, Borden Expires September 1997 [Page 9] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 UNI 3.x, the bearer class BCOB-A (or an equivalent BCOB-X formulation) must be used. In TM/UNI 4.0 either CBR or rtVBR is appropriate. In both cases, GS would use a value of CLR appropriately low for the link (i.e., such that congestion losses are dominated by losses due to bit errors). The use of rtVBR may encourage recovery of allocated bandwidth left unused by a source. It also accomm odates more bursty sources with a larger bucket parameter, and permits the use of tagging for excess traffic (see Section 2.2). Neither the BCOB-C bearer class, nor nrtVBR, UBR, ABR are good matches for the GS service. These provide no delay estimates and cannot guarantee consistently low delay for every packet. Specification of BCOB-A or CBR requires specification of a PCR. The PCR should be specified as the the token bucket rate parameter, with appropriate conversion from bytes to cells (accounting for overhead), of the GS TSpec. For both of these, the network provides a nominal clearing rate of PCR with jitter toleration (bucket size) CDVT, specified in a network specific manner (see below). Specification of rtVBR requires the specification of two rates, SCR and PCR. This models bursty traffic with specified peak and average rates. With rtVBR, it is appropriate to map the PCR to the line rate of incoming traffic and the SCR to the GS TSpec bucket rate. The ATM bucket sizes are CDVT, in a network specific manner, and CDVT+BT, respectively for the PCR and SCR parameters (see below). 2.1.2 Service Categories for Controlled Load There are three possible mappings for CLS: CBR (BCOB-A) ABR nrtVBR (BCOB-C) Note that under UNI 3.x, only the first and third choices are applicable. The first, with a CBR/BCOB-A connection, provides a higher level of QoS than is necessary, but it may be convenient to simply allocate a fixed-rate ``pipe'', which should be ubiquitously supported in ATM networks. However unless this is the only choice available, this will probably be wasteful of network resources. The ABR category with a positive MCR aligns with the CLS idea of ``best effort with floor.'' The ATM network agrees to forward cells with a rate of at least MCR, which should be directly converted from the token bucket rate of the TSpec. The bucket size parameter Garrett, Borden Expires September 1997 [Page 10] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 measures approximately the amount of buffer required at the IWF. The nrtVBR/BCOB-C category can also be used. The rtVBR category can be used, although the edge device must choose a value for CTD and CDV as a matter of local policy. The UBR category does not provide enough capability for Controlled Load. The point of CLS is to allow an allocation of resources, which is facilitated by the token bucket traffic descriptor, and is unavailable in UBR. 2.1.3 Service Categories for Best Effort All of the service categories have the capability to carry Best Effort service, but the natural service category is UBR (or, in UNI 3.x, BCOB-C or BCOB-X, with the best effort indication set). A CBR or rtVBR clearly could be used, and since the service is not real- time, a nrtVBR connection could also be used. In these cases the rate parameter used reflects a bandwidth allocation in support of the edge device's best effort connectivity to the far edge router. It would be normal for traffic from many source/destination pairs to be aggregated on this connection; indeed, since Best Effort is the default IP behavior, the individual flows are not necessarily identified or accounted for. CBR may be a preferred solution in the case where best effort traffic is sufficiently highly aggregated that a simple fixed-rate pipe is efficient. Both CBR and nrt-VBR provide bandwidth allocation which may be useful for billing purposes. An ABR connection could similarly be used to support Best Effort traffic. The support of data communications protocols such as TCP/IP is the explicit purpose for which ABR was specifically designed. It is conceivable that a separate ABR connection would be made for different IP flows, although the normal case would probably have all IP Best Effort traffic with a common egress router sharing a single ABR connection. The rt-VBR service category may be considered less suitable, simply because both the real-time delay constraint and the use of SCR/BT add unnecessary complexity. See specifications from the IETF ion working group [10, 11] for related work on support of Best Effort service with ATM. 2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions An ATM header carries the Cell Loss Priority (CLP) bit. Cells with Garrett, Borden Expires September 1997 [Page 11] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 CLP=1 are said to be ``tagged'' and have lower priority. This tagging may be done by the source, to indicate relative priority within the VC, or by a switch, to indicate traffic in violation of policing parameters. Options involving the use of tagging are decided at call setup time. A Conformance Definition is a rule that determines whether a cell is conforming to the traffic descriptor of the VC. The conformance definition is given in terms of a Generic Cell Rate Algorithm (GCRA), also known as a "leaky bucket" algorithm, for CBR and VBR services. (UBR and ABR have network-specific conformance definitions. Note, the term "compliance" in ATM is used to describe the behavior of a connection.) The network may tag cells which are non-conforming, rather than dropping them only if the VC is set up to request tagging and the network supports the tagging option. When congestion occurs, a switch must attempt to discard tagged cells in preference to the discarding of CLP=0 cells. However, the mechanism for doing this is completely implementation specific. Tagged cells are treated with a behavior which is Best Effort in the sense that they are transported when bandwidth is available, queued when buffers are available, and dropped when the resources are overcommitted. Since GS and CLS services require excess traffic to be treated as Best Effort, the tagging option should always be chosen (if supported) in the VC setup as a means of ``downgrading'' non- conformant cells. However, the term ``best effort'' seems to be used with two distinguishable meanings in the int-serv specs. The first is that of a service class that, in some typical scheduler implementations, would correspond to a separate queue. Placing excess traffic in best effort in this sense would be giving it lower delay priority. The other sense is more generic, meaning that the network would make a best effort to transport the traffic. A reasonable expectation is that a network with no contending traffic would transport the packet, while a very congested network would drop the packet. A packet that could be tagged with lower loss priority (such as the ATM CLP bit) would be more likely to be dropped, but would not normally be transported out of order with respect to the conforming portion of the flow. Such a mechanism would agree with the latter definition of best effort, but not the former. In TM/UNI 4.0 tagging does not apply to the CBR or ABR services. However, there are three conformance definitions of VBR service (for both rtVBR and nrtVBR) to consider. In VBR, only the conformance definition VBR.3 supports tagging and applies the GCRA with PCR to the aggregate CLP=0+1 cells, and another GCRA with SCR to the CLP=0 cells. Thus this conformance definition should always be used in Garrett, Borden Expires September 1997 [Page 12] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 support of IP integrated services. For UBR service, conformance definition UBR.2 supports the use of tagging, but a CLP=1 cell does not imply non-conformance; it may be a hint of network congestion. Once an ATM connection is established, and the particular conformance definition is determined, the resulting policing action is mandatory. Since the conformance algorithm operates on cells, when mapping rates and bucket sizes from IP services to corresponding ATM parameters, a correction needs to be made (at call setup time) for the ATM segmentation overhead. Unfortunately this overhead, as a ratio, depends on packet length, with the overhead largest for small packets. Thus the appropriate correction could be based on minimum packet size, expected packet size, or otherwise in a network specific manner, determined at the edge device IWF. See Section 4.1. It is always better fo the IWF to tag cells when it can anticipate that the ATM network would do so. This is because the IWF knows the IP packet boundaries and can tag all of the cells corresponding to a packet. If left to the ATM layer UPC, the network would inevitably carry some cells of packets which are worthless, because some other cells from those packet are dropped due to non-conformance. Therefore, the IWF, knowing the VC GCRA parameters, should always anticipate the cells which will be tagged by the ATM UPC and tag all of the cells uniformly across each affected packet. 2.3 ATM Adaptation Layer The AAL type 5 encoding must be used, as specified in RFC 1483 and RFC 1755. AAL5 requires specification of the maximum SDU size in both the forward and reverse directions. Both GS and CLS specify a maximum packet size as part of the TSpec and this value shall be used as the maximum SDU in each direction for unicast connections, but only in one direction for point-to-multipoint connections, which are unidirectional. When more than one flow aggregated into a single VC, the TSpecs are merged to yield the largest packet size. In no case can this exceed 65535 (or, of course, the MTU of the link). 2.4 Broadband Low Layer Information The B-LLI Information Element is transferred transparently by the ATM network between the edge devices and is used to specify the encapsulation method. Multiple B-LLI IEs may be sent as part of negotiation. The default encapsulation LLC/SNAP [16] must be supported as specified in RFC 1577 and RFC 1755. Additional Garrett, Borden Expires September 1997 [Page 13] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 encapsulations are discussed in RFC 1755 and we refer to the discussion there. 2.5 Traffic Descriptors The ATM traffic descriptor always contains specification of a peak cell rate (PCR) (in each direction). For variable rate services it also contains specification of a sustainable cell rate (SCR) and maximum burst size (MBS). The SCR and MBS form a leaky bucket pair (rate, depth), while the bucket depth parameter for PCR is CDVT. Note that CDVT is not signaled explicitly, but is determined by the network operator, and serves as a measure of the jitter imposed by the network. Since CDVT is not signaled, and is presumed to be small, the leaky bucket traffic descriptor (TSpec) of the Internet service cannot always be directly mapped into PCR/CDVT parameters. Additional buffering is needed at the IWF to account for the depth of the bucket. The Burst Tolerance is related to MBS (see TM 4.0 for details). Roughly, they are both expressions of the bucket depth parameter that goes with SCR. The units of BT is time while the units of MBS is cells. Since both SCR and MBS are signalled, they can be computed directly from the IP layer traffic description. The specific manner in which resources are allocated from the traffic description is implementation specific. Note that when translating the traffic parameters, the segmentation overhead and minimum policed unit need to be taken into account (see Section 4.2 below). In ATM UNI SIG 4.0 there are the notions of Alternative Traffic Descriptors and Minimal Traffic Descriptors. Alternative Traffic Descriptors enumerate other acceptable choices for traffic descriptors and are not considered here. Minimal Traffic Descriptors are used in ``negotiation,'' which refers to the specific way in which an ATM connection is set up. Very roughly it works like this, taking PCR as an example: A minimal PCR and a requested PCR are signalled, the requested PCR being the usual item signalled, and the minimal PCR being the absolute minimum that the source edge device will accept. When sensing the existence of both minimal and requested parameters, the intermediate switches along the path may reduce the requested PCR to a ``comfortable'' level. This choice is part of admission control, and is therefore implementation dependent. If at any point the requested PCR falls below the minimal PCR then the call is cleared. Minimal Traffic Descriptors can be used to present an acceptable range for parameters and ensure a higher Garrett, Borden Expires September 1997 [Page 14] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 likelihood of call admission. Whether anything more specific about Minimal Traffic Descriptors needs to be said here is left for further study (FFS). In general, our discussion of connection parameters assumes the values resulting from successful connection setup. The Best Effort indicator (used only with UBR) and Tagging indicators are also part of the signaled information element (IE) containing the traffic descriptor. In the UNI SIG 4.0 traffic descriptor IE there is an additional parameter, the Frame Discard indicator (see Section 2.7). 2.5.1 Translating Traffic Descriptors for Guaranteed Service For Guaranteed Service there is a peak rate, p, a source Tspec rate, r_s, a receiver Tspec rate r_r, and an Rspec rate, R. The two Tspec rates are intended to support receiver heterogeneity, in the sense that different receivers can accept different rates representing subsets of the sender's traffic. In this document we leave this feature for further study (FFS), and assume the two Tspec rates are always identical. The Tspec rate describes the traffic itself, and is used for policing, while the Rspec rate (which cannot be smaller) is the allocated service rate. A receiver increases R over r to reduce the delay. When mapping Guaranteed Service onto a rtVBR VC, the ATM traffic descriptor parameters (PCR, SCR, MBS) can be set within the following bounds: R <= PCR <= min(p, line rate) r <= SCR <= PCR 0 <= MBS <- b. Note that a receiver can choose R > p to lower the delay. This leaves the first equation somewhat subject to interpretation. If a receiver chooses R > line rate, it seems clear that the admission control would simply reject the reservation. The edge device has a buffer preceding the ATM network which must be sufficient to absorb bursts arriving faster than they can be admitted into the ATM network. For example, parameters may be set as PCR = R, SCR = r, MBS = b. The edge device buffer of size b would absorb a burst sent at any IP-level peak rate. Although this buffer exists, the ATM network must accept bursts at rate PCR, at least R, to ensure that the edge device delay is no greater than b/R. Since this buffer is not in the ATM network, its delay is not included in D_ATM. Garrett, Borden Expires September 1997 [Page 15] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 For GS over CBR, the service rate is mapped to the PCR parameter, using the same constraint for PCR given above. The edge device again requires adequate buffering to accommodate the TSpec bucket depth and ensure delay before entering the ATM network of no more than b/R. If PCR is greater than R, the buffer requirement may be relaxed accordingly. 2.5.2 Translating Traffic Descriptors for Controlled Load Service Controlled Load service has a peak rate, p, a Tspec rate, r, and a corresponding bucket depth parameter, b. The ATM traffic parameters for nrtVBR service category are constrained by r <= SCR <= PCR <= min(p, line rate) 0 <= MBS <- b. For ABR VCs, the Tspec rate would be used to set the minimum cell rate (MCR) parameter. The bucket depth parameter does not map directly to a signalled ATM parameter, so the edge device must have a buffer of at least b bytes. For CBR, the Tspec rate sets a lower bound on PCR, and again, the available buffering in the edge device must be adequate to accommodate possible bursts. 2.5.3 Translating Traffic Descriptors for Best Effort Service For Best Effort service, there is no traffic description. The UBR service category allows negotiation of PCR, simply to allow the source to discover the smallest physical bottleneck along the path. 2.6 QoS Classes and Parameters In TM/UNI 4.0 the three QoS parameters may be individually signalled. These parameters are the Cell Loss Ratio (CLR), Cell Transfer Delay (CTD), and Cell Delay Variation (CDV). In UNI 3.x the setup message includes only the QoS Class, which is essentially an index to a network specific table of values for these three parameters. A network provider may choose to associate other parameters, such as Severely Errored Cell Block Ratio, but these are less well understood and accepted compared to the basic loss, delay and jitter parameters Garrett, Borden Expires September 1997 [Page 16] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 mentioned here. The ITU has recently included a standard set of parameter values for a (small) number of QoS classes in the latest version of Recommendation I.356, October 1996. The network provider may choose to define further network-specific QoS classes in addition to these. The problem of agreement between network providers as to the definition of QoS classes is completely unaddressed to date. We will adopt a convention expressed in UNI 3.x, that assumes that QoS class 1 is appropriate for low-delay, low-loss CBR connections, and QoS class 3 is appropriate for variable rate connections with loss and delay roughly appropriate for non-real-time data applications. Note that the QoS class definitions in the new I.356 version may not align with this model. Since no IP layer counterparts to these ATM QoS parameters exist in any of the IP services, they must be set by policy of the edge device. The QoS classes can be chosen relatively easily. QoS class 1 should be used with Guaranteed Service and QoS class 3 should be used with Controlled Load Service. Best Effort Service always gets QoS class 0, which is unspecified QoS by definition. There are two issues which amount to the same thing: First, the choice of individually signalled parameter values (under TM/UNI 4.0) for GS and CLS is the edge device policy. The second issue is choosing parameter values for the two QoS classes, which is the ATM network policy. If the same network operator controls both, then these problems are identical; if not, an agreement to make the values identical would be extremely desirable. Note that we have mapped QoS class 1 and 3 onto Guaranteed and Controlled Load service respectively. This is regardless of what service category is used. So when running CLS over a CBR pipe, it would not be inappropriate to use QoS class 3. This leaves the delay unspecified (or much looser than with QoS 1). These comments should be taken as preliminary, as these issues are far from clear, and industry consensus should be sought. 2.7 Additional Parameters -- Frame Discard Mode In TM/UNI 4.0 ATM allows the user to choose a mode where a dropped cell causes all cells up to the last remaining in the AAL5 PDU to be also dropped. This improves efficiency and the behavior of end-to- end protocols such as TCP, since the remaining cells of a damaged PDU are useless to the receiver. For IP over ATM, Frame Discard should always be used in both directions, if available, for all services. Garrett, Borden Expires September 1997 [Page 17] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 3.0 Discussion of IP-IS Protocol Features 3.1 Handling of Excess Traffic (Placeholder for text.) Reiterate that whole packets should be tagged, See Section 2.2. 3.2 Use of AdSpec in Guaranteed Service with ATM The AdSpec is a feature of Guaranteed Service which allows a receiver to calculate the worst-case delay associated with a GS flow. Three quantities, C, D, and MPL, are accumulated (by simple addition of components, one for each network element) in the PATH message from source to receiver. The resulting values can be different for each unique receiver. The maximum delay is then found by delay <= b/R + C/R + D + MPL The Maximum Path Latency (MPL) includes propagation delay and any other unavoidable system delays. (We neglect the effect of maximum packet size and peak rate here; see the GS specification [8] for the more detailed equation.) The service rate requested by the receiver, R, can be greater than the sender's Tspec rate, r. The effect of the larger R is to allocate more bandwidth and, through this equation, lower the packet delay. The burst size, b, is the leaky bucket parameter from the Tspec, and is not changed by the receiver in the Rspec. The values of C and D which a router advertise will depend on both the particular packet scheduling algorithm used in the router, and the characteristics of the subnet attached to the router. We assume here that each router (or the source host) takes responsibility for its downstream subnet only. If the subnet is a simple point-to-point link, then the subnet-specific parts of C and D will account for the link transmission rate and MTU. An ATM subnet is more complex. The edge router will always have an internal packet scheduler, which will contribute to C and D. For this discussion we consider only the ATM subnet-specific components. We further assume that the ATM network will be represented as a "pure delay" element, contributing a component to D, but not to C. The reason for this is that C would Garrett, Borden Expires September 1997 [Page 18] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 depend on details of the cell scheduling algorithm inside the ATM switches, which is not known by the edge device, where the AdSpec parameters are accumulated. (In the special case where the edge device does have enough information to modify C, it would not be precluded.) Generally the delay behavior of the whole ATM cloud may be expressed abstractly as a fixed constant D_ATM. Since the AdSpec values are incremented before any reservation is made, the edge device must have some knowledge about the VC which would be set up in case a reservation were made. This does not really add to the complexity of the device, since it must also have this information in order to make an intelligent VC setup request. For example, the edge device may have a cached table with the propagation delay and a reasonable additional delay budget, from which it composes a value of CTD for the VC setup. The device may learn such information through VC setup negotiation, and, indeed, there may be no other way to obtain that information. However, it seems reasonable that these values would be cached for later use when new VCs to the same egress router need to be established. Therefore, we will presume a table with values of MPL (which includes propagation delay) and expected queueing delays for each possible egress edge device. (How such a table is maintained is implementation specific.) The latter quantity is simply D_ATM, the value added to the AdSpec D term to account for the ATM network. When a RESV message arrives, causing a VC to be set up, the requested value for CTD should then be given by CTD = D_ATM + MPL + S_ATM. The last term, S_ATM is the portion of the slack term applied to the ATM portion of the path. Recall that the slack term [8] is positive when the receiver can afford more delay than that computed from the AdSpec. The ATM edge device may take part (or all) of the slack term to relax the delay constraint on the ATM VC. The distribution of delay slack among the nodes and subnets is network specific. An important detail to note is the relationship between the b/R term of the (Internet) delay and the corresponding MBS/SCR in the ATM network, when using a VBR VC. The term b/R accounts for the delay experienced by the last byte of a burst, of size b, which encounters a congested node. In the simple ideal case, where the scheduling algorithm emulates a fixed rate server, at rate R, the delay of the last byte is b/R. Once this occurs, the stream has been smoothed, and such a delay will not occur at later congested nodes, as long as they also serve at rate R. The form of the delay equation expresses this ideal behavior with C and D acting as error terms. Now, since the delay which smooths the burst can occur outside of the ATM cloud, Garrett, Borden Expires September 1997 [Page 19] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 the b/R term cannot include any delay within the ATM cloud. However, a burst of size MBS is permitted to enter the ATM network, and it may be served at a rate no greater than SCR. We might reasonably expect a queueing delay of MBS/SCR to occur at a congested ATM switch. If the ATM network will impose this delay, then it must be included in the value of D_ATM advertised. If the ATM network can increase its bandwidth allocation (e.g., due to CTD being lower than MBS/SCR), to decrease this delay, then this behavior should be reflected in the value of D_ATM. So, the information from which the edge device determines D_ATM must reflect an accurate abstraction of the actual behavior of the ATM network. To the extent that D_ATM is approximate (and it must be an upper bound on the actual delay), it reduces the chance that the VC setup will succeed, and/or increases its cost. 4.0 Discussion of Miscellaneous Items 4.1 Units Conversion In the integrated services domain, bucket sizes and rates are measured in bytes and bytes/sec, respectively, whereas for ATM, they are measured in cells and cells/sec. Packets are segmented into 53 byte cells of which the first 5 bytes are header information. For B = number of Bytes, C = number of cells, a rough approximation between the token bucket parameters (rate and bucket depth) is C = B/48. This is actually a lower bound on C and does not take into account the extra padding at the end of a partially filled cell, or the 8 byte trailer in the last cell of an AAL5 encoding. The actual relationship between the number of cells and bytes of one packet is C = 1 + int(B/48) + x, where x = 1 if B mod 48 > 41 0 otherwise. where int() is the rounding down operation. The third term is 0 or 1 and is 1 only when the remainder of B/48 is 41 or more. (An additional cell is needed because the 41 bytes plus 8 byte trailer will not fit in a cell.) Garrett, Borden Expires September 1997 [Page 20] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 The above formula is not particularly amenable to engineering considerations. By equating the number of bytes before and after segmentation we have 48 C = B + 8 + A, where A is the additional padding used in the last 2 cells and has the range 0 <= A <= 47. From this we obtain a number of useful observations. For example, if one believes that the packet lengths are uniformly distributed mod 48, then on average, 48 C = B + 8 + 47/2, or C = B/48 + .65625. We can also make use of the upper bound on A to state that 48 C <= B + 55. This is true for any one packet. Considering the number of bytes in a stream of P packets, we have 48 C <= B + 55 P. The number of packets P may not be a readily available quantity. However, in terms of the minimum policed unit m, we know that P * m <= B. Hence P <= B/m and 48 C <= B ( 1 + 55/m). That is, C <= B/48 * (1 + 55/m). 5.0 Summary of ATM VC Setup Parameters for Guaranteed Service This section describes how to create ATM VCs appropriately matched for Guaranteed Service. The key points differentiating among ATM choices are that real-time timing is required, that the data flow may have a variable rate, and that demotion of non-conforming traffic to best effort is required to be in agreement with the definition of GS. For this reason, we prefer an rtVBR service in which tagging is supported. Another good match is to use CBR with special handling of any non-conforming traffic. Note, in all cases the encodings assume point to multipoint connections, where the backward channel is not used. This is done to be consistent with rsvp, which generally assumes a multicast scenerio. If a specific situation does not involve multicast, then the IWF may make use of the backward channel in a point-to-point VC, provided that the QoS parameters are mapped consistently for the service provided. Garrett, Borden Expires September 1997 [Page 21] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 5.1 Encoding GS Using Real-Time VBR (ATM Forum TM/UNI 4.0) AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size 0 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 Note 1 Backward PCR CLP=0+1 0 Forward SCR CLP=0 Note 1 Backward SCR CLP=0 0 Forward MBS (CLP=0) Note 1 Backward MBS (CLP=0) 0 BE indicator NOT included Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 2 ATM Transfer Capability 9 (Real time VBR) Note 3 Susceptible to Clipping 00 (bit encoding for Not susceptible) User Plane Configuration 01 (bit encoding for pt-to-mpt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 4 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 1 Note 5 QoS Class Backward 1 Note 5 QoS Parameters Note 6 Acceptable Forward CDV Acceptable Forward CLR Forward Max CTD Note 1: See discussion Section 2.5.1. Note 2: Value 3 (BCOB-C) can also be used. Note 3: The ATC value 19 is not used. The value 19 implies CLR Garrett, Borden Expires September 1997 [Page 22] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 objective applies to the aggregate CLP=0+1 stream and that does not give desirable treatment of excess traffic in the case of IP. Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. Note 5: Cf ITU I.365 (Oct 1996) for new definition. Note 6: See section 2.6 for the values to be used The cumulative CDV is also provided, but it depends on local implementation, and not on values mapped from IP level service parameters. 5.2 Encoding GS Using CBR (ATM Forum TM/UNI 4.0) It is also possible to support GS using a CBR ``pipe.'' The advantage of this is that CBR is probably supported; the disadvantage is that data flows may not fill the pipe (utilization loss) and there is no tagging option available. AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of TSpec SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR 0 Note 1 Backward PCR 0 Forward PCR 0+1 Note 1 Backward PCR 0+1 0 BE indicator NOT included Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 2 ATM Transfer Capability 5 (CBR) Note 3, 4 Susceptible to Clipping 00 (bit encoding for Not susceptible) User Plane Configuration 01 (bit encoding for pt-to-mpt) Broadband Low Layer Information Garrett, Borden Expires September 1997 [Page 23] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 5 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 1 Note 6 QoS Class Backward 1 Note 6 QoS Parameters Note 7 Acceptable Forward CDV Acceptable Forward CLR Forward Max CTD Note 1: See discussion Section 2.5.1. Note 2: Value 1 (BCOB-A) can also be used. Note 3: If bearer class A is chosen the ATC field must be absent. Note 4: The ATC value 7 is not used. The value 7 implies CLR objective applies to the aggregate CLP=0+1 stream and that does not give desirable treatment of excess traffic in the case of IP. Note 5: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. Note 6: Cf ITU I.365 (Oct 1996) for new definition. Note 7: See section 2.6 for the values to be used The cumulative CDV is also provided, but it depends on local implementation, and not on values mapped from IP level service parameters. 5.3 Encoding GS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0) The remaining ATM service categories, including nrtVBR, do not provide delay guarantees and cannot be recommended as the best fits. However in some circumstances, the best fits may not be available. If nrtVBR is used, no hard delay can be given. However by using a variable rate service with low utilization, delay may be `reasonable', but not controlled. The encoding of GS as nrtVBR is the same as that for CLS using nrtVBR, except that the Forward PCR would be derived from the Tspec peak rate. See Section 6.2 below. Garrett, Borden Expires September 1997 [Page 24] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 5.4 Encoding GS Using ABR (ATM Forum TM/UNI 4.0) This is a very unlikely combination. The objective of the ABR service is to provide `low' loss rates which, via flow control, can result in delays. The introduction of delays is contrary to the design objectives of GS. If ABR were used for GS, the VC parameters would follow as for CLS over ABR. See Section 6.1. 5.5 Encoding GS Using UBR (ATM Forum TM/UNI 4.0) The UBR service is the default lowest common denominator of the services. It cannot provide delay or loss guarantees. However if it is used for GS, it will be encoded in the same way as Best Effort over UBR, with the exception that the PCR would be determined from the peak rate of the Tspec. See Section 5.1. 5.6 Encoding GS Using ATM Forum UNI 3.0/3.1 Specifications It is not recommended to support GS using VBR for the following reasons. The Class C bearer class does not represent real-time behavior. Appendix F of UNI 3.1 specification precludes the specification of traffic type "VBR" with the timing requirement "End to End timing Required" in conjunction with bearer class X. It is possible to support GS using a CBR ``pipe.'' The following table specifies the support of GS using CBR. AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of TSpec Mode 1 (Message mode) Note 1 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR 0 Note 2 Garrett, Borden Expires September 1997 [Page 25] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 Backward PCR 0 Forward PCR 0+1 Note 2 Backward PCR 0+1 0 BE indicator NOT included Tagging Forward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 3 Traffic Type 001 (bit encoding for Constant Bit Rate) Timing Requirements 01 (bit encoding for Timing Required) Susceptible to Clipping 00 (bit encoding for Not susceptible) User Plane Configuration 01 (bit encoding for pt-to-mpt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 4 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 1 QoS Class Backward 1 QoS Parameters Parameters are implied by the QOS Class Note 1: Only included for UNI 3.0. Note 2: See discussion, Section 2.5.1. Note 3: Value 1 (BCOB-A) can also be used. If BCOB-A is used Traffic Type and Timing Requirements fields are not included. Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. 6.0 Summary of ATM VC Setup Parameters for Controlled Load Service This section describes how to create ATM VCs appropriately matched for Controlled Load. CLS traffic is partly delay tolerant and of variable rate. NrtVBR and ABR (for TM/UNI 4.0 only) are the possible Garrett, Borden Expires September 1997 [Page 26] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 choices in supporting CLS. Generally we prefer to use point-to-multipoint connections. However this is not yet available in ABR. Other than in ABR, the encodings assume a point-to-multipoint connection. For a unicast connection, the backward parameters would be equal to the forward parameters. 6.1 Encoding CLS Using ABR (ATM Forum TM/UNI 4.0) AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size parameter M of TSpec SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 From line rate Forward MCR CLP 0+1 From TSpec token bucket rate Backward MCR CLP 0+1 From TSpec token bucket rate BE indicator NOT included Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 0 (Tagging not requested) Tagging Backward bit 0 (Tagging not requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 1 ATM Transfer Capability 12 (ABR) Traffic Type 010 (Variable Bit Rate) Timing Requirements 10 (Timing Not Required) Susceptible to Clipping 00 (Not susceptible) User Plane Configuration 00 (For pt-to-pt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 2 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 3 Note 3 QoS Class Backward 3 Note 3 Garrett, Borden Expires September 1997 [Page 27] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 QoS Parameters Note 4 Acceptable Forward CDV Acceptable Forward CLR Forward Max CTD ABR Setup Parameters Note 5 ABR Additional Parameters Note 5 Note 1: Value 3 (BCOB-C) can also be used. Note 2: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. Note 3: Cf ITU I.365 (Oct 1996) for new definition. Note 4: See section 2.6 for the values to be used. The cumulative CDV is also provided, but it depends on local implementation, and not on values mapped from IP level service parameters. Note 5: Discussion of these parameters is beyond the scope of this draft. 6.2 Encoding CLS Using Non-Real-Time VBR (ATM Forum TM/UNI 4.0) AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size 0 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0 Forward SCR CLP=0 From TSpec token bucket rate Backward SCR CLP=0 0 Forward MBS (CLP=0) From TSpec bucket size param Backward MBS (CLP=0) 0 BE indicator NOT included Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 1 ATM Transfer Capability 10 (Non-real time VBR) Note 2, 3 Garrett, Borden Expires September 1997 [Page 28] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 Susceptible to Clipping 00 (bit encoding Not susceptible) User Plane Configuration 01 (bit encoding pt-to-mpt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 4 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 3 Note 5 QoS Class Backward 3 Note 5 QoS Parameters Note 6 Acceptable Forward CDV Acceptable Forward CLR Forward Max CTD Note 1: Value 3 (BCOB-C) can also be used. Note 2: If bearer class C is used, the ATC field must be absent Note 3: The ATC value 11 is not used. The value 11 implies CLR objective applies to the aggregate CLP=0+1 stream and that does not give desirable treatment of excess traffic in the case of IP. Note 4: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. Note 5: Cf ITU I.365 (Oct 1996) for new definition. Note 6: See section 2.6 for the values to be used. The cumulative CDV is also provided, but it depends on local implementation, and not on values mapped from IP level service parameters. 6.3 Encoding CLS Using Real-Time VBR (ATM Forum TM/UNI 4.0) The encoding of CLS using rtVBR imposes a hard limit on the delay, which is specified as an end-to-end delay in the ATM network. This is more stringent than the CLS service specifies and may result in less utilization of the network. If rtVBR is used to encode CLS, then the encoding is essentially the same as that for GS. The exceptions are that the Forward PCR is Garrett, Borden Expires September 1997 [Page 29] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 derived from the line rate and probably a different value of the transit delay and CDV will be specified. See Section 3.1. 6.4 Encoding CLS Using CBR (ATM Forum TM/UNI 4.0) The encoding of CLS using CBR is more stringent than using rtVBR since it does not take into account the variable rate of the data. Consequently there may be even lower utilization of the network. To use CBR for CLS, the same encoding as in Section 3.2 would be used. However a different set of values of the QoS parameters will likely be used. 6.5 Encoding CLS Using UBR (ATM Forum TM/UNI 4.0) This encoding gives no QoS guarantees and would be done in the same way as for BE traffic. See Section 5.1. 6.6 Encoding CLS Using Non-Real-Time VBR as in UNI 3.0/3.1 Specifications AAL Type 5 Forward CPCS-SDU Size parameter M of TSpec Backward CPCS-SDU Size 0 Mode 1 (Message mode) Note 1 SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0 Forward SCR CLP=0 From TSpec token bucket rate Backward SCR CLP=0 0 Forward MBS (CLP=0) From TSpec bucket size param Backward MBS (CLP=0) 0 BE indicator NOT included Tagging Forward bit 1 (Tagging requested) Garrett, Borden Expires September 1997 [Page 30] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 2 Traffic Type 010 (bit encoding for Variable Bit Rate) Timing Requirements 00 (bit encoding for No Indication) Susceptible to Clipping 00 (bit encoding for Not susceptible) User Plane Configuration 01 (bit encoding for For pt-to-mpt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 3 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 3 QoS Class Backward 3 QoS Parameters Parameters are implied by the QOS Class Note 1: Only included for UNI 3.0. Note 2: Value 3 (BCOB-C) can also be used. If BCOB-C is used Traffic Type and Timing Requirements fields are not included. Note 3: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. 7.0 Summary of ATM VC Setup Parameters for Best Effort Service This section describes how to create ATM VCs appropriately matched for Best Effort. The BE service does not need a reservation of resources. The following subsections are for information only. See the IETF ION working group draft on ATM signalling support for IP over ATM using UNI 4.0 [11] for recommendations. Garrett, Borden Expires September 1997 [Page 31] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 7.1 Encoding Best Effort Service Using UBR (ATM Forum TM/UNI 4.0) This section is for information only. For recommendation, see the IETF ION working group draft on ATM signalling support for IP over ATM using UNI 4.0 [11]. AAL Type 5 Forward CPCS-SDU Size MTU of link Backward CPCS-SDU Size MTU of link SSCS Type 0 (Null SSCS) Traffic Descriptor Forward PCR CLP=0+1 From line rate Backward PCR CLP=0+1 0 BE indicator included Forward Frame Discard bit 1 Backward Frame Discard bit 1 Tagging Forward bit 1 (Tagging requested) Tagging Backward bit 1 (Tagging requested) Broadband Bearer Capability Bearer Class 16 (BCOB-X) Note 1 ATM Transfer Capability 10 (Non-real time VBR) Note 2 Susceptible to Clipping 00 (bit encoding for Not susceptible) User Plane Configuration 01 (bit encoding for pt-to-mpt) Broadband Low Layer Information User Information Layer 2 Protocol 12 (ISO 8802/2) User Information Layer 3 Protocol 11 (ISO/IEC TR 9577) Note 3 ISO/IEC TR 9577 IPI 204 QoS Class QoS Class Forward 0 QoS Class Backward 0 Note 1: Value 3 (BCOB-C) can also be used. Note 2: If bearer class C is used, the ATC field must be absent Note 3: For QoS VCs supporting GS or CLS, the layer 3 protocol should be specified. For BE VCs, it can be left unspecified, allowing the VC to be shared by multiple protocols, following RFC 1755. .fi Garrett, Borden Expires September 1997 [Page 32] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 7.2 Encoding Best Effort Service Using Other ATM Service Categories See the IETF ION working group draft on ATM signalling support for IP over ATM using UNI 4.0 [11]. 8.0 Security Some security issues are raised in the rsvp specification [2], which would apply here as well. There are no additional security considerations raised in this document. 9.0 Acknowledgements The authors would like to thank the members of the ISSLL working group for their input. In particular, thanks to Jon Bennett of Fore Systems, Roch Guerin of IBM and Susan Thomson of Bellcore. Appendix 1 Abbreviations AAL ATM Adaptation Layer ABR Available Bit Rate ATM Asynchronous Transfer Mode B-LLI Broadband Low Layer Information BCOB Broadband Connection-Oriented Bearer Capability BCOB-{A,C,X} Bearer Class A, C, or X BE Best Effort BT Burst Tolerance CBR Constant Bit Rate CDV Cell Delay Variation CDVT Cell Delay Variation Tolerance CLP Cell Loss Priority (bit) CLR Cell Loss Ratio CLS Controlled Load Service CPCS Common Part Convergence Sublayer CTD Cell Transfer Delay EOM End of Message FFS For Further Study GCRA Generic Cell Rate Algorithm GS Guaranteed Service IE Information Element IETF Internet Engineering Task Force IP Internet Protocol Garrett, Borden Expires September 1997 [Page 33] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 IS Integrated Services ISSLL Integrated Services over Specific Link Layers ITU International Telecommunication Union IWF Interworking Function LIJ Leaf Initiated Join LLC Logical Link Control MBS Maximum Burst Size MCR Minimum Cell Rate MPL Minimum Path Latency MTU Maximum Transfer Unit nrtVBR Non-real-time VBR PCR Peak Cell Rate PDU Protocol Data Unit QoS Quality of Service RESV Reservation Message (of rsvp protocol) RFC Request for Comment RSVP Resource Reservation Protocol Rspec Reservation Specification rtVBR Real-time VBR SCR Sustained Cell Rate SDU Service Data Unit SIG ATM Signaling (ATM Forum document) SNAP Subnetwork Attachment Point SSCS Service-Specific Convergence Sub-layer Sw Switch TCP Transport Control Protocol TM Traffic Management TSpec Traffic Specification UBR Unspecified Bit Rate UNI User-Network Interface UPC Usage Parameter Control (ATM traffic policing function) VBR Variable Bit Rate VC (ATM) Virtual Connection REFERENCES [1] R. Braden, D. Clark and S. Shenker, "Integrated Services in the Internet Architecture: an Overview", RFC 1633, June 1994. [2] R. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin, "Resource ReSerVation Protocol (RSVP) - Version 1 Functional Specification", Internet Draft, May 1996, <draft-ietf-rsvp- spec-12.txt> [3] The ATM Forum, "ATM User-Network Interface Specification, Ver- sion 3.0", Prentice Hall, Englewood Cliffs NJ, 1993. Garrett, Borden Expires September 1997 [Page 34] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 [4] The ATM Forum, "ATM User-Network Interface Specification, Ver- sion 3.1", Prentice Hall, Upper Saddle River NJ, 1995. [5] The ATM Forum, "ATM User-Network Interface (UNI) Signalling Specification, Version 4.0", Prentice Hall, Upper Saddle River NJ, specification finalized July 1996; expected publication, late 1996; available at ftp://ftp.atmforum.com/pub. [6] The ATM Forum, "ATM Traffic Management Specification, Version 4.0", Prentice Hall, Upper Saddle River NJ; specification final- ized April 1996; expected publication, late 1996; available at ftp://ftp.atmforum.com/pub. [7] M. W. Garrett, "A Service Architecture for ATM: From Applica- tions to Scheduling", IEEE Network Mag., Vol. 10, No. 3, pp. 6- 14, May 1996. [8] S. Shenker, C. Partridge and R. Guerin, "Specification of Guaranteed Quality of Service", Internet Draft, August 1996, <draft-ietf-intserv-guaranteed-svc-06.txt> [9] J. Wroclawski, "Specification of the Controlled-Load Network Element Service", Internet Draft, August 1996, draft-ietf- intserv-ctrl-load-svc-03.txt [10] M. Perez, F. Liaw, A. Mankin, E. Hoffman, D. Grossman and A. Malis, "ATM Signaling Support for IP over ATM", RFC 1755, Febru- ary 1995. [11] M. Perez and A. Mankin, "ATM Signalling Support for IP over ATM - UNI 4.0 Update", Internet Draft, November 1996, <draft-ietf- ion-sig-uni4.0-01.txt> [12] S. Berson, L. Berger, "IP Integrated Services with RSVP over ATM", Internet Draft, September 1996, <draft-ietf-issll-atm- support-01.txt> [13] S. Shenker and J. Wroclawski, "Network Element Service Specifi- cation Template", Internet Draft, November 1995, <draft-ietf- intserv-svc-template-02.txt> [14] J. Wroclawski, "The Use of RSVP with IETF Integrated Services", Internet Draft, August 1996, <draft-ietf-intserv-use-00.txt> [15] M. Borden, E. Crawley, B. Davie and S. Batsell, "Integration of Real-time Services in an IP-ATM Network Architecture", "IP Authentication Header", RFC 1821, August 1995. Garrett, Borden Expires September 1997 [Page 35] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 [16] J. Heinanen, "Multiprotocol Encapsulation over ATM Adaptation Layer 5", RFC 1483, July 1993. AUTHORS' ADDRESSES Mark W. Garrett Marty Borden Bellcore New Oak Communications, Inc. 445 South Street 42 Nanog Park Morristown, NJ 07960 Acton MA, 01720 USA USA phone: +1 201 829-4439 phone: +1 508 266-1011 email: mwg@bellcore.com email: mborden@newoak.com Garrett, Borden Expires September 1997 [Page 36] INTERNET DRAFT Interoperation of CLS and GS with ATM March 1997 Table of Contents Garrett, Borden Expires September 1997 [Page 37]