MPLS Working Group L. Andersson, A. Fredette, B. Jamoussi Internet Draft Nortel Networks Expiration Date: July 1999 R. Callon IronBridge Networks P. Doolan Ennovate Networks N. Feldman IBM Corp E. Gray Lucent Technologies J. Halpern Newbridge Networks J. Heinanen Telia Finland T. E. Kilty Northchurch Communications A. G. Malis Ascend Communications, Inc. M. Girish SBC Technology Resources, Inc. K. Sundell Ericsson P. Vaananen Nokia Telecommunications T. Worster General DataComm, Inc. L. Wu, R. Dantu Alcatel January 1998 Constraint-Based LSP Setup using LDP draft-ietf-mpls-cr-ldp-00.txt Status of this Memo This document is an Internet-Draft. Internet-Drafts are working Jamoussi, et. al. January 26, 1999 [Page 1] CR-LDP Specification - 2 - Exp. Apr 1999 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), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract Label Distribution Protocol (LDP) is defined in [LDP] for distribution of labels inside one MPLS domain. One of the most important services that may be offered using MPLS in general and LDP in particular is support for constraint-based routing of traffic across the routed network. Constraint-based routing offers the opportunity to extend the information used to setup paths beyond what is available for the routing protocol. For instance, an LSP can be setup based on an explicit route constraint, a Service Class (SC) constraint, or both. Constraint-based routing (CR) and Traffic Engineering requirements have been proposed by [FRAME], [ARCH] and [TER]. These requirements may be met by extending LDP for support of constraint-based routed label switched paths (CRLSPs). Other uses exist for CRLSPs as well ([VPN1] and [VPN2]). This draft specifies mechanisms and TLVs for support of CRLSPs using LDP. The Explicit Route object and procedures are extracted from [ER]. 1. Introduction The need for constraint-based routing (CR) in MPLS has been explored elsewhere [ARCH], [FRAME], and [TER]. Explicit routing is a subset of the more general constraint-based routing function. At the MPLS WG meeting held during the Washington IETF there was consensus that LDP should support explicit routing of LSPs with provision for indication of associated (forwarding) priority. In the Chicago meeting, the decision was made that support for explicit path setup in LDP will be moved to a separate document. This document provides that support. We propose an end-to-end setup mechanism of a constraint-based routed LSP (CRLSP) initiated by the ingress LSR. We also specify mechanisms to provide means for reservation of resources for the explicitly routed LSP. We introduce TLVs and procedures that provide support for: Jamoussi, et. al. January 26, 1999 [Page 2] CR-LDP Specification - 3 - Exp. Apr 1999 - Strict and Loose Explicit Routing - Specification of Service Class - Specification of Traffic Parameters - Route Pinning - CRLSP bumping though setup/holding priority - Handling Failures 2. CRLSP Overview CRLSP over LDP Specification is designed with several goals in mind: 1. Meet the requirements outlined in [TER] for performing traffic engineering and provide a solid foundation for performing more general constrain-based routing. 2. Build on already specified functionality that meets the requirements whenever possible. Hence, this specifications is based on [LDP] and the Explicit Route object and procedures defined in [ER]. 3. Keep the solution simple and tractable. In this document, support for unidirectional point-to-point CRLSPs is specified. Support for point-to-multipoint, multipoint-to-point, is for further study (FFS). Support for explicitly routed LSPs in this specification depends on the following minimal LDP behaviors as specified in [LDP]: - Basic and/or Extended Discovery Mechanisms. - Use the Label Request Message defined in [LDP] in downstream on demand label advertisement mode with ordered control. - Use the Label Mapping Message defined in [LDP] in downstream on demand mode with ordered control. - Use the Notification Message defined in [LDP]. - Use the Withdraw and Release Messages defined in [LDP]. - Loop detection (in the case of loosely routed segments of a CRLSP) mechanisms. In addition, the following functionality is added to what's defined in [LDP]: - The Label Request Message used to setup a CRLSP includes a CR- TLV based on the path vector defined in [ER] and specified in Section 4 of this document. Jamoussi, et. al. January 26, 1999 [Page 3] CR-LDP Specification - 4 - Exp. Apr 1999 - An LSR implicitly infers ordered control from the existence of a CR-TLV in the Label Request Message. This means that the LSR can still be configured for independent control for LSPs established as a result of dynamic routing. However, when a Label Request Message includes a CR TLV, then ordered control is used to setup the CRLSP. Note that this is also true for the loosely routed parts of a CRLSP. - Traffic Parameters TLVs may optionally be carried in the Label Request Message to specify the CRLSP traffic characteristics. - New status codes are defined to handle error notification for failure of established paths specified in the CR-TLV. Examples of CRLSP establishment are given in Appendix A to illustrate how the mechanisms described in this draft work. 3. Required Messages and TLVs Any Messages, TLVs, and procedures not defined explicitly in this document are defined in the [LDP] Specification. The following subsections are meant as a cross reference to the [LDP] document and indication of additional functionality beyond what's defined in [LDP] where necessary. 3.1 Label Request Message The Label Request Message is as defined in 3.5.8 of [LDP] with the following modifications (required only if the CR-TLV is included in the Label Request Message): - Only a single FEC-TLV may be included in the Label Request Message. - The Optional Parameters TLV includes the definition of the Constraint-based TLV specified in Section 4 and the Traffic Parameters TLV specified in Section 5. - The Procedures to handle the Label Request are augmented by the procedures for processing of the CR-TLV as defined in Section 4. - The Procedures to handle Service Classes are defined in Section 5. 3.2 Label Mapping Message The Label Mapping Message is as defined in 3.5.7 of [LDP] with the following modifications: - Only a single Label-TLV may be included in the Label Mapping Message. Jamoussi, et. al. January 26, 1999 [Page 4] CR-LDP Specification - 5 - Exp. Apr 1999 - The FEC-Label Mapping TLV does not include any of the optional TLVs. - The Label Mapping Message Procedures are limited to downstream on demand ordered control mode of mapping. A Mapping message is transmitted by a downstream LSR to an upstream LSR under one of the following conditions: 1. The LSR is the egress end of the CRLSP and an upstream mapping has been requested. 2. The LSR received a mapping from its downstream next hop LSR for an CRLSP for which an upstream request is still pending. 3.3. Notification Message The Notification message is as defined in Section 3.5.1 of [LDP] and the Status TLV encoding is as defined in Section 3.4.7 of [LDP]. Establishment of an Explicitly Routed LSP may fail for a variety of reasons. All such failures are considered advisory conditions and they are signaled by the Notification Message. Notification messages carry Status TLVs to specify events being signaled. New status codes are defined in Section 4.8.3 to signal error notifications associated with the establishment of a CRLSP and the processing of the CR-TLV. 4. Constraint-based Routing TLV Label Request Messages defined in [LDP] optionally carry the Constraint-based Routing TLV (CR-TLV) based on the path vector defined in [ER] and described in this section of the specification. The inclusion of the CR TLV in the Label Request Message indicates the path to be taken in the network even if normal routing indicates otherwise. The format of the CR-TLV is described below. 4.1 CR-TLV The CR-TLV is an object that specifies the path to be taken by the LSP being established. In addition, the CR-TLV may also include the the Service Class (SC) constraints associated with the LSP, a setup and a holding priority used for path bumping, and an LSP pinning request flag. Reserved bits in the CR-TLV allow for the specification of other LSP attributes in the future. If the reserved bits are exhausted, additional TLVs may be specified to allow for the indication of other LSP attributes during the CRLSP setup. Jamoussi, et. al. January 26, 1999 [Page 5] CR-LDP Specification - 6 - Exp. Apr 1999 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| CR-TLV (0x0800) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Reserved | SC |P| Hp | Sp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ER-Hop TLV 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ER-Hop TLV 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ............ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ER-Hop TLV n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ U bit Unknown TLV bit. Upon receipt of an unknown TLV, if clear (=0), a notification must be returned to the message originator and the entire message must be ignored; if set (=1), the unknown TLV is silently ignored and the rest of the message is processed as if the unknown TLV did not exist. F bit Forward unknown TLV bit. This bit only applies when the U bit is set and the LDP message containing the unknown TLV is to be forwarded. If clear (=0), the unknown TLV is not forwarded with the containing message; if set (=1), the unknown TLV is forwarded with the containing message. Type A two byte field carrying the value of the CR-TLV type which is 0x800. Length Specifies the length of the value field in bytes. Reserved This field is reserved. It must be set to zero on transmission and must be ignored on receipt. We expect to use these fields for carrying information that support other constrain-based routing information. P bit Jamoussi, et. al. January 26, 1999 [Page 6] CR-LDP Specification - 7 - Exp. Apr 1999 When set indicates that the loosely routed segments must remain pinned-down. CRLSP must be rerouted only when adjacency is lost along the segment. When not set, it indicates that the loose segment is not pinned down and must be changed to match the underlying hop- by-hop path. SC The SC Field is used to specify the Service Class of the CRLSP. This field allows for the definition of up to 8 different Service Classes. Currently, Three Service Classes are defined: Best Effort (0), Throughput Sensitive (1), and Delay Sensitive (2) Service Classes. These SCs are further defined in Section 5. Sp A SetupPriority of value zero (0) is the priority assigned to the most important path. It is referred to as the highest priority. Four (4) is the priority for the least important path. The higher the setup priority, the more paths CR-LDP can bump to set up the path. The default value is 2. Values 5, 6, and 7 are reserved. Hp A HoldingPriority of value zero (0) is the priority assigned to the most important path. It is referred to as the highest priority. Four (4) is the priority for the least important path. The higher the holding priority, the less likely it is for CR-LDP to reallocate its bandwidth to a new path. The default value is 2. Values 5, 6, and 7 are reserved. 4.1.1 Setup and holding priorities CR-LDP signals the resources required by a path on each hop of the route. If a route with sufficient resources can not be found, existing paths may be rerouted to reallocate resources to the new path. This is the process of bumping paths. Setup and holding priorities are used to rank existing paths (holding priority) and the new path (setup priority) to determine if the new path can bump an existing path. The setupPriority of a new CRLSP and the holdingPriority attributes of the existing CRLSP are used to specify these priorities. The higher the holding priority, the less likely it is for CR-LDP to reallocate its bandwidth to a new path. Similarly, the higher the setup priority, the more paths CR-LDP can bump to set up the path. The setup and holding priority values range from zero (0) to four (4). The value zero (0) is the priority assigned to the most important path. It is referred to as the highest priority. Four (4) is the priority for the least important path. The default values for Jamoussi, et. al. January 26, 1999 [Page 7] CR-LDP Specification - 8 - Exp. Apr 1999 both setup and holding priority should be 2. By setting the default value of both setup and holding priorities at the middle of the range, all connections are initially treated the same. However, when network operators see a need for the use of path bumping, the values of setup and holding priorities can be gracefully adjusted up or down from the middle of the range. An existing path can be bumped if and only if the setupPriority of the new path is numerically less than the holdingPriority of the existing path. To illustrate the use of the setup and holding priority, consider a network which supports two service types (e.g., video and data services). The video traffic is given a low setup priority because new video paths can use an alternate public network if the primary network cannot accommodate the new path. However, the video traffic is given a high holding priority since it is undesirable for the path to be rerouted during an active LSP. For data traffic, high setup and holding priorities are desirable since data paths cannot be established on an alternate network. The setup and holding priorities can be different to allow setup at one priority and holding at an independent priority. This would allow some calls not to invoke bumping and not to be bumped at the same time. The setupPriority of a CRLSP should not be higher (numerically less) than its holdingPriority since it might bump an LSP and be bumped by next "equivalent" request. Bumping by default only happens as a last resort when there are no routes available for a given path. During the instantiation of a path that must bump other paths, lower holding priority paths are bumped before higher priority paths. The decision as to which of the available paths are bumped at each intermediate node by the new path is arbitrary. 4.2 ER-Hop TLV The contents of a constraint-based route TLV are a series of variable length ER-Hop TLVs. Each ER-Hop TLV has the form: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+ |L| Type | Length | Contents | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--------//--------------+ L Jamoussi, et. al. January 26, 1999 [Page 8] CR-LDP Specification - 9 - Exp. Apr 1999 The L bit is an attribute of the ER-Hop. The L bit is set if the ER-Hop represents a loose hop in the explicit route. If the bit is not set, the ER-Hop represents a strict hop in the explicit route. Type A seven-bit field indicating the type of contents of the ER-Hop. Currently defined values are: Value Type ----- ------------------------ 0 Reserved 1 IPv4 prefix 2 IPv6 prefix 32 Autonomous system number Length The Length field contains the total length of the ER-Hop in bytes. It includes the L bit, Type and Length fields. The length must always be a multiple of 4, and at least 4. Contents A variable length field containing the node or abstract node that is the consecutive nodes that make up the explicit routed LSP. 4.3 Applicability The CR-TLV in this version of the specification is intended for unicast only. CRLSPs for multicast are FFS. 4.4 Semantics of the CR-TLV Like any other LSP an CRLSP is a path through a network. The difference is that while other paths are setup solely based on information in routing tables or from a management system, the constraint-based route is calculated at one point at the edge of network based on criteria, including but not limited to routing information. The intention is that this functionality shall give desired special characteristics to the LSP in order to better support the traffic sent over the LSP. The reason for setting up CRLSPs, might be that one wants to assign certain bandwidth or other Service Class characteristics to the LSP, or that one wants to make sure that alternative routes use physically separate paths through the network. A CRLSP is represented in a Label Request Message as a list of nodes or groups of nodes along the constraint-based route. When the CRLSP is established, all or a subset of the nodes in a group may be Jamoussi, et. al. January 26, 1999 [Page 9] CR-LDP Specification - 10 - Exp. Apr 1999 traversed by the LSP. Certain operations to be performed along the path can also be encoded in the constraint-based route. The capability to specify, in addition to specified nodes, groups of nodes, of which a subset will be traversed by the CRLSP, allows the system a significant amount of local flexibility in fulfilling a request for a constraint-based route. This allows the generator of the constraint-based route to have some degree of imperfect information about the details of the path. The constraint-based route is encoded as a series of ER-Hops contained in a constraint-based route TLV. Each ER-Hop may identify a group of nodes in the constraint-based route. A constraint-based route is then a path including all of the identified groups of nodes. To simplify the discussion, we call each group of nodes an abstract node. Thus, we can also say that a constraint-based route is a path including all of the abstract nodes, with the specified operations occurring along that path. 4.5 Strict and Loose ER-Hops The L bit in the ER-Hop is a one-bit attribute. If the L bit is set, then the value of the attribute is "loose." Otherwise, the value of the attribute is "strict." For brevity, we say that if the value of the ER-Hop attribute is loose then it is a "loose ER-Hop." Otherwise, it's a "strict ER-Hop." Further, we say that the abstract node of a strict or loose ER-Hop is a strict or a loose node, respectively. Loose and strict nodes are always interpreted relative to their prior abstract nodes. The path between a strict node and its prior node MUST include only network nodes from the strict node and its prior abstract node. The path between a loose node and its prior node MAY include other network nodes which are not part of the strict node or its prior abstract node. 4.6 Loops While the constraint-based route TLV is of finite length, the existence of loose nodes implies that it is possible to construct forwarding loops during transients in the underlying routing protocol. This may be detected by the originator of the constraint- based route through the use a path vector object as defined in [LDP]. 4.7 ER-Hop semantics 4.7.1. ER-Hop 1: The IPv4 prefix The contents of an IPv4 prefix ER-Hop are a 4 byte IPv4 address, 1 Jamoussi, et. al. January 26, 1999 [Page 10] CR-LDP Specification - 11 - Exp. Apr 1999 byte of prefix length, and 1 byte of padding. The abstract node represented by this ER-Hop is the set of nodes which have an IP address which lies within this prefix. Note that a prefix length of 32 indicates a single IPv4 node. The length of the IPv4 prefix ER-Hop is 8 bytes. The contents of the 1 byte of padding must be zero on transmission and must not be checked on receipt. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L| Type | Length | IPv4 Address (4 bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Address (Continued) | Prefix |0 0 0 0 0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type IPv4 Address 0x01 Length A one byte field indicating the total length of the TLV in bytes. It includes the L-bit, the Type, Length, the IP Address, and the Prefix fields. The length is always 8 bytes. IP Address A four byte field indicating the IP Address. Prefix Length 1-32 Padding Zero on transmission. Ignored on receipt. 4.7.2. ER-Hop 2: The IPv6 address Jamoussi, et. al. January 26, 1999 [Page 11] CR-LDP Specification - 12 - Exp. Apr 1999 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L| Type | Length | IPV6 address (16 bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPV6 address (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPV6 address (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPV6 address (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPV6 address (continued) | Prefix |0 0 0 0 0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 0x02 IPv6 address Length The Length contains the total length of the ER-Hop TLV in bytes, including the Type and Length fields. The Length is always 20. IPv6 address A 128-bit unicast host address. Prefix Length 1-128 Padding Zero on transmission. Ignored on receipt. 4.7.3. ER-Hop 32: The autonomous system number The contents of an autonomous system (AS) number ER-Hop are a 2 byte autonomous system number. The abstract node represented by this ER- Hop is the set of nodes belonging to the autonomous system. The length of the AS number ER-Hop is 4 bytes. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L| Type | Length | Autonomous System number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type Jamoussi, et. al. January 26, 1999 [Page 12] CR-LDP Specification - 13 - Exp. Apr 1999 AS Number 0x20 Length A one byte field indicating the total length of the TLV in bytes. It includes the L-bit, the Type, and Length, and the AS number fields. The length is always 4 bytes. AS number A two byte field indicating the AS number. 4.8. Processing of the Constraint-Based Route TLV 4.8.1. Selection of the next hop A Label Request message containing a constraint-based route TLV must determine the next hop for this path. Selection of this next hop may involve a selection from a set of possible alternatives. The mechanism for making a selection from this set is implementation dependent and is outside of the scope of this specification. Selection of particular paths is also outside of the scope of this specification, but it is assumed that each node will make a best effort attempt to determine a loop-free path. Note that such best efforts may be overridden by local policy. To determine the next hop for the path, a node performs the following steps: 1) The node receiving the Label Request message must first evaluate the first ER-Hop. If the L bit is not set in the first ER-Hop and if the node is not part of the abstract node described by the first ER-Hop, it has received the message in error, and should return a "Bad initial ER-Hop" error. If the L bit is set and the local node is not part of the abstract node described by the first ER-Hop, the node selects a next hop that is along the path to the abstract node described by the first ER-Hop. If there is no first ER-Hop, the message is also in error and the system should return a "Bad Constraint-Based Routing TLV" error. 2) If there is no second ER-Hop, this indicates the end of the constraint-based route. The constraint-based route TLV should be removed from the Label Request message. This node may or may not be the end of the LSP. Processing continues with section 4.8.2, where a new constraint-based route TLV may be added to the Label Request message. 3) If the node is also a part of the abstract node described by the second ER-Hop, then the node deletes the first ER-Hop and continues processing with step 2, above. Note that this makes the second ER-Hop into the first ER-Hop of the next iteration. Jamoussi, et. al. January 26, 1999 [Page 13] CR-LDP Specification - 14 - Exp. Apr 1999 4) The node determines if it is topologically adjacent to the abstract node described by the second ER-Hop. If so, the node selects a particular next hop which is a member of the abstract node. The node then deletes the first ER-Hop and continues processing with section 4.8.2. 5) Next, the node selects a next hop within the abstract node of the first ER-Hop that is along the path to the abstract node of the second ER-Hop. If no such path exists then there are two cases: 5a) If the second ER-Hop is a strict ER-Hop, then there is an error and the node should return a "Bad strict node" error. 5b) Otherwise, if the second ER-Hop is a loose ER-Hop, then the node selects any next hop that is along the path to the next abstract node. If no path exists, then there is an error, and the node should return a "Bad loose node" error. 6) Finally, the node replaces the first ER-Hop with any ER-Hop that denotes an abstract node containing the next hop. This is necessary so that when the constraint-based route is received by the next hop, it will be accepted. 7) Progress the Label Request Message to the next hop. 4.8.2. Adding ER-Hops to the constraint-based route TLV After selecting a next hop, the node may alter the constraint-based route in the following ways. If, as part of executing the algorithm in section 4.8.1, the constraint-based route TLV is removed, the node may add a new constraint-based route TLV. Otherwise, if the node is a member of the abstract node for the first ER-Hop, then a series of ER-Hops may be inserted before the first ER-Hop or may replace the first ER-Hop. Each ER-Hop in this series must denote an abstract node that is a subset of the current abstract node. Alternately, if the first ER-Hop is a loose ER-Hop, an arbitrary series of ER-Hops may be inserted prior to the first ER-Hop. 4.8.3. Error subcodes In the processing described above, certain errors need to be reported as part of the Notification message. This section defines the status codes for the errors described above. Jamoussi, et. al. January 26, 1999 [Page 14] CR-LDP Specification - 15 - Exp. Apr 1999 Status Code Type -------------------------------------- ---------- Bad Constraint-Based Routing TLV Error 0x04000001 Bad Strict Node Error 0x04000002 Bad Loose Node Error 0x04000003 Bad Initial ER-Hop Error 0x04000004 Resource Unavailable 0x04000005 Service Class Unavailable 0x04000006 Traffic Parameters Unavailable 0x04000007 5.0 CRLSP Service Classes and Traffic Parameters The following sections describe the CRLSP Service Classes (SCs), and their associated traffic parameters. The CRLSP Service Class is signaled in the SC Field of the CR-TLV defined in Section 4.1. Three Service Classes are currently supported by CR-LDP: Service Class Value -------------------------- ----- Best Effort (BE) 0x0 Throughput Sensitive (TS) 0x1 Delay Sensitive (DS) 0x2 These service classes are specified in the following sections. 5.1 Best Effort (BE) The request of the BE SC implies that there are no expected service guarantees from the network. The service provided by the network is the familiar best effort service. The Peak Date Rate (PDR) is the only traffic parameter that may be specified with the BE SC. The specification of the PDR allows the network to perform traffic shaping and policing functions. 5.2 Throughput Sensitive (TS) In the service model for the Throughput Sensitive SC, the network commits to deliver with high probability user datagrams at a rate of at least CDR (Committed Data Rate). The user may transmit at a rate higher than CDR but datagrams in excess of CDR would have a lower probability of being delivered. If the user sends at a rate of CDR or lower the network commits to deliver with high probability all the user datagrams. The TS SC has an associated tolerance to the burstiness of arriving Jamoussi, et. al. January 26, 1999 [Page 15] CR-LDP Specification - 16 - Exp. Apr 1999 user datagrams. This tolerance is defined by the traffic parameter Committed Burst Tolerance (CBT). Ideally, a TS CRLSP request carries with it a rich set of three traffic parameters (PDR, CDR, and CBT) that accurately describe its traffic characteristics. This allows the network to perform resource reservation, traffic shaping, and traffic policing. However, for the sake of simplicity of the service definition, the CDR is the only parameter that MUST always be specified for a TS CRLSP. A peak data rate parameter (PDR) and a CBT are optional traffic parameters for the TS SC. The network should make every effort to preserve ordering of the delivered datagrams of a TS CRLSP. Network traffic that requires a low packet loss ratio at a given CDR but is not particularly sensitive to delay and jitter (e.g., network control traffic) is suited to the TS SC. The selection of the TS SC is used to signal to the various nodes along the path that the queuing and scheduling mechanisms used to handle the CRLSP should provide a low packet loss ratio. 5.3 Delay Sensitive (DS) In the service model for the Delay Sensitive SC, the network commits to deliver with high probability user datagrams at a rate of CDR (Committed Data Rate) with minimum delay and delay variation. The user MUST transmit data at a rate of CDR or lower in order to be eligible for DS service. Datagrams in excess of CDR may be discarded by the network. If the user sends at a rate of CDR or lower the network commits to deliver with high probability all user datagrams with low delay and delay variation. If the user sends at a rate higher than CDR the network does not provide any guarantees on the excess traffic. The Delay Sensitive SC has an associated tolerance to the burstiness of arriving user datagrams. This tolerance is defined by the traffic parameter Committed Burst Tolerance (CBT). Ideally, a DS CRLSP request carries with it a rich set of three traffic parameters (PDR, CDR, and CBT) that accurately describe its traffic characteristics. This allows the network to perform resource reservation, traffic shaping and policing. However, for the sake of simplicity of the service definition, the CDR is the only parameter that MUST always be specified for a DS CRLSP. A peak data rate parameter (PDR) and a CBT are optional traffic parameters for the DS SC. The network should make every effort to preserve ordering of the Jamoussi, et. al. January 26, 1999 [Page 16] CR-LDP Specification - 17 - Exp. Apr 1999 delivered datagrams of a DS CRLSP. Network traffic that requires a low delay and delay variation at a given CDR (e.g., voice traffic) is suited to the DS SC. The selection of the DS SC is used to signal to the various nodes along the path that the queuing and scheduling mechanisms used to handle the CRLSP should provide low delay and delay variation. 5.4 Traffic Parameters The CRLSP traffic parameters are defined in this section. The traffic parameters CDR, CBT and PDR are defined in terms of a TOKEN_BUCKET_TSPEC as specified in [RFC2215]. The following mapping of parameters in the TOKEN_BUCKET_TSPEC is used: Token rate, r = CDR Bucket depth, b = CBT Peak traffic rate, p = PDR Minimum policed unit, m = 1 Maximum packet size, M = MTU The Traffic Parameters TLV is used to signal the traffic characteristics of the CRLSP. These traffic parameters are used to perform functions such as resource reservation, Shaping, and Policing. See [SIN] for more details. The encoding for the Traffic Parameters TLV is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| Traffic TLV (0x0810) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PDR TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CDR TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CBT TLV | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.4.1 Peak data rate (PDR) TLV The value of traffic parameter PDR is given as a positive integer in bytes per second. Zero is not a valid value of PDR. The user may specify the value of PDR depending the SC of the CRLSP. Specifying the PDR allows the network to use traffic management functions such as shaping. Jamoussi, et. al. January 26, 1999 [Page 17] CR-LDP Specification - 18 - Exp. Apr 1999 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| PDR TLV (0x0811) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PDR in Bytes/sec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.4.2. Committed Data Rate (CDR) The value of traffic parameter CDR is given as a positive integer in bytes per second. Zero is not a valid value of CDR. The user may provide a requested value of CDR in the CRLSP request depending on the SC of the CRLSP. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| CDR TLV (0x0812) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CDR in Bytes/sec | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5.4.3. Committed Burst Tolerance (CBT) The value of traffic parameter CBT is given in bytes. Zero is not a valid value of CBT. The requested value of CBT MUST be no smaller than the MTU of the originating interface. The user may provide a requested value of CBT in the CRLSP request. If the user chooses not to specify a requested value of CBT and the network is policing the traffic, then any excess traffic will be dropped by the network. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |U|F| CBT TLV (0x0813) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CBT in Bytes | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6. Open Issues This section captures the issues that need further study. Jamoussi, et. al. January 26, 1999 [Page 18] CR-LDP Specification - 19 - Exp. Apr 1999 1) Review the FSM described in Appendix B and extend it by the CR-TLV processing defined in Sections 4.8.1 and 4.8.2. 2) Consider if all three traffic parameters have to be signaled at all times and if the network should supply default values for the missing parameters. 3) Consider the following extensions to the CR-TLV: 3.1) Changing the 'P' bit to "next hop flag" and making it a 2-bit wide field with the following values: - 00 "local repair", which means if it belongs to a loosely routed segment, and the LSR detects a next hop change, the LSR will try to establish a new LSP from this point on and switch it over to the new LSP when it is setup. - 01 "global repair", which means when the LSR detects a next hop change, the LSR will tear down the LSP, the ingress LSR will try to reestablish another LSP through the new path. - 10 "pinned", which means that the loosely routed segments must remain pinned down. - 11 Reserved. 3.2) Adding one more field "LSPID" before ER-Hop TLV. LSPID can be used to identify a network wide unique CRLSP. - The first 4 bytes carrying the ingress LSR IP address - The second 4 bytes carrying the unique ID value assigned by the ingress LSR. 4) Consider the following extension to the ER-Hop TLV: For Type field, add one more type, LSPID, which means the current CRLSP will go through another CRLSP which is identified with this LSPID value: Value Type ----- ----- 4 LSPID Extend processing the LSPID ER-Hop as follows: If the type of ER- Hop is LSPID, and the other end of this CRLSP is not part of the constraint-based route TLV, add it to the constraint-based TLV with L bit turned off. 5) Consider traffic parameter negotiation and the ability to change the traffic parameters associated with an already established path Jamoussi, et. al. January 26, 1999 [Page 19] CR-LDP Specification - 20 - Exp. Apr 1999 without tearing the old path down. 7. Security No security issues are discussed in this version of the draft. 8. Acknowledgments The messages used to signal the CRLSP setup are based on the work done by the [LDP] team. The Explicit Route object and procedures used in this specification are based on [ER]. The authors would also like to acknowledge the careful review and comments of Osama Aboul-Magd, Ken Hayward, Greg Wright, Geetha Brown, Brian Williams, Peter Ashwood-smith, Paul Beaubien, Matthew Yuen, Liam Casey, and Ankur Anand. 9. References [FRAME] Callon et al, "Framework for Multiprotocol Label Switching", work in progress (draft-ietf-mpls-framework-02), November 1997. [ARCH] Rosen et al, "Multiprotocol Label Switching Architecture", work in progress (draft-ietf-mpls-arch-02), July 1998. [LDP] Andersson et al, "Label Distribution Protocol Specification" work in progress (draft-ietf-mpls-ldp-02.txt), November 1998. [ER] Guerin et al, "Setting up Reservations on Explicit Paths using RSVP", work in progress (draft-guerin-expl-path-rsvp-01.txt, November 1997. [TER] Awduche et al, "Requirements for Traffic Engineering Over MPLS", work in progress (draft-awduche-mpls-traffic-eng-00), April 1998. [VPN1] Heinanen et al, "MPLS Mappings of Generic VPN Mechanisms", work in progress (draft-heinanen-generic-vpn-mpls-00), August 1998. [VPN2] Jamieson et al, "MPLS VPN Architecture" work in progress (draft-jamieson-mpls-vpn-00), August 1998. [RFC2215] S. Shenker and J. Wroclawski, General Characterization Parameters for Integrated Service Network Elements, RFC 2215, Sep 1997. [SIN] B. Jamoussi, N. Feldman, and L. Andersson, "MPLS Ships in the Night with ATM", (draft-jamoussi-mpls-sin-00.txt), August 1998. Jamoussi, et. al. January 26, 1999 [Page 20] CR-LDP Specification - 21 - Exp. Apr 1999 10. Author Information Loa Andersson Director Bay Architecture Lab, EMEA Kungsgatan 34, PO Box 1788 111 97 Stockholm, Sweden phone: +46 8 441 78 34 mobile +46 70 522 78 34 e-mail: loa_andersson@baynetworks.com Ross Callon IronBridge Networks 55 Hayden Avenue, Lexington, MA 02173 Phone: +1-781-402-8017 Email: rcallon@ironbridgenetworks.com Ram Dantu Alcatel USA Inc. IP Competence Center 1201 E. Campbell Road.,446-315 Richadson, TX USA., 75081-2206 Phone: 972 996 2938 Fax: 972 996 5902 Email: ram.dantu@aud.alcatel.com Paul Doolan Ennovate Networks 330 Codman Hill Rd Marlborough MA 01719 Phone: 978-263-2002 email: pdoolan@ennovatenetworks.com Nancy Feldman IBM Corp. 17 Skyline Drive Hawthorne NY 10532 Phone: 914-784-3254 email: nkf@us.ibm.com Andre Fredette Nortel Networks 3 Federal Street Billerica, MA 01821 email: fredette@baynetworks.com Eric Gray Lucent Technologies, Inc 1600 Osgood St. North Andover, MA 01847 email: ewgray@lucent.com Jamoussi, et. al. January 26, 1999 [Page 21] CR-LDP Specification - 22 - Exp. Apr 1999 Joel M. Halpern Newbridge Networks Inc. 593 Herndon Parkway Herndon, VA 20170 email: jhalpern@newbridge.com phone: 1-703-736-5954 fax: 1-703-736-5959 Juha Heinanen Telia Finland, Inc. Myyrmaentie 2 01600 VANTAA Finland Tel: +358 303 944 808 Email: jh@telia.fi Bilel Jamoussi Nortel Networks P O Box 3511 Station C Ottawa, ON K1Y 4H7 Canada phone: +1 613 765-4814 email: jamoussi@NortelNetworks.com Timothy E. Kilty Northchurch Communications 5 Corporate Drive, Andover, MA 018110 phone: 978 691-4656 Email: tkilty@northc.com Andrew G. Malis Ascend Communications, Inc. 1 Robbins Road Westford, MA 01886 phone: 978 952-7414 fax: 978 392-2074 Email: malis@ascend.com Muckai K Girish SBC Technology Resources, Inc. 4698 Willow Road Pleasanton, CA 94588 Phone: (925) 598-1263 Fax: (925) 598-1321 Email: mgirish@tri.sbc.com Kenneth Sundell Ericsson SE-126 25 Stockholm Sweden Jamoussi, et. al. January 26, 1999 [Page 22] CR-LDP Specification - 23 - Exp. Apr 1999 email: kenneth.sundell@etx.ericsson.se Pasi Vaananen Nokia Telecommunications 3 Burlington Woods Drive, Suite 250 Burlington, MA 01803 Phone: +1-781-238-4981 Email: pasi.vaananen@ntc.nokia.com Tom Worster General DataComm, Inc. 5 Mount Royal Ave. Marlboro MA 01752 Email: tom.worster@gdc.com Liwen Wu Alcatel U.S.A 44983 Knoll Square Ashburn, Va. 20147 USA Phone: (703) 724-2619 FAX: (703) 724-2005 Inet: liwen.wu@adn.alcatel.com Appendix A: CRLSP Establishment Examples A.1 Strict Constraint-Based Route Example This appendix provides an example for the setup of a strictly routed CRLSP. In this example, each abstract node is represented by a specific node. The sample network used here is a four node network with two edge LSRs and two core LSRs as follows: a b c LSR1------LSR2------LSR3------LSR4 LSR1 generates a Label Request Message as described in Section 3.1 of this draft and sends it to LSR2. This message includes the CR-TLV. The CR-TLV is composed by a vector of three ER-Hop TLVs . The ER-Hop TLVs used in this example are of type 0x01 (IPv4 prefix) with a prefix length of 32. Hence, each ER-Hop TLV identifies a specific node as opposed to a group of nodes. At LSR2, the following processing of the CR-TLV per Section 4.8.1 of this draft takes place: 1) The first hop is part of the abstract node LSR2. Therefore, the first step passes the test. Go to step 2. Jamoussi, et. al. January 26, 1999 [Page 23] CR-LDP Specification - 24 - Exp. Apr 1999 2) There is a second ER-Hop, . Go to step 3. 3) LSR2 is not part of the abstract node described by the second ER-Hop . Go to Step 4. 4) LSR2 determines that it is topologically adjacent to the abstract node described by the second ER-Hop . LSR2 selects a next hop (LSR3) which is the abstract node. LSR2 deletes the first ER-Hop from the CR-TLV which now becomes . Go to Section 4.8.2. At LSR2, the following processing of Section 4.8.2 takes place: Executing algorithm 4.8.1 did not result in the removal of the CR-TLV. Also, LSR2 is not a member of the abstract node described by the first ER-Hop . Finally, the first ER-Hop is a strict hop. Therefore, processing section 4.8.2 does not result in the insertion of new ER-Hops. The selection of the next hop has been already done is step 4 of Section 4.8.1 and the processing of the CR-TLV is completed at LSR2. In this case, the Label Request Message including the CR-TLV is progressed by LSR2 to LSR3. At LSR3, a similar processing to the CR-TLV takes place except that the incoming CR-TLV = and the outgoing CR-TLV is . At LSR4, the following processing of section 4.8.1 takes place: 1) The first hop is part of the abstract node LSR4. Therefore, the first step passes the test. Go to step 2. 2) There is no second ER-Hop, this indicates the end of the CRLSP. The CR-TLV is removed from the Label Request Message. Processing continues with Section 4.8.2. At LSR4, the following processing of Section 4.8.2 takes place: Executing algorithm 4.8.1 resulted in the removal of the CR-TLV. LSR4 does not add a new CR-TLV. Therefore, processing section 4.8.2 does not result in the insertion of new ER-Hops. This indicates the end of the CRLSP and the processing of the CR-TLV is completed at LSR4. At LSR4, processing of Section 3.2 is invoked. The first condition is satisfied (LSR4 is the egress end of the CRLSP and upstream mapping has been requested). Therefore, a Label Mapping Message is generated Jamoussi, et. al. January 26, 1999 [Page 24] CR-LDP Specification - 25 - Exp. Apr 1999 by LSR4 and sent to LSR3. At LSR3, the processing of Section 3.2 is invoked. The second condition is satisfied (LSR3 received a mapping from its downstream next hop LSR4 for a CRLSP for which an upstream request is still pending). Therefore, a Label Mapping Message is generated by LSR3 and sent to LSR2. At LSR2, a similar processing to LSR 3 takes place and a Label Mapping Message is sent back to LSR1 which completes the end-to-end CRLSP setup. A.2. Node Groups and Specific Nodes Example A request at an ingress LSR to setup a CRLSP might originate from a management system or an application, the details are implementation specific. The ingress LSR uses information provided by the management system or the application and possibly also information from the routing database to calculated the constraint-based route and to create the Label Request Message. The Label request message carries together with other necessary information a CR-TLV defining the constraint-based routed path. In our example the list of hops in the ER-Hop TLV is supposed to contain an abstract node representing a group of nodes, an abstract node representing a specific node, another abstract node representing a group of nodes, and an abstract node representing a specific egress point. In--{Group 1}--{Specific A}--{Group 2}--{Specific Out: B} The CR-TLV contains four ER-Hop TLVs: 1. An ER-Hop TLV that specifies a group of LSR valid for the first abstract node representing a group of nodes (Group 1). 2. An ER-Hop TLV that indicates the specific node (Node A). 3. An ER-Hop TLV that specifies a group of LSRs valid for the second abstract node representing a group of nodes (Group 2). 4. An ER-Hop TLV that indicates the specific egress point for the CRLSP (Node B). All the ER-Hop TLVs are strictly routed nodes. The setup procedure for this CRLSP works as follows: Jamoussi, et. al. January 26, 1999 [Page 25] CR-LDP Specification - 26 - Exp. Apr 1999 1. The ingress node sends the Label Request to a node that is a member the group of nodes indicated in the first ER-Hop TLV, following normal routing for the specific node (A). 2. The node that receives the message identifies itself as part of the group indicated in the first ER-Hop TLV, and that it is not the specific node (A) in the second. Further it realizes that the specific node (A) is not one of its next hops. 3. It keeps the ER-Hop TLVs intact and sends a Label Request Message to a node that is part of the group indicated in the first ER-Hop TLV (Group 1), following normal routing for the specific node (A). 4. The node that receives the message identifies itself as part of the group indicated in the first ER-Hop TLV, and that it is not the specific node (A) in the second ER-Hop TLV. Further it realizes that the specific node (A) is one of its next hops. 5. It removes the first ER-Hop TLVs and sends a Label Request Message to the specific node (A). 6. The specific node (A) recognizes itself in the first ER-Hop TLV. Removes the specific ER-Hop TLV. 7. It sends a Label Request message to a node that is a member of the group (Group 2) indicated in the ER-Hop TLV. 8. The node that receives the message identifies itself as part of the group indicated in the first ER-Hop TLV, further it realizes that the specific egress node (B) is one of its next hops. 9. It sends a Label Request message to the specific egress node (B). 10. The specific egress node (B) recognizes itself as the egress for the CRLSP, it returns a Label Mapping Message, that will traverse the same path as the Label Request Message in the opposite direction. Jamoussi, et. al. January 26, 1999 [Page 26] CR-LDP Specification - 27 - Exp. Apr 1999 Appendix B. CR-LDP Finite State Machine In this description of the CR-LDP FSM, behavior relating to the state of LDP messages is assumed to be defined (implicitly or explicitly) in [LDP]. In particular, LDP is assumed to retain state information relating a Label Request made of a downstream neighbor to the Label Request message(s) of upstream neighbors (downstream-on-demand mode) which the (downstream) Label Request is meant to satisfy. This will be true of many potential applications of LDP, of which CR-LDP is an example. Minimally, this state should include message IDs of Label Requests (both sent and received) and the LSR(s) from which pending Label Request(s) were received. The FSM describes CR-LDP behavior in the following operations: - Start of CRLSP setup (in which a Label Request is sent); - Processing the CR-TLV portion of Label Requests; - Completion of CRLSP setup (via Label Mapping messages); - Notification of originator when: - a loop is detected in a loose constraint-based route segment, - an ER-Hop is not reachable from a previous ER-Hop, - a next ER-Hop is strict and not directly connected to the current LSR or - the current LSR is strict and is not (part of the abstract node in) the first ER-Hop in the CR-TLV; - Withdrawing a CRLSP. For the description, the following pictorial representations may be used as an aid to understanding: LSR 1 LSR 2 ... LSR n .-----. .-----. .-----. | ER | | ER | | ER | `-----' `-----' `-----' | CR-TLV CR-TLV ^ | CR-TLV CR-TLV ^ | Next | | Next | | Hop | | Hop | V | V | .-----. Label .-----. Label Label .-----. | LDP |----------->| LDP |-------> ... ------->| LDP | `-----' Request `-----' Request Request `-----' Jamoussi, et. al. January 26, 1999 [Page 27] CR-LDP Specification - 28 - Exp. Apr 1999 CRLSP Setup propagation LSR 1 LSR 2 ... LSR n .-----. .-----. .-----. | ER | | ER | | ER | `-----' `-----' `-----' ^ Status Status | | Previous | | Hop | | V .-----. Label .-----. Label Label .-----. | LDP |<-----------| LDP |<------- ... <-------| LDP | `-----' Mapping `-----' Mapping Mapping `-----' CRLSP Status propagation .---------------. | ER | .---------------. | Link/Call | | LDP | | Admission | | | | Control | | Label | `---------------' | Allocation | `---------------' Related Tasks B.1. CR-LDP Primitives The following sections describe the logical interactions between Constrain-based Route and LDP state machines in terms of primitives that describe the minimal information exchange required. These assume an asynchronous exchange model involving locally significant IDs that is used to tie status of a request to the initial setup and to allow LDP to relate incoming/outgoing Label Request messages. A synchronous model - possibly based on multiple threads - is also possible and would eliminate the need for IDs. B.1.1. CR to LDP Primitives LDP_SEND_REQ( TLV_List, To_LSR, Identifier ) TLV_List TLVs to be sent to a neighboring LSR; includes at least an Jamoussi, et. al. January 26, 1999 [Page 28] CR-LDP Specification - 29 - Exp. Apr 1999 CR-TLV and may contain additional TLVs (i.e. QoS TLVs). To_LSR The neighbor LSR to which a Label Request is to be sent. Identifier Locally significant unique identifier. May be used to associate the Label Request to be sent either with a Label Request that was previously received (e.g. - LSR 2 above) or a subsequent CRLSP Status (e.g. - LSR 1 above). LDP_SEND_RSP( Status, Identifier ) Status Status of a specific CRLSP Setup Request. A Status of zero indicates success; other Status values are given in Error Subcodes section. This Status is carried in Label Mapping or Notification messages to the originator of the CRLSP setup. Identifier Locally significant unique identifier used to associate the Label Mapping to be sent with a Label Request received (e.g. LSR n above). B.1.2. LDP to CR Primitives CR_RECEIVED_REQ( TLV_List, Identifier ) TLV_List TLVs to be processed by the local constraint-based route function. Identifier Locally significant unique identifier used to associate the received request either with a subsequent further request or a response. For example, the identifier provided here would be used in a subsequent LDP_SEND_REQ or LDP_SEND_RSP. CR_LSP_STATUS( Status, Identifier ) Status Status of a specific CRLSP Setup Request. A Status of zero indicates success; other Status values are given in section Error Subcodes. This Status originated at the remote LSR Jamoussi, et. al. January 26, 1999 [Page 29] CR-LDP Specification - 30 - Exp. Apr 1999 which either completed the CRLSP setup or determined that CRLSP setup could not be done. Identifier Locally significant unique identifier used to associate the received response with the original request. For example, this identifier would be the same as was used in the initial LDP_SEND_REQ. B.2. CR-LDP States This document defines 3 states relative to any one specific CRLSP. They are: CR_Non_Existant - no state information exists relative to this CRLSP; CR_In_Progress - LDP_SEND_REQ has been called in result of external input (e.g. - management); CR_Established - a successful status has been received from an earlier setup. These states are defined such that no additional state is required to support CRLSPs using LDP at intermediate LSRs than is already required in LDP. B.3. CR-LDP Events This document defines 4 events impacting any one specific CRLSP. They are: CR_Start - a CRLSP is required based on an external stimulus (e.g. - management); CR_Req_Received - further CRLSP setup processing is required based on CR_RECEIVED_REQ (i.e. - from an upstream LSR's CRLSP Label Request); CR_Setup_Complete - CRLSP setup has been successfully completed based on CR_LSP_STATUS (with success status); CR_LSP_Failure - Either a CRLSP could not be established as requested, or a setup CRLSP has dropped; based on CR_LSP_STATUS (with error status). B.4. CR-LDP Transitions State transitions are defined as follows: Jamoussi, et. al. January 26, 1999 [Page 30] CR-LDP Specification - 31 - Exp. Apr 1999 State Event Action New State ==================== ================= ====== =============== CR_Non_Existant CR_Start 1 CR_In_Progress CR_Non_Existant CR_Req_Rec 2 CR_Non_Existant CR_In_Progress CR_Setup_Complete CR_Established CR_In_Progress CR_LSP_Failure 3 CR_Non_Existant CR_Established CR_LSP_Failure 3 CR_Non_Existant Actions: 1) Establish CRLSP state, create CR-TLV information, LDP_SEND_REQ. 2) Process CR-TLV (as described in "Processing of the Constraint-Based Route TLV" section) and either LDP_SEND_REQ or LDP_SEND_RSP. 3) Remove state information relative to this CRLSP (may notify management, other external source initially requiring setup). For the purposes of this transition table, illegal transitions (not included in the table) are ignored. Jamoussi, et. al. January 26, 1999 [Page 31]