RFC 5977
RMD-QOSM: The NSIS Quality-of-Service Model for Resource Management in Diffserv
Pages: 128
Experimental
Experimental
Part 1 of 5 – Pages 1 to 23
Internet Engineering Task Force (IETF) A. Bader Request for Comments: 5977 L. Westberg Category: Experimental Ericsson ISSN: 2070-1721 G. Karagiannis University of Twente C. Kappler ck technology concepts T. Phelan Sonus October 2010 RMD-QOSM: The NSIS Quality-of-Service Model for Resource Management in DiffservAbstract
This document describes a Next Steps in Signaling (NSIS) Quality-of- Service (QoS) Model for networks that use the Resource Management in Diffserv (RMD) concept. RMD is a technique for adding admission control and preemption function to Differentiated Services (Diffserv) networks. The RMD QoS Model allows devices external to the RMD network to signal reservation requests to Edge nodes in the RMD network. The RMD Ingress Edge nodes classify the incoming flows into traffic classes and signals resource requests for the corresponding traffic class along the data path to the Egress Edge nodes for each flow. Egress nodes reconstitute the original requests and continue forwarding them along the data path towards the final destination. In addition, RMD defines notification functions to indicate overload situations within the domain to the Edge nodes. Status of This Memo This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation. This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5977.
Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents
1. Introduction ....................................................4 2. Terminology .....................................................6 3. Overview of RMD and RMD-QOSM ....................................7 3.1. RMD ........................................................7 3.2. Basic Features of RMD-QOSM ................................10 3.2.1. Role of the QNEs ...................................10 3.2.2. RMD-QOSM/QoS-NSLP Signaling ........................11 3.2.3. RMD-QOSM Applicability and Considerations ..........13 4. RMD-QOSM, Detailed Description .................................15 4.1. RMD-QSPEC Definition ......................................16 4.1.1. RMD-QOSM <QoS Desired> and <QoS Reserved> ..........16 4.1.2. PHR Container ......................................17 4.1.3. PDR Container ......................................20 4.2. Message Format ............................................23 4.3. RMD Node State Management .................................23 4.3.1. Aggregated Operational and Reservation States at the QNE Edges ............................23 4.3.2. Measurement-Based Method ...........................25 4.3.3. Reservation-Based Method ...........................27 4.4. Transport of RMD-QOSM Messages ............................28 4.5. Edge Discovery and Message Addressing .....................31 4.6. Operation and Sequence of Events ..........................32 4.6.1. Basic Unidirectional Operation .....................32 4.6.1.1. Successful Reservation ....................34 4.6.1.2. Unsuccessful Reservation ..................46 4.6.1.3. RMD Refresh Reservation ...................50 4.6.1.4. RMD Modification of Aggregated Reservations ..............................54 4.6.1.5. RMD Release Procedure .....................55 4.6.1.6. Severe Congestion Handling ................64
4.6.1.7. Admission Control Using Congestion
Notification Based on Probing .............70
4.6.2. Bidirectional Operation ............................73
4.6.2.1. Successful and Unsuccessful Reservations ..77
4.6.2.2. Refresh Reservations ......................82
4.6.2.3. Modification of Aggregated Intra-Domain
QoS-NSLP Operational Reservation States ...82
4.6.2.4. Release Procedure .........................83
4.6.2.5. Severe Congestion Handling ................84
4.6.2.6. Admission Control Using Congestion
Notification Based on Probing .............87
4.7. Handling of Additional Errors .............................89
5. Security Considerations ........................................89
5.1. Introduction ..............................................89
5.2. Security Threats ..........................................91
5.2.1. On-Path Adversary ..................................92
5.2.2. Off-Path Adversary .................................94
5.3. Security Requirements .....................................94
5.4. Security Mechanisms .......................................94
6. IANA Considerations ............................................97
6.1. Assignment of QSPEC Parameter IDs .........................97
7. Acknowledgments ................................................97
8. References .....................................................97
8.1. Normative References ......................................97
8.2. Informative References ....................................98
Appendix A. Examples .............................................101
A.1. Example of a Re-Marking Operation during Severe
Congestion in the Interior Nodes .........................101
A.2. Example of a Detailed Severe Congestion Operation in the
Egress Nodes .............................................107
A.3. Example of a Detailed Re-Marking Admission Control
(Congestion Notification) Operation in Interior Nodes ....111
A.4. Example of a Detailed Admission Control (Congestion
Notification) Operation in Egress Nodes ..................112
A.5. Example of Selecting Bidirectional Flows for Termination
during Severe Congestion .................................113
A.6. Example of a Severe Congestion Solution for
Bidirectional Flows Congested Simultaneously on Forward
and Reverse Paths ........................................113
A.7. Example of Preemption Handling during Admission Control ..117
A.8. Example of a Retransmission Procedure within the RMD
Domain ...................................................120
A.9. Example on Matching the Initiator QSPEC to the Local
RMD-QSPEC ................................................122
1. Introduction
This document describes a Next Steps in Signaling (NSIS) QoS Model for networks that use the Resource Management in Diffserv (RMD) framework ([RMD1], [RMD2], [RMD3], and [RMD4]). RMD adds admission control to Diffserv networks and allows nodes external to the networks to dynamically reserve resources within the Diffserv domains. The Quality-of-Service NSIS Signaling Layer Protocol (QoS-NSLP) [RFC5974] specifies a generic protocol for carrying QoS signaling information end-to-end in an IP network. Each network along the end- to-end path is expected to implement a specific QoS Model (QOSM) specified by the QSPEC template [RFC5975] that interprets the requests and installs the necessary mechanisms, in a manner that is appropriate to the technology in use in the network, to ensure the delivery of the requested QoS. This document specifies an NSIS QoS Model for RMD networks (RMD-QOSM), and an RMD-specific QSPEC (RMD- QSPEC) for expressing reservations in a suitable form for simple processing by internal nodes. They are used in combination with the QoS-NSLP to provide QoS signaling service in an RMD network. Figure 1 shows an RMD network with the respective entities. Stateless or reduced-state Egress Ingress RMD Nodes Node Node (Interior Nodes; I-Nodes) (Stateful (Stateful | | | RMD QoS RMD QoS-NLSP | | | NSLP Node) Node) V V V +-------+ Data +------+ +------+ +------+ +------+ |-------|--------|------|------|------|-------|------|---->|------| | | Flow | | | | | | | | |Ingress| |I-Node| |I-Node| |I-Node| |Egress| | | | | | | | | | | +-------+ +------+ +------+ +------+ +------+ =================================================> <================================================= Signaling Flow Figure 1: Actors in the RMD-QOSM Many network scenarios, such as the "Wired Part of Wireless Network" scenario, which is described in Section 8.4 of [RFC3726], require that the impact of the used QoS signaling protocol on the network performance should be minimized. In such network scenarios, the performance of each network node that is used in a communication path
has an impact on the end-to-end performance. As such, the end-to-end
performance of the communication path can be improved by optimizing
the performance of the Interior nodes. One of the factors that can
contribute to this optimization is the minimization of the QoS
signaling protocol processing load and the minimization of the number
of states on each Interior node.
Another requirement that is imposed by such network scenarios is that
whenever a severe congestion situation occurs in the network, the
used QoS signaling protocol should be able to solve them. In the
case of a route change or link failure, a severe congestion situation
may occur in the network. Typically, routing algorithms are able to
adapt and change their routing decisions to reflect changes in the
topology and traffic volume. In such situations, the rerouted
traffic will have to follow a new path. Interior nodes located on
this new path may become overloaded, since they suddenly might need
to support more traffic than for which they have capacity. These
severe congestion situations will severely affect the overall
performance of the traffic passing through such nodes.
RMD-QOSM is an edge-to-edge (intra-domain) QoS Model that, in
combination with the QoS-NSLP and QSPEC specifications, is designed
to support the requirements mentioned above:
o Minimal impact on Interior node performance;
o Increase of scalability;
o Ability to deal with severe congestion
Internally to the RMD network, RMD-QOSM together with QoS-NSLP
[RFC5974] defines a scalable QoS signaling model in which per-flow
QoS-NSLP and NSIS Transport Layer Protocol (NTLP) states are not
stored in Interior nodes but per-flow signaling is performed (see
[RFC5974]) at the Edges.
In the RMD-QOSM, only routers at the Edges of a Diffserv domain
(Ingress and Egress nodes) support the (QoS-NSLP) stateful operation;
see Section 4.7 of [RFC5974]. Interior nodes support either the
(QoS-NSLP) stateless operation or a reduced-state operation with
coarser granularity than the Edge nodes.
After the terminology in Section 2, we give an overview of RMD and
the RMD-QOSM in Section 3. This document specifies several RMD-QOSM/
QoS-NSLP signaling schemes. In particular, Section 3.2.3 identifies
which combination of sections are used for the specification of each
RMD-QOSM/QoS-NSLP signaling scheme. In Section 4 we give a detailed
description of the RMD-QOSM, including the role of QoS NSIS entities
(QNEs), the definition of the QSPEC, mapping of QSPEC generic parameters onto RMD-QOSM parameters, state management in QNEs, and operation and sequence of events. Section 5 discusses security issues.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The terminology defined by GIST [RFC5971] and QoS-NSLP [RFC5974] applies to this document. In addition, the following terms are used: NSIS domain: an NSIS signaling-capable domain. RMD domain: an NSIS domain that is capable of supporting the RMD-QOSM signaling and operations. Edge node: a QoS-NSLP node on the boundary of some administrative domain that connects one NSIS domain to a node in either another NSIS domain or a non-NSIS domain. NSIS-aware node: a node that is aware of NSIS signaling and RMD-QOSM operations, such as severe congestion detection and Differentiated Service Code Point (DSCP) marking. NSIS-unaware node: a node that is unaware of NSIS signaling, but is aware of RMD-QOSM operations such as severe congestion detection and DSCP marking. Ingress node: an Edge node in its role in handling the traffic as it enters the NSIS domain. Egress node: an Edge node in its role in handling the traffic as it leaves the NSIS domain. Interior node: a node in an NSIS domain that is not an Edge node. Congestion: a temporal network state that occurs when the traffic (or when traffic associated with a particular Per-Hop Behavior (PHB)) passing through a link is slightly higher than the capacity allocated for the link (or allocated for the particular PHB). If no measures are taken, then the traffic passing through this link may temporarily slightly degrade in QoS. This type of congestion is usually solved using admission control mechanisms.
Severe congestion: the congestion situation on a particular link within the RMD domain where a significant increase in its real packet queue situation occurs, such as when due to a link failure rerouted traffic has to be supported by this particular link.3. Overview of RMD and RMD-QOSM
3.1. RMD
The Differentiated Services (Diffserv) architecture ([RFC2475], [RFC2638]) was introduced as a result of efforts to avoid the scalability and complexity problems of IntServ [RFC1633]. Scalability is achieved by offering services on an aggregate rather than per-flow basis and by forcing as much of the per-flow state as possible to the Edges of the network. The service differentiation is achieved using the Differentiated Services (DS) field in the IP header and the Per-Hop Behavior (PHB) as the main building blocks. Packets are handled at each node according to the PHB indicated by the DS field in the message header. The Diffserv architecture does not specify any means for devices outside the domain to dynamically reserve resources or receive indications of network resource availability. In practice, service providers rely on short active time Service Level Agreements (SLAs) that statically define the parameters of the traffic that will be accepted from a customer. RMD was introduced as a method for dynamic reservation of resources within a Diffserv domain. It describes a method that is able to provide admission control for flows entering the domain and a congestion handling algorithm that is able to terminate flows in case of congestion due to a sudden failure (e.g., link, router) within the domain. In RMD, scalability is achieved by separating a fine-grained reservation mechanism used in the Edge nodes of a Diffserv domain from a much simpler reservation mechanism needed in the Interior nodes. Typically, it is assumed that Edge nodes support per-flow QoS states in order to provide QoS guarantees for each flow. Interior nodes use only one aggregated reservation state per traffic class or no states at all. In this way, it is possible to handle large numbers of flows in the Interior nodes. Furthermore, due to the limited functionality supported by the Interior nodes, this solution allows fast processing of signaling messages. The possible RMD-QOSM applicabilities are described in Section 3.2.3. Two main basic admission control modes are supported: reservation- based and measurement-based admission control that can be used in
combination with a severe congestion-handling solution. The severe congestion-handling solution is used in the situation that a link/node becomes severely congested due to the fact that the traffic supported by a failed link/node is rerouted and has to be processed by this link/node. Furthermore, RMD-QOSM supports both unidirectional and bidirectional reservations. Another important feature of RMD-QOSM is that the intra-domain sessions supported by the Edges can be either per-flow sessions or per-aggregate sessions. In the case of the per-flow intra-domain sessions, the maintained per-flow intra-domain states have a one-to- one dependency to the per-flow end-to-end states supported by the same Edge. In the case of the per-aggregate sessions the maintained per-aggregate states have a one-to-many relationship to the per-flow end-to-end states supported by the same Edge. In the reservation-based method, each Interior node maintains only one reservation state per traffic class. The Ingress Edge nodes aggregate individual flow requests into PHB traffic classes, and signal changes in the class reservations as necessary. The reservation is quantified in terms of resource units (or bandwidth). These resources are requested dynamically per PHB and reserved on demand in all nodes in the communication path from an Ingress node to an Egress node. The measurement-based algorithm continuously measures traffic levels and the actual available resources, and admits flows whose resource needs are within what is available at the time of the request. The measurement-based algorithm is used to support a predictive service where the service commitment is somewhat less reliable than the service that can be supported by the reservation-based method. A main assumption that is made by such measurement-based admission control mechanisms is that the aggregated PHB traffic passing through an RMD Interior node is high and therefore, current measurement characteristics are considered to be an indicator of future load. Once an admission decision is made, no record of the decision need be kept at the Interior nodes. The advantage of measurement-based resource management protocols is that they do not require pre- reservation state nor explicit release of the reservations at the Interior nodes. Moreover, when the user traffic is variable, measurement-based admission control could provide higher network utilization than, e.g., peak-rate reservation. However, this can introduce an uncertainty in the availability of the resources. It is important to emphasize that the RMD measurement-based schemes described in this document do not use any refresh procedures, since these approaches are used in stateless nodes; see Section 4.6.1.3.
Two types of measurement-based admission control schemes are possible: * Congestion notification function based on probing: This method can be used to implement a simple measurement-based admission control within a Diffserv domain. In this scenario, the Interior nodes are not NSIS-aware nodes. In these Interior nodes, thresholds are set for the traffic belonging to different PHBs in the measurement-based admission control function. In this scenario, an end-to-end NSIS message is used as a probe packet, meaning that the <DSCP> field in the header of the IP packet that carries the NSIS message is re-marked when the predefined congestion threshold is exceeded. Note that when the predefined congestion threshold is exceeded, all packets are re-marked by a node, including NSIS messages. In this way, the Edges can admit or reject flows that are requesting resources. The frequency and duration that the congestion level is above the threshold resulting in re-marking is tracked and used to influence the admission control decisions. * NSIS measurement-based admission control: In this case, the measurement-based admission control functionality is implemented in NSIS-aware stateless routers. The main difference between this type of admission control and the congestion notification based on probing is related to the fact that this type of admission control is applied mainly on NSIS-aware nodes. With the measurement-based scheme, the requested peak bandwidth of a flow is carried by the admission control request. The admission decision is considered as positive if the currently carried traffic, as characterized by the measured statistics, plus the requested resources for the new flow exceeds the system capacity with a probability smaller than a value alpha. Otherwise, the admission decision is negative. It is important to emphasize that due to the fact that the RMD Interior nodes are stateless, they do not store information of previous admission control requests. This could lead to a situation where the admission control accuracy is decreased when multiple simultaneous flows (sharing a common Interior node) are requesting admission control simultaneously. By applying measuring techniques, e.g., see [JaSh97] and [GrTs03], which use current and past information on NSIS sessions that requested resources from an NSIS-aware Interior node, the decrease in admission control accuracy can be limited. RMD describes the following procedures:
* classification of an individual resource reservation or a resource
query into Per-Hop Behavior (PHB) groups at the Ingress node of the
domain,
* hop-by-hop admission control based on a PHB within the domain.
There are two possible modes of operation for internal nodes to
admit requests. One mode is the stateless or measurement-based
mode, where the resources within the domain are queried. Another
mode of operation is the reduced-state reservation or reservation-
based mode, where the resources within the domain are reserved.
* a method to forward the original requests across the domain up to
the Egress node and beyond.
* a congestion-control algorithm that notifies the Egress Edge nodes
about congestion. It is able to terminate the appropriate number
of flows in the case a of congestion due to a sudden failure (e.g.,
link or router failure) within the domain.
3.2. Basic Features of RMD-QOSM
3.2.1. Role of the QNEs
The protocol model of the RMD-QOSM is shown in Figure 2. The figure
shows QoS NSIS initiator (QNI) and QoS NSIS Receiver (QNR) nodes, not
part of the RMD network, that are the ultimate initiator and receiver
of the QoS reservation requests. It also shows QNE nodes that are
the Ingress and Egress nodes in the RMD domain (QNE Ingress and QNE
Egress), and QNE nodes that are Interior nodes (QNE Interior).
All nodes of the RMD domain are usually QoS-NSLP-aware nodes.
However, in the scenarios where the congestion notification function
based on probing is used, then the Interior nodes are not NSIS aware.
Edge nodes store and maintain QoS-NSLP and NTLP states and therefore
are stateful nodes. The NSIS-aware Interior nodes are NTLP
stateless. Furthermore, they are either QoS-NSLP stateless (for NSIS
measurement-based operation) or reduced-state nodes storing per PHB
aggregated QoS-NSLP states (for reservation-based operation).
Note that the RMD domain MAY contain Interior nodes that are not
NSIS-aware nodes (not shown in the figure).
These nodes are assumed to have sufficient capacity for flows that
might be admitted. Furthermore, some of these NSIS-unaware nodes MAY
be used for measuring the traffic congestion level on the data path.
These measurements can be used by RMD-QOSM in the congestion control
based on probing operation and/or severe congestion operation (see
Section 4.6.1.6).
|------| |-------| |------| |------| | e2e |<->| e2e |<------------------------->| e2e |<->| e2e | | QoS | | QoS | | QoS | | QoS | | | |-------| |------| |------| | | |-------| |-------| |-------| |------| | | | | | local |<->| local |<->| local |<->| local| | | | | | QoS | | QoS | | QoS | | QoS | | | | | | | | | | | | | | | | NSLP | | NSLP | | NSLP | | NSLP | | NSLP | | NSLP | |st.ful| |st.ful | |st.less/ |st.less/ |st.ful| |st.ful| | | | | |red.st.| |red.st.| | | | | | | |-------| |-------| |-------| |------| | | |------| |-------| |-------| |-------| |------| |------| ------------------------------------------------------------------ |------| |-------| |-------| |-------| |------| |------| | NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->|NTLP | |st.ful| |st.ful | |st.less| |st.less| |st.ful| |st.ful| |------| |-------| |-------| |-------| |------| |------| QNI QNE QNE QNE QNE QNR (End) (Ingress) (Interior) (Interior) (Egress) (End) st.ful: stateful, st.less: stateless st.less red.st.: stateless or reduced-state Figure 2: Protocol model of stateless/reduced-state operation3.2.2. RMD-QOSM/QoS-NSLP Signaling
The basic RMD-QOSM/QoS-NSLP signaling is shown in Figure 3. The signaling scenarios are accomplished using the QoS-NSLP processing rules defined in [RFC5974], in combination with the Resource Management Function (RMF) triggers sent via the QoS-NSLP-RMF API described in [RFC5974]. Due to the fact that within the RMD domain a QoS Model that is different than the end-to-end QoS Model applied at the Edges of the RMD domain can be supported, the RMD Interior node reduced-state reservations can be updated independently of the per-flow end-to-end reservations (see Section 4.7 of [RFC5974]). Therefore, two different RESERVE messages are used within the RMD domain. One RESERVE message that is associated with the per-flow end-to-end reservations and is used by the Edges of the RMD domain and one that is associated with the reduced-state reservations within the RMD domain. A RESERVE message is created by a QNI with an Initiator QSPEC describing the reservation and forwarded along the path towards the QNR.
When the original RESERVE message arrives at the Ingress node, an RMD-QSPEC is constructed based on the initial QSPEC in the message (usually the Initiator QSPEC). The RMD-QSPEC is sent in a intra- domain, independent RESERVE message through the Interior nodes towards the QNR. This intra-domain RESERVE message uses the GIST datagram signaling mechanism. Note that the RMD-QOSM cannot directly specify that the GIST Datagram mode SHOULD be used. This can however be notified by using the GIST API Transfer-Attributes, such as unreliable, low level of security and use of local policy. Meanwhile, the original RESERVE message is sent to the Egress node on the path to the QNR using the reliable transport mode of NTLP. Each QoS-NSLP node on the data path processes the intra-domain RESERVE message and checks the availability of resources with either the reservation-based or the measurement-based method. QNE Ingress QNE Interior QNE Interior QNE Egress NTLP stateful NTLP stateless NTLP stateless NTLP stateful | | | | RESERVE | | | | -------->| RESERVE | | | +--------------------------------------------->| | RESERVE' | | | +-------------->| | | | | RESERVE' | | | +-------------->| | | | | RESERVE' | | | +------------->| | | | RESPONSE'| |<---------------------------------------------+ | | | | RESERVE | | | +-------> | | | |RESPONSE | | | |<------- | | | RESPONSE | |<---------------------------------------------+ RESPONSE| | | | <--------| | | | Figure 3: Sender-initiated reservation with reduced-state Interior nodes When the message reaches the Egress node, and the reservation is successful in each Interior node, an intra-domain (local) RESPONSE' is sent towards the Ingress node and the original (end-to-end) RESERVE message is forwarded to the next domain. When the Egress node receives a RESPONSE message from the downstream end, it is forwarded directly to the Ingress node.
If an intermediate node cannot accommodate the new request, it indicates this by marking a single bit in the message, and continues forwarding the message until the Egress node is reached. From the Egress node, an intra-domain RESPONSE' and an original RESPONSE message are sent directly to the Ingress node. As a consequence, in the stateless/reduced-state domain only sender- initiated reservations can be performed and functions requiring per- flow NTLP or QoS-NSLP states, like summary and reduced refreshes, cannot be used. If per-flow identification is needed, i.e., associating the flow IDs for the reserved resources, Edge nodes act on behalf of Interior nodes.3.2.3. RMD-QOSM Applicability and Considerations
The RMD-QOSM is a Diffserv-based bandwidth management methodology that is not able to provide a full Diffserv support. The reason for this is that the RMD-QOSM concept can only support the (Expedited Forwarding) EF-like functionality behavior, but is not able to support the full set of (Assured Forwarding) AF-like functionality. The bandwidth information REQUIRED by the EF-like functionality behavior can be supported by RMD-QOSM carrying the bandwidth information in the <QoS Desired> parameter (see [RFC5975]). The full set of (Assured Forwarding) AF-like functionality requires information that is specified in two token buckets. The RMD-QOSM is not supporting the use of two token buckets and therefore, it is not able to support the full set of AF-functionality. Note however, that RMD-QOSM could also support a single AF PHB, when the traffic or the upper limit of the traffic can be characterized by a single bandwidth parameter. Moreover, it is considered that in case of tunneling, the RMD-QOSM supports only the uniform tunneling mode for Diffserv (see [RFC2983]). The RMD domain MUST be engineered in such a way that each QNE Ingress maintains information about the smallest MTU that is supported on the links within the RMD domain. A very important consideration on using RMD-QOSM is that within one RMD domain only one of the following RMD-QOSM schemes can be used at a time. Thus, an RMD router can never process and use two different RMD-QOSM signaling schemes at the same time. However, all RMD QNEs supporting this specification MUST support the combination of the "per-flow RMD reservation-based" and the "severe congestion handling by proportional data packet marking" scheme. If the RMD QNEs support more RMD-QOSM schemes, then the operator of that RMD domain MUST preconfigure all the QNE Edge nodes within one domain such that the <SCH> field included in the "PHR container" (Section
4.1.2) and the "PDR Container" (Section 4.1.3) will always use the same value, such that within one RMD domain only one of the below described RMD-QOSM schemes is used at a time. The congestion situations (see Section 2) are solved using an admission control mechanism, e.g., "per-flow congestion notification based on probing", while the severe congestion situations (see Section 2), are solved using the severe congestion handling mechanisms, e.g., "severe congestion handling by proportional data packet marking". The RMD domain MUST be engineered in such a way that RMD-QOSM messages could be transported using the GIST Query and DATA messages in Q-mode; see [RFC5971]. This means that the Path MTU MUST be engineered in such a way that the RMD-QOSM message are transported without fragmentation. Furthermore, the RMD domain MUST be engineered in such a way to guarantee capacity for the GIST Query and Data messages in Q-mode, within the rate control limits imposed by GIST; see [RFC5971]. The RMD domain has to be configured such that the GIST context-free flag (C-flag) MUST be set (C=1) for QUERY messages and DATA messages sent in Q-mode; see [RFC5971]. Moreover, the same deployment issues and extensibility considerations described in [RFC5971] and [RFC5978] apply to this document. It is important to note that the concepts described in Sections 4.6.1.6.2, 4.6.2.5.2, 4.6.1.6.2, and 4.6.2.5.2 contributed to the PCN WG standardization. The available RMD-QOSM/QoS-NSLP signaling schemes are: * "per-flow congestion notification based on probing" (see Sections 4.3.2, 4.6.1.7, and 4.6.2.6). Note that this scheme uses, for severe congestion handling, the "severe congestion handling by proportional data packet marking" (see Sections 4.6.1.6.2 and 4.6.2.5.2). Furthermore, the Interior nodes are considered to be Diffserv aware, but NSIS-unaware nodes (see Section 4.3.2). * "per-flow RMD NSIS measurement-based admission control" (see Sections 4.3.2, 4.6.1, and 4.6.2). Note that this scheme uses, for severe congestion handling, the "severe congestion handling by proportional data packet marking" (see Sections 4.6.1.6.2 and 4.6.2.5.2). Furthermore, the Interior nodes are considered to be NSIS-aware nodes (see Section 4.3.2).
* "per-flow RMD reservation-based" in combination with the "severe
congestion handling by the RMD-QOSM refresh" procedure (see
Sections 4.3.3, 4.6.1, 4.6.1.6.1, and 4.6.2.5.1). Note that this
scheme uses, for severe congestion handling, the "severe congestion
handling by the RMD-QOSM refresh" procedure (see Sections 4.6.1.6.1
and 4.6.2.5.1). Furthermore, the intra-domain sessions supported
by the Edge nodes are per-flow sessions (see Section 4.3.3).
* "per-flow RMD reservation-based" in combination with the "severe
the congestion handling by proportional data packet marking"
procedure (see Sections 4.3.3, 4.6.1, 4.6.1.6.2, and 4.6.2.5.2).
Note that this scheme uses, for severe congestion handling, the
"severe congestion handling by proportional data packet marking"
procedure (see Sections 4.6.1.6.2 and 4.6.2.5.2). Furthermore, the
intra-domain sessions supported by the Edge nodes are per-flow
sessions (see Section 4.3.3).
* "per-aggregate RMD reservation-based" in combination with the
"severe congestion handling by the RMD-QOSM refresh" procedure (see
Sections 4.3.1, 4.6.1, 4.6.1.6.1, and 4.6.2.5.1). Note that this
scheme uses, for severe congestion handling, the "severe congestion
handling by the RMD-QOSM refresh" procedure (see Sections 4.6.1.6.1
and 4.6.2.5.1). Furthermore, the intra-domain sessions supported
by the Edge nodes are per-aggregate sessions (see Section 4.3.1).
Moreover, this scheme can be considered to be a reservation-based
scheme, since the RMD Interior nodes are reduced-state nodes, i.e.,
they do not store NTLP/GIST states, but they do store per PHB-
aggregated QoS-NSLP reservation states.
* "per-aggregate RMD reservation-based" in combination with the
"severe congestion handling by proportional data packet marking"
procedure (see Sections 4.3.1, 4.6.1, 4.6.1.6.2, and 4.6.2.5.2).
Note that this scheme uses, for severe congestion handling, the
"severe congestion handling by proportional data packet marking"
procedure (see Sections 4.6.1.6.2 and 4.6.2.5.2). Furthermore, the
intra-domain sessions supported by the Edge nodes are per-aggregate
sessions (see Section 4.3.1). Moreover, this scheme can be
considered to be a reservation-based scheme, since the RMD Interior
nodes are reduced-state nodes, i.e., they do not store NTLP/GIST
states, but they do store per PHB-aggregated QoS-NSLP reservation
states.
4. RMD-QOSM, Detailed Description
This section describes the RMD-QOSM in more detail. In particular,
it defines the role of stateless and reduced-state QNEs, the RMD-QOSM
QSPEC Object, the format of the RMD-QOSM QoS-NSLP messages, and how
QSPECs are processed and used in different protocol operations.
4.1. RMD-QSPEC Definition
The RMD-QOSM uses the QSPEC format specified in [RFC5975]. The Initiator/Local QSPEC bit, i.e., <I> is set to "Local" (i.e., "1") and the <QSPEC Proc> is set as follows: * Message Sequence = 0: Sender initiated * Object combination = 0: <QoS Desired> for RESERVE and <QoS Reserved> for RESPONSE The <QSPEC Version> used by RMD-QOSM is the default version, i.e., "0", see [RFC5975]. The <QSPEC Type> value used by the RMD-QOSM is specified in [RFC5975] and is equal to "2". The <Traffic Handling Directives> contains the following fields: <Traffic Handling Directives> = <PHR container> <PDR container> The Per-Hop Reservation container (PHR container) and the Per-Domain Reservation container (PDR container) are specified in Sections 4.1.2 and 4.1.3, respectively. The <PHR container> contains the traffic handling directives for intra-domain communication and reservation. The <PDR container> contains additional traffic handling directives that are needed for edge-to-edge communication. The parameter IDs used by the <PHR container> and <PDR container> are assigned by IANA; see Section 6. The RMD-QOSM <QoS Desired> and <QoS Reserved>, are specified in Section 4.1.1. The RMD-QOSM <QoS Desired> and <QoS Reserved> and the <PHR container> are used and processed by the Edge and Interior nodes. The <PDR container> field is only processed by Edge nodes.4.1.1. RMD-QOSM <QoS Desired> and <QoS Reserved>
The RESERVE message contains only the <QoS Desired> object [RFC5975]. The <QoS Reserved> object is carried by the RESPONSE message. In RMD-QOSM, the <QoS Desired> and <QoS Reserved> objects contain the following parameters: <QoS Desired> = <TMOD-1> <PHB Class> <Admission Priority> <QoS Reserved> = <TMOD-1> <PHB Class> <Admission Priority> The bit format of the <PHB Class> (see [RFC5975] and Figures 4 and 5) and <Admission Priority> complies with the bit format specified in [RFC5975].
Note that for the RMD-QOSM, a reservation established without an <Admission Priority> parameter is equivalent to a reservation established with an <Admission Priority> whose value is 1. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DSCP |0 0 0 0 0 0 0 0 X 0| +---+---+---+---+---+---+---+---+ Figure 4: DSCP parameter 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PHB ID code |0 0 X X| +---+---+---+---+---+---+---+---+ Figure 5: PHB ID Code parameter4.1.2. PHR Container
This section describes the parameters used by the PHR container, which are used by the RMD-QOSM functionality available at the Interior nodes. <PHR container> = <O> <K> <S> <M>, <Admitted Hops>, <B> <Hop_U> <Time Lag> <SCH> <Max Admitted Hops> The bit format of the PHR container can be seen in Figure 6. Note that in Figure 6 <Hop_U> is represented as <U>. Furthermore, in Figure 6, <Max Admitted Hops> is represented as <Max Adm Hops>. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M|E|N|r| Parameter ID |r|r|r|r| 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S|M| Admitted Hops|B|U| Time Lag |O|K| SCH | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max Adm Hops | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: PHR container Parameter ID: 12-bit field, indicating the PHR type: PHR_Resource_Request, PHR_Release_Request, PHR_Refresh_Update.
"PHR_Resource_Request" (Parameter ID = 17): initiate or update the traffic class reservation state on all nodes located on the communication path between the QNE(Ingress) and QNE(Egress) nodes. "PHR_Release_Request" (Parameter ID = 18): explicitly release, by subtraction, the reserved resources for a particular flow from a traffic class reservation state. "PHR_Refresh_Update" (Parameter ID = 19): refresh the traffic class reservation soft state on all nodes located on the communication path between the QNE(Ingress) and QNE(Egress) nodes according to a resource reservation request that was successfully processed during a previous refresh period. <S> (Severe Congestion): 1 bit. In the case of a route change, refreshing RESERVE messages follow the new data path, and hence resources are requested there. If the resources are not sufficient to accommodate the new traffic, severe congestion occurs. Severe congested Interior nodes SHOULD notify Edge QNEs about the congestion by setting the <S> bit. <O> (Overload): 1 bit. This field is used during the severe congestion handling scheme that is using the RMD-QOSM refresh procedure. This bit is set when an overload on a QNE Interior node is detected and when this field is carried by the "PHR_Refresh_Update" container. <O> SHOULD be set to"1" if the <S> bit is set. For more details, see Section 4.6.1.6.1. <M>: 1 bit. In the case of unsuccessful resource reservation or resource query in an Interior QNE, this QNE sets the <M> bit in order to notify the Egress QNE. <Admitted Hops>: 8-bit field. The <Admitted Hops> counts the number of hops in the RMD domain where the reservation was successful. The <Admitted Hops> is set to "0" when a RESERVE message enters a domain and it MUST be incremented by each Interior QNE, provided that the <Hop_U> bit is not set. However, when a QNE that does not have sufficient resources to admit the reservation is reached, the <M> bit is set, and the <Admitted Hops> value is frozen, by setting the <Hop_U> bit to "1". Note that the <Admitted Hops> parameter in combination with the <Max Admitted Hops> and <K> parameters are used during the RMD partial release procedures (see Section 4.6.1.5.2). <Hop_U> (NSLP_Hops unset): 1 bit. The QNE(Ingress) node MUST set the <Hop_U> parameter to 0. This parameter SHOULD be set to "1" by a node when the node does not increase the <Admitted Hops> value. This is the case when an RMD-QOSM reservation-based node is not admitting the reservation request. When <Hop_U> is set to "1", the <Admitted
Hops> SHOULD NOT be changed. Note that this flag, in combination with the <Admitted Hops> flag, are used to locate the last node that successfully processed a reservation request (see Section 4.6.1.2). <B>: 1 bit. When set to "1", it indicates a bidirectional reservation. <Time Lag>: It represents the ratio between the "T_Lag" parameter, which is the time difference between the departure time of the last sent "PHR_Refresh_Update" control information container and the departure time of the "PHR_Release_Request" control information container, and the length of the refresh period, "T_period", see Section 4.6.1.5. <K>: 1 bit. When set to "1", it indicates that the resources/bandwidth carried by a tearing RESERVE MUST NOT be released, and the resources/bandwidth carried by a non-tearing RESERVE MUST NOT be reserved/refreshed. For more details, see Section 4.6.1.5.2. <Max Admitted Hops>: 8 bits. The <Admitted Hops> value that has been carried by the <PHR container> field used to identify the RMD reservation-based node that admitted or processed a "PHR_Resource_Request". <SCH>: 3 bits. The <SCH> value that is used to specify which of the 6 RMD-QOSM scenarios (see Section 3.2.3) MUST be used within the RMD domain. The operator of an RMD domain MUST preconfigure all the QNE Edge nodes within one domain such that the <SCH> field included in the "PHR container", will always use the same value, such that within one RMD domain only one of the below described RMD-QOSM schemes can be used at a time. All the QNE Interior nodes MUST interpret this field before processing any other PHR container payload fields. The currently defined <SCH> values are: o 0: RMD-QOSM scheme MUST be "per-flow congestion notification based on probing"; o 1: RMD-QOSM scheme MUST be "per-flow RMD NSIS measurement- based admission control", o 2: RMD-QOSM scheme MUST be "per-flow RMD reservation-based" in combination with the "severe congestion handling by the RMD-QOSM refresh" procedure; o 3 : RMD-QOSM scheme MUST be "per-flow RMD reservation-based" in combination with the "severe congestion handling by proportional data packet marking" procedure;
o 4: RMD-QOSM scheme MUST be "per-aggregate RMD reservation-
based" in combination with the "severe congestion handling
by the RMD-QOSM refresh" procedure;
o 5: RMD-QOSM scheme MUST be "per-aggregate RMD reservation-
based" in combination with the "severe congestion handling
by proportional data packet marking" procedure;
o 6 - 7: reserved.
The default value of the <SCH> field MUST be set to the value equal
to 3.
4.1.3. PDR Container
This section describes the parameters of the PDR container, which are
used by the RMD-QOSM functionality available at the Edge nodes.
The bit format of the PDR container can be seen in Figure 7.
<PDR container> = <O> <S> <M>
<Max Admitted Hops> <B> <SCH> [<PDR Bandwidth>]
In Figure 7, note that <Max Admitted Hops> is represented as <Max Adm
Hops>.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|E|N|r| Parameter ID |r|r|r|r| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|M| Max Adm Hops |B|O| SCH | EMPTY |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PDR Bandwidth(32-bit IEEE floating point.number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: PDR container
Parameter ID: 12-bit field identifying the type of <PDR container>
field.
"PDR_Reservation_Request" (Parameter ID = 20): generated by the
QNE(Ingress) node in order to initiate or update the QoS-NSLP per-
domain reservation state in the QNE(Egress) node.
"PDR_Refresh_Request" (Parameter ID = 21): generated by the QNE(Ingress) node and sent to the QNE(Egress) node to refresh, in case needed, the QoS-NSLP per-domain reservation states located in the QNE(Egress) node. "PDR_Release_Request" (Parameter ID = 22): generated and sent by the QNE(Ingress) node to the QNE(Egress) node to release the per-domain reservation states explicitly. "PDR_Reservation_Report" (Parameter ID = 23): generated and sent by the QNE(Egress) node to the QNE(Ingress) node to report that a "PHR_Resource_Request" and a "PDR_Reservation_Request" traffic handling directive field have been received and that the request has been admitted or rejected. "PDR_Refresh_Report" (Parameter ID = 24) generated and sent by the QNE(Egress) node in case needed, to the QNE(Ingress) node to report that a "PHR_Refresh_Update" traffic handling directive field has been received and has been processed. "PDR_Release_Report" (Parameter ID = 25) generated and sent by the QNE(Egress) node in case needed, to the QNE(Ingress) node to report that a "PHR_Release_Request" and a "PDR_Release_Request" traffic handling directive field have been received and have been processed. "PDR_Congestion_Report" (Parameter ID = 26): generated and sent by the QNE(Egress) node to the QNE(Ingress) node and used for congestion notification. <S> (PDR Severe Congestion): 1 bit. Specifies if a severe congestion situation occurred. It can also carry the <S> parameter of the <PHR_Resource_Request> or <PHR_Refresh_Update> fields. <O> (Overload): 1 bit. This field is used during the severe congestion handling scheme that is using the RMD-QOSM refresh procedure. This bit is set when an overload on a QNE Interior node is detected and when this field is carried by the "PDR_Congestion_Report" container. <O> SHOULD be set to "1" if the <S> bit is set. For more details, see Section 4.6.1.6.1. <M> (PDR Marked): 1 bit. Carries the <M> value of the "PHR_Resource_Request" or "PHR_Refresh_Update" traffic handling directive field. <B>: 1 bit. Indicates bidirectional reservation.
<Max Admitted Hops>: 8 bits. The <Admitted Hops> value that has been carried by the <PHR container> field used to identify the RMD reservation-based node that admitted or processed a "PHR_Resource_Request". <PDR Bandwidth>: 32 bits. This field specifies the bandwidth that either applies when the <B> flag is set to "1" and when this parameter is carried by a RESPONSE message or when a severe congestion occurs and the QNE Edges maintain an aggregated intra- domain QoS-NSLP operational state and it is carried by a NOTIFY message. In the situation that the <B> flag is set to "1", this parameter specifies the requested bandwidth that has to be reserved by a node in the reverse direction and when the intra-domain signaling procedures require a bidirectional reservation procedure. In the severe congestion situation, this parameter specifies the bandwidth that has to be released. <SCH>: 3 bits. The <SCH> value that is used to specify which of the 6 RMD scenarios (see Section 3.2.3) MUST be used within the RMD domain. The operator of an RMD domain MUST preconfigure all the QNE Edge nodes within one domain such that the <SCH> field included in the "PDR container", will always use the same value, such that within one RMD domain only one of the below described RMD-QOSM schemes can be used at a time. All the QNE Interior nodes MUST interpret this field before processing any other <PDR container> payload fields. The currently defined <SCH> values are: o 0: RMD-QOSM scheme MUST be "per-flow congestion notification based on probing"; o 1: RMD-QOSM scheme MUST be "per-flow RMD NSIS measurement- based admission control"; o 2: RMD-QOSM scheme MUST be "per-flow RMD reservation-based" in combination with the "severe congestion handling by the RMD-QOSM refresh" procedure; o 3 : RMD-QOSM scheme MUST be "per-flow RMD reservation-based" in combination with the "severe congestion handling by proportional data packet marking" procedure; o 4: RMD-QOSM scheme MUST be "per-aggregate RMD reservation- based" in combination with the "severe congestion handling by the RMD-QOSM refresh" procedure; o 5: RMD-QOSM scheme MUST be "per-aggregate RMD reservation- based" in combination with the "severe congestion handling by proportional data packet marking" procedure;
o 6 - 7: reserved. The default value of the <SCH> field MUST be set to the value equal to 3.
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