RFC 5975
QSPEC Template for the Quality-of-Service NSIS Signaling Layer Protocol (NSLP)
Pages: 64
Experimental
Experimental
Part 2 of 4 – Pages 7 to 33
3. QSPEC Framework
The overall framework for the QoS NSLP is that [RFC5974] defines QoS signaling and semantics, the QSPEC template defines the container and semantics for QoS parameters and objects, and informational specifications define QoS methods and procedures for using QoS signaling and QSPEC parameters/objects within specific QoS deployments. QoS NSLP is a generic QoS signaling protocol that can signal for many QOSMs.3.1. QoS Models
A QOSM is a method to achieve QoS for a traffic flow, e.g., IntServ Controlled Load [CL-QOSM], Resource Management with Diffserv [RFC5977], and QoS signaling for Y.1541 QoS classes [RFC5976]. A QOSM specifies a set of QSPEC parameters that describe the QoS desired and how resources will be managed by the RMF. The RMF implements functions that are related to resource management and processes the QSPEC parameters. QOSMs affect the operation of the RMF in NSIS-capable nodes and the information carried in QSPEC objects. Under some circumstances (e.g., aggregation), they may cause a separate NSLP session to be instantiated by having the RMF as a QNI. QOSM specifications may define RMF triggers that cause the QoS NSLP to run semantics within the underlying QoS NSLP signaling state and messaging processing rules, as defined in Section 5.2 of [RFC5974]. New QoS NSLP message processing rules can only be defined in extensions to QoS NSLP. If a QOSM specification defines triggers that deviate from existing QoS NSLP processing rules, the fallback for QNEs not supporting that QOSM are the QoS NSLP state transition/message processing rules. The QOSM specification includes how the requested QoS resources will be described and how they will be managed by the RMF. For this purpose, the QOSM specification defines a set of QSPEC parameters it uses to describe the desired QoS and resource control in the RMF, and it may define additional QSPEC parameters.
When a QoS NSLP message travels through different domains, it may
encounter different QOSMs. Since QOSMs use different QSPEC
parameters for describing resources, the QSPEC parameters included by
the QNI may not be understood in other domains. The QNI therefore
can flag those QSPEC parameters it considers vital with the M flag.
QSPEC parameters with the M flag set must be interpreted by the
downstream QNEs, or the reservation fails. QSPEC parameters without
the M flag set should be interpreted by the downstream QNEs, but may
be ignored if not understood.
A QOSM specification SHOULD include the following:
- role of QNEs, e.g., location, frequency, statefulness, etc.
- QSPEC definition including QSPEC parameters
- QSPEC procedures applicable to this QOSM
- QNE processing rules describing how QSPEC information is treated
and interpreted in the RMF, e.g., admission control, scheduling,
policy control, QoS parameter accumulation (e.g., delay)
- at least one bit-level QSPEC example
- QSPEC parameter behavior for new QSPEC parameters that the QOSM
specification defines
- a definition of what happens in case of preemption if the default
QNI behavior (teardown preempted reservation) is not followed (see
Section 4.3.5)
A QOSM specification MAY include the following:
- definitions of additional QOSM-specific error codes, as discussed
in Section 4.2.3
- the QoS-NSLP options a QOSM wants to use, when several options are
available for a QOSM (e.g., Local QSPEC to either a) hide the
Initiator QSPEC within a local domain message, or b) encapsulate
the Initiator QSPEC).
QOSMs are free, subject to IANA registration and review rules, to
extend QSPECs by adding parameters of any of the kinds supported by
the QSPEC. This includes traffic description parameters, constraint
parameters, and traffic handling directives. QOSMs are not
permitted, however, to reinterpret or redefine the QSPEC parameters
specified in this document. Note that signaling functionality is
only defined by the QoS NSLP document [RFC5974] and not by this
document or by QOSM specification documents.
3.2. QSPEC Objects
The QSPEC is the object of QoS NSLP containing QSPEC objects and parameters. QSPEC objects are the main building blocks of the QSPEC parameter set that is input or output of an RMF operation. QSPEC parameters are the parameters appearing in a QSPEC, which must include the traffic model parameter (TMOD), and may optionally include constraints (e.g., path latency), traffic handling directives (e.g., excess treatment), and traffic classifiers (e.g., PHB class). The RMF implements functions that are related to resource management and processes the QSPEC parameters. The QSPEC consists of a QSPEC version number and QSPEC objects. IANA assigns a new QSPEC version number when the current version is deprecated or deleted (as required by a specification). Note that a new QSPEC version number is not needed when new QSPEC parameters are specified. Later QSPEC versions MUST be backward compatible with earlier QSPEC versions. That is, a version n+1 device must support QSPEC version n (or earlier). On the other hand, if a QSPEC version n (or earlier) device receives an NSLP message specifying QSPEC version n+1, then the version n device responds with an 'Incompatible QSPEC' error code (0x0f) response, as discussed in Section 4.2.3, allowing the QNE that sent the NSLP message to retry with a lower QSPEC version. This document provides a template for the QSPEC in order to promote interoperability between QOSMs. Figure 1 illustrates how the QSPEC is composed of up to 4 QSPEC objects, namely QoS Desired, QoS Available, QoS Reserved, and Minimum QoS. Each of these QSPEC objects consists of a number of QSPEC parameters. A given QSPEC may contain only a subset of the QSPEC objects, e.g., QoS Desired. The QSPEC objects QoS Desired, QoS Available, QoS Reserved and Minimum QoS MUST all be supported by QNEs and MAY appear in any QSPEC object carried in any QoS NSLP message (RESERVE, QUERY, RESPONSE, NOTIFY). See [RFC5974] for descriptions of the QoS NSLP RESERVE, QUERY, RESPONSE, and NOTIFY messages.
+---------------------------------------+ | QSPEC Objects | +---------------------------------------+ \________________ ______________________/ V +----------+----------+---------+-------+ |QoS Desir.|QoS Avail.|QoS Rsrv.|Min QoS| +----------+----------+---------+-------+ \____ ____/\___ _____/\___ ____/\__ ___/ V V V V +-------------+... +-------------+... |QSPEC Para. 1| |QSPEC Para. n| +-------------+... +-------------+... Figure 1: Structure of the QSPEC Use of the 4 QSPEC objects (QoS Desired, QoS Available, QoS Reserved, and Minimum QoS) is described in Section 4.3 for 3 message sequences and 7 object combinations. The QoS Desired Object describe the resources the QNI desires to reserve, and hence this is a read-only QSPEC object in that the QSPEC parameters carried in the object may not be overwritten. QoS Desired is always included in a RESERVE message and sometimes included in the QUERY message (see Section 4.3 for details). As described in Section 4.3, the QoS Available object may travel in a RESERVE message, RESPONSE Message, or QUERY message and may collect information on the resources currently available on the path. In this case, QoS Available is a read-write object, which means the QSPEC parameters contained in QoS Available may be updated, but they cannot be deleted. As such, each QNE MUST inspect all parameters of this QSPEC object, and if resources available to this QNE are less than what a particular parameter says currently, the QNE MUST adapt this parameter accordingly. Hence, when the message arrives at the recipient of the message, <QoS Available> reflects the bottleneck of the resources currently available on a path. It can be used in a QUERY message, for example, to collect the available resources along a data path. When QoS Available travels in a RESPONSE message, it in fact just transports the result of a previous measurement performed by a RESERVE or QUERY message back to the initiator. Therefore, in this
case, QoS Available is read-only. In one other instance described in Section 4.3.2 (Case 3), QoS Available is sent by the QNI in a RESERVE message as a read-only QSPEC object (see Section 4.3.2 for details). The QoS Reserved object reflects the resources that are being reserved. It is a read-only object and is always included in a RESPONSE message if QoS Desired is included in the RESERVE message (see Section 4.3 for details). Minimum QoS does not have an equivalent in RSVP. It allows the QNI to define a range of acceptable QoS levels by including both the desired QoS value and the minimum acceptable QoS in the same message. Note that the term "minimum" is used generically, since for some parameters, such as loss rate and latency, what is specified is the maximum acceptable value. It is a read-only object, and may be included in a RESERVE message, RESPONSE message, or QUERY message (see Section 4.3 for details). The desired QoS is included with a QoS Desired and/or a QoS Available QSPEC object seeded to the desired QoS value. The minimum acceptable QoS value MAY be coded in the Minimum QoS QSPEC object. As the message travels towards the QNR, QoS Available is updated by QNEs on the path. If its value drops below the value of Minimum QoS, the reservation fails and is aborted. When this method is employed, the QNR signals back to the QNI the value of QoS Available attained in the end, because the reservation may need to be adapted accordingly (see Section 4.3 for details). Note that the relationship of QSPEC objects to RSVP objects is covered in Appendix A.3.3. QSPEC Parameters
QSPEC parameters provide a common language for building QSPEC objects. This document defines a number of QSPEC parameters; additional parameters may be defined in separate QOSM specification documents. For example, QSPEC parameters are defined in [RFC5976] and [RFC5977]. One QSPEC parameter, <TMOD>, is special. It provides a description of the traffic for which resources are reserved. This parameter must be included by the QNI, and it must be interpreted by all QNEs. All other QSPEC parameters are populated by a QNI if they are applicable to the underlying QoS desired. For these QSPEC parameters, the QNI sets the M flag if they must be interpreted by downstream QNEs. If QNEs cannot interpret the parameter, the reservation fails. QSPEC parameters populated by a QNI without the M flag set should be interpreted by downstream QNEs, but may be ignored if not understood.
In this document, the term 'interpret' means, in relation to RMF processing of QSPEC parameters, that the RMF processes the QSPEC parameter according to the commonly accepted normative procedures specified by references given for each QSPEC parameter. Note that a QNE need only interpret a QSPEC parameter if it is populated in the QSPEC object by the QNI; if not populated in the QSPEC, the QNE does not interpret it of course. Note that when an ingress QNE in a local domain defines a Local QSPEC and encapsulates the Initiator QSPEC, the QNEs in the interior local domain need only process the Local QSPEC and can ignore the Initiator (encapsulated) QSPEC. However, edge QNEs in the local domain indeed must interpret the QSPEC parameters populated in the Initiator QSPEC with the M flag set and should interpret QSPEC parameters populated in the Initiator QSPEC without the M flag set. As described in the previous section, QoS parameters may be overwritten depending on which QSPEC object and which message they appear in.3.3.1. Traffic Model Parameter
The <Traffic Model> (TMOD) parameter is mandatory for the QNI to include in the Initiator QSPEC and mandatory for downstream QNEs to interpret. The traffic description specified by the TMOD parameter is a container consisting of 5 sub-parameters [RFC2212]: o rate (r) specified in octets per second o bucket size (b) specified in octets o peak rate (p) specified in octets per second o minimum policed unit (m) specified in octets o maximum packet size (MPS) specified in octets The TMOD parameter takes the form of a token bucket of rate (r) and bucket size (b), plus a peak rate (p), minimum policed unit (m), and maximum packet size (MPS). Both b and r MUST be positive. The rate, r, is measured in octets of IP packets per second, and can range from 1 octet per second to as large as 40 teraoctets per second. The bucket depth, b, is also measured in octets and can range from 1 octet to 250 gigaoctets. The peak rate, p, is measured in octets of IP packets per second and has the same range and suggested representation as the bucket rate. The peak rate is the maximum rate at which the source and any reshaping (defined below) may inject bursts of traffic into the network. More precisely, it is a requirement that for all time periods the amount of data sent cannot exceed MPS+pT, where MPS is
the maximum packet size and T is the length of the time period. Furthermore, p MUST be greater than or equal to the token bucket rate, r. If the peak rate is unknown or unspecified, then p MUST be set to infinity. The minimum policed unit, m, is an integer measured in octets. All IP packets less than size m will be counted, when policed and tested for conformance to the TMOD, as being of size m. The maximum packet size, MPS, is the biggest packet that will conform to the traffic specification; it is also measured in octets. The flow MUST be rejected if the requested maximum packet size is larger than the MTU of the link. Both m and MPS MUST be positive, and m MUST be less than or equal to MPS. Policing compares arriving traffic against the TMOD parameters at the edge of the network. Traffic is policed to ensure it conforms to the token bucket. Reshaping attempts to restore the (possibly distorted) traffic's shape to conform to the TMOD parameters, and traffic that is in violation of the TMOD is discovered because the reshaping fails and the reshaping buffer overflows. The token bucket and peak rate parameters require that traffic MUST obey the rule that over all time periods, the amount of data sent cannot exceed MPS+min[pT, rT+b-MPS], where r and b are the token bucket parameters, MPS is the maximum packet size, and T is the length of the time period (note that when p is infinite, this reduces to the standard token bucket requirement). For the purposes of this accounting, links MUST count packets that are smaller than the minimum policing unit as being of size m. Packets that arrive at an element and cause a violation of the MPS + min[pT, rT+b-MPS] bound are considered non-conformant. All 5 of the sub-parameters MUST be included in the TMOD parameter. The TMOD parameter can be set to describe the traffic source. If, for example, TMOD is set to specify bandwidth only, then set r = peak rate = p, b = large, and m = large. As another example, if TMOD is set for TCP traffic, then set r = average rate, b = large, and p = large. When the 5 TMOD sub-parameters are included in QoS Available, they provide information, for example, about the TMOD resources available along the path followed by a data flow. The value of TMOD at a QNE is an estimate of the TMOD resources the QNE has available for packets following the path up to the next QNE, including its outgoing link, if this link exists. Furthermore, the QNI MUST account for the resources of the ingress link, if this link exists. Computation of
the value of this parameter SHOULD take into account all information available to the QNE about the path, taking into consideration administrative and policy controls, as well as physical resources. The output composed value is the minimum of the QNE's value and the input composed value for r, b, p, and MPS, and the maximum of the QNE's value and the input composed value for m. This quantity, when composed end-to-end, informs the QNR (or QNI in a RESPONSE message) of the minimal TMOD resources along the path from QNI to QNR. Two TMOD parameters are defined in Section 5, <TMOD-1> and <TMOD-2>, where the second parameter (<TMOD-2>) is specified as could be needed to support some Diffserv applications. For example, it is typically assumed that Diffserv Expedited Forwarding (EF) traffic is shaped at the ingress by a single rate token bucket. Therefore, a single TMOD parameter is sufficient to signal Diffserv EF traffic. However, for Diffserv Assured Forwarding (AF) traffic, two sets of token bucket parameters are needed -- one for the average traffic and one for the burst traffic. [RFC2697] defines a Single Rate Three Color Marker (srTCM), which meters a traffic stream and marks its packets according to three traffic parameters, Committed Information Rate (CIR), Committed Burst Size (CBS), and Excess Burst Size (EBS), to be either green, yellow, or red. A packet is marked green if it does not exceed the CBS; yellow if it does exceed the CBS, but not the EBS; and red otherwise. [RFC2697] defines specific procedures using two token buckets that run at the same rate. Therefore, 2 TMOD parameters are sufficient to distinguish among 3 levels of drop precedence. An example is also described in the Appendix to [RFC2597].3.3.2. Constraints Parameters
<Path Latency>, <Path Jitter>, <Path PLR>, and <Path PER> are QSPEC parameters describing the desired path latency, path jitter, packet loss ratio, and path packet error ratio, respectively. Since these parameters are cumulative, an individual QNE cannot decide whether the desired path latency, etc., is available, and hence they cannot decide whether a reservation fails. Rather, when these parameters are included in <Desired QoS>, the QNI SHOULD also include corresponding parameters in a QoS Available QSPEC object in order to facilitate collecting this information. The <Path Latency> parameter accumulates the latency of the packet forwarding process associated with each QNE, where the latency is defined to be the mean packet delay, measured in microseconds, added by each QNE. This delay results from the combination of link propagation delay, packet processing, and queuing. Each QNE MUST add the propagation delay of its outgoing link, if this link exists.
Furthermore, the QNI SHOULD add the propagation delay of the ingress link, if this link exists. The composition rule for the <Path Latency> parameter is summation with a clamp of (2^32) - 1 on the maximum value. This quantity, when composed end-to-end, informs the QNR (or QNI in a RESPONSE message) of the minimal packet delay along the path from QNI to QNR. The purpose of this parameter is to provide a minimum path latency for use with services that provide estimates or bounds on additional path delay [RFC2212]. The <Path Jitter> parameter accumulates the jitter of the packet forwarding process associated with each QNE, where the jitter is defined to be the nominal jitter, measured in microseconds, added by each QNE. IP packet jitter, or delay variation, is defined in [RFC3393], Section 3.4 (Type-P-One-way-ipdv), and where the [RFC3393] selection function includes the packet with minimum delay such that the distribution is equivalent to 2-point delay variation in [Y.1540]. The suggested evaluation interval is 1 minute. This jitter results from packet-processing limitations, and includes any variable queuing delay that may be present. Each QNE MUST add the jitter of its outgoing link, if this link exists. Furthermore, the QNI SHOULD add the jitter of the ingress link, if this link exists. The composition method for the <Path Jitter> parameter is the combination of several statistics describing the delay variation distribution with a clamp on the maximum value (note that the methods of accumulation and estimation of nominal QNE jitter are specified in clause 8 of [Y.1541]). This quantity, when composed end-to-end, informs the QNR (or QNI in a RESPONSE message) of the nominal packet jitter along the path from QNI to QNR. The purpose of this parameter is to provide a nominal path jitter for use with services that provide estimates or bounds on additional path delay [RFC2212]. The <Path PLR> parameter is the unit-less ratio of total lost IP packets to total transmitted IP packets. <Path PLR> accumulates the packet loss ratio (PLR) of the packet-forwarding process associated with each QNE, where the PLR is defined to be the PLR added by each QNE. Each QNE MUST add the PLR of its outgoing link, if this link exists. Furthermore, the QNI MUST add the PLR of the ingress link, if this link exists. The composition rule for the <Path PLR> parameter is summation with a clamp on the maximum value. (This assumes sufficiently low PLR values such that summation error is not significant; however, a more accurate composition function is specified in clause 8 of [Y.1541].) This quantity, when composed end-to-end, informs the QNR (or QNI in a RESPONSE message) of the minimal packet PLR along the path from QNI to QNR. Packet error ratio [Y.1540, Y.1541] is the unit-less ratio of total errored IP packet outcomes to the total of successful IP packet transfer outcomes plus errored IP packet outcomes in a population of
interest, with a resolution of at least 10^-9. If lesser resolution is available in a value, the unused digits MUST be set to zero. Note that the number of errored packets observed is directly related to the confidence in the result. The <Path PER> parameter accumulates the packet error ratio (PER) of the packet forwarding process associated with each QNE, where the PER is defined to be the PER added by each QNE. Each QNE MUST add the PER of its outgoing link, if this link exists. Furthermore, the QNI SHOULD add the PER of the ingress link, if this link exists. The composition rule for the <Path PER> parameter is summation with a clamp on the maximum value. (This assumes sufficiently low PER values such that summation error is not significant; however, a more accurate composition function is specified in clause 8 of [Y.1541].) This quantity, when composed end-to-end, informs the QNR (or QNI in a RESPONSE message) of the minimal packet PER along the path from QNI to QNR. The slack term parameter is the difference between desired delay and delay obtained by using bandwidth reservation, and it is used to reduce the resource reservation for a flow [RFC2212].3.3.3. Traffic-Handling Directives
An application MAY like to reserve resources for packets and also specify a specific traffic-handling behavior, such as <Excess Treatment>. In addition, as discussed in Section 3.1, an application MAY like to define RMF triggers that cause the QoS NSLP to run semantics within the underlying QoS NSLP signaling state / messaging processing rules, as defined in Section 5.2 of [RFC5974]. Note, however, that new QoS NSLP message processing rules can only be defined in extensions to the QoS NSLP. As with constraints parameters and other QSPEC parameters, Traffic Handling Directives parameters may be defined in QOSM specifications in order to provide support for QOSM-specific resource management functions. Such QOSM- specific parameters are already defined, for example, in [RFC5976], [RFC5977], and [CL-QOSM]. Generally, a Traffic Handling Directives parameters is expected to be set by the QNI in <QoS Desired>, and to not be included in <QoS Available>. If such a parameter is included in <QoS Available>, QNEs may change their value. The <Preemption Priority> parameter is the priority of the new flow compared with the <Defending Priority> of previously admitted flows. Once a flow is admitted, the preemption priority becomes irrelevant. The <Defending Priority> parameter is used to compare with the preemption priority of new flows. For any specific flow, its preemption priority MUST always be less than or equal to the defending priority. <Admission Priority> and <RPH Priority> provide an essential way to differentiate flows for emergency services, Emergency Telecommunications Service (ETS), E911, etc., and assign
them a higher admission priority than normal priority flows and best- effort priority flows. The <Excess Treatment> parameter describes how the QNE will process out-of-profile traffic. Excess traffic MAY be dropped, shaped, and/or re-marked.3.3.4. Traffic Classifiers
An application MAY like to reserve resources for packets with a particular Diffserv per-hop behavior (PHB) [RFC2475]. Note that PHB class is normally set by a downstream QNE to tell the QNI how to mark traffic to ensure the treatment that is designated by admission control; however, setting of the parameter by the QNI is not precluded. An application MAY like to reserve resources for packets with a particular QoS class, e.g., Y.1541 QoS class [Y.1541] or Diffserv-aware MPLS traffic engineering (DSTE) class type [RFC3564, RFC4124]. These parameters are useful in various QOSMs, e.g., [RFC5976], [RFC5977], and other QOSMs yet to be defined (e.g., DSTE- QOSM). This is intended to provide guidelines to QOSMs on how to encode these parameters; use of the PHB class parameter is illustrated in the example in the following section.3.4. Example of QSPEC Processing
This section illustrates the operation and use of the QSPEC within the NSLP. The example configuration in shown in Figure 2. +----------+ /-------\ /--------\ /--------\ | Laptop | | Home | | Cable | | Diffserv | | Computer |-----| Network |-----| Network |-----| Network |----+ +----------+ | No QOSM | |DQOS QOSM | | RMD QOSM | | \-------/ \--------/ \--------/ | | +-----------------------------------------------+ | | /--------\ +----------+ | | XG | | Handheld | +---| Wireless |-----| Device | | XG QOSM | +----------+ \--------/ Figure 2: Example Configuration of QoS-NSLP/QSPEC Operation In this configuration, a laptop computer and a handheld wireless device are the endpoints for some application that has QoS requirements. Assume initially that the two endpoints are stationary during the application session, later we consider mobile endpoints.
For this session, the laptop computer is connected to a home network that has no QoS support. The home network is connected to a CableLabs-type cable access network with dynamic QoS (DQOS) support, such as specified in the [DQOS] for cable access networks. That network is connected to a Diffserv core network that uses the Resource Management in Diffserv QoS Model [RFC5977]. On the other side of the Diffserv core is a wireless access network built on generation "X" technology with QoS support as defined by generation "X". And finally, the handheld endpoint is connected to the wireless access network. We assume that the laptop is the QNI, and the handheld device is the QNR. The QNI will signal an Initiator QSPEC object to achieve the QoS desired on the path. The QNI sets QoS Desired, QoS Available, and possibly Minimum QoS QSPEC objects in the Initiator QSPEC, and initializes QoS Available to QoS Desired. Each QNE on the path reads and interprets those parameters in the Initiator QSPEC and checks to see if QoS Available resources can be reserved. If not, the QNE reduces the respective parameter values in QoS Available and reserves these values. The minimum parameter values are given in Minimum QoS, if populated; they are zero if Minimum QoS is not included. If one or more parameters in QoS Available fails to satisfy the corresponding minimum values in Minimum QoS, the QNE generates a RESPONSE message to the QNI and the reservation is aborted. Otherwise, the QNR generates a RESPONSE to the QNI with the QoS Available for the reservation. If a QNE cannot reserve QoS Desired resources, the reservation fails. The QNI populates QSPEC parameters to ensure correct treatment of its traffic in domains down the path. Let us assume the QNI wants to achieve QoS guarantees similar to IntServ Controlled Load service, and also is interested in what path latency it can achieve. Additionally, to ensure correct treatment further down the path, the QNI includes <PHB Class> in <QoS Desired>. The QNI therefore includes in the QSPEC QoS Desired = <TMOD> <PHB Class> QoS Available = <TMOD> <Path Latency> Since <Path Latency> and <PHB Class> are not vital parameters from the QNI's perspective, it does not raise their M flags. There are three possibilities when a RESERVE message is received at a QNE at a domain border; they are described in the example: - the QNE just leaves the QSPEC as is.
- the QNE can add a Local QSPEC and encapsulate the Initiator QSPEC
(see discussion in Section 4.1; this is new in QoS NSLP -- RSVP
does not do this).
- the QNE can 'hide' the initiator RESERVE message so that only the
edge QNE processes the initiator RESERVE message, which then
bypasses intermediate nodes between the edges of the domain and
issues its own local RESERVE message (see Section 3.3.1 of
[RFC5974]). For this new local RESERVE message, the QNE acts as
the QNI, and the QSPEC in the domain is an Initiator QSPEC. A
similar procedure is also used by RSVP in making aggregate
reservations, in which case there is not a new intra-domain
(aggregate) RESERVE for each newly arriving inter-domain (per-flow)
RESERVE, but the aggregate reservation is updated by the border QNE
(or QNI) as need be. This is also how RMD works [RFC5977].
For example, at the RMD domain, a local RESERVE with its own RMD
Initiator QSPEC corresponding to the RMD-QOSM is generated based on
the original Initiator QSPEC according to the procedures described in
Section 4.5 of [RFC5974] and in [RFC5977]. The ingress QNE to the
RMD domain maps the TMOD parameters contained in the original
Initiator QSPEC to the equivalent TMOD parameter representing only
the peak bandwidth in the Local QSPEC. The local RMD QSPEC for
example also needs <PHB Class>, which in this case was provided by
the QNI.
Furthermore, if the node can, at the egress to the RMD domain, it
updates QoS Available on behalf of the entire RMD domain. If it
cannot (since the M flag is not set for <Path Latency>), it raises
the parameter-specific, Not Supported N flag, warning the QNR that
the final latency value in QoS Available is imprecise.
In the XG domain, the Initiator QSPEC is translated into a local
QSPEC using a similar procedure as described above. The Local QSPEC
becomes the current QSPEC used within the XG domain, and the
Initiator QSPEC is encapsulated. This saves the QNEs within the XG
domain the trouble of re-translating the Initiator QSPEC, and
simplifies processing in the local domain. At the egress edge of the
XG domain, the translated Local QSPEC is removed, and the Initiator
QSPEC returns to the number one position.
If the reservation was successful, eventually the RESERVE request
arrives at the QNR (otherwise, the QNE at which the reservation
failed aborts the RESERVE and sends an error RESPONSE back to the
QNI). If the RII was included in the QoS NSLP message, the QNR
generates a positive RESPONSE with QSPEC objects QoS Reserved and QoS
Available. The parameters appearing in QoS Reserved are the same as
in QoS Desired, with values copied from QoS Available. Hence, the
QNR includes the following QSPEC objects in the RESPONSE:
QoS Reserved = <TMOD> <PHB Class>
QoS Available = <TMOD> <Path Latency>
If the handheld device on the right of Figure 2 is mobile, and moves
through different XG wireless networks, then the QoS might change on
the path since different XG wireless networks might support different
QOSMs. As a result, QoS NSLP/QSPEC processing will have to
renegotiate the QoS Available on the path. From a QSPEC perspective,
this is like a new reservation on the new section of the path and is
basically the same as any other rerouting event -- to the QNEs on the
new path, it looks like a new reservation. That is, in this mobile
scenario, the new segment may support a different QOSM than the old
segment, and the QNI would now signal a new reservation explicitly
(or implicitly with the next refreshing RESERVE message) to account
for the different QOSM in the XG wireless domain. Further details on
rerouting are specified in [RFC5974].
For bit-level examples of QSPECs, see the documents specifying QOSMs:
[CL-QOSM], [RFC5976], and [RFC5977].
4. QSPEC Processing and Procedures
Three flags are used in QSPEC processing, the M flag, E flag, and N
flag, which are explained in this section. The QNI sets the M flag
for each QSPEC parameter it populates that MUST be interpreted by
downstream QNEs. If a QNE does not support the parameter, it sets
the N flag and fails the reservation. If the QNE supports the
parameter but cannot meet the resources requested by the parameter,
it sets the E flag and fails the reservation.
If the M flag is not set, the downstream QNE SHOULD interpret the
parameter. If the QNE does not support the parameter, it sets the N
flag and forwards the reservation. If the QNE supports the parameter
but cannot meet the resources requested by the parameter, it sets the
E flag and fails the reservation.
4.1. Local QSPEC Definition and Processing
A QNE at the edge of a local domain may either a) translate the
Initiator QSPEC into a Local QSPEC and encapsulate the Initiator
QSPEC in the RESERVE message, or b) 'hide' the Initiator QSPEC
through the local domain and reserve resources by generating a new
RESERVE message through the local domain containing the Local QSPEC. In either case, the Initiator QSPEC parameters are interpreted at the local domain edges. A Local QSPEC may allow a simpler control plane in a local domain. The edge nodes in the local domain must interpret the Initiator QSPEC parameters. They can either initiate a parallel session with Local QSPEC or define a Local QSPEC and encapsulate the Initiator QSPEC, as illustrated in Figure 3. The Initiator/Local QSPEC bit identifies whether the QSPEC is an Initiator QSPEC or a Local QSPEC. The QSPEC Type indicates, for example, that the initiator of the local QSPEC uses to a certain QOSM, e.g., CL-QSPEC Type. It may be useful for the QNI to signal a QSPEC Type based on some QOSM (which will necessarily entail populating certain QOSM-related parameters) so that a downstream QNE can chose amongst various QOSM-related processes it might have. That is, the QNI populates the QSPEC Type, e.g., CL-QSPEC Type and sets the Initiator/Local QSPEC bit to 'Initiator'. A local QNE can decide, for whatever reasons, to insert a Local QSPEC Type, e.g., RMD-QSPEC Type, and set the local QSPEC Type = RMD-QSPEC and set the Initiator/Local QSPEC bit to 'Local' (and encapsulate the Initiator QSPEC in the RESERVE or whatever NSLP message). +--------------------------------+\ | QSPEC Type, QSPEC Procedure | \ +--------------------------------+ / Common QSPEC Header | Init./Local QSPEC bit=Local |/ +================================+\ | Local-QSPEC Parameter 1 | \ +--------------------------------+ \ | .... | Local-QSPEC Parameters +--------------------------------+ / | Local-QSPEC Parameter n | / +--------------------------------+/ | +----------------------------+ | | | QSPEC Type, QSPEC Procedure| | | +----------------------------+ | | | Init./Local QSPEC bit=Init.| | | +============================+ | | | | | Encapsulated Initiator QSPEC | | .... | | | +----------------------------+ | +--------------------------------+ Figure 3: Defining a Local QSPEC
Here the QoS-NSLP only sees and passes one QSPEC up to the RMF.
Thus, the type of the QSPEC may change within a local domain. Hence:
o the QNI signals its QoS requirements with the Initiator QSPEC,
o the ingress edge QNE in the local domain translates the Initiator
QSPEC parameters to equivalent parameters in the local QSPEC,
o the QNEs in the local domain only interpret the Local QSPEC
parameters, and
o the egress QNE in the local domain processes the Local QSPEC and
also interprets the QSPEC parameters in the Initiator QSPEC.
The Local QSPEC MUST be consistent with the Initiator QSPEC. That
is, it MUST NOT specify a lower level of resources than specified by
the Initiator QSPEC. For example, in RMD the TMOD parameters
contained in the original Initiator QSPEC are mapped to the
equivalent TMOD parameter representing only the peak bandwidth in the
Local QSPEC.
Note that it is possible to use both a) hiding a QSPEC through a
local domain by initiating a new RESERVE at the domain edge, and b)
defining a Local QSPEC and encapsulating the Initiator QSPEC, as
defined above. However, it is not expected that both the hiding and
encapsulating functions would be used at the same time for the same
flow.
The support of Local QSPECs is illustrated in Figure 4 for a single
flow to show where the Initiator and Local QSPECs are used. The QNI
initiates an end-to-end, inter-domain QoS NSLP RESERVE message
containing the Initiator QSPEC for the Y.1541 QOSM. As illustrated
in Figure 4, the RESERVE message crosses multiple domains supporting
different QOSMs. In this illustration, the Initiator QSPEC arrives
in a QoS NSLP RESERVE message at the ingress node of the local-QOSM
domain. At the ingress edge node of the local-QOSM domain, the end-
to-end, inter-domain QoS-NSLP message triggers the generation of a
Local QSPEC, and the Initiator QSPEC is encapsulated within the
messages signaled through the local domain. The local QSPEC is used
for QoS processing in the local-QOSM domain, and the Initiator QSPEC
is used for QoS processing outside the local domain.
In this example, the QNI sets <QoS Desired>, <Minimum QoS>, and <QoS
Available> objects to include objectives for the <Path Latency>,
<Path Jitter>, and <Path PER> parameters. The QNE / local domain
sets the cumulative parameters, e.g., <Path Latency>, that can be
achieved in the <QoS Available> object (but not less than specified
in <Minimum QoS>). If the <QoS Available> fails to satisfy one or
more of the <Minimum QoS> objectives, the QNE / local domain notifies the QNI and the reservation is aborted. If any QNE cannot meet the requirements designated by the Initiator QSPEC to support a QSPEC parameter with the M bit set to zero, the QNE sets the N flag for that parameter to one. Otherwise, the QNR notifies the QNI of the <QoS Available> for the reservation. |------| |------| |------| |------| | e2e |<->| e2e |<------------------------->| e2e |<->| e2e | | QOSM | | QOSM | | QOSM | | QOSM | | | |------| |-------| |-------| |------| | | | NSLP | | NSLP |<->| NSLP |<->| NSLP |<->| NSLP | | NSLP | |Y.1541| |local | |local | |local | |local | |Y.1541| | QOSM | | QOSM | | QOSM | | QOSM | | QOSM | | QOSM | |------| |------| |-------| |-------| |------| |------| ----------------------------------------------------------------- |------| |------| |-------| |-------| |------| |------| | NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP |<->| NTLP | |------| |------| |-------| |-------| |------| |------| QNI QNE QNE QNE QNE QNR (End) (Ingress Edge) (Interior) (Interior) (Egress Edge) (End) Figure 4: Example of Initiator and Local Domain QOSM Operation4.2. Reservation Success/Failure, QSPEC Error Codes, and INFO-SPEC Notification
A reservation may not be successful for several reasons: - a reservation may fail because the desired resources are not available. This is a reservation failure condition. - a reservation may fail because the QSPEC is erroneous or because of a QNE fault. This is an error condition. A reservation may be successful even though some parameters could not be interpreted or updated properly: - a QSPEC parameter cannot be interpreted because it is an unknown QSPEC parameter type. This is a QSPEC parameter not supported condition. However, the reservation does not fail. The QNI can still decide whether to keep or tear down the reservation depending on the procedures specified by the QNI's QOSM. The following sections provide details on the handling of unsuccessful reservations and reservations where some parameters could not be met, as follows:
- details on flags used inside the QSPEC to convey information on
success or failure of individual parameters. The formats and
semantics of all flags are given in Section 5.
- the content of the INFO-SPEC [RFC5974], which carries a code
indicating the outcome of reservations.
- the generation of a RESPONSE message to the QNI containing both
QSPEC and INFO-SPEC objects.
Note that when there are routers along the path between the QNI and
QNR where QoS cannot be provided, then the QoS-NSLP generic flag
BREAK (B) is set. The BREAK flag is discussed in Section 3.3.5 of
[RFC5974].
4.2.1. Reservation Failure and Error E Flag
The QSPEC parameters each have a 'reservation failure error E flag'
to indicate which (if any) parameters could not be satisfied. When a
resource cannot be satisfied for a particular parameter, the QNE
detecting the problem raises the E flag in this parameter. Note that
the TMOD parameter and all QSPEC parameters with the M flag set MUST
be examined by the RMF, and all QSPEC parameters with the M flag not
set SHOULD be examined by the RMF, and the E flag set to indicate
whether the parameter could or could not be satisfied. Additionally,
the E flag in the corresponding QSPEC object MUST be raised when a
resource cannot be satisfied for this parameter. If the reservation
failure problem cannot be located at the parameter level, only the E
flag in the QSPEC object is raised.
When an RMF cannot interpret the QSPEC because the coding is
erroneous, it raises corresponding reservation failure E flags in the
QSPEC. Normally, all QSPEC parameters MUST be examined by the RMF,
and the erroneous parameters appropriately flagged. In some cases,
however, an error condition may occur and the E flag of the error-
causing QSPEC parameter is raised (if possible), but the processing
of further parameters may be aborted.
Note that if the QSPEC and/or any QSPEC parameter is found to be
erroneous, then any QSPEC parameters not satisfied are ignored and
the E Flags in the QSPEC object MUST NOT be set for those parameters
(unless they are erroneous).
Whether E flags denote reservation failure or error can be determined
by the corresponding error code in the INFO-SPEC in QoS NSLP, as
discussed below.
4.2.2. QSPEC Parameter Not Supported N Flag
Each QSPEC parameter has an associated 'Not Supported N flag'. If the Not Supported N flag is set, then at least one QNE along the data transmission path between the QNI and QNR cannot interpret the specified QSPEC parameter. A QNE MUST set the Not Supported N flag if it cannot interpret the QSPEC parameter. If the M flag for the parameter is not set, the message should continue to be forwarded but with the N flag set, and the QNI has the option of tearing down the reservation. If a QNE in the path does not support a QSPEC parameter, e.g., <Path Latency>, and sets the N flag, then downstream QNEs that support the parameter SHOULD still update the parameter, even if the N flag is set. However, the presence of the N flag will indicate that the cumulative value only provides a bound, and the QNI/QNR decides whether or not to accept the reservation with the N flag set.4.2.3. INFO-SPEC Coding of Reservation Outcome
As prescribed by [RFC5974], the RESPONSE message always contains the INFO-SPEC with an appropriate 'error' code. It usually also contains a QSPEC with QSPEC objects, as described in Section 4.3 ("QSPEC Procedures"). The RESPONSE message MAY omit the QSPEC in case of a successful reservation. The following guidelines are provided for setting the error codes in the INFO-SPEC, based on the codes provided in Section 5.1.3.6 of [RFC5974]: - NSLP error class 2 (Success) / 0x01 (Reservation Success): This code is set when all QSPEC parameters have been satisfied. In this case, no E Flag is set; however, one or more N flags may be set. - NSLP error class 4 (Transient Failure) / 0x07 (Reservation Failure): This code is set when at least one QSPEC parameter could not be satisfied, or when a QSPEC parameter with M flag set could not be interpreted. E flags are set for the parameters that could not be satisfied at each QNE up to the QNE issuing the RESPONSE message. The N flag is set for those parameters that could not be interpreted by at least one QNE. In this case, QNEs receiving the RESPONSE message MUST remove the corresponding reservation.
- NSLP error class 3 (Protocol Error) / 0x0c (Malformed QSPEC):
Some QSPEC parameters had associated errors, E Flags are set for
parameters that had errors, and the QNE where the error was found
rejects the reservation.
- NSLP error class 3 (Protocol Error) / 0x0f (Incompatible QSPEC):
A higher version QSPEC is signaled and not supported by the QNE.
- NSLP error class 6 (QoS Model Error):
QOSM error codes can be defined by QOSM specification documents. A
registry is defined in Section 7, IANA Considerations.
4.2.4. QNE Generation of a RESPONSE Message
- Successful Reservation Condition
When a RESERVE message arrives at a QNR and no E Flag is set, the
reservation is successful. A RESPONSE message may be generated
with INFO-SPEC code 'Reservation Success' as described above and in
Section 4.3 ("QSPEC Procedures").
- Reservation Failure Condition
When a QNE detects that a reservation failure occurs for at least
one parameter, the QNE sets the E Flags for the QSPEC parameters
and QSPEC object that failed to be satisfied. According to
[RFC5974], the QNE behavior depends on whether it is stateful or
not. When a stateful QNE determines the reservation failed, it
formulates a RESPONSE message that includes an INFO-SPEC with the
'reservation failure' error code and QSPEC object. The QSPEC in
the RESPONSE message includes the failed QSPEC parameters marked
with the E Flag to clearly identify them.
The default action for a stateless QoS NSLP QNE that detects a
reservation failure condition is that it MUST continue to forward
the RESERVE message to the next stateful QNE, with the E Flags
appropriately set for each QSPEC parameter. The next stateful QNE
then formulates the RESPONSE message as described above.
- Malformed QSPEC Error Condition
When a stateful QNE detects that one or more QSPEC parameters are
erroneous, the QNE sets the error code 'malformed QSPEC' in the
INFO-SPEC. In this case, the QSPEC object with the E Flags
appropriately set for the erroneous parameters is returned within
the INFO-SPEC object. The QSPEC object can be truncated or fully
included within the INFO-SPEC.
According to [RFC5974], the QNE behavior depends on whether it is
stateful or not. When a stateful QNE determines a malformed QSPEC
error condition, it formulates a RESPONSE message that includes an
INFO-SPEC with the 'malformed QSPEC' error code and QSPEC object.
The QSPEC in the RESPONSE message includes, if possible, only the
erroneous QSPEC parameters and no others. The erroneous QSPEC
parameter(s) are marked with the E Flag to clearly identify them.
If QSPEC parameters are returned in the INFO-SPEC that are not
marked with the E flag, then any values of these parameters are
irrelevant and MUST be ignored by the QNI.
The default action for a stateless QoS NSLP QNE that detects a
malformed QSPEC error condition is that it MUST continue to forward
the RESERVE message to the next stateful QNE, with the E Flags
appropriately set for each QSPEC parameter. The next stateful QNE
will then act as described in [RFC5974].
A 'malformed QSPEC' error code takes precedence over the
'reservation failure' error code, and therefore the case of
reservation failure and QSPEC/RMF error conditions are disjoint,
and the same E Flag can be used in both cases without ambiguity.
4.2.5. Special Case of Local QSPEC
When an unsuccessful reservation problem occurs inside a local
domain where a Local QSPEC is used, only the topmost (local) QSPEC
is affected (e.g., E flags are raised, etc.). The encapsulated
Initiator QSPEC is untouched. However, when the message (RESPONSE
in case of stateful QNEs; RESERVE in case of stateless QNEs)
reaches the edge of the local domain, the Local QSPEC is removed.
The edge QNE must update the Initiator QSPEC on behalf of the
entire domain, reflecting the information received in the Local
QSPEC. This update concerns both parameter values and flags. Note
that some intelligence is needed in mapping the E flags, etc., from
the local QSPEC to the Initiator QSPEC. For example, even if there
is no direct match between the parameters in the local and
Initiator QSPECs, E flags could still be raised in the latter.
4.3. QSPEC Procedures
While the QSPEC template aims to put minimal restrictions on usage
of QSPEC objects, interoperability between QNEs and between QOSMs
must be ensured. We therefore give below an exhaustive list of
QSPEC object combinations for the message sequences described in
QoS NSLP [RFC5974]. A specific QOSM may prescribe that only a
subset of the procedures listed below may be used.
Note that QoS NSLP does not mandate the usage of a RESPONSE
message. A positive RESPONSE message will only be generated if the
QNE includes an RII (Request Identification Information) in the
RESERVE message, and a negative RESPONSE message is always
generated in case of an error or failure. Some of the QSPEC
procedures below, however, are only meaningful when a RESPONSE
message is possible. The QNI SHOULD in these cases include an RII.
4.3.1. Two-Way Transactions
Here, the QNI issues a RESERVE message, which may be replied to by
a RESPONSE message. The following 3 cases for QSPEC object usage
exist:
MESSAGE | OBJECT | OBJECTS INCLUDED | OBJECTS INCLUDED
SEQUENCE | COMBINATION | IN RESERVE MESSAGE | IN RESPONSE MESSAGE
-----------------------------------------------------------------
0 | 0 | QoS Desired | QoS Reserved
| | |
0 | 1 | QoS Desired | QoS Reserved
| | QoS Available | QoS Available
| | |
0 | 2 | QoS Desired | QoS Reserved
| | QoS Available | QoS Available
| | Minimum QoS |
Table 1: Message Sequence 0: Two-Way Transactions
Defining Object Combinations 0, 1, and 2
Case 1:
If only QoS Desired is included in the RESERVE message, the
implicit assumption is that exactly these resources must be
reserved. If this is not possible, the reservation fails. The
parameters in QoS Reserved are copied from the parameters in QoS
Desired. If the reservation is successful, the RESPONSE message
can be omitted in this case. If a RESPONSE message was requested
by a QNE on the path, the QSPEC in the RESPONSE message can be
omitted.
Case 2:
When QoS Available is included in the RESERVE message also, some
parameters will appear only in QoS Available and not in QoS
Desired. It is assumed that the value of these parameters is
collected for informational purposes only (e.g., path latency).
However, some parameters in QoS Available can be the same as in QoS
Desired. For these parameters, the implicit message is that the
QNI would be satisfied by a reservation with lower parameter values
than specified in QoS Desired. For these parameters, the QNI seeds
the parameter values in QoS Available to those in QoS Desired
(except for cumulative parameters such as <Path Latency>).
Each QNE interprets the parameters in QoS Available according to
its current capabilities. Reservations in each QNE are hence based
on current parameter values in QoS Available (and additionally
those parameters that only appear in QoS Desired). The drawback of
this approach is that, if the resulting resource reservation
becomes gradually smaller towards the QNR, QNEs close to the QNI
have an oversized reservation, possibly resulting in unnecessary
costs for the user. Of course, in the RESPONSE the QNI learns what
the actual reservation is (from the QoS RESERVED object) and can
immediately issue a properly sized refreshing RESERVE. The
advantage of the approach is that the reservation is performed in
half-a-roundtrip time.
The QSPEC parameter IDs and values included in the QoS Reserved
object in the RESPONSE message MUST be the same as those in the QoS
Desired object in the RESERVE message. For those QSPEC parameters
that were also included in the QoS Available object in the RESERVE
message, their value is copied from the QoS Available object (in
RESERVE) into the QoS Reserved object (in RESPONSE). For the other
QSPEC parameters, the value is copied from the QoS Desired object
(the reservation would fail if the corresponding QoS could not be
reserved).
All parameters in the QoS Available object in the RESPONSE message
are copied with their values from the QoS Available object in the
RESERVE message (irrespective of whether they have also been copied
into the QoS Desired object). Note that the parameters in the QoS
Available object can be overwritten in the RESERVE message, whereas
they cannot be overwritten in the RESPONSE message.
In this case, the QNI SHOULD request a RESPONSE message since it
will otherwise not learn what QoS is available.
Case 3:
This case is handled as case 2, except that the reservation fails
when QoS Available becomes less than Minimum QoS for one parameter.
If a parameter appears in the QoS Available object but not in the
Minimum QoS object, it is assumed that there is no minimum value
for this parameter.
Regarding Traffic Handling Directives, the default rule is that all
QSPEC parameters that have been included in the RESERVE message by
the QNI are also included in the RESPONSE message by the QNR with
the value they had when arriving at the QNR. When traveling in the
RESPONSE message, all Traffic Handling Directives parameters are
read-only. Note that a QOSM specification may define its own
Traffic Handling Directives parameters and processing rules.
4.3.2. Three-Way Transactions
Here, the QNR issues a QUERY message that is replied to by the QNI
with a RESERVE message if the reservation was successful. The QNR
in turn sends a RESPONSE message to the QNI. The following 3 cases
for QSPEC object usage exist:
MSG.|OBJ.|OBJECTS INCLUDED |OBJECTS INCLUDED |OBJECTS INCLUDED
SEQ.|COM.|IN QUERY MESSAGE |IN RESERVE MESSAGE |IN RESPONSE MESSAGE
-------------------------------------------------------------------
1 |0 |QoS Desired |QoS Desired |QoS Reserved
| | | |
1 |1 |QoS Desired |QoS Desired |QoS Reserved
| |(Minimum QoS) |QoS Available |QoS Available
| | |(Minimum QoS) |
| | | |
1 |2 |QoS Desired |QoS Desired |QoS Reserved
| |QoS Available |QoS Available |
Table 2: Message Sequence 1: Three-Way Transactions
Defining Object Combinations 0, 1, and 2
Cases 1 and 2:
The idea is that the sender (QNR in this scenario) needs to inform
the receiver (QNI in this scenario) about the QoS it desires. To
this end, the sender sends a QUERY message to the receiver
including a QoS Desired QSPEC object. If the QoS is negotiable, it
additionally includes a (possibly zero) Minimum QoS object, as in
Case 2.
The RESERVE message includes the QoS Available object if the sender
signaled that QoS is negotiable (i.e., it included the Minimum QoS
object). If the Minimum QoS object received from the sender is
included in the QUERY message, the QNI also includes the Minimum
QoS object in the RESERVE message.
For a successful reservation, the RESPONSE message in case 1 is
optional (as is the QSPEC inside). In case 2, however, the
RESPONSE message is necessary in order for the QNI to learn about
the QoS available.
Case 3:
This is the 'RSVP-style' scenario. The sender (QNR in this
scenario) issues a QUERY message with a QoS Desired object
informing the receiver (QNI in this scenario) about the QoS it
desires, as above. It also includes a QoS Available object to
collect path properties. Note that here path properties are
collected with the QUERY message, whereas in the previous case, 2
path properties were collected in the RESERVE message.
Some parameters in the QoS Available object may be the same as in
the QoS Desired object. For these parameters, the implicit message
is that the sender would be satisfied by a reservation with lower
parameter values than specified in QoS Desired.
It is possible for the QoS Available object to contain parameters
that do not appear in the QoS Desired object. It is assumed that
the value of these parameters is collected for informational
purposes only (e.g., path latency). Parameter values in the QoS
Available object are seeded according to the sender's capabilities.
Each QNE remaps or approximately interprets the parameter values
according to its current capabilities.
The receiver (QNI in this scenario) signals the QoS Desired object
as follows: For those parameters that appear in both the QoS
Available object and QoS Desired object in the QUERY message, it
takes the (possibly remapped) QSPEC parameter values from the QoS
Available object. For those parameters that only appear in the QoS
Desired object, it adopts the parameter values from the QoS Desired
object.
The parameters in the QoS Available QSPEC object in the RESERVE
message are copied with their values from the QoS Available QSPEC
object in the QUERY message. Note that the parameters in the QoS
Available object can be overwritten in the QUERY message, whereas
they cannot be overwritten in the RESERVE message.
The advantage of this model compared to the sender-initiated
reservation is that the situation of over-reservation in QNEs close
to the QNI (as described above) does not occur. On the other hand,
the QUERY message may find, for example, a particular bandwidth is
not available. When the actual reservation is performed, however,
the desired bandwidth may meanwhile have become free. That is, the
'RSVP style' may result in a smaller reservation than necessary.
The sender includes all QSPEC parameters it cares about in the
QUERY message. Parameters that can be overwritten are updated by
QNEs as the QUERY message travels towards the receiver. The
receiver includes all QSPEC parameters arriving in the QUERY
message also in the RESERVE message, with the value they had when
arriving at the receiver. Again, QOSM-specific QSPEC parameters
and procedures may be defined in QOSM specification documents.
Also in this scenario, the QNI SHOULD request a RESPONSE message
since it will otherwise not learn what QoS is available.
Regarding Traffic Handling Directives, the default rule is that all
QSPEC parameters that have been included in the RESERVE message by
the QNI are also included in the RESPONSE message by the QNR with
the value they had when arriving at the QNR. When traveling in the
RESPONSE message, all Traffic Handling Directives parameters are
read-only. Note that a QOSM specification may define its own
Traffic Handling Directives parameters and processing rules.
4.3.3. Resource Queries
Here, the QNI issues a QUERY message in order to investigate what
resources are currently available. The QNR replies with a RESPONSE
message.
MESSAGE | OBJECT | OBJECTS INCLUDED | OBJECTS INCLUDED
SEQUENCE | COMBINATION | IN QUERY MESSAGE | IN RESPONSE MESSAGE
-----------------------------------------------------------------
2 | 0 | QoS Available | QoS Available
Table 3: Message Sequence 2: Resource Queries
Defining Object Combination 0
Note that the QoS Available object when traveling in the QUERY
message can be overwritten, whereas in the RESPONSE message it
cannot be overwritten.
Regarding Traffic Handling Directives, the default rule is that all
QSPEC parameters that have been included in the RESERVE message by
the QNI are also included in the RESPONSE message by the QNR with
the value they had when arriving at the QNR. When traveling in the
RESPONSE message, all Traffic Handling Directives parameters are
read-only. Note that a QOSM specification may define its own
Traffic Handling Directives parameters and processing rules.
4.3.4. Bidirectional Reservations
On a QSPEC level, bidirectional reservations are no different from unidirectional reservations, since QSPECs for different directions never travel in the same message.4.3.5. Preemption
A flow can be preempted by a QNE based on QNE policy, where a decision to preempt a flow may account for various factors such as, for example, the values of the QSPEC preemption priority and defending priority parameters as described in Section 5.2.8. In this case, the reservation state for this flow is torn down in the QNE, and the QNE sends a NOTIFY message to the QNI, as described in [RFC5974]. The NOTIFY message carries an INFO-SPEC with the error code as described in [RFC5974]. A QOSM specification document may specify whether a NOTIFY message also carries a QSPEC object. The QNI would normally tear down the preempted reservation by sending a RESERVE message with the TEAR flag set using the SII of the preempted reservation. However, the QNI can follow other procedures as specified in its QOSM specification document.4.4. QSPEC Extensibility
Additional QSPEC parameters MAY need to be defined in the future and are defined in separate informational documents. For example, QSPEC parameters are defined in [RFC5977] and [RFC5976]. Guidelines on the technical criteria to be followed in evaluating requests for new codepoint assignments for QSPEC objects and QSPEC parameters are given in Section 7, IANA Considerations.
(page 33 continued on part 3)