Network Working Group J. Wroclawski
Request for Comments: 2210 MIT LCS
Category: Standards Track September 1997
The Use of RSVP with IETF Integrated Services
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This note describes the use of the RSVP resource reservation protocol
with the Controlled-Load and Guaranteed QoS control services. The
RSVP protocol defines several data objects which carry resource
reservation information but are opaque to RSVP itself. The usage and
data format of those objects is given here.
1. Introduction
The Internet integrated services framework provides the ability for
applications to choose among multiple, controlled levels of delivery
service for their data packets. To support this capability, two
things are required:
- Individual network elements (subnets and IP routers) along the
path followed by an application's data packets must support
mechanisms to control the quality of service delivered to those
packets.
- A way to communicate the application's requirements to network
elements along the path and to convey QoS management information
between network elements and the application must be provided.
In the integrated services framework the first function is provided
by QoS control services such as Controlled-Load [RFC 2211] and
Guaranteed [RFC 2212]. The second function may be provided in a
number of ways, but is frequently implemented by a resource
reservation setup protocol such as RSVP [RFC 2205].
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Because RSVP is designed to be used with a variety of QoS control
services, and because the QoS control services are designed to be
used with a variety of setup mechanisms, a logical separation exists
between the two specifications. The RSVP specification does not
define the internal format of those RSVP protocol fields, or objects,
which are related to invoking QoS control services. Rather, RSVP
treats these objects as opaque. The objects can carry different
information to meet different application and QoS control service
requirements.
Similarly, interfaces to the QoS control services are defined in a
general format, so that the services can be used with a variety of
setup mechanisms.
This RFC provides the information required to use RSVP and the
integrated service framework's QoS control services together. It
defines the usage and contents of three RSVP protocol objects, the
FLOWSPEC, ADSPEC, and SENDER_TSPEC, in an environment supporting the
Controlled-Load and/or Guaranteed QoS control services. If new
services or capabilities are added to the integrated services
framework, this note will be revised as required.
2. Use of RSVP
Several types of data must be transported between applications and
network elements to correctly invoke QoS control services.
NOTE: In addition to the data used to directly invoke QoS control
services, RSVP carries authentication, accounting, and policy
information needed to manage the use of these services. This note
is concerned only with the RSVP objects needed to actually invoke
QoS control services, and does not discuss accounting or policy
objects.
This data includes:
- Information generated by each receiver describing the QoS
control service desired, a description of the traffic flow to
which the resource reservation should apply (the Receiver TSpec),
and whatever parameters are required to invoke the service (the
Receiver RSpec). This information is carried from the receivers to
intermediate network elements and the sender(s) by RSVP FLOWSPEC
objects. The information being carried in a FLOWSPEC object may
change at intermediate points in the network due to reservation
merging and other factors.
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- Information generated at each sender describing the data traffic
generated by that sender (the Sender TSpec). This information is
carried from the sender to intermediate network elements and the
receiver(s) by RSVP, but is never modified by intermediate
elements within the network. This information is carried in RSVP
SENDER_TSPEC objects.
- Information generated or modified within the network and used at
the receivers to make reservation decisions. This information
might include available services, delay and bandwidth estimates,
and operating parameters used by specific QoS control services.
this information is collected from network elements and carried
towards receivers in RSVP ADSPEC objects. Rather than carrying
information from each intermediate node separately to the
receivers, the information in the ADSPEC represents a summary,
computed as the ADSPEC passes each hop. The size of this summary
remains (roughly) constant as the ADSPEC flows through the
network, giving good scaling properties.
From the point of view of RSVP objects, the breakdown is as follows:
- The RSVP SENDER_TSPEC object carries the traffic specification
(sender TSpec) generated by each data source within an RSVP
session. It is transported unchanged through the network, and
delivered to both intermediate nodes and receiving applications.
- The RSVP ADSPEC object carries information which is generated at
either data sources or intermediate network elements, is flowing
downstream towards receivers, and may be used and updated inside
the network before being delivered to receiving applications.
This information includes both parameters describing the
properties of the data path, including the availability of
specific QoS control services, and parameters required by specific
QoS control services to operate correctly.
- The RSVP FLOWSPEC object carries reservation request
(Receiver_TSpec and RSpec) information generated by data
receivers. The information in the FLOWSPEC flows upstream towards
data sources. It may be used or updated at intermediate network
elements before arriving at the sending application.
NOTE: The existence of both SENDER_TSPEC and ADSPEC RSVP objects
is somewhat historical. Using the message format described in
this note it would be possible to place all of the service
control information carried "downstream" by RSVP in the same
object. However, the distinction between data which is not
updated within the network (in the SENDER_TSPEC object) and data
which is updated within the network (in the ADSPEC object) may
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be useful to an implementation in practice, and is therefore
retained.
2.1 Summary of operation
Operation proceeds as follows:
An application instance participating in an RSVP session as a data
sender registers with RSVP. One piece of information provided by the
application instance is the Sender TSpec describing the traffic the
application expects to generate. This information is used to
construct an RSVP SENDER_TSPEC object, which is included in RSVP PATH
messages generated for the application.
The sending application also constructs an initial RSVP ADSPEC
object. This adspec carries information about the QoS control
capabilities and requirements of the sending application itself, and
forms the starting point for the accumulation of path properties
described below. The ADSPEC is added to the RSVP PATH message created
at the sender.
NOTE: For the convenience of application programmers, a host RSVP
implementation may allow the sending application not to provide an
initial adspec, instead supplying its own default. This usage is
most likely when the application sender does not itself
participate in the end-to-end QoS control process (by actively
scheduling CPU usage and similar means) and does not itself care
which QoS control service is selected by the receivers.
Typically the default ADSPEC supplied by the host RSVP in this
case would support all QoS control services known to the host.
However, the exact behavior of this mechanism is implementation
dependent.
The ADSPEC is modified by subsequent network elements as the RSVP
PATH message moves from sender to receiver(s). At each network
element, the ADSPEC is passed from RSVP to the traffic control
module. The traffic control module updates the ADSPEC, which may
contain data for several QoS control services, by identifying the
services mentioned in the ADSPEC and calling each such service to
update its portion of the ADSPEC. If the traffic control module
discovers a QoS control service mentioned in the ADSPEC but not
implemented by the network element, a flag is set to report this to
the receiver. The updated ADSPEC is then returned to RSVP for
delivery to the next hop along the path.
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Upon arrival of the PATH message at an application receiver, the data
in the SENDER_TSPEC and ADSPEC objects is passed across the RSVP API
to the application. The application (perhaps with the help of a
library of common resource-reservation functions) interprets the
arriving data, and uses it to guide the selection of resource
reservation parameters. Examples of this include use of the arriving
"PATH_MTU" composed characterization parameter [RFC 2215] to
determine the maximum packet size parameter in the reservation
request and use of the arriving Guaranteed service "C" and "D"
parameters [RFC 2212] to calculate a mathematical bound on delivered
packet delay when using the Guaranteed service.
An application receiver wishing to make a resource reservation
supplies its local RSVP with the necessary reservation parameters.
Among these are the QoS control service desired (Guaranteed or
Controlled-Load), the traffic specifier (TSpec) describing the level
of traffic for which resources should be reserved, and, if needed by
the selected QoS control service, an RSpec describing the level of
service desired. These parameters are composed into an RSVP FLOWSPEC
object and transmitted upstream by RSVP.
At each RSVP-aware point in the network, the SENDER_TSPECs arriving
in PATH messages and the FLOWSPECs arriving in RESV messages are used
to request an appropriate resource reservation from the desired QoS
control service. State merging, message forwarding, and error
handling proceed according to the rules of the RSVP protocol.
Finally, the merged FLOWSPEC object arriving at each of an RSVP
session's data senders is delivered to the application to inform each
sender of the merged reservation request and properties of the data
path.
2.2. RSVP support for multiple QoS control services
The design described in this note supports RSVP sessions in which the
receivers choose a QoS control service at runtime.
To make this possible, a receiver must have all the information
needed to choose a particular service before it makes the choice.
This means that the RSVP SENDER_TSPEC and ADSPEC objects must provide
the receivers with information for all services which might be
chosen.
The Sender TSpec used by the two currently defined QoS control
services is identical. This simplifies the RSVP SENDER_TSPEC object,
which need carry only a single TSpec data structure in this shared
format. This common SENDER_TSPEC can be used with either Guaranteed
or Controlled-Load service.
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The RSVP ADSPEC carries information needed by receivers to choose a
service and determine the reservation parameters. This includes:
- Whether or not there is a non-RSVP hop along the path. If there
is a non-RSVP hop, the application's traffic will receive
reservationless best-effort service at at least one point on the
path.
- Whether or not a specific QoS control service is implemented at
every hop along the path. For example, a receiver might learn that
at least one integrated-services aware hop along the path supports
the Controlled-Load service but not the Guaranteed service.
- Default or global values for the general characterization
parameters described in [RFC 2215]. These values describe
properties of the path itself, irrespective of the selected QoS
control service. A value reported in this section of the ADSPEC
applies to all services unless a different, service-specific value
is also present in the ADSPEC.
- A service-specific value for one or more general
characterization parameters, if the service-specific value differs
from the default value.
- Values of the per-service characterization parameters defined by
each supported service.
Data in the ADSPEC is divided into blocks or fragments, each of which
is associated with a specific service. This allows the adspec to
carry information about multiple services, allows new services to be
deployed in the future without immediately updating existing code,
and allows an application which will never use a particular service
to omit the ADSPEC data for that service. The structure of the
ADSPEC is described in detail in Section 3.3.
A sender may indicate that a specific QoS control service should
*not* be used by the receivers within an RSVP session. This is done
by omitting all mention of that service from the ADSPEC, as described
in Section 3.3. Upon arrival at a receiver, the complete absence of
an ADSPEC fragment for a specific service indicates to receivers that
the service should not be used.
NOTE: In RSVP Version 1, all receivers within a session are
required to choose the same QoS control service. This restriction
is imposed by the difficulty of merging reservations requesting
different QoS control services, and the current lack of a general
service replacement mechanism. The restriction may be eliminated
in the future.
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Considering this restriction, it may be useful to coordinate the
receivers' selection of a QoS control service by having the
sender(s) offer only one choice, using the ADSPEC mechanism
mentioned above. All receivers must then select the same service.
Alternatively, the coordination might be accomplished by using a
higher-level session announcement and setup mechanism to inform
the receivers of the QoS control service in use, by manual
configuration of the receivers, or by an agreement protocol
running among the session receivers themselves.
As with the ADSPEC, the FLOWSPEC and SENDER_TSPEC object formats
described in Section 3 are capable of carrying TSpecs and RSpecs
for more than one QoS control service in separate data fragments.
Currently, use of a FLOWSPEC or SENDER_TSPEC containing fragments
for more than one QoS control service is not supported. In the
future, this capability may be used to implement a more flexible
service request and replacement scheme, allowing applications to
obtain useful end-to-end QoS control when not all intermediate
nodes support the same set of QoS services. RSVP-application APIs
should be designed to support passing SENDER_TSPEC, FLOWSPEC, and
ADSPEC objects of variable size and containing information about
multiple QoS control services between RSVP and its clients.
2.3. Use of ADSPEC Information
This section gives some details about setting reservation parameters
and the use of information conveyed by the RSVP ADSPEC object.
2.3.1. Determining the availability of a QoS control service
The RSVP ADSPEC carries flag bits telling the application receivers
whether or not a completely reservation-capable path exists between
each sender and the receiver. These bits are called "break bits",
because they indicate breaks in the QoS control along a network path.
Break bits are carried within the header which begins each per-
service data fragment of an RSVP ADSPEC.
Service number 1 is used within the ADSPEC to identify a fragment
carrying information about global parameter values that apply to all
services (see [RFC 2215] for more details). The break bit in service
1's per-service header is used to tell the receiver(s) whether all of
the network elements along the path from sender to receiver support
RSVP and integrated services. If a receiver finds this bit set, at
least one network element along the data transmission path between
the ADSPEC's sender and the receiver can not provide QoS control
services at all. This bit corresponds to the global NON_IS_HOP
characterization parameter defined in [RFC 2215].
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NOTE: If this bit is set, the values of all other parameters in
the ADSPEC are unreliable. The bit being set indicates that at
least one node along the sender-receiver path did not fully
process the ADSPEC.
Service-specific break bits tell the receiver(s) whether all of the
network elements along the path from sender to receiver support a
particular QoS control service. The break bit for each service is
carried within the ADSPEC's per-service header for that service. If
a bit is set at the receiver, at least one network element along the
data transmission path supports RSVP but does not support the QoS
control service corresponding to the per-service header. These bits
correspond to the service-specific NON_IS_HOP characterization
parameters defined in [RFC 2215].
Section 3 gives more information about break bits.
2.3.2. Determining Path MTU
Both Guaranteed and Controlled-Load QoS control services place an
upper bound on packet size, and require that the application limit
the maximum size of packets subject to resource reservation. For both
services, the desired maximum packet size is a parameter of the
reservation request, and the service will reject (with an admission
control error) reservation requests specifying a packet size larger
than that supported by the service.
Since RSVP reservation requests are made by receivers, this implies
that the *receivers* in an RSVP session, as well as the senders, need
to know the MTU supported by the QoS control services along a data
path. Further, in some unusual cases the MTU supported by a QoS
control service may differ from that supported by the same router
when providing best effort service.
A scalable form of MTU negotiation is used to address these problems.
MTU negotiation in an RSVP system works as follows:
- Each sending application joining an RSVP session fills in the M
(maximum packet size) parameter in its generated Sender_TSpec
(carried from senders to receivers in a SENDER_TSPEC object) with
the maximum packet size it wishes to send covered by resource
reservation.
- Each RSVP PATH message from a sending application also carries
an ADSPEC object containing at least one PATH_MTU characterization
parameter. When it arrives at the receiver, this parameter gives
the minimum MTU at any point along the path from sender to
receiver. Generally, only the "global" PATH_MTU parameter
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(service 1, parameter 9) will be present, in which case its value
is a legal MTU for all reservation requests. If a service specific
PATH_MTU parameter is present, its value will be smaller than that
of the global parameter, and should be used for reservation
requests for that service.
- Each receiver takes the minimum of all the PATH_MTU values (for
the desired QoS control service) arriving in ADSPEC messages from
different senders and uses that value as the MTU in its
reservation requests. This value is used to fill in the M
parameter of the TSpec created at the receiver. In the case of a
FF style reservation, a receiver may also choose to use the MTU
derived from each sender's ADSPEC in the FLOWSPEC generated for
that sender, if the receiver is concerned about obtaining the
maximum MTU on each data path. To accomodate changes in the data
path, the receiver may continue to watch the arriving ADSPECS, and
modify the reservation if a newly arriving ADSPEC indicates a
smaller MTU than is currently in use.
- As reservation requests (RESV messages) move from receivers to
senders, reservation parameters are merged at intermediate nodes.
As part of this merging, the smaller of two M parameters arriving
at a merge point will be forwarded in the upstream RESV message.
- As reservation requests arrive at intermediate RSVPs, the
minimum of the receivers' requested TSpec and the sum of the
sender TSpecs is taken, and a reservation for the resulting TSpec
is made. The reservation will use the smaller of the actual path
MTU value computed by the receivers and the largest maximum packet
size declared by any of the sender(s). (The TSpec sum() function
result's M parameter is the max of the summed TSpec M parameters).
- When the completely merged RESV message arrives at each sender,
the MTU value (M parameter) in the merged FLOWSPEC object will
have been set to the smallest acceptable MTU of the data paths
from that sender to any session receiver. This MTU should be used
by the sending application to size its packets. Any packets larger
than this MTU may be delivered as best-effort rather than being
covered by the session's resource reservation.
Note that senders do *not* adjust the value of their
Sender_TSpec's M field to match the actual packet size selected in
this step. The value of M represents the largest packet the sender
could send, not the largest packet the sender is currently
sending.
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Note that the scheme above will allow each sender in a session to use
the largest MTU appropriate for that sender, in cases where different
data paths or receivers have different acceptable MTU's.
3. RSVP Object Formats
This section specifies the detailed contents and wire format of RSVP
SENDER_TSPEC, ADSPEC, and FLOWSPEC objects for use with the
Guaranteed and Controlled-Load QoS control services. The object
formats specified here are based on the general message construction
rules given in Appendix 1.
3.1. RSVP SENDER_TSPEC Object
The RSVP SENDER_TSPEC object carries information about a data
source's generated traffic. The required RSVP SENDER_TSPEC object
contains a global Token_Bucket_TSpec parameter (service_number 1,
parameter 127, as defined in [RFC 2215]). This TSpec carries traffic
information usable by either the Guaranteed or Controlled-Load QoS
control services.
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | reserved | 7 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 1 (c) |0| reserved | 6 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 127 (e) | 0 (f) | 5 (g) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Token Bucket Rate [r] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | Token Bucket Size [b] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | Peak Data Rate [p] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | Minimum Policed Unit [m] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Maximum Packet Size [M] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Message format version number (0)
(b) - Overall length (7 words not including header)
(c) - Service header, service number 1 (default/global information)
(d) - Length of service 1 data, 6 words not including header
(e) - Parameter ID, parameter 127 (Token_Bucket_TSpec)
(f) - Parameter 127 flags (none set)
(g) - Parameter 127 length, 5 words not including header
In this TSpec, the parameters [r] and [b] are set to reflect the
sender's view of its generated traffic. The peak rate parameter [p]
may be set to the sender's peak traffic generation rate (if known and
controlled), the physical interface line rate (if known), or positive
infinity (if no better value is available). Positive infinity is
represented as an IEEE single-precision floating-point number with an
exponent of all ones (255) and a sign and mantissa of all zeros. The
format of IEEE floating-point numbers is further summarized in [RFC
1832].
The minimum policed unit parameter [m] should generally be set equal
to the size of the smallest packet generated by the application. This
packet size includes the application data and all protocol headers at
or above the IP level (IP, TCP, UDP, RTP, etc.). The size given does
not include any link-level headers, because these headers will change
as the packet crosses different portions of the internetwork.
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The [m] parameter is used by nodes within the network to compute the
maximum bandwidth overhead needed to carry a flow's packets over the
particular link-level technology, based on the ratio of [m] to the
link-level header size. This allows the correct amount of bandwidth
to be allocated to the flow at each point in the net. Note that
smaller values of this parameter lead to increased overhead
estimates, and thus increased likelyhood of a reservation request
being rejected by the node. In some cases, an application
transmitting a low percentage of very small packets may therefore
choose to set the value of [m] larger than the actual minimum
transmitted packet size. This will increase the likelyhood of the
reservation succeeding, at the expense of policing packets of size
less than [m] as if they were of size [m].
Note that the an [m] value of zero is illegal. A value of zero would
indicate that no data or IP headers are present, and would give an
infinite amount of link-level overhead.
The maximum packet size parameter [M] should be set to the size of
the largest packet the application might wish to generate, as
described in Section 2.3.2. This value must, by definition, be equal
to or larger than the value of [m].
3.2. RSVP FLOWSPEC Object
The RSVP FLOWSPEC object carries information necessary to make
reservation requests from the receiver(s) into the network. This
includes an indication of which QoS control service is being
requested, and the parameters needed for that service.
The QoS control service requested is indicated by the service_number
in the FLOWSPEC's per-service header.
3.2.1 FLOWSPEC object when requesting Controlled-Load service
The format of an RSVP FLOWSPEC object originating at a receiver
requesting Controlled-Load service is shown below. Each of the TSpec
fields is represented using the preferred concrete representation
specified in the 'Invocation Information' section of [RFC 2211]. The
value of 5 in the per-service header (field (c), below) indicates
that Controlled-Load service is being requested.
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | reserved | 7 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 5 (c) |0| reserved | 6 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 127 (e) | 0 (f) | 5 (g) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Token Bucket Rate [r] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | Token Bucket Size [b] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | Peak Data Rate [p] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | Minimum Policed Unit [m] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Maximum Packet Size [M] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Message format version number (0)
(b) - Overall length (7 words not including header)
(c) - Service header, service number 5 (Controlled-Load)
(d) - Length of controlled-load data, 6 words not including
per-service header
(e) - Parameter ID, parameter 127 (Token Bucket TSpec)
(f) - Parameter 127 flags (none set)
(g) - Parameter 127 length, 5 words not including per-service
header
In this object, the TSpec parameters [r], [b], and [p] are set to
reflect the traffic parameters of the receiver's desired reservation
(the Reservation TSpec). The meaning of these fields is discussed
fully in [RFC 2211]. Note that it is unlikely to make sense for the
[p] term to be smaller than the [r] term.
The maximum packet size parameter [M] should be set to the value of
the smallest path MTU, which the receiver learns from information in
arriving RSVP ADSPEC objects. Alternatively, if the receiving
application has built-in knowledge of the maximum packet size in use
within the RSVP session, and this value is smaller than the smallest
path MTU, [M] may be set to this value. Note that requesting a value
of [M] larger than the service modules along the data path can
support will cause the reservation to fail. See section 2.3.2 for
further discussion of the MTU value.
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The value of [m] can be chosen in several ways. Recall that when a
resource reservation is installed at each intermediate node, the
value used for [m] is the smaller of the receiver's request and the
values in each sender's SENDER_TSPEC.
If the application has a fixed, known minimum packet size, than that
value should be used for [m]. This is the most desirable case.
For a shared reservation style, the receiver may choose between two
options, or pick some intermediate point between them.
- if the receiver chooses a large value for [m], then the
reservation will allocate less overhead for link-level headers.
However, if a new sender with a smaller SENDER_TSPEC [m] joins the
session later, an already-installed reservation may fail at that
time.
- if the receiver chooses a value of [m] equal to the smallest
value which might be used by any sender, then the reservation will
be forced to allocate more overhead for link-level headers.
However it will not fail later if a new sender with a smaller
SENDER_TSPEC [m] joins the session.
For a FF reservation style, if no application-specific value is known
the receiver should simply use the value of [m] arriving in each
sender's SENDER_TSPEC for its reservation request to that sender.
3.2.2. FLOWSPEC Object when Requesting Guaranteed Service
The format of an RSVP FLOWSPEC object originating at a receiver
requesting Guaranteed service is shown below. The flowspec object
used to request guaranteed service carries a TSpec and RSpec
specifying the traffic parameters of the flow desired by the
receiver.
Each of the TSpec and RSpec fields is represented using the preferred
concrete representation specified in the 'Invocation Information'
section of [RFC 2212]. The value of 2 for the service header
identifier (field (c) in the picture below) indicates that Guaranteed
service is being requested.
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | Unused | 10 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 2 (c) |0| reserved | 9 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 127 (e) | 0 (f) | 5 (g) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Token Bucket Rate [r] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | Token Bucket Size [b] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | Peak Data Rate [p] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | Minimum Policed Unit [m] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Maximum Packet Size [M] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 | 130 (h) | 0 (i) | 2 (j) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
10 | Rate [R] (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
11 | Slack Term [S] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Message format version number (0)
(b) - Overall length (9 words not including header)
(c) - Service header, service number 2 (Guaranteed)
(d) - Length of per-service data, 9 words not including per-service
header
(e) - Parameter ID, parameter 127 (Token Bucket TSpec)
(f) - Parameter 127 flags (none set)
(g) - Parameter 127 length, 5 words not including parameter header
(h) - Parameter ID, parameter 130 (Guaranteed Service RSpec)
(i) - Parameter 130 flags (none set)
(j) - Parameter 130 length, 2 words not including parameter header
In this object, the TSpec parameters [r], [b], and [p] are set to
reflect the traffic parameters of the receiver's desired reservation
(the Reservation TSpec). The meaning of these fields is discussed
fully in [RFC 2212]. Note that it is unlikely to make sense for the
[p] term to be smaller than the [r] term.
The RSpec terms [R] and [S] are selected to obtain the desired
bandwidth and delay guarantees. This selection is described in [RFC
2212].
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The [m] and [M] parameters are set identically to those for the
Controlled-Load service FLOWSPEC, described in the previous section.
3.3. RSVP ADSPEC Object
An RSVP ADSPEC object is constructed from data fragments contributed
by each service which might be used by the application. The ADSPEC
begins with an overall message header, followed by a fragment for the
default general parameters, followed by fragments for every QoS
control service which may be selected by application receivers. The
size of the ADSPEC varies depending on the number and size of per-
service data fragments present and the presence of non-default
general parameters (described in Section 3.3.5).
The complete absence of a data fragment for a particular service
means that the application sender does not know or care about that
service, and is a signal to intermediate nodes not to add or update
information about that service to the ADSPEC. It is also a signal to
application receivers that they should not select that service when
making reservations.
Each fragment present is identified by a per-service data header.
Each header contains a field identifying the service, a break bit,
and a length field.
The length field allows the ADSPEC information for a service to be
skipped over by a network elements which does not recognize or
implement the service. When an element does this, it sets the break
bit, indicating that the service's ADSPEC data was not updated at at
least one hop. Note that a service's break bit can be set without
otherwise supporting the service in any way. In all cases, a network
element encountering a per-service data header it does not understand
simply sets bit 23 to report that the service is not supported, then
skips over the rest of the fragment.
Data fragments must always appear in an ADSPEC in service_number
order. In particular, the default general parameters fragment
(service_number 1) always comes first.
Within a data fragment, the service-specific data must alway come
first, followed by any non-default general parameters which may be
present, ordered by parameter_number. The size and structure of the
service-specific data is fixed by the service definition, and does
not require run-time parsing. The remainder of the fragment, which
carries non-default general parameters, varies in size and structure
depending on which, if any, of these parameters are present. This
part of the fragment must be parsed by examining the per-parameter
headers.
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Since the overall size of each data fragment is variable, it is
always necessary to examine the length field to find the end of the
fragment, rather than assuming a fixed-size structure.
3.3.1. RSVP ADSPEC format
The basic ADSPEC format is shown below. The message header and the
default general parameters fragment are always present. The fragments
for Guaranteed or Controlled-Load service may be omitted if the
service is not to be used by the RSVP session. Additional data
fragments will be added if new services are defined.
31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 (a) | reserved | Msg length - 1 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Default General Parameters fragment (Service 1) (c) |
| (Always Present) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Guaranteed Service Fragment (Service 2) (d) |
| (Present if application might use Guaranteed Service) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Controlled-Load Service Fragment (Service 5) (e) |
| (Present if application might use Controlled-Load Service) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Message format version number (0)
(b) - Overall message length not including header word
(c, d, e) - Data fragments
3.3.2. Default General Characterization Parameters ADSPEC data fragment
All RSVP ADSPECs carry the general characterization parameters
defined in [RFC 2215]. Values for global or default general
parameters (values which apply to the all services or the path
itself) are carried in the per-service data fragment for service
number 1, as shown in the picture above. This fragment is always
present, and always first in the message.
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 1 (c) |x| reserved | 8 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 4 (e) | (f) | 1 (g) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | IS hop cnt (32-bit unsigned integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | 6 (h) | (i) | 1 (j) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | Path b/w estimate (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | 8 (k) | (l) | 1 (m) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | Minimum path latency (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | 10 (n) | (o) | 1 (p) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 | Composed MTU (32-bit unsigned integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(c) - Per-Service header, service number 1 (Default General
Parameters)
(d) - Global Break bit ([RFC 2215], Parameter 2) (marked x) and
length of General Parameters data block.
(e) - Parameter ID, parameter 4 (Number-of-IS-hops param from
[RFC 2215])
(f) - Parameter 4 flag byte
(g) - Parameter 4 length, 1 word not including header
(h) - Parameter ID, parameter 6 (Path-BW param from [RFC 2215])
(i) - Parameter 6 flag byte
(j) - Parameter 6 length, 1 word not including header
(k) - Parameter ID, parameter 8 (minimum path latency from [RFC
2215])
(l) - Parameter 8 flag byte
(m) - Parameter 8 length, 1 word not including header
(n) - Parameter ID, parameter 10 (composed path MTU from [RFC 2215])
(o) - Parameter 10 flag byte
(p) - Parameter 10 length, 1 word not including header
Rules for composing general parameters appear in [RFC 2215].
In the above fragment, the global break bit (bit 23 of word 1, marked
with (x) in the picture) is used to indicate the existence of a
network element not supporting QoS control services somewhere in the
data path. This bit is cleared when the ADSPEC is created, and set
to one if a network element which does not support RSVP or integrated
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services is encountered. An ADSPEC arriving at a receiver with this
bit set indicates that all other parameters in the ADSPEC may be
invalid, since not all network elements along the path support
updating of the ADSPEC.
The general parameters are updated at every network node which
supports RSVP:
- When a PATH message ADSPEC encounters a network element
implementing integrated services, the portion of the ADSPEC
associated with service number 1 is passed to the module
implementing general parameters. This module updates the global
general parameters.
- When a PATH message ADSPEC encounters a network element that
does *not* support RSVP or implement integrated services, the
break bit in the general parameters service header must be set. In
practice, this bit will usually be set by another network element
which supports RSVP, but has been made aware of the gap in
integrated services coverage.
- In either case, the ADSPEC is passed back to RSVP for delivery
to the next hop along the path.
3.3.3. Guaranteed Service ADSPEC data fragment
The Guaranteed service uses the RSVP ADSPEC to carry data needed to
compute the C and D terms passed from the network to the application.
The minimum size of a non-empty guaranteed service data fragment is 8
32-bit words. The ADSPEC fragment for Guaranteed service has the
following format:
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 2 (a) |x| reserved | N-1 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 133 (c) | 0 (d) | 1 (e) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | End-to-end composed value for C [Ctot] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | 134 (f) | (g) | 1 (h) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | End-to-end composed value for D [Dtot] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | 135 (i) | (j) | 1 (k) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | Since-last-reshaping point composed C [Csum] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | 136 (l) | (m) | 1 (n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 | Since-last-reshaping point composed D [Dsum] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
10 | Service-specific general parameter headers/values, if present |
. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.
N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Per-Service header, service number 2 (Guaranteed)
(b) - Break bit and Length of per-service data in 32-bit
words not including header word.
(c) - Parameter ID, parameter 133 (Composed Ctot)
(d) - Parameter 133 flag byte
(e) - Parameter 133 length, 1 word not including header
(f) - Parameter ID, parameter 134 (Composed Dtot)
(g) - Parameter 134 flag byte
(h) - Parameter 134 length, 1 word not including header
(i) - Parameter ID, parameter 135 (Composed Csum).
(j) - Parameter 135 flag byte
(k) - Parameter 135 length, 1 word not including header
(l) - Parameter ID, parameter 136 (Composed Dsum).
(m) - Parameter 136 flag byte
(n) - Parameter 136 length, 1 word not including header
When a node which actually implements guaranteed service creates the
guaranteed service adspec fragment, the parameter values are set to
the local values for each parameter. When an application or network
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element which does not itself implement guaranteed service creates a
guaranteed service adspec fragment, it should set the values of each
parameter to zero, and set the break bit to indicate that the service
is not actually implemented at the node.
An application or host RSVP which is creating a guaranteed service
adspec fragment but does not itself implement the guaranteed service
may create a truncated "empty" guaranteed adspec fragment consisting
of only a header word:
31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 2 (a) |1| (b) | 0 (c) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Per-Service header, service number 2 (Guaranteed)
(b) - Break bit (set, service not implemented)
(c) - Length of per-service data in 32-bit words not
including header word.
This might occur if the sending application or host does not do
resource reservation iself, but still wants the network to do so.
Note that in this case the break bit will always be set, since the
creator of the adspec fragment does not itself implement guaranteed
service.
When a PATH message ADSPEC containing a per-service header for
Guaranteed service encounters a network element implementing
Guaranteed service, the guaranteed service data fragment is updated:
- If the data block in the ADSPEC is an empty (header-only) block
the header-only fragment must first be expanded into the complete
data fragment described above, with initial values of Ctot, Dtot,
Csum, and Dsum set to zero. An empty fragment can be recognized
quickly by checking for a size field of zero. The value of the
break bit in the header is preserved when the additional
Guaranteed service data is added. The overall message length and
the guaranteed-service data fragment size (field (b) in the
pictures above) are changed to reflect the increased message
length.
The values of Ctot, Csum, Dtot, and Dsum in the ADSPEC data
fragment are then composed with the local values exported by the
network element according to the composition functions defined in
[RFC 2212].
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- When a PATH message ADSPEC with a Guaranteed service header
encounters a network element that supports RSVP but does *not*
implement Guaranteed service, the network element sets the break
bit in the Guaranteed service header.
- The new values are placed in the correct fields of the ADSPEC,
and the ADSPEC is passed back to RSVP for delivery to the next hop
along the path.
When a PATH message ADSPEC containing a Guaranteed service data
fragment encounters a network element that supports RSVP but does
*not* implement Guaranteed service, the network element sets the
break bit in the Guaranteed service header.
When a PATH message ADSPEC *without* a Guaranteed service header
encounters a network element implementing Guaranteed service, the
Guaranteed service module of the network element leaves the ADSPEC
unchanged. The absence of a Guaranteed service per-service header in
the ADSPEC indicates that the application does not care about
Guaranteed service.
3.3.4. Controlled-Load Service ADSPEC data fragment
Unlike the Guaranteed service, the Controlled-Load service does not
require extra ADSPEC data to function correctly. The only ADSPEC data
specific to the Controlled-Load service is the Controlled-Load break
bit. Therefore the usual Controlled-Load service data block contains
no extra information. The minimum size of the controlled-load service
data fragment is 1 32-bit word.
31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 5 (a) |x| (b) | N-1 (c) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | Service-specific general parameter headers/values, if present |
. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.
N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Per-Service header, service number 5 (Controlled-Load)
(b) - Break bit
(c) - Length of per-service data in 32 bit words not including
header word.
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The Controlled-Load portion of the ADSPEC is processed according to
the following rules:
- When a PATH message ADSPEC with a Controlled-Load service header
encounters a network element implementing Controlled-Load service,
the network element makes no changes to the service header.
- When a PATH message ADSPEC with a Controlled-Load service header
encounters a network element that supports RSVP but does *not*
implement Controlled-Load service, the network element sets the
break bit in the Controlled-Load service header.
- In either case, the ADSPEC is passed back to RSVP for delivery
to the next hop along the path.
3.3.5. Overriding Global ADSPEC Data with Service-Specific Information
In some cases, the default values for the general parameters are not
correct for a particular service. For example, an implementation of
Guaranteed service may accept only packets with a smaller maximum
size than the link MTU, or the percentage of outgoing link bandwidth
made available to the Controlled-Load service at a network element
may be administratively limited to less than the overall bandwidth.
In these cases, a service-specific value, as well as the default
value, is reported to the receiver receiving the ADSPEC. Service-
specific information which overrides general information is carried
by a parameter with the same name as the general parameter, placed
within the data fragment of the QoS control service to which it
applies. These service-specific values are referred to as override or
service-specific general parameters.
For example, the following Controlled-Load ADSPEC fragment carries
information overriding the global path bandwidth estimate with a
different value:
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31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 5 (a) |x| (b) | 2 (c) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 6 (d) | 0 (d) | 1 (e) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | Path b/w estimate for C-L service (32b IEEE FP number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Per-Service header, service number 5 (Controlled-Load)
(b) - Break bit
(c) - Length of per-service data, two words not including header
(c) - Parameter ID, parameter 6
(AVAILABLE_PATH_BANDWIDTH general parameter from [RFC 2215])
(d) - Parameter 6 flags (none set)
(e) - Parameter 6 length, one word not including header
The presence of override parameters in a data fragment can be quickly
detected by examining the fragment's length field, which will be
larger than the "standard" length for the fragment. Specific
override parameters can be easily identified by examining the
parameter headers, because they have parameter_number's from the
general parameter portion of the number space (1-127), but are found
in service-specific data blocks (those with service_numbers between 2
and 254 in the per_service header field).
The presence of override parameters in a data fragment is optional. A
parameter header/value pair is added only when a particular
application or QoS control service wishes to override the global
value of a general parameter with a service-specific value.
As with IP options, it is only the use of these override parameters
that is optional. All implementations must be prepared to receive and
process override parameters.
The basic principle for handling override parameters is to use the
override value (local or adspec) if it exists, and to use the default
value otherwise. If a local node exports an override value for a
general parameter, but there is no override value in the arriving
adspec, the local node adds it. The following pseudo-code fragment
gives more detail:
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/* Adspec parameter processing rules *
<get arriving ADSPEC from RSVP>
for ( <each service number N with a fragment in the ADSPEC> ) {
if ( <the local node does not support the service> ) {
<set the break bit in the service header>
} else {
for ( <each parameter in the data fragment for service N> ) {
if ( < the local service N supplies a value for the parameter> ) {
<compose the arriving and values and update the adspec>
} else {
/* Must be a general parameter, or service N would have
* supplied a value..
*/
<compose the arriving value with the local default value
and update the adspec>
}
}
for ( <any parameters supplied by the local service N
implementation but not found in the adspec> ) {
/*
* Must be an override value for a general parameter,
* or the adspec would have contained a value..
*/
<compose the local override value with the arriving default
value (from the service 1 data fragment) and add the parameter
to the adspec's service N fragment in parameter_number order>
}
}
}
<pass updated ADSPEC back to RSVP>
In practice, the two 'for' loops can be combined. Since override
parameters within a service's fragment are transmitted in numerical
order, it is possible to determine whether a parameter is present
without scanning the entire fragment. Also, because the data
fragments are ordered by service_number, the default values for
general parameters will always be read before they might be needed to
update local override values in the second for loop.
3.3.6. Example
The picture below shows the complete adspec for an application which
can use either controlled-load or guaranteed service. In the example,
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data fragments are present for general parameters, guaranteed, and
controlled-load services. All fragments are of standard size, and
there are no override parameters present.
31 24 23 16 15 8 7 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | Unused | 19 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 1 (c) |x| reserved (d)| 8 (e) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 4 (f) | (g) | 1 (h) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | zero extension of .. IS hop cnt (16-bit unsigned) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | 6 (i) | (j) | 1 (k) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | Path b/w estimate (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | 8 (l) | (m) | 1 (n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Minimum path latency (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 | 10 (o) | (p) | 1 (q) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
10 | zero extension of .. composed MTU (16-bit unsigned) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
11 | 2 (r) |x| reserved (s)| 8 (t) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12 | 133 (u) | (v) | 1 (w) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
13 | End-to-end composed value for C [Ctot] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
14 | 134 (x) | (y) | 1 (z) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
15 | End-to-end composed value for D [Dtot] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16 | 135 (aa | (bb | 1 (cc) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17 | Since-last-reshaping point composed C [Csum] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
18 | 136 (dd) | (ee) | 1 (ff) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
19 | Since-last-reshaping point composed D [Dsum] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
20 | 5 (gg |x 0 (hh) | 0 (ii) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Wroclawski Standards Track [Page 26]
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Word 1: Message Header:
(a) - Message header and version number
(b) - Message length - 19 words not including header
Words 2-7: Default general characterization parameters
(c) - Per-Service header, service number 1
(Default General Parameters)
(d) - Global Break bit (NON_IS_HOP general parameter 2) (marked x)
(e) - Length of General Parameters data block (8 words)
(f) - Parameter ID, parameter 4 (NUMBER_OF_IS_HOPS
general parameter)
(g) - Parameter 4 flag byte
(h) - Parameter 4 length, 1 word not including header
(i) - Parameter ID, parameter 6 (AVAILABLE_PATH_BANDWIDTH
general parameter)
(j) - Parameter 6 flag byte
(k) - Parameter 6 length, 1 word not including header
(l) - Parameter ID, parameter 8 (MINIMUM_PATH_LATENCY
general parameter)
(m) - Parameter 8 flag byte
(n) - Parameter 8 length, 1 word not including header
(o) - Parameter ID, parameter 10 (PATH_MTU general parameter)
(p) - Parameter 10 flag byte
(q) - Parameter 10 length, 1 word not including header
Words 11-19: Guaranteed service parameters
(r) - Per-Service header, service number 2 (Guaranteed)
(s) - Break bit
(t) - Length of per-service data, 8 words not including header
(u) - Parameter ID, parameter 133 (Composed Ctot)
(v) - Composed Ctot flag byte
(w) - Composed Ctot length, 1 word not including header
(x) - Parameter ID, parameter 134 (Composed Dtot)
(y) - Composed Dtot flag byte
(z) - Composed Dtot length, 1 word not including header
(aa)- Parameter ID, parameter 135 (Composed Csum).
(bb)- Composed Csum flag byte
(cc)- Composed Csum length, 1 word not including header
(dd)- Parameter ID, parameter 136 (Composed Dsum).
(ee)- Composed Dsum flag byte
(ff)- Composed Dsum length, 1 word not including header
Word 20: Controlled-Load parameters
(gg - Per-Service header, service number 5 (Controlled-Load)
(hh)- Break bit
(ii)- Length of controlled-load data, 0 words not including header
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4. Security Considerations
The message formatting and usage rules described in this note raise
no security issues. The overall use of these rules to implement
multiple qualities of service using RSVP and integrated services
scheduling modules introduces a new security requirement; the need to
control and authenticate access to enhanced qualities of service.
This requirement is discussed further in [RFC 2205], [RFC 2212], and
[RFC 2211]. [RFCRSVPMD5] describes the mechanism used to protect the
integrity of RSVP messages carrying the information described here.
Wroclawski Standards Track [Page 28]
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Appendix 1: Message construction rules
This section gives the rule used to generate the object formats of
Section 3. It is a general wire format for encoding integrated
services data objects within setup and management protocol messages.
The format has a three-level structure:
- An overall message header carries a version number and message
length. Providing this header in a standard format allows the
same code library to handle data objects carried by multiple setup
protocols.
- Per-service fragments carry information about a specific QoS
control service, such as guaranteed [RFC 2212] or controlled load
[RFC 2211]. Each per-service fragment carries one or more
parameters. The set of parameters present in a fragment is
determined by the needs of the protocol in use. Examples are given
in Section 2.
- Parameters are the actual data used to control or monitor a
service. A parameter may be a single quantity such as an integer,
or a composite data structure such as a TSpec. The parameters
specific to a service are defined by the service specification.
The available general parameters, with definitions shared by many
services, are defined by [RFC 2215].
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A1.1. Message Header
The 32-bit message header specifies the message format version number
and total length of the message. The overall message must be aligned
to a 32-bit boundary within the transport protocol's data packet.
The message length is measured in 32-bit words *not including the
word containing the header*. This is to lower the probability of an
accidentally cleared word resulting in an infinite loop in the
message parser.
The Message Header is represented by a 32-bit bitfield laid out as
shown below and then encoded as an XDR unsigned integer. Encoding as
an XDR unsigned integer is equivalent to converting the bitfield from
the machine's native format to big-endian network byte order.
Message Header
MSB LSB
31 28 27 16 15 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| V | Unused | OVERALL LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
V - Message format version; currently 0
OVERALL LENGTH - Message length in 32-bit words not including header
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A1.2. Per-Service Data Header
The message header is followed by one or more service-specific data
blocks, each containing the data associated with a specific QoS
control service. Each service-specific data block begins with an
identifying header. This 32-bit header contains the service number, a
one-bit flag (the "break bit", because it indicates a break in the
QoS control path) and a length field. The length field specifies the
number of 32-bit words used to hold data specific to this service as
a count of 32-bit words *not including the word containing the
header*.
The break bit, if set, indicates that the service specified by the
header was unsupported or unrecognized at some point in the message's
path through the network. This bit corresponds to the general
parameter NON_IS_HOP defined in [RFC 2215]. It is cleared when a
message is first generated, and set whenever the message passes
through an element that does not recognize the service_number in the
per-service header.
The Per-Service Data Header is represented by a 32-bit bitfield laid
out as shown below and then encoded as an XDR unsigned integer.
Per-Service Data Header
MSB LSB
31 24 23 16 15 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SVC_NUMBER |B| Reserved | SVC_LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SVC_NUMBER - Service ID number (defined in service specification).
B - Break bit - service unsupported/break in path.
SVC_LENGTH - Service-specific data length in 32-bit words,
not including header.
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A1.3. Parameter Header
The per-service header is followed by one or more service parameter
blocks, each identified by a Parameter Header. This header contains
the parameter identifier (parameter number), the length of the data
carrying the parameter's value, and a flag field. The data field(s)
of the parameter follow. The parameter number, as well as the
meaning and format of the data words following the header, are given
by the specification which defines the parameter.
The Parameter Header is represented by a 32-bit bitfield laid out as
shown below and then encoded as an XDR unsigned integer.
Parameter Header
MSB LSB
31 24 23 16 15 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PARAM_NUM |I FLAGS | PARAM_LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PARAM_NUM - Parameter number (defined in service specification)
FLAGS - Per-parameter flags
PARAM_LENGTH - Length of per-parameter data in 32-bit words, not
including the header word.
The following flags are currently defined in the FLAGS field:
I (bit 23) - INVALID
This flag indicates that the parameter value was
not correctly processed at one or more network
elements along a data path. It is intended for use
in a possible future service composition scheme.
Other bits in the FLAGS field of the parameter header are currently
reserved, and should be set to zero.
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A1.4. Parameter Data
Following the Parameter Header is the actual data representing the
parameter value. Parameter values are encoded into one or more 32-bit
words using the XDR external data representation described in [RFC
1832], and the resulting words are placed in the message.
The document defining a parameter should provide an XDR description
of the parameter's data fields. If it does not, a description should
be provided in this note.
References
[RFC 2205] Braden, B., Ed., et. al., "Resource Reservation Protocol
(RSVP) - Version 1 Functional Specification", RFC 2205, September
1997.
[RFC 2216] Shenker, S., and J. Wroclawski. "Network Element QoS
Control Service Specification Template", RFC 2216, September 1997.
[RFC 2212] Shenker, S., Partridge, C., and R Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212, September 1997.
[RFC 2211] Wroclawski, J., "Specification of the Controlled Load
Quality of Service", RFC 2211, September 1997.
[RFC 2215] Shenker, S., and J. Wroclawski, "General Characterization
Parameters for Integrated Service Network Elements", RFC 2215,
September 1997.
[RFCRSVPMD5] Baker, F., "RSVP Cryptographic Authentication", Work in
Progress.
[RFC 1832] Srinivansan, R., "XDR: External Data Representation
Standard", RFC 1832, August 1995.
Author's Address
John Wroclawski
MIT Laboratory for Computer Science
545 Technology Sq.
Cambridge, MA 02139
Phone: 617-253-7885
Fax: 617-253-2673 (FAX)
EMail: jtw@lcs.mit.edu
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