wdiff draft-ietf-intserv-charac-01.txt draft-ietf-intserv-charac-02.txt

Internet Engineering Task Force Integrated Services WG
INTERNET-DRAFT S. Shenker/J. Shenker and J. Wroclawski
draft-ietf-intserv-charac-01.txt
draft-ietf-intserv-charac-02.txt Xerox PARC/MIT LCS
June,
October, 1996
Expires: 12/96

Specification of 3/97

General Characterization Parameters for
Integrated Service Network Elements

Status of this Memo

This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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This document is a product of the Integrated Services working group
of the Internet Engineering Task Force. Comments are solicited and
should be addressed to the working group's mailing list at int-
serv@isi.edu and/or the author(s).

Abstract

This memo defines a set of general control and characterization
parameters for network elements supporting enhanced qualities the IETF integrated
services QoS control framework. General parameters are those with
common, shared definitions across all QoS control services.

1. Introduction

This memo defines the set of service. general control and characterization
parameters used by network elements supporting the integrated
services framework. "General" means that the parameter has a common
definition and shared meaning across all QoS control services.

Control parameters are used by applications to provide information to
the network related to QoS control requests. An example is the
traffic specification (TSpec) generated by application senders and
receivers.

Characterization parameters are used to discover or characterize the service
QoS management environment along the path of a packet flow desiring requesting
active end-to-end QoS control.
General characterization parameters are those that are not
specific to a particular quality of service.

Introduction

This memo defines a standard for general, These characterizations may
eventually be used by the application requesting QoS control, or service-independent,
characterization parameters for by
other network elements. General
characterization parameters are those that elements along the path. Examples include information
about which QoS control services are not specific to available along a
particular quality of service. A discussion network path
and estimates of how these parameters
fit into an integrated services architecture can be found in [1].
Please the available path bandwidth.

Individual QoS control service specifications may refer to that document for these
parameter definitions and as well as defining additional
information about parameters
specific to the specification of qualities needs of service that service.

Parameters are assigned machine-oriented ID's using a method
described in [RFCTEMPLATE] and summarized here. These ID's may be
used within
the IP protocol family.

The specifications of the various qualities of service ([2-3]) messages and management interfaces to describe
the parameter values present. Each parameter ID is composed from two
numbers, one identifying the service associated characterization with the parameter
(the <service_number>), and the other (the <parameter_number>)
identifying the parameter itself. <parameter_number> values for the
parameters made available by
those services. However, there defined in this document are some quantities of interest assigned from the "general
parameters" range (1 - 127). Numbers in this range indicate that
are not the
parameter definition is shared by all QoS control services.

NOTE: Parameters numbered 128 - 254 have definitions specific to a
particular quality of QoS control service. These "general"
characterizations are described in this document.

Characterization In contrast to the general
parameters are named using a scheme described in
[1]. Each here, the parameter's meaning depends on the
service_number portion of the parameter ID.

Service number 1 is identified by a service_name reserved for use as described in Section 2 of
this note. Service numbers 2 through 254 will be allocated to
individual QoS control services. Currently, Guaranteed service
[RFCG] is allocated number 2, and Controlled-load service [RFCCL]
is allocated number 5.

In this note, the textual form

<service_number, parameter_number>

is used to write a
parameter_within_service field. service_number, parameter_number pair. The service-name associated with
general characterization parameters is 0. range
of possible of service_number and parameter_number values specified
in [RFCTEMPLATE] allow the parameter ID to directly form the tail
portion of a MIB object ID representing the parameter. This
simplifies the task of making parameter values available to network
management applications.

The
parameter_within_service value for definition of each parameter defined in this
document is given below.

Parameters described here are of used to characterize a path through
the network describes two types; types of values; local or and composed. Local
parameters
values reflect a value exported by conditions at a single network element. Composed parameters
values reflect the running composition of local
parameters values along a path,
as specified by a composition rule. The
definition of each Each parameter also definition
specifies the composition rule.

Both local and composed parameters are named so rule for that a network
management entity can request parameter. The composition
rule describes how to combine the arriving composed value of either a and the
local or path- value, to give a new composed parameter at any point within value which is passed to the network. next
network element in the path. Note that a particular service the composition may specify a service_specific
parameter which overrides a general proceed
either downstream, toward the receiver(s), or upstream, toward the
sender. Each parameter with may give only one definition for the same
information. For example, a service local
value, but may allow network elements to
specify a MTU give more than one definition for packets requesting that service which composition rules
and composed values. This is smaller
than because it may be useful to compose the physical MTU supported by
same local value several times following different composition rules.

Because characterization parameters are used to compute the network element.

Conceptually,
properties of a specific path through the internetwork, all
characterization parameter definitions are "per-
next-hop" conceptually "per-next-
hop", as opposed to "per interface" or "per network element". In
cases where the network element is a (or is controlling) a shared media
path,
or large-cloud subnet, the element may need to provide different
values for different next-hops. In some cases, parameter definitions practice, it may include be appropriate
for vendors to choose and document a tolerance range, such that if
all next-hop values are within the tolerance range only a single
value need be stored and provided.

This document is not yet stable,

Local and should not be taken composed characterization parameter values have distinct
ID's so that a network management entity can request the value of
either a local or path-composed parameter at any point within the
network.

Each parameter definition includes a description of the minimal
properties, such as range and precision, required of any wire
representation of that parameter's values. Each definition also
includes an
implementation specification.

Parameter Definitions

Number XDR [RFCXDR] description of IS Hops

IS stands the parameter, describing an
appropriate external (wire) data representation for "integrated services aware". An integrated services
aware network element the parameter's
values. This dual definition is one that conforms intended to encourage a common wire
representation format whenever possible, while still allowing other
representations when required by the various
requirements specific circumstances (e.g.,
ASN.1 within SNMP).

The message formats specified in [RFCRSVPUSE] for use with the RSVP
setup protocol use the XDR data representation parameters.

All of the parameters described in this document note are mandatory, in the
sense that a network element claiming to support integrated service
must recognize arriving values in setup and management protocol
messages, process them correctly, and export a reasonable value in
response. For certain parameters, it is required that the documents [1-3]. (The network
element need not offer those services, but if compute and export an *accurate* local value. For other
parameters, it does is acceptable for the network element to indicate that
it
supports cannot compute and characterizes export an accurate local value. The definition
of these parameters provides a reserved value which indicates
"indeterminate" or "invalid". This value signals that an element
cannot process the services parameter accurately, and consequently that the
result of the end-to-end composition is also questionable.

NOTE (temporary): Previous versions of this and the RSVP use
document used both the reserved-value approach and a separate
INVALID flag to record this fact. Now, the reserved-value
approach is used exclusively. This is so that any protocol which
retrieves a parameter value, including SNMP, can carry the invalid
indication without needing a separate flag. The INVALID flag
remains in conformance the RSVP message format but is reserved for use only
with a possible future service-composition scheme.

2. Default and Service-Specific Values for General Parameters

General parameters have a common *definition* across all QoS control
services. Frequently, the
relevant specification). The local same *value* of a general parameter always has will be
correct for all QoS control services supported at a network element.
In this circumstance, there is no need to export a separate copy of
the value for each QoS control service; instead the node can export
one copy which applies to all supported services.

A general parameter value which applies to all services supported at
a network node is called a default or global value. For example, if
all of 1. the QoS control services provided at a node support the same
maximum packet size, the node may export a single default value for
the PATH_MTU parameter described in Section 3, rather than providing
a separate copy of the value for each QoS control service. In the
common case, this reduces both message size and processing overhead
for the setup protocol.

Occasionally an individual service needs to report a value differing
from the default value for a particular general parameter. For completeness,
example, if the local implementation of Guaranteed Service [RFCG] at a
router is restricted by scheduler or hardware considerations to a
maximum packet size smaller than supported by the router's best-
effort forwarding path, the implementation may wish to export a
"service-specific" value of the PATH_MTU parameter so that
applications using the Guaranteed service will function correctly.
In the example above, the router might supply a value of 1500 for the
default PATH_MTU parameter, and a value of 250 for the PATH_MTU
parameter applying to guaranteed service. In this case, the setup
protocol providing path characterization carries (and delivers to the
application) both a value for Guaranteed service and a value for
other services.

The distinction between default and service-specific parameter values
makes no sense for non-general parameters (those defined by a
specific QoS control service, rather than this note), because both
the definition and value of the parameter are always specific to the
particular service.

The distinction between default and service-specific values for
general parameters is assigned reflected in the parameter_name
1. parameter ID name space. This
allows network nodes, setup protocols, and network management tools
to distinguish default from service-specific values, and to determine
which service a service-specific parameter value is associated with.

Service number 1 is used to indicate the default value. A parameter
value identified by the ID:

<1, parameter_number>

is a default value, which applies to all services unless it is
overridden by a service-specific value for the same parameter.

A parameter value identified by the ID:

<service_number, parameter_number>

where service_number is not equal to 1, is a service-specific value.
It applies only to the service identified by service_number.

These service-specific values are also called override values. When
both service-specific and default values are present for a parameter,
the service-specific value overrides the default value (for the
service to which it applies). The composition rule rules for composing service-
specific and global general parameters support this override
capability. The basic rule is to use the service-specific value if
it exists, and otherwise the global value.

A complete summary of the characterization parameter composition
process is given below. In this summary, the "arriving value" is the
incompletely composed parameter value arriving from a neighbor node.
The "local value" is the (global or service-specific) value made
available by the local node. The "result" is the newly composed value
to be sent to increment the counter next node on the data path.

1. Examine the <service_number, parameter_number> pair associated
with the arriving value. This information is conveyed by one at each IS-aware the setup
protocol together with the arriving value.

2. If the arriving value is for a parameter specific to a single
service (the parameter_number is larger than 128), compose the
arriving value with the locally value exported by the specified
service, and pass the result to the next hop. This quantity, when composed end-to-end,
informs

3. If the endpoint arriving value is a service-specific value for a general
parameter (the parameter_number is 127 or less, and the
service_number is other than 1), and the local implementation of
that service also exports a service-specific value for the number
parameter, compose the service-specific arriving value and the
service-specific local value of Integrated-Services aware
network elements traversed along the path from sender parameter, and pass the result
as a service-specific value to receiver.
The parameter_name the next-hop node.

4. If the arriving value is a service-specific value for a general
parameter (the parameter_number is 127 or less, and the
service_number is other than 1), and the local implementation of
that service does *not* export a service-specific value, compose
the service-specific arriving value with the global value for that
parameter exported by the local node, and pass the result as a
service-specific value to the next-hop node.

5. If the arriving value is a global value for a general parameter
(parameter_number is 127 or less, and the service_number is 1), and
the local implementation of *any* service exports a service-
specific value for that general parameter, compose the arriving
(global) value with the service-specific value for that parameter
exported by the local service, and pass the result as a service-
specific value to the next-hop node. This will require adding a new
data field to the message passed to the next hop, to hold the newly
generated service-specific value. Repeat this composed process for each
service that exports a service-specific value for the parameter.

6. If the arriving value is a global value for a general parameter
(the service_number is 2. The 1, and the parameter_number is 127 or less),
compose the arriving (global) value with the global parameter
may be represented value
exported by the local node, and pass the result as a single 16-bit unsigned integer global
(service 1) value to the next-hop node. This step is performed
whether or not any service-specific values were generated and
exported in network
byte order.

Non-IS hop encountered step 5.

3. General Parameter Definitions
3.1 NON-IS_HOP flag

For each outgoing path from a parameter

This parameter provides information about the presence of network element,
elements which do not implement QoS control services along the data
path.

The local value of the parameter is
0 1 if the network element is certain does not
implement the relevant QoS control service, or knows that there exists no is a
break in the
QoS control services between itself and the next IS-aware network
element on chain of elements which implement the path. service. The
local parameter is 1 0 otherwise. The local parameter is assigned parameter_name 3.
parameter_number 1.

The actual responsibility composition rule for computing this parameter is the OR function. A
composed parameter value of the local
parameter 1 arriving at the endpoint of a path
indicates that at least one point along the path does not offer the
indicated QoS control service. The parameter_number for the composed
quantity is 2.

The global NON_IS_HOP flag parameter thus has the ID <1,2>. If this
flag is set, it indicates that one or more network node elements along the
application's data path does not support the integrated services
framework at all. An example of such an element would be an IP router
offering only best-effort packet delivery and not supporting any
resource reservation requests.

Obviously, a network element which does not support this
specification will not know to set this flag. The actual
responsibility for determining that a network node does not support
integrated services may fall to the network element, the setup
protocol, or a manual configuration operation. operation and is dependent on
implementation and usage. This calculation must be conservative.
For example, a router sending packets into an IP tunnel must assume
that the tunneled packets will not receive QoS control services
unless it or the setup protocol can prove otherwise.

The composition rule for this parameter is the OR function. A
composed parameter value

Service-specific versions of 1 arriving at the endpoint of NON_IS_HOP flag indicate that one or
more network elements along a path don't support the particular
service. For example, the flag parameter identified by ID <2,2> being
set indicates that at least one point some network element along the path does not offer QoS
control services. The parameter_name for
support the composed quantity is 4.

These characterization parameters may be represented Guaranteed service, though it might support another
service such as 16-bit
unsigned integers in network byte order. Controlled-Load.

If the Non-IS-hop global NON_IS_HOP flag <1,2> is set for a path, the receiver
(network element or application) should consider the values of all
other parameters defined in this specification specification, including service-
specific NON_IS_HOP flags, as possibly inaccurate. If a service
specific NON_IS_HOP flag is set for a path, the receiver should
consider the values of all other parameters associated with that
service as possibly inaccurate.

The NON_IS_HOP parameter may be represented in any form which can
express boolean true and false. However, note that a network element
must set this flag precisely when it does *not* fully understand the
format or data representation of an arriving protocol message
(because it does not support the specified service). Therefore, the
data representation used for this parameter by setup and management
protocols must allow the parameter value to be considered
approximate.

NOTE: The previous version read and set even if
the network element cannot otherwise parse the protocol message.

An appropriate XDR description of this document defined parameter is:

bool NON_IS_HOP;

However, the standard XDR data encoding for this description will not
meet the requirement described above unless other restrictions are
placed on message formats. An alternative data representation may be
more appropriate.

NOTE: The message format described for RSVP in [RFCRSVPUSE] carries
this parameter as a count. Discussion within single-bit flag, referred to as the intserv and RSVP
groups suggests "break
bit".

3.2 NUMBER_OF_IS_HOPS

IS stands for "integrated services aware". An integrated services
aware network element is one that accurately counting non-IS hops conforms to the various
requirements described in all
situations is both difficult this and unnecessary.

Minimum Available Path Bandwidth other referenced documents. The
network element need not offer a specific service, but if it does it
must support and characterize the service in conformance with the
relevant specification, and if it does not it must correctly set the
NON_IS_HOP flag parameter for the service. For completeness, the
local parameter is assigned the parameter_number 3.

The composition rule for this parameter is to increment the counter
by one at each IS-aware hop. This quantity, when composed end-to-
end, informs the endpoint of the number of integrated-services aware
network elements traversed along the path. The parameter_number for
this composed parameter is 4.

Values of the composed parameter will range from 1 to 255, limited by
the bound on IP hop count.

The XDR representation of this parameter is:

unsigned int NUMBER_OF_IS_HOPS;

3.3. AVAILABLE_PATH_BANDWIDTH

This parameter provides information about the bandwidth available
along the path followed by a data flow. The local parameter is an
estimate of the minimum bandwidth the network element
makes has available to for
packets following the path. The Computation of the value of this
parameter must be as accurate as possible, should take into account all information available to the
network element about the path, taking into consideration
administrative and policy controls on bandwidth, as well as physical
resources. Computation of the value of this

NOTE: This parameter should take
into account all information reflect, as closely as possible, the
actual bandwidth available to packets following a path. However,
the bandwidth available may depend on a number of factors not
known to the network element about until a specific QoS request is in
place, such as the path. If destination(s) of the value packet flow, the service
to be requested by the flow, or external policy information
associated with a reservation request. Because the parameter must
in fact be provided before any specific QoS request is made, it is
frequently difficult to provide the parameter accurately. In
circumstances where the parameter cannot be calculated exactly, provided accurately,
the result network element should err on make the best attempt possible, but is
permitted to overestimate the side available bandwidth by a significant
amount.

The parameter_number for AVAILABLE_PATH_BANDWIDTH is 5. The global
parameter <1, 5> is an estimate of underestimating the bandwidth available bandwidth. to any
packet following the path, without consideration of which (if any)
QoS control service the packets may be subject to.

In cases where a particular service is administratively or
implementationally restricted to a limited portion of the overall
available bandwidth, the service module may wish to export an
override parameter which specifies this smaller bandwidth value.

The composition rule for this parameter is the MIN() function; the MIN function. The
composed value is the minimum of the network element's value and the
previously composed value. This quantity, when composed end-to-end,
informs the endpoint of the minimal bandwidth link along the path
from sender to receiver. The parameter_name for the bandwidth of the
network element is 4. The parameter_name parameter_number for the composed
minimal bandwidth along the path is 5.

These values 6.

Values of this parameter are measured in bytes per second, and can range second. The
representation must be able to express values ranging from 1 byte per
second to as large as 40 terabytes per second (or second, about what is believed to be the
maximum theoretical bandwidth of a single strand of fiber). Clearly, particularly fiber.
Particularly for large bandwidths, only the first few digits are significant and
significant, so the use of a floating point
representations, representation, accurate
to at least 0.1% 0.1%, is encouraged. These
characterizations

The XDR representation for this parameter is:

float AVAILABLE_PATH_BANDWIDTH;

For values of bandwidth can be represented by floating point
numbers in single-precision IEEE this parameter only valid non-negative floating point format. Only bit
patterns representing valid zero or positive floating-point
numbers are allowed. Bit patterns representing negative numbers, NAN's, or Negative numbers (including "negative zero" zero"),
infinities, and NAN's are illegal. not allowed.

NOTE: This parameter should reflect, as much as possible, policy
and administrative restrictions on bandwidth available to a path.
However, the actual value available An implementation which utilizes general-purpose hardware or
software IEEE floating-point support may depend on a number of
factors not available wish to verify that
arriving parameter values meet these requirements before using the network element, such as the
destination(s) of the packet flow, the service
values in floating-point computations, in order to be requested by
the flow, avoid
unexpected exceptions or external policy information associated with a
reservation request. This makes it difficult to provide traps.

If the
parameter accurately. Generally, a network element expected cannot or wishes not to provide an accurate estimate of
path bandwidth, it may export a local value of zero for this parameter would have to have in
hand all of the information necessary to process a resource
reservation request. In circumstances where the parameter cannot
be provided accurately, the
parameter. A network element or application receiving a composed
value of zero for this parameter should come as close
as possible, but assume that the actual
bandwidth available is not expected to be either "conservative"
(consistantly estimating low) or "liberal" (consistantly
estimating high).

Minimum Path Latency unknown.

3.4 MINIMUM_PATH_LATENCY

The local parameter is the latency of the link packet forwarding process
associated with the network element, where the latency is defined to
be the minimal *minimal* possible packet delay along the path taken added by the flow. network element
This delay may result from "speed-of-light" speed-of-light propagation delay, from
packet processing limitations, or both. It does not include any
variable queuing delay which may be present.

The purpose of this parameter is to provide a baseline minimal path
latency for use with services which provide estimates or bounds on
additional path delay, such as Guaranteed [RFCG]. In conjunction
with the queuing delay bound offered by Guaranteed and similar
services, this parameter gives the application knowledge of both the
minimum and maximum packet delivery delay. Knowing both the minimum
and maximum latency experienced by data packets allows the receiving
application to accurately compute its de-jitter buffer requirements.

Note that the quantity characterized by this parameter is the
absolute lower bound on the packet processing and transmission
latency of the network element. This value is the quantity required
to provide jitter bounding. The parameter does *not* provide the type
of upper-bound estimate on minimum latency which might be of interest
for best-effort traffic and QoS control services which do not
explicitly offer delay bounds. That is, the parameter will always
underestimate, rather than overestimate, latency, particularly in
multicast and large cloud situations.

When packets leaving traversing a network element may follow experience different paths,
such as virtual circuits within
minimal latencies, this parameter should ideally report an ATM cloud, different accurate
latency
values must be provided value for different paths. each path. For example, when an ATM point-
multipoint virtual circuit is used to implement IP multicast, the
mechanism used to implement this parameter would ideally compute a
separate value for each destination. Doing so may require cooperation
between the ingress and egress elements bounding a the multi-path
communication cloud. The method by which this cooperation is
achieved, and the choice of which IP-level network element actually
provides and composes the value, is technology-dependent.

An alternative choice is acceptable to provide a single value for multiple paths if the
latency values same value of this parameter
for all paths are within 10 percent or 100 microseconds
of each other, whichever is greater.

In certain cases determining through the correct latency cloud. The value to report is
extremely difficult. For instance, reported must be the speed-of-light delays on
smallest latency for any possible path. Note that in this situation,
QoS control services (e.g., Guaranteed) which provide an
ethernet bridged via satellite with another ethernet vary upper bound
on latency cannot simply add their queuing delay to the value
computed by several
orders of magnitude. this parameter; they must also compensate for path delays
above the minimum. In a case such as this case the network element may
either employ a latency estimation protocol, return range between the best-case
(longest) minimum latency between any two nodes using and
maximum packet delays reported to the shared
resource, or return application will be larger,
because the application will be told about the minimum delay along
the shortest path and the maximum delay along the actual path. This
is acceptable in many situations.

A third alternative is to report the "indeterminate" value, as
specified below.

NOTE: This parameter represents the "minimal minimum" path
latency. In a shared-media situation it should represent the
shortest latency between the local node and any other. The
rationale for this is that circumstance the parameter is intended for use with
services such as Guaranteed [ref] which provide client application may
either deduce a means to
advertise additional minimum path latency above the minimum. through measurement, or assume a
value of zero.

The composition rule for this parameter is summation with a clamp of
(2**32 - 1) on the maximum value. This quantity, when composed end-
to-end, informs the endpoint of the minimal packet delay along the
path from sender to receiver. The parameter_name parameter_number for the latency of
the network element's link is 6. 7. The parameter_name parameter_number for the
cumulative latency along the path is 7. 8.

The delays latencies are measured in units of one microsecond. An individual
element can advertise a delay latency value between 1 and 2**28 (somewhat
over two minutes) and the total delay latency added across all elements can
range as high as (2**32)-2. Should the sum of the different elements
delay exceed (2**32)-2, the end-to-end advertised delay should be
(2**32)-1.
reported as indeterminate. This value is explained in the next paragraph.

The value (2**32)-1 is taken to mean "indeterminate latency". A
network element which cannot accurately predict the latency of
packets it is processing should set its local parameter to this
value. Because the composition function limits the composed sum to
this value, presence of this value at the end-point of the path
indicates that the true path latency is not known. This may happen
because one or more network elements could not supply a value, or
because the range of the composition calculation was exceeded. described below.

Note that while the granularity of measurement is microseconds, a
conforming element is free to measure delays more loosely. The
minimum requirement is that the element estimate its delay accurately
to the nearest 100 microsecond granularity. Elements that can measure
more accurately are, of course, encouraged to do so.

NOTE: Measuring in milliseconds is not acceptable, because if the
minimum delay value is a millisecond, a path with several hops
will lead to a composed delay of at least several milliseconds,
which is likely to be misleading.

The characterization parameters may be represented as 32-bit XDR description of this parameter is:

unsigned
integers in int MINIMUM_PATH_LATENCY;

The distinguished value (2**32)-1 is taken to mean "indeterminate
latency". A network byte order.

Path element which cannot accurately predict the
latency of packets it is processing should set its local parameter to
this value. Because the composition function limits the composed sum
to this value, receipt of this value at a network element or
application indicates that the true path latency is not known. This
may happen because one or more network elements could not supply a
value, or because the range of the composition calculation was
exceeded.

3.5. PATH_MTU

This parameter computes the maximum transmission unit (MTU) for
packets following a data path. This value is required to invoke QoS
control services which require that IP packet size be strictly
limited to a specific MTU. Existing MTU discovery mechanisms cannot
be used because they provide information only to the sender and they
do not directly allow for QoS control services to specify MTU's
smaller than the physical MTU.

The local characterization parameter is the path IP MTU, where the MTU of
a network element is defined to be the maximum transmission unit the
network element can accommodate without fragmentation fragmentation, including IP
and upper-layer protocol headers, headers but not including link level
headers. The composition rule is to take the minimum of the network
element's MTU and the previously composed value. This quantity, when
composed end-to-end, informs the endpoint of the maximum transmission
unit that can traverse the path from sender to receiver without
fragmentation. The parameter_name parameter_number for the MTU of the network
element's link is 8. 9. The parameter_name parameter_number for the composed MTU along
the path is 9.

Service Availability 10.

A correct and valid value of this parameter must be provided by all
IS-aware network elements.

A specific service module may specify an MTU smaller than that of the
overall network element by overriding this parameter with one giving
the service's MTU value. A service module may not specify an MTU
value larger than that given by the global parameter.

Values of this parameter are measured in bytes. The INT SERV working group representation
must be able to express values ranging from 1 byte to 2**32-1 bytes.

The XDR description of this parameter is:

unsigned int PATH_MTU;

3.6. TOKEN_BUCKET_TSPEC

This parameter is still developing proposals used to describe data traffic parameters using a
simple token bucket filter. This parameter is used by data senders to
describe the traffic parameters of traffic it expects to generate,
and by QoS control services to describe the parameters of traffic for handling
heterogeneity. When that work
which the reservation should apply. It is complete, defined as a general rather
than service-specific parameter because the same traffic description
may be used by several QoS control services in some situations.

The TOKEN_BUCKET_TSPEC parameter is assigned parameter_number 127.

The TOKEN_BUCKET_TSPEC takes the form of a token bucket specification
plus a peak rate p, minimum policed unit m, and a maximum packet size
M.

The token bucket specification includes an average or token rate r
and a bucket depth b. Both r and b must be positive.

The token rate r is measured in bytes of IP datagrams per second.
Values of this parameter may range from 1 byte per second to 40
terabytes per second. In practice, only the first few digits of the r
and p parameters are significant, so the use of floating point
representations, accurate to at least 0.1% is encouraged.

The bucket depth, b, is measured in bytes. Values of this parameter
may range from 1 byte to 250 gigabytes. In practice, only the first
few digits of the b parameter are significant, so the use of floating
point representations, accurate to at least 0.1% is encouraged.

The peak traffic rate p is measured in bytes of IP datagrams per
second. Values of this parameter may range from 1 byte per second to
40 terabytes per second. In practice, only the first few digits of
the r and p parameters are significant, so the use of floating point
representations, accurate to at least 0.1% is encouraged. The peak
rate value may be set to positive infinity, indicating that it is
unknown or unspecified.

The range of requirement values allowed for these parameters is intentionally
large to allow for future network technologies. Any particular
network element is not expected to support the full range of values.

The minimum policed unit, m, is an integer measured in bytes. All IP
datagrams less than size m will be counted against the token bucket
as being of size m. The maximum packet size, M, is the biggest packet
that will conform to the traffic specification; it is also measured
in bytes. Both m and M must be defined. positive, and m must be less then or
equal to M.

The XDR description of this parameter is:

struct {
float r;
float b;
float p;
unsigned m;
unsigned M;
} TOKEN_BUCKET_TSPEC;

For the fields r and b only valid non-negative floating point numbers
are allowed. Negative numbers (including "negative zero), infinities,
and NAN's are not allowed.

For the field p, only valid non-negative floating point numbers or
positive infinity are allowed. Negative numbers (including "negative
zero), negative infinities, and NAN's are not allowed.

NOTE: An implementation which utilizes general-purpose hardware or
software IEEE floating-point support may wish to verify that
arriving parameter values meet these requirements before using the
values in floating-point computations, in order to avoid
unexpected exceptions or traps.

4. Security Considerations

Security considerations are not discussed in this memo.

5. References

[1]

[RFCRSVP] B. Braden, et. al. "Resource Reservation Protocol (RSVP) -
Version 1 Functional Specification", Internet Draft, July 1996,
<draft-ietf-rsvp-spec-13.txt>

[RFCRSVPUSE] J. Wroclawski. "The Use of RSVP with IETF Integrated
Services", Internet Draft, October, 1996, <draft-ietf-intserv-rsvp-
use-01.txt>

[RFCTEMPLATE] S. Shenker and J. Wroclawski. "Network Element QoS
Control Service Specification Template", Template". Internet Draft, June 1995, <draft-ietf-
intserv-svc-template-01.txt>

[3] October
1996, <draft-ietf-intserv-svc-template-03.txt>

[RFCG] S. Shenker and Shenker, C. Partridge. Specification Partridge, and R Guerin. "Specification of the
Guaranteed Quality of Service", Internet Draft, June July 1996, <draft-ietf-intserv-
guaranteed-svc-04.txt>

[3] <draft-
ietf-intserv-guaranteed-svc-06.txt>

[RFCCL] J. Wroclawski. "Specification of the Controlled Load Quality
of Service", Internet Draft, November 1995, July 1996, <draft-ietf-intserv-ctrl-
load-svc-01.txt>
load-svc-03.txt>

[RFCXDR] R. Srinivansan. "XDR: External Data Representation
Standard", RFC 1832, August 1995.

Author's Address:

Scott Shenker
Xerox PARC
3333 Coyote Hill Road
Palo Alto, CA 94304-1314
shenker@parc.xerox.com
415-812-4840
415-812-4471 (FAX)

John Wroclawski
MIT Laboratory for Computer Science
545 Technology Sq.
Cambridge, MA 02139
jtw@lcs.mit.edu
617-253-7885
617-253-2673 (FAX)