💾 Archived View for gmi.noulin.net › rfc › rfc2815.gmi captured on 2023-01-29 at 23:15:31. Gemini links have been rewritten to link to archived content
⬅️ Previous capture (2021-12-05)
-=-=-=-=-=-=-
Keywords: LAN, local area network, resource, reservation
Network Working Group M. Seaman
Request for Comments: 2815 Telseon
Category: Standards Track A. Smith
Extreme Networks
E. Crawley
Unisphere Solutions
J. Wroclawski
MIT LCS
May 2000
Integrated Service Mappings on IEEE 802 Networks
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.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document describes mappings of IETF Integrated Services over
LANs built from IEEE 802 network segments which may be interconnected
by IEEE 802.1D MAC Bridges (switches). It describes parameter
mappings for supporting Controlled Load and Guaranteed Service using
the inherent capabilities of relevant IEEE 802 technologies and, in
particular, 802.1D-1998 queuing features in switches.
These mappings are one component of the Integrated Services over IEEE
802 LANs framework.
Seaman, et al. Standards Track [Page 1]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
Table of Contents
1 Introduction ............................................... 2
2 Flow Identification and Traffic Class Selection ............ 3
3 Choosing a flow's IEEE 802 user_priority class ............. 5
3.1 Context of admission control and delay bounds ............ 6
3.2 Default service mappings ................................. 7
3.3 Discussion ............................................... 9
4 Computation of integrated services characterization parameters
by IEEE 802 devices .....................................10
4.1 General characterization parameters ......................10
4.2 Parameters to implement Guaranteed Service ...............11
4.3 Parameters to implement Controlled Load ..................11
4.4 Parameters to implement Best Effort ......................12
5 Merging of RSVP/SBM objects ................................12
6 Applicability of these service mappings ....................13
7 References .................................................14
8 Security Considerations ....................................15
9 Acknowledgments ............................................15
10 Authors' Addresses ........................................16
11 Full Copyright Statement ..................................17
1. Introduction
The IEEE 802.1 Interworking Task Group has developed a set of
enhancements to the basic MAC Service provided in Bridged Local Area
Networks (a.k.a. "switched LANs"). As a supplement to the original
IEEE MAC Bridges standard, IEEE 802.1D-1990 [802.1D-ORIG], the
updated IEEE 802.1D-1998 [802.1D] proposes differential traffic class
queuing in switches. The IEEE 802.1Q specification [802.1Q] extends
the capabilities of Ethernet/802.3 media to carry a traffic class
indicator, or "user_priority" field, within data frames.
The availability of this differential traffic queuing, together with
additional mechanisms to provide admission control and signaling,
allows IEEE 802 networks to support a close approximation of the IETF
Integrated Services capabilities [CL][GS]. This document describes
methods for mapping the service classes and parameters of the IETF
model into IEEE 802.1D network parameters. A companion document
[SBM] describes a signaling protocol for use with these mappings. It
is recommended that readers be familiar with the overall framework in
which these mappings and signaling protocol are expected to be used;
this framework is described fully in [IS802FRAME].
Within this document, Section 2 describes the method by which end
systems and routers bordering the IEEE Layer-2 cloud learn what
traffic class should be used for each data flow's packets. Section 3
describes the approach recommended to map IP-level traffic flows to
Seaman, et al. Standards Track [Page 2]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
IEEE traffic classes within the Layer 2 network. Section 4 describes
the computation of Characterization Parameters by the layer 2
network. The remaining sections discuss some particular issues with
the use of the RSVP/SBM signaling protocols, and describe the
applicability of all of the above to different layer 2 network
topologies.
2. Flow Identification and Traffic Class Selection
One model for supporting integrated services over specific link
layers treats layer-2 devices very much as a special case of routers.
In this model, switches and other devices along the data path make
packet handling decisions based on the RSVP flow and filter
specifications, and use these specifications to classify the
corresponding data packets. The specifications could either be used
directly, or could be used indirectly by mapping each RSVP session
onto a layer-2 construct such as an ATM virtual circuit.
This approach is inappropriate for use in the IEEE 802 environment.
Filtering to the per-flow level becomes expensive with increasing
switch speed; devices with such filtering capabilities are likely to
have a very similar implementation complexity to IP routers, and may
not make use of simpler mechanisms such as 802.1D user priority.
The Integrated Services over IEEE 802 LANs framework [IS802FRAME] and
this document use an "aggregated flow" approach based on use of
layer-2 traffic classes. In this model, each arriving flow is
assigned to one of the available classes for the duration of the flow
and traverses the 802 cloud in this class. Traffic flows requiring
similar service are grouped together into a single class, while the
system's admission control and class selection rules ensure that the
service requirements for flows in each of the classes are met. In
many situations this is a viable intermediate point between no QoS
control and full router-type integrated services. The approach can
work effectively even with switches implementing only the simplest
differential traffic classification capability specified in the
802.1D model. In the aggregated flow model, traffic arriving at the
boundary of a layer-2 cloud is tagged by the boundary device (end
host or border router) with an appropriate traffic class, represented
as an 802.1D "user_priority" value. Two fundamental questions are
"who determines the correspondence between IP-level traffic flows and
link-level classes?" and "how is this correspondence conveyed to the
boundary devices that must mark the data frames?"
One approach to answering these questions would be for the meanings
of the classes to be universally defined. This document would then
standardize the meanings of a set of classes; e.g., 1 = best effort,
2 = 100 ms peak delay target, 3 = 10 ms peak delay target, 4 = 1 ms
Seaman, et al. Standards Track [Page 3]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
peak delay target, etc. The meanings of these universally defined
classes could then be encoded directly in end stations, and the
flow-to-class mappings computed directly in these devices.
This universal definition approach would be simple to implement, but
is too rigid to map the wide range of possible user requirements onto
the limited number of available 802.1D classes. The model described
in [IS802FRAME] uses a more flexible mapping: clients ask "the
network" which user_priority traffic class to use for a given traffic
flow, as categorized by its flow-spec and layer-2 endpoints. The
network provides a value back to the requester that is appropriate
considering the current network topology, load conditions, other
admitted flows, etc. The task of configuring switches with this
mapping (e.g., through network management, a switch-switch protocol
or via some network-wide QoS-mapping directory service) is an order
of magnitude less complex than performing the same function in end
stations. Also, when new services (or other network reconfigurations)
are added to such a network, the network elements will typically be
the ones to be upgraded with new queuing algorithms etc. and can be
provided with new mappings at this time.
In the current model it is assumed that all data packets of a flow
are assigned to the same traffic class for the duration of the flow:
the characteristics of the MAC service, as defined by Clause 6 of
[802.1D], then ensure the ordering of the data packets of the flow
between adjacent Layer 3 routers. This is usually desirable to avoid
potential re-ordering problems as discussed in [IS802FRAME] and [CL].
Note that there are some scenarios where it might be desirable to
send conforming data traffic in one traffic class and non-conforming
traffic for the same flow in a different, lower traffic class: such a
division into separate traffic classes is for future study. When a
new session or "flow" requiring QoS support is created, a client must
ask "the network" which traffic class (IEEE 802 user_priority) to use
for a given traffic flow, so that it can label the packets of the
flow as it places them into the network. A request/response protocol
is needed between client and network to return this information. The
request can be piggy-backed onto an admission control request and the
response can be piggy-backed onto an admission control
acknowledgment. This "one pass" assignment has the benefit of
completing the admission control transaction in a timely way and
reducing the exposure to changing conditions that could occur if
clients cached the knowledge for extensive periods. A set of
extensions to the RSVP protocol for communicating this information
have been defined [SBM].
The network (i.e., the first network element encountered downstream
from the client) must then answer the following questions:
Seaman, et al. Standards Track [Page 4]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
1. Which of the available traffic classes would be appropriate for
this flow?
In general, a newly arriving flow might be assigned to a number
of classes. For example, if 10ms of delay is acceptable, the
flow could potentially be assigned to either a 10ms delay class
or a 1ms delay class. This packing problem is quite difficult to
solve if the target parameters of the classes are allowed to
change dynamically as flows arrive and depart. It is quite
simple if the target parameters of each class is held fixed, and
the class table is simply searched to find a class appropriate
for the arriving flow. This document adopts the latter
approach.
2. Of the appropriate traffic classes, which if any have enough
capacity available to accept the new flow?
This is the admission control problem. It is necessary to
compare the level of traffic currently assigned to each class
with the available level of network resources (bandwidth,
buffers, etc), to ensure that adding the new flow to the class
will not cause the class's performance to go below its target
values. This problem is compounded because in a priority queuing
system adding traffic to a higher-priority class can affect the
performance of lower-priority classes. The admission control
algorithm for a system using the default 802 priority behavior
must be reasonably sophisticated to provide acceptable results.
If an acceptable class is found, the network returns the chosen
user_priority value to the client.
Note that the client may be an end station, a router at the edge of
the layer 2 network, or a first switch acting as a proxy for a device
that does not participate in these protocols for whatever reason.
Note also that a device e.g., a server or router may choose to
implement both the "client" as well as the "network" portion of this
model so that it can select its own user_priority values. Such an
implementation would generally be discouraged unless the device has a
close tie-in with the network topology and resource allocation
policies. It may, however, work acceptably in cases where there is
known over-provisioning of resources.
3. Choosing a flow's IEEE 802 user_priority class
This section describes the method by which IP-level flows are mapped
into appropriate IEEE user_priority classes. The IP-level services
considered are Best Effort, Controlled Load, and Guaranteed Service.
Seaman, et al. Standards Track [Page 5]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
The major issue is that admission control requests and application
requirements are specified in terms of a multidimensional vector of
parameters e.g., bandwidth, delay, jitter, service class. This
multidimensional space must be mapped onto a set of traffic classes
whose default behavior in L2 switches is unidimensional (i.e., strict
priority default queuing). This priority queuing alone can provide
only relative ordering between traffic classes. It can neither
enforce an absolute (quantifiable) delay bound for a traffic class,
nor can it discriminate amongst Int-Serv flows within the aggregate
in a traffic class. Therefore, it cannot provide the absolute control
of packet loss and delay required for individual Int-Serv flows.
To provide absolute control of loss and delay three things must
occur:
(1) The amount of bandwidth available to the QoS-controlled flows
must be known, and the number of flows admitted to the network
(allowed to use the bandwidth) must be limited.
(2) A traffic scheduling mechanism is needed to give preferential
service to flows with lower delay targets.
(3) Some mechanism must ensure that best-effort flows and QoS
controlled flows that are exceeding their Tspecs do not damage
the quality of service delivered to in-Tspec QoS controlled
flows. This mechanism could be part of the traffic scheduler, or
it could be a separate policing mechanism.
For IEEE 802 networks, the first function (admission control) is
provided by a Subnet Bandwidth Manager, as discussed below. We use
the link-level user_priority mechanism at each switch and bridge to
implement the second function (preferential service to flows with
lower delay targets). Because a simple priority scheduler cannot
provide policing (function three), policing for IEEE networks is
generally implemented at the edge of the network by a layer-3 device.
When this policing is performed only at the edges of the network it
is of necessity approximate. This issue is discussed further in
[IS802FRAME].
3.1. Context of admission control and delay bounds
As described above, it is the combination of priority-based
scheduling and admission control that creates quantified delay
bounds. Thus, any attempt to quantify the delay bounds expected by a
given traffic class has to made in the context of the admission
control elements. Section 6 of the framework [IS802FRAME] provides
for two different models of admission control - centralized or
distributed Bandwidth Allocators.
Seaman, et al. Standards Track [Page 6]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
It is important to note that in this approach it is the admission
control algorithm that determines which of the Int-Serv services is
being offered. Given a set of priority classes with delay targets, a
relatively simple admission control algorithm can place flows into
classes so that the bandwidth and delay behavior experienced by each
flow corresponds to the requirements of the Controlled-Load service,
but cannot offer the higher assurance of the Guaranteed service. To
offer the Guaranteed service, the admission control algorithm must be
much more stringent in its allocation of resources, and must also
compute the C and D error terms required of this service.
A delay bound can only be realized at the admission control element
itself so any delay numbers attached to a traffic class represent the
delay that a single element can allow for. That element may
represent a whole L2 domain or just a single L2 segment.
With either admission control model, the delay bound has no scope
outside of a L2 domain. The only requirement is that it be understood
by all Bandwidth Allocators in the L2 domain and, for example, be
exported as C and D terms to L3 devices implementing the Guaranteed
Service. Thus, the end-to-end delay experienced by a flow can only
be characterized by summing along the path using the usual RSVP
mechanisms.
3.2. Default service mappings
Table 1 presents the default mapping from delay targets to IEEE 802.1
user_priority classes. However, these mappings must be viewed as
defaults, and must be changeable.
In order to simplify the task of changing mappings, this mapping
table is held by *switches* (and routers if desired) but generally
not by end-station hosts. It is a read-write table. The values
proposed below are defaults and can be overridden by management
control so long as all switches agree to some extent (the required
level of agreement requires further analysis).
In future networks this mapping table might be adjusted dynamically
and without human intervention. It is possible that some form of
network-wide lookup service could be implemented that serviced
requests from clients e.g., traffic_class = getQoSbyName("H.323
video") and notified switches of what traffic categories they were
likely to encounter and how to allocate those requests into traffic
classes. Alternatively, the network's admission control mechanisms
might directly adjust the mapping table to maximize the utilization
of network resources. Such mechanisms are for further study.
Seaman, et al. Standards Track [Page 7]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
The delay bounds numbers proposed in Table 1 are for per-Bandwidth
Allocator element delay targets and are derived from a subjective
analysis of the needs of typical delay-sensitive applications e.g.,
voice, video. See Annex H of [802.1D] for further discussion of the
selection of these values. Although these values appear to address
the needs of current video and voice technology, it should be noted
that there is no requirement to adhere to these values and no
dependence of IEEE 802.1 on these values.
user_priority Service
0 Default, assumed to be Best Effort
1 reserved, "less than" Best Effort
2 reserved
3 reserved
4 Delay Sensitive, no bound
5 Delay Sensitive, 100ms bound
6 Delay Sensitive, 10ms bound
7 Network Control
Table 1 - Example user_priority to service mappings
Note: These mappings are believed to be useful defaults but
further implementation and usage experience is required. The
mappings may be refined in future editions of this document.
With this example set of mappings, delay-sensitive, admission
controlled traffic flows are mapped to user_priority values in
ascending order of their delay bound requirement. Note that the
bounds are targets only - see [IS802FRAME] for a discussion of the
effects of other non-conformant flows on delay bounds of other flows.
Only by applying admission control to higher-priority classes can any
promises be made to lower-priority classes.
This set of mappings also leaves several classes as reserved for
future definition.
Note: this mapping does not dictate what mechanisms or algorithms
a network element (e.g., an Ethernet switch) must perform to
implement these mappings: this is an implementation choice and
does not matter so long as the requirements for the particular
service model are met.
Note: these mappings apply primarily to networks constructed from
devices that implement the priority-scheduling behavior defined as
the default in 802.1D. Some devices may implement more complex
scheduling behaviors not based only on priority. In that
circumstance these mappings might still be used, but other, more
Seaman, et al. Standards Track [Page 8]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
specialized mappings may be more appropriate.
3.3. Discussion
The recommendation of classes 4, 5 and 6 for Delay Sensitive,
Admission Controlled flows is somewhat arbitrary; any classes with
priorities greater than that assigned to Best Effort can be used.
Those proposed here have the advantage that, for transit through
802.1D switches with only two-level strict priority queuing, all
delay-sensitive traffic gets "high priority" treatment (the 802.1D
default split is 0-3 and 4-7 for a device with 2 queues).
The choice of the delay bound targets is tuned to an average expected
application mix, and might be retuned by a network manager facing a
widely different mix of user needs. The choice is potentially very
significant: wise choice can lead to a much more efficient allocation
of resources as well as greater (though still not very good)
isolation between flows.
Placing Network Control traffic at class 7 is necessary to protect
important traffic such as route updates and network management.
Unfortunately, placing this traffic higher in the user_priority
ordering causes it to have a direct effect on the ability of devices
to provide assurances to QoS controlled application traffic.
Therefore, an estimate of the amount of Network Control traffic must
be made by any device that is performing admission control (e.g.,
SBMs). This would be in terms of the parameters that are normally
taken into account by the admission control algorithm. This estimate
should be used in the admission control decisions for the lower
classes (the estimate is likely to be a configuration parameter of
SBMs).
A traffic class such as class 1 for "less than best effort" might be
useful for devices that wish to dynamically "penalty tag" all of the
data of flows that are presently exceeding their allocation or Tspec.
This provides a way to isolate flows that are exceeding their service
limits from flows that are not, to avoid reducing the QoS delivered
to flows that are within their contract. Data from such tagged flows
might also be preferentially discarded by an overloaded downstream
device.
A somewhat simpler approach would be to tag only the portion of a
flow's packets that actually exceed the Tspec at any given instant as
low priority. However, it is often considered to be a bad idea to
treat flows in this way as it will likely cause significant re-
ordering of the flow's packets, which is not desirable. Note that the
default 802.1D treatment of user_priorities 1 and 2 is "less than"
the default class 0.
Seaman, et al. Standards Track [Page 9]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
4. Computation of integrated services characterization parameters by
IEEE 802 devices
The integrated service model requires that each network element that
supports integrated services compute and make available certain
"characterization parameters" describing the element's behavior.
These parameters may be either generally applicable or specific to a
particular QoS control service. These parameters may be computed by
calculation, measurement, or estimation. When a network element
cannot compute its own parameters (for example, a simple link), we
assume that the device sending onto or receiving data from the link
will compute the link's parameters as well as it's own. The accuracy
of calculation of these parameters may not be very critical; in some
cases loose estimates are all that is required to provide a useful
service. This is important in the IEEE 802 case, where it will be
virtually impossible to compute parameters accurately for certain
topologies and switch technologies. Indeed, it is an assumption of
the use of this model by relatively simple switches (see [IS802FRAME]
for a discussion of the different types of switch functionality that
might be expected) that they merely provide values to describe the
device and admit flows conservatively. The discussion below presents
a general outline for the computation of these parameters, and points
out some cases where the parameters must be computed accurately.
Further specification of how to export these parameters is for
further study.
4.1. General characterization parameters
There are some general parameters [GENCHAR] that a device will need
to use and/or supply for all service types:
* Ingress link
* Egress links and their MTUs, framing overheads and minimum packet
sizes (see media-specific information presented above).
* Available path bandwidth: updated hop-by-hop by any device along
the path of the flow.
* Minimum latency
Of these parameters, the MTU and minimum packet size information must
be reported accurately. Also, the "break bits" must be set correctly,
both the overall bit that indicates the existence of QoS control
support and the individual bits that specify support for a particular
scheduling service. The available bandwidth should be reported as
accurately as possible, but very loose estimates are acceptable. The
minimum latency parameter should be determined and reported as
Seaman, et al. Standards Track [Page 10]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
accurately as possible if the element offers Guaranteed service, but
may be loosely estimated or reported as zero if the element offers
only Controlled-Load service.
4.2. Parameters to implement Guaranteed Service
A network element supporting the Guaranteed Service [GS] must be able
to determine the following parameters:
* Constant delay bound through this device (in addition to any value
provided by "minimum latency" above) and up to the receiver at the
next network element for the packets of this flow if it were to be
admitted. This includes any access latency bound to the outgoing
link as well as propagation delay across that link. This value is
advertised as the 'C' parameter of the Guaranteed Service.
* Rate-proportional delay bound through this device and up to the
receiver at the next network element for the packets of this flow
if it were to be admitted. This value is advertised as the 'D'
parameter of the Guaranteed Service.
* Receive resources that would need to be associated with this flow
(e.g., buffering, bandwidth) if it were to be admitted and not
suffer packet loss if it kept within its supplied Tspec/Rspec.
These values are used by the admission control algorithm to decide
whether a new flow can be accepted by the device.
* Transmit resources that would need to be associated with this flow
(e.g., buffering, bandwidth, constant- and rate-proportional delay
bounds) if it were to be admitted. These values are used by the
admission control algorithm to decide whether a new flow can be
accepted by the device.
The exported characterization parameters for this service should be
reported as accurately as possible. If estimations or approximations
are used, they should err in whatever direction causes the user to
receive better performance than requested. For example, the C and D
error terms should overestimate delay, rather than underestimate it.
4.3. Parameters to implement Controlled Load
A network element implementing the Controlled Load service [CL] must
be able to determine the following:
* Receive resources that would need to be associated with this flow
(e.g., buffering) if it were to be admitted. These values are used
by the admission control algorithm to decide whether a new flow
can be accepted by the device.
Seaman, et al. Standards Track [Page 11]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
* Transmit resources that would need to be associated with this flow
(e.g., buffering) if it were to be admitted. These values are used
by the admission control algorithm to decide whether a new flow
can be accepted by the device.
The Controlled Load service does not export any service-specific
characterization parameters. Internal resource allocation estimates
should ensure that the service quality remains high when considering
the statistical aggregation of Controlled Load flows into 802 traffic
classes.
4.4. Parameters to implement Best Effort
For a network element that implements only best effort service there
are no explicit parameters that need to be characterized. Note that
an integrated services aware network element that implements only
best effort service will set the "break bit" described in
[RSVPINTSERV].
5. Merging of RSVP/SBM objects
Where reservations that use the SBM protocol's TCLASS object [SBM]
need to be merged, an algorithm needs to be defined that is
consistent with the mappings to individual user_priority values in
use in the Layer-2 cloud. A merged reservation must receive at least
as good a service as the best of the component reservations.
There is no single merging rule that can prevent all of the following
side-effects:
* If a merger were to demote the existing branch of the flow into a
higher-delay traffic class then this is a denial of service to the
existing flow which would likely receive worse service than
before.
* If a merger were to promote the existing branch of the flow into a
new, lower-delay, traffic class, this might then suffer either
admission control failures or may cost more in some sense than the
already-admitted flow. This can also be considered as a denial-
of-service attack.
* Promotion of the new branch may lead to rejection of the request
because it has been re-assigned to a traffic class that has not
enough resources to accommodate it.
Therefore, such a merger is declared to be illegal and the usual SBM
admission control failure rules are applied. Traffic class selection
is performed based on the TSpec information. When the first RESV for
Seaman, et al. Standards Track [Page 12]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
a flow arrives, a traffic class is chosen based on the request, an
SBM TCLASS object is inserted into the message and admission control
for that traffic class is done by the SBM. Reservation succeeds or
fails as usual.
When a second RESV for the same flow arrives at a different egress
point of the Layer-2 cloud the process starts to repeat. Eventually
the SBM-augmented RESV may hit a switch with an existing reservation
in place for the flow i.e., an L2 branch point for the flow. If so,
the traffic class chosen for the second reservation is checked
against the first. If they are the same, the RESV requests are merged
and passed on towards the sender(s).
If the second TCLASS would have been different, an RSVP/SBM ResvErr
error is returned to the Layer-3 device that launched the second RESV
request into the Layer-2 cloud. This device will then pass on the
ResvErr to the original requester according to RSVP rules. Detailed
processing rules are specified in [SBM].
6. Applicability of these service mappings
Switches using layer-2-only standards (e.g., 802.1D-1990, 802.1D-
1998) need to inter-operate with routers and layer-3 switches. Wide
deployment of such 802.1D-1998 switches will occur in a number of
roles in the network: "desktop switches" provide dedicated 10/100
Mbps links to end stations and high speed core switches often act as
central campus switching points for layer-3 devices. Layer-2 devices
will have to operate in all of the following scenarios:
* every device along a network path is layer-3 capable and intrusive
into the full data stream
* only the edge devices are pure layer-2
* every alternate device lacks layer-3 functionality
* most devices lack layer-3 functionality except for some key
control points such as router firewalls, for example.
Where int-serv flows pass through equipment which does not support
Integrated Services or 802.1D traffic management and which places
all packets through the same queuing and overload-dropping paths,
it is obvious that some of a flow's desired service parameters
become more difficult to support. In particular, the two
integrated service classes studied here, Controlled Load and
Guaranteed Service, both assume that flows will be policed and
kept "insulated" from misbehaving other flows or from best effort
traffic during their passage through the network. This cannot be
Seaman, et al. Standards Track [Page 13]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
done within an IEEE 802 network using devices with the default
user_priority function; in this case policing must be approximated
at the network edges.
In addition, in order to provide a Guaranteed Service, *all*
switching elements along the path must participate in special
treatment for packets in such flows: where there is a "break" in
guaranteed service, all bets are off. Thus, a network path that
includes even a single switch transmitting onto a shared or half-
duplex LAN segment is unlikely to be able to provide a very good
approximation to Guaranteed Service. For Controlled Load service,
the requirements on the switches and link types are less stringent
although it is still necessary to provide differential queuing and
buffering in switches for CL flows over best effort in order to
approximate CL service. Note that users receive indication of such
breaks in the path through the "break bits" described in y
[RSVPINTSERV]. These bits must be correctly set when IEEE 802
devices that cannot provide a specific service exist in a network.
Other approaches might be to pass more information between
switches about the capabilities of their neighbours and to route
around non-QoS-capable switches: such methods are for further
study. And of course the easiest solution of all is to upgrade
links and switches to higher capacities.
7. References
[802.1D-ORIG] "MAC Bridges", ISO/IEC 10038, ANSI/IEEE Std 802.1D-1993
[802.1D] "Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Common specifications -
Part 3: Media Access Control (MAC) Bridges: Revision.
This is a revision of ISO/IEC 10038: 1993, 802.1j-1992
and 802.6k-1992. It incorporates P802.11c, P802.1p and
P802.12e." ISO/IEC 15802-3:1998"
[INTSERV] Braden, R., Clark, D. and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RSVP] Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
Jamin, "Resource Reservation Protocol (RSVP) - Version
1 Functional Specification", RFC 2205, September 1997.
[CL] Wroclawski, J., "Specification of the Controlled-Load
Network Element Service", RFC 2211, September 1997.
Seaman, et al. Standards Track [Page 14]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
[GS] Schenker, S., Partridge, C. and R. Guerin,
"Specification of Guaranteed Quality of Service", RFC
2212 September 1997.
[802.1Q] ANSI/IEEE Standard 802.1Q-1998, "IEEE Standards for
Local and Metropolitan Area Networks: Virtual Bridged
Local Area Networks", 1998.
[GENCHAR] Shenker, S., and J. Wroclawski, "General
Characterization Parameters for Integrated Service
Network Elements", RFC 2215, September 1997.
[IS802FRAME] Ghanwani, A., Pace, W., Srinivasan, V., Smith, A. and
M. Seaman, "A Framework for Providing Integrated
Services Over Shared and Switched LAN Technologies",
RFC 2816, May 2000.
[SBM] Yavatkar, R., Hoffman, D., Bernet, Y., Baker, F. and M.
Speer, "SBM (Subnet Bandwidth Manager): A Protocol for
Admission Control over IEEE 802-style Networks", RFC
2814, May 2000.
[RSVPINTSERV] Wroclawski, J., "The use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[PROCESS] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
8. Security Considerations
Any use of QoS requires examination of security considerations
because it leaves the possibility open for denial of service or theft
of service attacks. This document introduces no new security issues
on top of those discussed in the companion ISSLL documents
[IS802FRAME] and [SBM]. Any use of these service mappings assumes
that all requests for service are authenticated appropriately.
9. Acknowledgments
This document draws heavily on the work of the ISSLL WG of the IETF
and the IEEE P802.1 Interworking Task Group.
Seaman, et al. Standards Track [Page 15]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
10. Authors' Addresses
Mick Seaman
Telseon
480 S. California Ave
Palo Alto, CA 94306
USA
Email: mick@telseon.com
Andrew Smith
Extreme Networks
3585 Monroe St.
Santa Clara, CA 95051
USA
Phone: +1 408 579 2821
EMail: andrew@extremenetworks.com
Eric Crawley
Unisphere Solutions
5 Carlisle Rd.
Westford, MA 01886
Phone: +1 978 692 1999
Email: esc@unispheresolutions.com
John Wroclawski
MIT Laboratory for Computer Science
545 Technology Sq.
Cambridge, MA 02139
USA
Phone: +1 617 253 7885
EMail: jtw@lcs.mit.edu
Seaman, et al. Standards Track [Page 16]
RFC 2815 Int-Serv Mappings on IEEE 802 Networks May 2000
Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Seaman, et al. Standards Track [Page 17]