Y. Bernet, Microsoft
R. Yavatkar, Intel
P. Ford, Microsoft
F. Baker, Cisco
L. Zhang, UCLA
M. Speer, Sun Microsystems
R. Braden, ISI
Internet Draft
Expires: September, 1999
Document: draft-ietf-issll-diffserv-rsvp-01.txt March, 1999
Interoperation of RSVP/Intserv and Diffserv Networks
Status of this Memo
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1. Abstract
RSVP/Integrated Services and Differentiated Services provide
complementary approaches to the problem of providing end-to-end QoS
in the Internet. These approaches must be able to coexist and
effectively inter-operate. This document describes a framework by
which the two approaches inter-operate to provide end-to-end QoS for
quantitative applications (applications for which QoS requirements
are readily quantifiable, and which rely on these QoS requirements
to function properly).
2. Introduction
Work on QoS-enabled IP networks has led to two distinct approaches:
the Integrated Services architecture (intserv)[12] and its
accompanying signaling protocol, RSVP [1], vs. the Differentiated
Services architecture (diffserv)[10].
2.1 RSVP/Intserv
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RSVP is a signaling protocol that applications may use to request
resources from the network. The network responds by explicitly
admitting or rejecting RSVP requests. Certain applications that have
quantifiable resource requirements express these requirements using
intserv parameters. It is important to emphasize that RSVP and
intserv are separable; RSVP is a signaling protocol. Intserv is a
set of models for expressing service types, quantifying resource
requirements and for determining the availability of the requested
resources at relevant network elements (admission control).
The current prevailing model of RSVP usage is based on a combined
RSVP/intserv architecture. In this model, RSVP signals per-flow
resource requirements to network elements, using Intserv parameters.
These network elements apply Intserv admission control to signaled
requests. In addition, traffic control mechanisms on the network
element are configured to ensure that each admitted flow receives
the service requested in strict isolation from other traffic. To
this end, RSVP signaling configures 'MF' [10] packet classifiers in
intserv capable routers along the path of the traffic flow. These
classifiers enable per-flow classification of packets based on IP
addresses and port numbers.
The following factors have impeded deployment of the RSVP/Intserv
architecture in the Internet at large:
1. The use of per-flow state and per-flow processing raises
scalability concerns for large networks.
2. Only a small number of hosts currently generate RSVP signaling.
While this number is expected to grow dramatically, many
applications may never generate RSVP signaling.
3. The necessary policy control mechanisms -- access control,
authentication, and accounting -- are not available.
2.2 Diffserv
The market is pushing for immediate deployment of a QoS solution
that addresses the needs of the Internet as well as enterprise
networks. This push led to the development of diffserv. In contrast
to the per-flow orientation of RSVP/intserv, diffserv networks
classify packets into one of a small number of aggregated flows or
'classes', based on the diffserv codepoint (DSCP) in the packet's IP
header. This is known as 'BA' classification [10]. At each diffserv
router, packets are subjected to a 'per-hop behaviour' (PHB), which
is invoked by the DSCP. The primary benefit of diffserv is its
scalability. Diffserv eliminates the need for per-flow state and
per-flow processing and therefore scales well to large networks.
2.3 Complementary Roles of RSVP/Intserv and Diffserv
We view RSVP/intserv and diffserv as complementary technologies in
the pursuit of end-to-end QoS. Together, these mechanisms can
facilitate deployment of applications such as IP-telephony, video-
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on-demand, and various non-multimedia mission-critical applications.
RSVP/intserv enables hosts to request per-flow, quantifiable
resources, along end-to-end data paths and to obtain feedback
regarding admissibility of these requests. Diffserv enables
scalability across large networks.
2.3 Components of RSVP/intserv and Diffserv
Before proceeding, it is helpful to identify the following
components of the QoS technologies described:
RSVP signaling - This term refers to the standard RSVP per-flow
signaling protocol. RSVP signaling is used by hosts to signal per-
flow resource requirements to the network (and to each other).
Network elements use RSVP signaling to return an admission control
decision to hosts. RSVP signaling may or may not carry intserv
parameters. Admission control at a network element may or may not be
based on the intserv model.
RSVP/Intserv - This term is used to refer to the prevailing model of
RSVP usage which includes RSVP signaling with intserv parameters,
intserv admission control and per-flow traffic control at network
elements.
MF traffic control - This term refers to traffic control which is
applied independently to individual traffic flows and therefore
requires recognizing individual traffic flows via MF classification.
Aggregate traffic control - This term refers to traffic control
which is applied collectively to sets of traffic flows. These sets
of traffic flows are recognized based on BA (DSCP) classification.
In this draft, we use the terms 'aggregate traffic control' and
'diffserv' interchangeably.
We will refer to RSVP/intserv regions of the network and diffserv
regions of the network. RSVP/intserv regions are those regions in
which both RSVP signaling and MF traffic control are supported.
These regions include hosts and network elements that are
RSVP/intserv capable. (RSVP/intserv regions are not precluded from
supporting aggregate traffic control as well as MF traffic control).
Diffserv regions are those regions in which aggregate traffic
control is supported.
2.4 The Framework
In the framework we present, end-to-end, quantitative QoS is
provided by coupling RSVP/Intserv regions at the periphery of the
network with diffserv regions in the core of the network. The
diffserv regions may, but are not required to, participate in the
end-to-end RSVP signaling for the purpose of optimizing resource
allocation and supporting admission control.
From the perspective of RSVP/intserv, diffserv regions of the
network are treated as virtual links connecting RSVP/Intserv capable
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routers or hosts (much as an 802.1p network region is treated as a
virtual link in [5]). Within the diffserv regions of the network
routers implement specific PHBs (aggregate traffic control). We use
RSVP to apply admission control to each PHB in the diffserv region.
As a result we expect that the diffserv regions of the network will
be able to extend the intserv style services requested from the
periphery. As such, we often refer to the RSVP/intserv network
regions as 'customers' of the diffserv network regions.
In our framework, we address the inter-operability between the
RSVP/intserv regions of the network and the diffserv regions of the
network. Our goal is to enable seamless inter-operation. As a
result, the network administrator is free to choose which regions of
the network act as RSVP/intserv regions and which act as diffserv
regions. In one extreme the diffserv region is pushed all the way to
the periphery, with hosts alone comprising the RSVP/intserv regions
of the network. In the other extreme, RSVP/intserv is pushed all the
way to the core, with no diffserv region.
2.5 Contents
In section 3 we discuss the benefits that can be realized by using
RSVP/intserv together with the aggregate traffic control provided by
diffserv network regions. In section 4, we present the framework and
the reference network. Section 5 details two realizations of the
framework. Section 6 discusses the implications of the framework for
diffserv. Appendix A contains a list of some important terms used in
this document.
Though the primary goal of this draft is to describe a framework
for inter-operation of RSVP/intserv network regions and diffserv
network regions, the draft currently does not address the issues
specific to IP multicast flows.
3. Benefits of Using RSVP/intserv with Diffserv
The primary benefit of diffserv aggregate traffic control is its
scalability. In this section, we discuss the benefits that
interoperation with RSVP/intserv can bring to a diffserv network
region. Note that this discussion is in the context of servicing
quantitative applications specifically.
3.1 Resource Based Admission Control
In RSVP/Intserv networks, quantitative QoS applications use RSVP to
request resources from the network. The network may accept or reject
these requests in response. This is 'explicit admission control'.
Explicit admission control helps to assure that network resources
are optimally used. To further understand this issue, consider a
diffserv network region providing only aggregate traffic control
with no signaling. In the diffserv network region, admission control
is applied implicitly by provisioning policing parameters at network
elements. For example, a network element at the ingress to a
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diffserv network region could be provisioned to accept only 50 Kbps
of traffic for the EF DSCP.
While such implicit admission control does protect the network to
some degree, it can be quite ineffective. For example, consider that
there may be 10 IP telephony sessions originating outside the
diffserv network region, each requiring 10 Kbps of EF service from
the diffserv network region. Since the network element protecting
the diffserv network region is provisioned to accept only 50 Kbps of
traffic for the EF DSCP, it will discard half the offered traffic.
This traffic will be discarded from the aggregation of traffic
marked EF, with no regard to the microflow from which it originated.
As a result, it is likely that of the ten IP telephony sessions,
none will obtain satisfactory service when in fact, there are
sufficient resources available in the diffserv network region to
satisfy five sessions.
In the case of explicit admission control, the network will signal
rejection in response to requests for resources that would exceed
the 50 Kbps limit. As a result, upstream network elements (including
originating hosts) and applications will have the information they
require to take corrective action. The application might respond by
refraining from transmitting, or by requesting admission for a
lesser traffic profile. The host operating system might respond by
marking the application's traffic for the DSCP that corresponds to
best-effort service. Upstream network elements might respond by re-
marking packets on the rejected flow to a lower service level. In
any case, the integrity of those flows that were admitted would be
preserved, at the expense of the flows that were not admitted. Thus,
by appointing an RSVP conversant admission control agent for the
diffserv region of the network it is possible to enhance the service
that the network can provide to quantitative applications.
3.2 Policy Based Admission Control
In an RSVP/intserv network region, resource requests can be
intercepted by RSVP aware network elements and can be reviewed
against policies stored in policy databases. These resource requests
securely identify the user and the application for which the
resources are requested. Consequently, the network element is able
to consider per-user and/or per-application policy when deciding
whether or not to admit a resource request. So, in addition to
optimizing the use of resources in a diffserv network region (as
discussed in 3.1) RSVP conversant admission control agents can be
used to apply specific customer policies in determining the specific
customer traffic flows entitled to use the diffserv network region's
resources. Customer policies can be used to allocate resources to
specific users and/or applications.
By comparison, in diffserv network regions without per-flow RSVP
signaling, policies are typically applied based on the diffserv
customer network from which traffic originates, not on the
originating user or application within the customer network.
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3.3 Assistance in Traffic Identification/Classification
Within diffserv network regions, traffic is allotted service based
on the DSCP marked in each packet's IP header. Thus, in order to
obtain a particular level of service within the diffserv network
region, it is necessary to effect the marking of the correct DSCP in
packet headers. There are two mechanisms for doing so, host marking
and router marking. In the case of host marking, the host operating
system marks the DSCP in transmitted packets. In the case of router
marking, routers in the network are configured to identify specific
traffic (based on MF classification) and to mark the DSCP as packets
transit the router. There are advantages and disadvantages to each
scheme. Regardless of the scheme used, RSVP signaling offers
significant benefits.
3.3.1 Host Marking
In the case of host marking, the host operating system marks the
DSCP in transmitted packets. This approach has the benefit of
shifting per-flow classification and marking to the edge of the
network, where it scales best. It also enables the host to make
decisions regarding the mark (and hence the relative priority that
is requested) that is appropriate for each transmitted packet. The
host is generally better equipped to make this decision than the
network.
Host marking requires that the host be aware of the interpretation
of DSCPs by the network. This information can be configured into
each host. However, such configuration imposes a management burden.
Alternatively, RSVP/intserv hosts can use RSVP signaling to query
the network for a mapping from intserv service type to DSCP. This is
achieved via the RSVP DCLASS object [17] and is explained later in
this draft.
3.3.2 Router Marking
In the case of router marking, MF classification criteria must be
configured in the router. This may be done dynamically, by request
from the host operating system, or statically via manual
configuration or via automated scripts.
There are significant difficulties in doing so statically.
Typically, it is desirable to allot service to traffic based on the
application and/or user originating the traffic. At times it is
possible to identify packets associated with a specific application
by the IP port numbers in the headers. It may also be possible to
identify packets originating from a specific user by the source IP
address. However, such classification criteria may change
frequently. Users may be assigned different IP addresses by DHCP.
Applications may use transient ports. To further complicate matters,
multiple users may share an IP address. These factors make it very
difficult to manage static configuration of the classification
information required to mark traffic in routers.
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An attractive alternative to static configuration is to allow host
operating systems to signal classification criteria to the router on
behalf of users and applications. As we will show later in this
draft, RSVP signaling is ideally suited for this task. In addition
to enabling dynamic and accurate updating of MF classification
criteria, RSVP signaling enables classification of IPSec [16]
packets (by use of the SPI) which would otherwise be unrecognizable.
3.4 Traffic Conditioning
Those network elements that do provide RSVP/intserv support will
condition traffic at a per-flow granularity, by some combination of
shaping and/or policing. Pre-conditioning traffic in this manner
before it is submitted to the diffserv region of the network is
beneficial. In particular, it enhances the ability of the diffserv
region of the network to provide quantitative services using
aggregate traffic control.
4. The Framework
In the general framework we envision an Internet in which hosts use
RSVP/intserv to request reservations for specific services from the
network. The network includes some combination of RSVP/intserv
regions (in which MF classification and per-flow traffic control is
applied) and diffserv regions (in which aggregate traffic control is
applied). Individual routers may or may not participate in RSVP
signaling regardless of the type of network region in which they
reside.
We will consider two specific realizations of the framework. In the
first, resources within the diffserv regions of the network are
statically provisioned and these regions include no RSVP aware
devices. In the second, resources within the diffserv region of the
network are dynamically provisioned and select devices within the
diffserv network regions participate in RSVP signaling.
4.1 Reference Network
The two realizations of the framework will be discussed in the
context of the following reference network:
/ \ / \ / \
/ \ / \ / \
|---| | |---| |---| |---| |---| | |---|
|Tx |-| |ER1|---|BR1| |BR2|---|ER2| |-|Rx |
|---| | |-- | |---| |---| |---| | |---|
\ / \ / \ /
\______ / \___ _________ / \__ _____/
RSVP/Intserv region Diffserv region RSVP/Intserv region
Figure 1: Sample Network Configuration
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The reference network includes a diffserv region interconnecting two
RSVP/intserv regions. The diffserv region contains a mesh of
routers, at least some of which provide aggregate traffic control.
The RSVP/intserv regions contain meshes of routers and attached
hosts, at least some of which are RSVP/intserv capable.
In the interest of simplicity we consider a single QoS sender, Tx in
one of the RSVP/intserv network regions and a single QoS receiver,
Rx in the other. The edge routers (ER1, ER2) within the RSVP/intserv
regions interface to the border routers (BR1, BR1) within the
diffserv regions.
From an economic viewpoint, we may consider that the diffserv region
sells service to the RSVP/intserv regions, which provide service to
hosts. Thus, we may think of the RSVP/intserv regions as customers
of the diffserv region. In the following, we use the term
'customer' for the RSVP/intserv regions.
4.1.1 Components of the Reference Network
We now define the major components of the reference network.
4.1.1.1 Hosts
Both sending and receiving hosts use RSVP/intserv to communicate the
quantitative QoS requirements of QoS-aware applications running on
the host. Typically, a QoS process within the host operating system
generates RSVP signaling on behalf of applications. This process may
also invoke local traffic control.
In this example, traffic control in the host marks the DSCP in
transmitted packets, and it shapes transmitted traffic to the
requirements of the intserv service in use. In alternate
realizations of the framework, the first-hop router within the
RSVP/intserv network regions may provide these traffic control
functions.
4.1.1.2 End-to-End RSVP Signaling
We assume that RSVP signaling messages travel end-to-end between
hosts Tx and Rx to support RSVP/intserv reservations in the
RSVP/intserv network regions. We require that these end-to-end RSVP
messages are carried across the diffserv region. Depending on the
specific realization of the framework, these messages may be
processed by none, some or all of the routers in the diffserv
region.
4.1.1.3 Edge Routers
ER1 and ER2 are edge routers, residing in the RSVP/intserv network
regions. The functionality of the edge routers varies depending on
the specific realization of the framework. In the case in which the
diffserv network region is RSVP unaware, edge routers act as
admission control agents to the diffserv network. They process
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signaling messages from both Tx and Rx, and apply admission control
based on resource availability within the diffserv network region
and on customer defined policy. In the case in which the diffserv
network region is RSVP aware, the edge routers apply admission
control based on local resource availability and on customer defined
policy. In this case, the border routers act as the admission
control agent to the diffserv network region.
We will later describe the functionality of the edge routers in
greater depth for each of the two realizations of the framework.
4.1.1.4 Border Routers
BR1 and BR2 are border routers, residing in the diffserv network
region. The functionality of the border routers varies depending on
the specific realization of the framework. In the case in which the
diffserv network region is RSVP/intserv unaware, these routers act
as pure diffserv routers. As such, their sole responsibility is to
police submitted traffic based on the service level specified in the
DSCP and the agreement negotiated with the customer (aggregate
traffic control). In the case in which the diffserv network region
is RSVP/intserv aware, the border routers participate in RSVP
signaling and act as admission control agents for the diffserv
network region.
We will later describe the functionality of the border routers in
greater depth for each of the two realizations of the framework.
4.1.1.5 RSVP/Intserv Network Regions
Each RSVP/intserv network region consists of RSVP/intserv capable
hosts and some number of routers. These routers may reasonably be
assumed to be RSVP/intserv capable, although this might not be
required in the case of a small, over-provisioned network region. If
they are not RSVP/intserv capable, we assume that they will pass
RSVP messages unhindered. Routers in the RSVP/intserv network region
are not precluded from providing aggregate traffic control to non-
quantitative traffic passing through them.
4.1.1.6 Diffserv Network Region
The diffserv network region supports aggregate traffic control and
is not capable of MF classification. Depending on the specific
realization of the framework, some number of routers within the
diffserv region may be RSVP aware and therefore capable of per-flow
signaling and admission control. If devices in the diffserv region
are not RSVP aware, they will pass RSVP messages transparently with
negligible performance impact (see [8]).
The diffserv network region provides two or more levels of service
based on the DSCP in packet headers. It may include sub-regions
managed as different administrative domains.
4.1.1.7 Service Mapping
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RSVP/intserv signaling requests specify an intserv service type and
a set of quantitative parameters known as a 'flowspec'. At each hop
in an intserv network, the RSVP/intserv service requests are
interpreted in a form meaningful to the specific link layer medium.
For example at an 802.1 hop, the intserv parameters are mapped to an
appropriate 802.1p priority level [5].
In our framework, diffserv regions of the network are analogous to
the 802.1p capable switched segments described in [5]. Admission
control agents for diffserv network regions must map intserv service
types to a corresponding diffserv service level (DSCP or PHB) that
can reasonably extend the intserv service type requested by the
application. The admission control agent can then approve or reject
resource requests based on the capacity available in the diffserv
network region at the mapped service level.
One of two schemes may be used to map intserv service types to
diffserv service levels.
4.1.1.7.1 Default Mapping
In this scheme, there is some standard, well-known mapping from
intserv service type to a DSCP that will invoke the appropriate
behavior in the diffserv network.
4.1.1.7.2 Network Driven Mapping
In this scheme, RSVP aware routers in the diffserv network region
may override the well-known mapping described in 4.1.1.7.1. RSVP
RESV messages originating from receivers will carry the usual
intserv service type. RSVP aware routers within the diffserv network
region may append a DCLASS [17] object to RESV messages as they are
forwarded upstream. When a RESV message carrying a DCLASS object
arrives at a sending host (or in the case of router marking, at an
intermediate router), the sender starts marking transmitted packets
with the DSCP indicated.
A decision to override the well-known service mapping may be based
on configuration and/or a policy decision.
5. Detailed Examples of the Interoperation of RSVP/Intserv and Diffserv
In this section we provide detailed examples of our framework in
action. We discuss two examples, one in which the diffserv network
region is RSVP unaware, the other in which the diffserv network
region is RSVP aware.
5.1 RSVP Unaware Diffserv Network Region
In this example, no devices in the diffserv network region are RSVP
aware. The diffserv network region is statically provisioned. The
owner(s) of the RSVP/intserv network regions and the owner of the
diffserv network region have negotiated a static contract (service
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level agreement, or SLA) for the transmit capacity to be provided to
the customer at each of a number of standard diffserv service
levels.
It is helpful to consider the edge routers in the customer network,
to consist of two halves, a standard RSVP/intserv half, which
interfaces to the customer's RSVP/intserv network regions and a
diffserv half which interfaces to the diffserv network region. The
RSVP/intserv half has full RSVP capability. It is able to
participate in RSVP signaling and it is able to identify and process
traffic on per-flow granularity.
The diffserv half of the router can be considered to consist of a
number of virtual transmit interfaces, one for each diffserv service
level negotiated in the SLA. The router contains a table that
indicates the transmit capacity provisioned, per the SLA at each
diffserv service level. This table, in conjunction with the default
mapping described in 4.1.1.7.1, is used to apply admission control
decisions to the diffserv network region.
5.1.1 Sequence of Events in Obtaining End-to-end QoS
The following sequence illustrates the process by which an
application obtains end-to-end QoS.
1. The QoS process on the sending host Tx generates an RSVP PATH
message that describes the traffic offered by the sending
application.
2. The PATH message is carried toward the receiving host, Rx. In the
RSVP/intserv network region to which the sender is attached,
standard RSVP/intserv processing is applied at capable network
elements.
3. At the edge router ER1, the PATH message is subjected to standard
RSVP processing and PATH state is installed in the router. The PATH
message is sent onward to the diffserv network region.
4. The PATH message is carried transparently through the diffserv
network region and then processed at ER2 according to standard RSVP
processing rules.
5. When the PATH message reaches the receiving host Rx, the
operating system generates an RSVP RESV message, indicating interest
in offered traffic of a certain intserv service type.
6. The RESV message is carried back towards the diffserv network
region and the sending host. Consistent with standard RSVP/intserv
processing, it may be rejected at any RSVP node in the RSVP/intserv
network region if resources are deemed insufficient to carry the
traffic requested.
7. At ER2, the RESV message is subjected to standard RSVP/intserv
processing. It may be rejected if resources on the downstream
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interface of ER2 are deemed insufficient to carry the resources
requested. If it is not rejected, it will be carried transparently
through the diffserv network region, arriving at ER1.
8. In ER1, the RESV message triggers admission control processing.
ER1 compares the resources requested in the RSVP/intserv request to
the resources available in the diffserv network region at the
corresponding diffserv service level. The corresponding service
level is determined by the intserv to diffserv mapping discussed
previously. The availability of resources is determined by the
capacity provisioned in the SLA. ER1 may also apply a policy
decision such that the resource request may be rejected based on the
customer's specific policy criteria, even though the aggregate
resources are determined to be available per the SLA.
9. If ER1 approves the request, the RESV message is admitted and is
allowed to continue upstream towards the sender. If it rejects the
request, the RESV is not forwarded and the appropriate RSVP error
messages are sent. If the request is approved, ER1 updates its
internal tables to indicate the reduced capacity available at the
admitted service level on its transmit interface.
10. The RESV message proceeds through the RSVP/intserv network
region to which the sender is attached. Any RSVP node in this region
may reject the reservation request due to inadequate resources or
policy. If the request is not rejected, the RESV message will arrive
at the sending host, Tx.
11. At Tx, the QoS process receives the RESV message. It interprets
receipt of the message as indication that the specified traffic flow
has been admitted for the specified intserv service type (in the
RSVP/intserv network regions) and for the corresponding diffserv
service level (in the diffserv network regions).
12. Tx begins to mark the DSCP in the headers of packets that are
transmitted on the admitted traffic flow. The DSCP is the value
which maps to the intserv service type specified in the admitted
RESV message.
In this manner, we obtain end-to-end QoS through a combination of
networks that support RSVP/Intserv and networks that support
diffserv.
5.2 RSVP Aware Diffserv Network Region
In this example, the customer's edge routers are standard RSVP
routers. The border router, BR1 is RSVP aware. In addition, there
may be other routers within the diffserv network region which are
RSVP aware. Note that although these routers are able to participate
in RSVP signaling, they process traffic in aggregate, based on DSCP,
not on the per-flow classification criteria used by standard
RSVP/Intserv routers. It can be said that their control-plane is
RSVP while their data-plane is diffserv. This approach exploits the
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benefits of RSVP signaling while maintaining much of the scalability
associated with diffserv.
In the former example, there is no RSVP signaling between the
RSVP/intserv network regions and the diffserv network region. The
negotiation of an SLA is the only explicit exchange of resource
availability information between the two network regions. ER1 is
configured with the information represented by the SLA and as such,
is able to act as an admission control agent for the diffserv
network region. Such configuration does not readily support
dynamically changing SLAs, since ER1 requires reconfiguration each
time the SLA changes. It is also difficult to make efficient use of
the resources in the diffserv network region. This is because
admission control does not consider the availability of resources in
the diffserv network region along the specific path that would be
impacted.
By contrast, when the diffserv network region is RSVP aware, the
admission control agent is part of the diffserv network. As a
result, changes in the capacity available in the diffserv network
region can be indicated to the RSVP/intserv network regions via
traditional RSVP. By including routers interior to the diffserv
network region in RSVP signaling, it is possible to improve the
efficiency of resource usage. This is because admission control can
be linked to the availability of resources along the specific path
that would be impacted. We refer to this benefit of RSVP signaling
as 'topology aware admission control'. A further benefit of
supporting RSVP signaling within the diffserv network region is that
it is possible to effect changes in the provisioning of the diffserv
network region response to resource requests from the RSVP/intserv
network regions.
Various mechanisms may be used within the diffserv network region to
support dynamic provisioning and topology aware admission control.
These include aggregated RSVP, per-flow RSVP and bandwidth brokers,
as described in the following paragraphs.
5.2.1 Aggregated or Tunneled RSVP
A number of drafts [8,10,18, 19] propose mechanisms for extending
RSVP to reserve resources for an aggregation of flows between edges
of a network. Border routers may interact with core routers and
other border routers using aggregated RSVP to reserve resources
between edges of the diffserv network region. Initial reservation
levels for each service level may be established between major
border routers, based on anticipated traffic patterns. Border
routers could trigger changes in reservation levels as a result of
the cumulative per-flow RSVP requests from peripheral RSVP/intserv
network regions reaching high or low-water marks.
In this approach, admission of per-flow RSVP requests from
RSVP/intserv networks would be counted against the appropriate
aggregate reservations for the corresponding service level.
Bernet, ed. et. al 13
Use of RSVP with Diffserv March, 1999
The advantage of this approach is that it offers dynamic, topology
aware admission control to the diffserv network region without
requiring the level of RSVP signaling processing that would be
required to support per-flow RSVP.
5.2.3 Per-flow RSVP
In this approach, routers in the diffserv network region respond to
the standard per-flow RSVP signaling originating from the
RSVP/intserv network regions. This approach provides the benefits of
the previous approach (dynamic, topology aware admission control)
without requiring aggregated RSVP support. Resources are also used
more efficiently as a result of the per-flow admission control.
However, the demands on RSVP signaling resources within the diffserv
network region may be significantly higher.
5.2.4 Oracle
Border routers might not use any form of RSVP signaling within the
diffserv network region but might instead use custom protocols to
interact with an 'oracle'. The oracle is a hypothetical agent that
has sufficient topology awareness to make admission control
decisions. The set of RSVP aware routers in the previous two
examples can be considered collectively as a distributed oracle. In
various definitions of the 'bandwidth broker' [4], it is able to act
as a centralized oracle.
5.2.5 Granularity of Deployment of RSVP Aware Routers
In 5.2.2 and 5.2.3 some subset of the routers within the diffserv
network is RSVP signaling aware (though traffic control is
aggregated as opposed to per-flow). The relative number of routers
in the core that participate in RSVP signaling is a provisioning
decision that must be made by the network administrator.
In one extreme case, only the border routers participate in RSVP
signaling. In this case, either the diffserv network region must be
extremely over-provisioned and therefore, inefficiently used, or
else it must be carefully and statically provisioned for limited
traffic patterns. The border routers must enforce these patterns.
In the other extreme case, each router in the diffserv network
region might participate in RSVP signaling. In this case, resources
can be used with optimal efficiency, but signaling processing
requirements and associated overhead increase.
It is likely that network administrators will compromise by enabling
RSVP signaling on some subset of routers in the diffserv network
region. These routers will likely represent major traffic switching
points with over-provisioned or statically provisioned regions of
RSVP unaware routers between them.
6. Implications of the Framework for DiffServ Network Regions
Bernet, ed. et. al 14
Use of RSVP with Diffserv March, 1999
We have described a framework in which RSVP/intserv style QoS can be
provided across end-to-end paths that include diffserv network
regions. This section discusses some of the implications of this
framework for the diffserv network region.
6.1 Requirements from Diffserv Network Regions
A diffserv network region must meet the following requirements in
order for it to support the framework described in this draft.
1. A diffserv network region must be able to provide standard QoS
services between its border routers. It must be possible to invoke
these services by use of a standard DSCP.
2. There must be appropriate service mappings from intserv service
types to these diffserv services.
3. Diffserv network regions must provide admission control
information to intserv network regions. This information can be
provided by a dynamic protocol or, at the very least, through static
service level agreements.
4. Diffserv network regions must be able to pass RSVP messages, in
such a manner that they can be recovered at the egress of the
diffserv network region. The diffserv network region may, but is not
required to, process these messages. Mechanisms for transparently
carrying RSVP messages across a transit network are described in
[8,10,18, 19].
To meet these requirements, additional work is required in the areas
of:
1. Mapping intserv style service specifications to services that can
be provided by diffserv network regions.
2. Definition of the functionality required in network elements to
support RSVP signaling with aggregate traffic control (for network
elements residing in the diffserv network region).
3. Definition of mechanisms to efficiently and dynamically provision
resources in a diffserv network region (e.g. aggregated RSVP,
tunneling, MPLS, etc.).
6.2 Protection of Intserv Traffic from Other Traffic
Network administrators must be able to share resources in the
diffserv network region between three types of traffic:
a. RSVP/intserv signaled - this is traffic associated with
quantitative applications. It requires a specific quantity of
resources with a high degree of assurance.
b. Qualitative - this is traffic associated with applications that
are not quantitative. Its resource requirements are not readily
quantifiable. It requires a 'better than best-effort' level of
service.
Bernet, ed. et. al 15
Use of RSVP with Diffserv March, 1999
c. All other (best-effort) traffic
These classes of traffic must be isolated from each other by the
appropriate configuration of policers and classifiers at ingress
points to the diffserv network region, and by appropriate
provisioning within the diffserv network region. To provide
protection for RSVP/intserv signaled traffic in diffserv regions of
the network, we suggest that the DSCPs assigned to such traffic not
overlap with the DSCPs assigned to other traffic.
7. Multicast
To be written.
8. Security Considerations
8.1 General RSVP Security
We are proposing that RSVP signaling be used to obtain resources in
both diffserv and RSVP/intserv regions of a network. Therefore, all
RSVP security considerations apply [11]. In addition, network
administrators are expected to protect network resources by
configuring secure policers at interfaces with untrusted customers.
8.2 Host Marking
Though it does not mandate host marking, our proposal does recommend
it. Allowing hosts to set the DSCP directly may alarm network
administrators. The obvious concern is that hosts may attempt to
'steal' resources. In fact, hosts may attempt to exceed negotiated
capacity in diffserv network regions at a particular service level
regardless of whether they invoke this service level directly (by
setting the DSCP) or indirectly (by submitting traffic that
classifies in an intermediate marking router to a particular diff-
serv DSCP).
In either case, it will be necessary for each diffserv network
region to protect its resources by policing to assure that customers
do not use more resources than they are entitled to, at each service
level (DSCP). If the sending host does not do the marking, the
boundary router (or trusted intermediate routers) must provide MF
classification, mark and police. If the sending host does do the
marking, the boundary router needs only to provide BA classification
and to police to ensure that the customer is not exceeding the
aggregate capacity negotiated for the service level.
In summary, the security concerns of marking the DSCP at the edge of
the network can be dismissed since each diffserv provider will have
to police at their boundary anyway. Furthermore, this approach
reduces the granularity at which border routers must police, thereby
pushing finer grain shaping and policing responsibility to the edges
of the network, where it scales better. The larger diffserv network
regions are thus focused on the task of protecting their networks,
Bernet, ed. et. al 16
Use of RSVP with Diffserv March, 1999
while the RSVP/intserv network regions are focused on the task of
shaping and policing their own traffic to be in compliance with
their negotiated intserv parameters.
7. Acknowledgments
Authors thank the following individuals for their comments that led
to improvements to the previous version(s) of this draft: David
Oran, Andy Veitch, Curtis Villamizer, Walter Weiss, and Russel
White.
Many of the ideas in this document have been previously discussed in
the original intserv architecture document [12].
8. References
[1] Braden, R., Zhang, L., Berson, S., Herzog, S. and Jamin, S.,
"Resource Reservation Protocol (RSVP) Version 1 Functional
Specification", RFC 2205, Proposed Standard, September 1997
[2] Yavatkar, R., Hoffman, D., Bernet, Y., Baker, F. and Speer, M.,
"SBM (Subnet Bandwidth Manager): A Protocol For RSVP-based
Admission Control Over IEEE 802 Style Networks", Internet Draft,
March 1998
[3] Berson, S. and Vincent, R., "Aggregation of Internet Integrated
Services State", Internet Draft, December 1997.
[4] Nichols, K., Jacobson, V. and Zhang, L., "A Two-bit
Differentiated Services Architecture for the Internet", Internet
Draft, December 1997.
[5] Seaman, M., Smith, A. and Crawley, E., "Integrated Services Over
IEEE 802.1D/802.1p Networks", Internet Draft, June 1997
[6] Elleson, E. and Blake, S., "A Proposal for the Format and
Semantics of the TOS Byte and Traffic Class Byte in Ipv4 and
Ipv6 Headers", Internet Draft, November 1997
[7] Ferguson, P., "Simple Differential Services: IP TOS and
Precedence, Delay Indication, and Drop Preference", Internet
Draft, November 1997
[8] Guerin, R., Blake, S. and Herzog, S.,"Aggregating RSVP based QoS
Requests", Internet Draft, November 1997.
[9] Nichols, Kathleen, et al., "Definition of the Differentiated
Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC
2474, December 1998.
[10] Blake, S., et al., "An Architecture for Differentiated
Services." RFC 2475, December 1998.
[11] Baker, F., "RSVP Cryptographic Authentication", Internet Draft,
Bernet, ed. et. al 17
Use of RSVP with Diffserv March, 1999
August 1997
[12] Braden, R., Clark, D. and Shenker, S., "Integrated Services in
the Internet Architecture: an Overview", Internet RFC 1633,
June 1994
[13] Garrett, M. W., and Borden, M., "Interoperation of Controlled-
Load Service and Guaranteed Service with ATM", RFC2381, August
1998.
[14] Weiss, Walter, Private communication, November 1998.
[15] Berson, S. and Vincent, S., "Aggregation of Internet Integrated
Services State", Internet Draft, August 1998.
[16] Kent, S., Atkinson, R., "Security Architecture for the Internet
Protocol", RFC 2401, November 1998.
[17] Bernet, Y., "Usage and Format of the DCLASS Object with RSVP
Signaling", Internet Draft, February 1999.
[18] Baker, F., Iturralde, C., "RSVP Reservation Aggregation",
Internet Draft, February 1999.
[19] Terzis, A., Krawczyk, J., Wroclawski, J., Zhang, L., "RSVP
Operation Over IP Tunnels", Internet Draft, February 1999.
Author's Addresses:
Yoram Bernet
Microsoft
One Microsoft Way, Redmond, WA 98052
Phone: (425) 936-9568
Email: yoramb@microsoft.com
Raj Yavatkar
Intel Corporation
JF3-206 2111 NE 25th. Avenue, Hillsboro, OR 97124
Phone: (503) 264-9077
Email: raj.yavatkar@intel.com
Peter Ford
Microsoft
One Microsoft Way, Redmond, WA 98052
Phone: (425) 703-2032
Email: peterf@microsoft.com
Fred Baker
Cisco Systems
519 Lado Drive, Santa Barbara, CA 93111
Phone: (408) 526-4257
Email: fred@cisco.com
Lixia Zhang
Bernet, ed. et. al 18
Use of RSVP with Diffserv March, 1999
UCLA
4531G Boelter Hall Los Angeles, CA 90095
Phone: +1 310-825-2695
Email: lixia@cs.ucla.edu
Michael Speer
Sun Microsystems
901 San Antonio Road UMPK15-215 Palo Alto, CA 94303
Phone: +1 650-786-6368
Email: speer@Eng.Sun.COM
Bob Braden
USC Information Sciences Institute
4676 Admiralty Way Marina del Rey, CA 90292-6695
Phone: 310-822-1511
Email: braden@isi.edu
This draft expires September, 1999
Bernet, ed. et. al 19