Internet Engineering Task Force E. Crawley, Editor
Internet Draft Gigapacket Networks
draft-ietf-issll-atm-framework-00.txt L. Berger
Fore Systems
S. Berson
ISI
F. Baker
Cisco Systems
M. Borden
New Oak Communications
J. Krawczyk
ArrowPoint Communications
July 24, 1997
A Framework for Integrated Services and RSVP over ATM
Status of this Memo
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Abstract
This document outlines the framework and issues related to
providing IP Integrated Services with RSVP over ATM. It provides
an overall approach to the problem(s) and related issues. These
issues and problems are to be addressed in further documents from
the ISATM subgroup of the ISSLL working group.
Editor's Note
This document is the merger of two previous documents, draft-
ietf-issll-atm-support-02.txt by Berger and Berson and draft-
crawley-rsvp-over-atm-00.txt by Baker, Berson, Borden, Crawley,
and Krawczyk. The former document has been split into this
document and a set of documents on RSVP over ATM implementation
requirements and guidelines.
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1. Introduction
The Internet currently has one class of service normally referred
to as "best effort." This service is typified by first-come,
first-serve scheduling at each hop in the network. Best effort
service has worked well for electronic mail, World Wide Web (WWW)
access, file transfer (e.g. ftp), etc. For real-time traffic
such as voice and video, the current Internet has performed well
only across unloaded portions of the network. In order to
provide guaranteed quality real-time traffic, new classes of
service and a QoS signalling protocol are being introduced in the
Internet [1,6,7], while retaining the existing best effort
service. The QoS signalling protocol is RSVP [1], the Resource
ReSerVation Protocol.
One of the important features of ATM technology is the ability to
request a point-to-point Virtual Circuit (VC) with a specified
Quality of Service (QoS). An additional feature of ATM
technology is the ability to request point-to-multipoint VCs with
a specified QoS. Point-to-multipoint VCs allows leaf nodes to be
added and removed from the VC dynamically and so provides a
mechanism for supporting IP multicast. It is only natural that
RSVP and the Internet Integrated Services (IIS) model would like
to utilize the QoS properties of any underlying link layer
including ATM, and this draft concentrates on ATM.
Classical IP over ATM [10] has solved part of this problem,
supporting IP unicast best effort traffic over ATM. Classical IP
over ATM is based on a Logical IP Subnetwork (LIS), which is a
separately administered IP subnetwork. Hosts within an LIS
communicate using the ATM network, while hosts from different
subnets communicate only by going through an IP router (even
though it may be possible to open a direct VC between the two
hosts over the ATM network). Classical IP over ATM provides an
Address Resolution Protocol (ATMARP) for ATM edge devices to
resolve IP addresses to native ATM addresses. For any pair of
IP/ATM edge devices (i.e. hosts or routers), a single VC is
created on demand and shared for all traffic between the two
devices. A second part of the RSVP and IIS over ATM problem, IP
multicast, is being solved with MARS [5], the Multicast Address
Resolution Server.
MARS compliments ATMARP by allowing an IP address to resolve into
a list of native ATM addresses, rather than just a single
address.
The ATM Forum's LAN Emulation (LANE) [17 and 20] and
Multiprotocol Over ATM (MPOA) [18] also address the support of IP
best effort traffic over ATM through similar means.
A key remaining issue for IP in an ATM environment is the
integration of RSVP signalling and ATM signalling in support of
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the Internet Integrated Services (IIS) model. There are two main
areas involved in supporting the IIS model, QoS translation and
VC management. QoS translation concerns mapping a QoS from the
IIS model to a proper ATM QoS, while VC management concentrates
on how many VCs are needed and which traffic flows are routed
over which VCs.
1.1 Structure and Related Documents
This document provides a guide to the issues for IIS over ATM.
It is intended to frame the problems that are to be addressed in
further documents. In this document, the modes and models for
RSVP operation over ATM will be discussed followed by a
discussion of management of ATM VCs for RSVP data and control.
Lastly, the topic of encapsulations will be discussed in relation
to the models presented.
This document is part of a group of documents from the ISATM
subgroup of the ISSLL working group related to the operation of
IntServ and RSVP over ATM. [14] discusses the mapping of the
IntServ models for Controlled Load and Guaranteed Service to ATM.
[15 and 16] discuss implementation requirements and guidelines
for RSVP over ATM, respectively. While these documents may not
address all the issues raised in this document, they should
provide enough information for development of solutions for
IntServ and RSVP over ATM.
1.2 Terms
The terms "reservation" and "flow" are used in many contexts,
often with different meaning. These terms are used in this
document with the following meaning:
- Reservation is used in this document to refer to an RSVP
initiated request for resources. RSVP initiates requests for
resources based on RESV message processing. RESV messages that
simply refresh state do not trigger resource requests.
Resource requests may be made based on RSVP sessions and RSVP
reservation styles. RSVP styles dictate whether the reserved
resources are used by one sender or shared by multiple
senders. See [1] for details of each. Each new request is
referred to in this document as an RSVP reservation, or simply
reservation.
- Flow is used to refer to the data traffic associated with a
particular reservation. The specific meaning of flow is RSVP
style dependent. For shared style reservations, there is one
flow per session. For distinct style reservations, there is
one flow per sender (per session).
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2. Issues Regarding the Operation of RSVP and IntServ over ATM
The issues related to RSVP and IntServ over ATM fall into several
general classes:
- How to make RSVP run over ATM now and in the future
- When to set up a virtual circuit (VC) for a specific Quality
of Service (QoS) related to RSVP
- How to map the IntServ models to ATM QoS models
- How to know that an ATM network is providing the QoS necessary
for a flow
- How to handle the many-to-many connectionless features of IP
multicast and RSVP in the one-to-many connection-oriented
world of ATM
2.1 Modes/Models for RSVP and IntServ over ATM
[3] Discusses several different models for running IP over ATM
networks. [17, 18, and 20] also provide models for IP in ATM
environments. Any one of these models would work as long as the
RSVP control packets (IP protocol 46) and data packets can follow
the same IP path through the network. It is important that the
RSVP PATH messages follow the same IP path as the data such that
appropriate PATH state may be installed in the routers along the
path. For an ATM subnetwork, this means the ingress and egress
points must be the same in both directions for the RSVP control
and data messages. Note that the RSVP protocol does not require
symmetric routing. The PATH state installed by RSVP allows the
RESV messages to "retrace" the hops that the PATH message
crossed. Within each of the models for IP over ATM, there are
decisions about using different types of data distribution in ATM
as well as different connection initiation. The following
sections look at some of the different ways QoS connections can
be set up for RSVP.
2.1.1 UNI 3.x and 4.0
In the User Network Interface (UNI) 3.0 and 3.1 specifications
[8,9] and 4.0 specification, both permanent and switched virtual
circuits (PVC and SVC) may be established with a specified
service category (CBR, VBR, and UBR for UNI 3.x and VBR-rt and
ABR for 4.0) and specific traffic descriptors in point-to-point
and point-to-multipoint configurations. Additional QoS
parameters are not available in UNI 3.x and those that are
available are vendor-specific. Consequently, the level of QoS
control available in standard UNI 3.x networks is somewhat
limited. However, using these building blocks, it is possible to
use RSVP and the IntServ models. ATM 4.0 with the Traffic
Management (TM) 4.0 specification [21] allows much greater
control of QoS. [14] provides the details of mapping the IntServ
models to UNI 3.x and 4.0 service categories and traffic
parameters.
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2.1.1.1 Permanent Virtual Circuits (PVCs)
PVCs emulate dedicated point-to-point lines in a network, so the
operation of RSVP can be identical to the operation over any
point-to-point network. The QoS of the PVC must be consistent
and equivalent to the type of traffic and service model used.
The devices on either end of the PVC have to provide traffic
control services in order to multiplex multiple flows over the
same PVC. With PVCs, there is no issue of when or how long it
takes to set up VCs, since they are made in advance but the
resources of the PVC are limited to what has been pre-allocated.
PVCs that are not fully utilized can tie up ATM network resources
that could be used for SVCs.
2.1.1.2 Switched Virtual Circuits (SVCs)
SVCs allow paths in the ATM network to be set up "on demand".
This allows flexibility in the use of RSVP over ATM along with
some complexity. Parallel VCs can be set up to allow best-effort
and better service class paths through the network. The cost and
time to set up SVCs can impact their use. For example, it may be
better to initially route QoS traffic over existing VCs until an
SVC with the desired QoS has been set up. Scaling issues can
come into play if a single VC is used per RSVP flow. An RSVP
flow is a data flow from one or more sources to one or more
receivers as defined by an RSVP filter specification. The number
of VCs in any ATM device is limited so the number of RSVP flows
that can be handled by a device would be strictly limited to the
number of VCs available, if we assume one VC per flow.
2.1.1.3 Point to MultiPoint
In order to provide QoS for IP multicast, an important feature of
RSVP, data flows must be distributed to multiple destinations
from a given source. Point-to-multipoint VCs provide such a
mechanism. It is important to map the actions of IP multicasting
and RSVP (e.g. IGMP JOIN/LEAVE and RSVP RESV/RESV TEAR) to add
party and drop party functions for ATM. Point-to-multipoint VCs
as defined in UNI 3.x have a single service class for all
destinations. This is contrary to the RSVP "heterogeneous
receiver" concept. It is possible to set up a different VC to
each receiver requesting a different QoS, but this again can run
into scaling and resource problems when managing multiple VCs on
the same interface to different destinations.
RSVP sends messages both up and down the multicast distribution
tree. In the case of a large ATM cloud, this could result in a
RSVP message implosion at an RSVP traffic source with many
receivers.
ATM 4.0 expands on the point-to-multipoint VCs by adding a Leaf
Initiated Join (LIJ) capability. LIJ allows an ATM end point to
join into an existing point-to-multipoint VC without necessarily
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contacting the source of the VC. This will reduce the burden on
the ATM source point for setting up new branches and more closely
matches the receiver-based model of RSVP and IP multicast.
However, many of the same scaling issues exist and the new
branches added to a point-to-multipoint VC would use the same QoS
as existing branches.
2.1.1.4 Multicast Servers
IP-over-ATM has the concept of a multicast server or reflector
that can accept cells from multiple senders and send them via a
point-to-multipoint VC to a set of receivers. This moves the VC
scaling issues noted previously for point-to-multipoint VCs to
the multicast server. Additionally, the multicast server will
need to know how to interpret RSVP packets so it will be able to
provide VCs of the appropriate QoS for the flows.
2.1.2 Hop-by-Hop vs. Short Cut
If the ATM "cloud" is made up a number of logical IP subnets
(LISs), then it is possible to use "short cuts" from a node on
one LIS directly to a node on another LIS, avoiding router hops
between the LISs. NHRP [4], is one mechanism for determining the
ATM address of the egress point on the ATM network given a
destination IP address. It is a topic for further study to
determine if significant benefit is achieved from short cut
routes vs. the extra state required.
2.1.3 Future Models
ATM is constantly evolving. If we assume that RSVP and IntServ
applications are going to be wide-spread, it makes sense to
consider changes to ATM that would improve the operation of RSVP
and IntServ over ATM. Similarly, the RSVP protocol and IntServ
models will continue to evolve and changes that affect them
should also be considered. The following are a few ideas that
have been discussed that would make the integration of the
IntServ models and RSVP easier or more complete. They are
presented here to encourage continued development of ideas that
can help aid in the integration of RSVP, IntServ, and ATM.
2.1.3.1 Heterogeneous Point-to-MultiPoint
The IntServ models and RSVP support the idea of "heterogeneous
receivers"; e.g., not all receivers of a particular multicast
flow are required to ask for the same QoS from the network.
The most important scenario that can utilize this feature occurs
when some receivers in an RSVP session ask for a specific QoS
while others receive the flow with a best-effort service. In
some cases where there are multiple senders on a shared-
reservation flow (e.g., an audio conference), an individual
receiver only needs to reserve enough resources to receive one
sender at a time. However, other receivers may elect to reserve
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more resources, perhaps to allow for some amount of "over-
speaking" or in order to record the conference (post processing
during playback can separate the senders by their source
addresses).
In order to prevent denial-of-service attacks via reservations,
the service models do not allow the service elements to simply
drop non-conforming packets. For example, Controlled Load
service model [7] assigns non-conformant packets to best-effort
status (which may result in packet drops if there is congestion).
Emulating these behaviors over an ATM network is problematic and
needs to be studied. If a single maximum QoS is used over a
point-to-multipoint VC, resources could be wasted if cells are
sent over certain links where the reassembled packets will
eventually be dropped. In addition, the "maximum QoS" may
actually cause a degradation in service to the best-effort
branches.
The term "variegated VC" has been coined to describe a point-to-
multipoint VC that allows a different QoS on each branch. This
approach seems to match the spirit of the Integrated Service and
RSVP models, but some thought has to be put into the cell drop
strategy when traversing from a "bigger" branch to a "smaller"
one. The "best-effort for non-conforming packets" behavior must
also be retained. Early Packet Discard (EPD) schemes must be
used so that all the cells for a given packet can be discarded at
the same time rather than discarding only a few cells from
several packets making all the packets useless to the receivers.
2.1.3.2 Lightweight Signalling
Q.2931 signalling is very complete and carries with it a
significant burden for signalling in all possible public and
private connections. It might be worth investigating a lighter
weight signalling mechanism for faster connection setup in
private networks.
2.1.3.3 QoS Renegotiation
Another change that would help RSVP over ATM is the ability to
request a different QoS for an active VC. This would eliminate
the need to setup and tear down VCs as the QoS changed. RSVP
allows receivers to change their reservations and senders to
change their traffic descriptors dynamically. This, along with
the merging of reservations, can create a situation where the QoS
needs of a VC can change. Allowing changes to the QoS of an
existing VC would allow these features to work without creating a
new VC. In the ITU-T ATM specifications [??REF??], some cell
rates can be renegotiated. It is unclear if this is sufficient
for the QoS renegotiation needs of the IntServ models.
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2.1.3.4 Group Addressing
The model of one-to-many communications provided by point-to-
multipoint VCs does not really match the many-to-many
communications provided by IP multicasting. A scaleable mapping
from IP multicast addresses to an ATM "group address" can address
this problem.
2.1.3.5 Label Switching
The MultiProtocol Label Switching (MPLS) working group is
discussing methods for optimizing the use of ATM and other
switched networks for IP by encapsulating the data with a header
that is used by the interior switches to achieve faster
forwarding lookups. [22] discusses a framework for this work.
It is unclear how this work will affect IntServ and RSVP over
label switched networks but there may be some interactions.
2.1.4 QoS Routing
RSVP is explicitly not a routing protocol. However, since it
conveys QoS information, it may prove to be a valuable input to a
routing protocol that could make path determinations based on QoS
and network load information. In other words, instead of asking
for just the IP next hop for a given destination address, it
might be worthwhile for RSVP to provide information on the QoS
needs of the flow if routing has the ability to use this
information in order to determine a route. Other forms of QoS
routing have existed in the past such as using the IP TOS and
Precedence bits to select a path through the network. Some have
discussed using these same bits to select one of a set of
parallel ATM VCs as a form of QoS routing. The work in this area
is just starting and there are numerous issues to consider.
[23], as part of the work of the QoSR working group frame the
issues for QoS Routing in the Internet.
2.2 Reliance on Unicast and Multicast Routing
RSVP was designed to support both unicast and IP multicast
applications. This means that RSVP needs to work closely with
multicast and unicast routing. Unicast routing over ATM has been
addressed [10] and [11]. MARS [5] provides multicast address
resolution for IP over ATM networks, an important part of the
solution for multicast but still relies on multicast routing
protocols to connect multicast senders and receivers on different
subnets.
2.3 Aggregation of Flows
Some of the scaling issues noted in previous sections can be
addressed by aggregating several RSVP flows over a single VC if
the destinations of the VC match for all the flows being
aggregated. However, this causes considerable complexity in the
management of VCs and in the scheduling of packets within each VC
at the root point of the VC. Note that the rescheduling of flows
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within a VC is not possible in the switches in the core of the
ATM network. Additionally, virtual paths (VPs) could be used for
aggregating multiple VCs.
2.4 Mapping QoS Parameters
The mapping of QoS parameters from the IntServ models to the ATM
service classes is an important issue in making RSVP and IntServ
work over ATM. [14] addresses these issues very completely for
the Controlled Load and Guaranteed Service models. An additional
issue is that while some guidelines can be developed for mapping
the parameters of a given service model to the traffic
descriptors of an ATM traffic class, implementation variables,
policy, and cost factors can make strict standards problematic.
2.5 Directly Connected ATM Hosts
It is obvious that the needs of hosts that are directly connected
to ATM networks must be considered for RSVP and IntServ over ATM.
Functionality for RSVP over ATM must not assume that an ATM host
has all the functionality of a router, but such things as MARS
and NHRP clients might be worthwhile features.
2.6 Accounting and Policy Issues
Since RSVP and IntServ create classes of preferential service,
some form of administrative control and/or cost allocation is
needed to control abuse. There are certain types of policies
specific to ATM and IP over ATM that need to be studied to
determine how they interoperate with the IP policies being
developed. Typical IP policies would be that only certain users
are allowed to make reservations. This policy would translate
well to IP over ATM due to the similarity to the mechanisms used
for Call Admission Control (CAC). There may be a need for
policies specific to IP over ATM. For example, since signalling
costs in ATM are high relative to IP, an IP over ATM specific
policy might restrict the ability to change the prevailing QoS in
a VC. If VCs are relatively scarce, there also might be specific
accounting costs in creating a new VC. The work so far has been
preliminary, and much work remains to be done. The policy
mechanisms outlined in [12] and [13] provide the basic mechanisms
for implementing policies for RSVP and IntServ over any media,
not just ATM.
3. RSVP VC Management
This section goes into more detail on the issues related to the
management of SVCs for RSVP and IntServ.
3.1 VC Initiation
There is an apparent mismatch between RSVP and ATM. Specifically,
RSVP control is receiver oriented and ATM control is sender
oriented. This initially may seem like a major issue, but really
is not. While RSVP reservation (RESV) requests are generated at
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the receiver, actual allocation of resources takes place at the
subnet sender. For data flows, this means that subnet senders
will establish all QoS VCs and the subnet receiver must be able
to accept incoming QoS VCs. These restrictions are consistent
with RSVP version 1 processing rules and allow senders to use
different flow to VC mappings and even different QoS
renegotiation techniques without interoperability problems. All
RSVP over ATM approaches that have VCs initiated and controlled
by the subnet senders will interoperate.
The use of the reverse path provided by point-to-point VCs by
receivers is for further study. There are two related issues. The
first is that use of the reverse path requires the VC initiator
to set appropriate reverse path QoS parameters. The second issue
is that reverse paths are not available with point-to-multipoint
VCs, so reverse paths could only be used to support unicast RSVP
reservations.
3.2 Policy
RSVP allows for local policy control [13,14] as well as admission
control. Thus a user can request a reservation with a specific
QoS and with a policy object that, for example, offers to pay for
additional costs setting up a new reservation. The policy module
at the entry to a provider can decide how to satisfy that request
- either by merging the request in with an existing reservation
or by creating a new reservation for this (and perhaps other)
users. This policy can be on a per user-provider basis where a
user and a provider have an agreement on the type of service
offered, or on a provider-provider basis, where two providers
have such an agreement. With the ability to do local policy
control, providers can offer services best suited to their own
resources and their customers needs. Policy is expected to be
provided as a generic API which will return values indicating
what action should be taken for a specific reservation request.
The API is expected to have access to the reservation tables with
the QoS for each reservation. The RSVP Policy and Integrity
objects will be passed to the policy() call. Four possible return
values are expected. The request can be rejected. The request can
be accepted as is. The request can be accepted but at a different
QoS. The request can cause a change of QoS of an existing
reservation. The information returned from this call is be used
to call the admission control interface.
3.3 Data VC Management
Any RSVP over ATM implementation must map RSVP and RSVP
associated data flows to ATM Virtual Circuits (VCs). LAN
Emulation [17], Classical IP [10] and, more recently, NHRP [4]
discuss mapping IP traffic onto ATM SVCs, but they only cover a
single QoS class, i.e., best effort traffic. When QoS is
introduced, VC mapping must be revisited. For RSVP controlled QoS
flows, one issue is VCs to use for QoS data flows.
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In the Classic IP over ATM and current NHRP models, a single
point-to-point VC is used for all traffic between two ATM
attached hosts (routers and end-stations). It is likely that
such a single VC will not be adequate or optimal when supporting
data flows with multiple QoS types. RSVP's basic purpose is to
install support for flows with multiple QoS types, so it is
essential for any RSVP over ATM solution to address VC usage for
QoS data flows.
RSVP reservation styles will also need to be taken into account
in any VC usage strategy.
This section describes issues and methods for management of VCs
associated with QoS data flows. When establishing and maintaining
VCs, the subnet sender will need to deal with several
complicating factors including multiple QoS reservations,
requests for QoS changes, ATM short-cuts, and several multicast
specific issues. The multicast specific issues result from the
nature of ATM connections. The key multicast related issues are
heterogeneity, data distribution, receiver transitions, and end-
point identification.
3.3.1 Reservation to VC Mapping
There are various approaches available for mapping reservations
on to VCs. A distinguishing attribute of all approaches is how
reservations are combined on to individual VCs. When mapping
reservations on to VCs, individual VCs can be used to support a
single reservation, or reservation can be combined with others on
to "aggregate" VCs. In the first case, each reservation will be
supported by one or more VCs. Multicast reservation requests may
translate into the setup of multiple VCs as is described in more
detail in section 3.3.2. Unicast reservation requests will
always translate into the setup of a single QoS VC. In both
cases, each VC will only carry data associated with a single
reservation. The greatest benefit if this approach is ease of
implementation, but it comes at the cost of increased (VC) setup
time and the consumption of greater number of VC and associated
resources. We refer to the other case, when reservations are not
combined, as the "aggregation" model. With this model, large VCs
could be set up between IP routers and hosts in an ATM network.
These VCs could be managed much like IP Integrated Service (IIS)
point-to-point links (e.g. T-1, DS-3) are managed now. Traffic
from multiple sources over multiple RSVP sessions might be
multiplexed on the same VC. This approach has a number of
advantages. First, there is typically no signalling latency as
VCs would be in existence when the traffic started flowing, so no
time is wasted in setting up VCs. Second, the heterogeneity
problem (section 3.3.2) in full over ATM has been reduced to a
solved problem. Finally, the dynamic QoS problem (section 3.3.6)
for ATM has also been reduced to a solved problem.
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This approach can be used with point-to-point and point-to-
multipoint VCs. The problem with the aggregation approach is
that the choice of what QoS to use for which of the VCs is
difficult, but is made easier since the VCs can be changed as
needed. The advantages of this scheme makes this approach an
item for high priority study.
3.3.2 Heterogeneity
Heterogeneity occurs when receivers request different qualities
of service within a single session. This means that the amount
of requested resources differs on a per next hop basis. A related
type of heterogeneity occurs due to best-effort receivers. In
any IP multicast group, it is possible that some receivers will
request QoS (via RSVP) and some receivers will not. In shared
media, like Ethernet, receivers that have not requested resources
can typically be given identical service to those that have
without complications. This is not the case with ATM. In ATM
networks, any additional end-points of a VC must be explicitly
added. There may be costs associated with adding the best-effort
receiver, and there might not be adequate resources. An RSVP
over ATM solution will need to support heterogeneous receivers
even though ATM does not currently provide such support directly.
RSVP heterogeneity is supported over ATM in the way RSVP
reservations are mapped into ATM VCs. There are four alternative
approaches this mapping. There are multiple models for supporting
RSVP heterogeneity over ATM. Section 3.3.2.1 examines the
multiple VCs per RSVP reservation (or full heterogeneity) model
where a single reservation can be forwarded into several VCs each
with a different QoS. Section 3.3.2.2 presents a limited
heterogeneity model where exactly one QoS VC is used along with a
best effort VC. Section 3.3.2.3 examines the VC per RSVP
reservation (or homogeneous) model, where each RSVP reservation
is mapped to a single ATM VC. Section 3.3.2.4 describes the
aggregation model allowing aggregation of multiple RSVP
reservations into a single VC. Further study is being done on
the aggregation model.
3.3.2.1 Full Heterogeneity Model
RSVP supports heterogeneous QoS, meaning that different receivers
of the same multicast group can request a different QoS. But
importantly, some receivers might have no reservation at all and
want to receive the traffic on a best effort service basis. The
IP model allows receivers to join a multicast group at any time
on a best effort basis, and it is important that ATM as part of
the Internet continue to provide this service. We define the
"full heterogeneity" model as providing a separate VC for each
distinct QoS for a multicast session including best effort and
one or more qualities of service.
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Note that while full heterogeneity gives users exactly what they
request, it requires more resources of the network than other
possible approaches. The exact amount of bandwidth used for
duplicate traffic depends on the network topology and group
membership.
3.3.2.2 Limited Heterogeneity Model
We define the "limited heterogeneity" model as the case where the
receivers of a multicast session are limited to use either best
effort service or a single alternate quality of service. The
alternate QoS can be chosen either by higher level protocols or
by dynamic renegotiation of QoS as described below.
In order to support limited heterogeneity, each ATM edge device
participating in a session would need at most two VCs. One VC
would be a point-to-multipoint best effort service VC and would
serve all best effort service IP destinations for this RSVP
session.
The other VC would be a point to multipoint VC with QoS and would
serve all IP destinations for this RSVP session that have an RSVP
reservation established.
As with full heterogeneity, a disadvantage of the limited
heterogeneity scheme is that each packet will need to be
duplicated at the network layer and one copy sent into each of
the 2 VCs. Again, the exact amount of excess traffic will depend
on the network topology and group membership. If any of the
existing QoS VC end-points cannot upgrade to the new QoS, then
the new reservation fails though the resources exist for the new
receiver.
3.3.2.3 Homogeneous and Modified Homogeneous Models
We define the "homogeneous" model as the case where all receivers
of a multicast session use a single quality of service VC. Best-
effort receivers also use the single RSVP triggered QoS VC. The
single VC can be a point-to-point or point-to-multipoint as
appropriate. The QoS VC is sized to provide the maximum resources
requested by all RSVP next-hops.
This model matches the way the current RSVP specification
addresses heterogeneous requests. The current processing rules
and traffic control interface describe a model where the largest
requested reservation for a specific outgoing interface is used
in resource allocation, and traffic is transmitted at the higher
rate to all next-hops. This approach would be the simplest method
for RSVP over ATM implementations.
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While this approach is simple to implement, providing better than
best-effort service may actually be the opposite of what the user
desires. There may be charges incurred or resources that are
wrongfully allocated. There are two specific problems. The first
problem is that a user making a small or no reservation would
share a QoS VC resources without making (and perhaps paying for)
an RSVP reservation. The second problem is that a receiver may
not receive any data. This may occur when there is insufficient
resources to add a receiver. The rejected user would not be
added to the single VC and it would not even receive traffic on a
best effort basis.
Not sending data traffic to best-effort receivers because of
another receiver's RSVP request is clearly unacceptable. The
previously described limited heterogeneous model ensures that
data is always sent to both QoS and best-effort receivers, but it
does so by requiring replication of data at the sender in all
cases. It is possible to extend the homogeneous model to both
ensure that data is always sent to best-effort receivers and also
to avoid replication in the normal case. This extension is to
add special handling for the case where a best-effort receiver
cannot be added to the QoS VC. In this case, a best effort VC
can be established to any receivers that could not be added to
the QoS VC. Only in this special error case would senders be
required to replicate data. We define this approach as the
"modified homogeneous" model.
3.3.2.4 Aggregation
The last scheme is the multiple RSVP reservations per VC (or
aggregation) model. With this model, large VCs could be set up
between IP routers and hosts in an ATM network. These VCs could
be managed much like IP Integrated Service (IIS) point-to-point
links (e.g. T-1, DS-3) are managed now. Traffic from multiple
sources over multiple RSVP sessions might be multiplexed on the
same VC. This approach has a number of advantages. First, there
is typically no signalling latency as VCs would be in existence
when the traffic started flowing, so no time is wasted in setting
up VCs. Second, the heterogeneity problem in full over ATM has
been reduced to a solved problem. Finally, the dynamic QoS
problem for ATM has also been reduced to a solved problem. This
approach can be used with point-to-point and point-to-multipoint
VCs. The problem with the aggregation approach is that the choice
of what QoS to use for which of the VCs is difficult, but is made
easier since the VCs can be changed as needed. The advantages of
this scheme makes this approach an item for high priority study.
3.3.3 Multicast End-Point Identification
Implementations must be able to identify ATM end-points
participating in an IP multicast group. The ATM end-points will
be IP multicast receivers and/or next-hops. Both QoS and best-
effort end-points must be identified. RSVP next-hop information
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will provide QoS end-points, but not best-effort end-points.
Another issue is identifying end-points of multicast traffic
handled by non-RSVP capable next-hops. In this case a PATH
message travels through a non-RSVP egress router on the way to
the next hop RSVP node. When the next hop RSVP node sends a RESV
message it may arrive at the source over a different route than
what the data is using. The source will get the RESV message, but
will not know which egress router needs the QoS. For unicast
sessions, there is no problem since the ATM end-point will be the
IP next-hop router. Unfortunately, multicast routing may not be
able to uniquely identify the IP next-hop router. So it is
possible that a multicast end-point can not be identified.
In the most common case, MARS will be used to identify all end-
points of a multicast group. In the router to router case, a
multicast routing protocol may provide all next-hops for a
particular multicast group. In either case, RSVP over ATM
implementations must obtain a full list of end-points, both QoS
and non-QoS, using the appropriate mechanisms. The full list can
be compared against the RSVP identified end-points to determine
the list of best-effort receivers. There is no straightforward
solution to uniquely identifying end-points of multicast traffic
handled by non-RSVP next hops. The preferred solution is to use
multicast routing protocols that support unique end-point
identification. In cases where such routing protocols are
unavailable, all IP routers that will be used to support RSVP
over ATM should support RSVP. To ensure proper behavior,
implementations should, by default, only establish RSVP-initiated
VCs to RSVP capable end-points.
3.3.4 Multicast Data Distribution
Two models are planned for IP multicast data distribution over
ATM. In one model, senders establish point-to-multipoint VCs to
all ATM attached destinations, and data is then sent over these
VCs. This model is often called "multicast mesh" or "VC mesh"
mode distribution. In the second model, senders send data over
point-to-point VCs to a central point and the central point
relays the data onto point-to-multipoint VCs that have been
established to all receivers of the IP multicast group. This
model is often referred to as "multicast server" mode
distribution. RSVP over ATM solutions must ensure that IP
multicast data is distributed with appropriate QoS.
In the Classical IP context, multicast server support is provided
via MARS [5]. MARS does not currently provide a way to
communicate QoS requirements to a MARS multicast server.
Therefore, RSVP over ATM implementations must, by default,
support "mesh-mode" distribution for RSVP controlled multicast
flows. When using multicast servers that do not support QoS
requests, a sender must set the service, not global, break
bit(s).
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3.3.5 Receiver Transitions
When setting up a point-to-multipoint VCs there will be a time
when some receivers have been added to a QoS VC and some have
not. During such transition times it is possible to start
sending data on the newly established VC. The issue is when to
start send data on the new VC. If data is sent both on the new
VC and the old VC, then data will be delivered with proper QoS to
some receivers and with the old QoS to all receivers. This means
the QoS receivers would get duplicate data. If data is sent just
on the new QoS VC, the receivers that have not yet been added
will lose information. So, the issue comes down to whether to
send to both the old and new VCs, or to send to just one of the
VCs. In one case duplicate information will be received, in the
other some information may not be received.
This issue needs to be considered for three cases: when
establishing the first QoS VC, when establishing a VC to support
a QoS change, and when adding a new end-point to an already
established QoS VC.
The first two cases are very similar. It both, it is possible to
send data on the partially completed new VC, and the issue of
duplicate versus lost information is the same. The last case is
when an end-point must be added to an existing QoS VC. In this
case the end-point must be both added to the QoS VC and dropped
from a best-effort VC. The issue is which to do first. If the
add is first requested, then the end-point may get duplicate
information. If the drop is requested first, then the end-point
may loose information.
In order to ensure predictable behavior and delivery of data to
all receivers, data can only be sent on a new VCs once all
parties have been added. This will ensure that all data is only
delivered once to all receivers. This approach does not quite
apply for the last case. In the last case, the add operation
should be completed first, then the drop operation. This means
that receivers must be prepared to receive some duplicate packets
at times of QoS setup.
3.3.6 Dynamic QoS
RSVP provides dynamic quality of service (QoS) in that the
resources that are requested may change at any time. There are
several common reasons for a change of reservation QoS. First,
an existing receiver can request a new larger (or smaller) QoS.
Second, a sender may change its traffic specification (TSpec),
which can trigger a change in the reservation requests of the
receivers. Third, a new sender can start sending to a multicast
group with a larger traffic specification than existing senders,
triggering larger reservations. Finally, a new receiver can make
a reservation that is larger than existing reservations. If the
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limited heterogeneity model is being used and the merge node for
the larger reservation is an ATM edge device, a new larger
reservation must be set up across the ATM network. Since ATM
service, as currently defined in UNI 3.x and UNI 4.0, does not
allow renegotiating the QoS of a VC, dynamically changing the
reservation means creating a new VC with the new QoS, and tearing
down an established VC. Tearing down a VC and setting up a new VC
in ATM are complex operations that involve a non-trivial amount
of processor time, and may have a substantial latency. There are
several options for dealing with this mismatch in service. A
specific approach will need to be a part of any RSVP over ATM
solution.
The default method for supporting changes in RSVP reservations is
to attempt to replace an existing VC with a new appropriately
sized VC. During setup of the replacement VC, the old VC must be
left in place unmodified. The old VC is left unmodified to
minimize interruption of QoS data delivery. Once the replacement
VC is established, data transmission is shifted to the new VC,
and the old VC is then closed. If setup of the replacement VC
fails, then the old QoS VC should continue to be used. When the
new reservation is greater than the old reservation, the
reservation request should be answered with an error. When the
new reservation is less than the old reservation, the request
should be treated as if the modification was successful. While
leaving the larger allocation in place is suboptimal, it
maximizes delivery of service to the user. Implementations should
retry replacing the too large VC after some appropriate elapsed
time.
One additional issue is that only one QoS change can be processed
at one time per reservation. If the (RSVP) requested QoS is
changed while the first replacement VC is still being setup, then
the replacement VC is released and the whole VC replacement
process is restarted. To limit the number of changes and to avoid
excessive signalling load, implementations may limit the number
of changes that will be processed in a given period. One
implementation approach would have each ATM edge device
configured with a time parameter T (which can change over time)
that gives the minimum amount of time the edge device will wait
between successive changes of the QoS of a particular VC. Thus
if the QoS of a VC is changed at time t, all messages that would
change the QoS of that VC that arrive before time t+T would be
queued. If several messages changing the QoS of a VC arrive
during the interval, redundant messages can be discarded. At time
t+T, the remaining change(s) of QoS, if any, can be executed.
This timer approach would apply more generally to any network
structure, and might be worthwhile to incorporate into RSVP.
The sequence of events for a single VC would be
- Wait if timer is active
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- Establish VC with new QoS
- Remap data traffic to new VC
- Tear down old VC
- Activate timer
There is an interesting interaction between heterogeneous
reservations and dynamic QoS. In the case where a RESV message is
received from a new next-hop and the requested resources are
larger than any existing reservation, both dynamic QoS and
heterogeneity need to be addressed. A key issue is whether to
first add the new next-hop or to change to the new QoS. This is a
fairly straight forward special case. Since the older, smaller
reservation does not support the new next-hop, the dynamic QoS
process should be initiated first. Since the new QoS is only
needed by the new next-hop, it should be the first end-point of
the new VC. This way signalling is minimized when the setup to
the new next-hop fails.
3.3.7 Short-Cuts
Short-cuts [4] allow ATM attached routers and hosts to directly
establish point-to-point VCs across LIS boundaries, i.e., the VC
end-points are on different IP subnets. The ability for short-
cuts and RSVP to interoperate has been raised as a general
question. The area of concern is the ability to handle
asymmetric short-cuts. Specifically how RSVP can handle the case
where a downstream short-cut may not have a matching upstream
short-cut. In this case, PATH and RESV messages following
different paths.
Examination of RSVP shows that the protocol already includes
mechanisms that will support short-cuts. The mechanism is the
same one used to support RESV messages arriving at the wrong
router and the wrong interface. The key aspect of this mechanism
is RSVP only processing messages that arrive at the proper
interface and RSVP forwarding of messages that arrive on the
wrong interface. The proper interface is indicated in the NHOP
object of the message. So, existing RSVP mechanisms will support
asymmetric short-cuts. The short-cut model of VC establishment
still poses several issues when running with RSVP. The major
issues are dealing with established best-effort short-cuts, when
to establish short-cuts, and QoS only short-cuts. These issues
will need to be addressed by RSVP implementations.
The key issue to be addressed by any RSVP over ATM solution is
when to establish a short-cut for a QoS data flow. The default
behavior is to simply follow best-effort traffic. When a short-
cut has been established for best-effort traffic to a destination
or next-hop, that same end-point should be used when setting up
RSVP triggered VCs for QoS traffic to the same destination or
next-hop. This will happen naturally when PATH messages are
forwarded over the best-effort short-cut. Note that in this
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approach when best-effort short-cuts are never established, RSVP
triggered QoS short-cuts will also never be established.
3.3.8 VC Teardown
RSVP can identify from either explicit messages or timeouts when
a data VC is no longer needed. Therefore, data VCs set up to
support RSVP controlled flows should only be released at the
direction of RSVP. VCs must not be timed out due to inactivity by
either the VC initiator or the VC receiver. This conflicts with
VCs timing out as described in RFC 1755 [11], section 3.4 on VC
Teardown. RFC 1755 recommends tearing down a VC that is inactive
for a certain length of time. Twenty minutes is recommended. This
timeout is typically implemented at both the VC initiator and the
VC receiver. Although, section 3.1 of the update to RFC 1755
[11] states that inactivity timers must not be used at the VC
receiver.
When this timeout occurs for an RSVP initiated VC, a valid VC
with QoS will be torn down unexpectedly. While this behavior is
acceptable for best-effort traffic, it is important that RSVP
controlled VCs not be torn down. If there is no choice about the
VC being torn down, the RSVP daemon must be notified, so a
reservation failure message can be sent.
For VCs initiated at the request of RSVP, the configurable
inactivity timer mentioned in [11] must be set to "infinite".
Setting the inactivity timer value at the VC initiator should not
be problematic since the proper value can be relayed internally
at the originator. Setting the inactivity timer at the VC
receiver is more difficult, and would require some mechanism to
signal that an incoming VC was RSVP initiated. To avoid this
complexity and to conform to \cite{kn:1755up}, implementations
must not use an inactivity timer to clear received connections.
3.4 RSVP Control Management
One last important issue is providing a data path for the RSVP
messages themselves. There are two main types of messages in
RSVP, PATH and RESV. PATH messages are sent to a multicast
address, while RESV messages are sent to a unicast address. Other
1
RSVP messages are handled similar to either PATH or RESV . So
ATM VCs used for RSVP signalling messages need to provide both
unicast and multicast functionality. There are several different
approaches for how to assign VCs to use for RSVP signalling
messages.
The main approaches are:
- use same VC as data
- single VC per session
- single point-to-multipoint VC multiplexed among sessions
1
This can be slightly more complicated for RERR messages
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- multiple point-to-point VCs multiplexed among sessions
There are several different issues that affect the choice of how
to assign VCs for RSVP signalling. One issue is the number of
additional VCs needed for RSVP signalling. Related to this issue
is the degree of multiplexing on the RSVP VCs. In general more
multiplexing means less VCs. An additional issue is the latency
in dynamically setting up new RSVP signalling VCs. A final issue
is complexity of implementation. The remainder of this section
discusses the issues and tradeoffs among these different
approaches and suggests guidelines for when to use which
alternative.
3.4.1 Mixed data and control traffic
In this scheme RSVP signalling messages are sent on the same VCs
as is the data traffic. The main advantage of this scheme is that
no additional VCs are needed beyond what is needed for the data
traffic. An additional advantage is that there is no ATM
signalling latency for PATH messages (which follow the same
routing as the data messages). However there can be a major
problem when data traffic on a VC is nonconforming. With
nonconforming traffic, RSVP signalling messages may be dropped.
While RSVP is resilient to a moderate level of dropped messages,
excessive drops would lead to repeated tearing down and re-
establishing QoS VCs, a very undesirable behavior for ATM. Due to
these problems, this is not a good choice for providing RSVP
signalling messages, even though the number of VCs needed for
this scheme is minimized. One variation of this scheme is to use
the best effort data path for signalling traffic. In this scheme,
there is no issue with nonconforming traffic, but there is an
issue with congestion in the ATM network. RSVP provides some
resiliency to message loss due to congestion, but RSVP control
messages should be offered a preferred class of service. A
related variation of this scheme that is hopeful but requires
further study is to have a packet scheduling algorithm (before
entering the ATM network) that gives priority to the RSVP
signalling traffic. This can be difficult to do at the IP layer.
3.4.1.1 Single RSVP VC per RSVP Reservation
In this scheme, there is a parallel RSVP signalling VC for each
RSVP reservation. This scheme results in twice the minimum number
of VCs, but means that RSVP signalling messages have the
advantage of a separate VC. This separate VC means that RSVP
signalling messages have their own traffic contract and compliant
signalling messages are not subject to dropping due to other
noncompliant traffic (such as can happen with the scheme in
section 3.4.1). The advantage of this scheme is its simplicity -
whenever a data VC is created, a separate RSVP signalling VC is
created. The disadvantage of the extra VC is that extra ATM
signalling needs to be done. Additionally, this scheme requires
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twice the minimum number of VCs and also additional latency, but
is quite simple.
3.4.1.2 Multiplexed point-to-multipoint RSVP VCs
In this scheme, there is a single point-to-multipoint RSVP
signalling VC for each unique ingress router and unique set of
egress routers. This scheme allows multiplexing of RSVP
signalling traffic that shares the same ingress router and the
same egress routers. This can save on the number of VCs, by
multiplexing, but there are problems when the destinations of the
multiplexed point-to-multipoint VCs are changing. Several
alternatives exist in these cases, that have applicability in
different situations. First, when the egress routers change, the
ingress router can check if it already has a point-to-multipoint
RSVP signalling VC for the new list of egress routers. If the
RSVP signalling VC already exists, then the RSVP signalling
traffic can be switched to this existing VC. If no such VC
exists, one approach would be to create a new VC with the new
list of egress routers. Other approaches include modifying the
existing VC to add an egress router or using a separate new VC
for the new egress routers. When a destination drops out of a
group, an alternative would be to keep sending to the existing VC
even though some traffic is wasted. The number of VCs used in
this scheme is a function of traffic patterns across the ATM
network, but is always less than the number used with the Single
RSVP VC per data VC. In addition, existing best effort data VCs
could be used for RSVP signalling. Reusing best effort VCs saves
on the number of VCs at the cost of higher probability of RSVP
signalling packet loss. One possible place where this scheme
will work well is in the core of the network where there is the
most opportunity to take advantage of the savings due to
multiplexing. The exact savings depend on the patterns of
traffic and the topology of the ATM network.
3.4.1.3 Multiplexed point-to-point RSVP VCs
In this scheme, multiple point-to-point RSVP signalling VCs are
used for a single point-to-multipoint data VC. This scheme
allows multiplexing of RSVP signalling traffic but requires the
same traffic to be sent on each of several VCs. This scheme is
quite flexible and allows a large amount of multiplexing.
Since point-to-point VCs can set up a reverse channel at the same
time as setting up the forward channel, this scheme could save
substantially on signalling cost. In addition, signalling
traffic could share existing best effort VCs. Sharing existing
best effort VCs reduces the total number of VCs needed, but might
cause signalling traffic drops if there is congestion in the ATM
network. This point-to-point scheme would work well in the core
of the network where there is much opportunity for multiplexing.
Also in the core of the network, RSVP VCs can stay permanently
established either as Permanent Virtual Circuits (PVCs) or as
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long lived Switched Virtual Circuits (SVCs). The number of VCs in
this scheme will depend on traffic patterns, but in the core of a
network would be approximately n(n-1)/2 where n is the number of
IP nodes in the network. In the core of the network, this will
typically be small compared to the total number of VCs.
3.4.2 QoS for RSVP VCs
There is an issue for what QoS, if any, to assign to the RSVP
VCs. For other RSVP VC schemes, a QoS (possibly best effort) will
be needed. What QoS to use partially depends on the expected
level of multiplexing that is being done on the VCs, and the
expected reliability of best effort VCs. Since RSVP signalling is
infrequent (typically every 30 seconds), only a relatively small
QoS should be needed. This is important since using a larger QoS
risks the VC setup being rejected for lack of resources. Falling
back to best effort when a QoS call is rejected is possible, but
if the ATM net is congested, there will likely be problems with
RSVP packet loss on the best effort VC also. Additional
experimentation is needed in this area.
Implementations must, by default, send RSVP control (messages)
over the best effort data path, see figure. This approach
minimizes VC requirements since the best effort data path will
need to exist in order for RSVP sessions to be established and in
order for RSVP reservations to be initiated.
The specific best effort paths that will be used by RSVP are: for
unicast, the same VC used to reach the unicast destination; and
for multicast, the same VC that is used for best effort traffic
destined to the IP multicast group. Note that there may be
another best effort VC that is used to carry session data
traffic.
The disadvantage of this approach is that best effort VCs may not
provide the reliability that RSVP needs. However the best-effort
path is expected to satisfy RSVP reliability requirements in most
networks. Especially since RSVP allows for a certain amount of
packet loss without any loss of state synchronization. In all
cases, RSVP control traffic should be offered a preferred class
of service.
4. Encapsulation
Since RSVP is a signalling protocol used to control flows of IP
data packets, encapsulation for both RSVP packets and associated
IP data packets must be defined. There are currently two
encapsulation options for running IP over ATM, RFC 1483 and LANE.
There is also the possibility of future encapsulation options,
such as MPOA [18]. The first option is described in RFC 1483
[19] and is currently used for "Classical" IP over ATM and NHRP.
The second option is LAN Emulation, as described in [17]. LANE
encapsulation does not currently include a QoS signalling
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interface. If LANE encapsulation is needed, LANE QoS signalling
would first need to be defined by the ATM Forum. It is possible
that LANE 2.0 will include the required QoS support.
The default behavior for implementations must be to use a
consistent encapsulation scheme for all IP over ATM packets.
This includes RSVP packets and associated IP data packets. So,
encapsulation used on QoS data VCs and related control VCs must,
by default, be the same as used by best-effort VCs.
5. Security Considerations
The same considerations stated in [1] and [11] apply to this
document. There are no additional security issues raised in this
document.
6. References
[1] R. Braden, L. Zhang, S. Berson, S. Herzog, S.
Jamin. Resource
ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification. Internet Draft, draft-ietf-rsvp-spec-14.
November 1996.
[2] M. Borden, E. Crawley, B. Davie, S. Batsell.
Integration of
Real-time Services in an IP-ATM Network Architecture.
Request for Comments (Informational) RFC 1821, August 1995.
[3] R. Cole, D. Shur, C. Villamizar. IP over ATM: A
Framework
Document. Request for Comments (Informational), RFC 1932,
April 1996.
[4] D. Katz, D. Piscitello, B. Cole, J. Luciani.
NBMA Next Hop
Resolution Protocol (NHRP). Internet Draft, draft-ietf-rolc-
nhrp-11.txt, March 1997.
[5] G. Armitage, Support for Multicast over UNI
3.0/3.1 based ATM
Networks. RFC 2022. November 1996.
[6] S. Shenker, C. Partridge. Specification of
Guaranteed Quality
of Service. Internet Draft, draft-ietf-intserv-guaranteed-
svc-07.txt, February 1997.
[7] J. Wroclawski. Specification of the
Controlled-Load Network
Element Service. Internet Draft, draft-ietf-intserv-ctrl-
load-svc-05.txt, May 1997.
[8] ATM Forum. ATM User-Network Interface
Specification Version
3.0. Prentice Hall, September 1993
[9] ATM Forum. ATM User Network Interface (UNI)
Specification
Version 3.1. Prentice Hall, June 1995.
[10]M . Laubach, Classical IP and ARP over ATM.
Request for
Comments (Proposed Standard) RFC1577, January 1994.
[11]M . Perez, A. Mankin, E. Hoffman, G. Grossman,
A. Malis, ATM
Signalling Support for IP over ATM, Request for Comments
(Proposed Standard) RFC1755, February 1995.
[12]S . Herzog. RSVP Extensions for Policy
Control. Internet
Draft, draft-ietf-rsvp-policy-ext-02.txt, April 1997.
[13]S . Herzog. Local Policy Modules (LPM): Policy
Control for
RSVP, Internet Draft, draft-ietf-rsvp-policy-lpm-01.txt,
November 1996.
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[14]M . Borden, M. Garrett. Interoperation of
Controlled-Load and
Guaranteed Service with ATM, Internet Draft, draft-ietf-
issll-atm-mapping-02.txt, March 1997.
[15]L . Berger. RSVP over ATM Implementation
Requirements.
Internet Draft, draft-ietf-issll-atm-imp-req-00.txt, July
1997.
[16]L . Berger. RSVP over ATM Implementation
Guidelines. Internet
Draft, draft-ietf-issll-atm-imp-guide-01.txt, July 1997.
[17]A TM Forum Technical Committee. LAN Emulation
over ATM,
Version 1.0 Specification, af-lane-0021.000, January 1995.
[18]A TM Forum Technical Committee. Baseline Text
for MPOA, af-95-
0824r9, September 1996.
[19]J . Heinanen. Multiprotocol Encapsulation over
ATM Adaptation
Layer 5, RFC 1483, July 1993.
[20]A TM Forum Technical Committee. LAN Emulation
over ATM Version
2 - LUNI Specification, December 1996. [zzz Need to update
this ref.]
[21]A TM Forum Technical Committee. Traffic Management
Specification v4.0, af-tm-0056.000, April 1996.
[22]R . Callon, et al. A Framework for
Multiprotocol Label
Switching, Internet Draft, draft-ietf-mpls-framework-00.txt,
May 1997.
[23]B . Rajagopalan, R. Nair, H. Sandick, E.
Crawley. A Framework
for QoS-based Routing in the Internet, Internet Draft, draft-
ietf-qosr-framework-00.txt, March 1997.
7. Author's Address
Eric S. Crawley
Gigapacket Networks
25 Porter Road
Littleton, Ma 01460
+1 508 486-0665
esc@gigapacket.com
Lou Berger
FORE Systems
6905 Rockledge Drive
Suite 800
Bethesda, MD 20817
+1 301 571-2534
lberger@fore.com
Steven Berson
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
+1 310 822-1511
berson@isi.edu
Fred Baker
Cisco Systems
Expires January 1998 Page 24
Internet Draft Framework for IntServ and RSVP over ATM July 1997
519 Lado Drive
Santa Barbara, California 93111
+1 805 681-0115
fred@cisco.com
Marty Borden
New Oak Communications
42 Nanog Park
Acton, MA 01720
+1 508 266-1011
mborden@newoak.com
John J. Krawczyk
ArrowPoint Communications
235 Littleton Road
Westford, Massachusetts 01886
+1 508 692-5875
jj@arrowpoint.com
Expires January 1998 Page 25
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