INTERNET-DRAFT Mark W. Garrett,
Bellcore
Marty Borden,
New Oak, Inc.
November, 1996.
Interoperation of Controlled-Load and Guaranteed-Service with ATM
<draft-ietf-issll-atm-mapping-01.txt>
Status of this Memo
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Abstract
Service mappings are an important aspect of effective interoperation
between Internet Integrated Services and ATM networks. Both Internet
and ATM technologies have well-defined service architectures. These
include definitions of several services and associated parameters
which quantify source traffic and Quality of Service (QoS)
requirements.
This draft provides mappings between IP and ATM services which will
facilitate effective end-to-end Quality of Service for IP networks
containing ATM subnetworks. We discuss the various features of
Guaranteed Service and Controlled Load Service, and identify
appropriate mechanisms in ATM Virtual Circuits (VCs), which
facilitate these services.
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0.0 What's New in This Version
Section 3.2 on use of AdSpec in Guaranteed Service.
Expanded Section 2.5 on traffic descriptor mapping.
Placeholder Section 3.1 on handling of excess traffic
Mention of new I.356 version, which changes ITU QoS class definitions.
General cleanup of text.
1.0 Introduction
We consider the problem of providing IP Integrated Services [1] with
an ATM subnetwork. This document is intended to be consistent with
the rsvp protocol [2] for IP-level resource reservation (although it
is independent of rsvp to the extent that GS and CLS services could
be supported through another mechanism). In the ATM network, we
consider ATM Forum UNI Signaling, versions 3.0, 3.1 and 4.0 [3, 4,
5]. The latter uses the more complete service model of The ATM
Forum's TM 4.0 specification [6, 7].
This is a complex problem with many facets. In this draft, we focus
on the service types, parameters and signalling elements needed for
service interoperation. The resulting service mappings can be used
to provide effective end-to-end Quality of Service (QoS) for IP
traffic that traverses ATM networks.
The IP services considered are Guaranteed Service (GS) [8] and
Controlled Load Service (CLS) [9]. We also treat the default Best
Effort Service (BE) in parallel with these. Our recommendations for
BE are intended to be consistent with RFC 1755 [10], and its revision
(still in progress) [11], which defines how ATM VCs can be used in
support of normal BE IP service. The ATM services we consider are:
CBR Constant Bit Rate
rtVBR Real-time Variable Bit Rate
nrtVBR Non-real-time Variable Bit Rate
UBR Unspecified Bit Rate
ABR Available Bit Rate
(Note, Appendix 1 provides definitions for all abbreviations.) In
the case of UNI 3.0 and 3.1 signaling, where these service are not
all clearly distinguishable, we identify equivalent services where
possible.
The service mappings which follow most naturally from the service
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definitions are as follows:
Guaranteed Service -> CBR or rtVBR
Controlled Load -> nrtVBR or ABR (with a minimum cell rate)
Best Effort -> UBR or ABR
For completeness we provide detailed mappings for all service
combinations and identify how each meets or fails to meet the
requirements of the higher level IP services. The reason for not
restricting mappings to the most obvious or natural ones is that we
cannot assume now that these services will always be ubiquitously
available. A number of details, such as treatment of packets in
excess of the flow traffic descriptor, make service mapping a
complicated subject, which cannot be expressed briefly and accurately
at the same time.
The remainder of this introduction provides a general discussion of
the system configuration and other assumptions. Section 2 considers
the relevant ATM protocol elements and their effects as related to
Guaranteed, Controlled Load and Best Effort services (the latter
being the default "service"). Section 3 discusses a number of
important features of the IP services and how they can be handled on
an ATM subnetwork. Section 4 addresses a few miscellaneous problems
which are neither distinctly IP nor ATM. Section 5 gives detailed VC
setup parameters for Guaranteed Service, and considers the effect of
using each of the ATM service categories. Section 6 provides a
similar treatment for Controlled Load Service. Section 7 considers
Best Effort service.
This document is only a part of the total solution to providing the
interworking of IP integrated services with ATM subnetworks. The
important issue of VC management, including flow aggregation, is
considered in [12]. We do not consider how routing -- QoS sensitive
or not -- interacts with the use of VCs, especially in the case of
multicast (or point-to-multipoint) flows. We expect that a
considerable degree of implementation latitude will exist, even
within the guidelines presented here. Many aspects of interworking
between IP and ATM will depend on economic factors, and will not be
subject to standardization.
1.1 General System Architecture
We assume that the reader has a general working knowledge of IP, rsvp
and ATM protocols. The network architecture we consider is
illustrated in Figure 1, below. An IP-attached host may send unicast
datagrams to another host, or may use an IP multicast address to send
packets to all of the hosts which have "joined" the multicast "tree".
In either case, a destination host may then use RSVP to establish
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resource reservation in routers along the internet path for the data
flow.
An ATM network lies in the path (chosen by the IP routing), and
consists of one or many ATM switches. It uses VCs to provide both
resources and QoS within the ATM cloud. These connections are set
up, added to (in the case of multipoint trees), torn down, and
controlled by the edge devices, which act as both IP routers and ATM
interfaces, capable of initiating and managing VCs across the ATM
user-to-network (UNI) interface. The edge devices are assumed to be
fully functional in both the IP int-serv/RSVP protocols and the ATM
UNI protocols, as well as translating between them.
ATM Cloud
------------------
H ---- ( ) /------- H
H ---- R -- R -- E --( ATM Sw -- ATM Sw ) -- E -- R -- R -- H
H ----/ | ( ) (
| ------------------ ------- H
H ----------R
Figure 1: Network Architecture with hosts (H),
Routers (R) and Edge Devices (E).
The edge devices may be considered part of the IP internet or part of
the ATM cloud, or both. This is not an issue since they must provide
capabilities of both environments. The edge devices have normal RSVP
capability to process RSVP messages, reserve resources, and maintain
soft state (in the control path), and to classify and schedule
packets (in the data path). They also have the normal ATM
capabilities to initiate connections by signaling, and to accept or
refuse connections signaled to them. They police and schedule cells
going into the ATM cloud. An IP-level reservation (RESV message)
triggers the edge device to translate the RSVP service requirements
into ATM VC (UNI) semantics.
A range of VC management policies are possible, which determine
whether a flow should initiate a new VC or join an existing one. VCs
are managed according to a combination of standards and local policy
rules, which are specific to either the implementation (equipment) or
the operator (network service provider). Point-to-multipoint
connections within the ATM cloud can be used to support general IP
multicast flows. In ATM, a point to multipoint connection can be
controlled by the source (or root) node, or a leaf initiated join
(LIJ) feature in ATM may be used. Note, the topic of VC management
and mapping of flows onto VCs is considered at length in another
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issll working group draft [12].
will be written, either in as part of this draft or another one from
the issll working group at some point.
Figure 2 shows the functions of an edge device, summarizing the work
not part of IP or ATM abstractly as an InterWorking Function (IWF),
and segregating the control and data planes. (Note: for expositional
convenience, policy control and other control functions are included
as part of the admission control in the diagram.)
IP ATM
____________________
| IWF |
| |
admission <--> | service mapping | <--> ATM
control | VC management | signalling &
| address resolution | admission
|....................| control
| |
classification/ |ATM Adaptation Layer| cell
policing & <--> | Segmentation and | <--> scheduling/
scheduling | Reassembly | shaping
| Buffering |
____________________
Figure 2: Edge Device Functions showing the IWF
In the logical view of Figure 2, some functions, such as scheduling,
are shown separately, since these functions are required of both the
IP and ATM sides. However it may be possible in an integrated
implementation to combine such functions.
It is not possible to completely separate the service mapping and VC
management functions. Several illustrative examples come to mind:
(i) Multiple integrated-services flows may be aggregated to use one
point-to-multipoint VC. In this case, we assume the IP flows are of
the same service type and their parameters have been merged
appropriately. (ii) The VC management function may choose to
allocate extra resources in anticipation of further reservations or
based on an empiric of changing TSpecs. (iii) There must exist a
path for best effort flows and for sending the rsvp control messages.
How this interacts with the establishment of VCs for QoS traffic may
alter the characteristics required of those VCs. See [12] for
further details on VC management.
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Therefore, in discussing the service-mapping problem, we will assume
that the VC management function of the IWF can always express its
result in terms of an IP-level service with some QoS and TSpec. The
service mapping algorithm, which is the subject of this draft, can
then identify the appropriate VC parameters, whether the resulting
action is initiation of a new VC, the addition/deletion of a leaf to
an existing multipoint tree, or the modification of an existing VC to
one of another description.
1.2 Related Documents
Earlier ATM Forum documents were called UNI 3.0 and UNI 3.1. The 3.1
release was used to correct errors and fix alignment with the ITU.
Unfortunately UNI 3.0 and 3.1 are incompatible. However this is in
terms of actual codepoints, not semantics. Therefore, descriptions
of parameter values can generally be used for both.
After 3.1, the ATM Forum decided to release documents separately for
each technical working group. The Traffic Management and Signalling
4.0 documents are available publically at ftp.atmforum.com/pub. We
refer to the combination of traffic management and signalling as
TM/UNI 4.0, although specific references may be made to the TM 4.0
specification or the UNI SIG 4.0 specification.
Within the IETF area, related material includes the work of the rsvp
[2], int-serv [1, 8, 9, 13, 14] and ion working groups [10, 11] of
the IETF. Rsvp defines the resource reservation protocol (which is
analogous to signaling in ATM). Int-serv defines the behavior and
semantics of particular services (analogous e.g., to the Traffic
Management working group in the ATM Forum). Ion defines interworking
of IP and ATM for traditional Best Effort service, and covers all
issues related to routing and addressing.
RFC 1821 [15], represent an early discussions of issues involved with
interoperating IP and ATM protocols for integrated services and QoS.
2.0 Discussion of ATM Protocol Features
In this section, we discuss each of the items that must be specified
in the setup of an ATM VC. For each of these we discuss which
specified items and values may be most appropriate for each of the
three integrated services.
The ATM Call Setup is sent by the edge device to the ATM network to
establish end-to-end (ATM) service. This setup contains the
following information.
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Service Category/Broadband Bearer Capability
AAL Parameters
Broadband Low Layer Information
Calling and Called Party Addressing Information
Traffic Descriptors
QoS Parameters
Additional Parameters of TM/UNI 4.0
We will discuss each of these, except addressing information, as they
relate to the translation of GS and CLS to ATM services. Following
the discussion of the service categories, we discuss the tagging and
conformance definitions for IP and ATM, since the policing method is
implicit in the call setup. We then continue with mappings of the
other parameters and information elements.
2.1 Service Category and Bearer Capability
The highest level of abstraction distinguishing features of ATM VCs
is in the service category or bearer capability. Service categories
were introduced in TM/UNI 4.0; previously the bearer capability was
used to discriminate at this level.
In each version of the ATM specifications, these indicate the general
properties required of a VC: whether there is a real-time delay
constraint, whether the traffic is constant or variable rate, the
applicable traffic and QoS description parameters and (implicitly)
the complexity of some supporting switch mechanisms.
For UNI 3.0 and UNI 3.1, there are only two distinct options for
bearer capabilities (in our context):
BCOB-A: constant rate, timing required, unicast/multipoint;
BCOB-C: variable rate, timing not required, unicast/multipoint.
There is a third capability, BCOB-X, but in the case of AAL5 (which
we require -- see below) it can be used interchangeably and
consistently with the above two capabilities.
In TM/UNI 4.0 the service categories are:
Constant Bit Rate (CBR)
Real-time Variable Bit Rate (rtVBR)
Non-real-time Variable Bit Rate (nrtVBR)
Unspecified Bit Rate (UBR)
Available Bit Rate (ABR)
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The first two of these are real-time services, so that rtVBR is new
to TM/UNI 4.0. The ABR service is also new to TM/UNI 4.0. UBR
exists in all specifications, except perhaps in name, through the
``best effort'' indication flag and/or the QoS Class 0.
The encoding used in 4.0 is consistent with the earlier versions.
For example, the Service Category is indicated solely by the
combination of the Bearer Capability and the Best Effort indication
flag.
In principle, it is possible to support any foreseeable service
through the use of BCOB-A/CBR. This is because the CBR service is
equivalent to having a ``pipe'' with specified bandwidth/timing.
However, it may be desirable to make better use of the ATM network's
resources by using other, less demanding, services when available.
(See RFC 1821 for a discussion of this [15].)
2.1.1 Service Categories for Guaranteed Service
There are two possible mappings for GS:
CBR (BCOB-A)
rtVBR
GS requires real-time support, that is, timing is required. Thus in
UNI 3.x, the bearer class BCOB-A (or an equivalent BCOB-X
formulation) must be used. In TM/UNI 4.0 either CBR or rtVBR is
appropriate. In both cases, GS would use a value of CLR
appropriately low for the link (i.e., such that congestion losses are
dominated by losses due to bit errors). The use of rtVBR may
encourage recovery of allocated bandwidth left unused by a source.
It also accomm odates more bursty sources with a larger bucket
parameter, and permits the use of tagging for excess traffic (see
Section 2.2).
Neither the BCOB-C bearer class, nor nrtVBR, UBR, ABR are good
matches for the GS service. These provide no delay estimates and
cannot guarantee consistently low delay for every packet.
Specification of BCOB-A or CBR requires specification of a PCR. The
PCR should be specified as the the token bucket rate parameter, with
appropriate conversion from bytes to cells (accounting for overhead),
of the GS TSpec. For both of these, the network provides a nominal
clearing rate of PCR with jitter toleration (bucket size) CDVT,
specified in a network specific manner (see below).
Specification of rtVBR requires the specification of two rates, SCR
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and PCR. This models bursty traffic with specified peak and average
rates. With rtVBR, it is appropriate to map the PCR to the line rate
of incoming traffic and the SCR to the GS TSpec bucket rate. The ATM
bucket sizes are CDVT, in a network specific manner, and CDVT+BT,
respectively for the PCR and SCR parameters (see below).
2.1.2 Service Categories for Controlled Load
There are three possible mappings for CLS:
CBR (BCOB-A)
ABR
nrtVBR (BCOB-C)
Note that under UNI 3.x, only the first and third choices are
applicable. The first, with a CBR/BCOB-A connection, provides a
higher level of QoS than is necessary, but it may be convenient to
simply allocate a fixed-rate ``pipe'', which should be ubiquitously
supported in ATM networks. However unless this is the only choice
available, this will probably be wasteful of network resources.
The ABR category with a positive MCR aligns with the CLS idea of
``best effort with floor.'' The ATM network agrees to forward cells
with a rate of at least MCR, which should be directly converted from
the token bucket rate of the TSpec. The bucket size parameter
measures approximately the amount of buffer required at the IWF.
The nrtVBR/BCOB-C category can also be used. The rtVBR category can
be used, although the edge device must choose a value for CTD and CDV
as a matter of local policy.
The UBR category does not provide enough capability for Controlled
Load. The point of CLS is to allow an allocation of resources, which
is facilitated by the token bucket traffic descriptor, and is
unavailable in UBR.
2.1.3 Service Categories for Best Effort
Any of the service categories has the capability to carry Best Effort
service, but the natural service category is UBR (or, in UNI 3.x,
BCOB-C or BCOB-X, with the best effort indicator flag). A CBR or
rtVBR clearly could be used, and since the service is not real-time,
a nrtVBR connection could also be used. In these cases the rate
parameter used reflects a bandwidth allocation in support of the edge
device's best effort connectivity to the far edge router. It would
be normal for many flows to be aggregated on this connection; indeed,
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since Best Effort is the default IP behavior, the individual flows
are not necessarily identified or accounted for. CBR may be a
preferred solution in the case where best effort traffic is
sufficiently highly aggregated that a simple fixed-rate pipe is
efficient. An ABR connection could similarly be used to support Best
Effort traffic. This is the purpose for which ABR was specifically
designed. It is conceivable that a separate ABR connection would be
made for different IP flows, although the normal case would probably
have all IP Best Effort traffic with a common exit router sharing a
single ABR connection.
See specifications from the IETF ion working group [10, 11] for
related work on support of Best Effort service with ATM.
2.2 Cell Loss Priority Bit, Tagging and Conformance Definitions
An ATM header carries the Cell Loss Priority (CLP) bit. Cells with
bit CLP=1 are said to have been tagged and have lower priority. This
tagging may have been done by the source or an upstream switch.
Options involving the use of tagging are decided at call setup time.
A Conformance Definition is a rule that determines whether a cell is
conforming to the traffic descriptor of the VC. The conformance
definition is given in terms of a Generic Cell Rate Algorithm (GCRA),
also known as a "leaky bucket" algorithm, for CBR and VBR services.
(UBR and ABR have network-specific conformance definitions. Note,
the term "compliance" in ATM is used to describe the behavior of a
connection.)
The network may tag cells which are non-conforming, rather than
dropping them only if the VC is set up to request tagging and the
network supports the tagging option. When congestion occurs, a
switch must attempt to discard tagged cells in preference to the
discarding of CLP=0 cells. However, the mechanism for doing this is
completely implementation specific. Tagged cells are treated with a
behavior which is Best Effort in the sense that they are transported
when bandwidth is available, queued when buffers are available, and
dropped when the resources are overcommitted.
Since GS and CLS services require excess traffic to be treated as
Best Effort, the tagging option should always be chosen (if
supported) in the VC setup as a means of ``downgrading'' non-
conformant cells. However, we wish to point out that the term ``best
effort'' seems to be used with two distinguishable meanings in the
int-serv specs. The first interpretation is that of a service class
that, in some typical scheduler implementations, would correspond to
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a separate queue. Placing excess traffic in best effort in this
sense would be giving it lower delay priority. The other sense is
more generic, meaning that the network would make a best effort to
transport the traffic. A reasonable expectation is that a network
with no contending traffic would transport the packet, while a very
congested network would drop the packet. A packet that could be
tagged with lower loss priority (such as the ATM CLP bit) would be
more likely to be dropped, but would not normally be transported out
of order with respect to the conforming portion of the flow. Such a
mechanism would agree with the latter definition of best effort, but
not the former.
In TM/UNI 4.0 tagging does not apply to the CBR or ABR services.
However, there are three conformance definitions of VBR service (for
both rtVBR and nrtVBR) to consider. In VBR, only the conformance
definition VBR.3 supports tagging and applies the GCRA with PCR to
the aggregate CLP=0+1 cells, and another GCRA with SCR to the CLP=0
cells. Thus this conformance definition should always be used in
support of IP integrated services. For UBR service, conformance
definition UBR.2 supports the use of tagging, but a CLP=1 cell does
not imply non-conformance; it may be a hint of network congestion.
Once an ATM connection is established, the use of the conformance
definition and resulting policing action is mandatory. Since the
conformance algorithm operates on cells, when mapping rates and
bucket sizes from IP services to corresponding ATM parameters, a
correction needs to be made (at call setup time) for the ATM
segmentation overhead. Unfortunately this overhead, as a ratio,
depends on packet length, with the overhead largest for small
packets. Thus the appropriate correction could be based on minimum
packet size, expected packet size, or otherwise in a network specific
manner, determined at the edge device IWF.
2.3 ATM Adaptation Layer
The AAL type 5 encoding must be used, as specified in RFC 1483 and
RFC 1755. AAL5 requires specification of the maximum SDU size in both
the forward and reverse directions. Both GS and CLS specify a maximum
packet size as part of the TSpec and this value shall be used as the
maximum SDU in each direction for unicast connections, but only in
one direction for point-to-multipoint connections, which are
unidirectional. When more than one flow aggregated into a single VC,
the TSpecs are merged to yield the largest packet size. In no case
can this exceed 65535 (or, of course, the MTU of the link).
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2.4 Broadband Low Layer Information
The B-LLI Information Element is transferred transparently by the ATM
network between the edge devices and is used to specify the
encapsulation method. Multiple B-LLI IEs may be sent as part of
negotiation. The default encapsulation LLC/SNAP [16] must be
supported as specified in RFC 1577 and RFC 1755. Additional
encapsulations are discussed in RFC 1755 and we refer to the
discussion there.
2.5 Traffic Descriptors
The ATM traffic descriptor always contains specification of a peak
cell rate (PCR) (in each direction). For variable rate services it
also contains specification of a sustainable cell rate (SCR) and
maximum burst size (MBS). The SCR and MBS form a leaky bucket pair
(rate, depth), while the bucket depth parameter for PCR is CDVT.
Note that CDVT is not signaled explicitly, but is determined by the
network operator, and serves as a measure of the jitter imposed by
the network.
Since CDVT is not signaled, and is presumed to be small, the leaky
bucket traffic descriptor (TSpec) of the Internet service cannot
always be directly mapped into PCR/CDVT parameters. Additional
buffering is needed at the IWF to account for the depth of the
bucket.
The Burst Tolerance is related to MBS (see TM 4.0 for details).
Roughly, they are both expressions of the bucket depth parameter that
goes with SCR. The units of BT is time while the units of MBS is
cells. Since both SCR and MBS are signalled, they can be computed
directly from the IP layer traffic description. The specific manner
in which resources are allocated from the traffic description is
implementation specific. Note that when translating the traffic
parameters, the segmentation overhead and minimum policed unit need
to be taken into account (see Section 4.2 below).
In ATM UNI SIG 4.0 there are the notions of Alternative Traffic
Descriptors and Minimal Traffic Descriptors. Alternative Traffic
Descriptors enumerate other acceptable choices for traffic
descriptors and are not considered here. Minimal Traffic Descriptors
are used in ``negotiation,'' which refers to the specific way in
which an ATM connection is set up. Very roughly it works like this,
taking PCR as an example: A minimal PCR and a requested PCR are
signalled, the requested PCR being the usual item signalled, and the
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minimal PCR being the absolute minimum that the source edge device
will accept. When sensing the existence of both minimal and
requested parameters, the intermediate switches along the path may
reduce the requested PCR to a ``comfortable'' level. This choice is
part of admission control, and is therefore implementation dependent.
If at any point the requested PCR falls below the minimal PCR then
the call is cleared. Minimal Traffic Descriptors can be used to
present an acceptable range for parameters and ensure a higher
likelihood of call admission. Whether anything more specific about
Minimal Traffic Descriptors needs to be said here is left for further
study (FFS). In general, our discussion of connection parameters
assumes the values resulting from successful connection setup.
The Best Effort indicator (used only with UBR) and Tagging indicators
are also part of the signaled information element (IE) containing the
traffic descriptor. In the UNI SIG 4.0 traffic descriptor IE there
is an additional parameter, the Frame Discard indicator (see Section
2.7).
2.5.1 Translating Traffic Descriptors for Guaranteed Service
For Guaranteed Service there is a peak rate, p, a source Tspec rate,
r_s, a receiver Tspec rate r_r, and an Rspec rate, R. The two Tspec
rates are intended to support receiver heterogeneity, in the sense
that different receivers can accept different rates representing
subsets of the sender's traffic. In this document we leave this
feature for further study (FFS), and assume the two Tspec rates are
always identical. The Tspec rate describes the traffic itself, and
is used for policing, while the Rspec rate (which cannot be smaller)
is the allocated service rate. A receiver increases R over r to
reduce the delay.
When mapping Guaranteed Service onto a rtVBR VC, the ATM traffic
descriptor parameters (PCR, SCR, MBS) can be set within the following
bounds:
R <= PCR <= min(p, line rate)
r <= SCR <= PCR
b <= MBS.
Note that a receiver can choose R > p to lower the delay. This
leaves the first equation somewhat subject to interpretation. If a
receiver chooses R > line rate, it seems clear that the admission
control would simply reject the reservation.
The edge device has a buffer preceding the ATM network which must be
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sufficient to absorb bursts arriving faster than they can be admitted
into the ATM network. For example, parameters may be set as PCR = R,
SCR = r, MBS = b. The edge device buffer of size b would absorb a
burst sent at any IP-level peak rate. Although this buffer exists,
the ATM network must accept bursts at rate PCR, at least R, to ensure
that the edge device delay is no greater than b/R. Since this buffer
is not in the ATM network, its delay is not included in D_ATM.
For GS over CBR, the service rate is mapped to the PCR parameter,
using the same constraint for PCR given above. The edge device again
requires adequate buffering to accommodate the TSpec bucket depth and
ensure delay before entering the ATM network of no more than b/R. If
PCR is greater than R, the buffer requirement may be relaxed
accordingly.
2.5.2 Translating Traffic Descriptors for Controlled Load Service
Controlled Load service has a peak rate, p, a Tspec rate, r, and a
corresponding bucket depth parameter, b. The ATM traffic parameters
for nrtVBR service category are constrained by
r <= SCR <= PCR <= min(p, line rate)
b <= MBS.
For ABR VCs, the Tspec rate would be used to set the minimum cell
rate (MCR) parameter. The bucket depth parameter does not map
directly to a signalled ATM parameter, so the edge device must have a
buffer of at least b bytes.
For CBR, the Tspec rate sets a lower bound on PCR, and again, the
available buffering in the edge device must be adequate to
accommodate possible bursts.
2.5.2 Translating Traffic Descriptors for Best Effort Service
For Best Effort service, there is no traffic description. The UBR
service category allows negotiation of PCR, simply to allow the
source to discover the smallest physical bottleneck along the path.
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2.6 QoS Classes and Parameters
In TM/UNI 4.0 the three QoS parameters may be individually signalled.
These parameters are the Cell Loss Ratio (CLR), Cell Transfer Delay
(CTD), and Cell Delay Variation (CDV). In UNI 3.x the setup message
includes only the QoS Class, which is essentially an index to a
network specific table of values for these three parameters. A
network provider may choose to associate other parameters, such as
Severely Errored Cell Block Ratio, but these are less well understood
and accepted compared to the basic loss, delay and jitter parameters
mentioned here. The ITU has recently included a standard set of
parameter values for a (small) number of QoS classes in the latest
version of Recommendation I.356, October 1996. The network provider
may choose to define further network-specific QoS classes in addition
to these. The problem of agreement between network providers as to
the definition of QoS classes is completely unaddressed to date. We
will adopt a convention expressed in UNI 3.x, that assumes that QoS
class 1 is appropriate for low-delay, low-loss CBR connections, and
QoS class 3 is appropriate for variable rate connections with loss
and delay roughly appropriate for non-real-time data applications.
Note that the QoS class definitions in the new I.356 version may not
align with this model.
Since no IP layer counterparts to these ATM QoS parameters exist in
any of the IP services, they must be set by policy of the edge
device. The QoS classes can be chosen relatively easily. QoS class
1 should be used with Guaranteed Service and QoS class 3 should be
used with Controlled Load Service. Best Effort Service always gets
QoS class 0, which is unspecified QoS by definition. There are two
issues which amount to the same thing: First, the choice of
individually signalled parameter values (under TM/UNI 4.0) for GS and
CLS is the edge device policy. The second issue is choosing
parameter values for the two QoS classes, which is the ATM network
policy. If the same network operator controls both, then these
problems are identical; if not, an agreement to make the values
identical would be extremely desirable.
Note that we have mapped QoS class 1 and 3 onto Guaranteed and
Controlled Load service respectively. This is regardless of what
service category is used. So when running CLS over a CBR pipe, it
would not be inappropriate to use QoS class 3. This leaves the delay
unspecified (or much looser than with QoS 1). These comments should
be taken as preliminary, as these issues are far from clear, and
industry consensus should be sought.
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2.7 Additional Parameters -- Frame Discard Mode
In TM/UNI 4.0 ATM allows the user to choose a mode where a dropped
cell causes all cells up to the last remaining in the AAL5 PDU to be
also dropped. This improves efficiency and the behavior of end-to-
end protocols such as TCP, since the remaining cells of a damaged PDU
are useless to the receiver. For IP over ATM, Frame Discard should
always be used in both directions, if available, for all services.
3.0 Discussion of IP-IS Protocol Features
3.1 Handling of Excess Traffic
(Placeholder for text.)
3.2 Use of AdSpec in Guaranteed Service with ATM
The AdSpec is a feature of Guaranteed Service which allows a receiver
to calculate the worst-case delay associated with a GS flow. Three
quantities, C, D, and MPL, are accumulated (by simple addition of
components, one for each network element) in the PATH message from
source to receiver. The resulting values can be different for each
unique receiver. The maximum delay is then found by
delay <= b/R + C/R + D + MPL
The Maximum Path Latency (MPL) includes propagation delay and any
other unavoidable system delays. (We neglect the effect of maximum
packet size and peak rate here; see the GS specification [8] for the
more detailed equation.) The service rate requested by the receiver,
R, can be greater than the sender's Tspec rate, r. The effect of the
larger R is to allocate more bandwidth and, through this equation,
lower the packet delay. The burst size, b, is the leaky bucket
parameter from the Tspec, and is not changed by the receiver in the
Rspec.
The values of C and D which a router advertise will depend on both
the particular packet scheduling algorithm used in the router, and
the characteristics of the subnet attached to the router. We assume
here that each router (or the source host) takes responsibility for
its downstream subnet only. If the subnet is a simple point-to-point
link, then the subnet-specific parts of C and D will account for the
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link transmission rate and MTU. An ATM subnet is more complex.
The edge router will always have an internal packet scheduler, which
will contribute to C and D. For this discussion we consider only the
ATM subnet-specific components. We further assume that the ATM
network will be represented as a "pure delay" element, contributing a
component to D, but not to C. The reason for this is that C would
depend on details of the cell scheduling algorithm inside the ATM
switches, which is not known by the edge device, where the AdSpec
parameters are accumulated. (In the special case where the edge
device does have enough information to modify C, it would not be
precluded.) Generally the delay behavior of the whole ATM cloud may
be expressed abstractly as a fixed constant D_ATM.
Since the AdSpec values are incremented before any reservation is
made, the edge device must have some knowledge about the VC which
would be set up in case a reservation were made. This does not
really add to the complexity of the device, since it must also have
this information in order to make an intelligent VC setup request.
For example, the edge device may have a cached table with the
propagation delay and a reasonable additional delay budget, from
which it composes a value of CTD for the VC setup. The device may
learn such information through VC setup negotiation, and, indeed,
there may be no other way to obtain that information. However, it
seems reasonable that these values would be cached for later use when
new VCs to the same egress router need to be established.
Therefore, we will presume a table with values of MPL (which includes
propagation delay) and expected queueing delays for each possible
egress edge device. (How such a table is maintained is
implementation specific.) The latter quantity is simply D_ATM, the
value added to the AdSpec D term to account for the ATM network.
When a RESV message arrives, causing a VC to be set up, the requested
value for CTD should then be given by
CTD = D_ATM + MPL + S_ATM.
The last term, S_ATM is the portion of the slack term applied to the
ATM portion of the path. Recall that the slack term [8] is positive
when the receiver can afford more delay than that computed from the
AdSpec. The ATM edge device may take part (or all) of the slack term
to relax the delay constraint on the ATM VC. The distribution of
delay slack among the nodes and subnets is network specific.
An important detail to note is the relationship between the b/R term
of the (Internet) delay and the corresponding MBS/SCR in the ATM
network, when using a VBR VC. The term b/R accounts for the delay
experienced by the last byte of a burst, of size b, which encounters
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a congested node. In the simple ideal case, where the scheduling
algorithm emulates a fixed rate server, at rate R, the delay of the
last byte is b/R. Once this occurs, the stream has been smoothed,
and such a delay will not occur at later congested nodes, as long as
they also serve at rate R. The form of the delay equation expresses
this ideal behavior with C and D acting as error terms. Now, since
the delay which smooths the burst can occur outside of the ATM cloud,
the b/R term cannot include any delay within the ATM cloud. However,
a burst of size MBS is permitted to enter the ATM network, and it may
be served at a rate no greater than SCR. We might reasonably expect
a queueing delay of MBS/SCR to occur at a congested ATM switch. If
the ATM network will impose this delay, then it must be included in
the value of D_ATM advertised. If the ATM network can increase its
bandwidth allocation (e.g., due to CTD being lower than MBS/SCR), to
decrease this delay, then this behavior should be reflected in the
value of D_ATM. So, the information from which the edge device
determines D_ATM must reflect an accurate abstraction of the actual
behavior of the ATM network. To the extent that D_ATM is approximate
(and it must be an upper bound on the actual delay), it reduces the
chance that the VC setup will succeed, and/or increases its cost.
4.0 Discussion of Miscellaneous Items
4.1 Units Conversion
In the integrated services domain, bucket sizes and rates are
measured in bytes and bytes/sec, respectively, whereas for ATM, they
are measured in cells and cells/sec.
Packets are segmented into 53 byte cells of which the first 5 bytes
are header information. For
B = number of Bytes,
C = number of cells,
a rough approximation between the token bucket parameters (rate and
bucket depth) is
C = B/48.
This is actually a lower bound on C and does not take into account
the extra padding at the end of a partially filled cell, or the 8
byte trailer in the last cell of an AAL5 encoding. The actual
relationship between the number of cells and bytes of one packet is
C = 1 + int(B/48) + x,
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where x = 1 if B mod 48 > 41
0 otherwise.
where int() is the rounding down operation. The third term is 0 or
1 and is 1 only when the remainder of B/48 is 41 or more. (An
additional cell is needed because the 41 bytes plus 8 byte trailer
will not fit in a cell.)
The above formula is not particularly amenable to engineering
considerations. By equating the number of bytes before and after
segmentation we have
48 C = B + 8 + A,
where A is the additional padding used in the last 2 cells and has
the range 0 <= A <= 47. From this we obtain a number of useful
observations.
For example, if one believes that the packet lengths are uniformly
distributed mod 48, then on average, 48 C = B + 8 + 47/2, or C = B/48
+ .65625.
We can also make use of the upper bound on A to state that 48 C <= B
+ 55. This is true for any one packet. Considering the number of
bytes in a stream of P packets, we have
48 C <= B + 55 P.
The number of packets P may not be a readily available quantity.
However, in terms of the minimum policed unit m, we know that P * m
<= B. Hence P <= B/m and 48 C <= B ( 1 + 55/m). That is,
C <= B/48 * (1 + 55/m).
5.0 Summary of ATM VC Setup Parameters for Guaranteed Service
This section describes how to create ATM VCs appropriately matched
for Guaranteed Service. The key points differentiating among ATM
choices are that real-time timing is required, that the data flow may
have a variable rate, and that demotion of non-conforming traffic to
best effort is required to be in agreement with the definition of GS.
For this reason, we prefer an rtVBR service in which tagging is
supported. Another good match is to use CBR with special handling of
any non-conforming traffic.
The encodings assume a point-to-multipoint connection. For a unicast
connection, the backward parameters would be equal to the forward
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parameters.
5.1 Encoding GS Using Real-Time VBR
AAL
Type 5
Forward CPCS-SDU Size parameter M of TSpec
Backward CPCS-SDU Size 0
Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS)
Traffic Descriptor
Forward PCR CLP=0+1 Note 6
Backward PCR CLP=0+1 0
Forward SCR CLP=0 Note 6
Backward SCR CLP=0 0
Forward MBS (CLP=0) Note 6
Backward MBS (CLP=0) 0
BE indicator NOT included
Forward Frame Discard bit 1 Note 2
Backward Frame Discard bit 1 Note 2
Tagging Forward bit 1 (Tagging requested) Note 2
Tagging Backward bit 0 (No Tagging) Note 2
Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 3
ATM Transfer Capability 9 Note 2
Traffic Type 010 (Variable Bit Rate)
Timing Requirements 01 (Timing Required)
Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 01 (For pt-to-mpt)
Broadband Low Layer Information
Layer 2 protocol 12 (ISO 8802/2)
Layer 3 protocol 204 (ISO/IEC TR 9577)
QoS Class
QoS Class Forward 1 Note 4
QoS Class Backward 1 Note 4
QoS Parameters
Transit Delay 100ms Notes 2,5
Forward CLR (CLP=0) 1.0e-9 Notes 2,5,7
Backward CLR (CLP=0) 1.0e-9 Notes 2,5,7
Forward CDV 30ms Notes 2,5
Backward CDV 30ms Notes 2,5
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Note 1: Only included for UNI 3.0.
Note 2: Only included in TM/UNI 4.0.
Note 3: Value 1 (BCOB-A) can also be used.
Note 4: Optional in TM/UNI 4.0. Cf ITU I.365 (Oct 1996) for new definition.
Note 5: Values chosen to initiate discussion. May be network specific.
Note 6: See discussion on AdSpec, Section 3.2.
Note 7: CLR should include physical link errors with no queueing loss.
5.2 Encoding GS Using CBR
It is also possible to support GS using a CBR ``pipe.'' The
advantage of this is that CBR is probably supported; the disadvantage
is that data flows may not fill the pipe (utilization loss) and there
is no tagging option available.
AAL
Type 5
Forward CPCS-SDU Size parameter M of TSpec
Backward CPCS-SDU Size parameter M of TSpec
Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS)
Traffic Descriptor
Forward PCR 0+1 Note 6
Backward PCR 0+1 0
BE indicator NOT included
Forward Frame Discard bit 1 Note 2
Backward Frame Discard bit 1 Note 2
Tagging Forward bit 0 (No Tagging) Note 2
Tagging Backward bit 0 (No Tagging) Note 2
Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 3
ATM Transfer Capability 7 Note 2
Traffic Type 001 (Constant Bit Rate)
Timing Requirements 01 (Timing Required)
Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 01 (For pt-to-mpt)
Broadband Low Layer Information
Layer 2 protocol 12 (ISO 8802/2)
Layer 3 protocol 204 (ISO/IEC TR 9577)
QoS Class
QoS Class Forward 1 Note 4
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QoS Class Backward 1 Note 4
QoS Parameters
Transit Delay 100ms Notes 2,5
Forward CLR (CLP=0) 1.0e-9 Notes 2,5,7
Backward CLR (CLP=0) 1.0e-9 Notes 2,5,7
Forward CDV 30ms Notes 2,5
Backward CDV 30ms Notes 2,5
Note 1: Only included for UNI 3.0.
Note 2: Only included in TM/UNI 4.0.
Note 3: Value 1 (BCOB-A) can also be used.
Note 4: Optional in TM/UNI 4.0. Cf ITU I.365 (Oct 1996) for new definition.
Note 5: Values chosen to initiate discussion. May be network specific.
Note 6: See discussion on AdSpec, Section 3.2.
Note 7: CLR should include physical link errors with no queueing loss.
5.3 Encoding GS Using Non-Real-Time VBR
The remaining ATM service categories, including nrtVBR, do not
provide delay guarantees and cannot be recommended as the best fits.
However in some circumstances, the best fits may not be available.
If nrtVBR is used, no hard delay can be given. However by using a
variable rate service with low utilization, delay may be
`reasonable', but not controlled. The encoding of GS as nrtVBR is
the same as that for CLS using nrtVBR, except that the Forward PCR
would be derived from the Tspec peak rate. See Section 6.2 below.
5.4 Encoding GS Using ABR
The authors feel that this is a very unlikely combination. The
objective of the ABR service is to provide `low' loss rates which,
via flow control, can result in delays. The introduction of delays
is contrary to the point of GS.
5.5 Encoding GS Using UBR
The UBR service is the default lowest common denominator of the
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services. It cannot provide delay or loss guarantees. However if it
is used for GS, it will be encoded in the same way as Best Effort
over UBR, with the exception that the PCR would be determined from
the peak rate of the Tspec. See Section 5.1.
5.6 Encoding GS Using UNI 3.0 and UNI 3.1.
(Placeholder for text.)
6.0 Summary of ATM VC Setup Parameters for Controlled Load Service
This section describes how to create ATM VCs appropriately matched
for Controlled Load. CLS traffic is partly delay tolerant and of
variable rate. NrtVBR and ABR (for TM/UNI 4.0 only) are the possible
choices in supporting CLS.
Generally we prefer to use point-to-multipoint connections. However
this is not yet available in ABR. Other than in ABR, the encodings
assume a point-to-multipoint connection. For a unicast connection,
the backward parameters would be equal to the forward parameters.
6.1 Encoding CLS Using ABR
AAL
Type 5
Forward CPCS-SDU Size parameter M of TSpec
Backward CPCS-SDU Size parameter M of TSpec
SSCS Type 0 (Null SSCS)
Traffic Descriptor
Forward PCR CLP=0+1 From line rate
Backward PCR CLP=0+1 From line rate
Forward MCR CLP 0+1 From TSpec token bucket rate
Backward MCR CLP 0+1 From TSpec token bucket rate
BE indicator NOT included
Forward Frame Discard bit 1
Backward Frame Discard bit 1
Tagging Forward bit 0 (Tagging not requested)
Tagging Backward bit 0 (Tagging not requested)
Broadband Bearer Capability
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Bearer Class 16 (BCOB-X) Note 3
ATM Transfer Capability 12
Traffic Type 010 (Variable Bit Rate)
Timing Requirements 10 (Timing Not Required)
Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 00 (For pt-to-pt)
Broadband Low Layer Information
Layer 2 protocol 12 (ISO 8802/2)
Layer 3 protocol 204 (ISO/IEC TR 9577)
QoS Class
QoS Class Forward 3 Note 4
QoS Class Backward 3 Note 4
ABR Setup Parameters for further study (FFS)
ABR Additional Parameters for further study (FFS)
Note 3: Value 3 (BCOB-C) can also be used.
Note 4: Optional in TM/UNI 4.0. Cf ITU I.365 (Oct 1996) for new definition.
6.2 Encoding CLS Using Non-Real-Time VBR
AAL
Type 5
Forward CPCS-SDU Size parameter M of TSpec
Backward CPCS-SDU Size 0
Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS)
Traffic Descriptor
Forward PCR CLP=0+1 From line rate
Backward PCR CLP=0+1 0
Forward SCR CLP=0 From TSpec token bucket rate
Backward SCR CLP=0 0
Forward MBS (CLP=0) From TSpec bucket size param
Backward MBS (CLP=0) 0
BE indicator NOT included
Forward Frame Discard bit 1 Note 2
Backward Frame Discard bit 1 Note 2
Tagging Forward bit 1 (Tagging requested) Note 2
Tagging Backward bit 0 (No Tagging) Note 2
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Broadband Bearer Capability
Bearer Class 16 (BCOB-X) Note 3
ATM Transfer Capability Absent Note 2
Traffic Type 010 (Variable Bit Rate)
Timing Requirements 10 (Timing Not Required)
Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 01 (For pt-to-mpt)
Broadband Low Layer Information
Layer 2 protocol 12 (ISO 8802/2)
Layer 3 protocol 204 (ISO/IEC TR 9577)
QoS Class
QoS Class Forward 3 Note 4
QoS Class Backward 3 Note 4
QoS Parameters
Forward CLR (CLP=0) 1.0e-9 Notes 2,5,6
Backward CLR (CLP=0) 1.0e-9 Notes 2,5,6
Note 1: Only included for UNI 3.0.
Note 2: Only included in TM/UNI 4.0.
Note 3: Value 3 (BCOB-C) can also be used.
Note 4: Optional in TM/UNI 4.0. Cf ITU I.365 (Oct 1996) for new definition.
Note 5: Values chosen to initiate discussion. May be network specific.
Note 6: CLR should include physical link errors with no queueing loss.
6.3 Encoding CLS Using Real-Time VBR
The encoding of CLS using rtVBR imposes a hard limit on the delay,
which is specified as an end-to-end delay in the ATM network. This
is more stringent than the CLS service specifies and may result in
less utilization of the network.
If rtVBR is used to encode CLS, then the encoding is essentially the
same as that for GS. The exceptions are that the Forward PCR is
derived from the line rate and probably a different value of the
transit delay and CDV will be specified. See Section 3.1.
6.4 Encoding CLS Using CBR
The encoding of CLS using CBR is more stringent than using rtVBR
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since it does not take into account the variable rate of the data.
Consequently there may be even lower utilization of the network.
To use CBR for CLS, the same encoding as in Section 3.2 would be
used. However a different set of values of the QoS parameters will
likely be used.
6.5 Encoding CLS Using UBR
This encoding gives no QoS guarantees and would be done in the same
way as for BE traffic. See Section 5.1.
6.6 Encoding CLS Using UNI 3.0 and UNI 3.1.
(Placeholder for text.)
7.0 Summary of ATM VC Setup Parameters for Best Effort Service
This section describes how to create ATM VCs appropriately matched
for Best Effort. The BE service does not need a reservation of
resources.
7.1 Encoding Best Effort Service Using UBR
AAL
Type 5
Forward CPCS-SDU Size MTU of link
Backward CPCS-SDU Size MTU of link
Mode 1 (Message mode) Note 1
SSCS Type 0 (Null SSCS)
Traffic Descriptor
Forward PCR CLP=0+1 From line rate
Backward PCR CLP=0+1 0
BE indicator included
Forward Frame Discard bit 1 Note 2
Backward Frame Discard bit 1 Note 2
Tagging Forward bit 1 (Tagging requested) Note 2
Tagging Backward bit 0 (no tagging) Note 2
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Broadband Bearer Capability
Bearer Class 16 (BCOB-X)
Traffic Type 010 (Variable Bit Rate)
Timing Requirements 10 (Timing not required)
Susceptible to Clipping 00 (Not susceptible)
User Plane Configuration 01 (For pt-to-mpt)
Broadband Low Layer Information
Layer 2 protocol 12 (ISO 8802/2)
Layer 3 protocol 204 (ISO/IEC TR 9577)
QoS Class
QoS Class Forward 0
QoS Class Backward 0
Note 1: Only included for UNI 3.0.
Note 2: Only included in TM/UNI 4.0.
7.2 Encoding Best Effort Service Using Other ATM Service Categories
See the IETF ION working group draft on ATM signalling support for IP
over ATM using UNI 4.0 [11].
8.0 Acknowledgements
The authors would like to thank the members of the ISSLL working
group for their input. In particular, thanks to Jon Bennett of Fore
Systems, Roch Guerin of IBM and Susan Thomson of Bellcore.
Appendix 1 Abbreviations
AAL ATM Adaptation Layer
ABR Available Bit Rate
ATM Asynchronous Transfer Mode
B-LLI Broadband Low Layer Information
BCOB Broadband Connection-Oriented Bearer Capability
BCOB-{A,C,X} Bearer Class A, C, or X
BE Best Effort
BT Burst Tolerance
CBR Constant Bit Rate
CDV Cell Delay Variation
CDVT Cell Delay Variation Tolerance
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CLP Cell Loss Priority (bit)
CLR Cell Loss Ratio
CLS Controlled Load Service
CPCS
CTD Cell Transfer Delay
EOM End of Message
FFS For Further Study
GCRA Generic Cell Rate Algorithm
GS Guaranteed Service
IE Information Element
IETF Internet Engineering Task Force
IP Internet Protocol
IS Integrated Services
ISSLL Integrated Services over Specific Link Layers
ITU International Telecommunication Union
IWF Interworking Function
LIJ Leaf Initiated Join
LLC Logical Link Control
MBS Maximum Burst Size
MCR Minimum Cell Rate
MPL Minimum Path Latency
MTU Maximum Transfer Unit
nrtVBR Non-real-time VBR
PCR Peak Cell Rate
PDU Protocol Data Unit
QoS Quality of Service
RESV Reservation Message (of rsvp protocol)
RFC Request for Comment
RSVP Resource Reservation Protocol
Rspec Reservation Specification
rtVBR Real-time VBR
SCR Sustained Cell Rate
SDU Service Data Unit
SIG ATM Signaling (ATM Forum document)
SNAP Subnetwork Attachment Point
SSCS
Sw Switch
TCP Transport Control Protocol
TM Traffic Management
TSpec Traffic Specification
UBR Unspecified Bit Rate
UNI User-Network Interface
VBR Variable Bit Rate
VC (ATM) Virtual Connection
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REFERENCES
[1] R. Braden, D. Clark and S. Shenker, "Integrated Services in the
Internet Architecture: an Overview", RFC 1633, June 1994.
[2] R. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin,
"Resource ReSerVation Protocol (RSVP) - Version 1 Functional
Specification", Internet Draft, May 1996, <draft-ietf-rsvp-
spec-12.txt>
[3] The ATM Forum, "ATM User-Network Interface Specification, Ver-
sion 3.0", Prentice Hall, Englewood Cliffs NJ, 1993.
[4] The ATM Forum, "ATM User-Network Interface Specification, Ver-
sion 3.1", Prentice Hall, Upper Saddle River NJ, 1995.
[5] The ATM Forum, "ATM User-Network Interface (UNI) Signalling
Specification, Version 4.0", Prentice Hall, Upper Saddle River
NJ, specification finalized July 1996; expected publication,
late 1996; available at ftp://ftp.atmforum.com/pub.
[6] The ATM Forum, "ATM Traffic Management Specification, Version
4.0", Prentice Hall, Upper Saddle River NJ; specification final-
ized April 1996; expected publication, late 1996; available at
ftp://ftp.atmforum.com/pub.
[7] M. W. Garrett, "A Service Architecture for ATM: From Applica-
tions to Scheduling", IEEE Network Mag., Vol. 10, No. 3, pp. 6-
14, May 1996.
[8] S. Shenker, C. Partridge and R. Guerin, "Specification of
Guaranteed Quality of Service", Internet Draft, August 1996,
<draft-ietf-intserv-guaranteed-svc-06.txt>
[9] J. Wroclawski, "Specification of the Controlled-Load Network
Element Service", Internet Draft, August 1996, draft-ietf-
intserv-ctrl-load-svc-03.txt
[10] M. Perez, F. Liaw, A. Mankin, E. Hoffman, D. Grossman and A.
Malis, "ATM Signaling Support for IP over ATM", RFC 1755, Febru-
ary 1995.
[11] M. Perez and A. Mankin, "ATM Signalling Support for IP over ATM
- UNI 4.0 Update", Internet Draft, November 1996, <draft-ietf-
ion-sig-uni4.0-01.txt>
[12] S. Berson, L. Berger, "IP Integrated Services with RSVP over
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ATM", Internet Draft, September 1996, <draft-ietf-issll-atm-
support-01.txt>
[13] S. Shenker and J. Wroclawski, "Network Element Service Specifi-
cation Template", Internet Draft, November 1995, <draft-ietf-
intserv-svc-template-02.txt>
[14] J. Wroclawski, "The Use of RSVP with IETF Integrated Services",
Internet Draft, August 1996, <draft-ietf-intserv-use-00.txt>
[15] M. Borden, E. Crawley, B. Davie and S. Batsell, "Integration of
Real-time Services in an IP-ATM Network Architecture", "IP
Authentication Header", RFC 1821, August 1995.
[16] J. Heinanen, "Multiprotocol Encapsulation over ATM Adaptation
Layer 5", RFC 1483, July 1993.
AUTHORS' ADDRESSES
Mark W. Garrett Marty Borden
Bellcore New Oak, Inc.
445 South Street
Morristown, NJ 07960
USA USA
phone: +1 201 829-4439 phone: +1 508
email: mwg@bellcore.com email: mborden@newoak.com
Garrett, Borden Expires May, 1997 [Page 30]
