Danny Goderis, Alcatel
Yves T'joens, Alcatel
Christian Jacquenet, France Telecom R&D
George Memenios, NTUA
George Pavlou, UniS
Richard Egan, Racal Research Ltd
David Griffin, UCL
Panos Georgatsos, AlgoSystems
Leonidas Georgiadis, Univ. Thessaloniki
Pim Van Heuven, IMEC
INTERNET DRAFT <draft-tequila-sls-00.txt>
November, 2000
Expires March 2001
Service Level Specification Semantics and Parameters.
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document identifies the basic information to be included in
Service Level Specifications (SLS, [RFC 2475], [DS-TERMS]) when
considering the deployment of value-added IP service offerings over
the Internet. Such IP service offerings can be provided together with
a given quality of service (QoS), which is expected to be defined in
such SLS, from a technical perspective. Since these IP services are
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likely to be provided over the whole Internet, their corresponding
QoS will be based upon a set of technical parameters that both
customers and services providers will have to agree upon. From this
perspective, this draft aims at listing (and promoting a standard
formalism for) a set of basic parameters which will actually compose
the elementary contents of an SLS.
Such a specification effort tries to address the following concerns:
- Provide a standard set of information to be negotiated between a
customer and a service provider or amongst services providers within
the context of processing an SLS;
- Provide the corresponding semantics of such information, so that it
might be appropriately modeled and processed by the above-mentioned
parties (in an automated fashion).
Table of Contents
1. Introduction
1.1 Motivation
1.2 Objective
2. Basic assumptions and terminology
3. SLS content & template
3.1. Scope
3.2. Flow Description
3.3. Traffic Envelop and Traffic Conformance
3.4. Excess Treatment
3.5. Performance Guarantees
3.6. Service Schedule
3.7. Reliability
4. Service Level Specification examples
4.1. Virtual Leased Line
4.2. Bandwidth Pipe for data-services
4.3. Real-time micro-flows
4.4. Minimum rate guarantee with allowed excess
4.5. Qualitative Olympic Services
4.6. The funnel services
4.7. Best Effort Traffic
5. SLS negotiation requirements
6. Security considerations
7. Acknowledgements
0. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 ([RFC-2119]).
1. Introduction
1.0 Changes w.r.t. the previous version
This is the second version of an Internet Draft of the issue of
Service Level Specifications (SLS). The first version <draft-
tequila-sls-00.txt
1.1 Motivation
This document is presented to the IETF community to gauge the
interest for advancing the work on the specification of a Service
Level Specification (SLS) definition, its semantics and its potential
negotiation protocol(s). The deployment of QoS-based value-added IP
services over the global Internet is one of the most exciting
challenges that the service providers try to currently address,
especially when considering the deployment of such services over
administrative domains. From this perspective, it seems useful to
consider the specification of an SLS template these service providers
would agree upon, so as to enforce an inter-domain QoS policy. This
is the basic motivation for presenting this document to the IETF
community.
Mailing list: sls@ist-tequila.org
This list provides the medium for discussion on SLS template
definition and SLS negotiation protocol requirements. One of its
objectives is to gauge interest for the related work within the IETF
on these specific topics.
To subscribe to the list send an email to - majordomo@ist-tequila.org
- with the sentense - subscribe sls@ist-tequila.org - in the body and
nothing in the subject line.
1.2 Objective
This document presents an outline for the definition of the Service
Level Specification parameters, the semantics that go behind this
representation, and some early ideas on the requirements on
negotiation of SLSs.
The need to have such an agreed set of Service Level Specification
parameters and semantics is manifold.
First, it is necessary to be able to allow for a highly developed
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level of automation and dynamic negotiation of Service Level
Specifications between customers and providers. Automation and
dynamics are indeed helpful in providing customers (as well as
providers) the technical means for the dynamic provisioning of
quality of service. The automation in itself is e.g. necessary to
allow roaming (dial-in) and to enable mobile users to have access and
negotiate a transport Service Level, independent of their point of
attachment to the network.
Second, the design and the deployment of Bandwidth Broker
capabilities [TWOBIT] in a multi-vendor environment requires a
standardized set of semantics for Service Level Specifications being
negotiated at different locations:
- between the customer and the service provider (namely between
the Customer Premises Equipment (CPE) and its point of attachment
to the IP network managed by the service provider);
- within an administrative domain (for intra-domain SLS
negotiation purposes);
- between administrative domains (for inter-domain negotiation
purposes).
While the representation and semantics behind a Service Level
Specification need to be standardized, this document does not assume
that the syntax, nor the SLS negotiation protocol need to be uniquely
defined. E.g, the negotiation could make use of various other
protocols such as http, rsvp, IPCP, DHCP, etc. The latter is ffs, and
as such not part of this document.
The document is structured as follows.
Section 2 lists the basic assumptions underlying this work and some
terminology.
Section 3 describes the parameters of the Service Level Specification
(template). This draft only describes the semantics of the SLS-
parameters, omitting all implementation details as for instance the
parameter data types (at this moment).
Section 4 provides some examples of relevant SLS specifications, with
the aim to show the usage of the templates. The SLS formalism defined
in section 3 allows making a distinction between qualitative and
quantitative SLSs:
- SLSs depicting qualitative services should yield the
specification of relative QoS indicators, such as a low IP
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datagram loss ratio. From this standpoint, best effort traffic is
expected to be qualified by an SLS of that range of qualitative
services.
- SLSs depicting quantitative services should yield the accurate
measurement of QoS indicators, such as e.g., transit delay.
Sections 5 and 6 finally describe some SLS (protocol) negotiation
requirements and security considerations respectively.
The material presented in this draft derives from work within the
IST-TEQUILA project [TEQUILA].
2. Basic assumptions and terminology
The basic assumption of this draft is that IP services will be
deployed over a public IP infrastructure, which will be (partly if
not completely) composed of diffserv-aware network elements ([RFC-
2475], [DS-MODEL]). These network elements are able to implement Per
Hop Behaviors (PHBs), including the Assured Forwarding PHB ([RFC-
2597]), and the Expedited Forwarding PHB ([RFC-2598].
Customers of such services include Internet Service Providers (ISP),
who may well establish QoS-based peering agreements between
themselves, and usual customers of ISPs, like those who compose both
the residential and the corporate market.
The terminology used in this draft is in agreement with the DiffServ
Working Group terminology introduced and specified in [RFC-2475],
section 1.2 "terminology".
3. SLS content & template
The following describes the attributes of the Service Level
Specification. It should be remarked that some SLS-features are not
yet specified in this draft. For example, the Internet2 QoS Working
Group specifies an SLS for the EF-based Premium Service [QBONE]. One
of the attributes, i.e. "Route", is used for inter-domain routing
aspects. This and other SLS features are for further study.
3.1. Scope
The scope of an SLS associated to a given service offering indicates
where the Quality of Service (QoS) policy for that specific service
offering is to be enforced. Therefore the scope uniquely identifies
the geographical/topological region over which the QoS is to be
enforced by indicating the boundaries of that region.
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An SLS is associated with uni-directional traffic flows. Note however
that this does not exclude the provisioning by providers of
bidirectional transport service contracts, by combining one or more
SLSs.
The associated scope of the SLS MUST be expressed by a couple of
ingress and egress interfaces. Ingress/egress denote respectively the
entry/exit points of the IP packets relative to the region (network).
Scope = (ingress, egress) with ingress/egress defined as
- Ingress: interface identifier | set of interface identifiers |
any
- Egress : interface identifier | set of interface identifiers |
any
Remarks:
- "|" denotes an exclusive OR.
- "any" is logically equivalent with unspecified.
The following combinations of (ingress, egress) interfaces are
allowed:
- (1,1) - one-to-one communication
- (1,N) - one-to-many communication (N>1)
- (1,any) - one-to-any communication
- (N,1) - many-to-one communication (N>1)
- (any,1) - any-to-one communication
The above taxonomy excludes the many-to-many communication (M,N).
Either ingress OR egress MUST be specified to exactly ONE interface
identifier (with a non-exclusive OR). Many-to-many communication
(M,N) can be decomposed into M times one-to-many communication (1,N).
This taxonomy SHOULD avoid all ambiguity about the IP flow (defined
as a set of IP datagrams sharing at least one common characteristic,
like e.g. the same [source address; destination address] pair), and
its corresponding description. (see section 3.2 and 3.3). If the
ingress is a single interface identifier, then the traffic envelop
and flow description concerns the incoming IP packet stream at the
unique ingress point. If (only) the egress is a single interface,
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i.e. (N|any,1), then the traffic envelop and flow description
concerns the outgoing (aggregate) traffic on the egress link. More
details about the latter can be found in the example 4.5.
In the remaining part of this document SLSs with an associated scope
(topology) of (1,1) ; (1,N) ; (N,1) will be called respectively Pipe,
Hose and Funnel SLSs.
Disclaimer:
An ingress (or egress) interface identifier should uniquely determine
the boundary link as defined in [RFC-2475] on which packets
arrive/depart at the border of a DS domain. This link identifier MAY
be an IP address, but it may also be any other mutually agreed upon
identifier which uniquely identifies a boundary link. Fore example a
layer-two identifier in case of e.g. ethernet, or for unnumbered
links like in e.g. PPP(Point-to-Point Protocol, [RFC-1661])-based
access configurations. The interface identifier(s) may also
implicitly be derived from the source or destination address
information in the Flow Description field (see next section 3.2)
combined with e.g. BGP4 (Border Gateway Protocol, version 4, [RFC-
1771]) routing information.
3.2. Flow Description
The flow description of an SLS associated to a given service offering
indicates for which IP packets the QoS guarantees for that specific
service offering is to be enforced.
A flow description identifies a stream of IP datagrams sharing at
least one common characteristic. An SLS contains one (and only one)
flow description, which MAY formally be specified by providing one or
more of the following attributes:
flow description = (Differentiated Services information, source
information, destination information, application information)
- Differentiated Services information = DSCP value | set of DSCP
values | any
The Differentiated Services Code Point (DSCP) IP header field is
defined in [RFC-2474].
- Source information = source address | set of source addresses |
source prefix | set of source prefixes | any
- Destination information = destination address | set of
destination addresses | destination prefix | set of destination
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prefixes | any
- Application information = protocol number | protocol number and
source port, destination port | any
Note: "any" is again logically equivalent with unspecified.
Thus, the flow description may be expressed by information attributes
related to the source/destination nodes, the application or the DS
field in the IP header. The flow description provides the necessary
information for classifying the packets at a DS boundary node.
This datagram classification can either be Behaviour Aggregate (BA)
or Multi-Field (MF)classification based.
In case of MF-classification all attributes MAY be specified,
including the DSCP field. MF classification may depict as well
micro-flows as aggregate macro-flows, based on e.g. source network
prefix [DS-MODEL]. Also the "set-of" semantics allows for the
specification of aggregate flows. If a flow description is e.g.
specified by a set of two IP source addresses, then any packet with
either of the two concerned source addresses belongs to the IP packet
stream identified by this flow description.
In case of BA-classification [RFC-2475], the DSCP attribute MUST be
specified and the other attributes MUST NOT be specified. If a set of
DSCP-values is specified, then any packet having a DSCP belonging to
this set is part of the Flow (description) packet stream (analogous
to the example above with the IP source addresses). As an example
consider an Ordered Aggregate (OA) IP packet stream of a particular
Assured Forwarding Class AFx (AF1,AF2,AF3,AF4 - see [RFC 2597]). This
stream could be specified within one flow description using three
DSCP-values, indicating the three drop precedences levels,
respectively colored in green, yellow and red.
It should however be noticed that the DSCP-value(s) specified in the
SLS has (have) as such nothing to do with the DSCP-marking of packets
inside the DiffServ network. The latter, i.e. the "interior" DSCP is
used for differentiating packets according to Per Hop Behaviours
(PHBs). The former, i.e. the "ingress" DSCP value (specified in the
SLS), is just another way of identifying a packet stream, eventually
in combination with other IP header fields. At the ingress DiffServ
node (incoming) packets are classified based on the "ingress" DSCP
value (amongst others), after which they may be re-marked by the
"interior" DSCP-value.
Finally note also that the IP routing scheme MAY put restrictions on
combining scope and flow description within an SLS.
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In general, if (only) the flow description is specified by source and
destination IP address (IP-src, IP-dest), and the scope is
unspecified, then there is no a-priori assumption about the actual
ingress/egress points that this traffic will use. Indeed, it is the
responsibility of the service provider to define the most appropriate
route for this traffic, by enforcing the corresponding traffic
engineering and routing policy. Thus, the (ingress, egress)
information (which is in this case not in the SLS) is then derived
from the flow description and the routing policy of the service
provider.
On the other hand, if the flow description AND scope are specified in
the SLS, respectively by the pairs (IP-src, IP-dest) and (IP-ingr,
IP-egr) then it is clear that the IP packets MUST follow the route
(IP-src,...,IP-ingr,...,IP-egr,...,IP-dest). Thus the restriction is
that the scope (IP-ingr, IP-egr) is part of the route from IP-src to
IP-dest.
Further routing considerations are outside the scope of this
document.
Finally remark that the exclusion of the many-to-many communication
scope model puts similar constraints on the source/destination fields
of the Flow Description.
3.3 Traffic Envelop and Traffic Conformance
The traffic envelop describes the traffic (conformance)
characteristics of the IP packet stream identified by the flow
description. The traffic envelop is a set of Traffic Conformance
Parameters, describing how the packet stream should look like to get
the guarantees indicated by the performance parameters (defined in
section 3.5)
The Traffic Conformance Parameters are the basic input for the
Traffic Conformance Algorithm. Traffic Conformance Testing as the
combination of the Traffic Conformance Parameters and the Traffic
Conformance Algorithm. This will usually be done at a DS-boundary
node.
The algorithm and the conformance test can be binary-based or multi-
level based.
Binary Traffic Conformance Testing is a set of actions which uniquely
identifies the "in-profile" and "out-of profile" (or excess) packets
of an IP stream (identified by Flow-Id). In this case the Traffic
Conformance Parameters describe the reference values the traffic
(identified by the flow description) will have to comply with, thus
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yielding the notions of "in" and "out" of profile traffics. The
Traffic Conformance Algorithm is the mechanism enabling unambiguously
to identify all "in" or "out" of profile packets based on these
Conformance parameters.
In case of multi-level (n) Traffic Conformance Testing a packet will
be tagged (by the algorithm) as belonging to a particular level
(1...n). Packets tagged as level n are called "excess" packets.
The SLS MUST indicate the concerned level (n) of the conformance
testing algorithm:
- Multi-level conformance testing n (integer)
The following gives a (non-exhaustive) list of potential conformance
parameters.
- Peak rate p (bits per second)
- Token bucket rate r (bits per second)
- bucket depth b (bytes)
- Maximum Transport Unit (MTU) M (bytes)
- Minimum packet size (bytes)
Binary-based Traffic Conformance Testing examples:
- Conformance parameters = token bucket parameters (b,r);
conformance algorithm = token bucket algorithm.
- Conformance parameters = token bucket parameters and peak rate
(b,r,p) with p larger than r; conformance algorithm = the combined
token bucket (b,r) and (b,p). This is the conformance test for
Integrated Services Controlled Load and Guaranteed Service IP
flows in the IntSer QoS architecture [RFC-2211, RFC-2212]. The
scheme permits bursty traffic to be sent, limited to a burst of b
bytes, with a (long-term) average rate of r and a peak rate of no
more than p.
- Conformance parameters = MTU; conformance algorithm = all
packets allowed with size smaller than MTU; packets larger than
MTU are fragmented or dropped.
Three-level based Traffic Conformance Testing example
- The Two-rate Three-colour marker [REF] is based on two token
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buckets with rates r1 and r2 (larger than r1), containing
respectively green and yellow tokens. The simplest operational
mode is the "colour-blank" mode. A packet is tagged "green" if
there are green and yellow tokens available, yellow if only yellow
tokens are available and otherwise it is tagged red.
3.4. Excess Treatment
This section describes how the service provider will process excess
traffic, i.e. out-of-profile traffic (in case of binary conformance
testing) or n-level traffic (in case of n-level conformance testing).
The process takes place after Traffic Conformance Testing, described
previously.
Excess traffic may be dropped, shaped and/or remarked. The SLS MUST
specify the appropriate action by the following attribute.
- Excess Treatment
If Excess Treatment is not indicated, then excess traffic is dropped.
Depending on the appropriate action, more parameters MAY be required
The following is an indication in case of binary conformance testing.
Multi-level conformance testing (like the definition of a
hierarchical drop preference model) MAY also be enforced, but this
concern has been left for further study.
- If excess traffic is dropped, then all packets marked as "out-
of-profile" by the Traffic Conformance Algorithm are dropped. No
extra parameters are needed.
- If excess traffic is shaped, then all packets marked as "out-
of-profile" by the Traffic Conformance Algorithm are delayed until
they are "in-profile". The shaping rate is the policing/token
bucket rate r. The extra parameter is the buffer size of the
shaper.
- If excess traffic is marked or remarked, then all packets marked
as "out-of-profile" by the Traffic Conformance Algorithm are (re-)
marked with a particular DSCP-value (yellow or red). The extra
parameter is the DSCP.
3.5. Performance Guarantees
The performance parameters describe the service guarantees the
network offers to the customer for the packet stream described by the
flow description and over the geographical/topological extent given
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by the scope.
There are four performance parameters:
- delay, time interval, optional quantile
- jitter, time interval, optional quantile
- packet loss, time interval
- throughput, time interval
Delay, jitter and packet loss guarantees are for the in-profile
traffic in case of binary conformance testing. For multi-level (n)
conformance testing, delay, jitter and loss guarantees MAY be
specified for each conformance level-i, except the last one (n). For
example if n = 3, one can have a delay guarantee for the "conformance
level-1" packets and a different delay guarantee for the "conformance
level-2" packets. No guarantees are given for excess ("conformance
level-n") traffic.
The throughput is an overall guarantee for the IP packet stream,
independent of a particular level (see below).
The following definitions always consider the (measurable)
performance parameters related to the packet stream specified by the
flow description. For simplicity the definitions below are given for
binary conformance testing (n=2), but generalisation is
straightforward.
The delay and jitter indicate respectively the maximum packet
transfer delay and packet transfer delay variation from ingress to
egress, measured over (any) time period with a length equal to the
(indicated) time interval.
Delay and jitter may either be specified as worst case
(deterministic) bounds or as quantiles. Indeed, the worst case
delay/jitter bounds will be very rare events and customers may find
measurements of e.g. 99.5th percentile a more relevant empirical
gauge of delay/jitter.
Suppose e.g. that the SLS specifies the triple (delay = 10ms, time
interval = 5 minutes, quantile = 10E-3). Then the probability that
the transfer delay of a packet (between ingress-egress) is larger
than 10ms, is less than 10E-3; and this for any measurement period of
5 minutes.
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The above syntax for delay/jitter can be generalised by specifying in
the SLS an array of e.g. N (delay/jitter, quantile)-couples. The more
couples, the better the delay probability tail distribution can be
approximated. Such a specification together with the eventual need of
such a generalisation is for further study.
The packet loss probability is ratio of the lost (in-profile) packets
between ingress and egress and the offered (in-profile) packets at
ingress.
lost packets between (and including) ingress and egress
packet loss = -------------------------------------------------------
offered (injected) packets at ingress
The ratio is measured over (any) time period with a length equal to
the (indicated) time interval.
The throughput is the rate measured at egress counting all packets
identified by the flow description. Notice that all packets,
independently of their conformance level (in/out-of-profile)
contribute. Indeed, if the customer (only) wants a throughput
guarantee, then he/she does not care whether in- or out-profile
packets are dropped, but is only interested in the overall throughput
of its packet stream.
Note on the relation with the Traffic Conformance Parameters (section
3.3) in case of a binary-based conformance testing algorithm:
- The Traffic Conformance Algorithm (and parameters) MUST be
specified when guaranteeing delay/jitter or packet loss, i.e. if
one of these performance parameters is quantified in the SLS.
Conformance testing is required because the delay/jitter and loss
guarantees are only for the stream of in-profile packets.
- When only guaranteeing a throughput, or if non of the other
performance parameters is quantified, the traffic conformance
algorithm MAY be specified. It is not required to specify the
Conformance Algorithm, because the (eventual) troughput guarantee
does not require the strict distinction between in/out-of-profile
traffic. However, the network operator will probably protect his
network by implementing a Traffic Conditioner at Ingress and
specifying the token policing rate (r) (almost) equal to the
throughput guarantee R, r~R. He may or may not tag/mark excess
traffic, according to his own - internal - policy rules. See also
example 4.2.
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Note on the relation between throughput R, packet loss p and excess
treatment in case of a binary-based conformance testing algorithm:
- First consider the case where excess traffic is dropped (or
shaped to in-profile) based on the token bucket (b,r) traffic
conformance algorithm. As only in-profile packets are allowed at
ingress, the following equality holds:
throughput R = (1-p) * token rate r
Thus the throughput guarantee can be derived from the loss
probability and token rate and is therefore not an independent
parameter.
- If excess traffic is allowed (and marked accordingly), then
"throughput" is an independent parameter because it also takes
into account the out-of-profile packets (measured at egress). One
has obviously the inequality:
throughput R >= (1-p) * token rate r
Quantitative performance guarantees
A performance parameter is said to be quantified if its value is
specified to a numeric (quantitative) value.
The service guarantee described by the SLS is said to be quantitative
IF at least one of the 4 performance parameters is quantified.
Qualitative performance guarantees
If non of the SLS performance parameters are quantified, then the
performance parameters "delay" and "packet loss" MAY be "qualified".
Possible qualitative values (for delay and/or loss): high, medium,
low.
Relative delay guarantees:
- gold service : value = low
- silver service : value = medium
- bronze service : value = high or not indicated
Relative loss guarantees
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- green service : value = low
- yellow service : value = medium
- red service : value = high or not indicated
The quantification of relative difference between <high/medium/low>
is a provider policy (e.g. high = 2 x medium ; medium = 2 x low).
The above taxonomy yields the following combinations of qualitative
services.
-------------------------------------------------------
|\ delay | | | |
| \------| low | medium |high |
| loss | | | |
|------------------------------------------------------|
| low | gold green | silver green | bronze green |
| medium | gold yellow | silver yellow | bronze yellow |
| high | gold red | silver red | bronze red |
|------------------------------------------------------|
Combinations table
The service guarantee described by the SLS is said to be qualitative
if it is NOT quantitative and either delay or loss (non-exclusive)
are qualified to "medium" or "low", i.e. excluding bronze/red from
the above.
The service guarantee described by the SLS is said to be best-effort
if it is NOT quantified nor qualified.
3.6. Service schedule
The service schedule indicates the start time and end time of the
service, i.e. when is the service available.
This might be expressed as collection of the following parameters:
- Time of the day range
- Day of the week range
- Month of the year range
Some examples are:
- Time of the day range
08h00-18h00
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- Day of the week range
A single day
A group of sequential days
- Month of the year range
A single month
A group of sequential months
- Year range
A single year
A group of sequential years
Remark: service schedule "from now on" [now, infinity] can be
captured by putting the above to their full range.
3.7. Reliability
Reliability indicates the maximum allowed mean downtime per year
(MDT) and the maximum allowed time to repair (TTR) in case of service
breakdown (e.g. in case of cable cut).
The Mean Down Time might be expressed in minutes per year and the
Maximum Time To Repair might be expressed in seconds.
3.8 Others
Other parameters such as route, reporting guarantees, security,
scheduled maintenance, etc... remain for further study.
4. Service Level Specification examples.
Within this section a number of example instantiations of SLSs are
presented to illustrate the potential use of the SLS template defined
above.
4.1. Virtual Leased Line
The following specifies the SLS for a (uni-directional) VLL with
quantified throughput guarantee of e.g 1 Mbps, a delay guarantee of
20 ms for a 10E-3 quantile and zero packet loss.
- Scope: one-to-one communication (Ingress, Egress) specified
- Flow description: (source,destination) IP-addresses, DSCP=EF.
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- Traffic Conditioning: token bucket (b,r), r = 1 Mbps
- Excess Treatment = dropping. Thus only in-profile packets are
allowed.
- Delay guarantee = (d = 20 ms, t = 5 minutes, q = 10E-3)
- Loss guarantee p = 0 (imlying a throughput guarantee R = r)
- Service Schedule: may be indicated
- Reliability: may be indicated
Notice that in this example, the throughput guarantee is a derived
parameter from the packet loss p=0, the conditioning token bucket
parameter r=1 Mbps and the excess treatment=dropping.
4.2 Bandwidth Pipe for data-services
The following SLS specifies a bandwidth pipe with a strict throughput
guarantee, but with only a loose requirements for packet loss, i.e.
"low". Thus, the SLS only mentiones the scope (pipe), the flow
description and a throughput guarantee. Remark that there are now
traffic conformance parameters (and consequently no excess treatment
indication).
- Scope: one-to-one communication (Ingress, Egress) specified
- Flow description: (source,destination) IP-addresses
- Throughput guarantee R = 1 Mbps
- Service Schedule: may be indicated
- Reliability: may be indicated
Although there is no (explicit) traffic conditioning agreement
between the customer and the network operator (i.e. not mentioned in
the SLS), the operator is likely to protect his network by
implementing a traffic conditioner token bucket (b,r). If the
operator can guarantee a zero packet loss for the bandwidth pipe,
then the token rate equals the throughput guarantee. However, the SLS
can also be met by the operator without such a stringent loss
requirement, say p = 10E-5. In this case the token rate is derived
from the throughput guarantee and the loss probability:
token rate r = R / (1-p)
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The in-profile packet stream (according to the conditioner (b,r)) has
a throughput guarantee of R = r * (1-p) = 1 Mbps.
Further, it is up to the operator's policy whether or not excess
traffic (again according to the operator's conditioner (b,r), which
is not mentioned in the SLS agreement) is allowed or not in his
network.
4.3. Real-time micro-flows
- Scope: one-to-one communication (Ingress, Egress) specified
- Flow description: (source IP-address, destination IP-address,
source port number, destination port number, protocol)
- Traffic Conditioning: token bucket (b,r), peak rate p= r = 64 Kbps
- Excess Treatment = dropping.
- Performance Parameters: delay = 10 msec, packet loss = 10E-6,
guaranteed throughput R ~ r.
4.4 Minimum rate guarantee with allowed excess
The following could be for bulk FTP traffic that requires a minimum
throughput, but would take everything it can get (TCP). Also adaptive
applications, like video streaming, that however require a minimum
throughput for the service.
- Scope: one-to-one (Pipe)
- Flow description: e.g. DSCP-value indicating a possible AF-PHB.
- Traffic Conformance Parameters: (b,r) MUST be indicated
- Excess Treatment: Remarking MUST be indicated (excess is given a
higher drop precedence)
- Performance guarantees: guaranteed throughput R = r.
4.5. Qualitative Olympic services
The following SLS is meant for the Olympic Service. It could be used
for differentiating applications such as web-browsing and e-mail
traffic.
SLS 1 (on-line web-browsing) - Scope: one-to-one (pipe) or one-to-
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many (hose)
- Flow description: MAY be indicated
- Traffic Conformance Parameters: token parameters (b,r) The token
bucket rate r indicates an (average) maximum Committed Information
Rate (CIR) for which "better-than-best-effort" treatment will be
applied.
- Excess Treatment: remarking.
- Performance Parameter: Delay and Packet loss are indicated as
"low": gold/green class
SLS2 : (background e-mail traffic)
This is identical to SLS1 but targeting the silver/green class.
4.6. The Funnel service
The service offered by the funnel model is primarily a protection
service: the customer wants to set a maximum on the amount of traffic
(characterized by a DSCP) entering his network. It could e.g. be used
for business customers to restrict the amount of web browsing traffic
entering their network.
/---------------\
|Network _____|______ B
| _____/ |
A__________|___.___________|______ C
/_____ | _____ |
\a(out) | \_____|_______D
\---------------/
Figure 4: Funnel model
In [Figure 4], customer A requires that specific traffic entering his
network from B,C and D does not exceed the rate a_out.
- Scope: Funnel (N|all,1).
- Flow description: DSCP MUST be indicated. The filter (see below) is
applied to all traffic characterized by the DSCP -value.
- Traffic Conformance Parameters: (b, r) MUST be indicated. The token
bucket parameters indicate the maximum allowed throughput (r = a_out)
towards the customer network on the specified egress interface. This
maximum or filter is applied to all packets marked with the DSCP-
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value indicated above.
- Excess treatment: dropping (this is actually the service offered by
the network).
- Performance Parameter: not specified.
4.7. Best effort traffic
- Scope : all models
- Flow description : none
- Traffic Conformance Parameters: if not indicated, then the full
link capacity is allowed
- Excess Treatment: not specified
- Performance Parameters: none
- Service Schedule: may be indicated.
- Reliability: may be indicated.
5. SLS negotiation requirements
[This section is informational and preliminary. More detailed study
is required.]
A major goal of the availability of an SLS template is helping in the
deployment of dynamical SLS negotiation procedures between customer
and providers or between providers. This draft only discussed the SLS
template and its basic contents. The SLS negotiation protocol is for
further study. The following lists a number of conditions which
should be met by a (to be defined) SLS negotiation protocol.
The SLS negotiation protocol MUST allow for:
- Original service requests, according the components of the
specified SLS.
- Service acknowledgement (ACK), indicating agreement with the
requested service level.
- Service rejection (NAK) but indicating the possibility of offering
a closely related service (or indication of alternative DSCP to use
for a particular service). The reply message may indicate the related
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offering by overwriting the proposed SLS attributes (hints).
- Service rejection (REJECT) indicating incapability of providing
the service.
- The ACK/NACK procedures require a reliable transport mode for such
a negotiation protocol.
- Service modification from both user and provider.
The following are further requirements for the overall network
architecture which SHOULD be fulfilled.
- The protocol should be able to interact with feedback of events
related to the service. For example performance degradation MAY
result in re-negotiation of the SLS.
- The protocol should preferentially make use of / be an
extension of existing specifications protocol design work available
such as RSVP ([RFC-2205]) or PPP/IPCP ([RFC-1661]).
6. Security considerations
The information which will yield the instantiation of an SLS template
to address the specific requirements of a customer in terms of the
quality associated to the service it has subscribed to may require
the activation of security features so that:
- Identification and authentication of the requesting entity needs to
be performed;
- Identification and authentication of the peering entities which
will participate in the SLS negotiation process needs to be
performed;
- Preservation of the confidentiality of the information to be
conveyed during the SLS negotiation and instantiation procedures
between the peering entities is a MUST.
7. Acknowledgements
Part of this work has been funded under the European Commission 5th
framework IST program.
The authors would like to acknowledge all their colleagues in the
TEQUILA project for their input and reflection on this work.
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The authors also would like to acknowledge Werner Almesberger, Marcus
Brunner, Stefaan De Cnodder, Stefano Salsano, Alberto Kamienski and
Abdul Malick for their useful comments and suggestions on the mailing
list sls@ist-tequila.org and during private conversation.
References
[TEQUILA] IST-Tequila project http://www.ist-tequila.org/
[RFC 1661] "The Point-to-Point Protocol (PPP)", W. Simpson,
http://www.ietf.org/rfc/rfc1661.txt?number=1661
[RFC-1771] A Border Gateway Protocol 4 (BGP-4). Y. Rekhter, T.
Li. March 1995. http://www.ietf.org/rfc/rfc2205.txt?number=1771
[RFC 2205] "Resource ReSerVation Protocol (RSVP)- Version 1
Functional Specification", R. Braden et al.
http://www.ietf.org/rfc/rfc2205.txt?number=2205
[RFC-2211] J. Wroclawski, "Specification of the Controlled-Load
Network Element Service", RFC 2211, September 1997.
[RFC-2212] S. Shenker, C. Partridge, R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212, September 1997.
[RFC 2474] "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", K.Nichols, S. Blake, F. Baker,
D. Black, www.ietf.org/rfc/rfc2474.txt
[RFC 2475] "An Architecture for Differentiated Services", S. Blake,
D. Black, M.Carlson,E.Davies,Z.Wang,W.Weiss,
www.ietf.org/rfc/rfc2475.txt
[RFC 2597] "Assured Forwarding PHB Group", F. Baker, J. Heinanen, W.
Weiss, J. Wroclawski, www.ietf.org/rfc/rfc2597.txt
[RFC 2598] "An Expedited Forwarding PHB", V.Jacobson, K.Nichols,
K.Poduri, www.ietf.org/rfc/rfc2598.txt
[RFC 2698] "A Two Rate Three Color Marker." J. Heinanen, R. Guerin.
September 1999. www.ietf.org/rfc/rfc2698.txt
[DS-MODEL] "A Conceptual Model for Diffserv Routers", Y. Bernet et
al., draft-ietf-diffserv-model-03.txt, Work in Progress, May 2000
[DS-TERMS] "New terminology for diffserv", D. Grossman, draft-ietf-
diffserv-new-terms-02.txt, work in progress
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[QBONE] "Qbone Architecture (v1.0), Ben Teitelbaum (1999),
http://www.internet2.edu/qos/wg/papers/qbArch/
[TWOBIT] "A Two-bit Differentiated Services Architecture for the
Internet", ftp://ftp.ee.lbl.gov/parpers/dsarch.pdf, 1997
Full copyright statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works.
However, this document itself may not be modified in any way, such as
by removing the copyright notice or references to the Internet
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Authors Addresses
Danny Goderis
Alcatel Corporate Research Center
Fr. Wellesplein 1, 2018 Antwerpen, Belgium.
Tel : +32 3 240 7853
Fax : +32 3 240 9932
E-mail: Danny.Goderis@Alcatel.be
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Yves T'Joens
Alcatel Corporate Research Center
Fr. Wellesplein 1, 2018 Antwerpen, Belgium.
Tel : +32 3 240 7890
Fax : +32 3 240 9932
E-mail: Yves.TJoens@Alcatel.be
Christian Jacquenet
France Telecom Research and Development (FT R&D)
Rue des Coutures 42, BP6243, 14066 CAEN CEDEX 04 France
Tel : +33 2 31 75 94 28
Fax : +33 2 31 73 56 26
E-mail: christian.jacquenet@francetelecom.fr
George Memenios
Research Associate, Telecommunications Laboratory NTUA
Heroon Polytechniou 9, 157 73 Zografou, Athens, Greece
Tel : +30 1 772 1494
Fax : +30 1 772 2534
E-mail: gmemen@telecom.ntua.gr
George Pavlou
Centre for Communication Systems Research (CCSR)
Univ. of Surrey, Guildford, Surrey GU2 7XH, UK
Tel : +44 (0)1483 259480
Fax : +44 (0)1483 876011
E-mail: G.Pavlou@eim.surrey.ac.uk
Richard Egan
Racal Research Ltd
Worton Drive, Worton Grange Industrial Estate
Reading, Berkshire RG2 OSB, UK
Tel : +44 118 986 8601
Fax : +44 118 923 8399
E-mail: richard.egan@rrl.co.uk
David Griffin
Department of Electronic and Electrical Engineering
University College London, Torrington Place, London WC1E 7JE, UK
Tel : +44 (0)20 7679 3557
Fax : +44 (0)20 7388 9325
E-mail: D.Griffin@ee.ucl.ac.uk
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Panos Georgatsos
Algosystems S.A.
Sardeon str. 4, 172 34 Athens, Greece
Tel : +30 1 93 10 281
Fax : +30 1 93 52 873
E-mail: pgeorgat@algo.com.gr
Leonidas Georgiadis
Aristotel Univ. of Thessaloniki, Faculty of Engineering
School of Electrical and Computer Engineering, Telecommunications Dept.
PO Box 435, Thessaloniki, 54006, Greece
Tel : +30 31 996385
Fax : +30 31 996312
E-mail: leonid@eng.auth.gr
Pim Van Heuven
Inter-University Micro-Electronics Centre
Tel : +32 9 267 3592
E-mail: pvheuven@intec.rug.ac.be
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