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Versions: 00 01 02 RFC 4594

TSVWG                                                         J. Babiarz
Internet-Draft                                                   K. Chan
Expires: January 16, 2006                                Nortel Networks
                                                                F. Baker
                                                           Cisco Systems
                                                           July 15, 2005


         Configuration Guidelines for DiffServ Service Classes
              draft-ietf-tsvwg-diffserv-service-classes-01

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This paper summarizes the recommended correlation between service
   classes and their usage, with references to their corresponding
   recommended Differentiated Service Code Points (DSCP), traffic
   conditioners, Per-Hop Behaviors (PHB) and Active Queue Management
   (AQM) mechanism.  There is no intrinsic requirement that particular
   DSCPs, traffic conditioner PHBs and AQM be used for a certain service



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   class, but as a policy it is useful that they be applied consistently
   across the network.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1   Requirements Notation  . . . . . . . . . . . . . . . . . .  4
     1.2   Expected use in the Network  . . . . . . . . . . . . . . .  4
     1.3   Service Class Definition . . . . . . . . . . . . . . . . .  5
     1.4   Key Differentiated Services Concepts . . . . . . . . . . .  5
       1.4.1   Queuing  . . . . . . . . . . . . . . . . . . . . . . .  6
         1.4.1.1   Priority Queuing . . . . . . . . . . . . . . . . .  6
         1.4.1.2   Rate Queuing . . . . . . . . . . . . . . . . . . .  6
       1.4.2   Active Queue Management  . . . . . . . . . . . . . . .  7
       1.4.3   Traffic Conditioning . . . . . . . . . . . . . . . . .  7
       1.4.4   Differentiated Services Code Point (DSCP)  . . . . . .  8
       1.4.5   Per-Hop Behavior (PHB) . . . . . . . . . . . . . . . .  8
     1.5   Key Service Concepts . . . . . . . . . . . . . . . . . . .  8
       1.5.1   Default Forwarding (DF)  . . . . . . . . . . . . . . .  9
       1.5.2   Assured Forwarding (AF)  . . . . . . . . . . . . . . .  9
       1.5.3   Expedited Forwarding (EF)  . . . . . . . . . . . . . . 10
       1.5.4   Class Selector (CS)  . . . . . . . . . . . . . . . . . 10
       1.5.5   Admission Control  . . . . . . . . . . . . . . . . . . 11
   2.  Service Differentiation  . . . . . . . . . . . . . . . . . . . 11
     2.1   Service Classes  . . . . . . . . . . . . . . . . . . . . . 11
     2.2   Categorization of User Service Classes . . . . . . . . . . 13
     2.3   Service Class Characteristics  . . . . . . . . . . . . . . 16
     2.4   Deployment Scenarios . . . . . . . . . . . . . . . . . . . 21
       2.4.1   Example 1  . . . . . . . . . . . . . . . . . . . . . . 21
       2.4.2   Example 2  . . . . . . . . . . . . . . . . . . . . . . 22
       2.4.3   Example 3  . . . . . . . . . . . . . . . . . . . . . . 25
   3.  Network Control Traffic  . . . . . . . . . . . . . . . . . . . 27
     3.1   Current Practice in The Internet . . . . . . . . . . . . . 27
     3.2   Network Control Service Class  . . . . . . . . . . . . . . 27
     3.3   OAM Service Class  . . . . . . . . . . . . . . . . . . . . 29
   4.  User Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 30
     4.1   Telephony Service Class  . . . . . . . . . . . . . . . . . 31
     4.2   Signaling Service Class  . . . . . . . . . . . . . . . . . 32
     4.3   Multimedia Conferencing Service Class  . . . . . . . . . . 34
     4.4   Real-time Interactive Service Class  . . . . . . . . . . . 37
     4.5   Multimedia Streaming Service Class . . . . . . . . . . . . 38
     4.6   Broadcast Video Service Class  . . . . . . . . . . . . . . 40
     4.7   Low Latency Data Service Class . . . . . . . . . . . . . . 42
     4.8   High Throughput Data Service Class . . . . . . . . . . . . 44
     4.9   Standard Service Class . . . . . . . . . . . . . . . . . . 46
     4.10  Low Priority Data  . . . . . . . . . . . . . . . . . . . . 47
   5.  Additional Information on Service Class Usage  . . . . . . . . 48
     5.1   Mapping for Signaling  . . . . . . . . . . . . . . . . . . 48



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     5.2   Mapping for NTP  . . . . . . . . . . . . . . . . . . . . . 48
     5.3   VPN Service Mapping  . . . . . . . . . . . . . . . . . . . 49
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 49
   7.  Summary of Changes from Previous Draft . . . . . . . . . . . . 50
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51
   9.  Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 51
     9.1   Explanation of Ring Clipping . . . . . . . . . . . . . . . 51
   10.   References . . . . . . . . . . . . . . . . . . . . . . . . . 52
     10.1  Normative References . . . . . . . . . . . . . . . . . . . 52
     10.2  Informative References . . . . . . . . . . . . . . . . . . 53
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 54
       Intellectual Property and Copyright Statements . . . . . . . . 56







































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1.  Introduction

   This paper summarizes the recommended correlation between service
   classes and their usage, with references to their corresponding
   recommended Differentiated Service Code Points (DSCP), traffic
   conditioners, Per-Hop Behaviors (PHB) and Active Queue Management
   (AQM) mechanisms.  There is no intrinsic requirement that particular
   DSCPs, traffic conditioner PHBs and AQM be used for a certain service
   class, but as a policy it is useful that they be applied consistently
   across the network.

   Service classes are defined based on the different traffic
   characteristics and required performance of the applications/
   services.  This approach allows us to map current and future
   applications/services of similar traffic characteristics and
   performance requirements into the same service class.  Since the
   applications'/services' characteristics and required performance are
   end to end, the service class notion needs to be preserved end to
   end.  With this approach, a limited set of service classes is
   required.  For completeness, we have defined twelve different service
   classes, two for network operation/administration and ten for user/
   subscriber applications/services.  However, we expect that network
   administrators will implement a subset of these classes relevant to
   their customers and their service offerings.  Network Administrators
   may also find it of value to add locally defined service classes,
   although these will not necessarily enjoy end to end properties of
   the same type.

   Section 1, provides an introduction and overview of technologies that
   are used for service differentiation in IP networks.  Section 2, is
   an overview of how service classes are constructed to provide service
   differentiation with examples of deployment scenarios.  Section 3,
   provides configuration guidelines of service classes that are used
   for stable operation and administration of the network.  Section 4,
   provides configuration guidelines of service classes that are used
   for differentiation of user/subscriber traffic.  Section 5, provides
   additional guidance on mapping different applications/protocol to
   service classes.  Section 6, address security considerations.

1.1  Requirements Notation

   The key words "SHOULD", "SHOULD NOT", "REQUIRED", "SHALL", "SHALL
   NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in [RFC2119].

1.2  Expected use in the Network

   In the Internet today, corporate LANs and ISP WANs are generally not



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   heavily utilized - they are commonly 10% utilized at most.  For this
   reason, congestion, loss, and variation in delay within corporate
   LANs and ISP backbones is virtually unknown.  This clashes with user
   perceptions, for three very good reasons.
   o  The industry moves through cycles of bandwidth boom and bandwidth
      bust, depending on prevailing market conditions and the periodic
      deployment of new bandwidth-hungry applications.
   o  In access networks, the state is often different.  This may be
      because throughput rates are artificially limited, or are over
      subscribed, or because of access network design trade-offs.
   o  Other characteristics, such as database design on web servers
      (that may create contention points, e.g. in filestore), and
      configuration of firewalls and routers, often look externally like
      a bandwidth limitation.

   The intent of this document is to provide a consistent marking,
   conditioning and packet treatment strategy so that it can be
   configured and put into service on any link which itself is
   congested.

1.3  Service Class Definition

   A "service class" represents a set of traffic that requires specific
   delay, loss and jitter characteristics from the network for which a
   consistent and defined per-hop behavior (PHB) [RFC2474] applies.
   Conceptually, a service class pertains to applications with similar
   characteristics and performance requirements, such as a "High
   Throughput Data" service class for applications like the web and
   electronic mail, or a "Telephony" service class for real-time traffic
   such as voice and other telephony services.  Such service class may
   be defined locally in a Differentiated Services domain, or across
   multiple DS domains, including possibly extending end to end.

   A Service Class as defined here is essentially a statement of the
   required characteristics of a traffic aggregate; the actual
   specification of the expected treatment of a traffic aggregate within
   a domain may also be defined as a Per Domain Behavior [RFC3086].

   The Default Forwarding "Standard" service class is REQUIRED, all
   other service classes are OPTIONAL.  It is expected that network
   administrators will choose the level of service differentiation that
   they will support based on their need, starting off with three or
   four service classes for user traffic and add others as the need
   arises.

1.4  Key Differentiated Services Concepts

   The reader SHOULD be familiar with the principles of the



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   Differentiated Services Architecture [RFC2474].  However, we
   recapitulate key concepts here to save searching.

1.4.1  Queuing

   A queue is a data structure that holds packets that are awaiting
   transmission.  The packets may be delayed while in the queue,
   possibly due to lack of bandwidth, or because it is low in priority.
   There are a number of ways to implement a queue, a simple model of a
   queuing system, however, is a set of data structures for packet data,
   which we will call queues and a mechanism for selecting the next
   packet from among them, which we call a scheduler.

1.4.1.1  Priority Queuing

   A priority queuing system is a combination of a set of queues and a
   scheduler that empties them in priority sequence.  When asked for a
   packet, the scheduler inspects the highest priority queue, and if
   there is data present returns a packet from that queue.  Failing
   that, it inspects the next highest priority queue, and so on.  A
   freeway onramp with a stoplight for one lane, but which allows
   vehicles in the high occupancy vehicle lane to pass, is an example of
   a priority queuing system; the high occupancy vehicle lane represents
   the "queue" having priority.

   In a priority queuing system, a packet in the highest priority queue
   will experience a readily calculated delay - it is proportional to
   the amount of data remaining to be serialized when the packet arrived
   plus the volume of the data already queued ahead of it in the same
   queue.  The technical reason for using a priority queue relates
   exactly to this fact: it limits delay and variations in delay, and
   should be used for traffic which has that requirement.

   A priority queue or queuing system needs to avoid starvation of lower
   priority queues.  This may be achieved through a variety of means
   such as admission control, rate control, or network engineering.

1.4.1.2  Rate Queuing

   Similarly, a rate-based queuing system is a combination of a set of
   queues and a scheduler that empties each at a specified rate.  An
   example of a rate based queuing system is a road intersection with a
   stoplight - the stoplight acts as a scheduler, giving each lane a
   certain opportunity to pass traffic through the intersection.

   In a rate-based queuing system, such as WFQ or WRR, the delay that a
   packet in any given queue will experience is dependant on the
   parameters and occupancy of its queue and the parameters and



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   occupancy of the queues it is competing with.  A queue whose traffic
   arrival rate is much less than the rate at which it lets traffic
   depart will tend to be empty and packets in it will experience
   nominal delays.  A queue whose traffic arrival rate approximates or
   exceeds its departure rate will tend to be not empty, and packets in
   it will experience greater delay.  Such a scheduler can impose a
   minimum rate, a maximum rate, or both, on any queue it touches.

1.4.2  Active Queue Management

   "Active queue management" or AQM is a generic name for any of a
   variety of procedures that use packet dropping or marking to manage
   the depth of a queue.  The canonical example of such a procedure is
   Random Early Detection, in that a queue is assigned a minimum and
   maximum threshold, and the queuing algorithm maintains a moving
   average of the queue depth.  While the mean queue depth exceeds the
   maximum threshold, all arriving traffic is dropped.  While the mean
   queue depth exceeds the minimum threshold but not the maximum
   threshold, a randomly selected subset of arriving traffic is marked
   or dropped.  This marking or dropping of traffic is intended to
   communicate with the sending system, causing its congestion avoidance
   algorithms to kick in.  As a result of this behavior, it is
   reasonable to expect that TCP's cyclic behavior is desynchronized,
   and the mean queue depth (and therefore delay) should normally
   approximate the minimum threshold.

   A variation of the algorithm is applied in Assured Forwarding PHB
   [RFC2597], in that the behavior aggregate consists of traffic with
   multiple DSCP marks, which are intermingled in a common queue.
   Different minima and maxima are configured for the several DSCPs
   separately, such that traffic that exceeds a stated rate at ingress
   is more likely to be dropped or marked than traffic that is within
   its contracted rate.

1.4.3  Traffic Conditioning

   Additionally, at the first router in a network that a packet crosses,
   arriving traffic may be measured, and dropped or marked according to
   a policy, or perhaps shaped on network ingress as in A Rate Adaptive
   Shaper for Differentiated Services [RFC2963].  This may be used to
   bias feedback loops, such as is done in Assured Forwarding PHB
   [RFC2597], or to limit the amount of traffic in a system, as is done
   in Expedited Forwarding PHB [RFC3246].  Such measurement procedures
   are collectively referred to as "traffic conditioners".  Traffic
   conditioners are normally built using token bucket meters, for
   example with a committed rate and a burst size, as in Section 1.5.3
   of DiffServ Model [RFC3290].  With multiple rate and burst size
   measurements added to the basic single rate single burst size token



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   bucket meter to achieve multiple levels of conformance used by
   Assured Forwarding PHB [RFC2597].  Multiple rates and burst sizes can
   be realized using multiple levels of token buckets or more complex
   token buckets, these are implementation details.  Some traffic
   conditioners that may be used in deployment of differentiated
   services are:
   o  For Class Selector (CS) PHBs, a single token bucket meter to
      provide a rate plus burst size control
   o  For Expedited Forwarding (EF) PHB, a single token bucket meter to
      provide a rate plus burst size control
   o  For Assured Forwarding (AF) PHBs, usually two token buckets meters
      configured to provide behavior as outlined in Two Rate Three Color
      Marker (trTCM) [RFC2698] or the Single Rate Three Color Marker
      (srTCM) [RFC2697].  The two rate three color marker is used to
      enforce two rates whereas, the single rate three color marker is
      used to enforce a committed rate with two burst lengths.

1.4.4  Differentiated Services Code Point (DSCP)

   The DSCP is a number in the range 0..63, that is placed into an IP
   packet to mark it according to the class of traffic it belongs in.
   Half of these values are earmarked for standardized services, and the
   other half of them are available for local definition.

1.4.5  Per-Hop Behavior (PHB)

   In the end, the mechanisms described above are combined to form a
   specified set of characteristics for handling different kinds of
   traffic, depending on the needs of the application.  This document
   seeks to identify useful traffic aggregates and specify what PHB
   should be applied to them.

1.5  Key Service Concepts

   While Differentiated Services is a general architecture that may be
   used to implement a variety of services, three fundamental forwarding
   behaviors have been defined and characterized for general use.  These
   are basic Default Forwarding (DF) behavior for elastic traffic, the
   Assured Forwarding (AF) behavior, and the Expedited Forwarding (EF)
   behavior for real-time (inelastic) traffic.  The facts that four code
   points are recommended for AF, and that one code point is recommended
   for EF, are arbitrary choices, and the architecture allows any
   reasonable number of AF and EF classes simultaneously.  The choice of
   four AF classes and one EF class in the current document is also
   arbitrary, and operators MAY choose to operate more or fewer of
   either.

   The terms "elastic" and "real-time" are defined in [RFC1633] Section



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   3.1, as a way of understanding broad brush application requirements.
   This document should be reviewed to obtain a broad understanding of
   the issues in quality of service, just as [RFC2475] should be
   reviewed to understand the data plane architecture used in today's
   Internet.

1.5.1  Default Forwarding (DF)

   The basic forwarding behavior applied to any class of traffic are
   those described in [RFC2474] and [RFC2309].  Best Effort service may
   be summarized as "I will accept your packets", and is typically
   configured with some bandwidth guarantee.  Packets in transit may be
   lost, reordered, duplicated, or delayed at random.  Generally,
   networks are engineered to limit this behavior, but changing traffic
   loads can push any network into such a state.

   Application traffic in the internet which uses default forwarding is
   expected to be "elastic" in nature.  By this, we mean that the sender
   of traffic will adjust its transmission rate in response to changes
   in available rate, loss, or delay.

   For the basic best effort service, a single DSCP value is provided to
   identify the traffic, a queue to store it, and active queue
   management to protect the network from it and to limit delays.

1.5.2  Assured Forwarding (AF)

   The Assured Forwarding PHB [RFC2597] behavior is explicitly modeled
   on Frame Relay's DE flag or ATM's CLP capability, and is intended for
   networks that offer average-rate SLAs (as FR and ATM networks do).
   This is an enhanced best effort service; traffic is expected to be
   "elastic" in nature.  The receiver will detect loss or variation in
   delay in the network and provide feedback such that the sender
   adjusts its transmission rate to approximate available capacity.

   For such behaviors, multiple DSCP values are provided (two or three,
   perhaps more using local values) to identify the traffic, a common
   queue to store the aggregate and active queue management to protect
   the network from it and to limit delays.  Traffic is metered as it
   enters the network, and traffic is variously marked depending on the
   arrival rate of the aggregate.  The premise is that it is normal for
   users to occasionally use more capacity than their contract
   stipulates, perhaps up to some bound.  However, if traffic SHOULD be
   lost or marked to manage the queue, this excess traffic will be
   marked or lost first.






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1.5.3  Expedited Forwarding (EF)

   Expedited Forwarding PHB [RFC3246] behavior was originally proposed
   as a way to implement a virtual wire, and can be used in such a
   manner.  It is an enhanced best effort service: traffic remains
   subject to loss due to line errors and reordering during routing
   changes.  However, using queuing techniques, the probability of delay
   or variation in delay is minimized.  For this reason, it is generally
   used to carry voice and for transport of data information that
   requires "wire like" behavior through the IP network.  Voice is an
   inelastic "real-time" application that sends packets at the rate the
   codec produces them, regardless of availability of capacity.  As
   such, this service has the potential to disrupt or congest a network
   if not controlled.  It also has the potential for abuse.

   To protect the network, at minimum one SHOULD police traffic at
   various points to ensure that the design of a queue is not over-run,
   and then the traffic SHOULD be given a low delay queue (often using
   priority, although it is asserted that a rate-based queue can do
   this) to ensure that variation in delay is not an issue, to meet
   application needs.

1.5.4  Class Selector (CS)

   Class Selector provides support for historical codepoint definitions
   and PHB requirement.  The Class Selector DS field provides a limited
   backward compatibility with legacy (pre DiffServ) practice, as
   described in [RFC2474] Section 4.  Backward compatibility is
   addressed in two ways.  First, there are per-hop behaviors that are
   already in widespread use (e.g. those satisfying the IPv4 Precedence
   queuing requirements specified in [RFC1812], and we wish to permit
   their continued use in DS-compliant networks.  In addition, there are
   some codepoints that correspond to historical use of the IP
   Precedence field and we reserve these codepoints to map to PHBs that
   meet the general requirements specified in [RFC2474] Section 4.2.2.2.

   No attempt is made to maintain backward compatibility with the "DTR"
   or TOS bits of the IPv4 TOS octet, as defined in [RFC0791]and
   [RFC1349].

   A DS-compliant network can be deployed with a set of one or more
   Class Selector compliant PHB groups.  As well, network administrator
   may configure the network nodes to map codepoints to PHBs
   irrespective of bits 3-5 of the DSCP field to yield a network that is
   compatible with historical IP Precedence use.  Thus, for example,
   codepoint '011000' would map to the same PHB as codepoint '011010'.





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1.5.5  Admission Control

   Admission control including refusal when policy thresholds are
   crossed, can assure high quality communication by ensuring the
   availability of bandwidth to carry a load.  Inelastic real-time flows
   like VoIP (telephony) or video conferencing services can benefit from
   use of admission control mechanism, as generally the telephony
   service is configured with over subscription, meaning that some
   user(s) may not be able to make a call during peak periods.

   For VoIP (telephony) service, a common approach is to use signaling
   protocols such as SIP, H.323, H.248, MEGACO, RSVP, etc. to negotiate
   admittance and use of network transport capabilities.  When a user
   has been authorized to send voice traffic, this admission procedure
   has verified that data rates will be within the capacity of the
   network that it will use.  Since RTP voice does not react to loss or
   delay in any substantive way, the network SHOULD police at ingress to
   ensure that the voice traffic stays within its negotiated bounds.
   Having thus assured a predictable input rate, the network may use a
   priority queue to ensure nominal delay and variation in delay.

   Another approach that may be used in small and bandwidth constrained
   networks for limited number of flows is RSVP [RFC2205] [RFC2996].
   However, there is concern with the scalability of this solution in
   large networks where aggregation of reservations[RFC3175] is
   considered to be required.

2.  Service Differentiation

   There are practical limits on the level of service differentiation
   that should be offered in the IP networks.  We believe we have
   defined a practical approach in delivering service differentiation by
   defining different service classes that networks may choose to
   support to provide the appropriate level of behaviors and performance
   needed by current and future applications and services.  The defined
   structure for providing services allows several applications having
   similar traffic characteristics and performance requirements to be
   grouped into the same service class.  This approach provides a lot of
   flexibility in providing the appropriate level of service
   differentiation for current and new yet unknown applications without
   introducing significant changes to routers or network configurations
   when a new traffic type is added to the network.

2.1  Service Classes

   Traffic flowing in a network can be classified in many different
   ways.  We have chosen to divide it into two groupings, network
   control and user/subscriber traffic.  To provide service



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   differentiation, different service classes are defined in each
   grouping.  The network control traffic group can further be divided
   into two service classes (see  Section 3 for detailed definition of
   each service class):
   o  "Network Control" for routing and network control function.
   o  "OAM" (Operations, Administration and Management) for network
      configuration and management functions.

   The user/subscriber traffic group is broken down into ten service
   classes to provide service differentiation for all the different
   types of applications/services, (see Section 4 for detailed
   definition of each service class) in summary:
   o  Telephony service class is best suited for applications that
      require very low delay variation and are of constant rate, such as
      IP telephony (VoIP) and circuit emulation over IP applications.
   o  Signaling service class is best suited for peer-to-peer and
      client-server signaling and control functions using protocols such
      as SIP, SIP-T, H.323, H.248, MGCP, etc.
   o  Multimedia Conferencing service class is best suited for
      applications that require very low delay, and have the ability to
      change encoding rate (rate adaptive), such as H.323/V2 and later
      video conferencing service.
   o  Real-time Interactive service class is intended for interactive
      variable rate inelastic applications that require low jitter, loss
      and very low delay, such as interactive gaming applications that
      use RTP/UDP streams for game control commands, video conferencing
      applications that do not have the ability to change encoding rates
      or mark packets with different importance indications, etc.
   o  Multimedia Streaming service class is best suited for variable
      rate elastic streaming media applications where a human is waiting
      for output and where the application has the capability to react
      to packet loss by reducing its transmission rate, such as
      streaming video and audio, web cast, etc.
   o  Broadcast Video service class is best suited for inelastic
      streaming media applications that may be of constant or variable
      rate, requiring low jitter and very low packet loss, such as
      broadcast TV and live events, video surveillance and security.
   o  Low Latency Data service class is best suited for data processing
      applications where a human is waiting for output, such as web-
      based ordering, Enterprise Resource Planning (ERP) application,
      etc.
   o  High Throughput Data service class is best suited for store and
      forward applications such as FTP, billing record transfer, etc.
   o  Standard service class is for traffic that has not been identified
      as requiring differentiated treatment and is normally referred as
      best effort.





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   o  Low Priority Data service class is intended for packet flows where
      bandwidth assurance is not required.

2.2  Categorization of User Service Classes

   The ten defined user/subscriber services classes listed above can be
   grouped into a small number of application categories.  For some
   application categories, it was felt that more than one service class
   was needed to provide service differentiation within that category
   due to the different traffic characteristic of the applications,
   control function and the required flow behavior.  Figure 1 provides
   summary of service class grouping into four application categories.

   Application Control category:
   o  The Signaling service class is intended to be used to control
      applications or user endpoints.  Examples of protocols that would
      use this service class are, SIP or H.248 for IP telephone service
      and SIP or IGMP for control of broadcast TV service to
      subscribers.  Although user signaling flows have similar
      performance requirements as Low Latency Data they need to be
      distinguished and marked with a different DSCP.  The essential
      distinction is something like "administrative control and
      management" of the traffic affected as the protocols in this class
      tend to be tied to the media stream/session they signal and
      control.

   Media-Oriented category: Due to the vest number of new (in process of
   being deployed) and already in uses media-oriented services in IP
   networks, five service classes have been defined.
   o  Telephony service class is intended for IP telephony (VoIP)
      service as well it may be used for other applications that meet
      the defined traffic characteristics and performance requirements.
   o  Real-time Interactive service class is intended for inelastic
      video flows from such application like SIP based desktop video
      conferencing applications and for interactive gaming.
   o  Multimedia Conferencing service class is for video conferencing
      solutions that have the ability to reduce their transmission rate
      on detection of congestion, therefore these flows can be
      classified as rate adaptive.  As currently there are both types of
      video conferencing equipment used in IP networks, ones that
      generate inelastic and ones that generate rate adaptive traffic,
      therefore two service class are needed.  Real-time Interactive
      service class should be used for equipment that generate inelastic
      video flows and Multimedia Conferencing service class for
      equipment that generate rate adaptive video flows.
   o  Broadcast Video service class is to be used for inelastic traffic
      flows which is intended for broadcast TV service and for transport
      of live video and audio events.



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   o  Multimedia Streaming service class is to be used for elastic
      multimedia traffic flows.  This multimedia content is typically
      stored before being transmitted, as well it is buffered at the
      receiving end before being played out.  The buffering is
      sufficient large to accommodate any variation in transmission rate
      that is encountered in the network.  Multimedia entertainment over
      IP delivery services that are being developed can generate both
      elastic and/or inelastic traffic flows, therefore two service
      classes are defined to address this space.

   Data category: The data category is divided into three service
   classes.
   o  Low Latency Data for applications/services that require low delay
      or latency for bursty but short lived flows.
   o  High Throughput Data for applications/services that require good
      throughput for long lived bursty flows.  High Throughput and
      Multimedia Steaming are close in their traffic flow
      characteristics with High Throughput being a bit more bursty and
      not as long lived as Multimedia Steaming.
   o  Low Priority Data for applications or services that can tolerate
      short or long interruptions of packet flows.  Low Priority Data
      service class can be viewed as don't care to some degree.

   Best Effort category:
   o  All traffic that is not differentiated in the network falls into
      this category and is mapped into the Standard service class.  If a
      packet is marked with a DSCP value that is not supported in the
      network, it SHOULD be forwarded using the Standard service class.

   Figure 1 below provides a grouping of the defined user/subscriber
   service classes into four categories with indications of which ones
   use an independent flow for signaling or control, type of flow
   behavior elastic, rate adaptive or inelastic and finally the last
   column provides end user QoS rating as defined in ITU-T
   Recommendation G.1010.
















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    -----------------------------------------------------------------
   | Application |    Service    | Signaled |  Flow     |   G.1010   |
   |  Categories |     Class     |          | Behavior  |   Rating   |
   |-------------+---------------+----------+-----------+------------|
   | Application |   Signaling   |   N.A.   | Inelastic | Responsive |
   |   Control   |               |          |           |            |
   |-------------+---------------+----------+-----------+------------|
   |             |   Telephony   |   Yes    | Inelastic | Interactive|
   |             |---------------+----------+-----------+------------|
   |             |   Real-time   |   Yes    | Inelastic | Interactive|
   |             |  Interactive  |          |           |            |
   |             |---------------+----------+-----------+------------|
   |    Media-   |   Multimedia  |   Yes    |    Rate   | Interactive|
   |   Oriented  |  Conferencing |          |  Adaptive |            |
   |             |---------------+----------+-----------+------------|
   |             |Broadcast Video|   Yes    | Inelastic | Responsive |
   |             |---------------+----------+-----------+------------|
   |             |  Multimedia   |   Yes    |  Elastic  |   Timely   |
   |             |   Streaming   |          |           |            |
   |-------------+---------------+----------+-----------+------------|
   |             |  Low Latency  |    No    |  Elastic  | Responsive |
   |             |     Data      |          |           |            |
   |             |---------------+----------+-----------+------------|
   |   Data      |High Throughput|    No    |  Elastic  |   Timely   |
   |             |    Data       |          |           |            |
   |             |---------------+----------+-----------+------------|
   |             | Low Priority  |    No    |  Elastic  |Non-critical|
   |             |    Data       |          |           |            |
   |-------------+---------------+----------+-----------+------------|
   | Best Effort |   Standard    |    Not Specified     |Non-critical|
    -----------------------------------------------------------------
   Note: N.A. = Not Applicable.

            Figure 1: User/Subscriber Service Classes Grouping

   Here is a short explanation of end user QoS category as defined in
   ITU-T Recommendation G.1010.  User traffic is divided into four
   different categories, namely, interactive, responsive, timely, and
   non-critical.  An example of interactive traffic is between two
   humans and is most sensitive to delay, loss and jitter.  Another
   example of interactive traffic is between two servers where very low
   delay and loss is needed.  Responsive traffic is typically between a
   human and a server but also can be between two servers.  Responsive
   traffic is less affected by jitter and can tolerate longer delays
   than interactive traffic.  Timely traffic is either between servers
   or servers and humans and the delay tolerance is significantly longer
   than responsive traffic.  Non-critical traffic is normally between
   servers/machines where delivery may be delay for period of time.



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2.3  Service Class Characteristics

   This draft provides guidelines for network administrator in
   configuring their network for the level of service differentiation
   that is appropriate in their network to meet their QoS needs.  It is
   expected that network operators will configure and provide in their
   networks a subset of the defined service classes.  Our intent is to
   provide guidelines for configuration of Differentiated Services for a
   wide variety of applications, services and network configurations.
   Additionally, network administrators may choose to define and deploy
   in their network other service classes.

   Figure 2 provides a behavior view for traffic serviced by each
   service class.  The traffic characteristics column defines the
   characteristics and profile of flows serviced and the tolerance to
   loss, delay and jitter columns define the treatment the flows will
   receive.  End-to-end quantitative performance requirements may be
   obtained from ITU-T Recommendation Y.1541 and Y.1540.  There is also
   new work currently underway in ITU-T that applies to the service
   classes defined in this document.































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    -------------------------------------------------------------------
   |Service Class  |                              |    Tolerance to    |
   |    Name       |  Traffic Characteristics     | Loss |Delay |Jitter|
   |===============+==============================+======+======+======|
   |   Network     |Variable size packets, mostly |      |      |      |
   |   Control     |inelastic short messages, but |  Low |  Low | Yes  |
   |               | traffic can also burst (BGP) |      |      |      |
   |---------------+------------------------------+------+------+------|
   |               | Fixed size small packets,    | Very | Very | Very |
   |  Telephony    | constant emission rate,      |  Low |  Low |  Low |
   |               | inelastic and low rate flows |      |      |      |
   |---------------+------------------------------+------+------+------|
   |   Signaling   | Variable size packets, some  | Low  | Low  |  Yes |
   |               | what bursty short lived flows|      |      |      |
   |---------------+------------------------------+------+------+------|
   |  Multimedia   | Variable size packets,       | Low  | Very |      |
   | Conferencing  | constant transmit interval,  |  -   | Low  | Low  |
   |               |rate adaptive, reacts to loss |Medium|      |      |
   |---------------+------------------------------+------+------+------|
   |   Real-time   | RTP/UDP streams, inelastic,  | Low  | Very | Low  |
   |  Interactive  | mostly variable rate         |      | Low  |      |
   |---------------+------------------------------+------+------+------|
   |  Multimedia   |  Variable size packets,      |Low - |Medium|  Yes |
   |   Streaming   | elastic with variable rate   |Medium|      |      |
   |---------------+------------------------------+------+------+------|
   |   Broadcast   | Constant and variable rate,  | Very |Medium|  Low |
   |     Video     | inelastic, non bursty flows  |  Low |      |      |
   |---------------+------------------------------+------+------+------|
   |  Low Latency  | Variable rate, bursty short  | Low  |Low - |  Yes |
   |      Data     |  lived elastic flows         |      |Medium|      |
   |---------------+------------------------------+------+------+------|
   |      OAM      |  Variable size packets,      | Low  |Medium|  Yes |
   |               |  elastic & inelastic flows   |      |      |      |
   |---------------+------------------------------+------+------+------|
   |High Throughput| Variable rate, bursty long   | Low  |Medium|  Yes |
   |      Data     |   lived elastic flows        |      |- High|      |
   |---------------+------------------------------+------+------+------|
   |   Standard    | A bit of everything          |  Not Specified     |
   |---------------+------------------------------+------+------+------|
   | Low Priority  | Non real-time and elastic    | High | High | Yes  |
   |      Data     |                              |      |      |      |
    -------------------------------------------------------------------

                  Figure 2: Service Class Characteristics

   Note: A "Yes" in the jitter-tolerant column implies that data is
   buffered in the endpoint, and a moderate level of network-induced
   variation in delay will not affect the application.  Applications



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   that use TCP as a transport are generally good examples.  Routing
   protocols and peer-to-peer signaling also fall in this class; while
   loss can create problems in setting up calls, a moderate level of
   jitter merely makes call placement a little less predictable in
   duration.

   Service classes indicate the required traffic forwarding treatment in
   order to meet user, application or network expectations.  Section 3in
   this document defines the service classes that MAY be used for
   forwarding network control traffic and Section 4 defines the service
   classes that MAY be used for forwarding user traffic with examples of
   intended application types mapped into each service class.  Note that
   the application types are only examples and are not meant to be all-
   inclusive or prescriptive.  Also it should be noted that the service
   class naming or ordering does not imply any priority ordering.  They
   are simply reference names that are used in this document with
   associated QoS behaviors that are optimized for the particular
   application types they support.  Network administrators MAY choose to
   assign different service class names, to the service classes that
   they will support.  Figure 3 defines the RECOMMENDED relationship
   between service classes and DS codepoint(s) assignment with
   application examples.  It is RECOMMENDED that this relationship be
   preserved end to end.




























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    ------------------------------------------------------------------
   |   Service     |  DSCP   |    DSCP     |       Application        |
   |  Class name   |  name   |    value    |        Examples          |
   |===============+=========+=============+==========================|
   |Network Control|  CS6    |   110000    | Network routing          |
   |---------------+---------+-------------+--------------------------|
   | Telephony     |   EF    |   101110    | IP Telephony bearer      |
   |---------------+---------+-------------+--------------------------|
   |  Signaling    |  CS5    |   101000    | IP Telephony signaling   |
   |---------------+---------+-------------+--------------------------|
   | Multimedia    |AF41,AF42|100010,100100|   H.323/V2 video         |
   | Conferencing  |  AF43   |   100110    |  conferencing (adaptive) |
   |---------------+---------+-------------+--------------------------|
   |  Real-time    |  CS4    |   100000    | Video conferencing and   |
   |  Interactive  |         |             | Interactive gaming       |
   |---------------+---------+-------------+--------------------------|
   | Multimedia    |AF31,AF32|011010,011100| Streaming video and      |
   | Streaming     |  AF33   |   011110    |   audio on demand        |
   |---------------+---------+-------------+--------------------------|
   |Broadcast Video|  CS3    |   011000    |Broadcast TV & live events|
   |---------------+---------+-------------+--------------------------|
   | Low Latency   |AF21,AF22|010010,010100|Client/server transactions|
   |   Data        |  AF23   |   010110    | Web-based ordering       |
   |---------------+---------+-------------+--------------------------|
   |     OAM       |  CS2    |   010000    |         OAM&P            |
   |---------------+---------+-------------+--------------------------|
   |High Throughput|AF11,AF12|001010,001100|  Store and forward       |
   |    Data       |  AF13   |   001110    |     applications         |
   |---------------+---------+-------------+--------------------------|
   |    Standard   | DF,(CS0)|   000000    | Undifferentiated         |
   |               |         |             | applications             |
   |---------------+---------+-------------+--------------------------|
   | Low Priority  |  CS1    |   001000    | Any flow that has no BW  |
   |     Data      |         |             | assurance                |
    ------------------------------------------------------------------

                  Figure 3: DSCP to Service Class Mapping

   Note for Figure 3:
   o  Default Forwarding (DF) and Class Selector 0 (CS0) provide
      equivalent behavior and use the same DS codepoint '000000'.

   It is expected that network administrators will choose the service
   classes that they will support based on their need, starting off with
   three or four service classes for user traffic and add others as the
   need arises.

   Figure 4 provides a summary of DiffServ QoS mechanisms that SHOULD be



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   used for the defined service classes that are further detailed in
   Section 3 and Section 4 of this document.  Based on what
   applications/services that need to be differentiated, network
   administrators can choose the service class(es) that need to be
   supported in their network.
    ------------------------------------------------------------------
   |  Service      | DSCP | Conditioning at   |   PHB   | Queuing| AQM|
   |   Class       |      |    DS Edge        |  Used   |        |    |
   |===============+======+===================+=========+========+====|
   |Network Control| CS6  | See Section 3.1   | RFC2474 |  Rate  |Yes |
   |---------------+------+-------------------+---------+--------+----|
   |   Telephony   |  EF  |Police using sr+bs | RFC3246 |Priority| No |
   |---------------+------+-------------------+---------+--------+----|
   |   Signaling   | CS5  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+------+-------------------+---------+--------+----|
   |   Multimedia  | AF41 |  Using two rate   |         |        | Yes|
   | Conferencing  | AF42 |three color marker | RFC2597 |  Rate  | per|
   |               | AF43 | (such as RFC2698) |         |        |DSCP|
   |---------------+------+-------------------+---------+--------+----|
   |   Real-time   | CS4  |Police using sr+bs | RFC2474 |  Rate  | No |
   |   Interactive |      |                   |         |        |    |
   |---------------+------+-------------------+---------|--------+----|
   |  Multimedia   | AF31 |  Using two rate   |         |        | Yes|
   |  Streaming    | AF32 |three color marker | RFC2597 |  Rate  | per|
   |               | AF33 | (such as RFC2698) |         |        |DSCP|
   |---------------+------+-------------------+---------+--------+----|
   |Broadcast Video| CS3  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+------+-------------------+---------+--------+----|
   |    Low        | AF21 | Using single rate |         |        | Yes|
   |    Latency    | AF22 |three color marker | RFC2597 |  Rate  | per|
   |    Data       | AF23 | (such as RFC2697) |         |        |DSCP|
   |---------------+------+-------------------+---------+--------+----|
   |     OAM       | CS2  |Police using sr+bs | RFC2474 |  Rate  | Yes|
   |---------------+------+-------------------+---------+--------+----|
   |    High       | AF11 |  Using two rate   |         |        | Yes|
   |  Throughput   | AF12 |three color marker | RFC2597 |  Rate  | per|
   |    Data       | AF13 | (such as RFC2698) |         |        |DSCP|
   |---------------+------+-------------------+---------+--------+----|
   |   Standard    | DF   | Not applicable    | RFC2474 |  Rate  | Yes|
   |---------------+------+-------------------+---------+--------+----|
   | Low Priority  | CS1  | Not applicable    | RFC3662 |  Rate  | Yes|
   |     Data      |      |                   |         |        |    |
    ------------------------------------------------------------------

      Figure 4: Summary of QoS Mechanisms used for each Service Class

   Notes for Figure 4:




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   o  Conditioning at DS edge, means that traffic conditioning is
      performed at the edge of the DiffServ network where untrusted user
      devices are connected or between two DiffServ networks.
   o  "sr+bs" represents a policing mechanism that provides single rate
      with burst size control.
   o  The single rate three color marker (srTCM) behavior SHOULD be
      equivalent to RFC 2697 and the two rate three color marker (trTCM)
      behavior SHOULD be equivalent to RFC 2698.
   o  The PHB for Real-time Interactive service class SHOULD be
      configured to provide high bandwidth assurance.  It MAY be
      configured as a second EF PHB that uses relaxed performance
      parameters and a rate scheduler.
   o  The PHB for Broadcast Video service class SHOULD be configured to
      provide high bandwidth assurance.  It MAY be configured as a third
      EF PHB that uses relaxed performance parameters and a rate
      scheduler.
   o  In network segments that use IP precedence marking, only one of
      the two service classes can be supported, High Throughput Data or
      Low Priority Data.  We RECOMMEND that the DSCP value(s) of the
      unsupported service class to be changed to 000xx1 on ingress and
      changed back to original value(s) on egress of the network segment
      that uses precedence marking.  For example, if Low Priority Data
      is mapped to Standard service class, then 000001 DSCP marking MAY
      be used to distinguish it from Standard marked packets on egress.

2.4  Deployment Scenarios

   It is expected that network administrators will choose the service
   classes that they will support based on their need, starting off with
   three or four service classes for user traffic and add more service
   classes as the need arises.  In this section we provide three
   examples of possible deployment scenarios.

2.4.1  Example 1

   A network administrator determined that they need to provide
   different performance levels (quality of service) in their network
   for the services that they will be offering to their customers.  They
   need to enable their network to provide:
   o  Reliable VoIP (telephony) service, equivalent to PSTN
   o  A low delay assured bandwidth data service
   o  As well, support current Internet services

   For this example, the network administrator's needs are addressed
   with the deployment of the following six service classes:
   o  Network Control service class for routing and control traffic that
      is needed for reliable operation of the provider's network




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   o  Standard service class for all traffic that will receive normal
      (undifferentiated) forwarding treatment through their network for
      support of current Internet service
   o  Telephony service class for VoIP (telephony) bearer traffic
   o  Signaling service class for Telephony signaling to control the
      VoIP service
   o  Low Latency Data service class for the low delay assured bandwidth
      differentiated data service
   o  OAM service class for operation and management of the network

   Figure 5, provides a summary of the mechanisms need for delivery of
   service differentiation for Example 1.
    -------------------------------------------------------------------
   |  Service      |  DSCP | Conditioning at   |   PHB   |        |    |
   |   Class       |       |    DS Edge        |  Used   | Queuing| AQM|
   |===============+=======+===================+=========+========+====|
   |Network Control|  CS6  | See Section 3.1   | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |  Telephony    |   EF  |Police using sr+bs | RFC3246 |Priority| No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Signaling    |  CS5  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+-------+-------------------+---------+--------+----|
   |    Low        | AF21  | Using single rate |         |        |Yes |
   |   Latency     | AF22  |three color marker | RFC2597 |  Rate  |Per |
   |    Data       | AF23  | (such as RFC2697) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |      OAM      |  CS2  |Police using sr+bs | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |   Standard    |DF(CS0)| Not applicable    | RFC2474 |  Rate  | Yes|
   |               | +other|                   |         |        |    |
    -------------------------------------------------------------------

        Figure 5: Service Provider Network Configuration Example 1

   Notes for Figure 5:
   o  "sr+bs" represents a policing mechanism that provides single rate
      with burst size control.
   o  The single rate three color marker (srTCM) behavior SHOULD be
      equivalent to RFC 2697.
   o  Any packet that is marked with DSCP value that is not represented
      by the supported service classes, SHOULD be forwarded using the
      Standard service class.


2.4.2  Example 2

   With this example we show how network operators with Example 1
   capabilities can evolve their service offering to provide three new



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   additional services to their customers.  The new additional service
   capabilities that are to be added are:
   o  SIP based desktop video conference capability to complement VoIP
      (telephony) service
   o  Provide TV and on demand movie viewing service to residential
      subscribers
   o  Provide network based data storage and file backup service to
      business customers

   The new additional services that the network administrator would like
   to offer are addressed with the deployment of the following four
   additional service classes.  (These are additions to the six service
   classes already defined in Example 1):
   o  Real-time Interactive service class for transport of MPEG-4 real-
      time video flows to support desktop video conferencing.  The
      control/signaling for video conferencing is done using the
      Signaling service class.
   o  Broadcast Video service class for transport of IPTV broadcast
      information.  The channel selection and control is via IGMP
      (Internet Group Management Protocol) mapped into the Signaling
      service class.
   o  Multimedia Streaming service class for transport of stored MPEG-2
      or MPEG-4 content.  The selection and control of streaming
      information is done using the Signaling service class.  The
      selection of Multimedia Streaming service class for on demand
      movie service was chosen as the set-top box used for this service
      has local buffering capability to compensate for the bandwidth
      variability of the elastic streaming information.  Note, if
      transport of on demand movie service is inelastic, then the
      Broadcast Video service class SHOULD be used.
   o  High Throughput Data service class is for transport of bulk data
      for network based storage and file backup service to business
      customers.

   Figure 6, provides a summary of the mechanisms needed for delivery of
   service differentiation for all the service classes used in Example
   2.














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    -------------------------------------------------------------------
   |  Service      |  DSCP | Conditioning at   |   PHB   |        |    |
   |   Class       |       |    DS Edge        |  Used   | Queuing| AQM|
   |===============+=======+===================+=========+========+====|
   |Network Control|  CS6  | See Section 3.1   | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |  Telephony    |   EF  |Police using sr+bs | RFC3246 |Priority| No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Signaling    |  CS5  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Real-time    |  CS4  |Police using sr+bs | RFC2474 |  Rate  | No |
   |  Interactive  |       |                   |         |        |    |
   |---------------+-------+-------------------+---------+--------+----|
   |Broadcast Video|  CS3  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Multimedia   | AF31  |  Using two rate   |         |        |Yes |
   |  Streaming    | AF32  |three color marker | RFC2597 |  Rate  |Per |
   |               | AF33  | (such as RFC2698) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |    Low        | AF21  | Using single rate |         |        |Yes |
   |   Latency     | AF22  |three color marker | RFC2597 |  Rate  |Per |
   |    Data       | AF23  | (such as RFC2697) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |      OAM      |  CS2  |Police using sr+bs | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |    High       | AF11  |  Using two rate   |         |        |Yes |
   |  Throughput   | AF12  |three color marker | RFC2597 |  Rate  |Per |
   |    Data       | AF13  | (such as RFC2698) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |   Standard    |DF(CS0)| Not applicable    | RFC2474 |  Rate  | Yes|
   |               | +other|                   |         |        |    |
    -------------------------------------------------------------------

        Figure 6: Service Provider Network Configuration Example 2

   Notes for Figure 6:
   o  "sr+bs" represents a policing mechanism that provides single rate
      with burst size control.
   o  The single rate three color marker (srTCM) behavior SHOULD be
      equivalent to RFC 2697 and the two rate three color marker (trTCM)
      behavior SHOULD be equivalent to RFC 2698.
   o  Any packet that is marked with DSCP value that is not represented
      by the supported service classes, SHOULD be forwarded using the
      Standard service class.







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2.4.3  Example 3

   An enterprise network administrator determined that they need to
   provide different performance levels (quality of service) in their
   network for the new services that are being offered to corporate
   users.  The enterprise network needs to:
   o  Provide reliable corporate VoIP service
   o  Provide video conferencing service to selected Conference Rooms
   o  Support on demand distribution of prerecorded audio and video
      information to large number of users
   o  Provide a priority data transfer capability for engineering teams
      to share design information
   o  Reduce or deny bandwidth during peak traffic periods for selected
      applications
   o  Continue to provide normal IP service to all remaining
      applications and services

   For this example, the enterprise's network needs are addressed with
   the deployment of the following nine service classes:
   o  Network Control service class for routing and control traffic that
      is needed for reliable operation of the enterprise network
   o  OAM service class for operation and management of the network
   o  Standard service class for all traffic that will receive normal
      (undifferentiated) forwarding treatment
   o  Telephony service class for VoIP (telephony) bearer traffic
   o  Signaling service class for Telephony signaling to control the
      VoIP service
   o  Multimedia Conferencing service class for support of inter
      Conference Room video conferencing service using H.323/V2 or
      similar equipment.
   o  Multimedia Steaming service class for transfer of prerecorded
      audio and video information
   o  High Throughput Data service class to provide bandwidth assurance
      for timely transfer of large engineering files
   o  Low Priority Data service class for selected background
      applications where data transfer can be delayed or suspended for a
      period of time during peak network load conditions

   Figure 7, provides a summary of the mechanisms need for delivery of
   service differentiation for Example 3.











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    -------------------------------------------------------------------
   |  Service      |  DSCP | Conditioning at   |   PHB   |        |    |
   |   Class       |       |    DS Edge        |  Used   | Queuing| AQM|
   |===============+=======+===================+=========+========+====|
   |Network Control|  CS6  | See Section 3.2   | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |  Telephony    |   EF  |Police using sr+bs | RFC3246 |Priority| No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Signaling    |  CS5  |Police using sr+bs | RFC2474 |  Rate  | No |
   |---------------+-------+-------------------+---------+--------+----|
   |  Multimedia   | AF41  |  Using two rate   |         |        | Yes|
   | Conferencing  | AF42  | three color marker| RFC2597 |  Rate  | Per|
   |               | AF43  | (such as RFC2698) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |  Multimedia   | AF31  |  Using two rate   |         |        | Yes|
   |   Streaming   | AF32  | three color marker| RFC2597 |  Rate  | Per|
   |               | AF33  | (such as RFC2698) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   |      OAM      |  CS2  |Police using sr+bs | RFC2474 |  Rate  | Yes|
   |---------------+-------+-------------------+---------+--------+----|
   |    High       | AF11  |  Using two rate   |         |        |Yes |
   |   Throughput  | AF12  |three color marker | RFC2597 |  Rate  |Per |
   |    Data       | AF13  | (such as RFC2698) |         |        |DSCP|
   |---------------+-------+-------------------+---------+--------+----|
   | Low Priority  |  CS1  | Not applicable    | RFC3662 |  Rate  | Yes|
   |     Data      |       |                   |         |        |    |
   |---------------+-------+-------------------+---------+--------+----|
   |   Standard    |DF(CS0)| Not applicable    | RFC2474 |  Rate  | Yes|
   |               | +other|                   |         |        |    |
    -------------------------------------------------------------------

            Figure 7: Enterprise Network Configuration Example

   Notes for Figure 7:
   o  The Administrative service class MAY be implemented using Rate
      queuing method as long as sufficient amount of bandwidth is
      guaranteed and latency of scheduler is sufficiently low to meet
      the requirement.
   o  "sr+bs" represents a policing mechanism that provides single rate
      with burst size control.
   o  The single rate three color marker (srTCM) behavior SHOULD be
      equivalent to RFC 2697 and the two rate three color marker (trTCM)
      behavior SHOULD be equivalent to RFC 2698.
   o  Any packet that is marked with DSCP value that is not represented
      by the supported service classes, SHOULD be forwarded using the
      Standard service class.





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3.  Network Control Traffic

   Network control traffic is defined as packet flows that are essential
   for stable operation of the administered network as well for
   information that may be exchanged between neighboring networks across
   a peering point where SLAs are in place.  Network control traffic is
   different from user application control (signaling) that may be
   generated by some applications or services.  Network control traffic
   is mostly between routers and network nodes that are used for
   operating, administering, controlling or managing the network
   segments.  Network Control Traffic may be split into two service
   classes, i.e.  Network Control and OAM.

3.1  Current Practice in The Internet

   Based on today's routing protocols and network control procedures
   that are used in The Internet, we have determined that CS6 DSCP value
   SHOULD be used for routing and control and that CS7 DSCP value be
   reserved for future use, potentially for future routing and/or
   control protocols.  Network administrator MAY use a Local/
   Experimental DSCP therefore a locally defined service class within
   their network to further differentiate their routing and control
   traffic.

   RECOMMENDED Network Edge Conditioning for CS7 DSCP marked packets:
   o  Drop or remark CS7 marked packets at ingress to DiffServ network
      domain.
   o  CS7 marked packets SHOULD NOT be sent across peering points.
      Exchange of control information across peering points SHOULD be
      done using CS6 DSCP, using Network Control service class.

3.2  Network Control Service Class

   The Network Control service class is used for transmitting packets
   between network devices (routers) that require control (routing)
   information to be exchanged between nodes within the administrative
   domain as well across a peering point between different
   administrative domains.  Traffic transmitted in this service class is
   very important as it keeps the network operational and needs to be
   forwarded in a timely manner.

   The Network Control service class SHOULD be configured using the
   DiffServ Class Selector (CS) PHB defined in [RFC2474].  This service
   class SHOULD be configured so that the traffic receives a minimum
   bandwidth guarantee, to ensure that the packets always receive timely
   service.  The configured forwarding resources for Network Control
   service class SHOULD be such that the probability of packet drop
   under peak load is very low in this service class.  The Network



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   Control service class SHOULD be configured to use a Rate Queuing
   system such as defined in Section 1.4.1.2 of this document.

   Examples of protocols and application that SHOULD use the Network
   Control service class:
   o  Routing packet flows: OSPF, BGP, ISIS, RIP
   o  Control information exchange within and between different
      administrative domains across a peering point where SLAs are in
      place
   o  LSP setup using CR-LDP and RSVP-TE

   The following protocols and applications SHOULD NOT use the Network
   Control service class:
   o  User traffic

   Traffic characteristics of packet flows in the Network Control
   service class:
   o  Mostly messages sent between routers and network servers
   o  Ranging from 50 to 1,500 byte packet sizes, normally one packet at
      a time but traffic can also burst (BGP)
   o  User traffic is not allowed to use this service class.  By user
      traffic we mean packet flows that originate from user controlled
      end points that are connected to the network.

   RECOMMENDED DSCP marking is CS6 (Class Selector 6)

   RECOMMENDED Network Edge Conditioning:
   o  At peering points (between two DiffServ networks) where SLAs are
      in place, CS6 marked packets SHOULD be policed, e.g. using a
      single rate with burst size (sr+bs) token bucket policer to keep
      the CS6 marked packet flows to within the traffic rate specified
      in the SLA.
   o  CS6 marked packet flows from untrusted sources (for example, end
      user devices) SHOULD be dropped or remarked at ingress to DiffServ
      network.
   o  Packets from users/subscribers are not permitted access to the
      Network Control service classes.

   The fundamental service offered to the Network Control service class
   is enhanced best effort service with high bandwidth assurance.  Since
   this service class is used to forward both elastic and inelastic
   flows, the service SHOULD be engineered so the Active Queue
   Management (AQM) [RFC2309] is applied to CS6 marked packets.

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth, and the max-threshold specifies the
   queue depth above which all traffic is dropped or ECN marked.  Thus,
   in this service class, the following inequality should hold in queue



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   configurations:
   o  min-threshold CS6 < max-threshold CS6
   o  max-threshold CS6 <= memory assigned to the queue
   Note: Many other AQM algorithms exist and are used; they should be
   configured to achieve a similar result.

3.3  OAM Service Class

   The OAM (Operations, Administration and Management) service class is
   RECOMMENDED for OAM&P (Operations, Administration and Management and
   Provisioning) using protocols such as SNMP, TFTP, FTP, Telnet, COPS,
   etc.  Applications using this service class require a low packet loss
   but are relatively not sensitive to delay.  This service class is
   configured to provide good packet delivery for intermittent flows.

   The OAM service class SHOULD use the Class Selector (CS) PHB defined
   in [RFC2474].  This service class SHOULD be configured to provide a
   minimum bandwidth assurance for CS2 marked packets to ensure that
   they get forwarded.  The OAM service class SHOULD be configured to
   use a Rate Queuing system such as defined in Section 1.4.1.2 of this
   document.

   The following applications SHOULD use the OAM service class:
   o  For provisioning and configuration of network elements
   o  For performance monitoring of network elements
   o  For any network operational alarms

   Traffic characteristics:
   o  Variable size packets (50 to 1500 bytes in size)
   o  Intermittent traffic flows
   o  Traffic may burst at times
   o  Both elastic and inelastic flows
   o  Traffic not sensitive to delays

   RECOMMENDED DSCP marking:
   o  All flows in this service class are marked with CS2 (Class
      Selector 2)

   Applications or IP end points SHOULD pre-mark their packets with CS2
   DSCP value.  If the end point is not capable of setting the DSCP
   value, then the router topologically closest to the end point SHOULD
   perform Multifield (MF) Classification as defined in [RFC2475].

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  Packet flow marking (DSCP setting) from untrusted sources (end
      user devices) SHOULD be verified at ingress to DiffServ network
      using Multifield (MF) Classification methods defined in [RFC2475].




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   o  Packet flows from untrusted sources (end user devices) SHOULD be
      policed at ingress to DiffServ network, e.g. using single rate
      with burst size token bucket policer to ensure that the traffic
      stays within its negotiated or engineered bounds.
   o  Packet flows from trusted sources (routers inside administered
      network) MAY not require policing.
   o  Normally OAM&P CS2 marked packet flows are not allowed to flow
      across peering points, if that is the case, then CS2 marked
      packets SHOULD be policed (dropped) at both egress and ingress
      peering interfaces.

   The fundamental service offered to "OAM" traffic is enhanced best
   effort service with controlled rate.  The service SHOULD be
   engineered so that CS2 marked packet flows have sufficient bandwidth
   in the network to provide high assurance of delivery.  Since this
   service class is used to forward both elastic and inelastic flows,
   the service SHOULD be engineered so that Active Queue Management
   [RFC2309] is applied to CS2 marked packets.

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth for each DSCP, and the max-threshold
   specifies the queue depth above which all traffic with such a DSCP is
   dropped or ECN marked.  Thus, in this service class, the following
   inequality should hold in queue configurations:
   o  min-threshold CS2 < max-threshold CS2
   o  max-threshold CS2 <= memory assigned to the queue
   Note: Many other AQM algorithms exist and are used; they should be
   configured to achieve a similar result.

4.  User Traffic

   User traffic is defined as packet flows between different users or
   subscribers.  It is the traffic that is sent to or from end-terminals
   and that support very wide variety of applications and services.
   User traffic can be differentiated in many different ways, therefore
   we investigated several different approaches to classify user
   traffic.  We looked at differentiating user traffic as real-time
   versus non real-time, elastic or rate adaptive versus inelastic,
   sensitive versus insensitive to loss as well traffic categorization
   as interactive, responsive, timely and non-critical as defined in
   ITU-T Recommendation G.1010.  At the end, we added up using all of
   the above for service differentiation, mapping of applications that
   have the matching traffic characteristics that fit the traffic
   profile and performance requirements of the defined service classes.

   Network administrators can categorize their applications based on the
   type of behavior that they require and MAY choose to support all or
   subset of the defined service classes.  Figure 3 provides some common



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   applications and the forwarding service class that best supports them
   based on their performance requirements.

4.1  Telephony Service Class

   The Telephony service class is RECOMMENDED for applications that
   require real-time, very low delay, very low jitter and very low
   packet loss for relatively constant-rate traffic sources (inelastic
   traffic sources).  This service class SHOULD be used for IP telephony
   service.

   The fundamental service offered to traffic in the Telephony service
   class is minimum jitter, delay and packet loss service up to a
   specified upper bound.  Operation is in some respect similar to an
   ATM CBR service, which has guaranteed bandwidth and which, if it
   stays within the negotiated rate, experiences nominal delay and no
   loss.  The EF PHB has a similar guarantee.

   Typical configurations negotiate the setup of telephone calls over IP
   using protocols such as H.248, MEGACO, H.323, or SIP.  When a user
   has been authorized to send telephony traffic, the call admission
   procedure should have verified that the newly admitted flow will be
   within the capacity of the Telephony service class forwarding
   capability in the network.  For VoIP (telephony) service, call
   admission control is usually performed by a telephony call server/
   gatekeeper using signaling (SIP, H.323, H.248, MEGACO, etc.) on
   access points to the network.  The bandwidth in the core network and
   the number of simultaneous VoIP sessions that can be supported needs
   to be engineered and controlled so that there is no congestion for
   this service.  Since RTP telephony flows do not react to loss or
   substantial delay in any substantive way, the Telephony service class
   SHOULD forward packet as soon as possible.

   The Telephony service class SHOULD use Expedited Forwarding (EF) PHB
   as defined in [RFC3246] and SHOULD be configured to receive
   guaranteed forwarding resources so that all packets are forwarded
   quickly.  The Telephony service class SHOULD be configured to use a
   Priority Queuing system such as defined in Section 1.4.1.1 of this
   document.

   The following application SHOULD use the Telephony service class:
   o  VoIP (G.711, G.729 and other codecs)
   o  Voice-band data over IP (modem, fax)
   o  T.38 fax over IP
   o  Circuit emulation over IP, virtual wire, etc.
   o  IP VPN service that specifies single rate, mean network delay that
      is slightly longer then network propagation delay, very low jitter
      and a very low packet loss



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   Traffic characteristics:
   o  Mostly fixed size packets for VoIP (60, 70, 120 or 200 bytes in
      size)
   o  Packets emitted at constant time intervals
   o  Admission control of new flows is provided by telephony call
      server, media gateway, gatekeeper, edge router, end terminal or
      access node that provides flow admission control function.

   Applications or IP end points SHOULD pre-mark their packets with EF
   DSCP value.  If the end point is not capable of setting the DSCP
   value, then the router topologically closest to the end point SHOULD
   perform Multifield (MF) Classification as defined in [RFC2475].

   RECOMMENDED DSCP marking is EF for the following applications:
   o  VoIP (G.711, G.729 and other codecs)
   o  Voice-band data over IP (modem and fax)
   o  T.38 fax over IP
   o  Circuit emulation over IP, virtual wire, etc.

   RECOMMENDED Network Edge Conditioning:
   o  Packet flow marking (DSCP setting) from untrusted sources (end
      user devices) SHOULD be verified at ingress to DiffServ network
      using Multifield (MF) Classification methods defined in [RFC2475].
   o  Packet flows from untrusted sources (end user devices) SHOULD be
      policed at ingress to DiffServ network, e.g. using single rate
      with burst size token bucket policer to ensure that the telephony
      traffic stays within its negotiated bounds.
   o  Policing is OPTIONAL for packet flows from trusted sources whose
      behavior is assured via other means (e.g., administrative controls
      on those systems).
   o  Policing of Telephony packet flows across peering points where SLA
      is in place is OPTIONAL as telephony traffic will be controlled by
      admission control mechanism between peering points.

   The fundamental service offered to "Telephony" traffic is enhanced
   best effort service with controlled rate, very low delay and very low
   loss.  The service MUST be engineered so that EF marked packet flows
   have sufficient bandwidth in the network to provide guaranteed
   delivery.  Normally traffic in this service class does not respond
   dynamically to packet loss.  As such, Active Queue Management
   [RFC2309] SHOULD NOT be applied to EF marked packet flows.

4.2  Signaling Service Class

   The Signaling service class is RECOMMENDED for delay sensitive
   client-server (traditional telephony) and peer-to-peer application
   signaling.  Telephony signaling includes signaling between IP phone
   and soft-switch, soft-client and soft-switch, media gateway and soft-



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   switch as well as peer-to-peer using various protocols.  This service
   class is intended to be used for control of sessions and
   applications.  Applications using this service class requiring a
   relatively fast response as there are typically several message of
   different size sent for control of the session.  This service class
   is configured to provide good response for short lived, intermittent
   flows that require real-time packet forwarding.  To minimize the
   possibility of ring clipping at start of call for VoIP service that
   interface to a circuit switch Exchange in the Public Switch Telephone
   Network (PSTN), the Signaling service class SHOULD be configured so
   that the probability of packet drop or significant queuing delay
   under peak load is very low in IP network segments that provide this
   interface.  The term "ring clipping" refers to those instances where
   the front end of a ringing signal is altered because the bearer path
   is not made available in time to carry all of the audible ringing
   signal.  This condition may occur due to a race condition between
   when the tone generator in the circuit switch Exchange is turn on and
   when the bearer path through the IP network is enabled.  See
   Section 9.1 for additional explanation of "ring clipping" and
   Section 5.1 for explanation of mapping different signaling methods to
   service classes.

   The Signaling service class SHOULD use the Class Selector (CS) PHB
   defined in [RFC2474].  This service class SHOULD be configured to
   provide a minimum bandwidth assurance for CS5 marked packets to
   ensure that they get forwarded.  The Signaling service class SHOULD
   be configured to use a Rate Queuing system such as defined in
   Section 1.4.1.2of this document.

   The following applications SHOULD use the Signaling service class:
   o  Peer-to-peer IP telephony signaling (e.g., using SIP, H.323)
   o  Peer-to-peer signaling for multimedia applications (e.g., using
      SIP, H.323)
   o  Peer-to-peer real-time control function
   o  Client-server IP telephony signaling using H.248, MEGACO, MGCP, IP
      encapsulated ISDN or other proprietary protocols
   o  Signaling to control IPTV applications using protocols such as
      IGMP (Internet Group Management Protocol)
   o  Signaling flows between high capacity telephony call servers or
      soft switches using protocol such as SIP-T.  Such high capacity
      devices may control thousands of telephony (VoIP) calls.

   Traffic characteristics:
   o  Variable size packets (50 to 1500 bytes in size)
   o  Intermittent traffic flows
   o  Traffic may burst at times





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   o  Delay sensitive control messages sent between two end-points

   RECOMMENDED DSCP marking:
   o  All flows in this service class are marked with CS5 (Class
      Selector 5)

   Applications or IP end points SHOULD pre-mark their packets with CS5
   DSCP value.  If the end point is not capable of setting the DSCP
   value, then the router topologically closest to the end point SHOULD
   perform Multifield (MF) Classification as defined in [RFC2475].

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  Packet flow marking (DSCP setting) from untrusted sources (end
      user devices) SHOULD be verified at ingress to DiffServ network
      using Multifield (MF) Classification methods defined in [RFC2475].
   o  Packet flows from untrusted sources (end user devices) SHOULD be
      policed at ingress to DiffServ network, e.g. using single rate
      with burst size token bucket policer to ensure that the traffic
      stays within its negotiated or engineered bounds.
   o  Packet flows from trusted sources (application servers inside
      administered network) MAY not require policing.
   o  Policing of packet flows across peering points SHOULD be performed
      to the Service Level Agreement (SLA).

   The fundamental service offered to "Signaling" traffic is enhanced
   best effort service with controlled rate and delay.  The service
   SHOULD be engineered so that CS5 marked packet flows have sufficient
   bandwidth in the network to provide high assurance of delivery and
   low delay.  Normally traffic in this service class does not respond
   dynamically to packet loss.  As such, Active Queue Management
   [RFC2309] SHOULD NOT be applied to CS5 marked packet flows.

4.3  Multimedia Conferencing Service Class

   The Multimedia Conferencing service class is RECOMMENDED for
   applications that require real-time service for rate adaptive
   traffic.  H.323/V2 and later versions of video conferencing equipment
   with dynamic bandwidth adjustment is such an application.  The
   traffic sources (applications) in this service class have the
   capability to dynamically change their transmission rate based on
   feedback received from the receiving end, within bounds of packet
   loss by the receiver is sent using the applications control stream to
   the transmitter as an indication of possible congestion; the
   transmitter then selects a lower transmission rate based on pre-
   configured encoding rates (or transmission rates).  Note, today many
   H.323/V2 video conferencing solutions implement fixed step bandwidth
   change (usually reducing the rate), traffic resembling step-wise CBR.




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   Typical video conferencing configurations negotiate the setup of
   multimedia session using protocols such as H.323.  When a user/
   end-point has been authorized to start a multimedia session the
   admission procedure should have verified that the newly admitted data
   rate will be within the engineered capacity of the Multimedia
   Conferencing service class.  The bandwidth in the core network and
   the number of simultaneous video conferencing sessions that can be
   supported SHOULD be engineered to control traffic load for this
   service.

   The Multimedia Conferencing service class SHOULD use the Assured
   Forwarding (AF) PHB defined in [RFC2597].  This service class SHOULD
   be configured to provide a bandwidth assurance for AF41, AF42, and
   AF43 marked packets to ensure that they get forwarded.  The
   Multimedia Conferencing service class SHOULD be configured to use a
   Rate Queuing system such as defined in Section 1.4.1.2 of this
   document.

   The following application SHOULD use the Multimedia Conferencing
   service class:
   o  H.323/V2 and later versions of video conferencing applications
      (interactive video)
   o  Video conferencing applications with rate control or traffic
      content importance marking
   o  Application server to application server non bursty data transfer
      requiring very low delay
   o  IP VPN service that specifies two rates and mean network delay
      that is slightly longer then network propagation delay.
   o  Interactive, time critical and mission critical applications.

   Traffic characteristics:
   o  Variable size packets (50 to 1500 bytes in size)
   o  Higher the rate, higher is the density of large packets
   o  Constant packet emission time interval
   o  Variable rate
   o  Source is capable of reducing its transmission rate based on
      detection of packet loss at the receiver

   Applications or IP end points SHOULD pre-mark their packets with DSCP
   values as shown below.  If the end point is not capable of setting
   the DSCP value, then the router topologically closest to the end
   point SHOULD perform Multifield (MF) Classification as defined in
   [RFC2475] and mark all packets as AF4x.  Note: In this case, the two
   rate three color marker will be configured to operate in Color-Blind
   mode.

   RECOMMENDED DSCP marking when performed by router closest to source:




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   o  AF41 = up to specified rate "A"
   o  AF42 = in excess of specified rate "A" but below specified rate
      "B"
   o  AF43 = in excess of specified rate "B"
   o  Where "A" < "B"
   Note: One might expect "A" to approximate the sum of the mean rates
   and "B" to approximate the sum of the peak rates.

   RECOMMENDED DSCP marking when performed by H.323/V2 video
   conferencing equipment:
   o  AF41 = H.323 video conferencing audio stream RTP/UDP
   o  AF41 = H.323 video conferencing video control RTCP/TCP
   o  AF41 = H.323 video conferencing video stream up to specified rate
      "A"
   o  AF42 = H.323 video conferencing video stream in excess of
      specified rate "A" but below specified rate "B"
   o  AF43 = H.323 video conferencing video stream in excess of
      specified rate "B"
   o  Where "A" < "B"

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  The two rate three color marker SHOULD be configured to provide
      the behavior as defined in trTCM [RFC2698].
   o  If packets are marked by a trusted sources or previous trusted
      DiffServ domain, and the color marking is to be preserved, then
      the two rate three color marker SHOULD be configured to operate in
      Color-Aware mode.
   o  If the packet marking is not trusted or the color marking is not
      to be preserved, then the two rate three color marker SHOULD be
      configured to operate in Color-Blind mode.

   The fundamental service offered to "Multimedia Conferencing" traffic
   is enhanced best effort service with controlled rate and delay.  For
   video conferencing service, typically a 1% packet loss detected at
   the receiver triggers an encoding rate change, dropping to next lower
   provisioned video encoding rate.  As such, Active Queue Management
   [RFC2309] SHOULD be used primarily to switch video encoding rate
   under congestion, changing from high rate to lower rate i.e. 1472
   kbps to 768 kbps.  The probability of loss of AF41 traffic MUST NOT
   exceed the probability of loss of AF42 traffic, which in turn MUST
   NOT exceed the probability of loss of AF43 traffic.

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth for each DSCP, and the max-threshold
   specifies the queue depth above which all traffic with such a DSCP is
   dropped or ECN marked.  Thus, in this service class, the following
   inequality should hold in queue configurations:




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   o  min-threshold AF43 < max-threshold AF43
   o  max-threshold AF43 <= min-threshold AF42
   o  min-threshold AF42 < max-threshold AF42
   o  max-threshold AF42 <= min-threshold AF41
   o  min-threshold AF41 < max-threshold AF41
   o  max-threshold AF41 <= memory assigned to the queue
   Note: This configuration tends to drop AF43 traffic before AF42 and
   AF42 before AF41.  Many other AQM algorithms exist and are used; they
   should be configured to achieve a similar result.

4.4  Real-time Interactive Service Class

   The Real-time Interactive service class is RECOMMENDED for
   applications that require low loss, jitter and very low delay for
   variable rate inelastic traffic sources.  Interactive gaming and
   video conferencing applications that do not have the ability to
   change encoding rates or mark packets with different importance
   indications are such applications.  The traffic sources in this
   traffic class does not have the ability to reduce their transmission
   rate based on feedback received from the receiving end.

   Typically, applications in this service class are configured to
   negotiate the setup of RTP/UDP control session.  When a user/
   end-point has been authorized to start a new session the admission
   procedure should have verified that the newly admitted data rates
   will be within the engineered capacity of the Real-time Interactive
   service class.  The bandwidth in the core network and the number of
   simultaneous Real-time Interactive sessions that can be supported
   SHOULD be engineered to control traffic load for this service.

   The Real-time Interactive service class SHOULD use the Class Selector
   (CS) PHB defined in [RFC2474].  This service class SHOULD be
   configured to provide a high assurance for bandwidth for CS4 marked
   packets to ensure that they get forwarded.  The Real-time Interactive
   service class SHOULD be configured to use a Rate Queuing system such
   as defined in Section 1.4.1.2 of this document.  Note, this service
   class MAY be configured as a second EF PHB that uses relaxed
   performance parameter, a rate scheduler and CS4 DSCP value.

   The following application SHOULD use the Real-time Interactive
   service class:
   o  Interactive gaming and control
   o  Video conferencing applications without rate control or traffic
      content importance marking
   o  IP VPN service that specifies single rate and mean network delay
      that is slightly longer then network propagation delay





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   o  Inelastic, interactive, time critical and mission critical
      applications requiring very low delay

   Traffic characteristics:
   o  Variable size packets (50 to 1500 bytes in size)
   o  Variable rate non bursty
   o  Application is sensitive to delay variation between flows and
      sessions
   o  Packets lost if any are usually ignored by application

   RECOMMENDED DSCP marking:
   o  All flows in this service class are marked with CS4 (Class
      Selector 4)

   Applications or IP end points SHOULD pre-mark their packets with CS4
   DSCP value.  If the end point is not capable of setting the DSCP
   value, then the router topologically closest to the end point SHOULD
   perform Multifield (MF) Classification as defined in [RFC2475].

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  Packet flow marking (DSCP setting) from untrusted sources (end
      user devices) SHOULD be verified at ingress to DiffServ network
      using Multifield (MF) Classification methods defined in [RFC2475].
   o  Packet flows from untrusted sources (end user devices) SHOULD be
      policed at ingress to DiffServ network, e.g. using single rate
      with burst size token bucket policer to ensure that the traffic
      stays within its negotiated or engineered bounds.
   o  Packet flows from trusted sources (application servers inside
      administered network) MAY not require policing.
   o  Policing of packet flows across peering points SHOULD be performed
      to the Service Level Agreement (SLA).

   The fundamental service offered to "Real-time Interactive" traffic is
   enhanced best effort service with controlled rate and delay.  The
   service SHOULD be engineered so that CS4 marked packet flows have
   sufficient bandwidth in the network to provide high assurance of
   delivery.  Normally traffic in this service class does not respond
   dynamically to packet loss.  As such, Active Queue Management
   [RFC2309] SHOULD NOT be applied to CS4 marked packet flows.

4.5  Multimedia Streaming Service Class

   The Multimedia Streaming service class is RECOMMENDED for
   applications that require near-real-time packet forwarding of
   variable rate elastic traffic sources that are not as delay sensitive
   as applications using the Multimedia Conferencing service class.
   Such applications include streaming audio and video, some video
   (movies) on demand applications and Web casts.  In general, the



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   Multimedia Streaming service class assumes that the traffic is
   buffered at the source/destination and therefore, is less sensitive
   to delay and jitter.

   The Multimedia Streaming service class SHOULD use the Assured
   Forwarding (AF) PHB defined in [RFC2597].  This service class SHOULD
   be configured to provide a minimum bandwidth assurance for AF31, AF32
   and AF33 marked packets to ensure that they get forwarded.  The
   Multimedia Streaming service class SHOULD be configured to use Rate
   Queuing system such as defined in Section 1.4.1.2 of this document.

   The following applications SHOULD use the Multimedia Streaming
   service class:
   o  Buffered streaming audio (unicast)
   o  Buffered streaming video (unicast)
   o  Web casts
   o  IP VPN service that specifies two rates and is less sensitive to
      delay and jitter

   Traffic characteristics:
   o  Variable size packets (50 to 4196 bytes in size)
   o  Higher the rate, higher density of large packets
   o  Variable rate
   o  Elastic flows
   o  Some bursting at start of flow from some applications

   Applications or IP end points SHOULD pre-mark their packets with DSCP
   values as shown below.  If the end point is not capable of setting
   the DSCP value, then the router topologically closest to the end
   point SHOULD perform Multifield (MF) Classification as defined in
   [RFC2475] and mark all packets as AF3x.  Note: In this case, the two
   rate three color marker will be configured to operate in Color-Blind
   mode.

   RECOMMENDED DSCP marking:
   o  AF31 = up to specified rate "A"
   o  AF32 = in excess of specified rate "A" but below specified rate
      "B"
   o  AF33 = in excess of specified rate "B"
   o  Where "A" < "B"
   Note: One might expect "A" to approximate the sum of the mean rates
   and "B" to approximate the sum of the peak rates.

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  The two rate three color marker SHOULD be configured to provide
      the behavior as defined in trTCM [RFC2698].





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   o  If packets are marked by a trusted sources or previous trusted
      DiffServ domain, and the color marking is to be preserved, then
      the two rate three color marker SHOULD be configured to operate in
      Color-Aware mode.
   o  If the packet marking is not trusted or the color marking is not
      to be preserved, then the two rate three color marker SHOULD be
      configured to operate in Color-Blind mode.

   The fundamental service offered to "Multimedia Streaming" traffic is
   enhanced best effort service with controlled rate and delay.  The
   service SHOULD be engineered so that AF31 marked packet flows have
   sufficient bandwidth in the network to provide high assurance of
   delivery.  Since the AF3x traffic is elastic and responds dynamically
   to packet loss, Active Queue Management [RFC2309] SHOULD be used
   primarily to reduce forwarding rate to the minimum assured rate at
   congestion points.  The probability of loss of AF31 traffic MUST NOT
   exceed the probability of loss of AF32 traffic, which in turn MUST
   NOT exceed the probability of loss of AF33.

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth for each DSCP, and the max-threshold
   specifies the queue depth above which all traffic with such a DSCP is
   dropped or ECN marked.  Thus, in this service class, the following
   inequality should hold in queue configurations:
   o  min-threshold AF33 < max-threshold AF33
   o  max-threshold AF33 <= min-threshold AF32
   o  min-threshold AF32 < max-threshold AF32
   o  max-threshold AF32 <= min-threshold AF31
   o  min-threshold AF31 < max-threshold AF31
   o  max-threshold AF31 <= memory assigned to the queue
   Note: This configuration tends to drop AF33 traffic before AF32 and
   AF32 before AF31.  Many other AQM algorithms exist and are used; they
   should be configured to achieve a similar result.

4.6  Broadcast Video Service Class

   The Broadcast Video service class is RECOMMENDED for applications
   that require near-real-time packet forwarding with very low packet
   loss of constant and variable rate inelastic traffic sources that are
   not as delay sensitive as applications using the Real-time
   Interactive service class.  Such applications include broadcast TV,
   streaming of live audio and video events, some video on demand
   applications and video surveillance.  In general, the Broadcast Video
   service class assumes that the destination end point has a dejitter
   buffer, for video application usually a 2 - 8 video frames buffer (66
   to several hundred of milliseconds) therefore, is less sensitive to
   delay and jitter.




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   The Broadcast Video service class SHOULD use the Class Selector (CS)
   PHB defined in [RFC2474].  This service class SHOULD be configured to
   provide high assurance for bandwidth for CS3 marked packets to ensure
   that they get forwarded.  The Broadcast Video service class SHOULD be
   configured to use Rate Queuing system such as defined in
   Section 1.4.1.2 of this document.  Note, this service class MAY be
   configured as a third EF PHB that uses relaxed performance parameter,
   a rate scheduler and CS3 DSCP value.

   The following applications SHOULD use the Broadcast Video service
   class:
   o  Video surveillance and security (unicast)
   o  TV broadcast including HDTV (multicast)
   o  Video on demand (unicast) with control (virtual DVD)
   o  Streaming of live audio events (both unicast and multicast)
   o  Streaming of live video events (both unicast and multicast)

   Traffic characteristics:
   o  Variable size packets (50 to 4196 bytes in size)
   o  Higher the rate, higher density of large packets
   o  Mixture of variable and constant rate flows
   o  Fixed packet emission time intervals
   o  Inelastic flows

   RECOMMENDED DSCP marking:
   o  All flows in this service class are marked with CS3 (Class
      Selector 3)
   o  In some cases, like for security and video surveillance
      applications, it may be desirable to use a different DSCP marking.
      If so, then locally user definable (EXP/LU) codepoint(s) in the
      range '011xx1' MAY be used to provide unique traffic
      identification.  The locally user definable (EXP/LU) codepoint(s)
      MAY be associated with the PHB that is used for CS3 traffic.
      Further, depending on the network scenario, additional network
      edge conditioning policy MAY be need for the EXP/LU codepoint(s)
      used.

   Applications or IP end points SHOULD pre-mark their packets with CS3
   DSCP value.  If the end point is not capable of setting the DSCP
   value, then the router topologically closest to the end point SHOULD
   perform Multifield (MF) Classification as defined in [RFC2475].

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  Packet flow marking (DSCP setting) from untrusted sources (end
      user devices) SHOULD be verified at ingress to DiffServ network
      using Multifield (MF) Classification methods defined in [RFC2475].





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   o  Packet flows from untrusted sources (end user devices) SHOULD be
      policed at ingress to DiffServ network, e.g. using single rate
      with burst size token bucket policer to ensure that the traffic
      stays within its negotiated or engineered bounds.
   o  Packet flows from trusted sources (application servers inside
      administered network) MAY not require policing.
   o  Policing of packet flows across peering points SHOULD be performed
      to the Service Level Agreement (SLA).

   The fundamental service offered to "Broadcast Video" traffic is
   enhanced best effort service with controlled rate and delay.  The
   service SHOULD be engineered so that CS3 marked packet flows have
   sufficient bandwidth in the network to provide high assurance of
   delivery.  Normally traffic in this service class does not respond
   dynamically to packet loss.  As such, Active Queue Management
   [RFC2309] SHOULD NOT be applied to CS3 marked packet flows.

4.7  Low Latency Data Service Class

   The Low Latency Data service class is RECOMMENDED for elastic and
   responsive typically client/server based applications.  Applications
   forwarded by this service class are those requiring a relatively fast
   response and typically have asymmetrical bandwidth need, i.e. the
   client typically sends a short message to the server and the server
   responds with a much larger data flow back to the client.  The most
   common example of this is when a user clicks a hyperlink (~few dozen
   bytes) on a web page resulting in a new web page to be loaded (Kbytes
   of data).  This service class is configured to provide good response
   for TCP [RFC1633] short lived flows that require real-time packet
   forwarding of variable rate traffic sources.

   The Low Latency Data service class SHOULD use the Assured Forwarding
   (AF) PHB defined in [RFC2597].  This service class SHOULD be
   configured to provide a minimum bandwidth assurance for AF21, AF22
   and AF23 marked packets to ensure that they get forwarded.  The Low
   Latency Data service class SHOULD be configured to use a Rate Queuing
   system such as defined in Section 1.4.1.2 of this document.

   The following applications SHOULD use the Low Latency Data service
   class:
   o  Client/server applications
   o  SNA terminal to host transactions (SNA over IP using DLSw)
   o  Web based transactions (E-commerce)
   o  Credit card transactions
   o  Financial wire transfers
   o  Enterprise Resource Planning (ERP) applications (e.g., SAP/BaaN)





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   o  VPN service that supports CIR (Committed Information Rate) with up
      to two burst sizes

   Traffic characteristics:
   o  Variable size packets (50 to 1500 bytes in size)
   o  Variable packet emission rate
   o  With packet bursts of TCP window size
   o  Short traffic bursts
   o  Source capable of reducing its transmission rate based on
      detection of packet loss at the receiver or through explicit
      congestion notification

   Applications or IP end points SHOULD pre-mark their packets with DSCP
   values as shown below.  If the end point is not capable of setting
   the DSCP value, then the router topologically closest to the end
   point SHOULD perform Multifield (MF) Classification as defined in
   [RFC2475] and mark all packets as AF2x.  Note: In this case, the
   single rate three color marker will be configured to operate in
   Color-Blind mode.

   RECOMMENDED DSCP marking:
   o  AF21 = flow stream with packet burst size up to "A" bytes
   o  AF22 = flow stream with packet burst size in excess of "A" but
      below "B" bytes
   o  AF23 = flow stream with packet burst size in excess of "B" bytes
   o  Where "A" < "B"

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  The single rate three color marker SHOULD be configured to provide
      the behavior as defined in srTCM [RFC2697].
   o  If packets are marked by a trusted sources or previous trusted
      DiffServ domain, and the color marking is to be preserved, then
      the single rate three color marker SHOULD be configured to operate
      in Color-Aware mode.
   o  If the packet marking is not trusted or the color marking is not
      to be preserved, then the single rate three color marker SHOULD be
      configured to operate in Color-Blind mode.

   The fundamental service offered to "Low Latency Data" traffic is
   enhanced best effort service with controlled rate and delay.  The
   service SHOULD be engineered so that AF21 marked packet flows have
   sufficient bandwidth in the network to provide high assurance of
   delivery.  Since the AF2x traffic is elastic and responds dynamically
   to packet loss, Active Queue Management [RFC2309] SHOULD be used
   primarily to control TCP flow rates at congestion points by dropping
   packet from TCP flows that have large burst size.  The probability of
   loss of AF21 traffic MUST NOT exceed the probability of loss of AF22
   traffic, which in turn MUST NOT exceed the probability of loss of



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   AF23.  Active queue management MAY also be implemented using Explicit
   Congestion Notification (ECN) [RFC3168].

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth for each DSCP, and the max-threshold
   specifies the queue depth above which all traffic with such a DSCP is
   dropped or ECN marked.  Thus, in this service class, the following
   inequality should hold in queue configurations:
   o  min-threshold AF23 < max-threshold AF23
   o  max-threshold AF23 <= min-threshold AF22
   o  min-threshold AF22 < max-threshold AF22
   o  max-threshold AF22 <= min-threshold AF21
   o  min-threshold AF21 < max-threshold AF21
   o  max-threshold AF21 <= memory assigned to the queue
   Note: This configuration tends to drop AF23 traffic before AF22 and
   AF22 before AF21.  Many other AQM algorithms exist and are used; they
   should be configured to achieve a similar result.

4.8  High Throughput Data Service Class

   The High Throughput Data service class is RECOMMENDED for elastic
   applications that require timely packet forwarding of variable rate
   traffic sources and more specifically is configured to provide good
   throughput for TCP longer lived flows.  TCP [RFC1633] or a transport
   with a consistent Congestion Avoidance Procedure [RFC2581] [RFC2582]
   normally will drive as high a data rate as it can obtain over a long
   period of time.  The FTP protocol is a common example, although one
   cannot definitively say that all FTP transfers are moving data in
   bulk.

   The High Throughput Data service class SHOULD use the Assured
   Forwarding (AF) PHB defined in [RFC2597].  This service class SHOULD
   be configured to provide a minimum bandwidth assurance for AF11, AF12
   and AF13 marked packets to ensure that they are forwarded in timely
   manner.  The High Throughput Data service class SHOULD be configured
   to use a Rate Queuing system such as defined in Section 1.4.1.2 of
   this document.

   The following applications SHOULD use the High Throughput Data
   service class:
   o  Store and forward applications
   o  File transfer applications
   o  Email
   o  VPN service that supports two rates (committed information rate
      and excess or peak information rate)

   Traffic characteristics:




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   o  Variable size packets (50 to 1500 bytes in size)
   o  Variable packet emission rate
   o  Variable rate
   o  With packet bursts of TCP window size
   o  Source capable of reducing its transmission rate based on
      detection of packet loss at the receiver or through explicit
      congestion notification

   Applications or IP end points SHOULD pre-mark their packets with DSCP
   values as shown below.  If the end point is not capable of setting
   the DSCP value, then the router topologically closest to the end
   point SHOULD perform Multifield (MF) Classification as defined in
   [RFC2475] and mark all packets as AF1x.  Note: In this case, the two
   rate three color marker will be configured to operate in Color-Blind
   mode.

   RECOMMENDED DSCP marking:
   o  AF11 = up to specified rate "A"
   o  AF12 = in excess of specified rate "A" but below specified rate
      "B"
   o  AF13 = in excess of specified rate "B"
   o  Where "A" < "B"

   RECOMMENDED Conditioning Performed at DiffServ Network Edge:
   o  The two rate three color marker SHOULD be configured to provide
      the behavior as defined in trTCM [RFC2698].
   o  If packets are marked by a trusted sources or previous trusted
      DiffServ domain, and the color marking is to be preserved, then
      the two rate three color marker SHOULD be configured to operate in
      Color-Aware mode.
   o  If the packet marking is not trusted or the color marking is not
      to be preserved, then the two rate three color marker SHOULD be
      configured to operate in Color-Blind mode.

   The fundamental service offered to "High Throughput Data" traffic is
   enhanced best effort service with a specified minimum rate.  The
   service SHOULD be engineered so that AF11 marked packet flows have
   sufficient bandwidth in the network to provide assured delivery.  It
   can be assumed that this class will consume any available bandwidth,
   and packets traversing congested links may experience higher queuing
   delays and/or packet loss.  Since the AF1x traffic is elastic and
   responds dynamically to packet loss, Active Queue Management
   [RFC2309] SHOULD be used primarily to control TCP flow rates at
   congestion points by dropping packet from TCP flows that have higher
   rates first.  The probability of loss of AF11 traffic MUST NOT exceed
   the probability of loss of AF12 traffic, which in turn MUST NOT
   exceed the probability of loss of AF13.  In such a case, if one
   network customer is driving significant excess and another seeks to



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   use the link, any losses will be experienced by the high rate user,
   causing him to reduce his rate.  Active queue management MAY also be
   implemented using Explicit Congestion Notification (ECN) [RFC3168].

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth for each DSCP, and the max-threshold
   specifies the queue depth above which all traffic with such a DSCP is
   dropped or ECN marked.  Thus, in this service class, the following
   inequality should hold in queue configurations:
   o  min-threshold AF13 < max-threshold AF13
   o  max-threshold AF13 <= min-threshold AF12
   o  min-threshold AF12 < max-threshold AF12
   o  max-threshold AF12 <= min-threshold AF11
   o  min-threshold AF11 < max-threshold AF11
   o  max-threshold AF11 <= memory assigned to the queue
   Note: This configuration tends to drop AF13 traffic before AF12 and
   AF12 before AF11.  Many other AQM algorithms exist and are used; they
   should be configured to achieve a similar result.

4.9  Standard Service Class

   The Standard service class is RECOMMENDED for traffic that has not
   been classified into one of the other supported forwarding service
   classes in the DiffServ network domain.  This service class provides
   the Internet's "best effort" forwarding behavior.  This service class
   typically has minimum bandwidth guarantee.

   The Standard service class MUST use the Default Forwarding (DF) PHB
   defined in [RFC2474] and SHOULD be configured to receive at least a
   small percentage of forwarding resources as a guaranteed minimum.
   This service class SHOULD be configured to use a Rate Queuing system
   such as defined in Section 1.4.1.2 of this document.

   The following application SHOULD use the Standard service class:
   o  Network services, DNS, DHCP, BootP
   o  Any undifferentiated application/packet flow transported through
      the DiffServ enabled network

   Traffic Characteristics:
   o  Non deterministic, mixture of everything

   RECOMMENDED DSCP marking is DF (Default Forwarding) '000000'

   Network Edge Conditioning:
      There is no requirement that conditioning of packet flows be
      performed for this service class.

   The fundamental service offered to the Standard service class is best



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   effort service with active queue management to limit over-all delay.
   Typical configurations SHOULD use random packet dropping to implement
   Active Queue Management [RFC2309] or Explicit Congestion Notification
   [RFC3168], and MAY impose a minimum or maximum rate on the queue.

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold
   specifies a target queue depth, and the max-threshold specifies the
   queue depth above which all traffic is dropped or ECN marked.  Thus,
   in this service class, the following inequality should hold in queue
   configurations:
   o  min-threshold DF < max-threshold DF
   o  max-threshold DF <= memory assigned to the queue
   Note: Many other AQM algorithms exist and are used; they should be
   configured to achieve a similar result.

4.10  Low Priority Data

   The Low Priority Data service class serves applications that run over
   TCP [RFC0793] or a transport with consistent congestion avoidance
   procedure [RFC2581] [RFC2582], and which the user is willing to
   accept service without guarantees.  This service class is specified
   in [QBSS] and [RFC3662].

   The following applications MAY use the Low Priority Data service
   class:
   o  Any TCP based application/packet flow transported through the
      DiffServ enabled network that does not require any bandwidth
      assurances

   Traffic Characteristics:
   o  Non real-time and elastic

   Network Edge Conditioning:
      There is no requirement that conditioning of packet flows be
      performed for this service class

   RECOMMENDED DSCP marking is CS1 (Class Selector 1)

   The fundamental service offered to the Low Priority Data service
   class is best effort service with zero bandwidth assurance.  By
   placing it into a separate queue or class, it may be treated in a
   manner consistent with a specific service level agreement.

   Typical configurations SHOULD use Explicit Congestion Notification
   [RFC3168] or random loss to implement Active Queue Management
   [RFC2309].

   If RED [RFC2309] is used as an AQM algorithm, the min-threshold



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   specifies a target queue depth, and the max-threshold specifies the
   queue depth above which all traffic is dropped or ECN marked.  Thus,
   in this service class, the following inequality should hold in queue
   configurations:
   o  min-threshold CS1 < max-threshold CS1
   o  max-threshold CS1 <= memory assigned to the queue
   Note: Many other AQM algorithms exist and are used; they should be
   configured to achieve a similar result.

5.  Additional Information on Service Class Usage

   In this section we provide additional information on how some
   specific applications should be configured to use the defined service
   classes.

5.1  Mapping for Signaling

   There are many different signaling protocols, ways that signaling is
   used and performance requirements from applications that are
   controlled by these protocols.  We believe that different signaling
   protocols should use the service class that best meet the objectives
   of application or service they control.  The following mapping is
   recommended:
   o  Peer-to-peer signaling using SIP/H.323 are marked with CS5 DSCP
      (use Signaling service class).
   o  Client-server signaling as used in many implementation for IP
      telephony using H.248, MEGACO, MGCP, IP encapsulated ISDN or
      proprietary protocols are marked with CS5 DSCP (use Signaling
      service class).
   o  Signaling between call servers or soft-switches in carrier's
      network using SIP, SIP-T, IP encapsulated ISUP, are marked with
      CS5 DSCP (use Signaling service class).
   o  RSVP signaling, depends on the application.  If RSVP signaling is
      "on-path" as used in IntServ, then it needs to be forwarded from
      the same queue (service class) and marked with the same DSCP value
      as application data that it is controlling.  This may also apply
      to the "on-path" NSIS signaling protocol.
   o  IGMP (Internet Group Management Protocol).  If used for multicast
      session control such as channel changing in IPTV systems, then
      IGMP packets should be marked with CS5 DSCP (use Signaling service
      class).  When IGMP is used only for the normal multicast routing
      purpose, it should be marked with CS6 DSCP (use Network Control
      service class).

5.2  Mapping for NTP

   From tests that were performed, indications are that precise time
   distribution requires a very low packet delay variation (jitter)



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   transport.  Therefore we suggest the following guidelines for NTP
   (Network Time Protocol) be used:
   o  When NTP is used for providing high accuracy timing within
      administrator's (carrier's) network or to end users/clients, the
      Telephony service class should be used and NTP packets be marked
      with EF DSCP value.
   o  For applications that require "wall clock" timing accuracy, the
      Standard service class should be used and packets should be marked
      with DF DSCP.

5.3  VPN Service Mapping

   Differentiated Services and Tunnels [RFC2983] considers the
   interaction of DiffServ architecture with IP tunnels of various
   forms.  Further to guidelines provided in RFC 2983, below are
   additional guidelines for mapping service classes that are supported
   in one part of the network into a VPN connection.  This discussion is
   limit only to VPNs that use DiffServ technology for traffic
   differentiation.
   o  The DSCP value(s) that is/are used to represent a PHB or a PHB
      group should be the same for the networks at both ends of the VPN
      tunnel, unless remarking of DSCP is done as ingress/egress
      processing function of the tunnel.  DSCP marking needs to be
      preserve end-to-end.
   o  The VPN may be configured to support one or more service
      class(es).  It is left up to the administrators of the two
      networks to agree on the level of traffic differentiation that
      will be provide in the network that supports VPN service.  Service
      classes are then mapped into the supported VPN traffic forwarding
      behaviors that meet the traffic characteristics and performance
      requirements of the encapsulated service classes.
   o  The traffic treatment in the network that is providing the VPN
      service needs to be such that the encapsulated service class or
      classes receive comparable behavior and performance in terms of
      delay, jitter, packet loss and they are within the limits of the
      service specified.
   o  The DSCP value in the external header of the packet forwarded
      through the network providing the VPN service may be different
      than the DSCP value that is used end-to-end for service
      differentiation in end network.
   o  The guidelines for aggregation of two or more service classes into
      a single traffic forwarding treatment in the network that is
      providing the VPN service is for further study.

6.  Security Considerations

   This document discusses policy, and describes a common policy
   configuration, for the use of a Differentiated Services Code Point by



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   transports and applications.  If implemented as described, it should
   require the network to do nothing that the network has not already
   allowed.  If that is the case, no new security issues should arise
   from the use of such a policy.

   It is possible for the policy to be applied incorrectly, or for a
   wrong policy to be applied in the network for the defined service
   class.  In that case, a policy issue exists that the network SHOULD
   detect, assess, and deal with.  This is a known security issue in any
   network dependent on policy directed behavior.

   A well known flaw appears when bandwidth is reserved or enabled for a
   service (for example, voice transport) and another service or an
   attacking traffic stream uses it.  This possibility is inherent in
   DiffServ technology, which depends on appropriate packet markings.
   When bandwidth reservation or a priority queuing system is used in a
   vulnerable network, the use of authentication and flow admission is
   recommended.  To the author's knowledge, there is no known technical
   way to respond to an unauthenticated data stream using service that
   it is not intended to use, and such is the nature of the Internet.

   The use of a service class by a user is not an issue when the SLA
   between the user and the network permits him to use it, or to use it
   up to a stated rate.  In such cases, simple policing is used in the
   Differentiated Services Architecture.  Some service classes, such as
   Network Control, are not permitted to be used by users at all; such
   traffic should be dropped or remarked by ingress filters.  Where
   service classes are available under the SLA only to an authenticated
   user rather than to the entire population of users, AAA services such
   as described in [I-D.iab-auth-mech] are required.

7.  Summary of Changes from Previous Draft

   NOTE TO RFC EDITOR: Please remove this section during the publication
   process.

   Changes made to draft-ietf-tsvwg-diffserv-service-classes-00 based on
   minor typos on review by Mike Fidler.  Following typos were fixed.

   1. page 20 first paragraph, "than 000001 DSCP marking" should be
   "then 000001 DSCP marking"

   2. page 22 last sentence of third bullet "than the Broadcast Video
   service class" should be "then the Broadcast..."

   3. page 29 third bullet "than CS2 marked packet" should be "then CS2
   marked packets" (note plural also)




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   4. page 40 second sentence of second bullet under "RECOMMENDED DSCP
   marking"  "If so, than" should be "If so, then"

   5. page 47 section 5.1 fourth bullet "than it needs to be forwarded"
   should be "then it needs to be forwarded"

   6. page 48 section 5.3 second bullet "Service classes are than
   mapped" should be "Service classes are then mapped"

8.  Acknowledgements

   The authors thank the TSVWG reviewers, David Black, Brian E Carpenter
   and Alan O'Neill for their review and input to this draft.

   The authors acknowledge great many inputs, most notably from Bruce
   Davie, Dave Oran, Ralph Santitoro, Gary Kenward, Francois Audet,
   Morgan Littlewood, Robert Milne, John Shuler, Nalin Mistry, Al
   Morton, Mike Pierce, Ed Koehler Jr., Tim Rahrer, Fil Dickinson and
   Shane Amante.  Kimberly King, Joe Zebarth and Alistair Munroe each
   did a thorough proof-reading, and the document is better for their
   contributions.

9.  Appendix A

9.1  Explanation of Ring Clipping

   The term "ring clipping" refers to those instances where the front
   end of a ringing signal is altered because the bearer channel is not
   made available in time to carry all of the audible ringing signal.
   This condition may occur due to a race condition between when the
   tone generator located in the circuit switch Exchange is turn on and
   when the bearer path through the IP network is enabled.  To reduce
   ring clipping from occurring, delay of signaling path needs to be
   minimized.  Below is a more detailed explanation.

   The bearer path setup delay target is defined as the ISUP Initial
   Address Message (IAM) / Address Complete Message (ACM) round trip
   delay.  ISUP refers to ISDN User Part of Signaling System No. 7 (SS7)
   as defined by ITU-T.  This consists of the amount of time it takes
   for the ISUP Initial Address Message (IAM) to leave the Transit
   Exchange, travel through the SS7 network (including any applicable
   STPs (Signaling Transfer Points)), be processed by the End Exchange
   thus generating the Address Complete Message (ACM) and for the ACM to
   travel back through the SS7 network and return to the Transit
   Exchange.  If the bearer path has not been set up within the soft-
   switch, media gateway and the IP network that is performing the
   Transit Exchange function by the time the ACM is forwarded to the
   originating End Exchange, the phenomenon known as ring clipping may



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   occur.  If ACM processing within soft-switch, media gateway and delay
   through the IP network is excessive, it will delay the setup of the
   bearer path therefore may cause clipping of ring tone to be heard.

   A generic maximum ISUP IAM signaling delay value of 240ms for intra
   Exchange, which may consist of soft-switch, media gateways, queuing
   delay in routers and distance delays between media gateway and soft-
   switch implementations is assumed.  This value represents the
   threshold where ring clipping theoretically commences.  It is
   important to note that the 240ms delay objective as presented is a
   maximum value.  Service administrators are free to choose specific
   IAM delay values based on their own preferences (i.e., they may wish
   to set a very low mean delay objective for strategic reasons to
   differentiate themselves from other providers).  In summary, out of
   the 240ms delay budget, 200ms is allocated as cross-Exchange delay
   (soft-switch and media gateway) and 40ms for network delay (queuing
   and distance).

10.  References

10.1  Normative References

   [I-D.iab-auth-mech]
              Rescorla, E., "A Survey of Authentication Mechanisms",
              draft-iab-auth-mech-03 (work in progress), March 2004.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC1349]  Almquist, P., "Type of Service in the Internet Protocol
              Suite", RFC 1349, July 1992.

   [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
              RFC 1812, June 1995.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2309]  Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering,
              S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G.,
              Partridge, C., Peterson, L., Ramakrishnan, K., Shenker,
              S., Wroclawski, J., and L. Zhang, "Recommendations on
              Queue Management and Congestion Avoidance in the
              Internet", RFC 2309, April 1998.




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   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              December 1998.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [RFC2597]  Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [RFC3246]  Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
              J., Courtney, W., Davari, S., Firoiu, V., and D.
              Stiliadis, "An Expedited Forwarding PHB (Per-Hop
              Behavior)", RFC 3246, March 2002.

   [RFC3662]  Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
              Per-Domain Behavior (PDB) for Differentiated Services",
              RFC 3662, December 2003.

10.2  Informative References

   [QBSS]     "QBone Scavenger Service (QBSS) Definition", Internet2
              Technical Report Proposed Service Definition, March 2001.

   [RFC1633]  Braden, B., Clark, D., and S. Shenker, "Integrated
              Services in the Internet Architecture: an Overview",
              RFC 1633, June 1994.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2581]  Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
              Control", RFC 2581, April 1999.

   [RFC2582]  Floyd, S. and T. Henderson, "The NewReno Modification to
              TCP's Fast Recovery Algorithm", RFC 2582, April 1999.

   [RFC2697]  Heinanen, J. and R. Guerin, "A Single Rate Three Color
              Marker", RFC 2697, September 1999.

   [RFC2698]  Heinanen, J. and R. Guerin, "A Two Rate Three Color
              Marker", RFC 2698, September 1999.

   [RFC2963]  Bonaventure, O. and S. De Cnodder, "A Rate Adaptive Shaper
              for Differentiated Services", RFC 2963, October 2000.



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   [RFC2983]  Black, D., "Differentiated Services and Tunnels",
              RFC 2983, October 2000.

   [RFC2996]  Bernet, Y., "Format of the RSVP DCLASS Object", RFC 2996,
              November 2000.

   [RFC3086]  Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules for
              their Specification", RFC 3086, April 2001.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, September 2001.

   [RFC3175]  Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
              "Aggregation of RSVP for IPv4 and IPv6 Reservations",
              RFC 3175, September 2001.

   [RFC3290]  Bernet, Y., Blake, S., Grossman, D., and A. Smith, "An
              Informal Management Model for Diffserv Routers", RFC 3290,
              May 2002.


Authors' Addresses

   Jozef Babiarz
   Nortel Networks
   3500 Carling Avenue
   Ottawa, Ont.  K2H 8E9
   Canada

   Phone: +1-613-763-6098
   Fax:   +1-613-765-7462
   Email: babiarz@nortel.com


   Kwok Ho Chan
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA  01821
   US

   Phone: +1-978-288-8175
   Fax:   +1-978-288-4690
   Email: khchan@nortel.com






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   Fred Baker
   Cisco Systems
   1121 Via Del Rey
   Santa Barbara, CA  93117
   US

   Phone: +1-408-526-4257
   Fax:   +1-413-473-2403
   Email: fred@cisco.com










































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