RFC 4594
Configuration Guidelines for DiffServ Service Classes
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 in order 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 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): 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, and Media Gateway Control Protocol (MGCP). 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 and loss and very low delay, such as interactive gaming applications that use RTP/UDP streams for game control commands, and video conferencing applications that do not have the ability to change encoding rates or to mark packets with different importance indications. 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 and webcast. 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 or an Enterprise Resource Planning (ERP)
application.
o High-Throughput Data service class is best suited for store and
forward applications such as FTP and billing record transfer.
o Standard service class is for traffic that has not been identified
as requiring differentiated treatment and is normally referred to
as best effort.
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 service 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
a 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 Internet Group Management Protocol (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 vast number of new (in process of being deployed) and
already-in-use media-oriented services in IP networks, five service
classes have been defined.
o Telephony service class is intended for IP telephony (VoIP)
service. It may also 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 applications such as 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. These flows can therefore be
classified as rate adaptive. As currently two types of video
conferencing equipment are used in IP networks (ones that generate
inelastic traffic and ones that generate rate-adaptive traffic),
two service class are needed. The Real-Time Interactive service
class should be used for equipment that generates inelastic video
flows and the Multimedia Conferencing service class for equipment
that generates rate-adaptive video flows.
o Broadcast Video service class is to be used for inelastic traffic
flows, which are intended for broadcast TV service and for
transport of live video and audio events.
o Multimedia Streaming service class is to be used for elastic
multimedia traffic flows. This multimedia content is typically
stored before being transmitted. It is also buffered at the
receiving end before being played out. The buffering is
sufficiently 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 inelastic traffic flows; therefore, two service
classes are defined to address this space, respectively:
Multimedia Streaming and Broadcast Video.
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 Streaming.
o Low-Priority Data for applications or services that can tolerate
short or long interruptions of packet flows. The 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 the last column provides end user Quality of Service (QoS) rating as defined in ITU-T Recommendation G.1010. ----------------------------------------------------------------- | Application | Service | Signaled | Flow | G.1010 | | Categories | Class | | Behavior | Rating | |-------------+---------------+----------+-----------+------------| | Application | Signaling | Not | Inelastic | Responsive | | Control | |applicable| | | |-------------+---------------+----------+-----------+------------| | | 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| ----------------------------------------------------------------- Figure 1. User/Subscriber Service Classes Grouping
Here is a short explanation of the 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 are needed. Responsive traffic is typically between a human and a server but can also 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.2.3. Service Class Characteristics
This document provides guidelines for network administrators 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. In addition, network administrators may choose to define and deploy other service classes in their network. 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 Recommendations Y.1541 and Y.1540.
------------------------------------------------------------------- |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
Notes for Figure 2: A "Yes" in the jitter-tolerant column implies that data is buffered in the endpoint and that a moderate level of network-induced variation in delay will not affect the application. Applications that use TCP as a transport are generally good examples. Routing protocols and peer-to-peer signaling also fall in this class; although 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 3 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, note 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 assignment with application examples. It is RECOMMENDED that this relationship be preserved end to end.
------------------------------------------------------------------ | 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 Notes for Figure 3: 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 base their choice of the service classes that they will support on their need, starting off with three or four service classes for user traffic and adding others as the need arises.
Figure 4 provides a summary of DiffServ QoS mechanisms that SHOULD be used for the defined service classes that are further detailed in Sections 3 and 4 of this document. According to what applications/services 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 RFC 2698)| | |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 RFC 2698)| | |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 RFC 2697)| | |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 RFC 2698)| | |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: 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 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 base their choice of the service classes that they will support on their need, starting off with three or four service classes for user traffic and adding 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 determines that he needs to provide different performance levels (quality of service) in his network for the services that he will be offering to his customers. He needs to enable his network to provide:
o Reliable VoIP (telephony) service, equivalent to Public Switched
Telephone Network (PSTN).
o A low-delay assured bandwidth data service.
o Support for 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.
o Standard service class for all traffic that will receive normal
(undifferentiated) forwarding treatment through the 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 needed 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 RFC 2697)| | |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 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 TV and on-demand movie viewing service to residential subscribers. o 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 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 that 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. ------------------------------------------------------------------- | 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 RFC 2698)| | |DSCP| |---------------+-------+-------------------+---------+--------+----| | Low- | AF21 | Using single-rate,| | |Yes | | Latency | AF22 |three-color marker | RFC2597 | Rate |per | | Data | AF23 | (such as RFC 2697)| | |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 RFC 2698)| | |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.
2.4.3. Example 3
An enterprise network administrator determines 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 Streaming 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 needed for delivery of service differentiation for Example 3. ------------------------------------------------------------------- | 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 RFC 2698)| | |DSCP| |---------------+-------+-------------------+---------+--------+----| | Multimedia | AF31 | Using two-rate, | | | Yes| | Streaming | AF32 | three-color marker| RFC2597 | Rate | per| | | AF33 | (such as RFC 2698)| | |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 RFC 2698)| | |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 "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.
3. Network Control Traffic
Network control traffic is defined as packet flows that are essential for stable operation of the administered network as well as 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 SHOULD be reserved for future use, potentially for future routing or control protocols. Network administrators MAY use a Local/Experimental DSCP; therefore, they may use 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 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 and the 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 as across a peering point between different administrative domains. Traffic transmitted in this service class is very important as it keeps the network operational, and it 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
Control 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 are examples of protocols and applications 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. The following are traffic characteristics of packet flows in the Network Control service class: o Mostly messages sent between routers and network servers. o Variable size packets, 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. The 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 the 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 that 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 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 Simple Network Management Protocol (SNMP), Trivial File Transfer Protocol (TFTP), FTP, Telnet, and Common Open Policy Service (COPS). 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 Provisioning and configuration of network elements. o Performance monitoring of network elements. o Any network operational alarms. The following are traffic characteristics: o Variable size packets. 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]. 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.
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