QoS – DSCP Classification Guidelines (RFC 4594)
April 19th, 2010
RFC 4594 describes some example and provides guidelines for DiffServ service classification which may be used as guidelines or as a basis for a QoS Classification Strategy:
RFC 4594 Guidelines for DiffServ Service Classes August 2006 ------------------------------------------------------------------- |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 RFC 4594 Guidelines for DiffServ Service Classes August 2006 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. RFC 4594 Guidelines for DiffServ Service Classes August 2006 ------------------------------------------------------------------ | 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. RFC 4594 Guidelines for DiffServ Service Classes August 2006 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 RFC 4594 Guidelines for DiffServ Service Classes August 2006 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: RFC 4594 Guidelines for DiffServ Service Classes August 2006 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 RFC 4594 Guidelines for DiffServ Service Classes August 2006 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. RFC 4594 Guidelines for DiffServ Service Classes August 2006 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. RFC 4594 Guidelines for DiffServ Service Classes August 2006 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. RFC 4594 Guidelines for DiffServ Service Classes August 2006 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.