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