Internet DRAFT - draft-ietf-tsvwg-dscp-considerations
draft-ietf-tsvwg-dscp-considerations
TSVWG A. Custura
Internet-Draft G. Fairhurst
Intended status: Informational R. Secchi
Expires: 4 September 2023 University of Aberdeen
3 March 2023
Considerations for Assigning a new Recommended DiffServ Codepoint (DSCP)
draft-ietf-tsvwg-dscp-considerations-13
Abstract
This document discusses considerations for assigning a new
recommended DiffServ Code Point (DSCP) for a new standard Per Hop
Behavior (PHB). It considers the common observed re-marking
behaviors that the DiffServ field might be subjected to along an
Internet path. It also notes some implications of using a specific
DSCP.
Status of This Memo
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This Internet-Draft will expire on 4 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Current usage of DSCPs . . . . . . . . . . . . . . . . . . . 4
3.1. IP-Layer Semantics . . . . . . . . . . . . . . . . . . . 4
3.2. DSCPs used for Network Control Traffic . . . . . . . . . 6
4. Re-marking the DSCP . . . . . . . . . . . . . . . . . . . . . 7
4.1. Bleaching the DSCP Field . . . . . . . . . . . . . . . . 8
4.2. IP Type of Service manipulations . . . . . . . . . . . . 9
4.2.1. Impact of ToS Precedence Bleaching . . . . . . . . . 9
4.2.2. Impact of ToS Precedence Re-marking . . . . . . . . . 11
4.3. Re-marking to a Particular DSCP . . . . . . . . . . . . . 12
5. Interpretation of the IP DSCP at Lower Layers . . . . . . . . 12
5.1. Mapping Specified for IEEE 802 . . . . . . . . . . . . . 12
5.1.1. Mapping Specified for IEEE 802.1 . . . . . . . . . . 13
5.1.2. Mapping Specified for IEEE 802.11 . . . . . . . . . . 13
5.2. DiffServ and MPLS . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Mapping Specified for MPLS . . . . . . . . . . . . . 15
5.2.2. Mapping Specified for MPLS Short Pipe . . . . . . . . 15
5.3. Mapping Specified for Mobile Networks . . . . . . . . . . 17
5.4. Mapping Specified for Carrier Ethernet . . . . . . . . . 18
5.5. Re-marking as a Side-effect of Another Policy . . . . . . 18
5.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Considerations for DSCP Selection . . . . . . . . . . . . . . 19
6.1. Effect of Bleaching and Re-marking to a single DSCP . . . 19
6.2. Where the proposed DSCP > 0x07 (7) . . . . . . . . . . . 19
6.2.1. Where the proposed DSCP&0x07=0x01 . . . . . . . . . . 19
6.3. Where the proposed DSCP <= 0x07 (7) . . . . . . . . . . . 20
6.4. Impact on deployed infrastructure . . . . . . . . . . . . 20
6.5. Considerations to guide the discussion of a proposed new
DSCP . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . 26
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The Differentiated Services (DiffServ) architecture has been deployed
in many networks. It provides differentiated traffic forwarding
based on the DiffServ Code Point (DSCP) [RFC2474] carried in the
DiffServ field [RFC2474] of the IP packet header. A common set of
DSCPs are defined for both IPv4 and IPv6, and both network protocols
use a common IANA registry [DSCP-registry].
DiffServ associates traffic with a service class [RFC4594] and
categorises it into Behavior Aggregates [RFC4594]. Configuration
guidelines for service classes are provided in RFC4594 [RFC4594].
Behavior aggregates are associated with a DiffServ Code Point (DSCP),
which in turn maps to a Per Hop Behavior (PHB). Treatment
differentiation can be achieved using a variety of schedulers and
queues, and also by algorithms that implement access to the physical
media.
Within a DiffServ domain, operators can set service level
specifications [RFC3086], each of which maps to a particular Per
Domain Behavior (PDB) that is based on one or more PHBs. The PDB
defines which PHB (or set of PHBs) and hence for a specific operator,
which DSCP (or set of DSCPs) will be associated with specific
Behavior Aggregates (BAs) as the packets pass through a DiffServ
domain, and whether the packets are re-marked as they are forwarded
(i.e., changing the DSCP of a packet [RFC2475]).
Application -> Service
Traffic Class
|
Behavior -> DiffServ -> Per Hop
Aggregate Codepoint Behavior
|
Schedule,
Queue, Drop
Figure showing the role of DSCPs in classifying IP traffic for
differential network treatment by a DiffServ Node.
This document discusses considerations for assigning a new DSCP for a
standard PHB. It considers some commonly observed DSCP re-marking
behaviors that might be experienced along an Internet path. It also
describes some packet forwarding treatments that a packet with a
specific DSCP can expect to receive when forwarded across a link or
subnetwork.
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The document is motivated by new opportunities to use DiffServ end-
to-end across multiple domains, such as [I-D.ietf-tsvwg-nqb],
proposals to build mechanisms using DSCPs in other standards-setting
organisations, and the desire to use a common set of DSCPs across a
range of infrastructure (e.g., [RFC8622], [I-D.ietf-tsvwg-nqb],
[I-D.learmonth-rfc1226-bis]).
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
DSCPs are specified in the IANA registry [DSCP-registry], where a
variety of different formats are described. A DSCP can sometimes be
referred to by name, such as "CS1", and sometimes by a decimal, hex,
or binary value. Hex values are represented in text using prefix 0x.
Binary values use prefix 0b.
3. Current usage of DSCPs
This section describes the current usage of DSCPs.
3.1. IP-Layer Semantics
The DiffServ architecture specifies the use of the DiffServ field in
the IPv4 and IPv6 packet headers to carry one of 64 distinct DSCP
values. Within a given administrative boundary, each DSCP value can
be mapped to a distinct PHB [RFC2474]. When a new PHB is specified,
a recommended DSCP value among those 64 values is normally reserved
for that PHB, and is assigned by IANA. An operator is not formally
required to use the recommended value; indeed [RFC2474] states that
"the mapping of codepoints to PHBs MUST be configurable." However,
use of the recommended value is usually convenient and avoids
confusion.
The DSCP space is divided into three pools for the purpose of
assignment and management [DSCP-registry]. A summary of the pools is
provided in a table (where 'x' refers to a bit position with value
either '0' or '1').
DSCP Pool 1: A pool of 32 codepoints with a format 0bxxxxx0, to be
assigned by IANA Standards Action [RFC8126].
DSCP Pool 2: A pool of 16 codepoints with a format of 0bxxxx11,
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reserved for experimental or local (private) use by network
operators (see Sections 4.1 and 4.2 of [RFC8126].
DSCP Pool 3: A pool of 16 codepoints with a format of 0bxxxx01.
This was initially available for experimental (EXP) or Local Use
(LU), but was originally specified to be "preferentially utilized
for standards assignments" if Pool 1 is ever exhausted. Pool 3
codepoints are now "utilized for standards assignments and are no
longer available for assignment to experimental or local use"
[RFC8436]. [RFC8622] assigned 0x01 from this pool and
consequentially updated [RFC4594]. Any future request to assign
0x05 would be expected to similarly update [RFC4594].
Note that [RFC4594] previously recommended a local use of DSCP values
0x01, 0x03, 0x05 and 0x07 (codepoints with the format of 0b000xx1),
until updated by [RFC8436].
The DSCP space is shown in the following table.
+---------+------+---------+-----+---------+-----+---------+----+
| 56/CS7 | 57 | 58 | 59 | 60 | 61 | 62 | 63 |
+---------+------+---------+-----+---------+-----+---------+----+
| 48/CS6 | 49 | 50 | 51 | 52 | 53 | 54 | 55 |
+---------+------+---------+-----+---------+-----+---------+----+
| 40/CS5 | 41 | 42 | 43 | 44/VA | 45 | 46/EF | 47 |
+---------+------+---------+-----+---------+-----+---------+----+
| 32/CS4 | 33 | 34/AF41 | 35 | 36/AF42 | 37 | 38/AF43 | 39 |
+---------+------+---------+-----+---------+-----+---------+----+
| 24/CS3 | 25 | 26/AF31 | 27 | 28/AF32 | 29 | 30/AF33 | 31 |
+---------+------+---------+-----+---------+-----+---------+----+
| 16/CS2 | 17 | 18/AF21 | 19 | 20/AF22 | 21 | 22/AF23 | 23 |
+---------+------+---------+-----+---------+-----+---------+----+
| 8/CS1 | 9 | 10/AF11 | 11 | 12/AF12 | 13 | 14/AF13 | 15 |
+---------+------+---------+-----+---------+-----+---------+----+
| 0/CS0 | 1/LE | 2 | 3 | 4 | 5 | 6 | 7 |
+---------+------+---------+-----+---------+-----+---------+----+
Table showing the currently assigned DSCPs and their assigned PHBs.
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+-----+-----------------------+-----------+
| CS | Class Selector | RFC 2474 |
+-----+-----------------------+-----------+
| BE | Best Effort (CS0) | RFC 2474 |
+-----+-----------------------+-----------+
| AF | Assured Forwarding | RFC 2597 |
+-----+-----------------------+-----------+
| EF | Expedited Forwarding | RFC 3246 |
+-----+-----------------------+-----------+
| VA | Voice Admit | RFC 5865 |
+-----+-----------------------+-----------+
| LE | Lower Effort | RFC 8622 |
+-----+-----------------------+-----------+
Table showing the summary of the DSCP abbreviations used in published
RFCs.
The above table summarises the DSCP abbreviations used in currently
published RFCs [RFC2474] [RFC2597] [RFC3246] [RFC5865] [RFC8622], as
described in the IANA registry [DSCP-registry]. BE, also known as
CS0, describes the default forwarding treatment.
NOTE: [RFC4594] specified a now deprecated use of Class Selector 1
(CS1) as the codepoint for the Lower Effort PHB. [RFC8622] updated
[RFC4594] and [RFC8325], and obsoleted [RFC3662], assigning the LE
DSCP codepoint to the Lower Effort PHB.
The DiffServ architecture allows forwarding treatments to be
associated with each DSCP, and the RFC series describes some of these
as PHBs. Although DSCPs are intended to identify specific treatment
requirements, multiple DSCPs might also be mapped (aggregated) to the
same forwarding treatment. DSCPs can be mapped to treatment
aggregates that might result in re-marking (e.g., RFC5160 [RFC5160]
suggests Meta-QoS-Classes to help enable deployment of standard end-
to-end QoS classes)
3.2. DSCPs used for Network Control Traffic
Network Control Traffic is defined as packet flows that are essential
for stable operation of the administered network (see [RFC4594],
Section 3). The traffic consists of the network control service
class and the OAM service class. This traffic is marked with a value
from a set of Class Selector (CS) DSCPs. This traffic is often a
special case within a provider network, and ingress traffic with
these DSCP markings can be re-marked.
DSCP CS2 is recommended for the OAM (Operations, Administration, and
Maintenance) service class (see [RFC4594], Section 3.3).
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DSCP CS6 is recommended for local network control traffic. This
includes routing protocols and OAM traffic that are essential to
network operation administration, control and management.
Section 3.2 of RFC4594 [RFC4594] recommends that "CS6 marked packet
flows from untrusted sources (for example, end-user devices) SHOULD
be dropped or re-marked at ingress to the DiffServ network".
DSCP CS7 is reserved for future use by network control traffic. "CS7
marked packets SHOULD NOT be sent across peering points" [RFC4594].
RFC2474 recommends PHBs selected by CS6 and CS7 "MUST give packets
preferential forwarding treatment by comparison to the PHB selected
by codepoint '000000'"[RFC2474].
At the time of writing, there is evidence to suggest CS6 is actively
used by network operators for control traffic. A study of traffic at
a large Internet Exchange showed around 40% of ICMP traffic carried
this mark [IETF115-IEPG]. Similarly, another study found many
routers re-mark all traffic, except for packets carrying a DSCP with
the format 0b11xxxx (i.e. setting the higher order bits to 0b11, see
Section 4.2.1 of this document).
4. Re-marking the DSCP
It is a feature of the DiffServ architecture that the DiffServ field
of packets can be re-marked at the Diffserv domain boundaries (see
Section 2.3.4.2 of [RFC2475]). A DSCP can be re-marked at the
ingress of a domain. This re-marking can change the DSCP value used
on the remainder of an IP path, or the network can restore the
initial DSCP marking at the egress of the domain. The DiffServ field
can also be re-marked based on common semantics and agreements
between providers at an exchange point. Furthermore, [RFC2474]
states that re-marking must occur when there is a possibility of
theft or denial-of-service attack.
The treatment of packets that are marked with an unknown or an
unexpected DSCP at DiffServ domain boundaries is determined by the
policy for a DiffServ domain. If packets are received that are
marked with an unknown or an unexpected DSCP by a DiffServ domain
interior node, [RFC2474] recommends forwarding the packet using a
default (best effort) treatment, but without changing the DSCP. This
seeks to support incremental DiffServ deployment in existing networks
as well as preserve DSCP markings by routers that have not been
configured to support DiffServ. (See also Section 4.3). [RFC3260]
clarifies that this re-marking specified by RFC2474 is intended for
interior nodes within a DiffServ domain. For DiffServ ingress nodes
the traffic conditioning required by RFC 2475 applies first.
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Reports measuring existing deployments have defined a set of
categories for DSCP re-marking [Cus17] [Bar18] into the following
seven observed re-marking behaviors:
Bleach-DSCP: bleaches all traffic (sets the DSCP to zero);
Bleach-ToS-Precedence: set the first three bits of the DSCP field to
0b000 (reset the 3 bits of the former ToS Precedence field,
defined in [RFC0791], and clarified in [RFC1122]);
Bleach-some-ToS: set the first three bits of the DSCP field to 0b000
(reset the 3 bits of the former ToS Precedence field), unless the
first two bits of the DSCP field are 0b11;
Re-mark-ToS: set the first three bits of the DSCP field to any value
different from 0b000 (replace the 3 bits of the former ToS
Precedence field);
Bleach-low: set the last three bits of the DSCP field to 0b000;
Bleach-some-low: set the last three bits of the DSCP field to 0b000,
unless the first two bits of the DSCP field are 0b11;
Re-mark-DSCP: re-marks all traffic to one or more particular (non-
zero) DSCP values.
These behaviours are explained in the following subsections and
cross-referenced in the remainder of the document.
The network nodes forming a particular path might or might not have
supported DiffServ. It is not generally possible for an external
observer to determine which mechanism results in a specific re-
marking solely from the change in an observed DSCP value.
NOTE: More than one mechanism could result in the same DSCP re-
marking (see below). These behaviors were measured on both IPv4 and
IPv6 Internet paths between 2017 and 2021[Cus17]. IPv6 routers were
found to perform all the types of re-marking described above to a
lesser extent than IPv4 ones.
4.1. Bleaching the DSCP Field
A specific form of re-marking occurs when the DiffServ field is re-
assigned to the default treatment, CS0 (0x00). This results in
traffic being forwarded using the BE PHB. For example, AF31 (0x1a)
would be bleached to CS0.
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A survey reported that resetting all the bits of the DiffServ field
to 0 was seen to be more prevalent at the edge of the network, and
rather less common in core networks [Cus17].
4.2. IP Type of Service manipulations
The IETF first defined ToS precedence for IP packets in [RFC0791],
and updated it to be part of the ToS Field in [RFC1349]. Since 1998,
this practice has been deprecated by [RFC2474]. RFC 2474 defines
DSCPs 0bxxx000 as the Class Selector codepoints, where PHBs selected
by these codepoints MUST meet the Class Selector PHB Requirements"
described in Sec. 4.2.2.2 of that RFC.
However, a recent survey reports practices based on ToS semantics
have not yet been eliminated from the Internet, and need to still be
considered when making new DSCP assignments [Cus17].
4.2.1. Impact of ToS Precedence Bleaching
Bleaching of the ToS Precedence field (Bleach-ToS-Precedence
(Section 4)) resets the first three bits of the DSCP field to zero
(the former ToS Precedence field), leaving the last three bits
unchanged (see Section 4.2.1 of [RFC2474]). A DiffServ node can be
configured in a way that results in this re-marking. This re-marking
can also occur when packets are processed by a router that is not
configured with DiffServ (e.g., configured to operate on the former
ToS precedence field [RFC0791]). At the time of writing, this is a
common manipulation of the DiffServ field. The following
Figure depicts this re-marking.
+-+-+-+-+-+-+
|0 0 0|x x x|
+-+-+-+-+-+-+
Figure showing bleaching of the ToS Precedence (Bleach-ToS-Precedence
(Section 4)), based on Section 3 of [RFC1349]. The bit positions
marked "x" are not changed.
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+--------+------+---------+----+---------+----+---------+----+
| 56/CS7 | 57 | 58 | 59 | 60 | 61 | 62 | 63 |
+--------+------+---------+----+---------+----+---------+----+
| 48/CS6 | 49 | 50 | 51 | 52 | 53 | 54 | 55 |
+--------+------+---------+----+---------+----+---------+----+
| 40/CS5 | 41 | 42 | 43 | 44/VA | 45 | 46/EF | 47 |
+--------+------+---------+----+---------+----+---------+----+
| 32/CS4 | 33 | 34/AF41 | 35 | 36/AF42 | 37 | 38/AF43 | 39 |
+--------+------+---------+----+---------+----+---------+----+
| 24/CS3 | 25 | 26/AF31 | 27 | 28/AF32 | 29 | 30/AF33 | 31 |
+--------+------+---------+----+---------+----+---------+----+
| 16/CS2 | 17 | 18/AF21 | 19 | 20/AF22 | 21 | 22/AF23 | 23 |
+--------+------+---------+----+---------+----+---------+----+
| 8/CS1 | 9 | 10/AF11 | 11 | 12/AF12 | 13 | 14/AF13 | 15 |
+========+======+=========+====+=========+====+=========+====+
| 0/CS0 | 1/LE | 2 | 3 | 4 | 5 | 6 | 7 |
+========+======+=========+====+=========+====+=========+====+
Table of DSCP values. As a result of ToS Precedence Bleaching, each
of the DSCPs in a column are re-marked to the smallest DSCP in that
column. Therefore, the DSCPs in the bottom row have higher
survivability across an end-to-end Internet path.
Data on the observed re-marking at the time of writing was presented
in [IETF115-IEPG].
+=======+======+=============+====+======+===+=========+====+
| 0/CS0 | 1/LE | 2 | 3 | 4 | 5 | 6 | 7 |
+=======+======+=============+====+======+===+=========+====+
|Assigned |Re-marked |EXP/| * | |Re-marked|EXP/|
| |from AF11..41|LU | | |from |LU |
| | | | | |AF13..EF | |
+==============+=============+====+======+===+=========+====+
Table showing 0b000xxx DSCPs. This highlights any current
assignments and whether they are affected by any known re-marking
behaviors, such as ToS Precdence bleaching. * DSCP 4 has been
historically used by the SSH application. [Kol10].
DSCPs of the form 0b000xxx can be impacted by known re-marking
behaviours of other assigned DSCPs. For example, ToS Precedence
Bleaching of popular DSCPs AF11, AF21, AF31, AF41 would result in
traffic being re-marked with DSCP 2 in the Internet core. The Lower-
Effort Per-Hop Behavior PHB (LE) uses a DSCP of 1. The DSCP value of
4 has been historically used by the SSH application, following
semantics that precede DiffServ [Kol10].
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Bleach-ToS-Precedence (Section 4) of packets with a DSCP 'x' result
in the DSCP being re-marked to 'x' & 0x07 and then forwarded using
the PHB specified for the resulting DSCP in that Diffserv domain. In
subsequent networks the packet will receive treatment as specified by
the domain's operator corresponding to the re-marked codepoint.
A variation of this observed re-marking behavior clears the top three
bits of a DSCP, unless these have values 0b110 or 0b111
(corresponding to the CS6 and CS7 DSCPs). As a result, a DSCP value
greater than 48 decimal (0x30) is less likely to be impacted by ToS
Precedence Bleaching.
4.2.2. Impact of ToS Precedence Re-marking
[RFC2474] states "Implementors should note that the DSCP field is six
bits wide. DS-compliant nodes MUST select PHBs by matching against
the entire 6-bit DSCP field, e.g., by treating the value of the field
as a table index which is used to select a particular packet handling
mechanism which has been implemented in that device". This replaced
re-marking according to ToS precedence (Re-mark-ToS (Section 4))
[RFC1349]. These practices based on ToS semantics have not yet been
eliminated from deployed networks.
+-+-+-+-+-+-+
|0 0 1|x x x|
+-+-+-+-+-+-+
Figure showing the ToS Precedence Re-marking (Re-mark-ToS
(Section 4)) observed behavior, based on Section 3 of [RFC1349]. The
bit positions marked "x" remain unchanged.
A less common re-marking, ToS Precedence Re-marking sets the first
three bits of the DSCP to a non-zero value corresponding to a CS PHB.
This re-marking occurs when routers are not configured to perform
DiffServ re-marking.
If ToS Precedence Re-marking occurs, packets are forwarded using the
PHB specified for the resulting DSCP in that domain. For example,
the AF31 DSCP (0x1a) could be re-marked to either AF11 or AF21. If
such a re-marked packet further traverses other Diffserv domains, it
would receive treatment as specified by each domain's operator
corresponding to the re-marked codepoint.
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4.3. Re-marking to a Particular DSCP
A network device might re-mark the DiffServ field of an IP packet
based on a local policy with a specific (set of) DSCPs (Re-mark-DSCP
(Section 4)).
Section 3 of [RFC2474] recommends: "Packets received with an
unrecognized codepoint SHOULD be forwarded as if they were marked for
the Default behavior, and their codepoints should not be changed."
Some networks might not follow this recommendation and instead re-
mark packets with these codepoints to the default class, CS0 (0x00).
This re-marking is sometimes performed using a Multi-Field (MF)
classifier [RFC2475] [RFC3290] [RFC4594].
If re-marking occurs, packets are forwarded using the PHB specified
for the resulting DSCP in that domain. As an example, re-marking
traffic AF31, AF32 and AF33 all to a single DSCP, e.g. AF11, stops
any drop probability differentiation, which may have been expressed
by these three DSCPs. If such a re-marked packet further traverses
other domains, it would receive treatment as specified by the
domain's operator corresponding to the re-marked codepoint.
Bleaching (Bleach-DSCP (Section 4)) is a specific example of this
observed re-marking behavior that re-marks to CS0 (0x00) - see
Section 4.1.
5. Interpretation of the IP DSCP at Lower Layers
Transmission systems and subnetworks can, and do, utilize the
DiffServ field in an IP packet to set a QoS-related field or function
at the lower layer. A lower layer could also implement a traffic
conditioning function that could re-mark the DSCP used at the IP
layer. This function is constrained by designs that utilize fewer
than 6 bits to express the service class, and therefore infer a
mapping to a smaller L2 QoS field, for example, the 3-bit PCP field
in an IEEE Ethernet 802.1Q header, the 3-bit UP field or the 3-bit
Traffic Class field of Multi-Protocol Label Switching (MPLS). A
Treatment Aggregate (TA) [RFC5127] is an optional intermediary
mapping groups of BAs to PHBs.
5.1. Mapping Specified for IEEE 802
The IEEE specifies standards that include mappings for DSCPs to lower
layer elements.
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5.1.1. Mapping Specified for IEEE 802.1
IEEE 802.1Q specified a 3-bit Priority Code Point (PCP) field, which
includes a tag that allows Ethernet frames to be marked as one of
eight priority values [IEEE-802-1Q]. Use of this field is described
by various documents, including IEEE P802.1p, and IEEE 802.1D.
The mapping specified in [IEEE-802-1Q] revises a previous standard
[IEEE-802-1D], in an effort to align with DiffServ practice
[RFC4594]. In 802.1Q, the traffic types are specified to match the
first three bits of a suitable DSCP (e.g., the first three bits of
the EF DSCP are mapped to a PCP of 5).
In this mapping, PCP0 is used to indicate the default best effort
treatment, and PCP1 indicates a background traffic class. This
aligned with the now deprecated use of CS1 as the codepoint for the
lower effort service, as previously specified in [RFC4594]. The
remaining PCP values indicate increasing priority. Internet control
traffic can be marked as CS6, and network control is marked as CS7.
Other re-marking behaviors have also been implemented in Ethernet
equipment. Historically, a previous standard [IEEE-802-1D] used both
PCP1 (Background) and PCP2 (Spare) to indicate lower priority than
PCP0, and some other devices do not assign a lower priority to PCP1.
5.1.2. Mapping Specified for IEEE 802.11
Section 6 of [RFC8325] provides a brief overview of IEEE 802.11 QoS.
The IEEE 802.11 standards [IEEE-802-11] provide MAC functions to
support QoS in WLANs using Access Classes (AC). The upstream User
Priority (UP) in the 802.11 header has a 3-bit QoS value. A DSCP can
be mapped to the UP. [RFC8622] added mapping for the LE DSCP,
mapping this to AC_BK (Background)
Most current Wi-Fi implementations use a default mapping that maps
the first three bits of the DSCP to the 802.11 UP value. This is an
example of equipment still classifying on ToS Precedence (which could
be seen as a simple method to map IP layer DiffServ to layers
offering only 3-bit QoS codepoints). Then, in turn, this is mapped
to the four Wi-Fi Multimedia (WMM) Access Categories. The Wi-Fi
Alliance has also specified a more flexible mapping that follows
RFC8325 and provides functions at an AP to re-mark packets as well as
a QoS Map that maps each DSCP to an AC [WIFI-ALLIANCE].
+-+-+-+-+-+-+
|x x x|. . .|
+-+-+-+-+-+-+
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Figure showing the DSCP bits commonly mapped to the UP in 802.11.
The bit positions marked "x" are mapped to the 3-bit UP value, while
the ones marked "." are ignored.
RFC8325 [RFC8325] notes inconsistencies that can result from such re-
marking, and recommends a different mapping to perform this re-
marking, dependent on the direction in which a packet is forwarded.
It provides recommendations for mapping a DSCP to an IEEE 802.11 UP
for interconnection between wired and wireless networks. The
recommendation in Section 5.1.2 maps network control traffic, CS6 and
CS7, as well as unassigned DSCPs, to UP 0 when forwarding in the
upstream direction (wireless-to-wired). It also recommends mapping
CS6 and CS7 traffic to UP 7, when forwarding in the downstream
direction (Section 4.1).
For other UPs, RFC8325 recommends a mapping in the upstream direction
that derives the DSCP from the value of the UP multiplied by 8. This
mapping can result in a specific DSCP re-marking behavior.
In the upstream direction (wireless-to-wired interconnections), this
mapping can result in a specific DSCP re-marking behavior. Some
Access Points (APs) currently use a default UP-to-DSCP mapping
[RFC8325], wherein "DSCP values are derived from the layer 2 UP
values by multiplying the UP values by eight (i.e., shifting the
three UP bits to the left and adding three additional zeros to
generate a 6-bit DSCP value). This derived DSCP value is used for
QoS treatment between the wireless AP and the nearest classification
and marking policy enforcement point (which may be a central wireless
LAN controller, relatively deep within the network). Alternatively,
in the case where there is no other classification and marking policy
enforcement point, then this derived DSCP value will be used on the
remainder of the Internet path." This can result in re-marking by
Bleach-low (Section 4).
+-+-+-+-+-+-+
|x x x|0 0 0|
+-+-+-+-+-+-+
Figure showing the observed re-marking behavior resulting from
deriving from UP-to-DSCP mapping in some 802.11 networks.
An alternative to UP-to-DSCP remapping uses the DSCP value of a
downstream IP packet (e.g., the Control And Provisioning of Wireless
Access Points (CAPWAP) protocol, RFC5415 [RFC5415], maps an IP packet
DiffServ field to the DiffServ field of the outer IP header in a
CAPWAP tunnel).
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Some current constraints of Wi-Fi mapping are discussed in Section 2
of [RFC8325]. A QoS profile can be used to limit the maximum DSCP
value used for the upstream and downstream traffic.
5.2. DiffServ and MPLS
Multi-Protocol Label Switching (MPLS) specified eight MPLS Traffic
Classes (TCs), which restrict the number of different treatments
[RFC5129]. RFC 5127 describes the aggregation of DiffServ TCs
[RFC5127] and introduces four DiffServ Treatment Aggregates. Traffic
marked with multiple DSCPs can be forwarded in a single MPLS TC.
There are three Label-Switched Router (LSR) models: the Pipe, the
Short Pipe and the Uniform Model [RFC3270]. In the Uniform and Pipe
models, the egress MPLS router forwards traffic based on the received
MPLS TC. The Uniform Model includes an egress DSCP rewrite. With
the Short Pipe Model, the egress MPLS router forwards traffic based
on the DiffServ DSCP as present at the egress router. If the domain
supports IP and MPLS QoS differentiation, controlled behavior
requires the DSCP of an (outer) IP header to be assigned or re-
written by all domain ingress routers to conform with the domain's
internal DiffServ deployment. Note that the Short Pipe Model is
prevalent in MPLS domains.
5.2.1. Mapping Specified for MPLS
RFC3270 [RFC3270] defines a flexible solution for support of DiffServ
over MPLS networks. This allows an MPLS network administrator to
select how BAs (marked by DSCPs) are mapped onto Label Switched Paths
(LSPs) to best match the DiffServ, Traffic Engineering and protection
objectives within their particular network.
Mappings from the IP DSCP to the MPLS header are defined in
Section 4.2 of [RFC3270].
The Pipe Model conveys the "LSP Diff-Serv Information" to the LSP
Egress so that its forwarding treatment can be based on the IP DSCP.
When Penultimate Hop Popping (PHP) is used, the Penultimate LSR needs
to be aware of the encapsulation mapping for a PHB to the label
corresponding to the exposed header to perform DiffServ Information
Encoding (Section 2.5.2 of [RFC3270]).
5.2.2. Mapping Specified for MPLS Short Pipe
The Short Pipe Model is an optional variation of the Pipe Model
[RFC3270].
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ITU-T Y.1566 [ITU-T-Y-1566] further defined a set of four common QoS
classes and four auxiliary classes to which a DSCP can be mapped when
interconnecting Ethernet, IP and MPLS networks. [RFC8100] describes
four treatment aggregates for interconnection with four defined
DSCPs. This was motivated by the requirements of MPLS network
operators that use Short-Pipe tunnels, but can be applicable to other
networks, both MPLS and non-MPLS.
RFC8100 recommends preserving the notion of end-to-end service
classes, and recommends a set of standard DSCPs mapped to a small set
of standard PHBs at interconnection. The key requirement is that the
DSCP at the network ingress is restored at the network egress. The
current version of RFC8100 limits the number of DSCPs to 6 and 3 more
are suggested for extension. RFC8100 respects the deployment of PHB
groups for DS domain internal use, which limits the number of
acceptable external DSCPs (and possibilities for their transparent
transport or restoration at network boundaries). In this design,
packets marked with DSCPs not part of the RFC8100 codepoint scheme
are treated as unexpected and will possibly be re-marked (a
Re-mark-DSCP (Section 4) behavior) or dealt with via an additional
agreement(s) among the operators of the interconnected networks.
RFC8100 can be extended to support up to 32 DSCPs by future
standards. RFC8100 is operated by at least one Tier 1 backbone
provider. Use of the MPLS Short Pipe Model favours re-marking
unexpected DSCP values to zero in the absence of an additional
agreement(s), as explained in [RFC8100]. This can result in
bleaching (Bleach-DSCP (Section 4)).
+--------------------------------------+--------+
| RFC8100 | DSCP |
| Agg. Class | |
+--------------------------------------+--------+
|Telephony Service Treatment Aggregate | EF |
| | VA |
+--------------------------------------+--------+
|Bulk Real-Time Treatment Aggregate | AF41 |
| May be added | (AF42) |
| May be added | (AF43) |
+--------------------------------------+--------+
|Assured Elastic Treatment Aggregate | AF31 |
| | AF32 |
| Reserved for the extension of PHBs| (AF33) |
+--------------------------------------+--------+
|Default / Elastic Treatment Aggregate | BE/CS0 |
+--------------------------------------+--------+
|Network Control: Local Use (LU) | CS6 |
+--------------------------------------+--------+
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Table: The short-pipe MPLS mapping from RFC 8100.
5.3. Mapping Specified for Mobile Networks
Mobile LTE and 5G standards have evolved from older UMTS standards,
and support DiffServ. LTE (4G) and 5G standards [SA-5G] identify
traffic classes at the interface between User Equipment (UE) and the
mobile Packet Core network by QCI (QoS Class Identifiers) and 5QI (5G
QoS Identifier). The 3GPP standards do not define or recommend any
specific mapping between each QCI or 5QI and DiffServ (and mobile
QCIs are based on several criteria service class definitions). The
way packets are mapped at the Packet Gateway (P-GW) boundary is
determined by network operators. However, TS 23.107 (version 16.0.0,
applies to LTE and below) mandates that Differentiated Services,
defined by IETF, shall be used to interoperate with IP backbone
networks.
The GSM Association (GSMA) has defined four aggregated classes and
seven associated PHBs in their guidelines for IPX Provider networks
[GSMA-IR-34]. This was previously specified as the Inter-Service
Provider IP Backbone Guidelines, and provides a mobile ISP to ISP QoS
mapping mechanism, and interconnection with other IP networks in the
general Internet. If provided an IP VPN, the operator is free to
apply its DS Domain internal codepoint scheme at outer headers and
inner IPX DSCPs may be transported transparently. The guidelines
also describe a case where the DSCP marking from a Service Provider
cannot be trusted (depending on the agreement between the Service
Provider and its IPX Provider), in which situation the IPX Provider
can re-mark the DSCP value to a static default value.
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+---------------+-------+
| GSMA IR.34 | PHB |
| Agg. Class | |
+---------------+-------+
|Conversational | EF |
+---------------+-------+
| Streaming | AF41 |
+---------------+-------+
| Interactive | AF31 |
+ +-------+
| (ordered by | AF32 |
+ priority, +-------+
| AF3 highest) | AF21 |
+ +-------+
| | AF11 |
+---------------+-------+
| Background | CS0 |
+---------------+-------+
Table showing the PHB mapping recommended in the guidelines
recommended in [GSMA-IR-34].
5.4. Mapping Specified for Carrier Ethernet
Metro Ethernet Forum (MEF) provides a mapping of DSCPs at the IP
layer to quality of service markings in the Ethernet frame headers
[MEF23.1].
5.5. Re-marking as a Side-effect of Another Policy
This includes any other re-marking that does not happen as a result
of traffic conditioning, such as policies and L2 procedures that
result in re-marking traffic as a side-effect of other functions
(e.g., in response to Distributed Denial of Service, DDoS).
5.6. Summary
This section has discussed the various ways in which DSCP re-marking
behaviors can arise from interactions with lower layers.
A provider service path may consist of sections where multiple and
changing layers use their own code points to determine differentiated
forwarding (e.g., IP - MPLS - IP - Ethernet - Wi-Fi).
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6. Considerations for DSCP Selection
This section provides advice for the assignment of a new DSCP value.
It is intended to aid the IETF and IESG in considering a request for
a new DSCP. The section identifies known issues that might influence
the finally assigned DSCP, and provides a summary of considerations
for assignment of a new DSCP.
6.1. Effect of Bleaching and Re-marking to a single DSCP
Section 4 describes re-marking of the DSCP. New DSCP assignments
should consider the impact of bleaching (Bleach-DSCP (Section 4)) or
re-marking (Re-mark-DSCP (Section 4)) to a single DSCP, which can
limit the ability to provide the expected treatment end-to-end. This
is particularly important for cases where the codepoint is intended
to result in lower than best effort treatment, as was the case when
defining the LE PHB [RFC8622]. Forwarding LE using the default PHB
is in line with RFC8622, but it is recommended to maintain the
distinct LE DSCP codepoint end-to-end to allow for differentiated
treatment by domains supporting LE. Rewriting the LE DSCP to the
default class (CS0) results in an undesired promotion of the priority
for LE traffic in such a domain. Bleaching the lower three bits of
the DSCP (both Bleach-low (Section 4) and Bleach-some-low
(Section 4)), as well as re-marking to a particular DSCP can result
in similar changes of priority relative to traffic that is marked
with other DSCPs.
6.2. Where the proposed DSCP > 0x07 (7)
Although the IETF specifications require systems to use DSCP marking
semantics in place of methods based on the former ToS field, the
current recommendation is that any new assignment where the DSCP is
greater than 0x07 should consider the semantics associated with the
resulting DSCP when the ToS Precedence is bleached
(Bleach-ToS-Precedence (Section 4) and Bleach-some-ToS (Section 4))
or ToS Precedence Re-marking (Re-mark-ToS (Section 4)) is
experienced. For example, it can be desirable to avoid choosing a
DSCP that could be re-marked to LE, Lower Effort [RFC8622], which
could otherwise potentially result in a priority inversion in the
treatment.
6.2.1. Where the proposed DSCP&0x07=0x01
As a consequence of assigning the LE PHB [RFC8622], the IETF
allocated the DSCP 0b000001 from Pool 3.
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When making assignments where the DSCP has a format: 0bxxx001, the
case of Bleach-ToS-Precedence (Section 4) of a DSCP to a value of
0x01 needs to be considered. ToS Precedence Bleaching will result in
demoting the traffic to the lower effort traffic class. Care should
be taken to consider the implications of re-marking when choosing to
assign a DSCP with this format.
6.3. Where the proposed DSCP <= 0x07 (7)
ToS Precedence Bleaching or ToS Precedence Re-marking can
unintentionally result in extra traffic aggregated to the same DSCP.
For example, after experiencing ToS Precedence Bleaching, all traffic
marked AF11, AF21, AF31 and AF41 would be aggregated with traffic
marked with DSCP 2 (0x02), increasing the volume of traffic which
receives the treatment associated with DSCP 2. New DSCP assignments
should consider unexpected consequences arising from this observed
re-marking behavior.
6.4. Impact on deployed infrastructure
Behavior of deployed PHBs and conditioning treatments also needs to
be considered when assigning a new DSCP. Network operators have
choices when it comes to configuring DiffServ support within their
domains, and the observed re-marking behaviors described in the
previous section can result from different configurations and
approaches:
Networks not re-marking DiffServ: A network that either does not
implement PHBs, or implements one or more PHBs whilst restoring
the DSCP field at network egress with the value at network
ingress. Operators in this category pass all DSCPs transparently.
Networks that condition the DSCP: A network that implements more
than one PHB and enforces Service Level Agreements (SLAs) with its
peers. Operators in this category use conditioning to ensure that
only traffic that matches a policy is permitted to use a specific
DSCP (see [RFC8100]). Operators need to classify the received
traffic, assign it to a corresponding PHB, and could re-mark the
DSCP to a value that is appropriate for the domain's deployed
DiffServ infrastructure.
Networks that re-mark in some other way, which includes:
1. Networks containing misconfigured devices that do not comply
with the relevant RFCs.
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2. Networks containing devices that implement an obsolete
specification or contain software bugs.
3. Networks containing devices that re-mark the DSCP as a result
of lower layer interactions.
The DSCP re-marking corresponding to the Bleach-ToS-Precedence
(Section 4) observed behavior described in Section 4 can arise for
various reasons, one of which is old equipment which precedes
DiffServ. The same re-marking can also arise in some cases when
traffic conditioning is provided by DiffServ routers at operator
boundaries or as a result of misconfiguration.
6.5. Considerations to guide the discussion of a proposed new DSCP
A series of questions emerge that need to be answered when
considering a proposal to the IETF that requests a new assignment.
These questions include:
* Is the request for local use within a DiffServ domain that does
not require interconnection with other DiffServ domains? This
request can use DSCPs in Pool 2 for local or experimental use,
without any IETF specification for the DSCP or associated PHB.
* What are the characteristics of the proposed service class?: What
are the characteristics of the traffic to be carried? What are
the expectations for treatment?
* Service classes [RFC4594] that can utilize existing PHBs should
use assigned DSCPs to mark their traffic: Could the request be met
by using an existing IETF DSCP?
* Specification of a new recommended DSCP requires Standards Action.
RFC2474 states: "Each standardized PHB MUST have an associated
RECOMMENDED codepoint". If approved, new IETF assignments are
normally made by IANA in Pool 1, but the IETF can request
assignments to be made from Pool 3 [RFC8436]. Does the Internet
Draft contain an appropriate request to IANA?
* The value selected for a new DSCP can impact the ability of an
operator to apply logical functions (e.g., a bitwise mask) to
related codepoints when configuring DiffServ. A suitable value
can simplify configurations by aggregating classification on a
range of DSCPs. This classification based on DSCP ranges can
increase the comprehensibility of documenting forwarding
differentiation.
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* Section 5.2 describes examples of treatment aggregation. What are
the effects of treatment aggregation on the proposed DSCP?
* Section 5 describes some observed treatments by layers below IP.
What are the implications of the treatments and mapping described
in Section 5 on the proposed DSCP?
* DSCPs are assigned to PHBs and can be used to enable nodes along
an end-to-end path to classify the packet for a suitable PHB.
Section 4 describes some observed re-marking behavior, and
Section 6.4 identifies root causes for why this re-marking is
observed. What is the expected effect of currently-deployed re-
marking on the service, end-to-end or otherwise?
7. Acknowledgements
The authors acknowledge the helpful discussions and analysis by Greg
White and Thomas Fossati in a draft concerning NQB. Ruediger Geib
and Brian Carpenter contributed comments, along with other members of
the TSVWG.
8. IANA Considerations
IANA is requested to append the page for the Differentiated Services
Field Codepoints (DSCP) registry at:
https://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml.
This request is to add the following separate paragraph to the Note
at the top of the registry page: "See [RFC-to-be] for considerations
when assigning a new codepoint from the DSCP registry."
9. Security Considerations
The security considerations are discussed in the security
considerations of each cited RFC.
10. References
10.1. Normative References
[DSCP-registry]
IANA, "Differentiated Services Field Codepoints (DSCP)
Registry", https://www.iana.org/assignments/dscp-
registry/dscp-registry.xhtml, 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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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,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<https://www.rfc-editor.org/info/rfc3260>.
[RFC3290] Bernet, Y., Blake, S., Grossman, D., and A. Smith, "An
Informal Management Model for Diffserv Routers", RFC 3290,
DOI 10.17487/RFC3290, May 2002,
<https://www.rfc-editor.org/info/rfc3290>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
[RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
Marking in MPLS", RFC 5129, DOI 10.17487/RFC5129, January
2008, <https://www.rfc-editor.org/info/rfc5129>.
[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <https://www.rfc-editor.org/info/rfc8100>.
[RFC8436] Fairhurst, G., "Update to IANA Registration Procedures for
Pool 3 Values in the Differentiated Services Field
Codepoints (DSCP) Registry", RFC 8436,
DOI 10.17487/RFC8436, August 2018,
<https://www.rfc-editor.org/info/rfc8436>.
10.2. Informative References
[Bar18] Barik, R., Welzl, M., Elmokashfi, A., Dreibholz, T., and
S. Gjessing, "Can WebRTC QoS Work? A DSCP Measurement
Study", ITC 30, September 2018.
[Cus17] Custura, A., Venne, A., and G. Fairhurst, "Exploring DSCP
modification pathologies in mobile edge networks", TMA ,
2017.
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[GSMA-IR-34]
GSM Association, "IR.34 Guidelines for IPX Provider
networks (Previously Inter-Service Provider IP Backbone
Guidelines)", IR 34, 2017.
[I-D.ietf-tsvwg-nqb]
White, G. and T. Fossati, "A Non-Queue-Building Per-Hop
Behavior (NQB PHB) for Differentiated Services", Work in
Progress, Internet-Draft, draft-ietf-tsvwg-nqb-15, 11
January 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-tsvwg-nqb-15>.
[I-D.learmonth-rfc1226-bis]
Learmonth, I. R., "Internet Protocol Encapsulation of
AX.25 Frames", Work in Progress, Internet-Draft, draft-
learmonth-rfc1226-bis-03, 19 May 2020,
<https://datatracker.ietf.org/doc/html/draft-learmonth-
rfc1226-bis-03>.
[IEEE-802-11]
IEEE, "Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications", IEEE 802.11, 2007.
[IEEE-802-1D]
IEEE, "IEEE Standard for Local and Metropolitan Area
Network-- Media Access Control (MAC) Bridges",
IEEE 802.1D, 2004.
[IEEE-802-1Q]
IEEE, "IEEE Standard for Local and Metropolitan Area
Network-- Bridges and Bridged Networks", IEEE 802.1Q,
2018.
[IETF115-IEPG]
Custura, A., "Real-world DSCP Traversal Measurements",
online
https://datatracker.ietf.org/meeting/115/materials/slides-
115-iepg-sessa-considerations-for-assigning-dscps-01,
2022.
[ITU-T-Y-1566]
ITU-T, "Quality of Service Mapping and Interconnection
Between Ethernet, Internet Protocol and Multiprotocol
Label Switching Networks", ITU-T Y.1566, 2012.
[Kol10] Kolu, A., "Bogus DSCP value for SSH", online
https://lists.freebsd.org/pipermail/freebsd-
stable/2010-July/057710.html, 2010.
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[MEF23.1] MEF, "MEF Technical Specification MEF 23.1-- Carrier
Ethernet Class of Service ? Phase 2", MEF 23.1, 2012.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1349] Almquist, P., "Type of Service in the Internet Protocol
Suite", RFC 1349, DOI 10.17487/RFC1349, July 1992,
<https://www.rfc-editor.org/info/rfc1349>.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597,
DOI 10.17487/RFC2597, June 1999,
<https://www.rfc-editor.org/info/rfc2597>.
[RFC3086] Nichols, K. and B. Carpenter, "Definition of
Differentiated Services Per Domain Behaviors and Rules for
their Specification", RFC 3086, DOI 10.17487/RFC3086,
April 2001, <https://www.rfc-editor.org/info/rfc3086>.
[RFC3246] Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
Boudec, J.Y., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002,
<https://www.rfc-editor.org/info/rfc3246>.
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, DOI 10.17487/RFC3270, May 2002,
<https://www.rfc-editor.org/info/rfc3270>.
[RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
Per-Domain Behavior (PDB) for Differentiated Services",
RFC 3662, DOI 10.17487/RFC3662, December 2003,
<https://www.rfc-editor.org/info/rfc3662>.
[RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of
Diffserv Service Classes", RFC 5127, DOI 10.17487/RFC5127,
February 2008, <https://www.rfc-editor.org/info/rfc5127>.
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[RFC5160] Levis, P. and M. Boucadair, "Considerations of Provider-
to-Provider Agreements for Internet-Scale Quality of
Service (QoS)", RFC 5160, DOI 10.17487/RFC5160, March
2008, <https://www.rfc-editor.org/info/rfc5160>.
[RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415,
DOI 10.17487/RFC5415, March 2009,
<https://www.rfc-editor.org/info/rfc5415>.
[RFC5865] Baker, F., Polk, J., and M. Dolly, "A Differentiated
Services Code Point (DSCP) for Capacity-Admitted Traffic",
RFC 5865, DOI 10.17487/RFC5865, May 2010,
<https://www.rfc-editor.org/info/rfc5865>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to
IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February
2018, <https://www.rfc-editor.org/info/rfc8325>.
[RFC8622] Bless, R., "A Lower-Effort Per-Hop Behavior (LE PHB) for
Differentiated Services", RFC 8622, DOI 10.17487/RFC8622,
June 2019, <https://www.rfc-editor.org/info/rfc8622>.
[SA-5G] 3GPP, "System Architecture for 5G", TS 23.501, 2019.
[WIFI-ALLIANCE]
Wi-Fi Alliance, "Wi-Fi QoS Management Specification
Version 2.0", Wi-Fi QoS Management Specification
Version 2.0, 2021.
Appendix A. Revision Notes
Note to RFC-Editor: please remove this entire section prior to
publication.
* Individual draft -00, initial document.
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* Individual draft -01, address comments from Martin Duke; Brian
Carpenter; Ruediger Geib, and revisions to improve language
consistency.
* Individual draft -02, revise to improve language consistency.
* Working Group -00, replace individual draft.
* Working Group -01, address feedback in preparation for IETF 113
Vienna.
* Working Group -02:
Consolidate terminology after IETF 113 Vienna.
Add clarification to RFC2474 and RFC2475 addressed in RFC3260
(comments from Ruediger Geib).
Include figures to show the full list of codepoints, their
assigned PHBs & impact of ToS Precedence Bleaching.
Add network categories that differentiate between network
operator approaches to DiffServ.
Add Terminology section to clarify representations of DSCPs.
* Working Group -03
Add table to explain DSCP abbreviations (comment from Brian
Carpenter).
Add some refs, improve language consistency (comments from
Brian Carpenter).
Clarify figure captions.
* Working Group -04
Reference RFC3086 (comment from Brian Carpenter).
Improve references (comments from Ruediger Geib).
Clarify intended document audience and scope (comments from
Ruediger Geib).
Clarify terms and language around re-marking, DiffServ domains
and nodes, RFC8100 (comments from Ruediger Geib).
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More in-depth on mappings specified for mobile networks/MPLS
short-pipe (comments from Ruediger Geib).
* Working Group -05
Clarify meaning of RFC2474 with respect to IP precedence
(comments from Ruediger Geib).
Add note on understanding the process of re-marking (comments
from Ruediger Geib).
Improve readability.
* Working Group -06
Quote RFC2474 with respect to IP precedence (comments from
Ruediger Geib).
Ensure it is clear that different re-marking processes may
result in the same observed re-marking.
Clarify Treatment Aggregates are part of methods such as MPLS
(comments from David Black).
Clarify implications on the rest of the path by re-marking in
one domain.
Include all observed re-marking behaviors in Section 6.
Remove mentions of DSCP 5 being provisionally assigned to NQB.
Clarify scope of network control traffic in Section 3.2.
Improve readibility.
* Working Group -07
Update Section 4 to clarify both types of paths measured.
Revised paragraph 2 in Introduction
* Working Group -08
Update after Shepherd review with additional comments from R.
Geib. D. Black and B. Carpenter provided comments on
relationship to RFC 2474.
* Working Group -09
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Updates to document structure to avoid references in artwork
legend.
Fix DSCP table indentation
Update ref to nqb draft to -15
* Working Group -10
Document updated after AD review
Add clarification on former use of CS1
* Working Group -11
Updated to complete response to AD review and resolved
pathology types to xrefs.
* Working Group -12
Finalize response to AD review, address comment from Brian
Carpenter.
* Working Group -13
Review by Erik Kline
Added recommended change by IANA to cite this document from the
registry when it is published.
The latest DSCP contribution to IEPG was at IETF-115.
Consistently use re-mark instead of remark.
Improve artwork abbreviations
Address NiTs from John Scudder
Authors' Addresses
Ana Custura
University of Aberdeen
School of Engineering
Fraser Noble Building
Aberdeen
AB24 3UE
United Kingdom
Email: ana@erg.abdn.ac.uk
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Godred Fairhurst
University of Aberdeen
School of Engineering
Fraser Noble Building
Aberdeen
AB24 3UE
United Kingdom
Email: gorry@erg.abdn.ac.uk
Raffaello Secchi
University of Aberdeen
School of Engineering
Fraser Noble Building
Aberdeen
AB24 3UE
United Kingdom
Email: r.secchi@abdn.ac.uk
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