Denver, CO (October 8, 2015): Today, the
Broadband Internet Technical Advisory Group (“BITAG”) announced the publication
of its technical report on the subject of Differentiated Treatment of Internet
Traffic. The executive summary of the report can be found further below – including
the full set of observations and recommendations – and the report itself can be
found at:http://www.bitag.org/documents/BITAG_-_Differentiated_Treatment_of_Internet_Traffic.pdf.
Differentiated treatment of Internet
Access Service traffic has been a subject of debate and regulatory scrutiny. In
February 2015, the Federal Communications Commission (FCC) adopted Open
Internet rules that address paid prioritization as well as other topics. This
report touches on a broad range of questions associated with differentiation,
but is not intended to address or analyze the economic, legal, regulatory, or
public policy issues that the differentiated treatment of Internet access
service traffic may raise, focusing instead on the technical issues.
The data transmitted across the networks
that make up the Internet is formatted as packets, which contain information
payloads encapsulated within one or more headers. These headers provide the
information needed to deliver the packets to their destinations. As these
packets travel across networks, they contend with other packets for network
resources. The simplest way to handle this contention would be on a first come,
first served basis (also known as First In First Out, or FIFO). In practice,
however, network operators make many exceptions to FIFO, using the packet
header information to classify packets into flows and treating those flows
differently, for example rearranging the order or the timing with which packets
are sent, or sending them along different network paths. This is done for
various reasons, including meeting service level agreement (SLA) guarantees and
selecting paths for traffic from different applications, among other things.
Differentiated treatment of traffic can also contribute both to the efficiency
of a network and to the predictability of the manner in which network resources
are shared. The ability to treat traffic differentially has been built into
Internet protocols from the beginning but has not been deployed end-to-end due
to a number of issues.
Observations. From the analysis made in the report and
the combined experience of its members when it comes to the differentiated
treatment of Internet traffic, the BITAG Technical Working Group makes the
following observations (See Executive Summary below or
full report for the complete explanation of each):
· TCP causes recurring momentary
congestion.
· A nominal level of packet discard
is normal.
· The absence of differentiation
does not imply comparable behavior among applications.
· Differentiated treatment can
produce a net improvement in Quality of Experience (QoE).
· Access technologies differ in
their capabilities and characteristics.
· Security of traffic has at times
been downgraded to facilitate differentiation techniques.
Recommendations. The BITAG Technical Working Group also has
the following recommendations (See Executive Summary below or
full report for the complete explanation of each):
· Network operators should disclose
information on differential treatment of traffic.
· Network operators and ASPs should
be encouraged to implement efficient and adaptive network resource management
practices.
· Quality of Service metrics should
be interpreted in the context of Quality of Experience.
· Network operators should not
downgrade, interfere with, or block user-selected security in order to apply
differentiated treatment.
Ken Ko, Senior Staff Scientist at ADTRAN, and Fred Baker, a Fellow
at Cisco, served as the lead editors of the report. Douglas Sicker, Executive Director
of BITAG, Chair of BITAG’s Technical Working Group, Department Head of
Engineering and Public Policy and a professor of Computer Science at Carnegie
Mellon University, chaired the review itself.
About BITAG. BITAG is a non-profit, multi-stakeholder organization
focused on bringing together
engineers and technologists in a Technical Working Group (TWG) to develop
consensus on broadband network management practices and other related technical
issues that can affect users’ Internet experience, including the impact to and
from applications, content and devices that utilize the Internet.
This is BITAG’s eighth report. BITAG’s previous
reports have focused on: Internet interconnection; VoIP impairment, failure,
and restrictions; Real-time network management of Internet congestion; Port
blocking; SNMP DDoS attack mitigation; Large scale network address translation;
and IPv6 whitelisting. Copies of these technical reports can be found on the BITAG website at www.bitag.org.
Questions
or Comments? BITAG
welcomes any questions, comments or suggestions. Please contact our
Executive Director, Douglas Sicker, at dsicker@bitag.org or our Deputy Director, Kaleb Sieh, at ksieh@bitag.org.
– ATTACHMENT –
Executive Summary of BITAG
Report on Differentiated Treatment of Internet Traffic
The Internet is composed of interconnected networks, each having
its own architecture and technical characteristics. The data transmitted across
these networks is formatted as packets containing information payloads
encapsulated within one or more headers, which in turn provide the information
needed by networks to deliver the packets to their destinations. As these
packets travel across networks, they contend with other packets for network
resources. Contention can occur at any point where two or more packets can
compete for a resource at the same time. The simplest way to handle such
requests would be on a first come, first served basis (also known as First In
First Out, or FIFO). In practice, however, network operators make many
exceptions to FIFO, using the packet header information to classify packets into
flows and treating those flows differently, for example rearranging the order
or the timing with which packets are sent, or sending them along different
network paths.
Differentiated treatment of Internet
Access Service traffic has been a subject of debate and regulatory scrutiny. In
February 2015, the Federal Communications Commission (FCC) adopted Open
Internet rules that address paid prioritization as well as other topics [1].
This report touches on a broad range of questions associated with differentiation,
but is not intended to address or analyze the economic, legal, regulatory, or
public policy issues that the differentiated treatment of Internet access
service traffic may raise, focusing instead on the technical issues.
The ability to treat traffic
differentially has been built into Internet protocols from the beginning. The
specifications for both IPv4 and IPv6 have included fields to support traffic
differentiation since their inception (initially IPv4’s Type of Service or ToS
field) to indicate to routers the quality of service desired, in terms of
queuing precedence and routing parameters around delay, rate, and reliability.
This was changed to more generic service descriptions with the definition of
the Differentiated Services Field, and implemented in IPv4 and IPv6. Notably,
traffic differentiation in this sense has not been implemented in
multi-provider environments, although it is extensively used within specific
networks. End to end deployment would
require the harmonization and cooperation of a large number, if not all, of the
relevant network operators.
In its broadest sense, traffic
differentiation includes any technique that classifies and applies potentially
different treatment to two or more traffic flows contending for resources on a
network (a flow being a group of packets that share a common set of
properties). Differentiated treatment of network traffic is a two-part process:
(1) traffic is classified into traffic streams, and (2) a prescribed set of
actions is applied to each stream. This treatment may determine the order in
which routers and switches send packets from different flows across the link,
the rate of transmission of a given flow, or even whether certain packets are
sent at all.
While the techniques used for traffic differentiation
overlap with those used to manage congestion, differentiation has a broader
purpose that includes meeting service level agreement (SLA) guarantees and
selecting paths for traffic from different applications, among other things.
Differentiated treatment of traffic can also contribute both to the efficiency
of a network and to the predictability of the manner in which network resources
are shared.
Differentiation can be complex, and a
common vocabulary is key. This report uses the terms “differentiated treatment”
or “differentiation,” as opposed to “prioritization” when referring to the full
range of treatments that may be applied to traffic flows. The technical
definition of “prioritization” is narrow and generally applies only to certain
scheduling, dropping, and marking techniques. This report uses
“differentiation” in a much broader sense, including most of the ways in which
packets may be treated differently from each other while en route to their
respective destinations across one or more networks. The scope of
differentiation in this report encompasses the classic techniques of
scheduling, shaping and queue management by which packets are processed at a
network node, and also includes the techniques by which traffic flows are
segregated or forwarded onto different physical or logical network paths where
they may encounter greater or lesser propagation delays or contention for
resources.
This report addresses differentiation
applied to traffic on Internet access services, as well as the impacts to
Internet access services when differentiation is applied to other traffic
carried over the same network. Traffic for mass-market Internet access services
is often carried over a common infrastructure with traffic associated with
other IP services, as well as the network management traffic used to control
devices and report status from them. Since differential treatment of other
network traffic has the potential to affect the performance of Internet access
services, it is considered here.
The subjective experience perceived by the
user of a networked application is known as Quality of Experience, or QoE, and
the factors that contribute to QoE vary significantly from one application to
the next. In contrast, Quality of Service, or QoS, describes the performance of
a network service using objective metrics such as throughput, delay, delay
variation, and loss. The relationship between QoS and QoE is highly dependent
on the type of application, but variations in QoS have been mapped to
corresponding variations in QoE for a number of applications. It is possible to
use knowledge about the relationships between network performance parameters
and their effects on QoE to attempt to optimize the performance of network
flows for their intended applications. Differentiation is often also used to
address impairments to QoS.
Broadband networks use different network
architectures and access technologies. Several of these network architectures
have developed to take advantage of existing access infrastructure that was originally
deployed for other services – for example, telephone service over twisted
copper pairs or video over coaxial cable. Other networks were developed to meet
specific needs, such as for mobility or for access in remote rural areas. In
many cases, differences in network design can be traced to the different
characteristics of the access technology used. Access technologies can require
different approaches to differentiation of traffic.
Observations. From the analysis made in this report and
the combined experience of its members when it comes to the differentiated
treatment of Internet traffic, the BITAG Technical Working Group makes the
following observations:
· TCP causes recurring momentary
congestion
When
TCP transfers a large file, such as video content or a large web page, it
practically guarantees that it will create recurring momentary congestion at
some point in its network path. This effect exists by design, and it cannot
necessarily be eliminated by increasing capacity. Given the same traffic
load, however, the severity of the momentary congestion should decrease with
increased capacity.
· A nominal level of packet discard
is normal
Packet
discard occurs by design in the Internet. Protocols such as TCP use packet
discard as a means of detecting congestion, responding by reducing the amount
of data outstanding and with it self-induced congestion on the transmission
path. Rather than being an impairment, packet discard serves as an important
signaling mechanism that keeps congestion in check.
· The absence of differentiation does
not imply comparable behavior among applications
In
the absence of differentiation, the underlying protocols used on the Internet
do not necessarily give each application comparable bandwidth. For example:
- TCP tends to share available capacity (although not
necessarily equally) between competing connections. However, some applications
use many connections at once while other applications only use one connection.
- Some applications using RTP/UDP or other transport
protocols balance transmission rate against experienced loss and latency,
reducing the capacity available to competing applications.
· Differentiated treatment can
produce a net improvement in Quality of Experience (QoE)
When
differentiated treatment is applied with an awareness of the requirements for
different types of traffic, it becomes possible to create a benefit without an
offsetting loss. For example, some differentiation techniques improve the
performance or quality of experience (QoE) for particular applications or
classes of applications without negatively impacting the QoE for other
applications or classes of applications. The use and development of these
techniques has value.
· Access technologies differ in their
capabilities and characteristics
Specific
architectures and access technologies have unique characteristics which are
addressed using different techniques for differentiated treatment.
· Security of traffic has at times
been downgraded to facilitate differentiation techniques
Encrypted
traffic is on the rise and it has implications for current differentiation
techniques. In response to this increase, some satellite and in-flight network
operators have deployed differentiation mechanisms that downgrade security
properties of some connections to accomplish differentiation. The resulting
risks to the security and privacy of end users can be significant, and differentiation
via observable information such as ports and traffic heuristics is more
compatible with security.
Recommendations. The BITAG Technical Working Group also has
the following recommendations:
· Network operators should disclose
information on differential treatment of traffic.
In previous reports, BITAG has recommended
transparency with respect to a number of aspects of network management.
BITAG continues to recommend transparency when it comes to the practices used
to implement the differential treatment of Internet traffic.
Specifically with respect to consumer-facing services such as
mass-market Internet access, network operators should disclose the use of
traffic differentiation practices that impact an end user’s Internet access
service. The disclosure should be readily accessible to the public (e.g. via a
webpage) and describe the practice with its impact to end users and expected
benefits in terms meaningful to end users. The disclosure should include any
differentiation amongst Internet traffic and should disclose the extent and
manner in which other services offered over the same end user access facilities
(for example video services) may affect the performance of the Internet access
service.
· Network operators and ASPs should
be encouraged to implement efficient and adaptive network resource management
practices
In a previous report BITAG recommended that ASPs and CDNs
implement efficient and adaptive network resource management practices; we reiterate
that recommendation here, extending it to network operators. Examples of such
practices might target the minimization of latency and variation in latency
induced in network equipment, ensuring sufficient bandwidth for expected
traffic loads, and the use of queue management techniques to manage resource
contention issues.
· Quality of Service metrics should
be interpreted in the context of Quality of Experience
Common Quality of Service metrics, often included in commercial
service level agreements, include capacity, delay, delay variation, and loss
rate, among other things. From the viewpoint of the end user application, these
metrics trade off against each other and must be considered in the context of
Quality of Experience. For example, since TCP Congestion Control and adaptive
codecs depend on loss to infer network behavior, actively trying to reduce loss
to zero leads to unintended consequences. On the other hand, non-negligible
loss rates often directly reduce the user's Quality of Experience. Hence, such
metrics should be interpreted in the context of improving user experience.
· Network operators should not
downgrade, interfere with, or block user-selected security in order to apply
differentiated treatment.
Network operators should refrain from preventing users from
applying over-the-top encryption or other security mechanisms without user
knowledge and consent. Networks should not interfere with, modify, or drop
security parameters requested by an endpoint to apply differentiated treatment.
Given the potential for possible exposure of sensitive, confidential, and
proprietary information, prior notice should be given to end users of traffic
differentiation features that affect security properties transmitted by
endpoints.
