Internet DRAFT - draft-svshah-tsvwg-lln-diffserv-recommendations
draft-svshah-tsvwg-lln-diffserv-recommendations
Network Working Group S. Shah
Internet-Draft P. Thubert
Intended status: Informational Cisco Systems
Expires: August 7, 2015 February 03, 2015
Differentiated Service Class Recommendations for LLN Traffic
draft-svshah-tsvwg-lln-diffserv-recommendations-04
Abstract
Differentiated services architecture is widely deployed in
traditional networks. There exist well defined recommendations for
the use of appropriate differentiated service classes for different
types of traffic (eg. audio, video) in these networks. Per-Hop
Behaviors are typically defined based on this recommendations. With
emerging Low-power and Lossy Networks (LLNs), it is important to have
similar defined differentiated services recommendations for LLN
traffic. Defined recommendations are for LLN class of traffic
exiting out of LLNs towards high-speed backbones, converged campus
network and for the traffic in the reverse direction.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Application Types and Traffic Patterns . . . . . . . . . . . . 6
3.1. Alert signals . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Control signals . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Deterministic control signals . . . . . . . . . . . . 7
3.3. Monitoring data . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Video data . . . . . . . . . . . . . . . . . . . . . . 8
3.3.2. Query based data . . . . . . . . . . . . . . . . . . . 8
3.3.3. Periodic reporting/logging, Software downloads . . . . 8
3.4. Traffic Class Characteristics Table . . . . . . . . . . . 10
4. Differentiated Service recommendations for LLN traffic . . . . 10
4.1. Alert signals . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Control signals . . . . . . . . . . . . . . . . . . . . . 11
4.2.1. Deterministic Control Signals . . . . . . . . . . . . 11
4.3. Monitoring Data . . . . . . . . . . . . . . . . . . . . . 11
4.3.1. Video Data . . . . . . . . . . . . . . . . . . . . . . 11
4.3.2. Query based data . . . . . . . . . . . . . . . . . . . 11
4.3.3. Periodic reporting/logging, Software downloads . . . . 11
4.4. Summary of Differentiated Code-points and QoS
Mechanics for them . . . . . . . . . . . . . . . . . . . . 12
5. Deployment Scenario . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
With emerging LLN applications, it is anticipated that more and more
LLNs will be federated by high-speed backbones, possibly supporting
deterministic Ethernet service, and be further connected to some
converged campus networks for less demanding usages such as
supervisory control like traffic originated in a LLN, such as
metering, command and control, may transit over a converged campus IP
network.
---+------------------------
| Converged Campus Network
|
+-----+
| | Gateway
| |
+-----+
|
| Backbone
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | LLN border | | LLN border | | LLN border
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o
o o o o o o o o o o o
o o o o o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o o
o o M o o o o o o o o o o o o o
o o o o o o o o o
o o o o o
LLN
o : stationary wireless field device, seldom acting as an LLN router
In an example figure shown above, Per-Hop Behaviors (PHB) and Service
Level Agreements (SLAs), for LLN traffic, require to be defined at
the LLN Borders as well as Backbone and possibly in the Converged
Campus network.
In this document, we will first categorize different types of LLN
traffic into service classes and then provide recommendations for
Differentiated Service Code-Point(DSCP) for those service classes.
Mechanisms to be used, like Traffic Conditioning and Active Queue
Management, for differentiated services is well defined in RFC4594.
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This document does not focus to re-call them again here but the
document will call out any specific mechanism that requires
particular consideration.
This document focuses on Diffserv recommendations for LLN class of
traffic in managed IP networks outside of LLNs, that is for the
traffic from LLN towards LLN Border, Backbone, Campus Network as well
as for the traffic in the reverse direction. It does not focus on
Diffserv architecture or any other QoS recommendations within the
LLNs itself. Given constraints of LLNs and their unique
requirements, it is expected of a focus within a separate efforts.
Though nodes inside LLNs MAY use code-points recommended here.
In Section 3 we categorize different types of traffic from Different
LLNs. Section 4 recommends differentiated services, including DSCPs
and QoS mechanics, for categorized classes of traffic. Section 5
evaluates one of the deployment scenario.
1.1. Definitions
DSCP: Differentiated Service Code Point. It is a 6-bits value in the
TOS and Traffic Class field of the IPv4 and IPv6 header
respectively. This 6-bits numerical value defines standard set
of behavior to be performed by Differentiated Services capable
hops.
Diffserv
Class: Diffser Class in this document is used to refer to DSCP code-
point(s) and associated Per-hop Behaviors for it.
LLN: Low-power and lossy Network. Network constructed with sensors,
actuators, routers that are low-power and with higher loss/
success transmission ratio, due to transmission medium and
nature of dynamics of changing topology, compare to wired and
other traditional networks.
SLA: Service Level Agreement. It is a collection of Traffic
classification rules and set of services associated with each
Traffic Class. Traffic classification may be defined based
on just DSCP code-points or additionally (or otherwise)
based on some other packet attributes.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in RFC2119.
3. Application Types and Traffic Patterns
Different types of traffic can be collapsed into following network
service classes.
- Alert signals
- Control signals
- Monitoring data
- Video data
- Query-based response data
- Periodic reporting/logging, Software downloads
3.1. Alert signals
Alerts/alarms reporting fall in this category where such signal is
triggered in a rare un-usual circumstances. An alert may be
triggered for an example when environmental hazard level goes beyond
certain threshold. Such alerts require to be reported with in the
human tolerable time. Note that certain critical alert reporting in
certain automation systems may be reported via very closely and
tightly managed method that is not implemented within LLNs, due to
the nature of transmission media of LLNs and due to the stringent
latency requirement for those alerts. Such types of signals are not
considered here since they are not within the scope of LLN or any
other IP networks.
Examples :
- Environmental hazard level goes beyond certain threshold
- Measured blood pressure exceeds the threshold or a person falls to
the ground
- Instructional triggers like start/stop traffic lights during
certain critical event
Traffic Pattern:
Typically size of such packets is very small. any specific device of
LLN is expected to trigger only handful of packets (may be only 1
packet). That too only during an event which is not a common
occurrence.
In an affected vicinity, only a designated device or each affected
devices may send alerts. In certain type of sensor networks, it is
predictable and expected to have only a designated device to trigger
such an alert while in certain other types scale number of alert
flows may be expected.
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Latency required for such traffic is not stringent but is to be
within human tolerable time bound.
3.2. Control signals
Besides alerts, LLNs also trigger and/or receive different types of
control signals, to/from control applications outside of LLNs. These
control signals are important enough for the operation of sensors,
actuators and underneath network. Administrator controlling
applications, outside of LLN network, may trigger a control signal in
response to alerts/data received from LLN (in some cases control
signal trigger may be automated without explicit human interaction in
the loop) or administrator may trigger an explicit control signal for
a specific function.
Examples:
- auto [demand] response (e.g. manage peak load, service
disconnect, start/stop street lights)
- manual remote service disconnect, remote demand reset
- open-loop regulatory control
- non-critical close-loop regulatory control
- critical closed-loop control signals
- trigger to start Video surveillance
Traffic Pattern:
Variable size packets but typically size of such packets is small.
Certain control signals may be regular and so with number of devices
in a particular LLN, it is predictable on average, how many such
signals to expect. However, certain other control signals are
irregular or on-demand.
Typically most of the open-loop, that requires manual interaction,
signals are tolerant to latency above 1 second. Certain close-loop
control signals require low jitter and low latency, latency in the
order of 100s of ms.
3.2.1. Deterministic control signals
Some of the LLN applications, like Industrial automation, have class
of control signals that require very strict time scheduled service.
This traffic is very sensitive to jitter. Applications may be able
to handle a loss of packet or two but are very sensitive to jitter
and any delivery outside of the deterministic time schedule can have
expensive effects on the Network. Critical closed-loop control
signals example falls in this category.
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Deterministic control signals are very sensitive to jitter. Scope of
such traffic is contained to LL Network and to the IP backbone
connecting to two or more such networks. This traffic is not
expected to be transmitted over Campus, WAN and Internet.
3.3. Monitoring data
Reaction to control signals may initiate flow of data-traffic in
either direction. Sensors/Actuators in LLNs may also trigger
periodic data (eg. monitoring, reporting data). All different types
of data may be categorized in following classes.
3.3.1. Video data
A very common example of this type of monitoring data is Video
surveillance or Video feed, triggered thru control signals. This
Video feed is typically from LLN towards an application outside of
LLN.
Traffic Pattern:
Video frame size is expected to be big with a flow of variable rate.
3.3.2. Query based data
Application at the controller, outside the LLN, or user explicitly
may launch query for the data. For example, query for an urban
environmental data, query for health report etc. Since this data is
query based data, it is important to report data with reasonable
latency though not stringent. In addition, some periodic logging
data also may require timely reporting and so may expect same type of
service (eg. at-home health reporting).
Traffic Pattern:
Size of packets can vary from small to big. While rate may be
predictable in some cases, in most of the cases traffic rate for such
data is variable. The traffic is bursty in the nature.
3.3.3. Periodic reporting/logging, Software downloads
Many sensors/actuator in different LLNs report data periodically.
With some exceptions, as mentioned above for healthcare monitoring
logs, most of such data do not have any latency requirement and can
be forwarded either thru lower priority assured forwarding or with
service of store and forward or even best effort.
Sensors/actuators may require software/firmware upgrades where
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software/ firmware may be downloaded on demand bases. These upgrades
and so downloads do not have stringent requirement of timely delivery
to the accuracy of seconds. This data also can be forwarded thru
lower priority assured forwarding.
Traffic Pattern:
Periodic reporting/logging typically can be predicated as constant
rate. Data may be bursty in the nature. Software download data also
may be bursty in nature. Such traffic is tolerant to jitter and
latency.
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3.4. Traffic Class Characteristics Table
-------------------------------------------------------------------
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+==============================+======+======+======|
| Alerts/ |Packet size = small | Low |Low | N/A |
| alarms |Rate = typically 1-few packets| | | |
| |Short lived flow | | | |
| |Burst = none to some-what | | | |
|---------------+------------------------------+------+------+------|
| Control |Packet size = variable, | Yes |Low | Yes |
| Signals | typically small | | | |
| |Rate = few packets | | | |
| |Short lived flow | | | |
| |Burst = none to some-what | | | |
|---------------+------------------------------+------+------+------|
| Deterministic |Packet size = variable, | Low |Very | Very |
| Control | typically small | |Low | Low |
| Signals |Rate = few packets | | | |
| |Short lived flow | | | |
| |Burst = none to some-what | | | |
|---------------+------------------------------+------+------+------|
| Video |Packet size = big | Low |Low - | Low |
|Monitoring/feed|Rate = variable | |Medium| |
| |Long lived flow | | | |
| |Burst = non-bursty | | | |
|---------------+------------------------------+------+------+------|
| Query-based |Packet size = variable | Low |Medium| Yes |
| Data |Rate = variable | | | |
| |Short lived elastic flow | | | |
| |Burst = bursty | | | |
|---------------+------------------------------+------+------+------|
| Periodic |variable packet size, rate | Yes |Medium| Yes |
|Reporting/log, |bursty | |- High| |
| Software | | | | |
| downloads | | | | |
-------------------------------------------------------------------
4. Differentiated Service recommendations for LLN traffic
4.1. Alert signals
Alerts/alarms signaling service requires transmission of few packets
with low delay, tolerable to human. This requirement is very similar
to signaling traffic in the traditional networks. Alert signals MAY
use Diffserv code-point CS5.
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4.2. Control signals
As described in earlier section, control signals over IP are divided
in two categories. Control signals that require deterministic
forwarding service, and control signals that require relatively low
delay. Service requirement for later class of control signals is
very similar to service for signaling traffic in the traditional
networks. Recommendation for this class of control signals is to use
Diffserv code-point CS5.
4.2.1. Deterministic Control Signals
PHB for this class of traffic is defined as forwarding of a packet at
determined/scheduled time providing no jitter service.
Recommended DSCP code-point for this class of traffic is EF. Since
this class of traffic is not expected to co-exist with voice like
traffic, that implements EF code-point as used in traditional Campus
and WAN networks, the same code-point is re-used here for the purpose
of deterministic control signals. However, a note to be made for
defined PHB for this code-point as deterministic forwarding behavior
as defined in this document.
Scheduling MUST pre-empt service of any other class of traffic during
the scheduled time for this class of traffic.
4.3. Monitoring Data
4.3.1. Video Data
RFC4594 has well documented recommendations for different types of
Video traffic. If there is any Video traffic from/to LLNs to/from
outside of LLNs, they should use same recommended dscp from RFC4594.
For example, surveillance video feed is recommended to use dscp CS3.
4.3.2. Query based data
Low latency data, like query based report and non-critical signals,
is recommended to use AF2 assured forwarding service. Also, certain
periodic reporting/logging data that are critical to be reported with
regular interval with relatively low jitter is recommended to use
AF2x service.
4.3.3. Periodic reporting/logging, Software downloads
Non-critical periodic reporting/logging and rest all other data MAY
use AF1x or BE service class.
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4.4. Summary of Differentiated Code-points and QoS Mechanics for them
- Alert Signals CS5
- Control Signaling CS5
- Deterministic Control Signals EF
- Video broadcast/feed CS3
- Query-based data AF2x
- Assured monitoring data AF1x
high throughput
- Best Effort monitoring data BE
Reporting (periodic reporting.certain types of periodic monitoring
MAY require assured forwarding)
------------------------------------------------------------------
| Service | DSCP | Conditioning at | PHB | Queuing| AQM|
| Class | | DS Edge | Used | | |
|===============+======+===================+=========+========+====|
| Deterministic | EF | | |Time | No |
|control signals| |Police using sr+bs | |Schedule| |
|---------------+------+-------------------+---------+--------+----|
|Alert signals/| | | | | |
|Control signals| CS5 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+------+-------------------+---------+--------+----|
| Video feed | CS3 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+------+-------------------+---------+--------+----|
| Query- | AF21 | Using single-rate,| | | Yes|
| based | AF22 |three-color marker | RFC2597 | Rate | per|
| Data | AF23 | (such as RFC 2697)| | |DSCP|
|---------------+------+-------------------+---------+--------+----|
| Periodic | AF11 | Using two-rate, | | | Yes|
| Reporting/ | AF12 |three-color marker | RFC2597 | Rate | per|
| logging | AF13 | (such as RFC 2698)| | |DSCP|
------------------------------------------------------------------
* "sr+bs" represents a policing mechanism that provides single rate
with burst size control [RFC4594]
5. Deployment Scenario
Industrial Automation, as described in [RFC5673] and [ISA100.11a],
classifies different types of traffic in following six classes
ranging in complexity from Class 5 to Class 0 where Class 0 is the
most time sensitive class.
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o Safety
* Class 0: Emergency action - Always a critical function
o Control
* Class 1: Closed-loop regulatory control - Often a critical
function
* Class 2: Closed-loop supervisory control - Usually a non-
critical function
* Class 3: Open-loop control - Operator takes action and controls
the actuator (human in the loop)
o Monitoring
* Class 4: Alerting - Short-term operational effect (for example,
event-based maintenance)
* Class 5: Logging and downloading / uploading - No immediate
operational consequence (e.g., history collection, sequence-of-
events, preventive maintenance)
It might not be appropriate to transport Class 0 traffic over a
wireless network or a multihop network, unless tight mechanisms are
put in place such as TDM and frequency hopping. Today this class of
traffic is expected to use other tightly managed method outside of
IP networks. Excluding class 0 traffic, following table maps Class 1
thru Class 5 service classes to Diffserv code-point.
-------------------------
| Service | DSCP |
| Class | |
|===============+=========|
| Class 1 | EF |
+-------------------------+
| Class 2 | CS5 |
+-------------------------+
| Class 3 | CS5 |
+-------------------------+
| Class 4 | AF2x |
+-------------------------+
| class 5 | AF1x/BE |
+-------------------------+
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6. Security Considerations
A typical trust model, as much is applicable in traditional networks,
is applicable with LLN traffic as well. At the border of the LLN, a
trust model needs to be established for any traffic coming out of
LLN. Without appropriate trust model to accept/mark dscp code-point
for LLN traffic, misbehaving flow may attack a specific Diffserv
class disrupting expected service for other traffic from the same
Diffserv class. Trust models are typically established at the border
router by employing rate-limiting and even marking down dscp code-
point to Best Effort for non-trusted flows or dropping them as
required.
7. Acknowledgements
Thanks to Fred Baker, James Polk for their valuable comments and
suggestions.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
August 2006.
[RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of
Diffserv Service Classes", RFC 5127, February 2008.
[RFC5548] Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
"Routing Requirements for Urban Low-Power and Lossy
Networks", RFC 5548, May 2009.
[RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney,
"Industrial Routing Requirements in Low-Power and Lossy
Networks", RFC 5673, October 2009.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
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Lossy Networks", RFC 5867, June 2010.
8.2. Informative References
[ISA100.11a]
ISA, "ISA-100.11a-2011 - Wireless systems for industrial
automation: Process control and related applications",
May 2011.
[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,
December 1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC6272] Baker, F. and D. Meyer, "Internet Protocols for the Smart
Grid", RFC 6272, June 2011.
Authors' Addresses
Shitanshu Shah
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Email: svshah@cisco.com
Pascal Thubert
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE
Email: pthubert@cisco.com
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