Internet DRAFT - draft-garneij-6man-nd-m2m-issues
draft-garneij-6man-nd-m2m-issues
6man WG F. Garneij
Internet-Draft S. Chakrabarti
Intended status: Informational S. Krishnan
Expires: January 5, 2015 Ericsson
July 4, 2014
Impact of IPv6 Neighbor Discovery on Cellular M2M Networks
draft-garneij-6man-nd-m2m-issues-00
Abstract
The use of IPv6 in 3GPP cellular broadband networks for accessing the
Internet and other data services like voice-over-LTE(VoLTE) has
increased greatly as a result of EPS network deployments worldwide
and new IPv6 capable smartphones and tablets. The upcoming rise of
IoT/M2M is anticipated to bring billions of new devices into these
networks and the majority of these devices will be using only IPv6.
This document discusses the EPS network impact of IoT/M2M IPv6
connectivity specifically targeting the IPv6 Stateless Address Auto
Configuration (SLAAC), as specified in [RFC4861] and [RFC4862], which
currently is the only supported IPv6 address configuration mechanism
in 3GPP standards.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 5, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definition Of Terms . . . . . . . . . . . . . . . . . . . . 4
2. The M2M Scenario and IPv6 Neighbor Discovery Impact . . . . . . 5
3. Analysis of Results . . . . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
Several of the IPv6 core protocols make widespread use of multicast
messages as they wished to avoid broadcast messages. Unfortunately,
in practice, the multicast operation at many link layers the
degenerates into broadcast messages. 3GPP links are cellular links
consuming expensive and limited radio spectrum. Thus such radio
networks like to limit unnecessary signals in the network. IPv6
neighbor discovery is one of the core protocols required for the
operation of IPv6, and this document shows how it can affect the
cellular networks for M2M. M2M networks are usually low bandwidth
radio networks.
In 3GPP networks, mobility and connectivity is generated by the
arrangement of allocated radio resources and EPC node resources into
a PDN connection. The following list gives the logical functions
performed within the Evolved Packet System (EPS):
o Network Access Control Functions.
o Packet Routing and Transfer Functions
o Mobility Management Functions.
o Security Functions
o Radio Resource management functions
o Network Management Functions
For a User Equipment (UE) attached to a 3GPP network there are
procedures defined related to device mobility, EPS Mobility
Management (EMM) states and connectivity session, EPS Connectivity
Management (ECM) states as described in [TS.23401] Section 4.6. The
purpose of this document is to analyze the EPS resources impacted by
the procedures of the IPv6 Stateless Address Auto Configuration
(SLAAC), as specified in [RFC4861] and [RFC4862], as it is utilized
in 3GPP standards. Special attention is put on EPS control signaling
load and the packets destined to UE generated by IPv6 periodic Router
Advertisements (unsolicited multicast Router Advertisements). 3GPP
also specifies its own values and behavior for Router Advertisement
as described in 3GPP TS 29.061 Section 11.2.1.3.4 IPv6 Router
Configuration Variables. This 3GPP adaptation defines how to send
initial and periodic Router Advertisements in order to preserve radio
resources and UE power consumption while still allowing for
appropriate robustness and fast user-plane set-up time even in bad
radio conditions to the radio.
Since in EPS, radio and network resources are not permanently
assigned to a specific UE there is a cost associated with the
allocation and release of resources and associated changes of states
in EPS nodes. Thus, it is desirable to reduce or avoid any
additional periodic packets that are not of any use to the
application using the 3GPP derived UE connectivity. 2G and 3G radio
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resource allocation have their own mechanisms with similar
functionality but these are not described or considered in this
document. The following M2M usecase scenario will clarify why
periodic RA in 3GPP networks are harmful in especially for the M2M
scenario.
Note that there are IETF informational guidelines for IPv6 usage in
3GPP EPS networks [RFC6459], but this draft requests an update in
Standard IPv6 Neighbor Discovery specification to disallow periodic
RAs.
1.1. Definition Of Terms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3GPP Terminology
Second Generation Mobile Telecommunications, such as Global System
for Mobile Communications (GSM) and GPRS technologies
Third Generation Mobile Telecommunications, such as UMTS
technology
Fourth Generation Mobile Telecommunications, such as LTE
technology.
3GPP
Third Generation Partnership Project. Throughout the document,
the term "3GPP networks" refers to architectures standardized by
3GPP, in Second, Third, and Fourth Generation releases: 99, 4, and
5, as well as future releases.
eNodeB
The eNodeB is a base station entity that supports the Long-Term
Evolution (LTE) radio interface.
EPS
Evolved packet System in LTE
GTP-U
GPRS Tunneling protocol for user plane
LTE
Long Term Evolution 3GPP Specification. It is a 4G mobile
communication specification. The network speed in LTE is up to 10
times faster than the 3G network
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Paging
A 3GPP defined mechanism for finding the radio base station at
which a specific UE currently can be reached.
PDN Connection
The association between a UE represented by one IP address and/or
one IPv6 prefix and a Packet Data network(PDN) assosiated to an
Access Point Name(APN).
PGW or PDN GW
Packet Data Network Gateway (the default router for 3GPP IPv6
cellular hosts in EPS).
SGW or Serving GW
Serving Gateway: The user plane equivalent of a Serving GPRS
Support Node (SGSN) in EPS and the default router for 3GPP IPv6
cellular hosts when using Proxy Mobile IPv6 (PMIPv6).
MME
Mobility Management Entity
UE
User Equipment or host terminal
M2M
Machine to Machine Communication networks and related standards.
M2M includes industrial networks and communication. M2M uses IPv6
as dataplane.
2. The M2M Scenario and IPv6 Neighbor Discovery Impact
The analysis considers an IoT/M2M UE deployment scenario with
infrequent packet communications occurrences than would normally be
seen in an interactive device such as a smartphone. Given such an
infrequent communication pattern, the UE is highly likely be in IDLE
ECM state when a downlink packet is sent from the PGW or the SGW.
Sending a packet to the UE while in ECM IDLE state triggers a paging
process followed by a UE Service Request and radio resource
allocation. These procedures are considered as among the heavier
procedures in EPS with regards to control signaling load and node
state changes. They cause increased utilization of the radio
interface as well as increased processing loads in the nodes involved
in the procedures. It is also likely that other devices with
different communications usage patterns like smartphones may compete
over network resources causing the procedure to be repeated in order
to complete. Thus, unnecessary control signals such as periodic RA
causes paging and waste of radio resources in cellular networks.
The M2M use case below considers the following network dimensioning
for a single PGW node based on information derived from real world
network deployment best practices:
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o There are 10,000,000 simultaneous IPv6 connections to IoT/M2M
devices from PGW. There are no dedicated bearers available.
Communication direction for IoT/M2M service is from network to UE
infrequent (e.g. twice a day or less). GTP-U is used between PGW
and SGW as described in TS.23401 of 3GPP specification. The
following list shows the condition of the network, number of
resources and UE behavior in a typical 10M IPv6 connection-based
M2M network.
o If EPS Connectivity Management (ECM) state is ECM_IDLE, paging
will be triggered when a packet is received by the UE
o Each Tracking Area (TA) contains 100 base stations (eNodeB)
o MME UE Tracking Area Identifier (TAI) list containing 10 TA which
gives 10 * 100 eNodeB = 1000 eNodeB for a UE TAI list
o The MaxRtrAdvInterval configuration of RFC4861 has been set to its
maximum allowed value to minimize unsolicited multicast RAs
Based on the above data, the following analysis has been done. The
analysis focuses on the connectivity state changes and resource
allocation related to 1) Packet Routing and Transfer Functions 2)
Mobility Management Functions 3) Radio Resource Management Functions
3. Analysis of Results
The unsolicited mulicast RAs are sent at randomized intervals based
on a timer that is set to uniformly distributed random values between
the interface's configured MinRtrAdvInterval and MaxRtrAdvInterval as
described in Section 6.2.4. of RFC4861. We assume maximum possible
values for MinRtrAdvInterval and MaxRtrAdvInterval in order to
discover the *best-case* scenario.
MaxRtrAdvInterval = 1800 seconds
MinRtrAdvInterval = 0.75 * 1800 = 1350 seconds
Average RA interval = (1800 + 1350) / 2 = 1575 seconds
RAs/second = number of nodes/average RA interval
= 10e7/1575 = 6349
If the periodic router advertisements are allowed in the network, the
measurement result shows that approximately 6300 Router advertisement
packets can be sent to the eNodeB(base station) from the Edge Router/
Gateway device(PGW). And there is ~100 to ~1000 state changes per
second for MME, eNodeB, UE in the network.
If we assume there are 1000 base stations (eNodeBs) in the network
there will be approximately 6.3 million paging messages per second as
each unsolicited RA will initiate paging on each eNodeB. Each of
these RAs will also trigger state changes in the MME, the SGW, the
eNodeB and the UE radio bearer. There will be approximately 50000
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(12600*4) state changes per second in the network. This causes
significant increases in processing power as well as network traffic.
This will cause serious issues to network operators. This
illustrates the point is that even when unsolicited multicast RAs are
fairly infrequent, there is a huge effect on the M2M/IOT 3GPP
networks.
It has been shown that a single unsolicited downlink packet can
consume energy and bandwidth and ties up resources in the EPS network
and UE. It is desirable to free up the 3GPP networks from such
periodic signaling traffic (in this case IPv6 ND) so that energy and
bandwith can be saved and the saved energy and bandwidth can be used
for actual data traffic destined to users. Given the result above
the unsolicited RA traffic generated by the PGW is roughly equal to
the effort needed to poll all 53 million UK gas and electricity
meters once a day. If it amuses the reader, the number of
unsolicited RA sent by the PGWs connecting the IPv6-only UK smart
meters during a day can easliy be derived using the data in this
document.
Since all the UE are known to the PGW which acts as their default
router and packets to one UE to another go via PGW in many
deployments, the Address Registration Method(ARO) described in
[efficient-nd] is quite useful for reducing/avoiding periodic RA and
having the PGW or SGW keeping track of the UE registration status for
selectively exchanging the IPv6 Neighbor Discovery messages. In
addition the Address Registration Method(ARO) allows the PGW to learn
the IPv6 address that is used by the UE which is not possible using
currently defined 3GPP usage of SLAAC.
4. Acknowledgements
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[6LOWPAN-ND]
Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"ND Optimizations for 6LoWPAN", RFC 6775, November 2012.
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[efficient-nd]
Chakrabarti, S., Nordmark, E., Thubert, P., and M.
Wasserman, "IPv6 Neighbor Discovery Optimizations for
Wired and Wireless Networks",
draft-chakrabarti-nordmark-6man-efficient-nd-05 (work in
progress), February 2014.
[ND] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6", RFC 4861,
September 2007.
5.2. Informative References
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6), Specification", RFC 2460, December 1998.
[AUTOCONF]
Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Autoconfiguration", RFC 4862, September 2007.
[RFC6459] Korhonen, J., "IPv6 in 3rd Generation Partnership Project
(3GPP) Evolved Packet System (EPS)", RFC 6459,
January 2012.
Appendix A.
Authors' Addresses
Fredrik Garneij
Ericsson
Sweden
Email: fredrik.garneij@ericsson.com
Samita Chakrabarti
Ericsson
USA
Email: samita.chakrabarti@ericsson.com
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Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
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