Network Working Group Basavaraj Patil
Internet-Draft Nokia
Intended status: Standards Track Frank Xia
Expires: June 29, 2007 Behcet Sarikaya
Huawei USA
JH. Choi
Samsung AIT
Syam Madanapalli
LogicaCMG
December 26, 2006
IPv6 Over the IP Specific part of the Packet Convergence sublayer in
802.16 Networks
draft-ietf-16ng-ipv6-over-ipv6cs-04
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
IEEE Std 802.16 is an air interface specification. IEEE has
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specified several service specific convergence sublayers (CS) for
802.16 which are used by upper layer protocols. The ATM CS and
Packet CS are the two main service-specific convergence sublayers and
these are a part of the 802.16 MAC which the upper layers interface
to.The packet CS is used for transport for all packet-based protocols
such as Internet Protocol (IP), IEEE Std. 802.3 (Ethernet) and, IEEE
Std 802.1Q (VLAN). The IP specific part of the Packet CS enables
transport of IPv6 packets directly over the MAC. This document
specifies the addressing and operation of IPv6 over the IPv6 specific
part of the packet CS for hosts served by a network that utilizes the
IEEE Std 802.16 air interface. It recommends the assignment of a
unique prefix (or prefixes) to each host and allows the host to use
multiple identifiers within that prefix, including support for
randomly generated identifiers.
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Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IEEE 802.16 convergence sublayer support for IPv6 . . . . . . 5
4.1. IPv6 encapsulation over the IP CS of the MAC . . . . . . . 7
5. Generic network architecture using the 802.16 air interface . 8
6. IPv6 link . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. IPv6 link in 802.16 . . . . . . . . . . . . . . . . . . . 9
6.2. IPv6 link establishment in 802.16 . . . . . . . . . . . . 10
6.3. Maximum transmission unit in 802.16 . . . . . . . . . . . 11
7. IPv6 prefix assignment . . . . . . . . . . . . . . . . . . . . 11
8. Router Discovery . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Router Solicitation . . . . . . . . . . . . . . . . . . . 11
8.2. Router Advertisement . . . . . . . . . . . . . . . . . . . 11
8.3. Router lifetime and periodic router advertisements . . . . 12
9. IPv6 addressing for hosts . . . . . . . . . . . . . . . . . . 12
9.1. Interface Identifier . . . . . . . . . . . . . . . . . . . 12
9.2. Duplicate address detection . . . . . . . . . . . . . . . 12
9.3. Stateless address autoconfiguration . . . . . . . . . . . 12
9.4. Stateful address autoconfiguration . . . . . . . . . . . . 13
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. WiMAX network architecture and IPv6 support . . . . . 15
Appendix B. IPv6 link in WiMAX . . . . . . . . . . . . . . . . . 16
Appendix C. IPv6 link establishment in WiMAX . . . . . . . . . . 17
Appendix D. Maximum transmission unit in WiMAX . . . . . . . . . 17
Appendix E. Stateless address autoconfiguration . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 20
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1. Conventions used in this document
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
levels for compliant implementations.
2. Introduction
IPv6 packets can be carried over the IEEE Std 802.16 specified air
interface via either:
1. the IP specific part of the Packet CS or,
2. the 802.3 specific part of the Packet CS or,
3. the 802.1Q specific part of the Packet CS.
The 802.16 [802.16] specification includes the Phy and MAC details.
The convergence sublayers are a part of the MAC. This document
specifies IPv6 from the perspective of the transmission of IPv6 over
the IP specific part of the packet convergence sublayer. The mobile
station/host is attached to an access router via a base station (BS).
The host and the BS are connected via the IEEE Std 802.16 air
interface at the link and physical layers. The IPv6 link from the MS
terminates at an access router which may be a part of the BS or an
entity beyond the BS. The base station is a layer 2 entity (from the
perspective of the IPv6 link between the MS and AR) and relays the
IPv6 packets between the AR and the host via a point-to-point
connection over the air interface. The WiMAX (Worldwide
Interoperability for Microwave Access) forum [WMF] has defined a
network architecture in which the air interface is based on the IEEE
802.16 standard. The addressing and operation of IPv6 described in
this document is applicable to the WiMAX network as well. The
various aspects of IPv6 over 802.16 as applicable to WiMAX are
captured in the appendix sections of this document.
3. Terminology
The terminology in this document is based on the definitions in
[PSDOC], in addition to the ones specified in this section.
Access Service Network (ASN) - The ASN is defined as a complete set
of network functions needed to provide radio access to a WiMAX
subscriber. The ASN is the access network to which the MS attaches.
The IPv6 access router is an entity within the ASN. The term ASN is
specific to the WiMAX network architecture.
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4. IEEE 802.16 convergence sublayer support for IPv6
The IEEE 802.16 MAC specifies two main service specific convergence
sublayers:
1. ATM Convergence sublayer
2. Packet Convergence sublayer
The Packet CS is used for the transport of packet based protocols
which inclide:
1. IEEE Std 802.3(Ethernet)
2. IEEE Std 802.1Q(VLAN)
3. Internet Protocol (IPv4 and IPv6)
The service specific CS resides on top of the MAC Common Part
Sublayer (CPS). The service specific CS is responsible for:
o accepting packets (PDUs) from the upper layer,
o performing classification of the packet/PDU based on a set of
classifiers that are defined which are service specific,
o delivering the CS PDU to the appropriate service flow and
transport connection and,
o receiving PDUs from the peer entity.
Payload header suppression (PHS) is also a function of the CS but is
optional.
The figure below shows the concept of the service-specific CS in
relation to the MAC:
-----------------------------\
| ATM CS | Packet CS | \
----------------------------- \
| MAC Common Part Sublayer | \
| (Ranging, scheduling, etc)| 802.16 MAC
----------------------------- /
| Security | /
|(Auth, encryption,key mgmt)| /
-----------------------------/
| PHY |
-----------------------------
Figure 1: The 802.16 MAC
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Classifiers for each of the specific upper-layer protocols, i.e
Ethernet, VLAN and IP, are defined which enable the packets from the
upper layer to be processed by the appropriate service-specific part
of the packet CS. IPv6 can be transported directly over the IP
specific part of the packet CS or over 802.3/Ethernet (which in turn
is handled by the Ethernet specific part of the packet CS) or over
802.1Q (which is handled by the 802.1Q specific part of the packet
CS).
The figure below shows the options for IPv6 transport over the packet
CS of 802.16:
----------------- -----------------
| IPv6 | | IPv6 |
---------------- |---------------| |----------- |
| IPv6 | | Ethernet | | 802.1Q |
|--------------| |---------------| |----------- |
| IP Specific | | 802.3 specific| |802.1Q specific|
|part of Pkt CS| |part of Pkt CS | |part of Pkt CS |
|..............| |...............| |...............|
| MAC | | MAC | | MAC |
|--------------| |---------------| |---------------|
| PHY | | PHY | | PHY |
---------------- ----------------- -----------------
(1) IPv6 over (2) IPv6 over (3) IPv6 over
IP Specific part 802.3/Ethernet 802.1Q
of Packet CS
Figure 2: IPv6 over IP, 802.3 and 802.1Q specific parts of the Packet
CS
The scope of this document is limited to IPv6 operation over the IP
specific part of the Packet CS only. It should be noted that
immediately after ranging (802.16 air interface procedure), the MS
and BS exchange their capability negotiation via REG-REQ and REG-RSP.
These management frames negotiate parameters such as the Convergence
Sublayer support. By default, Packet, IPv4 and 802.3/Ethernet are
supported. IPv6 via the Packet CS is supported by the MS and the BS
only when the bit specifying such support is indicated in the
parameter "Classification/PHS options and SDU encapsulation support"
(Refer to [802.16]). Additionally during the establishment of the
transport connection for transporting IPv6 packets, the DSA-REQ and
DSA-RSP messages between the BS and MS indicate via the CS-
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Specification TLV the CS that the connection being setup shall use.
When the IPv6 packet is enacapsulated by the 802.16 six byte MAC
header there is no specific indication in the MAC header itself about
the payload type. The processing of the packet is based entirely on
the classifiers.
Transmission of IPv6 as explained above is possible via multiple
methods, i,e via the IP specific part of the packet CS or via
Ethernet or 802.1Q interfaces. The choice of which method to use is
implementation specific. In order to ensure interoperability the BS
should at least support both the IP specific part of the packet CS
and the Ethernet specific part of the packet CS for IPv6 transport.
Hosts which may implement one or the other method for transmission
would be assured of the ability to establish a transport connection
that would enable the transport of IPv6 packets. Inability to
negotiate a common convergence sublayer for the transport connection
between the MS and BS will result in failure to setup the transport
connection and thereby the ability to send and receive IPv6 packets.
In the case of a host which implements more than one method of
transporting IPv6 packets, the choice of which method to use (i.e
IPv6 over the IP specific part of the packet CS or IPv6 over 802.3
or, IPv6 over 802.1Q) is implementation specific.
4.1. IPv6 encapsulation over the IP CS of the MAC
The IPv6 payload when carried over the IP specfic part of the Packet
CS is encapsulated by the 6 byte 802.16 MAC header. Header
suppression can also be applied to the IP packet. The format of the
IPv6 packet with and without header suppression is shown in the
figure below:
---------/ /-----------
| MAC SDU |
--------/ /------------
||
||
\/
---------------------------------------------------------
| PHSI=0 | IPv6 Packet (including Header) |
---------------------------------------------------------
(i) IPv6 packet without header suppression
---------------------------------------------------------
| PHSI=1 | (Header suppressed IPv6 packet) |
---------------------------------------------------------
(ii) IPv6 packet with header suppression
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Figure 3: IPv6 encapsulation
For transmission of IPv6 packets via the IP specific part of the
Packet CS of 802.16, the IPv6 layer interfaces with the 802.6 MAC
directly. The IPv6 layer delivers the IPv6 packet to the Packet CS
of the 802.16. The packet CS defines a set of classifiers that are
used to determine how to handle the packet. The IP classifiers that
are used at the MAC operate on the fields of the IP header and the
transport protocol and these include the IP ToS/DSCP, IP Protocol
field, Masked IP source and destination addresses and, Protocol
source and destination port ranges. Using the classifiers, the MAC
maps an upper layer packet to a specific service flow and transport
connection to be used. The MAC encapsulates the IPv6 packet in the 6
byte MAC header and transmits it.
5. Generic network architecture using the 802.16 air interface
In a network that utilizes the 802.16 air interface the host/MS is
attached to an IPv6 access router (AR) in the network. The BS is a
layer 2 entity only. The AR can be an integral part of the BS or the
AR could be an entity beyond the BS within the access network. IPv6
packets between the MS and BS are carried over a point-to-point
transport connection which has a unique connection identifier (CID).
The transport connection is a MAC layer link between the MS and the
BS. The figures below describe the possible network architectures
and are generic in nature. More esoteric architectures are possible
but not considered in the scope of this document. Option A:
+-----+ CID1 +--------------+
| MS1 |------------/| BS/AR |-----[Internet]
+-----+ / +--------------+
. /---/
. CIDn
+-----+ /
| MSn |---/
+-----+
Figure 4: The IPv6 AR as an integral part of the BS
Option B:
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+-----+ CID1 +-----+ +-----------+
| MS1 |----------/| BS1 |----------| AR |-----[Internet]
+-----+ / +-----+ +-----------+
. / ____________
. CIDn / ()__________()
+-----+ / L2 Tunnel
| MSn |-----/
+-----+
Figure 5: The IPv6 AR is separate from the BS, which acts as a bridge
The above network models serve as examples and are shown to
illustrate the point to point link between the MS and the AR.
Appendix A shows a realization of the generic architecture by the
WiMAX forum.
6. IPv6 link
RFC 2461 defines link as a communication facility or medium over
which nodes can communicate at the link layer, i.e., the layer
immediately below IP [RFC2461]. A link is bounded by routers that
decrement TTL. When an MS moves within a link, it can keep using its
IP addresses. This is a layer 3 definition and note that the
definition is not identical with the definition of the term '(L2)
link' in IEEE 802 standards. This section presents a model for the
last mile link, i.e. the link to which MSs attach themselves.
6.1. IPv6 link in 802.16
In 802.16, there exists an L2 Transport Connection between an MS and
a BS which is used to transport user data, i.e IPv6 packets in this
case. A Transport Connection is represented by a CID (Connection
Identifier) and multiple Transport Connections can exist between an
MS and BS.
When an AR and a BS are collocated, the collection of Transport
Connections to an MS is defined as a single link. When an AR and a
BS are separated, it is recommended that a tunnel is established
between the AR and a BS whose granuality is no greater than 'per MS'
or 'per service flow' ( An MS can have multiple service flows which
are identified by a service flow ID). Then the tunnel(s) for an MS,
in combination with the MS's Transport connections, forms a single
point-to-point link.
The collection of service flows (tunnels) to an MS is defined as a
single link. Each link has only an MS and an AR. Each MS belongs to
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a different link. No two MSs belong to the same link. A different
prefix should be assigned to each unique link. This link is fully
consistent with a standard IP link, without exception and conforms
with the definition of a point-to-point link in RFC2461 [RFC2461].
Hence the point-to-point link model for IPv6 operation over the IP
specific part of the Packet CS in 802.16 is recommended. A unique
IPv6 prefix(es) per link (MS) is also recommended.
6.2. IPv6 link establishment in 802.16
In order to enable the sending and receiving of IPv6 packets between
the MS and the AR, the link between the MS and the AR via the BS
needs to be established. This section illustrates the link
establishment procedure.
The MS goes through the network entry procedure as specified by
802.16. A high level description of the network entry procedure is
as follows:
1. MS performs initial ranging with the BS. Ranging is a process by
which an MS becomes time aligned with the BS. The MS is
synchronized with the BS at the succesful completion of ranging
and is ready to setup a connection.
2. MS and BS perform capability exchange as per 802.16 procedures.
The CS capability parameter indicates which classification/PHS
options and SDU encapsulation the MS supports. By default,
Packet, IPv4 and 802.3/Ethernet shall be supported, thus absence
of this parameter in REG-REQ (802.16 message) means that named
options are supported by the MS/SS. Support for IPv6 over the IP
specific part of the packet CS is indicated by Bit#2 of the CS
capability parameter (Refer to [802.16]).
3. The MS progresses to an authentication phase. Authentication is
based on PKMv2 as defined in the IEEE Std 802.16 specification.
4. On succesfull completion of authentication, the MS performs
802.16 registration with the network.
5. The MS can request the establishment of a service flow for IPv6
packets over the IP specific part of the Packet CS. The service
flow can also be triggered by the network as a result of pre-
provisioning. The service flow establishes a link between the MS
and the AR over which IPv6 packets can be sent and received.
6. The AR sends a router advertisement to the MS. Alternatively or
in addition, the MS can also send a router solicitation.
The above flow does not show the actual 802.16 messages that are used
for ranging, capability exchange or service flow establishment.
Details of these are in [802.16].
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6.3. Maximum transmission unit in 802.16
The 802.16 MAC header is a 6 byte header followed by the payload and
a 4 byte CRC which covers the whole PDU (Protocol Data Unit). The
length of the PDU is indicated by the Len parameter in the Generic
MAC HDR. The Len parameter has a size of 11 bits. Hence the total
PDU size is 2048 bytes. The IPv6 payload can be a max value of 2038
bytes (MAC Hader - CRC). The Max value of the IPv6 MTU for 802.16 is
2038 bytes and the minimum value of 1280 bytes. The default MTU for
IPv6 over 802.16 SHOULD be the same as specified in RFC2460 which is
1500 octets. RFC2461 defines an MTU option that an AR can advertise
to an MN. If an AR advertises an MTU via the RA MTU option, the MN
should use the MTU from the RA.
7. IPv6 prefix assignment
Each MS can be considered to be on a separate subnet as a result of
the point-to-point connection. A CPE (Customer Premise Equipment)
type of device which serves multiple IPv6 hosts, may be the end point
of the connection. Hence one or more /64 prefixes should be assigned
to a link. The prefixes are advertised with the on-link (L-bit) flag
set. Each MS MUST be considered to be on a separate subnet as a
result of the point-to-point connection. The size and number of the
prefixes is a configuration issue. Also, prefix delegation may be
used to provide additional prefixes for a router connected over
802.16. The other properties of the prefixes are also a
configuration issue.
8. Router Discovery
8.1. Router Solicitation
On completion of the establishment of the IPv6 link, the MS may send
a router solicitation message to solicit a Router Advertisement
message from the AR to acquire necessary information as per RFC2461.
An MS that is network attached may also send router solicitations at
any time as per RFC2461.
8.2. Router Advertisement
The AR should send a number (configurable value) of router
advertisements as soon as the IPv6 link is established, to the MS.
The AR sends unsolicited router advertisements periodically as per
RFC2461.
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8.3. Router lifetime and periodic router advertisements
The router lifetime should be set to a large value, preferably in
hours. This document over-rides the specification for the value of
the router lifetime in RFC2461 [RFC2461]. The AdvDefaultLifetime in
the router advertisement MUST be either zero or between
MaxRtrAdvInterval and 43200 seconds. The default value is 2 *
MaxRtrAdvInterval.
802.16 hosts have the capability to transition to an idle mode in
which case the radio link between the BS and MS is torn down. Paging
is required in case the network needs to deliver packets to the MS.
In order to avoid waking a mobile which is in idle mode and consuming
resources on the air interface, the interval between periodic router
advertisements should be set quite high. The MaxRtrAdvInterval value
specified in this document over-rides the recommendation in RFC2461
[RFC2461]. The MaxRtrAdvInterval MUST be no less than 4 seconds and
no greater than 21600 seconds. Thee default value for
MaxRtrAdvInterval is 10800 seconds.
9. IPv6 addressing for hosts
The addressing scheme for IPv6 hosts in 802.16 network follows the
IETFs recommendation for hosts specified in RFC 4294. The IPv6 node
requirements RFC RFC4294 [RFC4294] specifies a set of RFCs that are
applicable for addressing and the same is applicable for hosts that
use 802.16 as the link layer for transporting IPv6 packets.
9.1. Interface Identifier
The MS has a 48-bit MAC address as specified in 802.16 [802.16].
This MAC address can be used if EUI-64 -based interface identifier is
needed for autoconfiguration RFC4291 [RFC4291]. As in other links
that support IPv6, EUI-64 -based interface identifiers are not
mandatory and other mechanisms, such as random interface identifiers
RFC3041 [RFC3041] may also be used.
9.2. Duplicate address detection
DAD is performed as per RFC2461 [RFC2461] and, RFC2462 [RFC2462].
9.3. Stateless address autoconfiguration
If the A-bit in the prefix information option (PIO) is set, the MS
performs stateless address autoconfiguration as per RFC 2461, 2462.
The AR is the default router that advertises a unique prefix (or
prefixes) that is used by the MS to configure an address.
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9.4. Stateful address autoconfiguration
The Stateful Address Autoconfiguration is invoked if the M-flag is
set in the Router Advertisement. Obtaining the IPv6 address through
stateful address autoconfiguration method is specified in RFC3315
[RFC3315].
10. IANA Considerations
This draft does not require any actions from IANA.
11. Security Considerations
This document does not introduce any new vulnerabilities to IPv6
specifications or operation. The security of the 802.16 air
interface is the subject of [802.16]. In addition, the security
issues of the network architecture spanning beyond the 802.16 base
stations is the subject of the documents defining such architectures,
such as WiMAX Network Architecture [WiMAXArch].
12. Acknowledgments
The authors would like to acknowledge the contributions of the 16NG
working group chairs Daniel Soohong Park and Gabriel Montenegro as
well as Jari Arkko, Jonne Soininen, Max Riegel, Prakash Iyer, DJ
Johnston and Dave Thaler for their review and comments.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997,
<ftp://ftp.isi.edu/in-notes/rfc2119>.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998, <ftp://ftp.isi.edu/in-notes/rfc2461>.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998,
<ftp://ftp.isi.edu/in-notes/rfc2462>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
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Architecture", RFC 4291, February 2006,
<ftp://ftp.isi.edu/in-notes/rfc4291>.
13.2. Informative References
[802.16] "IEEE Std 802.16e: IEEE Standard for Local and
metropolitan area networks, Amendment for Physical and
Medium Access Control Layers for Combined Fixed and Mobile
Operation in Licensed Bands", October 2005.
[FRD] Choi, JH., Shin, DongYun., and W. Haddad, "Fast Router
Discovery with L2 support", August 2006, <http://
www.ietf.org/internet-drafts/draft-ietf-dna-frd-02.txt>.
[PSDOC] Jee, J., "IP over 802.16 Problem Statement and Goals",
October 2006, <http://www.ietf.org/internet-drafts/
draft-ietf-16ng-ps-goals-00.txt>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998,
<ftp://ftp.isi.edu/in-notes/rfc2464>.
[RFC3041] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", August 2006, <http://www.ietf.org/internet-drafts/
draft-ietf-ipv6-privacy-addrs-v2-05.txt>.
[RFC3315] Droms, Ed., R., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, July 2003,
<ftp://ftp.isi.edu/in-notes/rfc3315>.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004, <ftp://ftp.isi.edu/in-notes/rfc3756 >.
[RFC4135] Choi, JH. and G. Daley, "Goals of Detecting Network
Attachment in IPv6", RFC 4135, August 2005,
<ftp://ftp.isi.edu/in-notes/rfc4135>.
[RFC4294] Loughney, Ed., J., "IPv6 Node requirements", RFC 4294,
April 2006, <ftp://ftp.isi.edu/in-notes/rfc4294>.
[WMF] "http://www.wimaxforum.org".
[WiMAXArch]
"WiMAX End-to-End Network Systems Architecture
http://www.wimaxforum.org/technology/documents",
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August 2006.
Appendix A. WiMAX network architecture and IPv6 support
The WiMAX network architecture consists of the Access Service Network
(ASN) and the Connectivity Service Network (CSN). The ASN is the
access network which includes the BS and the AR in addition to other
functions such as AAA, Mobile IP Foreign agent, Paging controller,
Location Register etc. The CSN is the entity that provides
connectivity to the Internet and includes functions such as Mobile IP
Home agent and AAA. The figure below shows the WiMAX reference
model:
-------------------
| ---- ASN | |----|
---- | |BS|\ R6 -------| |---------| | CSN|
|MS|-----R1----| ---- \---|ASN-GW| R3 | CSN | R5 | |
---- | |R8 /--|------|----| |-----|Home|
| ---- / | | visited| | NSP|
| |BS|/ | | NSP | | |
| ---- | |---------| | |
| NAP | \ |----|
------------------- \---| /
| | /
| (--|------/----)
|R4 ( )
| ( ASP network )
--------- ( or Internet )
| ASN | ( )
--------- (----------)
Figure 6: WiMAX Network reference model
Three different types of ASN realizations called profiles are defined
by the architecture. ASNs of profile types A and C include BS' and
ASN-gateway(s) (ASN-GW) which are connected to each other via an R6
interface. An ASN of profile type B is one in which the
functionality of the BS and other ASN functions are merged together.
No ASN-GW is specifically defined in a profile B ASN. The absence of
the R6 interface is also a profile B specific characteristic. The MS
at the IPv6 layer is associated with the AR in the ASN. The AR may
be a function of the ASN-GW in the case of profiles A and C and is a
function in the ASN in the case of profile B. When the BS and the AR
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are separate entities and linked via the R6 interface, IPv6 packets
between the BS and the AR are carried over a GRE tunnel. The
granularity of the GRE tunnel should be on a per MS basis or on a per
service flow basis (an MS can have multiple service flows, each of
which are identified uniquely by a service flow ID). The protocol
stack in WiMAX for IPv6 is shown below:
|-------|
| App |- - - - - - - - - - - - - - - - - - - - - - - -(to app peer)
| |
|-------| /------ -------
| | / IPv6 | | |
| IPv6 |- - - - - - - - - - - - - - - - / | | |-->
| | --------------- -------/ | | IPv6|
|-------| | \Relay/ | | | |- - - | |
| | | \ / | | GRE | | | |
| | | \ /GRE | - | | | | |
| |- - - | |-----| |------| | | |
| IPv6CS| |IPv6CS | IP | - | IP | | | |
| ..... | |...... |-----| |------|--------| |-----|
| MAC | | MAC | L2 | - | L2 | L2 |- - - | L2 |
|-------| |------ |-----| |----- |--------| |-----|
| PHY |- - - | PHY | L1 | - | L1 | L1 |- - - | L1 |
-------- --------------- ----------------- -------
MS BS AR/ASN-GW CSN Rtr
Figure 7: WiMAX protocol stack
As can be seen from the protocol stack description, the IPv6 end-
points are constituted in the MS and the AR. The BS provides lower
layer connectivity for the IPv6 link.
Appendix B. IPv6 link in WiMAX
WiMAX is an example of a network based on the IEEE Std 802.16 air
interface. This section describes the IPv6 link in the context of a
WiMAX network. The MS and the AR are connected via a combination of
:
1. The transport connection which is identified by a Connection
Identifier (CID) over the air interface, i.e the MS and BS and,
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2. A GRE tunnel between the BS and AR which transports the IPv6
packets
From an IPv6 perspective the MS and the AR are connected by a point-
to-point link. The combination of transport connection over the air
interface and the GRE tunnel between the BS and AR creates a (point-
to-point) tunnel at the layer below IPv6.
The collection of service flows (tunnels) to an MS is defined as a
single link. Each link has only an MS and an AR. Each MS belongs to
a different link. No two MSs belong to the same link. A different
prefix should be assigned to each unique link. This link is fully
consistent with a standard IP link, without exception and conforms
with the definition of a point-to-point link in RFC2461 [RFC2461].
Appendix C. IPv6 link establishment in WiMAX
The mobile station performs initial network entry as specified in
802.16. On succesful completion of the network entry procedure the
ASN gateway/AR triggers the establishment of the initial service flow
(ISF) for IPv6 towards the MS. The ISF is a GRE tunnel between the
ASN-GW/AR and the BS. The BS in turn requests the MS to establish a
transport connection over the air interface. The end result is a
transport connection over the air interface for carrying IPv6 packets
and a GRE tunnel between the BS and AR for relaying the IPv6 packets.
On succesful completion of the establishment of the ISF, IPv6 packets
can be sent and received between the MS and AR. The ISF enables the
MS to communicate with the AR for host configuration procedures.
After the establishment of the ISF, the AR can send a router
advertisement to the MS. An MS can establish multiple service flows
with different QoS characteristics. The ISF can be considered as the
primary service flow. The ASN-GW/ AR treats each ISF, along with the
other service flows to the same MS, as a unique link which is managed
as a (virtual) interface.
Appendix D. Maximum transmission unit in WiMAX
The WiMAX forum [WMF] has specified the Max SDU size as 1522 octets.
Hence the IPv6 path MTU can be 1500 octets. However because of the
overhead of the GRE tunnel used to transport IPv6 packets between the
BS and AR and the 6 byte MAC header over the air interface, using a
value of 1500 would result in fragmentation of packets. It is
recommended that the default MTU for IPv6 be set to 1400 octets for
the MS in WiMAX networks. Note that the 1522 octet specification is
a WiMAX forum specification and not the size of the SDU that can be
transmitted over 802.16, which is higher.
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Appendix E. Stateless address autoconfiguration
The MS can perform stateless address autoconfiguration as per
RFC2461, 2462 if the A-bit in the prefix information option (PIO) is
set. The AR is the default router that advertises a unique /64
prefix (or prefixes) that is used by the MS to configure an address.
Authors' Addresses
Basavaraj Patil
Nokia
6000 Connection Drive
Irving, TX 75039
USA
Email: basavaraj.patil@nokia.com
Frank Xia
Huawei USA
1700 Alma Dr. Suite 100
Plano, TX 75075
Email: xiayangsong@huawei.com
Behcet Sarikaya
Huawei USA
1700 Alma Dr. Suite 100
Plano, TX 75075
Email: sarikaya@ieee.org
JinHyeock Choi
Samsung AIT
Networking Technology Lab
P.O.Box 111
Suwon, Korea 440-600
Email: jinchoe@samsung.com
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Syam Madanapalli
LogicaCMG
125 Yemlur P.O.
Off Airport Road
Bangalore, India 560037
Email: smadanapalli@gmail.com
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Full Copyright Statement
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