Network Working Group S. Chakrabarti
Internet-Draft Azaire Networks
Expires: May 18, 2008 A. Muhanna
Nortel Networks
G. Montenegro
Microsoft
A. Bachmutsky
Nokia Siemens Network
Y. Wu
Huawei
B. Patil
Nokia Siemens Networks
P. Yegani
Cisco Systems
November 15, 2007

IPv4 Mobility extension for Multicast and Broadcast Packets
draft-chakrabarti-mip4-mcbc-02

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This Internet-Draft will expire on May 18, 2008.

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Intended Status <To Be Removed Upon Publication>

Intended status: Informational

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Abstract

The IP Mobility Protocol [RFC3344] describes multicast and broadcast
packet transmission between the mobile node and the home network or
visited network. Reverse Tunneling for Mobile IP [RFC3024] includes
support for reverse tunneling of multicast and broadcast packets to
the home network using the encapsulating delivery style between
mobile nodes and the foreign agent. However, [RFC3024] says that
once the encapsulated delivery style is negotiated, all packets must
be encapsulated. In particular, this imposition prevents direct
delivery of unicast packets. This causes tunnel overhead in the
(typically) wireless medium between the mobile and the foreign agent.
This document removes this imposition It also provides alternatives
of direct delivery of multicast-broadcast packets between a foreign
agent and a mobile node if allowed by the underlying link-layer.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definition Of Terms . . . . . . . . . . . . . . . . . . . . . 6
3. Multicast-Broadcast Encapsulating Delivery Style . . . . . . . 7
3.1. Packet header formats for visited network traffic . . . . 8
3.2. Packet header formats for homebound traffic . . . . . . . 9
4. Multicast-Broadcast Encapsulating delivery Style Vs
RFC3024 Encapsulating delivery . . . . . . . . . . . . . . . . 10
5. Link-layer Assisted Delivery Style (LLADS) . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative references . . . . . . . . . . . . . . . . . . . 16
9.2. Informative references . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 19

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1. Introduction

[RFC3344] section 4.3 and 4.4 discusses multicast and broadcast
routing to and from the mobile node in the presence of triangular
routing and with a co-located Care-of-address. Reverse tunneling for
Mobile IP [RFC3024] uses the optimal direct delivery style from the
mobile node via the foreign agent if only unicast traffic is being
reverse tunneled. If, however, multicast or broadcast packets are
also meant to be reverse tunneled, it introduces the Encapsulating
Delivery Style Unfortunately, once the encapsulated delivery style is
negotiated, it applies to all reverse tunneling, including unicast.
[RFC3344] also mandates that all multicast and broadcast packets
should be delivered encapsulated from foreign agent to mobile-node.
This imposes tunnel overhead for multicast and broadcast packets.
While tunneling overhead on wired links may be acceptable, it has a
higher cost and throughput impact in wireless links. Even though,
Mobile IP has been deployed for 3G data services, there has not been
much usage of multicast or broadcast data transfer to or from the
mobile node. The Wimax Network Architecture [NWG] uses Mobile IP
services as one of the mobility services which could be used for both
Voice-over-IP and data. In the future, PTT (Push-To-Talk) service
may be popular and thus demands efficient usage of multicast delivery
from the mobile to the network acess provider network. Similary,
IPTV may use multicast to distribute streaming media across high
bandwidth wireless network such as Wimax [NWG].

Moreover, neither RFC3344 nor RFC3024 clearly specify multicast/
broadcast packet delivery for FA Care-of address; for example, for
encapsulated delivery, the source address of the outer and inner IP
header is the home address of the mobile (RFC3024, section 5.2.2),
and section 5.4 talks about local delivery of multicast/broadcast
packets in the visited network but some border cases are not
completely specified. In particular, multicast messages from the
mobile node to the visited network may be needed for retrieving
service information. The all Mobility-agents multicast address is
used for router solicitation by the mobile node, so foreign agent
implementations must it as a special address. This leads to
complexity if in the reverse tunnel the mobile node uses its home
address as the source address for other multicast messages destined
to the home and visited network.

Currently different organizations [3GPP2] define their own mechanism
to obtain local information such as DNS server IP address through
AAA. All Mobility-agent multicast is used for router solicitation by
the mobile and the implementation can treat this address specially at
the foreign-agent. However, the implementation of foreign agent
needs to apply multicast-address filtering and gets very complex if
the mobile client uses home-address as source address for other

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multicast messages destined to the home and visited network, in the
reverse tunnel mode. Even if multicast packets are delivered
locally, the return packet which will have destination address as the
home-address will be dropped at foreign-agent as they are not coming
from the reverse tunnel. RFC3024 recommends selective reverse
tunneling by delivering packets directly to foreign agent, while
encapsulating them for reverse tunnel delivery. But the
specification is not clear about the source addresses of the packets
from the mobile in case of selective direct-delivery. Although it
clearly states that for the mobile using co-located care-of-address.

This document aims to clarify multicast messages with reverse
tunneling, adds the capability of using encapsulated delivery only
for multicast/broadcast packets from mobile to foreign agent (while
allowing direct delivery for unicast), and explores direct delivery
options of multicast messages between the mobile and the foreign
agent by using link-layer capabilities.

Section 3 describes the new delivery extension for multicast-
broadcast messages in reverse tunnel mode.

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2. 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 RFC 2119.

MN
Mobile Node

FA
Foreign Agent

FA-COA
Foreign Agent as care-of-address.

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3. Multicast-Broadcast Encapsulating Delivery Style

The Mobile IP reverse tunneling [RFC3024] defines the Encapsulating
delivery style for delivering multicast and broadcast packets from
the mobile to the foreign agent in the FA-CoA mode. It also mandates
Encapsulating delivery mode for sending multicast/broadcast packets
to reverse-tunnel to home agent via the foreign agent. But RFC3024
section 2 says that all reverse-tunneled traffic is encapsulated when
Encapsulating Delivery is negotiated. The "Multicast-Broadcast
Encapsulating Delivery Style" (MBEDS) extension defined here applies
encapsulation only to the reverse-tunneled multicast and broadcast
packets, leaving direct delivery for reverse-tunneled unicast
packets. The main motivation for adding this extension is to save
the overhead of additional IP header for unicast packets. This
procedure works for both shared media like ethernet, IEEE 802.11 and
links of a point-to-point nature such as those defined by 3GPP, 3GPP2
and IEEE 802.16.

Foreign agents SHOULD support the Multicast-Broadcast Encapsulating
Delivery Style Extension. A registration request MAY include either
a regular Encapsulating delivery extension (see section 3.3 in
RFC3024) or a Multicast-Broadcast Encapsulating Delivery extension,
but not both. If both extensions are present, only the first
extension will be taken into consideration and the second one will be
skipped.

If a foreign agent supports MBEDS, then the foreign agent SHOULD
advertise the MBEDS extension int its router advertisement to inform
the mobile about the type of delivery style it supports. This will
avoid the possiblity of multiple registration requests to figure out
which encapsulating method the foreign agent supports.

If the MN includes an MBEDS extension, if MUST do so after the
Mobile-Home Authentication Extension, and before the Mobile-Foreign
Authentication Extension, if present. The Encapsulating Delivery
Style Extension MUST NOT be included if the 'T' bit is not set in the
Registration Request.

If no delivery style extension is present, Direct Delivery per RFC
3024 is assumed.

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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Bit-field Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

TBD

Length

Value
It is a 16-bit bit-field. Value specifies what type of packets are encapsulated.
The following bits are defined (0 being the right-most bit, 15 the left-most bit):

0 : All packets are encapsulated between a mobile node and a foreign agent. It is same
as the Encapsulating Delivery Style in RFC3024. NOTE: obsolete EDS in 3024?
1 : Only multicast and broadcast packets are encapsulated (MBEDS)
2 : Link-layer Assisted Delivery Style (LLAS) for local network

NOTE: Only MBEDS packets are reverse tunneled after being de-capsulated at
the foreign agent, not those directly destined to the foreign-agent address
or all mobility agent address. These are processed locally by the foreign agent.

3.1. Packet header formats for visited network traffic

Other than Mobile IP agent solicitation packets, There might be some
multicast or broadcast packets meant for consumption at the visited
network. If the mobile node can acquire a local IP address, then it
MUST direct deliver the multicast and broadcast traffic for local
use. If the mobile node can have only one IP address, (i.e. home
address ) then it MUST send all the multicast and broadcast packets
encapsulated. These packets will be sent to the home network through
the reverse tunnel after decapsulation at the foreign agent; only
exceptions are the multicast solicitation messages for the mobility
agent.

In some cases, the mobile may want to send multicast or broadcast
packets to visited network entities other than the foreign agent. In
those cases they should always be direct delivered by acquiring a
local IP address or using link-layer mechanism if possible. Please
see the section 'Link-layer Assisted Delivery Style' below for
details.

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3.2. Packet header formats for homebound traffic

The packet format and processing for encapsulated multicast and
broadcast traffic is the same as defined in section 5.2 of Mobile IP
Reverse tunnel document.

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4. Multicast-Broadcast Encapsulating delivery Style Vs RFC3024
Encapsulating delivery

RFC3024 encapsulating delivery style does not require the foreign-
agent to advertise an extension as well for the mobile node
efficiency. MBEDS provides an option for foreign agent to advertise
the extension with supported extension types, so that a mobile node
can request a delivery style that the foreign agent supports.

RFC3024 encapsulating delivery style requires all multicast,
broadcast and unicast traffic to be encapsulated in order to be
reverse tunneled. In MBEDS unicast packets are always direct
delivered to the foreign-agent. Most of the the cases a node sends
unicast packets for communication with a correspondent node and
occassionally it may send broadcast or multicast packets to the home
network. Thus this new style of delivery relieves the overhead of
encapsulation for most traffic.

MBEDS introduces TLV style extension for delivery style. Therefore,
this extension can be used to negotiate different delivery styles in
the future. Currently, it can be backward compatible with RFC3024
encapsulating delivery style when the value field is zero. NOTE: We
should make this a bit field to allow for easier advertisement and
other extensions.

A mobile node SHOULD use either RFC3024 style encapsulating delivery
extension or the MBEDS extension (defined in this document), but not
both at the same time. If both extensions are received at the
foreign-agent, it sends an error (70) in the registration reply
message. On the other hand, a foreign-agent MUST not send both old
and new extensions at the same time with the registration request.

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5. Link-layer Assisted Delivery Style (LLADS)

This section discusses direct-delivery of multicast and broadcast
packets between the mobile node and the foreign agent by taking
advantage of link-layer mechanisms. Certain link-layers allow for
direct delivery from the MN to the FA (and viceversa) without the
need for encapsulation. In effect, this is assumed by RFC 3024 for
Direct Delivery Style. In this mode, a unicast packet at the IP
layer is carried over a unicast link-layer delivery mechanism. For
example, the FA's MAC address is the link-layer destination address,
or the packet is sent on a link of a point-to-point nature as in 3G
or WiMAX networks. Broadcast and multicast packets, however are
typically sent using a link-layer broadcast or multicast mechanism: a
broadcast or multicast MAC address for IEEE 802.11 networks. If,
however, these packets had the FA unicast MAC address while carrying
an IP layer broadcast or multicast destination, then there would be
no need for encapsulation to remove the ambiguity. The packet would
be unequivocally directed at, and consumed by the FA. Notice that in
links of a point-to-point nature, there is no ambiguity even for
multicast and broadcast packets: these are unequivocally delivered to
the FA. The Link-layer Assisted Delivery Style allows for direct
delivery of unicast, multicast and broadcast packets over link-layers
that can support it. In particular, it requires that regardless of
whether the IP layer packet is unicast, broadcast or multicast, (1)
when sending from MA to FA, the FA unicast address always be used,
and (2) when sending from FA to MN, the MN unicast address always be
used. The FA advertises such capability per the extension defined
above, and the MN requests it in its registration request.

The LLADS imposes the least amount of tunneling overhead of the
delivery styles as it effectively uses the equivalent of direct
delivery for unicast, broadcast and multicast. It enables the MN to
deliver packets to the FA for the foreign agent to reverse tunnel
them back to the MN's home network.

However LLADS does not by itself allow the MN to deliver packets such
that the FA know whether or not it should reverse tunnel them, or
process them as local packets (e.g., perhaps forwarding them to local
services). Certain networks have the capability of enabling
additional context at the link-layer to effect different
classification and treatment of packets otherwise indistinguishable
at the IP layer, e.g., by establishing additional PDP contexts in
3GPP or additional service flows (and the corresponding CIDs) in
WiMAX networks. In such networks, it is possible for the MN and the
FA to establish additional context such that packets sent by the MN
to the FA are classified correctly upon arrival into either packets
meant for local consumption, or packets meant to be reverse tunneled.
In the absence of any IP layer differentiation (i.e., by sending

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packets meant for local consumption with the MN's local care-of
address as source address), such link-layer mechanisms can provide
the necessary means for the FA to select the correct processing for
packets received from the MN. Such link-layer mechanisms, however,
are out of scope of this document.

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6. Security Considerations

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7. IANA Considerations

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8. Acknowledgments

The authors like to thank Charlie Perkins, De Juan Huarte Federico,
Parviz Yeghani, Jayshree Bharatia for their comments and contribution
in shaping up this document. We also thank the Wimax Forum NWG
members for their valuable input and suggestions for the intial
discussion of the problem. Thanks to Prakash Iyer for approving this
work for Wimax forum.

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9. References

9.1. Normative references

[RFC3024] Montenegro, G., "Reverse Tunneling for Mobile IP,
revised", RFC 3024, January 2001.

[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.

9.2. Informative references

[3GPP2] "3GPP2 - Third Generation Partership Project 2: X.P0028-
200", Online web site http://www.3gpp2.org.

[NWG] "NWG - Wimax Network Architecture Group", Online web
site http://www.wimaxforum.org.

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Authors' Addresses

Samita Chakrabarti
Azaire Networks

Email: samita.chakrabarti@azairenet.com

Ahmad Muhanna
Nortel Networks

Email: amuhanna@nortel.com

Gabriel Montenegro
Microsoft

Email: gabriel.montenegro@microsoft.com

Alexander Bachmutsky
Nokia Siemens Network

Email: alexander.bachmutsky@nsn.com

Yingzhe Wu
Huawei

Email: ywu@huawei.com

Basavaraj Patil
Nokia Siemens Networks

Email: basavaraj.patil@nsn.com

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Parviz Yegani
Cisco Systems

Email: pyegani@cisco.com

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