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

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Intended Status <To Be Removed Upon Publication>

Intended status: Informational

Abstract

The IP Mobility Protocol (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] describes multicast and broadcast packet transmission between the mobile node and the home network or visited network. Reverse Tunneling for Mobile IP (Montenegro, G., “Reverse Tunneling for Mobile IP, revised,” January 2001.) [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] (Montenegro, G., “Reverse Tunneling for Mobile IP, revised,” January 2001.) 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
2.  Definition Of Terms
3.  Multicast-Broadcast Encapsulating Delivery Style
    3.1.  Packet header formats for visited network traffic
    3.2.  Packet header formats for homebound traffic
4.  Multicast-Broadcast Encapsulating delivery Style Vs RFC3024 Encapsulating delivery
5.  Link-layer Assisted Delivery Style (LLADS)
6.  Security Considerations
7.  IANA Considerations
8.  Acknowledgments
9.  References
    9.1.  Normative references
    9.2.  Informative references
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

[RFC3344] (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) 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] (Montenegro, G., “Reverse Tunneling for Mobile IP, revised,” January 2001.) 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] (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) 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] (, “NWG - Wimax Network Architecture Group,” .) 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] (, “NWG - Wimax Network Architecture Group,” .).

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 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.

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.

3.  Multicast-Broadcast Encapsulating Delivery Style

The Mobile IP reverse tunneling [RFC3024] (Montenegro, G., “Reverse Tunneling for Mobile IP, revised,” January 2001.) 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.

       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

         2

       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.

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.

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.

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 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.

6.  Security Considerations

7.  IANA Considerations

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.

9.  References

9.1. Normative references

9.2. Informative references

Authors' Addresses

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