6LowPANer:
As David mentioned, mulitcast is definitely needed in 6LowPAN. My previous
comments just want to give out some idea about the problem using MAC
multicast. In the matter of fact, our lab have introduced an controlled
flooding
to solve the IP multicast problem recently.
The flooding way is simple: all IP packet with multicast destination address
will
be encapsuled in an adaptation Broadcast Frame. However, the format of
adaptation Broadcast Frame is somewhat different from the standard header
format. The modified format showed below.
1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LF| prot_type |M|B| rsv |Payload (or MD/Broadcast Hdr)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
As the figure showed, a "B" bit is added(replacing one rsv bit). When the "B"
bit is set, a Broadcast Field will be included in the frame immediately
following
the LoWPAN header. If there is a Broadcast Field, we will call the
adaptation frame as a Broadcast Frame. The "Broadcast" field is defined as
follows
1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|Broad Radius |Sequence Number|Source Address, followed by...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S: 0 if use EUI-64 address, or 1 if use 16-bit address.
Broad Radius: Broadcast Radius, 7 bits, should be decrement by each
broadcast relay node, if it is decremented to 0, discard the frame.
Sequence Number: A 8-bit number to identify different Broadcast Frame from
the same source node. The originator will increment the field after each
sending.
Source Address: The Originator's MAC address.
With the support of the "Broadcast" field, an originator or a relay node will
send the Broadcast Frame like that: first, deliver the frame to all Coordinator
and Routers around using MAC broadcast(with the MAC destination address
set to 0xFFFF, just need broadcast once), then, if there are End Devices in
the node's neighbor table, unicast the frame to them one by one. Besides, to
avoid broadcast storm, a Broadcast Record Table will be needed. The table will
record the Source Address and Sequence Number in "Broadcast" field of each
received Broadcast Frame after re-broadcasting it first(End Device don't need
to re-broadcasting). Sequentially, a Broadcast Valid Time will be initialized
for
the newly added Broadcast Record Entry. Then, before the entry is timed out
(Broadcast Valid Time is decremented to 0), all Broadcast Frame with the same
Source Address and Sequence Number should be discarded but not relayed.
In practice, with the relatively simple way, the controlled flooding could just
solve the problem of how to multicasting. We find it still a high-costing method
to broadcast periodic Multicast IP packet(like Router Advertisement,
RFC2461). So, more details about the up-layer protocol(especially about
NDP) need be considered. For example, using an dynamic advertising
algorithm to reduce the broadcast times.
Hope these ideas will do some help.
Regards,
Mario Mao
----- Original Message -----
From: "David Rahusen" <[EMAIL PROTECTED]>
To: "'Ian Chakeres'" <[EMAIL PROTECTED]>; "'Mario Mao'" <[EMAIL PROTECTED]>;
<[email protected]>
Sent: Wednesday, June 07, 2006 3:48 PM
Subject: AW: [6lowpan] Comments about the use of Multicast Ability
Hi all,
I'm pretty new to this WG, so please correct me if I've been overlooking
anything.
I agree with Mario, that another protocol or even more complexity isn't
reasonable for low power nodes. But multicast may be a useful solution for
some applications.
In case of different PANs within one network, it is possible to transmit
messages to anyone of a single PAN: Isn't it multicast? We know that all
associated nodes within this PAN are directly reachable by the appropriate
coordinator. The main problem is, to reach this PAN (multi-hop). So my
question is: Is it possible to specify a flag within the header of the
adaptation layer to indicate, whether this message is a multicast message or
not? Therefore this message could be routed and transmitted as unicast to
the appropriate PAN coordinator. In case this flag is set, the coordinator
broadcasts the message within the PAN. Otherwise, the message is directed to
the coordinator itself.
Please let me know if I'm totally wrong or this may be an approach.
Best regards,
David
-----Ursprüngliche Nachricht-----
Von: Ian Chakeres [mailto:[EMAIL PROTECTED]
Gesendet: Sonntag, 21. Mai 2006 18:01
An: Mario Mao; [email protected]
Betreff: Re: [6lowpan] Comments about the use of Multicast Ability
I think that a protocol like SMF (draft-ietf-manet-smf-02.txt) for non-group
based simple multicast would be appropriate for 6lowpan. The SMF draft deals
mainly with duplicate packet detection (DPD). Though it should be used in
conjunction with another algorithm to determine an optimized relay set.
That brings me to another point, to support mutlicast I think the adaptation
layer should have a sequence number for multicast packets.
This will be used to detect duplicate packets. SMF defines a IPv6 hop by hop
option to assist DPD, this field should be integrated into the shim layer.
Ian Chakeres
On 5/20/06, Mario Mao <[EMAIL PROTECTED]> wrote:
>
>
> Hi all:
> There is some comments about recently introduced Multicast ability.
>
> I have read Format-02 document and the Carsten's mail about
> addressing map for 16-bit addresses. I think it is a good solution for
> the address confusion problem.
> However, looks like there needs other precondition to make Multicast
> work properly and effectively in 6LowPAN.
>
> First condition is the MAC filter, as I mentioned in last mail,
> IEEE
> 802.15.4
> MAC can't fliter Multicast frame, the reception and rejection
> algorithm are descripted as bellow in specification:
> - If a destination PAN identifier is included in the frame, it shall
> match macPANId or shall be the broadcast PAN identifier (0 x ffff).
> - If a short destination address is included in the frame, it shall
> match either macShortAddress or the broadcast address (0 x ffff).
> Otherwise, if an extended destination address is included in the
> frame, it shall match aExtendedAddress.
> According to this algorithm, when the MAC layer of some 802.15.4
> node receive a frame with Multicast destination address, how will it
> judge the frame should be handled but not be discarded? For 802.15.4
> MAC PIB could just hold one 64-bits
> EUI-64 address and one 16-bits short address(for node's unicast
> address), may be the only way to get Multicast frame is to set the MAC
> sublayer to promiscuous mode.
> By doing this job, Adaptation Layer could get all of frame arrived in
> MAC sublayer and filter what it want by itself, including Multicast
> frame.
> Unfortunately, the solution for the previous problem also cause
> another problem.
> That is how to foward the Multicast frame to right destinations(group
> members). The document "6LoWPAN Meeting 65 IETF Dallas Format Document
> changes"
> mentioned following possible method: dumb flooding, controlled
> flooding and unicasting to the PAN COORDINATOR. As my understanding,
> all three above still need
> 802.15.4 MAC broadcast and Adapatation Layer broadcast flooding relay
> to make all possible receiver get Multicast frame. The requirement of
> Adapatation Layer broadcast flooding relay is because not all of
> 802.15.4 node will be in the broadcast range of the sender in Mesh
> Topology, unlike in Ethernet. So, maybe we should need an Adaptation
> Multicast Route Potocol(like PIM-SM in Internet) to build a Multicast
> Tree when some node join some Multicast group. After the Multicast
> tree has been built, node in the tree will know where are the group
> members in and how to forward Multicast frame to them.
> In the matter of fact, we could also use the special Multicast
> address in a much simple way, that is just make Adaptation Layer be a
> Multicast frame filter.
> In this way,
> IPv6 Layer will tell Adaptation Layer which Multicast group it has
> joined, and Adaptation Layer will discard the frame not belong to
> these groups before handing it to IP Layer. However, if we want the
> sepcial Multicast address really do some work, controlled forwarding
> in Multicast Tree may be necessary. Otherwise, node will fill
> Multicast MAC address in Adaptation or MAC header but could only
> broadcast Multicast frame to all the node in the PAN.
>
> Actually, I think 6LowPANers will find a good way to solve the
> multicast problem eventually. But what I want to say is does it worth?
> For 802.15.4 MAC don't support multicast, we have to do all the work
> in Adaptation Layer. In LowPAN node, resource is limited(except
> energy, memory for code is tight either). If we make the protocol more
> complex, more code space will be needed. Take the platform we are
> using as an example, the Freescale MC9S08GB60 MCU has 60K Flash for
> code, hardware driver and 802.15.4 MAC library(supplied by Freescale)
> will take at least 33K, current Adaptation Layer will take about
> 12K(including Route and Topology Maintenance), this means only 15K is
> left for IPv6, NDP and up-layer. For our lab has implemented an
> IPv6/IPv4 dual protocol stack in ARM platform before, we consider 15K
> code space is very tight for a reduced IPv6 stack. The point is, if we
> could just use MAC broadcast to let IP Multicast work well, why not
> just do it? If we add more and more function to Adaptation Layer, I
> really worry about a low power and low cost device having the ability
> to run it.
>
> Thanks.
>
> Regards,
>
> Mario Mao
> _______________________________________________
> 6lowpan mailing list
> [email protected]
> https://www1.ietf.org/mailman/listinfo/6lowpan
>
>
>
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