Subject: [manet] Re: Gateway Advertisements

From: Anders Nilsson <[email-masked]>
Date: Tue, 09 Jul 2002 11:28:37 +0200

Hello Fredrik!

For the solution described in the draft, unsolicited gateway 
advertisments are not neccessary
for the correct operation of the protocol.

I see your point and I think that it is question of whether a reactive 
or a more proactive approach
should be used. One of the reasons for not recomending gateway 
advertisement flooding is when you consider the scenario where some 
nodes might need internet access, and some might not.
When flooding of advertisements is being used,  packets are being 
flooded periodicly over all
nodes in the ad hoc network, regardsless of their need for internet 
connectivity. This is where hop_limit (TTL) considerations becomes 
important since every advertisement is rebroadcasted
as long as allowed by the hop_limit. So, what value for this hop_limit 
should be used? If we choose
a too small value we might not reach all nodes, and choosing a high 
value will introduce lots of traffic. Nodes that have no need for 
internet connectivity will also receive and process this traffic, 
uneccessary.
In the draft we instead propose that the node itself should initiate 
this process, the gateway discovery process. In the case where there are 
multiple gateways, the node should upon receiving these advertisements 
choose the closest gateway.

regards,

Anders

Fredrik Alriksson (EAB) wrote:

>Hi Ryuji,
>
>In what sense are the gateway advertisements unnecessary?
>
>In case there are multiple gateways, the flooding of gateway advertisements may actually _decrease_ the total number of packet transmissions (control and user data transmissions) in the MANET! 
>
>Flooding gateway advertisements can enable manet nodes which already have a global address to select a _closer_ gateway. This means that the average distance between gateway and manet node can be decreased. This in turn decreases the number of packet transmissions required to deliver user data between the gateways and the manet nodes. Depending on the user activity, this reduction can be larger than the increase in control packet transmissions. 
>
>Other benefits are that the average user data delay decreases, and that the manet nodes loose contact with their gateway less frequently.
>
>Regarding TTL, I don't see the problem, unless advertisements were forwarded on non-manet interfaces. Can you please elaborate a bit?
>
>BR,
>Fredrik
>
>>-----Original Message-----
>>From: Ryuji Wakikawa [mailto:[email-masked]]
>>Sent: den 8 juli 2002 18:40
>>To: [email-masked]
>>Cc: [email-masked]; [email-masked];
>>[email-masked]; [email-masked]; [email-masked];
>>[email-masked]
>>Subject: Re: Gateway Advertisements
>>
>>
>>
>>Hello Fredrik.
>>
>>In the draft, unnecessary packets basically indicates un-necessary
>>gateway advertisements. For example, if a gateway generates a route
>>advertisement every 1 sec, most of router advertisements are redundant
>>for manet nodes which have already had a global address. They may
>>update lifetime of their global address, but the interval(1sec) is
>>still too short for this operations.
>>
>>Since flooding packets is easy to cause performance damage in manet,
>>our approach tries to reduce a number of packets which are 
>>flooded over
>>manet. I think manet nodes should not wait flooded advertisements from
>>gateway, instead manet node should discover gateways on their
>>initiative.
>>
>>It is also difficult for gateways to decide TTL for flooded
>>advertisements. Expanding ring search technique can not be applied to
>>this situation, because advertisements should reach at the edge of
>>manet. It can imagine that unnecessary network-wide dissemination of
>>advertisements will occur when a gateway sets larger TTL than manet
>>scale.
>>
>>regards,
>>ryuji
>>
>>
>>At Mon, 8 Jul 2002 17:27:19 +0200 ,
>>Fredrik Alriksson (EAB) wrote:
>>
>>>Hi All,
>>>
>>>In draft-wakikawa-manet-globalv6-00.txt you claim that 
>>>
>>sending gateway advertisements peridically would generate 
>>unnecessary packets in the Manet. Can you please explain how 
>>you came to that conclusion? Our simulation study on MIPMANET 
>>from '99 (http://www.e.kth.se/~e94_fal/mipmanet.pdf) 
>>indicates that it actually can decrease the number of packet 
>>transmissions in the MANET.
>>
>>>BR,
>>>Fredrik
>>>
>>>---
>>>Fredrik Alriksson, Ericsson Research
>>>Email: [email-masked]
>>>
>>>
>

---

From: Anders Nilsson <[email-masked]>
Date: Tue, 09 Jul 2002 11:28:37 +0200

Hello Fredrik!

regards,

Anders

---

From: Ryuji Wakikawa<[email-masked]>
Date: Thu, 11 Jul 2002 09:38:11 +0900

Hello Fredrik

I am catching up now, but let me reply to this first.

At Tue, 9 Jul 2002 09:46:15 +0200 ,
> In what sense are the gateway advertisements unnecessary?

I did not say all RAs which are periodically advertising are
un-necessary.  If gateway advertise RAs periodically, some of RAs are 
not processed by any nodes. And these RAs are flooded over manet
network untill TTL is expired.

> In case there are multiple gateways, the flooding of gateway
> advertisements may actually _decrease_ the total number of packet
> transmissions (control and user data transmissions) in the MANET!
> 
> Flooding gateway advertisements can enable manet nodes which already
> have a global address to select a _closer_ gateway. This means that
> the average distance between gateway and manet node can be
> decreased. This in turn decreases the number of packet transmissions
> required to deliver user data between the gateways and the manet
> nodes. Depending on the user activity, this reduction can be larger
> than the increase in control packet transmissions.
>
> Other benefits are that the average user data delay decreases, and
> that the manet nodes loose contact with their gateway less
> frequently.

The draft said that once manet node gets global info from a GW, it can
update the info by unicasting request message to the GW. Manet node may change
the GW to closer one any time by re-selecting an appropriate GW from
the node's GW lists or by re-flooding requests to discover closer
depending on some events like topology change.  
GW lists is node introduced in the draft, but let's say it is the
lists of GWs which are replyig to node's gateway discovery.

In appendix A, we explain how to use the most appropriate GW with a
routing header. I think the draft can be adapted to your above
situation. What do you think?

--Snip from the drat
   Using a routing header is also preferable if there are more than two
Internet-gateways, because the node then have the ability to decide
which Internet-gateway is the best, by distance in hops, or by some
other priority.  By assign a priority number for each Internet-gateway,
the route reply message and the Manet Router Advertisement messages
could be extended to support a candidate Internet-gateway option in it.
-----

I think we should clarify much more about situations when multiple GWs
are located.

# Can you explain more about simulated unicast situation.  Can a manet
  node receive RA from only associated GW? Didn't you use solicited
  request from the manet node? If not, GW will discover the manet node
  route, when it sends RA to the node and can not find fresh route for
  the node. This does not happen to our solution.

> Regarding TTL, I don't see the problem, unless advertisements were
> forwarded on non-manet interfaces. Can you please elaborate a bit?

In your thesis, you mentioned "Limited TTL". This is almost what I
want to explain here. If there is a single GW in manet, RA should be
flooded over whole manet. You can not use optimization like expanding
ring search for flooding. If Manet nodes can not get RAs sent with
limited TTL by GW, it has to discover GW by solicited requests.

best regards,
ryuji

> > > Email: [email-masked]

_______________________________________________
manet mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/manet

---

From: Ryuji Wakikawa<[email-masked]>
Date: Thu, 11 Jul 2002 09:38:11 +0900

Hello Fredrik

--Snip from the drat

best regards,
ryuji