Subject: RE: Questions

From: vishwas <[email-masked]>
Date: Tue, 17 Nov 98 16:22:00 PST

I feel there can be two ways to join a group and receive traffic for the   
mobile host when it moves to a new subnet.

1) It can join the group locally, which is straight forward.
2) If the foreign subnet doesent provide a multicast routing support, it   
can register with the Home Agent (H.A) and the H.A. should take are of   
redirecting the traffic for that group which the M.H has joined. This   
ensures that M.H. can retain its home address and will continue to be in   
the group. But this ha tunnelling overhead.

The Problem the Multicast Guys has to solve now is,
1) when a multicst traffic comes to a router, it will be handled by   
Multicast routing modules like (DVMRP, PIM, etc.,.) which either use   
local routing table or may be independent of unicast routing table.   
Mobile IP will use its own routing table (policy table) for its own   
routing decisions (DOG LEG, TRIANGULAR, BI-DIRECTIONAL TUNNELLING).
 Now, the Multicast router has to interact with the Mobile routing table   
and has to make the routing decisions, (IT IS ASSUMED THAT, SOURCES OF   
MULTICAST ARE STATIONARY, and receivers alone are Mobile),Rather Mobile   
IP has to make routing Decisions for Multicsat Packets (Sounds Crazy, but   
MAY be true) based on specific groups for which each of the M.H's have   
joined the group. But the decisions (RPF) are taken by Multicast routers.   
Once Mobile IP takes a decision on routing, it can emply Bi-directional   
Tunnels to route the Multicast packets, encapsulated by Unicast, to the   
current location of the M.H.

 We may have to look into Multicast extensions to the Mobile Hosts, where   
in a M.H. can tell the H.A, wether or not it needs Multicast traffic to   
be forwarded to it.

I need to have lot of Comments on this issue.

Regards
Vishwanath S. Edavayyanamath
 --------------------------------------------------------------------------  
 ------------------------
Software Engineer, Future Software Pvt. Ltd, Chennai, India
Ph : +91-44-4330550 (335)
Private e-mail : [email-masked]

 -----Original Message-----
From: vishwas [SMTP:[email-masked]]
Sent: Wednesday, November 18, 1998 2:40 AM
To: [email-masked]'; [email-masked]
Cc: [email-masked]'
Subject: RE: Questions

[vishwas]
I thought it may be usefull for PIM implementors.

I'm a student of Changsha Institute of Technology in Changsha,
P.R.China. I have some questions about mobile host issues in IGMP v.2
(RFC 2236).

1) How does a host know it is the first member of that group on the
network ?

[vishwas]
Need Not bother to know that.

2) When a mobile host moves into a new subnet, is it possible to send an
unsolicited version 2 membership report immediatly for each group it
joins ? As the "reports sent by mobile hosts without addresses on the
local subnet will be ignored", a mobile host can send the membership
report messages only after it obtains a local address (care-of address
in mobile IP), doesn't it ?

[vishwas]
Very much TRUE, Provided the new subnet has a multicast router.

3) How about the join latency when a mobile host moves into a new subnet
and need to receive messages from the previous multicast session ? I
noticed that the query interval for the IGMP is by default 125 seconds
(it may be too long in mobile host cases).

[vishwas]
It is an administratively configurable value, U can even set it to 60
secs. For the latency and Lost packets, U can provide some kind of cache   

agent. But generally U cant help it.

Mean while I was wondering what if the mobile host has moved to a
location where in the local subnet doesent have a Multicast router..!!
Then we may have to go for some thing like, Dynamic Tunnelling with the   

nearest Multicast router. In this case MSDP may be of some use (Just a
hunch). Though it can be thought of joinig the nearest router through
tunnel somehow, there may be security and administrative issues, which
cant provide a seamless mobility to a Mobile host.
     If we consider again the Home Agent to redirect the multicast
traffic to the new location by tunnelling them, again there may be
Modifications required to the Multicast routing protocol, to support
MOBILITY extensions.

In general what I would like to ask is, Does Mobility is in the scope of   

Multicast routing...?

Comments pl.
 -vishu

Regards
Vishwanath S. Edavayyanamath
 -------------------------------------------------------------------------  
 -
 ------------------------
Software Engineer, Future Software Pvt. Ltd, Chennai, India
Ph : +91-44-4330550 (335)
Private e-mail : [email-masked]