Subject: [Mip4] regional registration draft

From: "Niko A. Fikouras" <[email-masked]>
Date: Mon, 01 Sep 2003 15:43:10 +0200

Hi all,

I have a question on the regional registrations draft 
(draft-ietf-mobileip-reg-tunnel-07.txt). According to Appendix Section 
"B.1. Registration with Home Agent" (p.32-33), a foreign agent may have 
to include in its agent advertisements the addresses of all mobility 
agents (RFAs, GFAs) in its hierarchy branch.  I would like to know what 
the reason is behind this action, because considering a MIP hierarchy 
with several levels then agent advertisements may acquire a significant 
size. Moreover, considering that foreign agents may have to increase 
their advertisement period in order to accelrate MIP hand-offs, then the 
transmission of agent advertisements of some size may result in a 
significant overhead with an effect to network efficiency.

Thanks in advance
niko

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---

From: "Jee J.Z." <[email-masked]>
Date: Thu, 4 Sep 2003 17:47:05 +0100

Hi Niko,

I think this is for the MN to choose a closest anchor point to send a
regional registration request next time.

Cheers,
Jee

---

From: "Niko A. Fikouras" <[email-masked]>
Date: Fri, 05 Sep 2003 10:01:57 +0200

Hi Jee,

I suppose this might be the reason, but IMHO this is not necessary. 
Assume a three level hierarchy as shown below (hope ASCII graphic is 
coming through ok) and further assume that the FAs do not include in 
their advertisements any of hierarchical mobility agents in their 
hierarchy branch.

             GFA
             /      \
            /         \
          RFA1     RFA2
          /     \        /    \
       FA1  FA2 FA3   FA4

Initially MN enters the hierarchy below FA1. This first RegReq 
propagates through the hierarchy making a binding at every hierarchical 
mobility agent it encounters, namely RFA1, GFA, HA. The RegReply is 
initiated by the HA. In RFA1's binding the MN has as COA the address of 
the FA1, while in the GFA's binding it has as COA the address of RFA1.
As the MN moves to FA2 it initiates a new RegReq that again propagates 
through the hierarchy. Only this time, when the RFA1 received the 
RegReq, it goes through its bindings table and determines that it 
allready maintains a binding for this MN. Then it compares the existing 
COA with the one in the RegReq. If it they are the same then this is 
probably a RegReq with the purpose of renewing the lifetime of a binding 
and should be forwarded, otherwise the MN is trying to establish a new 
binding. Depending on the status of the 'S' bit, the request is handled 
locally and a RegReply is locally issued.
Finally, should the MN move between FA2 and FA3 then the RegReq would 
traverse the hierarchy all the way to the GFA who would go through its 
bindings table and determine that the MN is already known to him. At 
that point it may decide to terminate the RegReq and issue a RegReply.
All of this may happen transparently without increasing complexity at 
the mobile node or without increasing the size of the agent 
advertisements. Besides the size and rate of the advertisements may 
affect the efficiency of the network. This URL 
(http://www.comnets.uni-bremen.de/~niko/efficiency.eps) leads to a graph 
acquired with ns-2 that indicates the efficiency of a simulated WLAN 
with a single FA and MN. Different advertisement sizes and rates where used.

Best Regards
niko

---

From: "Jee J.Z." <[email-masked]>
Date: Fri, 5 Sep 2003 15:27:39 +0100

Hi Niko,

You are right that including all foreign agents' address in the hierarchy in agent advertisements is not a necessity. The draft only states that the foreign agent MAY do so. IMHO by doing so, the choice of registration anchor point is left to Mobile Nodes, and therefore foreign agents do not need to go through their visitor list every time they get a registration request and thus speed up the processing. However, as you mentioned, large advertisement packets may affect the network efficiency. There may be a tradeoff involved. Both methods assume keys have been distributed to the GFA/RFA/FA, and RFA/FA may process registration requst message addressed to the GFA, if not including all foreign agents' address in the hierarchy in advertisments.

Other comments are very welcome.

Regards,
Jee

----- Original Message ----- 
  From: Niko A. Fikouras 
  To: Jee J.Z. 
  Cc: Mobile IP v4 
  Sent: Friday, September 05, 2003 9:01 AM
  Subject: Re: [Mip4] regional registration draft

  Hi Jee,

  I suppose this might be the reason, but IMHO this is not necessary. Assume a three level hierarchy as shown below (hope ASCII graphic is coming through ok) and further assume that the FAs do not include in their advertisements any of hierarchical mobility agents in their hierarchy branch.

               GFA
               /      \
              /         \
            RFA1     RFA2
            /     \        /    \
         FA1  FA2 FA3   FA4

  Initially MN enters the hierarchy below FA1. This first RegReq propagates through the hierarchy making a binding at every hierarchical mobility agent it encounters, namely RFA1, GFA, HA. The RegReply is initiated by the HA. In RFA1's binding the MN has as COA the address of the FA1, while in the GFA's binding it has as COA the address of RFA1.
  As the MN moves to FA2 it initiates a new RegReq that again propagates through the hierarchy. Only this time, when the RFA1 received the RegReq, it goes through its bindings table and determines that it allready maintains a binding for this MN. Then it compares the existing COA with the one in the RegReq. If it they are the same then this is probably a RegReq with the purpose of renewing the lifetime of a binding and should be forwarded, otherwise the MN is trying to establish a new binding. Depending on the status of the 'S' bit, the request is handled locally and a RegReply is locally issued.
  Finally, should the MN move between FA2 and FA3 then the RegReq would traverse the hierarchy all the way to the GFA who would go through its bindings table and determine that the MN is already known to him. At that point it may decide to terminate the RegReq and issue a RegReply. 
  All of this may happen transparently without increasing complexity at the mobile node or without increasing the size of the agent advertisements. Besides the size and rate of the advertisements may affect the efficiency of the network. This URL (http://www.comnets.uni-bremen.de/~niko/efficiency.eps) leads to a graph acquired with ns-2 that indicates the efficiency of a simulated WLAN with a single FA and MN. Different advertisement sizes and rates where used.

  Best Regards
  niko

  Jee J.Z. wrote:

Hi Niko,

Cheers,
Jee

----- Original Message -----
From: "Niko A. Fikouras" <[email-masked]>
To: <[email-masked]>
Sent: Monday, September 01, 2003 2:43 PM
Subject: [Mip4] regional registration draft

Hi all,

Thanks in advance
niko