Re: [netext] Comments on I-D: draft-wolfner-netext-pmip6-connid-00

[jouni korhonen <[e-mail]>]

Hi Xiangsong,

On Jul 30, 2009, at 12:58 PM, Xiangsong Cui wrote:

> Hello Raj and Jouni,
>
> I have a question about the draft.
>
> Firstly, I agree the requirement of multiple PDN connections
> to the same APN.
>
> IMO, the major idea of this draft is as mentioned in the draft:
>
> The combination of MN-Identifier + Service Selection +
> Connection Identifier can uniquely identify mobility sessions even if
> the selected service on each mobility session for the same MN-
> Identifier are the same.
>
> It recall me to another draft, "draft-ietf-netlmm-grekey- 
> option-09.txt".
> In the GREKEY draft, it says:
>  This specification defines the GRE Key option to be used for the
>  negotiation of GRE encapsulation mode and exchange of the uplink and
>  downlink GRE keys.  The negotiated downlink and uplink GRE keys can
>  be used for marking the downlink and uplink traffic for a specific
>  mobility session.
>
> The connid draft is used to identify a certain session among
> multiple sessions, while the grekey draft is used to identify a
> certain link/flow in the tunnel between the MAG and the LMA.
>
> When I look at figure 1 in the grekey draft, it seems similar for the
> both cases, because we just need to identify a connection, and the
> connection may be a session or a flow.
>
> So I have the question:
> if we expand the meaning of GRE Key option, without protocol  
> expansion,
> can we use the combination "MN-Identifier + Service Selection + GRE  
> key"
> to identify the connections to the same APN?

There are few reasons. First, which GRE key to use? Uplink or  
downlink? Obviously, the MAG does not know the uplink GRE key when  
sending a PBU during the initial attach or after a handover.. so you  
would lack the "identifier" in the MAG in some situations. If we were  
to use the downlink key, according to the GRE key draft it is not  
guaranteed that the downlink remains the same between inter-MAG  
handover.

Second, the use of GRE keys and GRE tunneling is optional in PMIP6.  
Well, so is Service Selection too but I would avoid building  
additional dependencies between different documents if just possible.

Third, overloading the function of the GRE key option does not sound a  
good idea in general, even if it were possible.

Cheers,
	Jouni





>
> Regards
>
> Xiangsong
>
> ----- Original Message ----- From: <[e-mail]>
> To: <[e-mail]>
> Sent: Thursday, July 16, 2009 5:33 AM
> Subject: [netext] Comments on I-D: draft-wolfner-netext-pmip6- 
> connid-00
>
>
>>
>>
>> Hello,
>>
>> A few questions/comments related to the proposal to add a connection
>> identifier to the PMIP6 signaling and BCE:
>>
>> 1. Each of the PDN bearers will have a unique prefix assigned to it  
>> by
>>  the LMA, right? Even though the MN-ID remains the same the LMA will
>>  have to create multiple BCEs for the MN. The scenario is equivalent
>>  to the MN attaching via different interfaces thru the same MAG/LMA
>>  pair.
>>
>> 2. The I-D says that the mechanism by which the MAG figures out that
>>  a new bi-directional tunnel is needed to be established (and a new
>>  prefix obtained) is out of scope. In certain networks you are
>>  obtaining this information from L2 and is used by the MAG. Current
>>  RFC5213 lacks the ability by which an MN (which is already attached
>>  via an interface) can request dynamically a new prefix to be
>>  assigned to it for the same interface. The connection ID would be
>>  useful if we were to also specify how the MN can request an
>>  additional prefix via an interface that is already attached and has
>>  been assigned a prefix from a MAG/LMA pair.
>>  It might be useful to explain how L2s can provide such indications  
>> in an
>> appendix.
>>
>> 3. In the case of HO the target MAG will not be aware of the CID
>>  unless there a context transfer mechanism between the MAGs. Please
>>  note the I-D draft-ietf-mipshop-pfmipv6-08.txt which proposes
>>  context transfer capability between MAGs.
>>
>> 4. If each PDN bearer is assigned a unique prefix, can you not use  
>> the
>>  HNP assigned as the CID?
>>
>> I do agree with the need to support the ability by which multiple
>> mobility sessions to the same LMA (via the same MAG) from a single
>> interface is needed. This is applicable in EPC and other networks
>> which use PMIP6.
>>
>> -Raj
>>
>> _______________________________________________
>> netext mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/netext
>