Subject: [rohc] state retention priority - SIGCOMP

From: sasidhar <[email-masked]>
Date: Fri, 23 Apr 2004 15:54:03 +0530

Hi all,
    I have some doubt regarding state retention priority in SIGCOMP. Consider the following call flow..

    Endpoint A                                   Endpoint B
            S0* -----------------M1-----------------------> S0
    
       S0,S1  <---------------M2--------------------------S1*,S0

   S0,S1,S2* ----------------M3(S0)------------------->S2,S1,S0
    
S0,S1,S2,S3<---------------M4(S1)-------------------S3*,S2,S1.S0

    * implies unacked.

Doubts:
   1. Endpoint A creates a state S0 locally and remotely. Do both the states have the same priority(priority doesn't effect state id)?
   2. Suppose endpoint A has SMS equal to the size of two states (say 1kb each). If A gives constant priority 1 for its states and B gives a priority of 10, when A receives M3 it will be having states <S1,S2>. And on receiving M4 it will be <S1,S3>. Endpoint A will have no states to use for compressing the next message. So it has to go stateless. This will effect the compression ratio.

Please clarify my doubts.

Thanks,
Sasidhar

---

From: [email-masked]
Date: Fri, 23 Apr 2004 18:34:10 +0530

Hi Sasidhar,

Refer to Section 6.2.(  Memory Management) of RFC 3320. It states that
" Note that locally available state items (as described in Section
   3.3.3) need not be mapped to any particular compartment.  However, if
   they are created on a per-compartment basis, then they must not
   interfere with the state created at the request of the remote
   endpoint.  The special state_retention_priority of 65535 is reserved
   for locally available state items to ensure that this is the case."

1) Locally created states have the least priority i.e 65535, if created on
a per compartment basis. The state_retention_priority of 65535 is
      reserved for locally available states; these states must always be
freed first.   This clearly states that the remotely created states have
a higher priority, since there priority would range from (0 - 65534) and
locally created states whose priority is always 65535.

2) Regarding your second point you need not store the local states on a per
compartment basis, there could be stored globally
(refer sec 5.3 of RFC 3321), hence the state would not be deleted   when a
new state creation request comes from the remote. However if
you still decide to go ahead with maintaining the local states on a per
compartment basis then they would be deleted if no states memory
is available and a new request for state creation has come from the remote.

Thanks
    Azim

               The answer to your first question is

             sasidhar                                                      
             <[email-masked]                                             
             m>                                                         To 
             Sent by:                  [email-masked]                       
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             rg                                                            
                                                                   Subject 
                                       [rohc] state retention priority -   
             04/23/04 03:54 PM         SIGCOMP                             

             Please respond to                                             
                 sasidhar                                                  
             <[email-masked]                                             
                    m>                                                     

Hi all,
    I have some doubt regarding  state retention priority in SIGCOMP.
Consider the following call  flow..

    Endpoint A                                   Endpoint  B

    * implies unacked.

Doubts:
   1. Endpoint A creates a  state S0 locally and remotely. Do both the
states have the same  priority(priority doesn't effect state id)?
   2. Suppose endpoint A has  SMS equal to the size of two states (say 1kb
each). If A gives constant priority  1 for its states and B gives a
priority of 10, when A receives M3 it  will be having states <S1,S2>.
And on receiving M4 it will be  <S1,S3>. Endpoint A will have no states to
use for  compressing the next message. So it has to go stateless. This will
effect  the compression ratio.

Thanks,
Sasidhar

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---

From: sasidhar <[email-masked]>
Date: Fri, 23 Apr 2004 20:11:02 +0530

Hi Azim,
    Thanks for the explaination. Now let me reiterate the things which i
understood.
    The locally available state items will include the states like static
dictionary and also the states that have been saved by the compressor at the
local endpoint after the successful compression of a message. These states
need not be maintained in the STATE memory and should not reflect in the SMS
advertised to the remote endpoint.
    Please let me know if my understanding is correct.

And i have few more queries:

    1. You have mentioned that the locally available states(specially the
states created by compressor) can be maitained on a global basis. I cannot
think of any good reason for this. Can you throw some more light on it? As
per my understanding, states will be created by the compressor on a per
message basis
and each message will be specific to one compartment. So there is very
little probability that these states will be same across all compartments.

    2. what does SMS that is advertised in the returned sigcomp parameters
imply? Does it mean the actual capability of the endpoint or is it the
presently available free state memory size ?

    3. How can the compressor decide about the minimum access length for a
state to be stored on the remote side? Because it won't be having any idea
about the number of states that are existing on the remote side. And in the
decompression process for STATE-ACCESS instruction, the state has to be
accessed without knowing the compartment in which it has been stored.
Consider a scenario in which all the endpoints make the minimum access
length as 6 for all the states and access the states using 6 bytes. Then, is
this SHA-1 hash so efficient that it can avoid collisions among the states
even for the FIRST 6 bytes?

Thanks,
Sasidhar

----- Original Message -----
From: <[email-masked]>
To: "sasidhar" <[email-masked]>
Cc: <[email-masked]>; <[email-masked]>
Sent: Friday, April 23, 2004 6:34 PM
Subject: Re: [rohc] state retention priority - SIGCOMP

Hi Sasidhar,

Thanks
    Azim

             sasidhar
             <[email-masked]
             m>                                                         To
             Sent by:                  [email-masked]
             [email-masked]                                          cc
             rg
                                                                   Subject

             Please respond to
                 sasidhar
             <[email-masked]
                    m>

Hi all,

Endpoint A Endpoint  B

* implies unacked.

Doubts:

Thanks,
Sasidhar