Subject: Re: [Fwd: FW: Application for port-number]

From: "Rosen, Brian" <[email-masked]>
Date: Wed, 19 Jan 2000 08:15:20 -0500

One reason the MGC may wish to change ports is that the MGC may be
implemented with more than one
processor, or more than one IP interface.  I'll adjust the words to allow
it, but not "require" it.

Brian

-----Original Message-----
From: Tom-PT Taylor [mailto:[email-masked]]
Sent: Wednesday, January 19, 2000 7:54 AM
To: [email-masked]
Subject: Re: [Fwd: FW: Application for port-number]

        -----Original Message-----
From:   Pekka Pessi [SMTP:[email-masked]]
Sent:   Wednesday, January 19, 2000 5:16 AM
To:     Taylor, Tom-PT [CAR:B904:EXCH]
Cc:     [email-masked]
Subject:        Re: [Fwd: FW: Application for port-number]

        Tom-PT Taylor <[email-masked]> writes:
>To start with, there's a difference between TCP and UDP.  In TCP, once
>someone has connected to a TCP, no one else can.

                I don't understand.
[[TomT]]
Sorry -- wasn't thinking.  This is a wrong statement.  The reason the MGC
might want to move the MG away from the contact port is more a matter of
process relationships at the implementation level.

>Hence the MGC has to tell
>the MG to back off and use another.  When the MG does that, the MG end of
>the connection is fixed, just as it was the first time, so there's no point

>in the MG passing a contact address to the MGC.

                Agreed.

>With UDP, the MGC has the option of providing an alternate port or not,
>depending on implementation: the option is there for everyone to use the
>same port.  Moreover, the MGC has to know where to send the reply to the
MG,
>since it's not pre-determined, so the MG-supplied address and port do have
>an use.

                I agree with Brian. MGC can send all further messages back
to the
        same IP address/port that was used to send the service change
        request. There is absolutely no need to specify a port number in
        ServiceChange.
[[TomT]]
OK.

                I propose that we zap the following text:

        >The ServiceChange command contains a ServiceChangeAddress
parameter.  If TCP
>is used, the MG need not include this parameter, since it is implicit in
the
>TCP connection set up between the MG and the MGC.  The MGC will typically
include this parameter in order to tell the MG to move to a new port.

                Replace it with text as follows.

        The ServiceChange command or response may contain a
ServiceChangeAddress
parameter.  The MGC can include this parameter in order to tell the MG to
move to another MGC.

                Also, the last paragraph should be zapped:

        >If UDP/ALF is used, the ServiceChange Command from the MG must
contain the
>ServiceChangeAddress parameter, so that the MGC knows where to send its
>messages.  The MGC may include this parameter in its response, if it wishes

>to change the address and/or port to which the MG sends messages during the

>life of the association."

                                                Pekka

        >> -----Original Message-----
>> From: Rosen, Brian [SMTP:[email-masked]]
>> Sent: Friday, January 14, 2000 3:02 PM
>> To:   'Chuong Nguyen'
>> Cc:   Taylor, Tom-PT [CAR:B904:EXCH]
>> Subject:      RE: [Fwd: FW: Application for port-number]

        >> I had a long winded answer here, then went and talked to some of
my
>> people, and now I
>> think I am thoroughly confused.

        >> So I'm going to ask the "question first principals" question -
why do we
>> need any of this?

        >> There is exactly one control association between an MG and an
MGC.  The MG
>> is the client,
>> and it initiates the association.  Therefore this circumstance is exactly

>> analogous to
>> the control channel of FTP, or of TELNET, etc.  The MG sends its source
>> address and
>> desired port in the TCP SYN, addressed to the MGC at the well known port.

>> The MGC
>> replies with its source address and the well known port, and the MG's
>> address and its
>> desired port.  Rules state that flows are differentiated by the 4-tuple
>> (Source Address,
>> Source Port, Destination Address, Destination Port), so why do we need a
>> port number
>> in the protocol?   Same effect with UDP, right?

        >> And, as I understand it, putting port numbers in protocol
messages screws
>> up NAT and
>> firewalls.

        >> Even if there were reasons why it looked like you needed multiple

>> associations (the Virtual MG for example), the MG must use separate port
>> numbers, and the tuple remains unique.  The MGC
>> never initiates the connection, so there isn't a problem there.

        >> So, why are we doing this?