Re: [tcpm] comments on draft-kang-tcpm-accurate-data-scheduling-by-server-00
Christoph Paasch <cpaasch@apple.com> Thu, 23 July 2020 14:41 UTC
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Date: Thu, 23 Jul 2020 07:40:58 -0700
From: Christoph Paasch <cpaasch@apple.com>
To: Kangjiao <kangjiao@huawei.com>
Cc: Yoshifumi Nishida <nsd.ietf@gmail.com>, "tcpm@ietf.org Extensions" <tcpm@ietf.org>, Liangqiandeng <liangqiandeng@huawei.com>
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Subject: Re: [tcpm] comments on draft-kang-tcpm-accurate-data-scheduling-by-server-00
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On 07/23/20 - 04:38, Kangjiao wrote: > Hi Christoph, > > From my perspective, I think following are two different requirements: > > 1. Making all the traffic towards S2 (for this case, MP_PRIO may be enough) > > 2. Making traffic only from <IP_C1, IP_S1> to the destination IP_S2, which means diverting traffic that should be scheduled to <IP_C1, IP_S1> to one subflow belonging to the target network interface (it is "on-demand scheduling", for this case, MP_PRIO is not enough) What is the use-case for such a scheme? I don't see how a multipath scheduler could assign the traffic that "would" have been sent to <C1,S1> to a different subflow. Because for that he would need to know what *would* have been sent on <C1,S1> which he can only know once he actually sends traffic on that subflow as that will be driving the congestion-window which will allow to send more (or less) traffic on <C1,S1>. Christoph > > What do you think? > > Sincerely > Jiao > > -----Original Message----- > From: Christoph Paasch [mailto:cpaasch@apple.com] > Sent: Thursday, July 23, 2020 11:11 AM > To: Kangjiao <kangjiao@huawei.com> > Cc: Yoshifumi Nishida <nsd.ietf@gmail.com>; tcpm@ietf.org Extensions <tcpm@ietf.org>; Liangqiandeng <liangqiandeng@huawei.com> > Subject: Re: [tcpm] comments on draft-kang-tcpm-accurate-data-scheduling-by-server-00 > > Hello, > > > On Jul 22, 2020, at 7:01 PM, Kangjiao <kangjiao@huawei.com> wrote: > > > > Hi Christoph and Yoshi, > > > > If I understand right, you both point to the same question whether reusing the MP_PRIO can finish accurate data scheduling for server. I think MP_PRIO may be not enough even if setting all the "non-target" subflows to backup ones. I can give a scenario: > > > > Six subflows have been established between client and server that are <IP_C1, IP_S1>, <IP_C2, IP_S1>, <IP_C1, IP_S2>, <IP_C2, IP_S2>, <IP_C1, IP_S3> and <IP_C2, IP_S3>. The client has IP_C1 and IP_C2. The server has IP_S1, IP_S2 and IP_S3. > > > > Server tool detects that KPI of IP_S2 is better now so the server wants to switch data traffic from <IP_C1, IP_S1> to the destination IP_S2. If we set <IP_C1, IP_S1> as "backup", it is not guaranteed that all the load over <IP_C1, IP_S1> can be diverted to IP_S2 because of the ongoing suflows towards IP_S3. > > But we could simply also set <IP_C1,IP_S3> ans <IP_C2,IP_S3> as backup as well, no? > > Now, all the traffic will be steered towards S2. > > Christoph > > > > > > So I think MP_PRIO can reduce the chance of data transmission on a specific subflow but it cannot convey the info of target network interface from server to client. > > > > Thanks > > Jiao > > > > -----Original Message----- > > From: Christoph Paasch [mailto:cpaasch@apple.com] > > Sent: Wednesday, July 22, 2020 12:00 AM > > To: Kangjiao <kangjiao@huawei.com> > > Cc: Yoshifumi Nishida <nsd.ietf@gmail.com>; tcpm@ietf.org Extensions > > <tcpm@ietf.org>; Liangqiandeng <liangqiandeng@huawei.com> > > Subject: Re: [tcpm] comments on > > draft-kang-tcpm-accurate-data-scheduling-by-server-00 > > > > Hello, > > > > as an overall comment, I agree that one of the difficulties around multipath is how the hosts can communicate to the peers the desired scheduling mechanisms. Currently there is no reliable way besides backup-bits which is a "hard" switch. However, often scheduling is much more fine-grained as shown in a number of the schedulers described in https://tools.ietf.org/html/draft-bonaventure-iccrg-schedulers-00. > > > > It's a bit similar to TCP which can't pick the peer's congestion-control and for example if one wants the peer to use a background-CC the host needs to resort to tuning the receive-window a la draft-bagnulo-iccrg-rledbat-00. > > > > So, having a way to communicate the scheduling "requirements" to the peer (and let the peer match these requirements with its local policies), would be good! > > > > > > One more comment inline: > > > >> On 07/20/20 - 03:54, Kangjiao wrote: > >> Hi Yoshi, > >> > >> Thanks for your suggestions. We clarify the issues as below: > >> > >> 1: One thing I'm not very clear is why we cannot use MP_PRIO for the > >> use cases described in the draft. I believe the draft should describe > >> the cases where existing features cannot fulfill the requirements > >> more specifically. > >> > >> KJ: The new MP_Navigation Option is used for the server to indicate > >> destination network interface to client for which server wants to use > >> for traffic switching. For my understanding, MP_PRIO is used to > >> signal a change in priority of subflows to the peer. In application, > >> MP_PRIO can reduce the chance of data transmission on a specific > >> subflow but it cannot tell its peer which network interface is the destination from server side. > >> For example, if there are multiple subflows with high priority from > >> difference network interfaces, client receiving MP_PRIO does not know > >> which is the target one. > > > > For this particular scenario the server could send the MP_PRIO with backup-bit set on all subflows that the client should not use. Thus implicitly the high-priority network-interfaces can then be used by the client, right? > > > > > > Christoph > > > >> 2: Clients also have their own constraints. (e.g. policy or routing) > >> So, even though servers send a navigation request, they might not > >> follow it. I think this point should be clarified. > >> > >> KJ: If the mechanism of accurate-data-scheduling-by-server is > >> deployed, the principle is that the server takes precedence. > >> > >> 3: What's the meaning of 'r', 'E', 'B' flags in Section 4.1? > >> > >> KJ: For the protocol design, the definition of ’r’, ‘E’ and ’B’ are > >> as > >> following: Flag ‘r’: reserved for future usage. Flag ‘E’: exists to > >> provide reliability for this option (like that in ”ADD_ADDR”). Flag ’B’: > >> indicates whether the subflow over which the option is received is a > >> backup one (that is compatiable with the value by MP_PRIO). > >> > >> But we are thinking whether these fields are necessary and should be > >> set as mandatory. > >> > >> Sincerely, Jiao From: tcpm [mailto:tcpm-bounces@ietf.org] On Behalf > >> Of Yoshifumi Nishida Sent: Sunday, July 19, 2020 7:26 PM To: > >> tcpm@ietf.org Extensions <tcpm@ietf.org> Subject: [tcpm] comments on > >> draft-kang-tcpm-accurate-data-scheduling-by-server-00 > >> > >> Hi, I've read draft-kang-tcpm-accurate-data-scheduling-by-server-00. > >> I think this is an interesting topic for mptcp, but I think it would > >> be better to clarify the following points. > >> > >> 1: One thing I'm not very clear is why we cannot use MP_PRIO for the > >> use cases described in the draft. I believe the draft should describe > >> the cases where existing features cannot fulfill the requirements > >> more specifically. > >> > >> 2: Clients also have their own constraints. (e.g. policy or routing) > >> So, even though servers send a navigation request, they might not > >> follow it. I think this point should be clarified. > >> > >> 3: What's the meaning of 'r', 'E', 'B' flags in Section 4.1? > >> > >> Thanks, -- Yoshi > > > >> _______________________________________________ > >> tcpm mailing list > >> tcpm@ietf.org > >> https://www.ietf.org/mailman/listinfo/tcpm > >
- [tcpm] comments on draft-kang-tcpm-accurate-data-… Yoshifumi Nishida
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Kangjiao
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Christoph Paasch
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Yoshifumi Nishida
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Kangjiao
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Christoph Paasch
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Kangjiao
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Christoph Paasch
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Olivier Bonaventure
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Kangjiao
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Christoph Paasch
- Re: [tcpm] comments on draft-kang-tcpm-accurate-d… Kangjiao