Accurate Data Scheduling by Server in MPTCP

Internet-Draft	Accurate Data Scheduling by Server	November 2020
Kang & Liang	Expires 6 May 2021	[Page]

Abstract

This document defines a new mechanism that enables MPTCP server to send request to MPTCP client for data scheduling between specified subflows during a MPTCP session.¶

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 6 May 2021.¶

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶

1. Introduction

MPTCP protocol is now being deployed in more and more networks. In most scenarios, MPTCP scheduling strategies for these subflows are implemented on client considering RTT and congestion, or sending packets redundantly. MPTCP server cannot participate in such decision-making.¶

However, in actual deployment, MPTCP server is configured with multiple network interfaces from different operators. There are some scenarios that MPTCP server wants to set scheduling on these network interfaces to MPTCP client based on its own rules, network planning and operating policies during a MPTCP session. Requirements for these use cases are listed below:¶

Network fault prevention. Server tools can help detect quality of deployed network interfaces such as packet loss, delay and jitter. If key performance indicators (KPI) of one network interface becomes worse, MPTCP server hopes to indicate MPTCP client to switch the traffic into another network interface with better KPI.¶
A new entrance is deployed or an emergency entrance of 5G card is added during a MPTCP session. In this case, MPTCP server may hope to lead the traffic on some subflows to the additional network interface. One purpose is to test new network in trial operation. Other purposes include avoiding congestion and improving transmission reliability on existing networks. For example, MPTCP server is using network of Operator A for data transmission and a network of operator B is added when data traffic increases. At this time, MPTCP server wants to arrange traffic from network of Operator A to Operator B. In this case, network of Operator B is the target network.¶
Value-added services. This requirement comes from the operating policies. MPTCP server is required to help provide customers with diversified services in order to satisfy individual demand. For example,it should be possible that MPTCP server indicates MPTCP client to switch the traffic of VIP users to a network interface with better KPIs.¶
Another typical scenario is that MPTCP server hopes to adjust traffic to a specific subflow because of the changes in network cost, for example, the expiration of discounts. This requirement also comes from the operating policies.¶

There are two related implementations. RFC8684 defines REMOVE_ADDR Option to delete one address during a MPTCP session and it also closes all subflows bound to this address. draft-hoang-mptcp-sub-rate-limit-00 proposes a Subflow Rate Limit Option which can be used by sender to receiver for setting the rate of one subflow to zero. But for the use cases in this document, existing technologies are somewhat inadequate because they do not provide a clear indication of which subflow to switch to.¶

2. Typical flows for accurate data scheduling by server

This document proposes an accurate data scheduling mechanism for server. Two typical flows are illustrated in Figure 1 and Figure 2.¶

       +--------+                            +--------+
       | Client |                            | Server |
       +--------+                            +--------+
           |                                      |
           |<----Session setup with subflows----->|
           |                                      |
           |                            Determine Address ID
           |                       for target network Interface
           |                                      |
           |<--Sending MP_Navigation for request--|
           |        on one ongoing subflow        |
           |                                      |
   Determine target subflow                       |
  by Address ID in MP_Navigation                  |
           |                                      |
   Traffic switching to                           |
   the target subflow                             |
           |                                      |
           |----Data transfer over the target---->|
           | subflow of target network interface  |
           |                                      |
           |                                      |

Figure 1: Server request client to perform traffic switching

       +--------+                            +--------+
       | Client |                            | Server |
       +--------+                            +--------+
           |                                      |
           |<---Subflow with diverted traffic --->|
           |       is still kept alive            |
           |                                      |
           |                         Determine to cancel MP_Navigation
           |                            for target network Interface
           |                                      |
           |<----Sending MP_Navigation on the-----|
           |    subflow with diverted traffic     |
           |          for cancellation            |
           |                                      |
Cancel traffic switching to                       |
 target network interface                         |
   on the MP_Navigation                           |
           |                                      |
           |-----Continue data transfer over----->|
           |   the subflow with diverted traffic  |
           |                                      |
           |                                      |

Figure 2: Server sends a request to client to cancel previous navigation setting

For the use case of adding a new network interface to MPTCP session for navigation, normal process of ADD_ADDR should be executed before traffic switching.¶

If it is determined to cancel the data switching on the subflow, the client should delete the navigation information. The navigation information is generated by the client and is used to determine the target subflow for data switching based on the address ID of the target network interface.¶

After data switching, if the subflow with diverted traffic is disconnected, the client should delete the navigation information and configuration information for it. The navigation information is generated by the client and is used to determine the target subflow for data switching based on the address ID of the target network interface.¶

3. Examples

3.1. Traffic switching to a newly-added network interface

Four subflows have been established between client and server that are <IP1, IP3>, <IP2, IP3>, <IP1, IP4> and <IP2, IP4>. On the client, IP1 and IP2 are the address IDs for WiFi and a cellular network. On the server, IP3 and IP4 are the address IDs for Ethernet and WiFi. When a new 5G network is deployed on the server, the server can switch the data traffic on the subflow <IP2,IP4> to the destination IP5 corresponding to 5G. In this case, the target network interface is IP5.¶

3.2. Traffic switching to a network interface already in the session

Four subflows have been established between client and server that are <IP1, IP3>, <IP2, IP3>, <IP1, IP4> and <IP2, IP4>. On the client, IP1 and IP2 are the address IDs for WiFi and a cellular network. On the server, IP3 and IP4 are the address IDs for Ethernet and WiFi. Server tool detects that KPI for IP4 is better now so the server can switch data traffic on the subflow <IP1, IP3> to the destination IP4.¶

4. MP_Navigation Option

In this solution, a MP_Navigation option is defined and sent from server to forces client to switch traffic from the subflow over which the option was received to a target subflow or to cancel the traffic switching when it is not required, which is indicated by a flag 'R'. If it is set, the target subflow is determined through the Address ID of the target network interface in MP_Navigation option.¶

This MP_Navigation Option can be sent in ACK.¶

It is noted that if this option is not supported by the client, it should be omitted.¶

4.1. Option Format

The format of the MP_Navigation option is depicted in Figure 3:¶

                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------+-------+---------------+
|     Kind      |    Length     |Subtype|r|R|E|B|   Address ID  |
+---------------+---------------+-------+-------+---------------+

Figure 3: MP_Navigation Option

Subtype: A new subtype should be allocated to indicate MP_Navigation Option.¶

Flag 'r': reserved for future usage.¶

Flag 'R': when set, defines the content of this option, as follows:¶

When value of 'R' is set to zero, server want to use this option to inform client of navigation policy and the client will perform traffic switching as requested by the server. When value of 'R' is set to 1, the server requests to cancel current navigation policy in client and the client will delete corresponding navigation information to the Address ID.¶

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).¶

Address ID: Address ID in MP_Navigation Option is used to identify the address ID of target network Interface.¶

When the client receives the MP_Navigation Option, it will determine the target network interface by the Address ID. Address ID may map to one or more ongoing subflows and the client will select one for each data transfer by its local strategies.¶

8. References

8.1. Normative References

[RFC0793]: Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <https://www.rfc-editor.org/info/rfc793>.
[RFC6824]: Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013, <https://www.rfc-editor.org/info/rfc6824>.
[RFC8684]: Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C. Paasch, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March 2020, <https://www.rfc-editor.org/info/rfc8684>.