Internet-Draft Accurate Data Scheduling by Server February 2022
Kang & Liang Expires 12 August 2022 [Page]
Workgroup:
TCP Maintenance and Minor Extensions
Internet-Draft:
draft-kang-tcpm-accurate-data-scheduling-by-server-02
Published:
Intended Status:
Informational
Expires:
Authors:
J. Kang, Ed.
Huawei
Q. Liang
Huawei

Accurate Data Scheduling by Server in MPTCP

Abstract

This document defines a new mechanism that enables MPTCP server to send requests 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.

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This Internet-Draft will expire on 12 August 2022.

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Table of Contents

1. Introduction

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

However, in actual deployment, MPTCP server is configured with multiple network interfaces and these network interfaces are from different operators. There are some scenarios in which MPTCP server wants to set scheduling algorithms on these network interfaces based on its own rules, network planning and operating policies. These scheduling algorithms need to be passed to the MPTCP client and executed on the client during a MPTCP session. Requirements for these use cases are described below:

Currently, there are two implementations related to these requirements. [RFC8684] defines REMOVE_ADDR Option to delete one address during a MPTCP session but it will close 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.

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

An accurate data scheduling mechanism for MPTCP server is proposed in this document. 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 is swichted to----->|
           |      the target subflow of           |
           |     target network interface         |
           |                                      |
           |                                      |
Figure 1: Server requests 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                         |
   in 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 a MPTCP session for data shceduling, normal process of ADD_ADDR should be executed before traffic switching.

If it is determined to cancel the data switching on a subflow, the client should delete the navigation information for it. Navigation information is generated by MPTCP 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 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

MP_Navigation option is defined and sent from server to force client to switch traffic from the subflow over which the option was received to a target subflow, or to cancel traffic switching when it is not required. MP_Navigation option includes a Flag 'R' to distinguish this two functions. If it is set, the target subflow is determined through the Address ID of the target network interface in MP_Navigation option.

MP_Navigation option can be sent in ACK.

Noted that if MP_Navigation option is not supported by the MPTCP client, it should be omitted when received.

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:

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 data transfer by its local strategies.

5. Data scheduling on client when receiving MP_Navigation

This section will be finished later.

6. IANA Considerations

IANA is requested to assign a MPTCP option subtype for the MP_Navigation option.

7. Security Considerations

Since MP_Navigation option is neither encrypted nor authenticated, on-path attackers and middleboxes could remove, add or modify the MP_Navigation option on observed Multipath TCP connections.

8. References

8.1. Normative References

[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, , <https://www.rfc-editor.org/info/rfc8684>.

Authors' Addresses

Jiao Kang (editor)
Huawei
D2-03,Huawei Industrial Base
Shenzhen
China
Qiandeng Liang
Huawei
No. 207, Jiufeng 3rd Road, East Lake High-tech Development Zone
Wuhan
China

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