Internet-Draft | Accurate Data Scheduling by Server | July 2020 |
Kang & Liang | Expires 14 January 2021 | [Page] |
This document defines a new mechanism that enables server to send request to client for data scheduling between the subflows during a MPTCP session.¶
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MPTCP protocol is now being deployed in more and more networks. In most scenarios, MPTCP scheduling strategies for these subflows are implemented on client side considering RTT and congestion, or sending packets redundantly. Application server cannot actively participate in such decision-making.¶
However in real deployment, application server supports multiple network interfaces from different operators when MPTCP protocol is adopted. There are such scenarios that the server wants to set scheduling to the client on these network interfaces based on server-side rules in a MPTCP session. The requirements for these use cases are listed below:¶
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.¶
This document proposes an accurate data scheduling mechanism for server. Two typical flows are illustrated in Figure 1 and Figure 2.¶
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.¶
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.¶
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.¶
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.¶
The format of the MP_Navigation option is depicted in Figure 3:¶
Subtype: A new subtype should be allocated to indicate MP_Navigation Option.¶
Address ID: Address ID in MP_Navigation Option is used to identify the address ID of target network Interface.¶
The flag 'R', when set, define the content of this option, as follows:¶
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.¶
IANA is requested to assign a MPTCP option subtype for the MP_Navigation option.¶
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.¶