Olivier Bonaventure Biography & Facts
Multipath TCP (MPTCP) is an ongoing effort of the Internet Engineering Task Force's (IETF) Multipath TCP working group, that aims at allowing a Transmission Control Protocol (TCP) connection to use multiple paths to maximize throughput and increase redundancy.In January 2013, the IETF published the Multipath specification as an Experimental standard in RFC 6824. It was replaced in March 2020 by the Multipath TCP v1 specification in RFC 8684.
The redundancy offered by Multipath TCP enables inverse multiplexing of resources, and thus increases TCP throughput to the sum of all available link-level channels instead of using a single one as required by standard TCP. Multipath TCP is backward compatible with standard TCP.
Multipath TCP is particularly useful in the context of wireless networks; using both Wi-Fi and a mobile network is a typical use case. In addition to the gains in throughput from inverse multiplexing, links may be added or dropped as the user moves in or out of coverage without disrupting the end-to-end TCP connection.The problem of link handover is thus solved by abstraction in the transport layer, without any special mechanisms at the network or link layers. Handover functionality can then be implemented at the endpoints without requiring special functionality in the subnetworks - in accordance to the Internet's end-to-end principle.
Multipath TCP also brings performance benefits in datacenter environments. In contrast to Ethernet channel bonding using 802.3ad link aggregation, Multipath TCP can balance a single TCP connection across multiple interfaces and reach very high throughput.Multipath TCP causes a number of new issues. From a network security perspective, multipath routing causes cross-path data fragmentation that results in firewalls and malware scanners becoming inefficient when they only see one path's traffic. In addition, SSL decryption will become inefficient by way of the end-to-end encryption protocols.
In order to facilitate its deployment, Multipath TCP presents the same socket interface as TCP. This implies that any standard TCP application can be used above Multipath TCP while in fact spreading data across several subflows.
Some applications could benefit from an enhanced API to control the underlying Multipath TCP stack. Two different APIs have been proposed to expose some of features of the Multipath TCP stack to applications: an API that extends Netlink on Linux and an enhanced socket API.
In July 2013, the MPTCP working group reported five independent implementations of Multipath TCP, including the reference implementation in the Linux kernel.The currently available implementations are:
Linux kernel (reference implementation) from Université catholique de Louvain researchers and other collaborators ,
FreeBSD (IPv4 only) from Swinburne University of Technology,
F5 Networks BIG-IP LTM,
Apple iOS 7, released on September 18, 2013 is the first large scale commercial deployment of Multipath TCP. Since iOS 7, any application can use Multipath TCP.
Apple Mac OS X 10.10, released on October 16, 2014.
Alcatel-Lucent released MPTCP proxy version 0.9 source code on October 26, 2012.In July 2014, Oracle reported that an implementation on Solaris was being developed. In June 2015, work is in progress.During the MPTCP WG meeting at IETF 93, SungHoon Seo announced that KT had deployed since mid June a commercial service that allows smartphone users to reach 1 Gbit/s using a MPTCP proxy service. Tessares uses the Linux kernel implementation to deploy Hybrid Access Networks
There is an ongoing effort to push a new Multipath TCP implementation in the mainline Linux kernel,
Multipath TCP was designed to be backward compatible with regular TCP. As such, it can support any application. However, some specific deployments leverage the ability of simultaneously using different paths.
Apple uses Multipath TCP to support the Siri application on iPhone. Siri sends voice samples over an HTTPS session to Apple servers. Those servers reply with the information requested by the users. According to Apple engineers, the main benefits of Multipath TCP with this application are :
User-feedback (Time-to-First-Word) 20% faster in the 95th percentile
5x reduction of network failuresOther deployment use Multipath TCP to aggregate the bandwidth of different networks. For example, several types of smartphones, notably in Korea, use Multipath TCP to bond WiFi and 4G through SOCKS proxies. Another example are the Hybrid Access Networks that are deployed by network operators willing to combine xDSL and LTE networks. In this deployment, Multipath TCP is used to efficiently balance the traffic over the xDSL and the LTE network.In standardisation of converged fixed and mobile communication networks 3GPP and BBF are interoperating to provide an ATSSS (Access Traffic Selection, Switching, Splitting) feature to support multipath sessions, e.g, by applying Multipath TCP both in the User Equipment (UE) or Residential Gateway (RG) and on the network side.
Multipath TCP options
Multipath TCP uses options that are described in detail in RFC 6824. All Multipath TCP options are encoded as TCP options with Option Kind is 30, as reserved by IANA.The Multipath TCP option has the Kind (30), length (variable) and the remainder of the content begins with a 4-bit subtype field, for which IANA has created and will maintain a sub-registry entitled "MPTCP Option Subtypes" under the "Transmission Control Protocol (TCP) Parameters" registry. Those subtype fields are defined as follows:
Values 0x8 through 0xe are currently unassigned.
The core idea of multipath TCP is to define a way to build a connection between two hosts and not between two interfaces (as standard TCP does).
For instance, Alice has a smartphone with 3G and WiFi interfaces (with IP addresses 10.11.12.13 and 10.11.12.14) and Bob has a computer with an Ethernet interface (with IP address 18.104.22.168).
In standard TCP, the connection should be established between two IP addresses. Each TCP connection is identified by a four-tuple (source and destination addresses and ports). Given this restriction, an application can only create one TCP connection through a single link. Multipath TCP allows the connection to use several paths simultaneously. For this, Multipath TCP creates one TCP connection, called subflow, over each path that needs to be used.
The purpose of the different protocol operations (defined in RFC 6824) are:
to handle when and how to add/remove paths (for instance if there's a connection lost or some congestion control)
to be compatible with legacy TCP hardware (such as some firewalls that can automatically reject TCP connections if the sequence number aren't successive)
to define a fair congestion control strategy between the different links and the different hosts (especially with those that don't .... Discover the Olivier Bonaventure popular books. Find the top 100 most popular Olivier Bonaventure books.