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The Socket Intents Prototype

Socket Intents enable an application to express what it knows about its communication patterns and preferences for a new connection or transfer. This information can then be used by our Informed Access Network Selection (IANS) policies to choose the appropriate access network, e.g., WiFi or cellular, combine multiple networks using MPTCP, or tune protocol parameters. This prototype implements Socket Intents as well as multiple networking APIs that enable applications to use Socket Intents. Note that Socket Intents do not provide any guarantee of any specific kind of service. They are strictly best-effort.

The actual decision-making is implemented within policies, which are running in the context of the Multi Access Manager, a daemon that manages the various network interfaces on a host. The policy is loaded as a shared library within the Multi Access Manager.


Copyright (c) 2013-2019, Internet Network Architectures Group, Berlin Institute of Technology, Philipp S. Tiesel and Theresa Enghardt and Mirko Palmer.
All rights reserved.
This project has been licensed under the New BSD License.

Building and Installing the Socket Intents Prototype

Supported platforms: Linux (tested on Debian and Ubuntu), Mac OS X (until release-0.6)

Note: Path characteristics collection is currently only supported on Linux. Furthermore, release-0.7 currently does not compile on Mac OS.

Prerequisites: cmake, pkg-config, bison, flex, libltdl-dev, libevent-dev, libglib2.0-dev, libargtable2-dev, uuid-dev, libnl-3-dev, libnl-genl-3-dev, libnl-idiag-3-dev, libnl-route-3-dev, libpcap-dev, (liburiparser-dev)

To build and install:

$ mkdir build
$ cd build/
$ cmake ..
$ make
$ sudo make install

This will install:

  • The client library, containing the Socket Intents
  • The Multi Access Manager binary mamma
  • The policies for the Multi Access Manager as dynamically loaded libraries, to a subdirectory called mam-policies
  • The Socks Daemon binary muacsocksd
  • The header files to let you use the client library and/or write your own policies

After installing and before running the Multi Access Manager, you may have to update the shared library cache using


Testing the Socket Intents Prototype

First, you need to run the Multi Access Manager (MAM) with a policy.

  1. Pick a policy from the policies subdirectory of the source tree, e.g., policy_sample, and create or adjust its configuration file, e.g. policy_sample.conf:
  • Adjust the "prefix" statements to contain the current IP prefixes of the interfaces you want the MAM to manage. Make sure they are "enabled". You have to set separate prefixes for IPv4 and IPv6 addresses.
  • Example:
policy "" {
prefix {
	enabled 1;
  • Depending on the policy, you may want to add additional parameters or options to the prefix statements, e.g. for policy_sample.conf to make one of them the default interface:
policy "" {
prefix {
	enabled 1;
	set default = 1;
  1. Run the MAM executable mamma (MAM Master) with your policy configuration file:
$ mamma policy_sample.conf

If it works correctly, you should see output from the policy, e.g.:

Policy module "sample" is loading.
Configured addresses:
    AF_INET: (default)
Policy module "sample" has been loaded.

If the list of local addresses does not show up, check mamma's output for error messages, such as: loading of module failed: file not found. If this happens, check the configuration file again and make sure the policy .so file has been correctly built and installed to the policy path, e.g. /usr/local/lib/mam-policies.

Now, you can build and run an initial test, e.g. with make check

To test with different parameters, run the following to see what is available:

./tests/socketconnecttest --help

Notable policies

  • Sample Policy: Always use a single default interface. See policies/policy_sample.c
  • MPTCP: Always enable MPTCP for every socket. Bind to lower latency interface so the first subflow will be established there. See policies/mptcp_simple.c
  • Threshold Policy: This Informed Access Network Selection Policy first judges whether a new resource load is latency-dominated or capacity-dominated. If it is latency-dominated, it chooses the interface (i.e., the network) with the lowest latency. If it is capacity-dominated, it compares the predicted completion times (latency + capacity part) of all interfaces and chooses the lowest completion time. See policies/threshold_policy.c
  • Optimist and Pessimist Policy: This Informed Access Network Selection Policy is intended to improve the performance of HTTP Adaptive Streaming (HAS). It loads video segments over the network with the higher available capacity while taking different capacity estimates into account, e.g., capacity observed in the last 1 second, 10 seconds, 1 minute, or 10 minutes. Both policies are implemented in the same module, policies/policy_video.c. Selecting between the Optimist and the Pessimist Policy depends on a configuration variable, see policies/optimist_policy.conf and policies/pessimist_policy.conf.
  • Selective MPTCP Policy: This Informed Access Network Selection Policy enables MPTCP only for transfers with category BULK and only if sufficient capacity is available. Otherwise, for BULK transfers, it uses the single network with the highest capacity, and for QUERY transfers, it uses the single network with the shortest latency.

Creating a new policy

Policies are implemented as modules for the Multi Access Manager (MAM), i.e., dynamically loaded libraries written in C, compiled, and loaded by MAM at runtime.

Policies are located in the directory policies/. Each policy implements callbacks, which the MAM will later call when it receives a request from an application. Each such request corresponds to, e.g., a decision which local interface to use for a new connection (on_connect_request), on which interface to resolve a name (on_resolve_request), or whether to open or reuse a socket on a particular local interface (on_socketconnect_request and on_socketchoose_request). If a policy is only used with applications that use socketconnect, it is not necessary to implement connect or resolve requests, but only socketconnect and socketchoose. Furthermore, each policy requires a init() and a cleanup() function. Policies usually use these functions to set up or tear down any required data structures, such as lists of available prefixes/local interfaces and Intents associated with them.

As a starting point, consider copying the existing policy_sample.c and modifying it to your needs. This policy also contains examples of how to use any Intents that were set by the application. For examples of how to use the network characteristics collected by MAM, refer to, e.g., the threshold_policy.c or the policy_video.c (Optimist and Pessimist policy).

To compile a policy, please add it to policies/CMakeLists.txt. To enable the MAM to load this policy, please create a config file that provides the path to the compiled policy file, see policies/policy_sample.conf for an example. Note that every configured prefix can set its own DNS nameserver or even its own resolv.conf config file.

Adding a new application

See also: Code examples in the examples/ directory.

Using the socketconnect API

This is a high-level API that enables your application to specify Socket Intents for every object or message. The API then returns to you a connected socket over the most suitable interface.

How it works:

  • Before sending or receiving something to a particular host and port, the application calls socketconnect to get a socket which is connected to that destination. When called the first time, this will be a newly connected socket (return value is 1).
  • The socket that was returned is also stored in a socket set, a collection of sockets that have the same destination and type, and can thus be used interchangeably by the application. However, they may have different source addresses or socket options.
  • Once the application has finished sending or receiving, it can mark the socket as free for reuse by calling socketrelease.
  • The next time socketconnect is called, it is possible that an already existing socket from the socket set is returned (return value is 0).
  • When the socket is no longer needed, instead of releasing it, it can be closed by calling socketclose.

API variants:

  • Basic blocking socketconnect API: The socketconnect() call blocks until a connected socket can be returned (or the call failed). This API is found in client_socketconnect.h.
  • Non-blocking socketconnect API: The socketconnect() call is implemented in a non-blocking way. This API is found in client_socketconnect_asyc.h.

Using the classic BSD Socket API

This is a more low-level API that enhances the classic BSD sockets. Using this API, your application can specify Socket Intents for every connection or flow.

API variants:

  • Classic BSD Sockets with explicit context handling: This API extends the calls to getaddrinfo(), socket(), bind(), connect() etc. with a muacc_context, explicitly linking all calls that belong to the same flow. This API is found in client_socketapi.h.
  • Classic BSD Sockets with most functionality in getaddrinfo: This API extends getaddrinfo() with additional hints including Socket Intents. The results of this call can then be applied when creating and using the socket. This API is found in client_addrinfo.h.

Further documentation

You can generate API documentation using Doxygen. From the top directory of the repository:

$ doxygen Doxyfile


Augmented Socket API selecting the best suitable access network based on application needs and network performance characteristics.







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