The information below is taken from MDK v.0.2
The Ara network stack uses MIPI UniPro (V1.6 6-August-2013) at the data link, transport, and network layers. UniPro is designed specifically for mobile applications and enables a lightweight, low-latency packet-switched network between modules on an Ara phone. A UniPro switch in the Endo routes packets between modules and provides quality of service guarantees to system-level functions and modules.
The UniPro PHY adapter layer (Layer 1.5) serves to hide the differences between the different MIPI PHY options (D-PHY or M-PHY). This layer allows configuration of various power states and symbol encoding schemes.
The UniPro data link layer (Layer 2) defines 2 traffic classes: TC0 and TC1. TC1 data frames are sent before TC0. A credit based flow control mechanism enables receivers to tell the transmitter how much buGer space is available and pause the transmission to avoid a receive buffer overflow. An incorrect frame checksum at Layer 2 triggers an automatic retransmission.
A unique identification number is assigned to each interface block on the Endo frame. The interface block ID is assigned by ISO convention, starting from the rear of the Endo, from the left and top, moving in the counterclockwise direction, and ending at the front of the Endo. Since the interface block locations are the same regardless of rib placement, they can be statically assigned. The result is shown in figure below.
The UniPro transport layer (Layer 4) handles connections between modules using logical data streams. UniPro uses CPorts for communication between endpoints, which are roughly analogous to sockets used in TCP or UDP. A pair of CPorts, one on each of two modules, can form a bi-directional connection. Each module may have multiple CPorts, which enables a module to simultaneously connect and communicate with multiple modules on an Ara device.
Project Ara is working with the MIPI UniPro standards committee to define a standard implementation of strong cryptographic protection for information transmitted over the UniPro bus, which may be incorporated in a future MDK release as it becomes more mature.