UDP Transport

This user-guide explains the configuration of the built-in UDP transport.

Introduction

This document describes the built-in RTI Connext DDS Micro UDP transport and how to configure it.

• Overview
• Registering the UDP Transport
• Threading Model
• UDP Configuration

Overview

The built-in UDP transport (UDP) is a fairly generic UDPv4 transport. The major functionality supported is:

• Unicast
• Multicast
• Automatic detection of available network interfaces
• Manual configuration of network interfaces
• Allow/Deny lists to select which network interfaces can be used
• Simple NAT configuration
• Configuration of receive threads

Registering the UDP Transport

The built-in UDP transport is a RTI Connext DDS Micro component that is automatically registered when the DDS_DomainParticipantFactory_get_instance() method is called. In order to change the UDP configuration it is necessary to first unregister the transport as shown below:

    DDS_DomainParticipantFactory *factory = NULL; 
    RT_Registry_T *registry = NULL; 
    
    factory = DDS_DomainParticipantFactory_get_instance();    
    registry = DDS_DomainParticipantFactory_get_registry(factory); 

    /* The built-in transport does not return any properties (3rd param) or 
       listener (4th param)
     */
    if (!RT_Registry_unregister(registry, "_udp", NULL, NULL)) 
    { 
        /* ERROR */ 
    } 

When a component is registered, the registration takes the properties and a listener as the 3rd and 4th parameters. In general, it is up to the caller to manage the memory for the properties and the listeners. There is no guarantee that a component makes a copy.

The following code-snippet shows how to register the UDP transport with new parameters.

    struct UDP_InterfaceFactoryProperty *udp_property = NULL; 
    struct UDP_InterfaceFactoryProperty udp_property = 
                                UDP_INTERFACE_FACTORY_PROPERTY_DEFAULT;   

    /* Allocate a property structure for the heap, it must be valid as long
       as the component is registered
     */
    udp_property = (struct UDP_InterfaceFactoryProperty *)
                        malloc(sizeof(struct UDP_InterfaceFactoryProperty)); 
    *udp_property = UDP_INTERFACE_FACTORY_PROPERTY_DEFAULT; 
    
    /* Only allow network interface "eth0" to be used;
     */
    REDA_StringSeq_set_maximum(&udp_property->allow_interface, 1);
    REDA_StringSeq_set_length(&udp_property->allow_interface, 1);

    *REDA_StringSeq_get_reference(&udp_property->allow_interface, 0) = 
                                                     REDA_String_dup("eth0");

    /* Register the transport again, using the built-in name
     */
    if (!RT_Registry_register(registry, "_udp",
                         UDP_InterfaceFactory_get_interface(),
                        (struct RT_ComponentFactoryProperty*)udp_property, 
                        NULL))
    {
        /* ERROR */
    }

It should be noted that the UDP transport can be registered with any name, but all transport QoS policies and initial peers must refer to this name. If a transport is referred to and it does not exist an error message is logged.

While it is possible to register multiple UDP transports, it is not possible to use multiple UDP transports within the same participant. The reason is that UDP port allocation is not synchronized between transports.

Threading Model

The UDP transport creates one receive thread for each unique UDP receive address and port. Thus, by default three UDP threads are created:

• A multicast receive thread for discovery data (assuming multicast is available and enabled)
• A unicast receive thread for discovery data
• A unicast receive thread for user data

Additional threads may be created depending on the transport configuration for a domain-participant, data-reader and data-writer. The UDP transport creates threads based on the following criteria:

• Each unique unicast port creates a new thread
• Each unique multicast address and port creates a new thread

For example, if a data-reader specifies its own multicast receive address, a new receive thread will be created.

Configuring UDP Receive Threads

All threads in the UDP transport share the same thread settings. It is important to note that all the UDP properties must be set before the UDP transport is registered. RTI Connext DDS Micro preregisters the UDP transport with default settings when the DomainParticipantFactory is initialized. To change the UDP thread settings, use the following code.

    struct UDP_InterfaceFactoryProperty *udp_property = NULL; 
    struct UDP_InterfaceFactoryProperty udp_property = 
                                UDP_INTERFACE_FACTORY_PROPERTY_DEFAULT;   

    /* Allocate a property structure for the heap, it must be valid as long
       as the component is registered
     */
    udp_property = (struct UDP_InterfaceFactoryProperty *)
                        malloc(sizeof(struct UDP_InterfaceFactoryProperty)); 
    *udp_property = UDP_INTERFACE_FACTORY_PROPERTY_DEFAULT; 
    
    /* Please refer to OSAPI_ThreadOptions for possible options */
    udp_property->recv_thread.options = ...; 
    
    /* The stack-size is platform dependent, it is passed directly to the OS */
    udp_property->recv_thread.stack_size = ....
    
    /* The priority is platform dependent, it is passed directly to the OS */    
    udp_property->recv_thread.priority = ....
    
    if (!RT_Registry_register(registry, "_udp", 
                              UDP_InterfaceFactory_get_interface(), 
                              (struct RT_ComponentFactoryProperty*)udp_property, 
                              NULL)) 
    { 
        /* ERROR */ 
    } 

UDP Configuration

All the configuration of the UDP transport is done via the struct UDP_InterfaceFactoryProperty structure:

struct UDP_InterfaceFactoryProperty
{
    /* Inherited from */
    struct NETIO_InterfaceFactoryProperty _parent;

    /* Sequence of allowed interface names */
    struct REDA_StringSeq allow_interface;

    /* Sequence of denied interface names */
    struct REDA_StringSeq deny_interface;

    /* The size of the send socket buffer */
    RTI_INT32 max_send_buffer_size;

    /* The size of the receive socket buffer */
    RTI_INT32 max_receive_buffer_size;
    
    /* The maximum size of the message which can be received */
    RTI_INT32 max_message_size;

    /* The maximum TTL */
    RTI_INT32 multicast_ttl;

#ifndef RTI_CERT
    struct UDP_NatEntrySeq nat;
#endif

    /* The interface table if interfaces are added manually */
    struct UDP_InterfaceTableEntrySeq if_table;

    /* The network interface to use to send to multicast */
    REDA_String_T multicast_interface;

    /* If this should be considered the default UDP interfaces if
       no other UDP interface is found to handle a route
     */
    RTI_BOOL is_default_interface;

    /* Disable reading of available network interfaces using system
       information and instead rely on the manually configured
       interface table
     */
    RTI_BOOL disable_auto_interface_config;

    /* Thread properties for each receive thread created by this
       NETIO interface.
     */
    struct OSAPI_ThreadProperty recv_thread;
};

allow_interface

The allow_interface string sequence determines which interfaces are allowed to be used for communication. Each string element is the name of a network interface, such as "en0" or "eth1".

If this sequence is empty, all interface names pass the allow test. The default value is empty. Thus, all interfaces are allowed.

deny_interface

The deny_interface string sequence determines which interfaces are not allowed to be used for communication. Each string element is the name of a network interface, such as "en0" or "eth1".

If this sequence is empty, the test is false. That is the interface is allowed. Note that the deny list is checked after the allow list. Thus, if an interface appears in both, it is denied. The default value is empty, thus no interfaces are denied.

max_send_buffer_size

The max_send_buffer_size is the maximum size of the send socket buffer and it must be at least as big as the largest sample. Typically this buffer should be a multiple of the maximum number of samples that can be sent at any given time. The default value is 8KB.

max_receive_buffer_size

The max_receive_buffer_size is the maximum size of the receive socket buffer and it must be at least as big as the largest sample. Typically this buffer should be a multiple of the maximum number of samples that can be received at any given time. The default value is 8KB.

max_message_size

The max_message_size is the maximum size of the message which can be received including any packet overhead. The default value is 8KB. Note that RTI Connext DDS Micro does not support fragmentation.

multicast_ttl

The Time-To-Live (TTL) value is only used for multicast. It limits the number of hops a packet can pass through before it is dropped by a router. The default value is 1.

nat

RTI Connext DDS Micro supports firewalls with NAT. However, this feature has limited use and only supports translation between a private and public IP address. UDP ports are not translated. Furthermore, because RTI Connext DDS Micro does not support any hole punching technique or WAN server, this feature is only useful when the private and public address mapping is static and known in advance. For example, to test between an Android emulator and the host, the following configuration can be used:

    UDP_NatEntrySeq_set_maximum(&udp_property->nat,2);
    UDP_NatEntrySeq_set_length(&udp_property->nat,2);

    /* Translate the local emulator  eth0 address 10.10.2.f:7410 to
       127.0.0.1:7410. This ensures that the address advertised by the
       emulator to the host machine is the host's loopback interface, not
       the emulator's host interface
     */
    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                local_address.kind = NETIO_ADDRESS_KIND_UDPv4;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                local_address.port = 7410;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                local_address.value.ipv4.address = 0x0a00020f;

    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                public_address.kind = NETIO_ADDRESS_KIND_UDPv4;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                public_address.port = 7410;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,0)->
                                public_address.value.ipv4.address = 0x7f000001;

    /* Translate the local emulator  eth0 address 10.10.2.f:7411 to
       127.0.0.1:7411. This ensures that the address advertised by the
       emulator to the host machine is the host's loopback interface
     */
    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                local_address.kind = NETIO_ADDRESS_KIND_UDPv4;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                local_address.port = 7411;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                local_address.value.ipv4.address = 0x0a00020f;

    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                public_address.kind = NETIO_ADDRESS_KIND_UDPv4;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                public_address.port = 7411;
    UDP_NatEntrySeq_get_reference(&udp_property->nat,1)->
                                public_address.value.ipv4.address = 0x7f000001;

if_table

The if_table provides a method to manually configure which interfaces are available for use, for example when using IP stacks that do not support reading interface lists. The following example shows how to manually configure the interfaces.

    /* The arguments to the UDP_InterfaceTable_add_entry functions are:
       The if_table itself
       The network address of the interface
       The netmask of the interface
       The name of the interface
       Interface flags. Valid flags are:
         UDP_INTERFACE_INTERFACE_UP_FLAG        - The interface is UP
         UDP_INTERFACE_INTERFACE_MULTICAST_FLAG - The interface supports multicast
     */
    if (!UDP_InterfaceTable_add_entry(&udp_property->if_table,
                                      0x7f000001,0xff000000,"loopback",
                                      UDP_INTERFACE_INTERFACE_UP_FLAG |
                                      UDP_INTERFACE_INTERFACE_MULTICAST_FLAG))

    {
        /* Error */
    }

multicast_interface

The multicast_interface may be used to select a particular network interface to be used to send multicast packets. The default value is any interface(that is, the OS selects the interface).

is_default_interface

The is_default_interface flag is used to indicate that this RTI Connext DDS Micro network transport shall be used if no other transport is found. The default value is RTI_TRUE.

disable_auto_interface_config

Normally, the UDP transport will try to read out the interface list (on platforms that support it). Setting disable_auto_interface_config to RTI_FALSE will prevent the UDP transport from reading the interface list.

recv_thread

The recv_thread field is used to configure all the receive threads. Please refer to Threading Model for details.