EMS Channels

An EMS channel provides publish-subscribe messaging among eFTL applications, and between eFTL applications and EMS applications.

Each EMS channel is a client of an EMS server, which acts as a store-and-forward intermediary for all messages through the channel.

In the diagram, channels B and D are EMS channels.

Messages from eFTL Publishers

The purple arrow within channel B indicates forwarding into the EMS side. When PubB1 sends a message, channel B translates it and publishes it to a topic within the EMS server.

The EMS server forwards the message in two ways:

  • The downward black arrow indicates ordinary EMS delivery to subscriber SubB2.
  • The upward blue arrow indicates the two phases that carry the message into the eFTL side:
    1. The EMS server delivers the message to channel B.
    2. Channel B retranslates the message and forwards it to all its eFTL subscribers, represented by SubB1 in the diagram.

Messages from EMS Publishers

The diagram also traces the path of a message from EMS publisher PubD2 to its topic in the EMS server.

  • The downward black arrow indicates ordinary EMS delivery to subscriber SubD2.
  • The upward blue arrow indicates the two phases that carry the message into the eFTL side:
    1. The EMS server forwards the message to channel D.
    2. Channel D translates the message, and delivers it to all the eFTL subscribers on channel D, represented by SubD1 in the diagram.

Isolation

Administrators can use separate channels to isolate message streams from one another. With proper configuration, messages in channel B remain within channel B. Similarly for channel D, and all the other channels. Each channel gives rise to a separate message network. The diagram shows channel B’s network in green, and channel D’s network in yellow.

Nonetheless, if subscribers on two channels access the same EMS topic, the EMS server can merge the two message streams. For more information about EMS crosstalk and an administrative remedy, see EMS Topic Prefix.

  • EMS Topic Prefix
    Channels isolate message streams. However, the EMS server merges message streams that share a topic name. Configuring a distinct topic prefix on each EMS channel can prevent crosstalk among channels through the EMS server.
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