Understanding the Message Flow in a Distributed SMPP Connection with Multilink

Overview

This article explains how the messages are sent to the client SMPP (Short Message Peer-to-Peer) when the SMPP connection has multilink activated.

Solution

The SMPP Multilink feature allows multiple bind requests from the SMPP client with the same system_id.  The SMserver handles the load sharing mechanism for each link to deliver the messages to the SMPP client. Also, it manages the sliding window protocol for each link between the SMPP client and SMserver. During the message delivery to SMPP client, if the existing link goes dead, SMserver switches to next alive links.

• The SMPP Multiple Links feature is provided to handle multiple bind requests from the same SMPP client, which binds with the same system_id and same bind type. SMPP Multilink support is license controlled. When the license is enabled, SMPP accepts the multiple bind requests with the same bind type. Each SMPP client in SMPPCL needs to be configured to enable this feature. If the SMPP client is not configured to enable this feature, it sends one TX, RX, and TRX bind at the same time.

As the client can be connected with multiple links, the messages destined for the client are distributed among all the links on which the client has been bound as RX or TRX. So, SMPP handles the load sharing mechanism. After using one link, SMPP uses the next link to deliver the next message. This mechanism is applicable only for deliver_sm/data_sm messages.

• During the message delivery, if a link is found to be dead, then SMPP tries to send the message through another link, without dropping the message delivery. The switchover to the next alive link is handled for the deliver_sm/data_sm messages.

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