You can optionally configure TCP keep-alive connections in the ase.conf file of ASE. Following is a snippet of ase.conf displaying the enable_sideband_keepalive variable. The default value is set to false. 
; enable connection keepalive for requests from gateway to ase.
; This setting is applicable only in sideband mode.
; Once enabled ase will add 'Connection: keep-alive' header in response
; Once disabled ase will add 'Connection: close' header in response
enable_sideband_keepalive=false
If this variable is set to true, then you must configure persistent connections in Axway Policy Studio by completing the following steps:
  1. Click on Environment Configuration
  2. Under Environment Configuration, click Listeners > API Gateway.
  3. Click On your ASE IP address in Sample Services
  4. In the Remote Host Settings pop-up window, un-check Allow HTTP 1.1
  5. Check Include Content Length in request. Make sure all other options are not selected.
  6. Click OK and Deploy the policy