First - Maintain the Sender R/3 System:
- SM59 : Create a RFC destination to XI 
 - WE21 : Create a TRFC Port ->Specify the RFC Destination Created 
 - BD54 : Create a Logical System for the Idoc Receiver 
 - WE20 : Create Partner Profile ->Maintain Outbound and the Inbound Parameters
Second - Log on to XI System:
 - SM59 : RFC Destination for Sender System 
 - IDX1 : Create the port to get Idoc Metadata from Sender System ( The Port Name must match the port name in the idoc header - Usually in format SAP<System ID>. eg. SAPID1 [Optional Step. Not mandatory]
 - IDX2 : Maintain the Idoc Metadata. This is needed only by XI, and not by other SAP systems. IDX2 is needed because XI needs to construct IDoc-XML from the IDoc. No other SAP system needs to do that.
To Enable Acknowledgement:
 - SXMB_ADM ->Integration Engine Configuration ->Specific Configuration ->Add New entry -> Select parameters as: 
 - Category: RUNTIME 
 - Parameters: ACK_SYSTEM_FAILURE 
 - Current Value: 1
GO TO SLD:
 - Create Technical System: Choose WEB AS ABAP if the system is R/3 -> Define SAP SID, Installation Number and Database Host Name a Maintain message Server Details according to Sender System -> Maintain Client Details of Sender System ->Select a Installed Product for Sender System 
 - Create Business System: Choose WEB AS ABAP if the system is R/3 -> Choose the Technical System and the client Created Before -> Choose the Installed Product -> Set:
 - Business System Role: Application System 
 - Related Integration Server: Integration Server
Idoc Tunneling in XI
To prevent performance consuming XMLization and de-XMLization IDOCs are tunneled through SAP XI IDOC adapter meaning no XMLiziation is executed before the IDOC is passed onto the pipeline. Note the message is converted to UTF-8 codepage.
Start transaction SXMB_ADMIN on SAP XI.
Select option Configuration->Integration Engine Configuration and add two parameter EXTERNAL_MAPPER in the category IDOC.
Configure the parameter according to the conditions below:
If Message Code and Message Function are specified in the partner profile:
<Snd.Syst.Id>.<Snd.Syst.Client>.ReceiverPort.<Mess.Type>.<Mess.Code>.<Mess.Function>If only the Message Code is specified in the partner profile:
<Snd. System Id>.<Snd. System Client>.ReceiverPort.<Mess. Type>.<Mess. Code>If only Message Function is specified in the partner profile:
<Snd.Syst.Id>.<Snd.Syst.Client>.ReceiverPort.<Mess.Type>..<Mess.Function>Integration Builder
Integration Directory:
 -  Add Business System:  Adapter Specific Identifiers -> 'Logical System' identical to the 'Logical System Name' in the SLD Business System   
 -  IDoc Receiver Communication Channel: port the same as XI System IDX1 
 
