There are no general High Availability (HA) requirements for SAP Gateway. High availability applications allow you to maximize downtime security and minimize downtimes. You can achieve this by controlling the growth of redundant data and implementing redundant systems control logic.
At SAP, high availability is always focused on business applications and their related components. SAP relies on the high availability applications of partner products for components which are mandatory for implementing the infrastructure, such as the operating system, database, and hardware.
Collaborative business can give you a competitive advantage. This means integrating existing heterogeneous system landscapes to include business partners, customers, and suppliers. You may also have requirements of your own, depending on the availability requirements of the implemented IT management processes.
For information on high availability on the SAP Service Marketplace, see http://service.sap.com/ha.
For information on high availability on the SAP Help Portal, see the SAP NetWeaver documentation about Hight Availability.