SNA Server computers communicate with each other using mailslot messages or directed datagrams over a network. SNA Server allows you to make choices concerning these broadcasts.
You can select among the following protocols for server broadcasts: Microsoft Networking, Novell NetWare (IPX/SPX), Banyan VINES, and TCP/IP.
Important You must make sure that at least one protocol is available on all SNA Server computers in the subdomain, and that this protocol is used for server/server communication and client/server communication.
For example, if all SNA Server computers in a subdomain use TCP/IP, but only some use IPX/SPX, the protocol used for server-server communication must be TCP/IP, and all servers must use TCP/IP for client-server communication, as well.Using multiple server-server transport protocols can add significantly to network overhead; this is because every server broadcast must be sent out through all protocols selected in SNA Server Manager.
For highest efficiency, select only one protocol for broadcasts between SNA Server computers. Remember that the protocol must be available on all SNA Server computers in the subdomain. Where multiple choices are available (in other words, multiple protocols are bound to the network adapters on all SNA Server computers), select a protocol other than Microsoft Networking (Named Pipes). This is recommended because of design requirements for mailslot broadcasts. When these broadcasts are sent over Microsoft Networking, there is no way for the local system to tell which protocol the receiving system will be using, so the broadcast is sent over all protocols bound to the local adapter. This causes multiple mailslot broadcasts by means of Microsoft Networking for adapters to which several protocols are bound. The multiple broadcasts cause an increase in network traffic.
In other words, in subdomains in which all SNA Server adapters can use multiple protocols, selecting one (and only one) of the following protocols is recommended: IPX/SPX, Banyan VINES, or TCP/IP. You may be able to select extra protocols that do not exist in your network; however, selecting these has no effect.
The SNA Server Manager also allows you to specify a parameter called Mean Time Between Server Broadcasts. For optimum efficiency, you should specify a value greater than or equal to 60 seconds (the default). The smaller this value, the less the efficiency, but the more likely the broadcasts will compensate for lost messages. It is recommended that you choose a value of 120 seconds or greater initially. If you encounter an increased number of lost messages, this value should be reduced until a low number of messages is lost.