Logo: TUG TORONTO USERS GROUP for Midrange Systems
e -server magazine

May 1997: Volume 11, Number 6

Communicating with Sam

SNA Gateways vs. TCP/IP

By Sam Johnston

From the questions submitted, the selected issue to be addressed in this issue is:


ur company is in the distribution industry and we have several branch locations across Canada. We have been on the AS/400 platform for several years. Many of the branch locations have installed Local Area Networks (LANs) in the past few years to improve local productivity. Last year we implemented a Frame Relay Wide Area Network (WAN) for a corporate E-mail application (Lotus cc:Mail) and our plan is to use Lotus Notes groupware. We integrated both the AS/400 (5X94) and LAN (Ethernet) communications on the WAN backbone. We have installed 5250 emulation adapters and connected directly to the AS/400 for the PC LAN users that have required access. In the branches we have connected to the remote controllers. This solution has been effective because the number of PC LAN users requiring access to the AS/400 has been limited.

However, all of our PC LAN users are now requesting AS/400 access. Our 5X94 remote controllers are at capacity. We do not want to invest further in 5250 emulation adapters and remote controller technology. Many of the branches are suggesting that we install an SNA gateway product at our head office LAN to provide PC LAN access. This solution seems easy to implement and would solve our problem in the short term. What other options do we have and what is the best long term solution?


t would appear that your company is quickly moving towards PC LAN technology. Therefore, your strategy to not invest further in 5250 emulation and remote controller technology is a wise long-term decision.

With regards to PC LAN to AS/400 connectivity, I would recommend that you approach your solution by viewing the AS/400 as any other server on the network. I would assume that you are connecting directly via the Ethernet LANs to the PC servers using a protocol such as IPX, TCP/IP or Netbeui.

The one key benefit that an AS/400 gateway solution provides versus direct connection is reduced protocol support. PC users will connect to the gateway server using the LAN protocol and the gateway will then control the SNA communications to the AS/400. However, your network already does support multiple protocols. The WAN is supporting your LAN protocol and SNA. Remember you invested in multi-protocol routers.

For a direct connection you can utilize PC Support or Client Access from the AS/400. If your AS/400 is at Version 3 Release 1, or higher, then you should have already purchased the licensing for Client Access. Connecting directly to the AS/400 with Client Access will provide five key benefits:

  1. Eliminates a single point of failure by providing dedicated connection for each user. A gateway is a single access point for all AS/400 connectivity. If the gateway fails, all connectivity to the AS/400 is lost. Directly connecting users to the AS/400 will isolate connectivity problems to single users.
  2. Better performance versus the gateway by eliminating a potential bottleneck, considering the amount of AS/400 LAN activity it would appear that you plan to have. With a direct approach each user has a dedicated connection to the AS/400, whereas the gateway is a single access point and users will contend for the connection.
  3. Maintain the security that is currently being used for AS/400 access. With a gateway solution, because the user passes through the gateway, it is critical to evaluate how the gateway controls the security to the AS/400.
  4. Allow users to run multiple sessions at the desk top. The gateway supports only a single session for each device connection.
  5. Eliminates the need to invest in the gateway software program and the hardware required to support it, as well as managing another server. Additionally, from a reliability perspective, in a gateway environment all AS/400 connectivity would be reliant upon the stability of a PC hardware device.

In summary, while the gateway solution seems to be a feasible short term solution, a direct approach has more long term benefits. From a planning perspective I would recommend that as a first step you review the capacity of the LANs. The connectivity solution aside; your LANs will be required to support additional traffic as you provide access to the AS/400 via the network. If a direct approach is adopted, then I recommend that you investigate the desk top PC configurations and verify that a multi-protocol stack can be supported. There are two key issues to be aware of, and these are: 1) the network PC adapters support coexistence of multi-protocol drivers. 2) there is sufficient memory available to support the additional drivers.

For long term planning purposes I recommend that you begin to investigate utilizing TCP/IP as the network protocol. Implementing TCP/IP would allow you to have a single network protocol and attach directly to each server. The AS/400 supports TCP/IP as does Novell and Microsoft NT LANs. However, if you have been following previous articles there are many issues to consider before implementing TCP/IP. T < G

Note: Any TUG member wishing to submit a question to Sam can e-mail or forward their typewritten material to the TUG office, or to Intesys. We would be pleased to publish your question and Sam's answer in an upcoming issue of the TUG/400 e-server magazine.