OS/2 Days Seminar: Misc. Communications Server Questions (59584)

SUMMARY

OS/2 Days Developer's Conference DCA/Microsoft Communication Server

Questions and Answers Follow-Up Responses

Why is user security data stored in the COM.SEC file? This makes it possible to compromise security by taking the file to another machine. According to the customer, this scheme matches the implementation under IBM EE Communication Manager.

Answer

The ability to compromise APPC conversation security requires an APPC Transaction Program (TP) to know the user ID and password when issuing an [MC_]ALLOCATE request to initiate a conversation. Ultimately, the Comm Server administrator must prevent unauthorized access to this file through either of the following:
- Physical security (limiting physical access to the server machine).
- Using the LAN Manager 2.00 Local Security feature to limit unauthorized local access to server-based files. This also prevents access to the file when booting the server from a floppy disk.
How does Comm Server perform load balancing with LU pools that span multiple connections? Does load balancing only relate to session balancing, or does network traffic play any part in the balancing scheme?

Answer

Comm Server allows an administrator to define a pool of 3270 LUs that may span multiple host connections. In this case, one or more Comm Server machines (residing on the same LAN) are supporting more than one link to one or more IBM host machines. If a Comm Server client is configured to have access to the LU pool and a user activates a 3270 session associated with the pool, the Comm Server client machine will randomly select a connection to use.

While this random selection method for 3270 LU load balancing is very rudimentary under Comm Server 1.00, this will be modified under future versions of the Comm Server to provide more reliable LU load balancing. Factors that are being considered to improve the load balancing algorithms include: link traffic volume, server utilization, server CPU type and clock rate, server LAN I/O performance, and host adapter type.

Why isn't Comm Server set up as a LAN Manager service like SQL server?

Answer

The LAN Manager Service facility does not currently provide the amount of detailed control required to fully implement Comm Server as a LAN Manager service. Note that SQL Server is implemented as a single LAN Manager service, not as multiple distributed services that require specialized managing facilities that Comm Server supports. This idea was considered in the early design phases of the product, and is still under consideration for future versions of LAN Manager.

Through the "COMM" command, an effort has been made to manage Comm Server services similar to the way the NET command works under LAN Manager. For example:

       Command                Description
       -------                -----------

       comm start <service>   Starts a Comm Server service on the
                              local machine, where <service> is the
                              name of a Comm Server node or link
                              service. This includes the Comm Server
                              network access program (NAP), which is
                              referred to as the Comm Server
                              Workstation service (for clients) and
                              the Server service (for servers).

       comm stop <service>    Stops a Comm Server service on the local
                              machine.

       comm view              Displays all active Comm Server services
                              on the LAN (on all Comm Server server
                              machines).

       comm manage            Start the Comm Server MANAGE interface.

       comm config            Start the Comm Server CONFIGURATION
                              interface.

       comm browse            Start the Comm Server BROWSE interface.

Will Comm Server include any tools to monitor overall throughput performance and session load? The intention here is to provide tools to help an administrator fine-tune performance, or identify potential bottlenecks so that software and/or hardware reconfiguration could lead to increased performance.

Answer

The Comm Workstation/Server already supports a full range of Link Tracing, Error and Audit logging messages, and client session monitoring/control facilities provided by the MANAGE utility. While statistical data for throughput analysis is not available in version 1.00, this information can be retrieved at the IBM host using Netview. Microsoft welcomes any comments you have regarding additional tools that that you would like to be included in the Comm Workstation/Server products.

How much memory will be left over for DOS applications, once the necessary Comm Server client software is loaded?

Answer

This subject is fairly complicated, since the Comm Server DOS client software includes different modules that allow a customer to optimize memory usage depending on the desired functionality at the workstation. For example, there are three versions of the 3270 Emulator (DOS3270S, DOS3270M, DOS3270L) and two versions of the Comm Server Network Access Program (MINNAP, COMXNAP). The following is a brief description of these different modules:

       Module       Description
       ------       -----------

       DOS3270S     Supports up to five display sessions. Doesn't
                    support API interface. Only requires MINNAP to
                    interface to Comm Server. Doesn't support file
                    transfer options.

       DOS3270M     Supports up to five display sessions, including
                    API support. Requires COMXNAP. Supports file
                    transfer, but this requires extra memory.

       DOS3270L     Supports up to five display and printer sessions,
                    including API support. Requires COMXNAP. Supports
                    file transfer, but this requires extra memory.

       MINNAP       Limited-function Comm Server Network Access
                    Program for the DOS client. Only supports
                    DOS3270S. Doesn't support the DOS client APIs.

       COMXNAP      Full-function Comm Server Network Access Program
                    for the DOS client. Includes support for APIs and
                    3270 emulators.

The following are PRELIMINARY memory usage estimates for different scenarios. Note that these estimates do not include potential memory savings by using 64K of expanded memory. DOS LAN Manager 2.00 numbers reflect debug version memory use, which will decrease when the final version is shipped. Also, these estimates assume that the DOS client is only attached to one LAN, and is using Microsoft's NETBEUI protocol over Token Ring.

Estimated Base Memory Requirements

        DOS Operating System  ....................  50K  (Minimum DOS 3.30)
        Enhanced DOS LAN Manager 2.00 ............  60K *
        DOS LAN Manager Transport & MAC Driver ...  36K
                                                   ----
              Estimated Base Memory Requirements = 146K

         * Preliminary version, using minimum settings and without use
           of high memory.

Memory Usage Under Different Scenarios

One DOS 3270 display emulation session, no API support:

          Estimated Base Memory Requirements ....... 146K
          MINNAP (limited-function NAP) ............  27K
          DOS3270S (small emulator) ................ 103K
                                                     ----
                                             Total = 276K

One DOS 3270 display emulation session with API support:

          Estimated Base Memory Requirements ....... 146K
          COMXNAP (full-function NAP) ..............  40K
          DOS3270M (medium emulator) ............... 121K
                                                     ----
                                             Total = 307K

Three DOS 3270 display emulation sessions and two printer sessions, including API support and one 3270 Model 2 file transfer session active:

          Estimated Base Memory Requirements ....... 146K
          COMXNAP (full-function NAP) ..............  40K
          DOS3270L (large emulator) ................ 263K
          One file transfer session ................  47K
                                                     ----
                                             Total = 493K

APPC API support, with no 3270 functionality:

          Estimated Base Memory Requirements ....... 146K
          COMXNAP (full-function NAP) ..............  40K
                                                     ----
                                             Total = 186K