Operating Systems

This article traces the transition from mainframe SNA connectivity to Ethernet for access to remote mainframe CICS applications and printing services. Our experiences with converting a portion of a mainframe SNA network to Ethernet using IBM’s Communications Server software may be useful to other sites and can help systems programmers and network staff seeking ways to consolidate SNA end-node connectivity with lower-cost solutions.


The  State  University  of  New  York (SUNY)  at  Albany’s IBM  mainframe computing  era  began  in  1985,  when IBM  won  the  contract  to  replace  the Unisys 1100-series machines at Albany and  three  sister  sites.  The  university’s Unisys 1100/90 system was replaced by an IBM 3083BX that ran VM/SP HPO with  MVS/SP  running  as  a  preferred guest.  Mainframe  connectivity  to SUNY  Central  Administration  five miles  away  was  accomplished  with  a T-1  leased  line  and  a  refrigerator-size 3725  Communications  Front-End Processor (FEP) running NCP/EP. 

In  1987,  a  Periphonics  Touch-Tone Voice  Response  (TTVR)  controller  was added, allowing student telephone access to  grades  and  course  registration.  The Periphonics TTVR attached to the FEP, using  the  SDLC  protocol  over  a  V.35 connection, and emulated a remote IBM 3274 control unit. The TTVR controller could  handle  36  simultaneous  phone connections emulating CICS sessions.

The  IBM  3083  was  eventually upgraded to a 3084QX and the operating  systems  were  replaced  with  their XA-architecture  counterparts.  Most users  were  utilizing IBM  3270  terminals or PC-based IRMA 3270 emulation cards to connect to MVS/CICS or VM/  CMS  over  a  coaxial  network.  The  university  was  also  installing  a  thin-wire Ethernet  network  for  connectivity  to Sun workstations for academic computing purposes.

Noting  the  expense  of  running  two separate networks, we replaced most of the SNA coaxial network with Ethernet and installed a (then) revolutionary new product  from  McGill  University  called NET3270  that  allowed  PCs  to  be  used as network gateway servers to the mainframe.  These  servers  connected  to  the mainframe  using  coaxial  Distributed Function Terminal (DFT) port connections  to  IBM  3174  communications controllers.  Users  installed  Ethernet cards  running  the  IPX/SPX  (NetWare) protocol  stack  to  connect  to  the NET3270 servers. Adding new NET3270 users was initially cumbersome because many  departments  were  involved  in ordering, installing, and configuring PC Ethernet  cards.  Once  completed,  however, we gained the benefits of scalability and standardization. Eventually, McGill sold  the  product  to  Hummingbird Software,  and  the  product  evolved  to HostExplorer,  a  client-based  terminal emulation program that uses TCP/IP.

We added direct Ethernet capability to  the  mainframe  in  the  early  ’90s  by purchasing  a  Bus-Tech  controller  and adding  TCP/IP  software  to  VM  and MVS.  We  then  migrated  all  our  mainframe users to HostExplorer. Since only registered  users  were  allowed  access  to CICS systems, we had to track SNA terminal  Logical  Unit  (LU)  names  and their associated IP addresses in the MVS TCP/IP  configuration  file.  Because  our user population was growing and users often  changed  IP  addresses,  it  was  an administrative  challenge  to  keep  up with these changes. We instituted a list-serv e-mail list that departmental technical  coordinators  could  send  requests to, and moved routine TCP/IP LU to IP mapping  configuration  changes  from the Systems group to an administrative function.  Users  had  to  wait  until  the next  day  for  changes  to  take  effect because the TCP/IP server needed to be restarted during off-hours.

In 1997, we upgraded to a 9672/R21 mainframe  running  VM/ESA  and OS/390  Version  1.2.  One  of  the  best things  to  happen  as  a  result  of  this upgrade  was  the  installation  of  a RAMAC  disk  subsystem  with  built-in RAID  5  redundancy.  Our  antiquated 3380 disks were regularly failing. Shortly after this upgrade, we decided to phase out  VM/ESA  and  run  OS/390  natively due to the plethora of operating systems the university was supporting,

In  1999,  IBM  dropped  support  for the  3725  FEP.  We  replaced  it  and  the Bus-Tech  controller  with  an  IBM  2216 multi-protocol  communications  controller.  This  little  wonder  could  handle all  our  TCP/IP  HostExplorer  terminal users,  our  SNA  link  to  SUNY  Central, and the Periphonics TTVR controller.

Since many of our users were installing  network  printers  (mostly  Hewlett-Packard  JetDirects)  that  spoke  TCP/IP, we  needed  to  support  CICS  and  JES printing to these devices. The Network Print  Facility  (NPF),  then  an  option  to the  TCP/IP  product,  fit  this  need  well.  NPF acts as a print gateway between the SNA  world  and  the  TCP/IP  world, allowing  CICS  users  to  share  departmental LAN printers.

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