 






     Software
     Product
     Description

     ________________________________________________________________

     PRODUCT NAME:  DECserver 500 for VMS, Version 2.1   SPD 26.97.03

     DESCRIPTION

     The DECserver 500 series server is an Ethernet Communications
     Server for Ethernet Local Area Networks (LANs). The DECserver
     500 series server can provide up to 128 EIA-423-A or 64 RS-232
     asynchronous port connections to Digital asynchronous termi-
     nals. Both RS-232, via the 8 port CXY08 communication option
     card, and EIA-423-A, via the 16 port CXA16 communication option
     card and EIA-422 16 port CXB16 communication option card can be
     mixed together in any combination from two to eight cards in one
     server. The DECserver 500 series server provides a convenient
     method to connect logically up to 128 Digital asynchronous ter-
     minals to one or more service nodes (hosts) on an Ethernet. Once
     the terminal is connected, a user can use application programs
     and utilities as though the terminal was directly connected to
     a host via a DZ11, DMF32, or DHU11 device, with a few excep-
     tions. Thus, it may be possible to use the DECserver 500 series
     server to connect all terminals to service nodes in place of
     traditional interfaces, except for host console terminals. Re-
     mote connection via dial-in modems is fully supported. See the
     Restrictions section for limitations.

     The DECserver 550 server provides the additional support of
     IBM[R] 3270 CUT type displays through the use of the CXM04
     option card (refer to the product description SPD 25.G5.xx for
     more details on the CXM04).





                                  DIGITAL                October 1990

                                                          AE-KN88D-TE

 


     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     The DECserver 500 series server also allows for VMS host-
     initiated connections to asynchronous printers. A special print
     symbiont on VMS service nodes can initiate connections to asyn-
     chronous printers connected to DECserver 500 series ports. This
     allows the printers to be distributed throughout a facility and
     accessed transparently by service node users. Incoming host-
     initiated connect requests may be queued FIFO at the server.
     This special print symbiont is included in the software distri-
     bution kits for VMS V5.0 to V5.4.

     The DECserver 500 series server also provides the capability
     to connect host systems that do not support the LAT protocol,
     Digital personal computers, and dial-out modems directly to
     ports on the server. Interactive server users can issue commands
     to connect to services that are offered on such ports. Port-to-
     port connections on the same server are also supported.

     The DECserver 500 series server implements the Local Area Trans-
     port (LAT) protocol for communication with service nodes that
     implement this protocol on the same Ethernet. This interface
     has been optimized for high terminal I/O performance over an
     Ethernet, while reducing host CPU cycles required to handle
     interrupts. Hence, under most I/O loading conditions, a signifi-
     cant performance gain may be realized by using the DECserver 500
     series servers as opposed to direct terminal connections.

     The DECserver 500 series server implements the On-Demand Loading
     (ODL) font loading protocol, which allows Asian terminals that
     implement the ODL protocol to communicate with a suitable VMS
     host via a terminal server. The Asian terminals will be able to
     request font definitions from a suitable VMS host when connected
     to a DECserver 500 series server.

     The DECserver 500 series server also implements and supports
     the Terminal Device/Session Management Protocol (TD/SMP) to
     manage multiple sessions at the device level. The DECserver 500
     series servers provide the ability to communicate with devices
     that also implement this protocol, and assist in the management
     of multiple sessions for these devices. By implementing this

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     protocol, the DECserver 500 series servers can permit attached
     devices to maintain screen and keyboard context for multiple
     LAT sessions, as well as allow these devices to run multiple LAT
     sessions concurrently.

     Software that runs on the DECserver 500 series server is down-
     line loaded over the network from a Phase IV DECnet load host.
     Terminal access using the DECserver 500 series server does not
     require DECnet running in the same service node; LAT uses the
     Ethernet addressing mechanism to transport terminal messages.

     For wide area network (WAN) communications, terminal users can
     connect to a LAN service node running DECnet where they can "SET
     HOST" to a remote system via the DECnet network terminal proto-
     col. If this system has the prerequisite X.29 or SNA 3270 access
     routines, a terminal user could communicate to a remote SNA or
     X.25 host through the appropriate gateway and this intervening
     host. A DECserver 500 series terminal user cannot communicate
     directly to remote hosts through DECnet Routers or X.25/SNA
     Gateways. Wide area network traffic will not provide the same
     high level of performance as local terminal connections, due to
     the additional DECnet and internet protocol overhead.

     Features

     Terminal Connection Management

     Through the use of a simple command, users can establish a
     logical connection, called a session, to any service node that
     implements the LAT protocol on the same Ethernet LAN. This
     connection makes the terminal appear as if it were physically
     connected to the service node, and the terminal user can use
     standard system utilities and applications supported by that
     node. Each terminal connected to the server can connect to the
     same or a different service node on the Ethernet. Furthermore,
     several servers can be used to connect many terminals to one or
     more service nodes.


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     A service node can have one or more services that are offered
     to DECserver 500 series server users. Services and nodes are
     identified by name. Users usually connect to services, not to
     nodes, although often one of the service names will be the node
     name. Users can optionally specify a node and/or a port name
     when they connect to a service.

     In a VAXcluster environment, the DECserver 500 series server
     sees each VAXcluster on the Ethernet as a collection of service
     nodes offering a common service. Each cluster node may also
     offer a service whose name is equivalent to its node name. In
     this case, a terminal user can connect either to the cluster
     service or to a service associated with a particular cluster
     node.

     Non-LAT Host Support

     The DECserver 500 series server can be used to provide logical
     terminal connections to hosts that do not implement the LAT
     protocol. In this type of configuration, the server becomes the
     Ethernet connection and protocol support for these hosts. This
     expands the LAT network accessibility to the terminal user to
     include LAT hosts directly connected to the same Ethernet, and
     hosts connected to the LAT network via the DECserver 500 series
     server. Non-LAT host support should be implemented through the
     use of the CXY08 hardware option only.

     A host that supports XON/XOFF, ASCII standards, and EIA RS-232-
     C/CCITT V.24/V.28 interfaces can be connected to the DECserver
     500 series server. This provides the terminal user with a trans-
     parent connection to the non-LAT host. It is strongly recom-
     mended that the server port and the host-side port use the modem
     control signals to signal the host automatically on session dis-
     connection. In this application the server port appears to the
     host as a dial-in modem. However, hosts that require more than
     one transition of the RING signal are not supported.



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     In this configuration there is a one-to-one correspondence be-
     tween the port on a DECserver 500 series server and the con-
     nection on the host. The server manager assigns service names
     to individual ports or groups of ports that connect the host
     interface to the server.

     Load Balancing

     When a connection is made to a service, the actual node for the
     connection is determined by load balancing. Load balancing is a
     process the server uses when more than one node offers the same
     service. Service nodes do not have to be configured in a cluster
     in order for load balancing to be used. Service nodes with the
     same names may be running different operating systems. Using the
     load balancing process, the server connects to the node with the
     highest rating for the service desired. This rating is based on
     the current loading on the nodes that offer the service.

     Multiple Sessions

     The DECserver 500 series server allows a single user to estab-
     lish and maintain up to eight sessions to one or more service
     nodes (up to 64), up to a maximum of 512 sessions per DECserver
     550 unit. The DECserver 500 supports up to 256 sessions. The
     DECserver 500, when equipped with the optional upgrade, will
     support up to a maximum of 512 sessions. Only one session can
     be active at a time on each port. Through simple switching
     commands, the user can access the different sessions without
     repeating a login dialog each time. The number of simultaneous
     LAT sessions supported by a service node depends on the type of
     operating system running on that node.

     Multiple Session Management

     The DECserver 500 series servers allow direct communication with
     devices that support TD/SMP protocol. This protocol provides the
     ability for the attached device to maintain screen and keyboard
     context for the multiple LAT sessions that the DECserver 500
     series servers provide. By implementing the ability to commu-
     nicate with this protocol directly to the attached device, the

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     DECserver 500 series servers can now assist in the management of
     context of these multiple sessions, as well as allow for simul-
     taneous output to multiple LAT sessions being maintained by the
     device.

     Outbound Connection Queues

     If a terminal user requests a connection to a server, and the
     requested service is currently in use, the terminal server
     may opt to have the connection request queued to the remote
     service. This feature will happen automatically whenever a
     connection fails for this reason if the user's port has been
     appropriately configured. The connection request is queued at
     the service node end and is processed first-in/first-out until
     the user's connection request can be completed. This feature
     assists in the fair management of limited resources. Once queued
     for connection, the user also has the option to cancel the queue
     entry and proceed with other sessions.

     Welcome Identification

     The DECserver 500 series servers standard welcome banner, which
     includes terminal server type, version number, and protocol
     version number, is issued whenever a user successfully logs
     in to the server. The server will also print a server manager
     settable identification string. This can be useful for automatic
     server identification, or for small daily messages used for
     communication with the terminal server users.

     Local Mode and Service Mode

     For the most part, the environment provided by the DECserver 500
     series server is identical to that the user would experience if
     attached directly to the service node. When operating in this
     mode, the user is said to be in Service Mode. Occasionally, such
     as during connection establishment, the user interacts directly
     with the DECserver 500 series unit. When operating in this mode,
     the user is in Local Mode.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     In Local Mode, the terminal input is interpreted directly
     by DECserver 500 software as commands to be performed by the
     server.

     Local Mode has three different levels of privilege: privileged,
     nonprivileged, and secure. Privileged mode is provided for the
     server manager to control the environment of the server and
     the terminal users. Access to this mode is password protected.
     Nonprivileged commands allow the terminal user to control that
     user's service sessions, set terminal characteristics, and show
     server information. The server manager can set the server to
     secure mode on a per-terminal basis, which further limits the
     commands users can enter to only those that directly relate to
     the user's own terminal.

     The server manager environment is a logical extension of the
     user environment. The server manager is treated as a server user
     with a privileged status. The server manager sets a terminal
     to this status using a command that requires a password. This
     privileged status allows the server manager to enter commands
     not normally available to server users. These commands set
     server characteristics, provide control over server port usage,
     and provide the ability to control the user's access to the
     server and network services.

     The LIMITED VIEW port characteristic is a mechanism by which
     the server manager can prevent certain ports from executing SHOW
     NODES and SHOW SERVICES commands.

     In Service Mode, the terminal input is passed directly to the
     connected service node, with several exceptions. One exception,
     called the local switch character, allows the user to enter Lo-
     cal Mode from Service Mode. The <BREAK> key may also be used for
     this function. Other exceptions, called the forward and backward
     switch characters, allow the user to switch between sessions
     without the need to enter local mode. The switch characters are
     disabled by default but may be enabled by command. Both CTRL/S
     and CTRL/Q are normally interpreted locally, but flow control
     using these characters can be disabled.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     Autoconnection

     Autoconnection is a function that automatically connects a
     user terminal to a service node when connection failures occur
     or upon user login to the server. In conjunction with this
     function, a dedicated or preferred service can be specified
     for each terminal user. If a failure occurs, the server will
     automatically try every 30 seconds to re-establish a connection
     to the desired service.

     If a dedicated service is specified for a port, the DECserver
     500 series server will attempt to connect the port to that
     service when a character is typed on the terminal keyboard or
     when an existing connection fails. In dedicated service mode,
     only one session is available per port. As this mode is designed
     to simulate a direct terminal connection, no local mode commands
     or messages are available to the terminal user.

     If a preferred service is specified for a port, the DECserver
     500 series server will attempt to connect the port to the ser-
     vice as with the dedicated service mode of operation. However,
     the terminal user can enter local mode and establish other ses-
     sions.

     Node/Database Improvements

     With the increasing size of LAN's, servers on some networks
     may temporarily find themselves in the situation of having more
     nodes available to them than they can store in server memory.
     This feature will purge all unused nodes and allow the server
     to update its node database, eventually allowing the user to
     connect to the desired service.

     Automatic Session Failover

     If a service is available on two or more service nodes and
     a connection to a service fails, the server will attempt to
     connect the user to another service node offering the same
     service. The user does not have to be already connected to that
     service node. However, the user's context at the time of failure

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     is not automatically restored and login to the new service is
     required.

     Line Card Redundancy

     This feature provides the server manager with the ability to
     redirect an active line card to a stand-by line card already
     installed in the server without bringing the server down. There
     are a few restrictions associated with the Line Card Redundancy
     feature:

     o  Stand-by line cards must be previously defined using the
        Terminal Server Configurator(TSC) or Terminal Server Man-
        ager(TSM).

     o  The physical stand-by line card must be present in the server
        at initialization time.

     o  Source and target line cards must be of the same type.

     o  Once a stand-by card becomes active as a result of a MOVE
        command, it can not go back to stand-by without reloading the
        server.

     For security, the line card redundancy feature does not attempt
     to preserve any sessions that the source (failed) line card
     users may have had before the move.

     Groups

     Every terminal and service node in a LAT network is a member
     of one or more groups, which are specified by a list of numbers
     from 0 - 255. Groups allow an easy means of subdividing the net-
     work into what appears to be many smaller networks. A terminal
     user is only aware of the services that are offered by nodes in
     the same group(s).

     The server manager can specify the authorized group(s) in which
     a terminal is a member. The authorized groups define the set of
     services that the user is allowed to access. In addition, a user
     can further restrict access to services by disabling some of

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     the authorized groups using a non-privileged group command. The
     user-settable groups are a subset of the authorized groups.

     Groups provide a restrictive view of the network. This re-
     stricted view is mainly for user convenience and, although it
     also provides a form of security, it is not intended to be the
     primary form of access authorization or system security for a
     node. Groups can also be used by the server manager to tune the
     server's usage of its available memory.

     Security

     The DECserver 500 software provides functions that enhance secu-
     rity features already available in the service nodes. Security
     features include the ability to lock a terminal's keyboard from
     other users, optional login protection, and nonprivileged local
     mode of operation as a default.

     A user may lock the terminal using a lock password. This allows
     the user to leave sessions running at the terminal without fear
     of security violations. When a terminal is locked, all input
     from the terminal is ignored until the lock password is re-
     entered. The lock feature may be disabled by the Server Manager
     on a per-port basis or on a server-wide basis.

     Each terminal port can be set on the server to operate in a
     secure mode that causes all commands that relate to other users
     to be disabled for that port. The server manager can also define
     a unique password for each set of server ports offered as a
     service. This is useful for restricting access to devices like
     dial-out modems.

     Login password protection can be enabled on a per-line basis by
     the Server Manager. If enabled, the terminal user must enter a
     login password to access server functions. The login password is
     changeable, but is a server-wide password.

     There is also a maintenance password for protecting unautho-
     rized downline loads of the server or use of the Remote Console
     Facility (RCF) to manage the server remotely.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     The DSRLOGOUT feature can be set for any terminal and is used
     with the CXY08 and BC22D, BC17D or BC22R cable to detect termi-
     nal power-down and enact an automatic port logout that dis-
     connects all sessions established from that port. On modem
     controlled dial-in ports, the server will automatically dis-
     connect an incoming call if the user does not successfully log
     in to the server within 60 seconds.

     In Local Mode, DECserver 500 series users normally can use only
     the server's nonprivileged commands. In this mode, users may
     only issue commands that affect their own terminal environment.
     The server has a privileged mode for the server manager's use.
     This mode is password protected.

     Online HELP Facility

     A full online reference HELP facility is available. The server's
     HELP command provides information on correct syntax and details
     about each command. In addition, a tutorial HELP feature allows
     new users to learn quickly the basics of DECserver 500 oper-
     ation. Tutorial HELP may be entered before logging in to the
     server by typing HELP at the username prompt.

     A limited help characteristic is available. When this character-
     istic is enabled by TSM/TSC, an abbreviated help file will be
     loaded into the server freeing up more memory for session/nodes.
     When enabled, all help requests will result in the same abbrevi-
     ated help screen, which lists the syntax of every server command
     available to the user. This characteristic could be enabled for
     DECserver 500's running with the KDJ11-SB processor to increase
     the number of sessions/nodes obtainable. Enabling LIMITED HELP
     on a DECserver 500 running with the KDJ11-SD processor will not
     result in any additional sessions/nodes.

     Directory Service




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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     Any suitable DECserver 500 series server user can obtain a di-
     rectory of services available to that user with a SHOW SERVICES
     command. Services for which the user is not authorized will not
     be displayed. If limited view is enabled on the port, the user
     cannot perform a SHOW SERVICE.

     Permanent Characteristics

     Each DECserver 500 series server has a unique software image
     on its downline load host. A database of permanent character-
     istics is kept within each image. These characteristics can be
     changed prior to downline load by the server manager or load
     host manager. All permanent characteristics can be changed by
     using the Terminal Server Configurator (TSC) utility provided in
     the DECserver 500 software distribution kit.

     TSC now supports the modification of CXM04 keyboard mapping ta-
     bles from within the TSC program. Keyboard language table files
     are provided with the 3270 Terminal Software Option layered
     product. This product provides the firmware and keyboard tables
     needed to use the CXM04 line card on the DECserver 550.

     The keyboard table files, one for each supported keyboard lan-
     guage, are used by the CXM04 firmware to translate IBM scan
     codes to Digital keys. Digital provides a default mapping that
     is described in the 3270 Terminal Option User's Guide. For ex-
     ample, by default, the 3270 ATTN key maps to the Digital VT220
     BREAK (F5) key on the 3178 Models C1 and C2 keyboards.

     Port Characteristics Configuration

     Characteristics governing the operation of an individual port
     can be displayed by a nonprivileged terminal user interactively
     from that user's terminal. Many of the characteristics can be
     set up by the user, but certain characteristics are privileged
     and can only be changed by the server manager.

     Port parameters that can be set and displayed include: speed,
     character size, group, parity, terminal type, access, autobaud,
     modem, and password protection.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     Port Access

     A port on a DECserver 500 series server may be set up in differ-
     ent ways depending on the device attached to the port and its
     intended use. Port access is the characteristic that determines
     how a port can access or be accessed by interactive users and
     service nodes.

     o  Access Local - Designed for interactive terminals. This al-
        lows the device (typically an interactive terminal) attached
        to the port to CONNECT to LAT services. This type of access
        is also used for dial-in modems.

     o  Access Remote - Designed for applications-driven devices
        (like asynchronous printers) that are allocated by a service
        node process. This allows the implementation of certain
        shared printers by multiple service nodes. This type of
        access is also used for connections to dial-out modems and
        non-LAT host systems by interactive users.

     o  Access Dynamic - Designed for devices (like dial-in/dial-out
        modems or printers with keyboards) that require both Local
        and Remote access, but not simultaneously.

     o  Access None - Designed to allow the server manager to disable
        the use of a port.

     With printer support capabilities, the setup procedure of remote
     printers needs to be done once and is automatically reconfigured
     on server and/or system startup. The particular server port
     must be configured for remote access and set up to match the
     characteristics of the printer. The system startup command file
     must be modified to call the two command files provided with
     the service node software. Finally, the command files themselves
     must be customized to reflect the environment of their node. The
     server can optionally queue remote connects if these connects
     cannot be satisfied immediately. This queue management can be
     enabled for the server by the server manager. Note that this is
     a connection queue only.

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     Asynchronous Device Operation

     The DECserver 500 software supports the simultaneous operation
     of up to 128 asynchronous devices at speeds from 50 bps to 38.4K
     bps under specified application conditions. The software also
     supports:

     o  Full modem control support (with CXY08 hardware option only)

     o  Data-leads-only support

     o  XON/XOFF flow control

     o  CTS/RTS and DSR/DTR flow control (with CXY08 hardware option
        only)

     o  Split speed (transmit and receive) terminal operation

     o  Block Mode transfers

     o  Automatic line speed detection

     o  Digital personal computer file transfer and terminal emula-
        tion

     o  Data transparency mode

     o  Ability to pass BREAK condition and error notification

     o  Ability to assist in multiple session management via TD/SMP

     Server Management

     Several facilities exist for managing and troubleshooting server
     operation. The server manager in privileged mode can set up
     server identification information, change port characteristics,
     or fine tune the operating characteristics of the server. The
     server manager can also assign service names to groups of one
     or more ports that are connected to non-LAT hosts or modems.
     Troubleshooting facilities include diagnostic tests, a remote
     console feature, online statistics and modem signal and flow
     control monitoring.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     A privileged user can diagnose Ethernet communications problems
     by looping messages to an Ethernet host and through the Ethernet
     hardware interface at the server. To diagnose terminal prob-
     lems, users can execute a command to transmit test data to their
     terminal. The server manager can send test data to any termi-
     nal, optionally using internal or external loopback with data
     comparison.

     The capability also exists for the server manager to test a
     service connection by sending data from the initiating port to
     the service node and back again. The data is then compared and
     any discrepancies reported. At the service node, the data can be
     looped back by the LAT protocol, or internally or externally at
     the service port. This feature is supported by the DECserver 500
     series service nodes; VAX/VMS service nodes do not support this
     service loopback capability.

     The server maintains a variety of statistics and counters. These
     include: Ethernet data link statistics, LAT protocol statistics,
     and port error statistics. This data can be displayed and zeroed
     by the server manager. Server parameters that can be modified
     and displayed include: the server identification, circuit timer,
     session limits, and login limits.

     Remote Server Management

     The DECserver 500 software implements the Maintenance Operations
     Protocol (MOP) console carrier protocol, which enables access to
     the DECserver 500 series server from a Phase IV DECnet host on
     the same LAN. The entire local mode user interface is accessible
     to the remote management port user. This includes the privileged
     commands if the user knows the server's privileged password.
     This capability allows centralized server management and remote
     server diagnosis.

     Communications

     DECserver 500 software is exclusively designed to run on DEC-
     server 500 series hardware that includes an Ethernet interface
     for connection to an Ethernet transceiver cable.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     The CXY08 hardware option has eight EIA RS-232-C/CCITT V.24
     asynchronous line interfaces for connecting terminals to the
     unit.

     The CXB16 hardware option has sixteen EIA-422 asynchronous line
     interfaces for connecting terminals to the unit.

     The CXA16 hardware option has sixteen DECconnect connections
     (EIA-423-A) for connecting terminals to the unit.

     The CXM04 hardware option has eight coax A 3270 synchronous
     line interfaces for connecting 3270 CUT mode devices and Cluster
     Controllers.

     Using the CXY08 hardware option, each port can be set up by
     the server manager to operate using full-duplex modem control.
     The CXY08 hardware option is compatible with the Digital family
     of modems and with Bell 100 and 200 series modems and their
     equivalents. A BREAK feature is available and can be set on
     a per-port basis. This allows a BREAK condition to be passed
     through from a terminal connected on the server to the non-LAT
     host connected to a port on a DECserver 500 series server.

     DECserver 500 Series Server Operation

     The DECserver 500 series server provides the necessary Mainte-
     nance Operation Protocol boot ROM support for downline loading
     DECserver 500 software from a Phase IV DECnet load host over
     the Ethernet into server memory and also for upline dumping. All
     self-test diagnostics are in DECserver ROM; downline loading is
     not a precondition for DECserver self-test. In the event of a
     bugcheck caused by a fatal error, the unit will normally attempt
     to upline dump server memory to a DECnet Phase IV host. Fol-
     lowing this, the unit will automatically initialize itself and
     invoke a downline load.

     DECserver 500 Series Server Configuration and Performance


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     The process of configuring the DECserver 500 series server is
     based primarily on tradeoffs of cost and performance within
     the realm of satisfying user application requirements. Network
     applications will range from low-speed, low-cost situations
     (e.g., connecting remote terminals through low-speed modems),
     to those of relatively high performance (e.g., connecting high-
     speed local terminals to local hosts within a local area network
     or connecting to non-LAT systems). The performance of a given
     server is a function of the expected network traffic, the load
     on hosts to which terminals are connected, and resultant pro-
     cessing pursuant to the dedicated function of the unit. Thus
     performance depends on several factors:

     o  Number of terminals

     o  Number of host systems with active connections to the server

     o  Number of active connections to non-LAT hosts

     o  Terminal speeds

     o  Terminal user applications

     o  Number and size of host buffers

     o  Terminal workload

     The DECserver 500 series server can sustain an aggregate user-
     data output throughput (from server to port devices) of 173,000
     characters per second using a 10 millisecond circuit timer. The
     DECserver can sustain an aggregate user-data input throughput
     (port device to server) of 16,500 characters per second using an
     80 millisecond circuit timer.

     In order to achieve a viable configuration, the user and/or a
     Digital software specialist should perform a level of appli-
     cation analysis that addresses the factors above. The actual
     maximum data throughput cannot be calculated by multiplying the
     number of lines by the line speed since many factors already
     discussed in this section may reduce the actual throughput.

     Restrictions on DECserver 500 Series Server Usage

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     While terminal connections using the DECserver 500 series ter-
     minal servers have been designed to simulate direct terminal
     connections as much as possible, a few differences necessarily
     exist because of the nature of the product. Under most circum-
     stances, these differences are not noticed by terminal users
     or service node application programs. However, applications
     which are directly dependent on the following functions may not
     operate as with a direct connection.

     o  Applications that depend on reading or setting the terminal
        speed, character size, and parity by manipulating system data
        structures

     o  Applications that depend on an extremely fast response time
        (typically less than 200 ms) to operate

     o  Applications that use an alternate terminal driver in the
        service node

     o  Applications that expect incoming connections to have fixed
        device names or to obtain information about the name of the
        server and/or port

     Applications that depend on certain physical device response
     times or do their own modem signal handling are not supported.

     There are two restrictions that should be noted; for connections
     from the server, the LAT device created has an unpredictable
     name, and for host initiated connections, application program-
     ming will not be supported.

     The DECserver 500 terminal server does not support the CXM04
     communications option card.

     HARDWARE REQUIREMENTS

     VAX, MicroVAX, VAXstation, or VAXserver configuration as speci-
     fied in the System Support Addendum (SSA 26.97.03-x).

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     SOFTWARE REQUIREMENTS*

     VMS Operating System

     *  Refer to the System Support Addendum for availability and
        required versions of prerequisite/optional software (SSA
        26.97.03-x).

     Refer to the following Software Product Descriptions (SPDs)
     for information on other supported DECserver 500 series servers
     for RSX-11M-PLUS and Micro/RSX (SPD 18.53.xx), and ULTRIX (SPD
     33.54.xx).

     ORDERING INFORMATION

     Software Licenses: QL-03KA9-AA
     Software Media: QA-03KAA-H*
     Software Documentation: QA-03KAA-GZ
     Software Product Services QT-03KA*-**
     LAT Network Concept Guide AA-LD84B-TK

     *  Denotes variant fields. For additional information on avail-
        able licenses, services and media, refer to the appropriate
        price book.

     SOFTWARE LICENSING

     The DECserver 500 software license applies to the DECserver 500
     series servers on which the software runs, not the service host
     node CPU in the network.

     This product does not provide support for the VMS License Man-
     agement Facility. A Product Authorization Key (PAK) is not
     required for installation or use of this version of the product.

     This software is furnished under the licensing provisions of
     Digital Equipment Corporation's Terms and Conditions. For more
     information about Digital's terms and policies, contact your
     local Digital office.

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     DECserver 500 for VMS, Version 2.1                  SPD 26.97.03



     SOFTWARE PRODUCT SERVICES

     A variety of service options are available from Digital. For
     more information contact your local Digital office.

     SOFTWARE WARRANTY

     Warranty for this software product is provided by Digital with
     the purchase of a license for the product as defined in the
     Software Warranty Addendum of this SPD.

     [R]  IBM is a registered trademark of International Business
          Machines Corporation.

     [TM] IBM PC, IBM PC/AT, and IBM PC/XT are trademarks of Interna-
          tional Business Machines Corporation.

     [TM] The DIGITAL Logo, DECconnect, DECmate, DECmodem, DECnet-
          VAX, DECOM, DECserver, DECstation, DELNI, LAT, MicroVAX,
          VAX, VAXft, VAXmate, VAXserver, VAXstation, VMS, and VT are
          trademarks of Digital Equipment Corporation.


















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