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Versions: 00 01 02 03 04 05 RFC 3049

TN3270E Working Group                                        Jim Naugle
Internet-Draft                                  Kasthuri Kasthurirangan
<draft-ietf-tn3270e-service-loc-05.txt>                             IBM
Expiration Date: December 2000                            Gregg Ledford
                                                     Zephyr Development
                                                        August 12, 2000


           TN3270E Service Location and Session Balancing


Status of This Memo

   This document is an Internet-Draft and is in full conformance
   with all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document discusses the implementation of Service Location
   Protocol and session balancing with a TN3270E emulator in a client
   server implementation with a TN3270E server.

   Application program developer's can locate TN3270E services and
   load balance among those services (3270 host sessions), by using
   this Service Location Protocol support.











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1. Table of Contents

Status of This Memo
Abstract
 1. Table of Contents
 2. Introduction and Terminology
     2.1 Terminology
 3. An Overview of RFC 2165
     3.1 SLP Agents
     3.2 Service Agents
     3.3 User Agents
 4. TN3270E Server Environment and Load
     4.1 TN3270E Server Load
 5. TN3270E Client Configuration
     5.1 SLP Scope
     5.2 DA-Discovery Time-Out
     5.3 SA-Discovery Time-Out
 6. TN3270E Client Implementation Information
     6.1 Overview
     6.2 How to Obtain List of TN3270E Servers Supporting SLP
     6.3 TN3270E Sample Client Flow
        6.3.1 Open the SLP connection
        6.3.2 Query the list of TN3270E servers
        6.3.3 Forward Looking Example using SLPv2
        6.3.4 Determine loading of each TN3270E server
     6.4 Recommendations
 7. Sample Trace Flow of SLP and Session Balancing
 8. Service Templates and Service Registration
     8.1 The TN3270E Service Type Template
     8.2 The Server Service Template
     8.3 Template Contact Information
     8.4 Security Considerations
     8.5 Sample TN3270 Service Registration Message
     8.6 Sample Server Service Registration Message
 9. References
10. Author's Addresses
















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2. Introduction and Terminology

   This document will provide information on Service Location Protocol
   implementation to discover TN3270E servers in a network and session
   balance among those servers.  This implementation follows the
   standards track RFC 2165, Service Location Protocol [1] but also
   provides some examples when using Service Location Prtotocol version
   2 to be forward looking. Service Location Protocol version 2 is
   documented in RFC 2608 [4] and RFC 2609 [2].


2.1 Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119  [1].

   Session Balance -
   This refers to the ability of TN3270E client to use
   server load information to establish a TN3270E connection to the
   TN3270E server with the least load at that time. The purpose is to
   distribute the connection of TN3270E sessions among more than one
   TN3270E server, and one server will not be excessively loaded.
   The term "load balance" is a more general term, with respect to
   server load, and in this document we are focusing on the
   TN3270E session connections to least loaded servers.

   SNA Gateway -
   A Systems Network Architecture (SNA) gateway allows multiple
   LAN-attached workstations to access SNA hosts through one or more
   physical connections to one or more hosts. A SNA gateway acts as a
   protocol converter between workstations attached to a LAN and a
   WAN host line. It typically would support the SNA protocols LU 0,
   1, 2, 3, and dependent LU 6.2 (APPC). SNA gateways typically
   include a TN3270E server capability.

   LU Pool -
   The Logical Units (LUs) defined in the gateway can be dedicated
   to a particular workstation or pooled among multiple workstations.
   Pooling allows workstations to share common Logical Units (LUs),
   which increases the efficiency of the LUs and reduces the
   configuration and startup requirements at the host. When a client
   connects to the gateway, the gateway retrieves an LU from the pool
   to establish a session. The LU is returned to the pool for access
   by other workstations when the session is ended.

   Commserver Service Type Template -
   Commserver service type is defined as an SNA Gateway server as
   previously defined above in this terminology section. A template
   describing the attributes for this service type is in section 8.2.


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3. An overview of RFC 2165

   RFC 2165, Service Location Protocol (SLP) [1], provides an automatic
   way for clients to discover services within an administrative
   domain.

   These services have various attributes associated with them from
   which a client can base a service selection. The basic design
   involves the use of three agent types.  These are: User Agents
   (UA's), Service Agents (SA's) and Directory Agents (DA's).

3.1 SLP Agents

   User Agents are used to query Service Agents or Directory Agents.
   They acquire/request service information based upon the desired
   attributes and service needed for the user application.

   Service Agents represent a specific service and advertise service
   information.

   Directory Agents act as a central collection point for service
   registration information by Service Agents which is later requested
   by "user agents" in "intranets".

3.2 Service Agents

   The service registers itself with the service agent so that the SA
   can start advertising this information over the network. The process
   of registration consists of the service giving the SA all relevant
   configuration information and attribute tag/value list pairs
   specific to this service. The Service template is an abstract schema
   that applies to the service type. The service template for TN3270E
   is shown later, contains the URL which is the address of the server
   with the port, which should be used to connect to it. The URL also
   contains the service type which in this case is TN3270. The template
   also contains all the other attributes associated with this service.

3.3 User Agents
   The User Agent working on the TN3270E client's behalf retrieves
   service information from the Service Agent(s) or a Directory Agent.
   Based on the gathered information and required attributes the
   TN3270E client or user can decide whether or not to connect with a
   particular server. Based on the service advertisements from various
   TN3270E servers, the client looks at the load attribute and can
   decide to connect to the least loaded server. If by the time it
   connects to that particular TN3270E server, the server becomes
   unavailable it can try connecting to the next server in its list
   (ie: the second least loaded server whose advertisement was
   retrieved by the client/user agent).



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4. TN3270E Server Environment and Load

   TN3270E Servers are pervasive in today's networked environment. SLP
   provides emulator clients with a way to discover TN3270E servers in
   the network and session balance among the servers.  The TN3270E
   servers could be distributed across different SNA gateways with
   different connection methods to hosts.  The use of LU pools provides
   an easy way for administrators to provide users access to hosts.
   Administrators can add users to LU pools that have pre-configured
   LU's with specific attributes, like LU types and model types.

   These LU pools would typically have LUs from several different
   gateways assigned, and as members of the LU pool make TN3270E
   session connections, they would be making connections to different
   TN3270E servers, with different load factors, so that session
   balancing could be accomplished. The use of LU pools is not a
   requirement for SLP and session balancing.  A TN3270E client could
   obtain a session by using SLP and session balancing to locate the
   least loaded server in the network.  On a service request a wild
   card "*" could be used when asking for LUPOOL if the emulator
   doesn't care which device types are supported in given pools or if
   it can assume given pools support only certain device types.

4.1 TN3270E Server Load

   TN3270E servers providing load information, SHOULD include
   number of sessions available, not in current use, as part of the
   calculation in determining the total load for the server. There can
   be other factors that might have an effect on server load.  An
   example would be if a server is not dedicated to only SNA traffic,
   and is handling other processes, like file services and print
   services, etc.  It is beyond the scope of this document to
   standardize the method of individual server load calculations.
   Different vendors server's may calculate load information based
   upon factors they consider important, and methods for calculating
   load may change over time.

   If the TN3270E server coexists in a network with other TN server
   implementations using SLP for session balancing, TN3270E server load
   could be adjusted to compensate for differences in load
   calculations.

   One way to allow TN3270E server administrators to compensate for
   differences in implementations of calculating server load
   measurement is to provide the ability to modify the load calculation
   on the TN3270E server.  An element of control can be provided by
   allowing the administrator to modify the load measurement, by using
   an integral number between 0 and 100 (100 being the highest) to
   change the load. This load measurement acts as an additional factor
   on the server's actual load calculation, so that the administrator


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   could bias up or down, the likelihood of that server being selected
   by a TN3270E client.

   Load MUST be defined as one of the attributes for the TN3270E
   server. The Load attribute provided at the server will allow
   clients to determine which server to make a connection. If a UA
   provides only a Service Type, in an Attribute Request,  then the
   reply includes all attributes and all values for that Service Type,
   and Load would be included.  Attribute Requests MAY include a select
   clause, so you could be returned just load information. For more
   information on Attribute Requests refer to Service Location Protocol
   [1].

   An application could issue a Service Request to locate a TN3270E
   server. Then an application designed to perform least-load
   location of  a TN3270E service, could issue a series of Attribute
   Requests to obtain the load measurement of each server specified
   with a URL. It would specify a select clause similar to the one
   below to receive only load information.

   URL = service:tn3270://9.37.51.254:23
   Attribute filter = LOAD

   The attribute LOAD would be returned along with its value.  The
   application could then issue other Attribute Request calls for each
   URL.

   The application would then select the least loaded server as a
   connection target.  If it tries to connect to a server and that
   connection fails, it could then try to connect to the next
   least-loaded server.

5. TN3270E Client Configuration

5.1 SLP Scope

   Scope is a parameter used to control and manage access by clients to
   servers in a network. It is the same as the Service Location
   Protocol scope defined in RFC 2165 [1]. The control scope provides
   is necessary for two reasons:

   As your network, the number of clients, and the number of servers
   grow, it becomes necessary to partition access to those servers by
   the growing number of clients in order to reduce overall traffic on
   the network. It allows administrators to organize users and servers
   into administrative groups.

   The meaning of the values of scope is defined by the administrator
   of the network. These values can represent any entity. Commonly,
   they fall along either departmental, geographical, or organizational
   lines.

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   Each TN3270E server can be assigned to a single scope or multiple
   scopes. TN3270E clients using these servers can be configured for a
   single specific scope.  If TN3270E clients are not configured with a
   scope they MUST use the scope "default".

   SLP Service Agents and Directory Agents (DA) need to reside in the
   network that support the TN3270E server with configured scopes.

   Attribute information for Service Types pertaining to a specific
   scope can be obtained from Directory Agents (DA).  The DA will not
   return a result unless the requested scope matches.

   For more information on SLP scope refer to Service Location Protocol
   [1].

5.2 DA Discovery time-out

   The DA Discovery time-out value, is used to control how long the SLP
   API must wait to discover Directory Agents (DAs) in the network. The
   discovery request is a multicast, and the amount of time required to
   gather all DA responses might vary depending on many factors. If
   there are no DAs in the network, this time-out value can be set to
   zero to indicate that no DA discovery is to be done. The time-out is
   expressed in milliseconds.

5.3 SA Multicast time-out

   The SA Multicast time-out value, is used to control how long the SLP
   API must wait to discover services, attributes, or service types in
   a network without at least one DA that supports the scope of the
   request. In this situation, these requests are multicast and the
   User Agent waits the time-out value to gather the multiple responses
   that are returned. The time-out is expressed in milliseconds.

6. TN3270E Client Implementation Information

6.1 Overview

   A TN3270E client that implements TN3270E SLP session balancing does
   not need to configure an IP Host Address or TCP Port for the TN3270E
   server it desires to connect to. Instead, the IP Host Address and
   TCP Port of the least loaded TN3270E server is discovered by using
   the SLP session balancing described in this document.

   The discovery of the least loaded TN3270E server is done entirely
   outside of and before the TN3270E telnet negotiation. Once the IP
   Host address and TCP Port of the least loaded TN3270E server is
   discovered, the TN3270E client can then start normal TN3270E telnet
   negotiation.



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   The TN3270E client MUST allow for configuration of the following
   parameters. These SLP specific configuration items are covered by
   configuration parameters in the SLP API [5].

   Enable SLP Session Balancing

   This configuration parameter indicates whether or not SLP session
   balancing is enabled. If it is enabled the following three
   configuration parameters MUST also be configurable. If this
   parameter is disabled, SLP session balancing is not supported and
   normal TN3270E telnet negotiation is performed.

   Scope Name
   The scope name is a text string that specifies a group of TN3270E
   servers. The scope name can be used to identify groups of TN3270E
   servers in a departmental or geographic setting. For example, if the
   scope name is Building-D, then the SLP session balancing would
   search all TN3270E servers in the Building-D scope to find the least
   loaded TN3270E server.

   If the scope name is blank, then the scope name is not used. This is
   referred to as unscoped. It should be noted as in section 5.1 above
   that any reference to unscoped services applies to Service Location
   Protocol version 1 only [1]. Service Location Protocol version 2
   doesn't allow unscoped services but does allow the use of default
   scope [4]. In this case all TN3270E servers, with or without scope
   names, can be used to satisfy the request for least loaded TN3270E
   servers. In order to cut down on network overhead, it is recommended
   that either all servers be scoped or no servers be scoped. Refer
   back to section 5.1 for more discussion of scope.

   DA Discovery Time Out Value

   This value is specified in milliseconds and is fully described
   in section 5.2 of this document.

   SA Multicast Time Out Value

   This value is specified in milliseconds and is fully described
   in section 5.3 of this document.

6.2 How to obtain the list of TN3270E servers supporting SLP

   A TN3270E client that implements SLP session balancing uses API
   calls to obtain the list of TN3270E servers supporting SLP session
   balancing.

   The following Service Location Version 2 API [5] calls, could be
   used with TN3270E SLP session balancing:

   SLPOpen - returns an SLPHandle handle to be used

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  SLPFindSrvs - issues the query for services

   SLPFindAttrs - returns service attributes matching the attribute ids
   for the indicated service URL or service type.

   SLPClose - frees all resources associated with the handle.

6.3 TN3270E Sample Client Flow

6.3.1 Open the SLP connection

   The TN3270E client must first open a handle with the SLP User
   Agent. For Service Location Protocol version 2, SLPOpen API call [5]
   The SA multicast time out and DA discovery time out values would be
   passed as parameters to the SLPOpen API call.

6.3.2 Query the list of TN3270E servers

   The TN3270E client then queries for the list of TN3270E servers
   supporting SLP. This is done by using the Service Request API call.

   The request string contains information that determines which type
   of TN3270E servers that this client desires to connect to. The
   request string can contain the scope name, pool name, session type
   and 3270 screen size.

   The SLPv1 query string has the following format:

   TN3270/<scope name>/LUPOOL/ == <pool name><TAB><device type>

   The <scope name> is the name of the scope that is configured
   for the TN3270E client. If the scope is blank or null (unscoped
   request), then the scope is not inserted into the request string.

   The <pool name> is a 1 to 8 character upper case string that
   indicates the name of the pool to which the TN3270E client desires
   to connect. For SLP session balancing, the same pool name must
   be configured on different TN3270E servers.

   The <TAB> is the '/t' tab character which is hexadecimal 0x09.
   the <TAB> is a literal and is used as a separator.

   The <device type> can be any of the following:

    3270DSC for TN3270E device type IBM-3287-1
    3270002 for TN3270E device types IBM-3278-2 and IBM-3278-2-E
    3270003 for TN3270E device types IBM-3278-3 and IBM-3278-3-E
    3270004 for TN3270E device types IBM-3278-4 and IBM-3278-4-E
    3270005 for TN3270E device types IBM-3278-5 and IBM-3278-5-E
    * for TN3270E device type IBM-DYNAMIC


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   Example:

   For a TN3270E client searching for TN3270E servers in the
   ENGINEERING scope for a model 2 screen size and LUPOOL name pool2,
   the following request SLPv1 string would be constructed:

   "TN3270/ENGINEERING/LUPOOL/ == POOL2<TAB>3270002"

   Note: The " characters before and after the string are not
   part of the request string.

6.3.3 Forward Looking Example for SLPv2

   For SLPv2 the scope and service type are no longer part of the query
   string. These are now separate fields in the message. The service
   type name is required to have the "service:" prepended. The service
   type field would look like "service:TN3270", and the scope field
   would be a comma separated list of scopes. A scope name is always
   required in SLPv2, if no other name is known, the scope name
   "DEFAULT" is used. The example below uses the same parameters as
   used in above section 6.3.2.

   Example:
   Service Type: service:TN3270
   Scope string: ENGINEERING
   The query string would have the following format:

        (LUPOOL=<POOL2> <32700002>)

   In SLPv2 queries, all whitespace is compressed to a single space
   character during matching, so the identity of the separator
   character does not matter. The tab character could be added for
   readability, but it will not affect the outcome of the query.

6.3.4 Determine loading of each TN3270E server

   An attribute request for "service:tn3270e" specifying the
   attribute LOAD can be made and you will get back all the available
   loads. Say these are 35,88,78.  You can then issue a service request
   for all tn3270E servers with "LOAD<40" for instance.  Even if the
   load changes between the time you get the attribute reply and when
   you issue the request, you will still get the best the network has
   to offer.

   The TN3270E client then uses the TN3270E server's IP Host address to
   start normal Telnet TN3270E negotiation.






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6.4 Recommendations

   The TN3270E client SHOULD display the IP hostname and TCP Port
   that is being used for the TN3270E connection. This gives the user
   knowledge of which TN3270E server the session is connected to. For
   example, the IP host address could be displayed in the window system
   status bar.

   The TN3270E client SHOULD display the resource name that is returned
   by the TN3270E server after connection and TN3270E negotiation is
   completed. This gives the user knowledge of which LU resource name
   in the LUPOOL the session is connected to. For example, the resource
   name could be displayed in the Windows status bar, or even in the
   3270 OIA line.

   In the event that after the TN3270E client has determined the least
   loaded server and the connection to that server fails for some
   reason, the connection should be closed and an attempt made to
   connect to other TN3270E servers in the list of least loaded
   servers.

   For example, a TN3270E server may reject a connection to a specific
   pool if the pool is full, or if the device type does not match what
   is available in the pool. If this occurs, then an attempt to other
   least loaded TN3270E servers SHOULD be performed.

7. Sample Trace Flow of SLP and Session Balancing

   This sample trace flow is provided for informational purposes only.

   SLP API: Service Request: TN3270//LUPOOL == POOL2 3270002/

   SLP API: Service Reply: service:tn3270://206.109.45.139:23

   SLP API: Service Reply: service:tn3270://206.109.45.140:23

   Connecting to 206.109.45.139:23...

   TerminalType=NVT

   Connection established

   Recv <- DO TN3270E

   Send -> WILL TN3270E

   TerminalType=TN3270E

   Recv <- SEND DEVICE_TYPE

   Send -> DEVICE_TYPE REQUEST IBM-3278-2-E CONNECT POOL2

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   Recv <- DEVICE_TYPE IS IBM-3278-2-E CONNECT TN8003

   Send -> FUNCTIONS REQUEST BIND_IMAGE SYSREQ

   Recv <- FUNCTIONS IS BIND_IMAGE SYSREQ

8. Service Templates and Service Registration

   The Service Location Protocol uses the ''service:'' URL scheme name
   to define URLs called ''service: URLs''. These schemes provide a
   way for clients to obtain configuration information that is needed
   to establish a 3270 session through the TN3270E server. The Service
   Location Protocol provides for service: URLs to be registered and
   discovered.

   Service Registration
   These service registrations contain a service: URL, and possible
   attributes associated with that service.  The service registration
   information are shown below for the server.

   Service Templates
   Service templates are documents defining in a formal way the
   attributes associated with that service that a client may want to
   use. For more information on service templates please refer to,
   Service Templates and service:  Schemes. [2]. The server service
   template and TN3270 service templates are shown below.

8.1 The TN3270E Service Type Template


   The 'service:tn3270:' template defined below conforms to the grammar
   described in "Service Templates and service: Schemes".  Please refer
   to [2] for detailed explanation of the syntax.

   Name of submitters: Jim Naugle <jnaugle@us.ibm.com>
                       Gregg Ledford <gledford@zephyrcorp.com>
                       K. Kasthurirangan <kasthuri@us.ibm.com>
   Language of service template: en
   Security Considerations:
   Service Location Protocol can help clients discover security
   services supported by the TN3270E server.  If security services are
   important or required, using SLP authentication, and protected
   scopes in Service Location Protocol version 1 is recommended [1].
   Well known ciphersuite names are used in the template [3].








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   Template text:
   ----------------------template begins here -------------------------

   template-type=tn3270e

   template-version=1.0

   template-description=
    The tn3270 service provides 3270 gateway access to an SNA network
    via the TN3270 protocol. The attributes reflect the types of 3270
    devices, LU Pools, and load information available on the server.

   template-url-syntax=
   # service:tn3270://<hostname>:<port>
   # <hostname>
   # <port>

   load=integer
   # This is the load balancing quantity to use in determining the
   # least loaded TN3270E server to attach to for the service. The
   #range of valid values is an integral 0 to 100 with 0 indicating the
   #lowest possible load and 100 the highest

   LUPool=string X M L
   # This attribute takes on one or more values as defined below.
   # The <TAB> char. 0x09 is literal and will be used as a separator.
   #
   #
   #   <pool name> = <name> / <name> "<TAB>" <dev type>
   #   <name>      = 1*ALPHANUM
   #                 "3270DSC"
   #
   #
   #
   #
   # Identifies the LU pool names of LU pools available for use on this
   # service with the associated device types supported in each pool.
   # Each value is a record where the first token is the pool name of
   # the pool and the second token is a device type supported in that
   # pool. A pool name without a device type indicates that LUs of
   # unknown type are included in the pool. Records associated with a
   # given pool name are repeated for each supported device type. A
   # given pool is included in a registration request if any PU profile
   # that contributes at least one LU to the pool is active on the
   # server. The range of valid dev_types are:
   #
   # dev_type    Meaning
   #
   # 3270002     Lu Type 2 Model 2
   #
   # 3270003     Lu Type 2 Model 3
   #
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   # 3270004     Lu Type 2 Model 4
   #
   # 3270005     Lu Type 2 Model 5
   #
   # 3270DSC     Printer LU
   #

   BIND=keyword
   # The server supports the SNA bind image TN3270E function.

   DATA=keyword
   # The non-SNA 3270 data stream is supported by server.

   RESPONSES=keyword
   # The server supports SNA response mode.

   SCS=keyword
   # The server supports SNA 3270 SCS data stream.

   SYSREQ=keyword
   # The SYSREQ keyboard key is supported on server.

   RFC1576=keyword
   # RFC1576 options supported.

   RFC1646=keyword
   # RFC1646 options supported.

   RFC2355=keyword
   # RFC2355 options supported.

   security=string M
   # This is the security technique supported on the server.
   # The defined values are:
   NONE
   SSLV3

   Ciphersuites=string M
   # Cipher specifications supported by this server.
   # Additional values will be defined in future templates.
   NULL_NULL,
   NULL_MD5,
   NULL_SHA,
   RC4_MD5_EXPORT,
   RC4_MD5_US,
   RC4_SHA_US,
   RC2_MD5_EXPORT,
   DES_SHA_EXPORT,
   TRIPLE_DES_SHA_US




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   platform=string X
   # This is the network operating system platform underlying the
   # advertising service. The defined values are:
   #
   # IW          Server uses IntranetWare or NetWare operating system
   #
   # NT          Server uses the Microsoft NT operating system
   #
   # OS2         Server uses the OS2 operating system
   #
   # AIX         Server uses the AIX operating system
   #
   IW,NT,OS2,AIX

   protocol=string X
   #   This is the protocol(s) supported by the server providing this
   #   service. The defined values are:
   #
   # IP          Server supports client connections over IP (TCP/IP or
   #             UDP/IP)
   #
   # IPX         Server supports client connections over IPX (SPX/IPX)
   #
   IP,IPX

   server name=string
   # This is the name of the server that was configured during
   # installation.

   release=string X
   # This is the version and release level of the server advertising
   # services. Its format is vv.rr.mm where "vv" is the major version
   # number, "rr" is the minor version number, and "mm" is the
   # modification level. All numbers are padded on the left with zeroes
   # to two characters.
   # Example: version 3, release 0, mod level 0 is "03.00.00"

---------------------template ends here -------------------------------

8.2 Server Service Type Template

   The 'service:commserver:' template defined below conforms to the
   grammar described in "Service Templates and service: Schemes".
   Please refer to [2] for detailed explanation of the syntax.

   Name of submitters: Jim Naugle <jnaugle@us.ibm.com>
                      Gregg Ledford <gledford@zephyrcorp.com>
                      K. Kasthurirangan <kasthuri@us.ibm.com>
   Language of service template: en



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   Security Considerations:
   Service Location Protocol can help clients discover security
   services supported by the TN3270E server.  If security services are
   important or required, using SLP authentication, and protected
   scopes [1] is recommended.

   Template text:

----------------------template begins below this line------------------

  template-type=commserver

  template-version=1.0

  template-description=
   The server service type is registered whenever the communications
   software is loaded on the server. It describes generic attributes of
   the server.  These attributes are also repeated on the other service
   types provided.

  template-url-syntax=
   # service:commserver://<hostname>:<port>
   # <hostname>
   # <port>

  platform=string X
   # This is the network operating system platform underlying the
   # advertising service. The defined values are:
   #
   # IW          Server uses Novell IntranetWare or NetWare operating
   #             system
   # NT          Server uses the Microsoft NT operating system
   #
   # OS2         Server uses the OS2 operating system
   #
   # AIX         Server uses the AIX operating system
   #
   IW,NT,OS2,AIX

  protocol=string X
   #   This is the protocol(s) supported by the server providing this
   #   service. The defined values are:
   #
   # IP          Server supports client connections over IP (TCP/IP or
   #             UDP/IP)
   #
   # IPX         Server supports client connections over IPX (SPX/IPX)
   #
   IP,IPX



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  server name=string
   # This is the name of the server that was configured during
   # installation.

  release=string X
   # This is the version and release level of the commserver
   # advertising services. Its format is vv.rr.mm where "vv" is the
   # major version number, "rr" is the minor version number, and "mm"
   # is the modification level. All numbers are padded on the left with
   # zeroes to two characters.
   #
   # Example: version 3, release 0, mod level 0 is "03.00.00"

---------------------template ends above this line---------------------

8.3 Template Contact Information

   Jim Naugle <jnaugle@us.ibm.com>
   Kasthuri Kasthurirangan <kasthuri@us.ibm.com>
   Gregg Ledford <gledford@zephyrcorp.com>

8.4 Security Considerations

   Service type templates provide information that is used to
   interpret information obtained by the Service Location Protocol.
   If these templates are modified or if false templates are
   distributed, services may not correctly register themselves, or
   clients might not be able to interpret service information.

   The service: URLs themselves specify the service access point and
   protocol for a particular service type.  These service: URLs could
   be distributed and indicate the location of a service other than
   that normally wanted to used. SLP [1] provides an authentication
   mechanism that allows service: URLs of registered services to be
   signed and for the signatures to be verified by clients.

   Service Location Protocol can help clients discover security
   services supported by the TN3270E server.  If security services are
   important or required, using SLP authentication, and protected
   scopes [1] is recommended.

8.5 Sample TN3270 Service Registration Message

   URL: service:tn3270://<addr-spec>:<port-number>
   Attributes:

   [(SCOPE=<string>),]

   (RELEASE=03.00.00),

   (PLATFORM=IW),

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   (PROTOCOL=IP),

   (SERVERNAME=<string>),

   (LOAD=<integer 0 to 100>),

   [(LUPOOL=pool-name0/tANY,

   pool-name1/tdevice_type1,

   pool-name2/tdevice-type2, ...

   pool-namen/tdevice-typen)]

   BIND,

   DATA,

   RESPONSES,

   SCS,

   SYSREQ,

   (SECURITY=NONE),

   RFC1576,

   RFC1646,

   RFC2355

8.6 Sample Server Service Registration Message

   URL:service:commserver://<addr-spec>:<port-number>

   Attributes:
   [(SCOPE=<string>),]

   (RELEASE=03.00.00),

   (PLATFORM=IW),

   (PROTOCOL=IP),

   (SERVERNAME=<string>)






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9. References

   Request For Comments (RFC) and Internet-Draft documents are
   available from <URL:ftp://ftp.internic.net> and numerous mirror
   sites.

   [1]  J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
        Location Protocol. RFC 2165, July 1997.

   [2]  Guttman, E., Perkins, C. and J. Kempf, "Service Templates and
        service: Schemes", RFC 2609, June 1999.

   [3]  T. Dierks, and C. Allen. The TLS Protocol Version 1.0,
        RFC 2246, January 1999.

   [4]  Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
        Location Protocol Version 2", RFC 2608, June 1999.

   [5]  J. Kempf, E. Guttman, "An API for Service Location", RFC 2614,
        June 1999.

   [6]  Bradner, S., "Key Words for Use in RFCs to Indicate
        Requirement Levels", BCP 14, RFC 2119, March 1997.

10. Authors' Addresses

   Jim Naugle
   IBM
   P.O. Box 12195
   Research Triangle Park, N.C. 27709-2195
   USA
   Phone:  (919) 254-8789
   EMail:  jnaugle@us.ibm.com

   Kasthuri Kasthurirangan
   IBM
   P.O. Box 12195
   Research Triangle Park, N.C. 27709-2195
   USA
   Phone: (919) 254-5721
   Email: kasthuri@us.ibm.com

   Gregg Ledford
   Zephyr Development Corporation
   8 Greenway Plaza Suite 1400
   Houston, Texas 77046
   USA
   Phone: (713) 623-0089
   Email:  gledford@zephyrcorp.com

   Draft Expiration Date: December 2000

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