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Q190022: XCON: Comparison of X.400 and Site Connectors

Article: Q190022
Product(s): Microsoft Exchange
Version(s): WINDOWS:4.0,5.0,5.5
Operating System(s): 
Keyword(s): 
Last Modified: 15-APR-1999

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The information in this article applies to:

- Microsoft Exchange Server, versions 4.0, 5.0, 5.5 
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SUMMARY
=======

This article is designed to help Microsoft Exchange Server administrators
compare the features, capabilities, and limitations of Site Connector and X.400
Connectors. This information may help administrators decide which connector will
work best within their organization. This article is not an in-depth technical
discussion of connector configuration, but rather a discussion of the general
capabilities and limitations of the site and X.400 Connector. Each customer
environment is unique and proper testing and analysis of results should be
performed to determine the best connector solution.

MORE INFORMATION
================

Site Connector
--------------

The Site Connector is relatively easy to use, especially when the Exchange Server
computers involved are in the same Windows NT domain, or both servers trust the
same master domain. Unfortunately, there are also fewer configuration options
available for the Site Connector.

The Site Connector cannot be scheduled to send messages at selected time. A Site
Connector is always active. Nor can message size limitations be configured on
the Site Connector. If message size limitations are desired over the Site
Connector, you must restrict message size at the server's message transfer agent
(MTA) level (or at the store level), which will also limit message size over all
other connectors, and on message transfer between servers within the site using
remote procedure call (RPC).

The difference in message delivery times between a Site Connector and an X.400
Connector (set to always) is negligible. The time for delivery depends on
bandwidth, physical distance traveled, number of routers traversed, and so on,
but all things being equal the difference in time is usually a matter of
milliseconds.

As a general guideline, a Site Connector needs at least 56 Kbps of network
bandwidth, available for Exchange Server communications only. It must be heavily
stressed that the 56-Kbps transfer rate is a bare minimum for light mail flow,
with little or no directory replication traffic.


More would be better, especially in a busy production environment. If there is a
56-Kbps dedicated line, which is also being used for file transfer, voice
communications, or any other network activity, a Site Connector may not work
well on a consistent basis. If thousands of messages/hour (including user mail,
public folder, directory replication, and link monitor messages) are going
across this link, 56 Kbps may not be enough to consistently establish and
maintain a connection between servers.

Exchange Server MTAs communicating by Site Connectors use RPCs. RPCs run on top
of network protocols such as TCP/IP (recommended).

For additional information regarding RPC bandwidth requirements, please see the
following articles in the Microsoft Knowledge Base:

  Q177446 : How to Test Microsoft Remote Procedure Call Performance

X.400 Connector
---------------

The Microsoft X.400 Connector requires one of three different MTA transport
stacks (which must be installed and configured prior to installing the
connector). The three choices are:

- TCP/IP. Installed by default with Microsoft Windows NT. This is the most
  common transport stack used by the X.400 Connector.

- TP4. Defined by the ITU (International Telecommunications Union, formerly
  known as the CCITT, or Commite Consultatif International de Telegraphie et
  Telephonie), TP4 provides connectionless network connectivity. It is often
  used on Ethernet networks.

  For additional information on installing the TP4 transport stack, please see
  the following articles in the Microsoft Knowledge Base:

  Q148288 : XADM: Microsoft Exchange TP4 Transport Stack

  Q152961 : How to Install TP4 Components on Windows NT 4.0

- TP0. Another ITU standard for network communications. TP0 requires X.25
  hardware and software provided by an X.25 public carrier. Use of this
  transport stack is more common in Europe than in the United States. Eicon,
  SAT, and Cirel hardware/software is supported for use with Microsoft Exchange
  Server.

  For additional information, please see the following articles in the Microsoft
  Knowledge Base:

  Q149062 : XCON: Eicon Tech. X.25 Diagnostic Commands for WinNT &
  Exchange

  Q169668 : XCON: X.25 Support for SAT Cards

  Q169667 : XCON: X.25 Support for Cirel Cards

There are several advantages to using the X.400 Connector instead of the Site
Connector.

No trust relationships are required to connect two Microsoft MTAs with an X.400
Connector. Microsoft fully complies with the ITU's X.400 communications
standards, which do not require Microsoft NT LAN Manager (NTLM) authentication.
Additional security is not usually necessary, but can be added to the connection
by adding a remote MTA password and/or Outgoing/Incoming Open System
Interconnect (OSI) address information on the Transport Stack and the X.400
Connector property pages.

Message size limitations can be enforced on individual X.400 Connectors, which
can be useful in low bandwidth environments.

Message delivery is also flexible when using the X.400 Connector. On the Schedule
tab of the X.400 Connector property page, you can set one of four different
options:

- Remotely Initiated. No queued mail will be sent until a remote MTA connects
  to this MTA. Both MTAs must have the two-way alternate option selected on the
  Advanced tab of the X.400 Connector for this to work, and only one of these
  connectors can be set to remotely initiated, or mail will not flow.

- Never. Mail will never flow over this connection. Can be useful for testing
  other routes.

- Always. The connector is scheduled to be active for consecutive 15- minute
  time segments. In essence, it is continuously active.

- Selected Times. This option schedules the connector to be active in one- hour
  or 15-minute time segments (see the Detail View option on the right side of
  the page).

Generally, with the same traffic load, an X.400 Connector can work successfully
on less bandwidth than a Site Connector, because X.400 connectivity does not use
RPC. An X.400 Connector can use 56-Kbps links or even lower, depending on
traffic.

Summary
-------

A Site Connector requires more bandwidth than an X.400 Connector, and can only
connect to other Exchange Server sites. Site Connectors also rely on Microsoft
Windows NTLM authentication to work successfully. If these three conditions are
met (bandwidth, Exchange Server, and NTLM), then a Site Connector will work
fine.

There are many more configuration options available with the X.400 connector,
including transport stacks, message size limitations, scheduled connection
times, and connections to foreign MTAs. If the default values are used when
setting up an X.400 Connector, the configuration is not difficult.

A Microsoft Exchange X.400 Connector can also be used to connect and transfer
mail between non-Microsoft MTAs. While some information included in this
document might be useful if connecting to a foreign MTA, an in- depth discussion
of such connections is largely beyond the scope of this document.

For configuration/installation specifics of these connectors, see the following
Knowledge Base articles, or query the knowledge base for "site connector" or
"X.400 Connector".

  Q165119 : XCON:Site Connector Configuration Basics

  Q165324 : XCON:Basic Site Connector Troubleshooting Checklist

  Q154624 : XCON:Configuring the Site Connector Between Untrusted Domains

  Q165111 : XCON:Configuring X.400 Connector Between Two Exchange Servers

  Q169159 : XCON:X.400 Connector Configuration Checklist

Additional query words: X.400 site connector Cirel SAT Eicon Remote Procedure Call Untrusted foreign TP4 TP0 X.25 TCP/IP

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Keywords          :  
Technology        : kbExchangeSearch kbExchange500 kbExchange550 kbExchange400 kbZNotKeyword2
Version           : WINDOWS:4.0,5.0,5.5
Hardware          : ALPHA x86
Issue type        : kbinfo

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