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Sun Java System Communications Services 6 2005Q1 Deployment Planning Guide 

Chapter 5
Developing a Communications Services Logical Architecture

This chapter describes how to develop your Communications Services logical architecture. The logical architecture is a design that depicts the logical building blocks of the Communications Services components and the infrastructure services needed to support them.

This chapter contains the following sections:

Communications Services Deployment Logical Architectures Overview

You can deploy Communications Services in either a single-tiered or two-tiered logical architecture. Deciding on your logical architecture is crucial, as it determines which machine types you will need, as well as how many.

In general, enterprise corporate deployments use a single-tiered architecture while internet service providers (ISPs) and telecommunications deployments use a two-tiered architecture. However, as with all generalities, the exceptions prove the rule. Small ISPs might just as well deploy on a single machine, and larger, centralized enterprises might deploy in a two-tiered architecture for many of the same reasons that ISPs do. As more and more corporations look to offer ease of access to employees working remotely, their deployments will begin to look more and more like an ISP.

This section discuss the following Communications Services logical architectures:

Whether you deploy Communications Services in a single-tiered or multiple-tiered architecture, you need to understand the advantages and disadvantages of both models.

Single-tiered Logical Architecture for One Host

As its name implies, the single-tiered logical architecture for one host locates all services onto a single machine. In general, such an architecture is best suited for enterprises that are:

The following figure represents the single-tiered logical architecture for one host.

Figure 5-1  Single-tiered Architecture for One Host

This diagram shows the single-tiered logical architecture for one host.

End-user client programs, such as Outlook and Messenger Express, form the User Tier. Tier 1 is a single machine running all services, including messaging, calendar, instant messaging, and directory. If you deploy Communications Express, the single machine is also running Web Server (or Application Server). The distinction of the single tier deployment is that end users communicate directly to the stores, and not through proxies or other agents.

The single-tiered logical architecture for one host requires a machine that provides sufficient CPU, memory, and storage. You should work with your Sun representative to determine the machine that best meets your organization’s needs for this type of deployment.

When implementing the single-tiered logical architecture for one host, you can position the deployment for growth into a multi-tiered architecture by assigning logical names to services. Such a configuration makes use of DNS mapping to direct users to the same front-end process (machine). If, in the future, you need to make changes to accommodate growth, such as splitting out services in a tiered fashion, users do not need to reconfigure their client applications. See Using Logical Service Names for more information.

Single-tiered Logical Architecture for Multiple Hosts

The single-tiered logical architecture for multiple hosts is a set of servers that each run the services particular to a component product. For example, the Messaging Server host is installed and configured to run all the Messaging Server services, the Calendar Server host is installed and configured to run all the Calendar Server services, and so on. This architecture might also be configured for high availability.

The distinction of the single-tiered logical architecture is that end users communicate directly to the data stores, and not through proxies or other agents. For example, in Messaging Server, users would not be routed through MMPs or MTAs. The single-tiered logical architecture might have standalone MTA routers for routing mail between servers, or in and out of the corporate network, but end users submit mail to the MTA on their message stores. No MMPs are involved in intranet connection to the message stores.

The same idea applies to both Calendar Server and Instant Messaging. In the single-tiered logical architecture, no front-end processes are located on separate machines.

Figure 5-2 represents the single-tiered logical architecture for multiple hosts.

Figure 5-2  Single-tiered Architecture for Multiple Hosts

This diagram shows the single-tiered architecture for multiple hosts.

In the preceding figure, end-user client programs, such as Outlook and Messenger Express, form the User Tier. Tier 1 is a set of four servers. One server runs the Calendar Server processes, the second runs the Messaging Server processes, the third runs the Instant Messaging processes, and the fourth runs the Directory Server process. If you are deploying Communications Express, the Messaging Server host also includes a web server, either Web Server or Application Server, (for Webmail).

Single-tiered Distributed Logical Architecture

The single-tiered distributed logical architecture is a variant of the single-tiered architecture in that the Directory Server is deployed in two tiers. Such a deployment works well for enterprises with small departments or organizations that are geographically distributed. Each department or office has its own services (mail, calendar, instant messaging) and a local directory instance (consumer). All the local directory instances are cached, but are synchronized with the centralized, master corporate repository. This is a fairly common scenario for offices with low bandwidth connectivity. The directory is architected in a two-tiered fashion and replicated over the low-bandwidth to keep data local.

Figure 5-3 represents the single-tiered distributed logical architecture.

Figure 5-3  Single-tiered Distributed Architecture

This diagram shows the single-tiered distributed logical architecture.

In the preceding figure, end-user client programs, such as Outlook and Messenger Express, form the User Tier. Tier 0 consists of load balancers that distribute load across the Tier 1 layer. Tier 1 is a set of multiple servers for the Communications Services processes. Multiple servers run the Calendar Server processes, multiple servers run the Messaging Server processes, and multiple servers run the Instant Messaging processes. Directory Server processes are split between a consumer server in Tier 1 running a local, replicated copy of the directory, and another server situated in Tier 2, which contains the master copy of the directory. Notice that in this kind of deployment, client queries are directed to the local directory copy, not to the master copy. Only the local Directory Server communicates to the master Directory Server.


When deploying a single-tiered architecture with Internet connectivity, use a separate access layer. For example, you direct access to the data stores from inside the intranet without having to use SSL. However, you direct access to the data stores from the Internet through an access layer over SSL. This offloads much of the SSL load on the data stores to the access layer that separates it from the Internet.

The downside to this type of deployment is that users who make use of the server from a system that is sometimes on the corporate intranet and sometimes accessing the server from the Internet must configure their client applications to use SSL all the time. This is because it is too much trouble to switch back and forth. Therefore, there will still be a substantial percentage of SSL traffic being put on the stores directly. By using an access layer inside the intranet, you can remove that problem and by limiting connection directions further protect the intranet from illegal access.

Two-tiered Logical Architecture

In a two-tiered logical architecture, the data stores communicate through front-end processes. In the case of Messaging Server, this means MMPs, MEMs, and MTAs are residing on separate machines from the data store processes. A two-tiered architecture enables the mail store to offload important and common tasks and focus on receiving and delivering mail. In the case of Calendar Server, this means the HTTP service and Administration service reside on a separate machine from the store processes. In the case of Instant Messaging, this means the proxy service is residing on a separate machine from the back-end processes.

There might be some level of cohabitation with other services. For example, you could have the Calendar store and the Message Store on the same machine. Similarly, you could have the calendar front end on the MMP machine.

In a two-tiered logical architecture, Directory Server is usually a complex deployment in its own right, with multi-master and replication to a set of load-balanced consumer directories.

Figure 5-4 represents the two-tiered logical architecture.

Figure 5-4  Two-tiered Architecture

This diagram shows the two-tiered logical architecture.

In the preceding figure, end-user client programs, such as Outlook and Messenger Express, form the User Tier. The load balancers form Tier 0. The Calendar Server, Messaging Server, Instant Messaging, and web proxy and MEM front ends form Tier 1. Finally, the Directory Server, Calendar Server, Messaging Server, and Instant Messaging back ends form Tier 2. When deploying Communications Express, you could have Web Server in Tier 2 as well.

A two-tiered architecture enables you to deploy Tier 1 and Tier 2 elements as separate instances, increasing overall flexibility of design. Additionally, you enhance system security by assigning discrete functions to individual instances.

For typical deployments, place the messaging and calendar front ends within the network Demilitarized Zone (DMZ), connecting to the main messaging and calendar services through a firewall. This configuration enables you to scale the system horizontally, as the Tier 1 elements can be scaled independently. Do not scale these elements beyond the capacity of the back-end servers.

When the front-end elements have reached the capacity of the back-end servers, you can scale the back-end Tier 2 elements to support more users. In general, the front end should scale as a function of the traffic. The back end should be scaled as a function of the number of users.


For specific instructions on sizing components in single-tiered or two-tiered architectures, contact your Client Services representative.

Edge Logical Architecture

The edge logical architecture adds security for remote access to the two-tiered logical architecture. An edge deployment grants access to a remote, mobile workforce over the public Internet by using only name/password authentication (SMTPAuth). As messages travel to and from the corporate network over the public Internet, they are encrypted through the use of SSL. No virtual private network is involved. The internal side of the communications transmission is “in the clear” for maximum performance. Access is contained on the “edge” of the deployment, protecting the data stores from unauthorized intrusion.

Business reasons for an edge deployment include:

Figure 5-5 represents the edge logical architecture.

Figure 5-5  Edge Architecture

This diagram shows the edge logical architecture.

In the preceding figure, the data stores are located in Tier 2, which is a secure, private network, connected only to the “edge” and “internal” front-end servers. Remote clients connect to front-end servers by using SSL. Internal clients do not need to use SSL to connect, as the assumption is made that internal access is inherently secure.

Edge Architecture Design Recommendations

Benefits of a Single-tiered Architecture

The benefits of the single-tiered architecture come down to cost savings, as you do not have to purchase nor maintain additional hardware.

Answer the following questions to help decide if the single-tiered architecture is best for your enterprise:

Answering yes to these questions suggests that your enterprise could use a single-tiered architecture.

Benefits of a Two-tiered Architecture

All services within the Communications Services offering rely on network capabilities. A two-tiered architecture provides for a network design with two separate networks: the public (user-facing) network, and the private (data center) network.

Separating your network into two tiers provides the following benefits:

Horizontal Scalability Strategy

Scalability is critical to organizations needing to make the most cost-effective use of their computing resources, handle peak workloads, and grow their infrastructure as rapidly as their business grows. Keep these points in mind:

When deployed in a two-tiered architecture, the Communications Services offering is meant to scale very effectively in a horizontal manner. Each functional element can support increased load by adding additional machines to a given tier.

Scaling Front-end and Back-end Services

In practice, the method for scaling the front-end and back-end services differs slightly.

For Tier 1 elements, you start the scaling process when traffic to the front end grows beyond current capacity. You add relatively low cost machines to the tier and load balance across these machines. Thus, load balancers can precede each of the Tier 1 service functions as overall system load, service distribution, and scalability requirements dictate.

For Tier 2 elements, you start the scaling process when the back-end services have exceeded user or data capacity. As a general rule, design the Tier 2 services to accommodate just under double the load capacity of the Tier 1 services.

For example, for an architecture designed for 5,000 users, the Tier 1 front-end services are designed to support 5,000 users. The back-end services are then doubled, and designed to accommodate 10,000 users. If the system capacity exceeds 5,000 users, the front-end services can be horizontally scaled. If the overall capacity reaches 5,000 users, then the back-end services can be scaled to accommodate. Such design enables flexibility for growth, whether the growth is in terms of users or throughput.

Other Deployment Issues

This section describes some common Communications Services deployment best practices and other deployment considerations.

Implementing Local Message Transfer Protocol (LMTP) for Messaging Server

Best practices say you should implement LMTP to replace SMTP for message insertion. An LMTP architecture is more efficient for delivering to the back-end Message Store because it:

You need a two-tiered architecture to implement LMTP. See the Sun Java System Messaging Server Administration Guide for instructions on configuring LMTP:

Implementing Realtime Blackhole List (RBL)

The Mail Abuse Protection System’s Realtime Blackhole List (MAPS RBL) is a dynamically updated list of known unsolicited bulk email (UBE) sources identified by source IP address. The Messaging Server SMTP server supports use of the RBL and can reject mail coming from sources identified by the RBL as originators of UBE or spam.

Implementing an RBL should be a consideration of every deployment. In general, a good RBL deployed in front of MTAs reduces traffic to the MTAs by a minimum of 10 percent, and in some cases, much higher.

RBLs, and anti-spam and anti-virus servers, such as BrightMail, can work together. For example, if your anti-spam server rejects 95 to 99 out of 100 emails from a particular IP address, you can add that IP address to the RBL. You can also adjust the RBL for BrightMail’s false positives when you conduct your BrightMail analysis. Thus, you make the RBL much more proactive in handling a specific wave of UBE.

See the Sun Java System Messaging Server Administration Reference for information on configuring the ENABLE_RBL option of the MTA Dispatcher:

Using Logical Service Names

Design your deployment around the use of logical names for Communications Services servers. You should use logical names even on a single-system deployment, to position it for ease of future growth and expansion. Using logical names does not impose any additional deployment setup costs other than populating your DNS.

You can think of these logical names as falling into two categories: those that affect end users, such as settings in email client programs; and those affecting back-end administration, such as inbound SMTP servers.

The following tables describes these logical entities.

Table 5-1  User Facing Logical Names



Name of the server from which end users collect their email.

Name of the IMAP server from which end users collect their email.

Name of the POP server from which the end users collect their email.

Name of the SMTP server users set as outgoing mail server. or

Name of the Communications Express (formerly Calendar Express) server.

Table 5-2  Maintenance Level Logical Names



Corresponds to a bank of inbound SMTP servers.

Corresponds to a bank of outbound SMTP servers.

Corresponds to a bank of MMP servers.

Corresponds to a bank of MEM servers.

Back-end message store. Select a naming scheme to work with your topology, for example, through

Back-end calendar store. Select naming scheme to work with topology, for example, through

Table 5-3  Mapping of User Level to Maintenance Level Logical Names

Maintenance Level

User Level


Any one or more of,, and -

N/A, hidden from end users -

N/A, hidden from end users

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Part No: 819-0063-10.   Copyright 2005 Sun Microsystems, Inc. All rights reserved.