Applies to: Exchange Server 2007 SP3, Exchange Server
2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2006-06-12
A physical topology for Microsoft Exchange Server 2007 maps physical elements to geographical locations. A physical topology is typically used to describe a network or the location of servers. Generally, all physical topologies are based on specific and unique organizational requirements to scope resources based on security and business requirements.
Physical topologies also frequently classify the distribution of servers and management roles into two primary categories: centralized servers and administration, and distributed servers and administration.
Centralized vs. Distributed Messaging Systems
If your company is composed of offices that are all connected by high-bandwidth and reliable network connections, regardless of the distance between offices, you can implement a centralized messaging system. A centralized messaging system means that all of your servers that are running Exchange are located and managed in a central data center. When planning your messaging system, it is best to start by considering this model because it is the most cost-effective and easily managed.
If your company contains remote offices with low-bandwidth, high-latency, or unreliable network connections, you can introduce servers to control how messaging traffic is routed from one location to another. However, remote locations and multiple routing groups do not prevent you from centralizing your administrative model. In addition, with the features in Microsoft Windows Server 2003, Exchange 2007, and Microsoft Office Outlook 2007, you can also consolidate your server hardware by removing servers that are running Exchange from remote sites. With these changes, users can log on remotely to Microsoft Windows services and Exchange 2007 and experience fewer problems related to a decrease in performance or connectivity.
Service Level Management
Regardless of whether you choose a centralized or distributed messaging system, your deployment should include service level management (SLM). SLM aims to align and manage information technology (IT) services through a process of definition, agreement, operation measurement, and review. The scope of SLM includes defining the IT services for the organization and establishing service level agreements (SLAs) for them. Fulfilling SLAs is assured by using underpinning contracts and operating level agreements for internal or external delivery of the services. SLM also includes continual measurement of mutually agreed–on service-level thresholds and the initiation of corrective actions if the thresholds are breached. Services are monitored and measured according to the agreed-on SLA criteria to ensure compliance with the SLAs.
Characteristics of a Centralized Messaging System
A centralized messaging system consists of a large data center that hosts all server resources, including the Active Directory directory service, global catalog servers, domain controllers, and Exchange servers. The data center supports all messaging system users, whether they connect locally or remotely. The following are characteristics of a centralized messaging system:
- Data is hosted and managed in a centralized location regardless
of whether the users are connected remotely. This contrasts with
the distributed model, where users have local access to mailboxes
but server administration is more complex.
- Software upgrades can be rolled out from a centralized
- The data center incorporates power-insulating devices such as
an uninterruptible power supply (UPS) and hot site, warm
site, or cold site contingencies. A hot site is a
full-service commercial site that is up and running continuously
with data replicated to it, so that it can be used immediately. A
warm site is a full-service site that provides all the equipment
needed for a company to continue operations if a disaster were to
occur. However, the equipment is not ready for immediate use, and
some administrative tasks are required to make the site user-ready.
A cold site is a service that provides space, but it is a site that
the company must furnish and set up. A hot site gets the company
operational faster, but a cold site is a less expensive option.
Business requirements associated with reducing cost and security requirements are usually the driving forces behind centralizing systems. The requirements revolve around location centralization (reducing the number of sites that provide server resources), physical consolidation (replacing smaller servers with high-end servers), administrative consolidation, and data consolidation (centralizing storage solutions that provide backup and disaster recovery capabilities).
Consider a centralized design only if prerequisites in the following areas are already met or are included in the project plan:
- Data center hardware costs Compare the
cost of installing high-end servers and clusters in the data center
to the administrative cost savings of centralizing the servers. We
recommend that you cluster the back-end servers to build high
availability and redundancy into the system, but this choice does
involve greater initial costs. However, these costs may be more
than offset by reductions in operational costs, infrastructure
costs, reduced downtime, and greater scalability.
- Contingency planning When you
centralize server and data resources across the organization, you
increase the number of possible single points of failure. You must
make contingency plans in the event a catastrophic event affects
your data center.
- Network outages Consider the impact
that a network outage will have on users in remote locations. If
the users have Cached Exchange Mode enabled in Outlook, this
consideration is less of an issue.
- Operational and administrative cost
reductions Centralizing server resources can
reduce operational costs because service capacity and growth are
achieved by having better use of resources. It also reduces
infrastructure costs associated with storage and backup
- Data storage With larger centralized
data volumes, you must use more reliable storage systems to improve
the integrity of your data. Additionally, by reducing the
complexity of the server infrastructure, you can more easily
restore services and data when a failure occurs.
- LAN and WAN connectivity If your
current network does not provide the type of bandwidth and speed
required for centralizing servers, you have to build a network
upgrade into the project plan.
- Security A centralized model gives you
easier security management, and therefore, more control. This
control makes it easier for security staff to maintain up-to-date
virus signatures and take timely action in response to security
incidents. Another advantage of a centralized design is that it
locates your servers in a data center that you can physically
Characteristics of a Distributed Messaging System
A branch office or distributed messaging deployment is one where many branch offices or smaller distributed sites have slow connections to a corporate hub or data center. The branches contain their own servers that are running Exchange, domain controllers, and global catalog servers. A distributed messaging system is usually adopted when the network cannot handle traffic to a central hub for services. Therefore, the operating system and messaging servers are placed locally. User requirements may be another factor. If the requirements for user experience and availability cannot be met by connecting to a data center, you may have no choice but to position servers in the remote sites.
An Exchange branch office deployment has the following characteristics:
- The messaging system consists of many locations (branches), and
each contains a server that is running Exchange, domain
controllers, and at least one global catalog server.
- The branch office locations usually contain a small or varying
number of users.
- The network is usually structured as a hub-and-spoke
- The network connections between the branch office locations and
the central hub or data center are typically low-bandwidth,
high-latency, or unreliable.
The main reasons for deploying a distributed messaging system include the following:
- The company's users are dispersed across sites.
- The company's network infrastructure cannot handle traffic to a
central hub for services.
- The user requirements dictate that a server be placed locally
to provide optimal user experience and availability.
Consider the following issues when you think about a distributed design:
- Software upgrades Rolling out important
updates can be much more challenging in a distributed messaging
- Using Outlook Anywhere If
you want to use Outlook Anywhere (formerly RPC over HTTP), all
computers in your messaging environment that users will have to use
with Outlook Anywhere communication must be running
Windows Server 2003. This requirement extends to all
global catalog servers and all servers that are running Exchange
that your Outlook users will access.
- Operational and administrative
costs Distributed messaging systems require
more servers and cause higher operational and administrative
- Data storage With distributed servers,
the service infrastructure is more complex, which makes it more
difficult to restore services and data when a failure occurs.
Features such as local continuous replication (LCR) and cluster
continuous replication (CCR) are especially useful in a distributed
messaging environment. For more information about LCR, see Local Continuous
Replication. For more information about CCR, see Cluster Continuous
- Network connections For remote offices,
we recommend that the network connection to the hub site or data
center be no less than 64 kilobits per second (Kbps) between
servers. However, we recommend a higher connection speed between a
hub and an office.
- Security The physical security of
servers in branch offices is a major consideration. In a branch
office design, you must take precautions to make sure that servers
are not located in open areas and that the servers are physically