Network Bandwidth

For each type of network, performance is determined by many factors, including network bandwidth (how much data can be transmitted across the network). The amount of bandwidth available depends on the data transfer rate across the network and the physical characteristics of the communications line. When deciding on server locations, you need to consider bandwidth. For example, servers in the same site require faster and higher bandwidth connections than servers in different sites.

You should consider both total available bandwidth (the bandwidth provided by a network connection) and net available bandwidth (the bandwidth available after consumption by other applications).

Consider total available bandwidth so that you can:

• Choose the best type of connection between sites.
• Set directory and public folder replication schedules.
• Set costs appropriately.
• Configure public folder affinity values, which are used to determine which site Microsoft Outlook uses to connect to remote public folder replicas.

Microsoft Exchange Server performance is greatly affected by net available bandwidth, because performance decreases as traffic increases and applications compete for bandwidth. For example, if a database application is running with Microsoft Exchange Server, you should consider how much of the total available bandwidth the application consumes when it transfers data. You must also consider the bandwidth that a client consumes when sending messages and attachments.

The client/server architecture of Microsoft Exchange Server efficiently uses bandwidth by minimizing unnecessary overhead. Nevertheless, you should think about ways to minimize network traffic. For example, if you configure public folder replication to occur after business hours, bandwidth consumption will be lower during peak hours.

When designing your organization, consider the network bandwidth costs. The way that you transmit data also affects bandwidth costs. You should make sure that network connections between servers have enough bandwidth to handle bursts in traffic as well as typical traffic.

When choosing the appropriate bandwidth range, consider the number of servers, the message volume, and the traffic volume generated by public folder replication. The higher the traffic volume, the more bandwidth needed. Generally, you should design sites so that connections between servers are in the medium-to-high or very high-bandwidth range. You may be able to use the low-to-medium bandwidth range if you have low message volume or little public folder use. For example, if two servers are connected by a 64 kilobyte (KB) connection and you expect a high volume of messages, you should consider placing the servers in different sites. On the other hand, if they are connected by a 128KB connection, you can place them in the same site.