Windows Server 2003 on Proliants. Deployment Techniques and Management Tools for System Administrators

In the assessment phase covered in Chapter 4, the existing network, including LANs, VLANs, and WAN interconnects, should have been analyzed and documented. During the design phase, the network topology helps to define message routing, server placement, and potential links that might require upgrading if server consolidation is a goal for your design. At this point, it's also good to document any planned upgrades to the network or other projects that require bandwidth like Voice over IP (VoIP).

This documentation should be done in three parts . If you do not have a diagram of the network, now is a good time to create one. Some of the key information to capture is

• Office or site LANs : Collect the number of workstations, the type of network, and any issues currently being experienced with the network.

• WAN connectivity : Record the site name , type of WAN connection (frame, dedicated), backup network, and service provider.

• Utilization of WAN links : Collect statistics over the course of a week broken down to hourly utilization.

• Network latency between sites : Since Active Directory replication will put a load on the network, it is a good idea to document the existent latency as a baseline. This allows you to determine the effect of AD on the network and make changes if needed.

In simplistic enterprises with only one or two sites; a campus of close, well-connected buildings ; or perhaps a single building with several floors; it isn't necessary to perform a detailed analysis of bandwidth. However, in large enterprises with many sites, perhaps spanning the globe, gathering that data is important for designing the replication topology. For each WAN link, collect information to better understand and graph the utilization. Collect this information over the course of a week or two, not including weekend and holiday traffic unless the business is fairly active during these times. Most WAN routers have the capability of collecting statistical information about the circuit. Your network service provider might also be able to provide this information.

For planning purposes, you are interested in the available bandwidth for each link. That is, the existing bandwidth that your exchange routing and end-users can use before having to upgrade the links.

When working with Frame Relays, always take into account

• The committed information rates and not the burst frame rates.

• The size of the Permanent Virtual Circuits (PVCs) between locations.

• If there is a central hub, the sum total of the PVCs it services should not exceed the size of the WAN link.

• The average network utilization should be within 40% to 60% of the total capacity of the network links. This extra utilization will be available for peak times such as Monday morning and Friday afternoon. This is especially true with Frame Relay. As the links become saturated , packets can be tossed causing latency for the end user .

• If you have clients connecting via Outlook to servers over the WAN, make sure you take into account not only the total number of users connecting, but also the number of active users over a select period of time. You will usually see that out of 100 clients that could connect to the server, only 60 are connected. Out of that 60, you might see only 30 to 40 actually actively doing work with the servers.

In addition to the considerations in this list, look not only at the total number of users connecting via a WAN, but also the size of the messages and frequency with which they interact with the servers. This is necessary because of the nature of how people work with e-mail. HP recommends looking at LAN traces for random ten-minute intervals throughout the day and collecting the following information:

• Number of users connected to the existing Exchange server (Perfmon or Exchange Manager can give you this count)

• Number of users who had transactions with the servers over the past ten minutes

• The average size of the transaction per user

From these numbers , you will see that an average Outlook Exchange user consumes someplace between 2.1Kbps to 4.6Kbps. Although this is not a hard and fast number, it gives you an idea of the required size of WAN links needed to support a given remote user community. Remember to keep a minimum of 40% free bandwidth when designing WAN links to ensure you have room to handle spikes and future growth.

warning

Frame Relay is typical in branch office deployments. Many times we have seen low Committed Information Rates (CIR) and large latencies affect Windows replication, applying Group Policies and slowing response from Exchange servers.