NETWORK CONSIDERATIONS

In the next sections, we discuss some important factors to consider when planning the data network connections into a data center. Chapter 6 is dedicated to network design and provides much more detail on these and other topics.

User Geography and Location of the Data Center

The geographic dispersion of the user community plays a major role in the site selection for a data center. Whether a company has only domestic or domestic and international offices has a profound influence on data center aspects such as availability for WAN bandwidth and hot sites. Ideally, the chosen site should yield the lowest overall network cost from the national exchange carriers while meeting all the other requirements mentioned in this chapter. One of the single largest cost items in building your data center will be the data network. Anyone who has ever ordered a data line from a local or national carrier knows that the distance from their office ( demarcation point or demark ) to the carrier's point of presence (POP) can translate into hundreds or thousands of dollars per month. A data center is no exception. If installing high-bandwidth connections such as ATM, an organization could be looking at thousands of dollars in cost for a very short distance to the local POP.

Time Zones

Both Windows 2003 and Citrix Presentation Server support time-zone translationmeaning that the client machine will display the time based on its local time zone rather than the time zone of the server. This is a critical feature for organizations whose users may be in physically disparate time zones relative to where the servers are physically located.

Bandwidth Availability

Another consideration in planning network connections is bandwidth availability in the area where the data center is located. The required circuits may be easily ordered now, but what about in six months or a year? It is vital that a company understands the capacity available, usually from the LEC, and its growth plans. We have seen many customers experience delays in their entire data center build-outs because there were no additional circuits available from the LEC, and no one thought to check in advance (or they were over- promised by the LEC when they did enquire).

Tip 

It has been our experience over many years that telecommunication carriers are often overly optimistic when estimating the time required to install a circuit. They are similarly overly optimistic about the time required to make an installed circuit work smoothly. It is important to build extra time into the schedule for getting the circuit in and working.

Bandwidth Management

Due to the nature of IP, any amount of network bandwidth can be swallowed up by a variety of both important and unimportant applications, with no respect to priority. Thus, having the tools in place to manage, understand, report, and prioritize bandwidth is critical. A discussion of tools for managing and prioritizing bandwidth is included in Chapter 6.

Reliability

An unreliable network can kill a project. It is crucial that an organization ensure that its bandwidth carrier can provide detailed reliability statistics of the circuits to be used. Especially in the case of newer topologies like ATM, incorrect assumptions of flawless performance may lead to project failure. It is wise to get customer references, and ask those companies how the carrier's product is working for them. Organizations should also allow adequate time for their own testing to make sure the circuits are sufficiently reliable to meet their needs.

Network Redundancy

It makes little sense to design all of the components of a data center with fail-over capability if the network represents a single point of failure. This is especially important with a server-based computing design. Users will rely on the network to reach one or a few data centers; it must be resistant to production outages. Buying a redundant circuit can be expensive, but carriers are often able to sell access to a circuit to more than one company for far less than the circuit itself would cost. In case the primary circuit fails, they can switch customers to this backup so that they can continue operation. If a secondary live circuit is not practical or affordable, another option is putting a second type of lower-bandwidth circuit in place. These backups will not provide as much bandwidth, of course, but some access would at least be available.

Using the Internet as a Redundant Network

Since most businesses and many households today have Internet access, the Internet makes an obvious choice ( assuming it can be secured) for access into the data center or as a backup network access path into the data center if private line access is lost. With the release of Citrix Secure Gateway, Citrix made it very easy for organizations to utilize the Internet as an access point into the data center. With Secure Gateway, all ICA data traversing from the Internet to the data center (and back to the Internet) is encrypted using SSL encryption (port 443), and no additional firewall port holes or client side software is required.

Virtual private network (VPN) technology may also be utilized for this same purpose (encryption of ICA traffic going over the Internet). In the case of VPN technology, we strongly recommend the use of hardware encryption devices at the data center rather than software termination. Additionally, we have found that VPNs tend to require a significant amount of administrative overhead due to the complexity and update requirements of the client-side VPN software. Both Secure Gateway and VPN technology are discussed in detail in Chapter 6.

Cable Management

Just as managing the data center requires more meticulous methods than in a distributed environment, setting up the cabling requires careful organization. Cable management systems with easy-to-understand labeling and adequate capacity for growth should be used. Color coding can contribute significantly to finding the right cable quickly. Red could be used for critical LAN and WAN ports, for example. Green could be used for mission-critical servers, and so on.

Just as important, power cables should not be a pile of spaghetti. Cable trays and ties will keep cables out of the way and help to organize them. Equipment power cables should plug neatly into racks and cabinets , and the large power cables from the racks should plug into the under-floor power grid with only enough slack to allow for moving the floor panels.



Citrix Access Suite 4 for Windows Server 2003. The Official Guide
Citrix Access Suite 4 for Windows Server 2003: The Official Guide, Third Edition
ISBN: 0072262893
EAN: 2147483647
Year: 2004
Pages: 137

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