Satellite links involve an additional round-trip latency of approximately one second, and this limits the speed of TCP/IP communication. Wastie cites a real-life example of a 1Mbit/sec line with a latency of 1.1 seconds that achieves a maximum throughput of 100Kbit/sec. TCP acceleration removes that bottleneck and allows the line to run at its nominal speed.
Adjusting packet sizes can also help, says Gibb. As mentioned above, large file transfer packets can block small packets from interactive applications. The problem is that even if the small packets are prioritised, they may be delayed for the time it takes to send a large packet. The answer is to split the large packet into smaller pieces. This can be achieved by configuring the client, server or router.
Increasing the window size so the sender doesn't wait for an acknowledgement of one packet before sending the next can reduce the effects of high latency, and incorporating error-correction information can reduce or eliminate the need for retransmission when an error does occur, explains Gibb.
5. User involvement and education
Poor performance can occur as a result of bad user behaviour, but it may be more effective to get your colleagues onside through participation and education rather than imposing harsh standards and technical lockdowns. Prichard relates a situation where a mining company in WA experienced network slowdowns at lunchtime. The cause was traced to Doom sessions between staff at the minehead and down the shaft. Once the problem was explained, play ceased. "It's education, not Big Brother. People don't understand [the effect they can have on the network]," he says.
Similarly, encouraging people to save PowerPoint files on a shared drive instead of e-mailing copies to everyone concerned can help. Hayes notes that user education may be required to discourage people from doing things like unnecessarily replicating e-mail databases from a server to their PCs.
Modesto says malware often gets inside the firewall on notebook computers, so their security is a priority and user education about safe practices is an important element of avoiding problems, in addition to locking down configurations as far as possible without excessively impinging on user activities.
HR issues can affect performance in other ways: if incentive payments to IT staff are based on technical criteria such as the uptime of WAN links, they may concentrate on these rather than business outcomes, suggests Prichard.
6. Out of band management
How often does cycling the power fix a transient problem with a server or other device? If you don't trust branch office staff with the key to the broom cupboard -- sorry, the server room -- for fear they will flip the wrong switch it can take hours to get a technician on site. Another problem is that if a device becomes misconfigured and drops off the network, you can't use the normal remote management facilities to reconfigure it.
Out of band management using products such as those from Cyclades can overcome both types of issue, and is becoming increasingly important with the trend to geographically separate data centres and systems administration staff (which may or may not include the outsourcing of administration). Charlie Waters, senior vice president for global marketing at Cyclades, says that reducing the mean time to repair a fault increases overall productivity, as well as that of the staff involved in fixing it. If a customer has 3000 servers, of which six are usually down at any one time, it is important to get failed servers back online quickly for performance reasons, even if service availability is 100 percent due to redundancy.
Out-of-band management uses separate, secure communications paths into the production infrastructure to minimise downtime. Devices such as console servers and power managers are co-located with the servers and other devices and connected to them using serial, KVM, or Ethernet links. The important points are that the connections between the administration point and these devices are completely separate from the production channels, and a single management console can support all the infrastructure components.
According to Waters, a European telco reduced overtime costs by 88 percent, the average fault fix time by 97 percent, and the total fault hours by 88 percent as a result of using this technology -- and the cost was recovered in around a year.
"There is tremendous pressure on IT managers to improve service levels and efficiency," Waters says. He says the separation of the control network from the data network is an architecture proven by the high service levels delivered by the phone system.
