Gold class Internet

• Article 2 of 77
• Information Age, November 2000
• View the original article online

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In order to reduce the demands placed on their networks by their users, most ISPs have their own caching systems installed through which all their users’ transactions pass. Commonly visited sites have a high proportion of their content cached at local ISPs and so transactions don’t have to passed across the Internet to obtain this content, saving the ISPs’ bandwidth. Although most companies wouldn’t want to deal with the thousands of ISPs worldwide in order to have their content cached, Akamai has also been giving servers with cached content to local ISPs for free to improve their selling-point with customers. “I do rate Akami very highly,” says Crosby. “If your problem’s not your back-end system, Akamai can really help, more so than someone like CacheFlow or Alteon with a switching box.”

But companies with very popular servers who don’t have the budget to fund unlimited bandwidth have had to prioritise applications and users to ensure Quality of Service (QoS) levels. At its simplest, QoS techniques involve the web server ascertaining (from a user’s login name, IP address or from a cookie stored on the user’s hard drive) whether he or she is more important than the other users, and then prioritising traffic to and from the client accordingly.

One way to do this is to set up mirror servers on a VPN (Virtual Private Network: a portion of the Internet secured for use by a company. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted) and have their load-balancer redirect high-priority business customers to it after giving them access to the VPN.

Another technique often used is to have traffic aimed at clients browsing important pages prioritised at the expense of traffic related to ancillary pages. And web-based applications such as sales tools can be classed as more important than casual browsers, and traffic carrying text marked as more important then that carrying pictures.

The best way to mark traffic is using ‘switches’, fast network devices that direct packets to their destinations, says Donkin. There are various emerging protocols, such as RSVP (Resource Preservation Protocol), for applications to notify network devices that they want priority and for the devices to notify the sender if they’re capable of providing the resources required. If they are, the resources are pre-allocated to the traffic between the server and the client application. The switch or router can tag TCP/IP packets by inserting data into their headers, marking them as having a certain priority level. Network devices that can understand this tagging then transmit the packets with appropriate speed when the network is congested, delaying or even deleting low priority traffic and passing on high priority traffic.

Switches, because they don’t have to open up each packet, only reading the headers, are quicker at this than routers so are preferred QoS devices.

The latest version of Cisco’s IOS (internetworking operating systems) software contains NBAR (Network-based application recognition), a classification engine that can recognise traffic from web-based applications and then apply appropriate QoS measures. Microsoft Windows, too, has a built in QoS API (an application-programming interface: a pre-built tool that programmers can use in their own applications) that Windows Media Player and Internet Explorer use to notify servers of their respective network demands. Packets from WMP are given priority over IE’s traffic because web traffic is less vulnerable to interruption than streaming media’s.

The drawback with packet-marking is that once packets have left a ‘QoS’ network, their priority tags are removed so the QoS is only guaranteed on that network, not on the Internet or another connected network.

Further problems may set in when traffic isn’t HTTP-based but is HTTPS-based (a secure version of HTTP that encrypts the traffic using Netscape’s Secure Sockets Layer protocol). Servers alone can experience a 50-fold degradation of performance, according to Networkshop tests, in many cases allowing only a few transactions a second, as they process the encrypted transaction information and encrypt their responses.

Worse still, load-balancers cannot access header information, and so don’t know how to redirect packets based on the information within. That means that if a customer’s been prioritised to a fast server, as soon as they try to pay or perform a secure transaction, they suffer a massive slowdown.

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