Adjust bandwidth saving via QoS (Part 1)

Brien M. Posey

One of the biggest trends in networking today is the transmission of both voice and video signals over traditional data networks. One of the problems with this convergence is how to do it, video and voice packets need to be delivered to recipients quickly and reliably, with no jitter and excess latency. limit.

One solution to this problem is to use QoS. QoS, or Quality of Service, is a priority packet processing technology. In essence, QoS allows you to handle sensitive packets with higher priority than other packages.

This is an industry standard, not Microsoft proprietary. Microsoft for the first time introduced QoS in Windows 2000. Microsoft's QoS version has been growing steadily ever since, but still adapts to industry standards.

In Windows XP Professional, QoS works primarily as a bandwidth width reserve mechanism. When QoS is enabled, the application is allowed to reserve up to 20% of the total bandwidth, which is provided by each of the network adapters. The amount of bandwidth a reserve application is fully adjustable. We will show you how to change the amount of bandwidth reserved in Part 3 of this series.

To see how the reserved bandwidth is used, assume that you already have a video conferencing application that requires high priority bandwidth. Assuming that this application has QoS enabled, it will reserve 20% of the entire bandwidth of the machine, leaving 80% of the bandwidth for the rest of the network traffic.

Applications other than video conferencing will use the best delivery mechanism. This means that these packages will be sent in the 'first come, first served' way. In other words, the video conferencing application's traffic will have higher priority than other traffic, but never be allowed to consume more than 20% of the total bandwidth.

However, although Windows XP establishes reserved bandwidth for high priority traffic, that does not mean that conventional priority applications cannot use this reserved bandwidth. In other words, although high-priority, bandwidth-intensive video conferencing applications, Windows still allows other applications to use both reserved bandwidth and non-reserved bandwidth to achieve The purpose of the most effective distribution is as long as the application that the reserved bandwidth is not in use.

When the video conferencing application is launched, Windows will start its reserve work. Even so, the reserve is not absolute now. Suppose Windows has reserved 20% of network bandwidth for video conferencing applications, but the application does not need all of this 20%. In such a case, Windows will allow other applications to use the remaining bandwidth but will constantly check the application's bandwidth needs with high priority. If the application requires a lot of bandwidth then the bandwidth will be assigned to it, up to 20% overall.

As we mentioned above, QoS is an industry standard rather than Microsoft proprietary technologies. Therefore, QoS is implemented within Windows, but Windows cannot perform it on its own. In order for QoS to work, each hardware component between the sender and the receiver must support QoS. This means that NICs, switches, routers and related things must be aware of QoS.

In case you're still wondering, you don't have to perform some unnecessary action to use QoS. Asynchronous Transfer Mode (ATM) is an ideal networking technology for use with QoS because it is a connection-oriented technology, but you can also use QoS with other technologies such as Frame Relay, Ethernet or even Wi-FI (802.11x).

The reason why ATM is an ideal choice for QoS is because it is capable of enforcing bandwidth reserves and distributing resources based on hardware level. While these types of resource distribution are beyond the capabilities of Etherrnet and similar networking technologies, that does not mean that QoS cannot be used which means that it must be implemented in ATM environment.

In an ATM environment the resources are fully dynamic (on the fly) at the hardware level. Due to Ethernet and similar technologies it cannot divide resources in this way, its technology types are based on priority instead of dynamic division. This means that bandwidth reserves occur at a higher level within the OSI model. When bandwidth is reserved, higher priority packets are transmitted first.

One important thing to note here when considering QoS implementation on Ethernet, Wi-Fi, or on similar networks is that these technologies are not interconnected. That means that the sender cannot check the recipient's status or the state of the network between the sender and the recipient. This also means that the sender can ensure that higher priority packets are transmitted before the lower priority packet, but cannot guarantee that the packets will arrive at the recipient in a specific amount of time. . In contrast, QoS is able to secure this problem on ATM networks because ATM is a connection-oriented technology.

Windows 2000 and Windows Server 2003

As we mentioned earlier, Microsoft first introduced QoS in Windows 2000, and Microsoft's QoS implementation has been significantly developed since that time. Therefore there is a slight difference between QoS in Windows 2000, Windows XP and Windows Server 2003.

The implementation of QoS on Windows 2000 is based on the Intserv architecture, which is not supported in Windows XP or Windows Server 2003. The reason why Microsoft does not use this architecture anymore is because of the very basic APIs. Difficult to use and architecture has many problems while expanding.

Some organizations still use Windows 2000, so I want to introduce a bit of information about how the Windows 2000 QoS architecture works. Windows 2000 uses a protocol called RSVP to reserve bandwidth resources. When bandwidth is required, Windows will specify when the packets are sent. To do so, Windows 2000 uses a signaling protocol called SBM (Sunbelt Bandwidth manager) to inform the sender that the packets are ready on the receiving side. Admission Control Service (ACS) will verify available bandwidth and then allow or deny bandwidth requests.

The whole process is a bit more complicated than the above, but there are some key parts that Windows 2000 differs from Windows Server 2003 and Windows XP. The remaining Windows 2000, 2003 and XP use the same traffic control mechanisms. As for these mechanisms, I will show you in part 2.

Conclude

In this article, I have shown you that packets carrying voice and video information must be delivered at a faster rate than regular data packets to avoid jitter. We also explained how QoS technologies can be used to help protect voice and video traffic from being delivered effectively. In Part 2 of this series we will explain how QoS works.

Adjust bandwidth saving via QoS (Part 2)

Adjust bandwidth saving via QoS (Part 3)

Adjust bandwidth saving via QoS (Part 4)