Hello there Huawei family!
In today's blog post we are going to address QoS, or Quality of Service, one of the most essential concepts in the routing and switching sector.
Naturally, QoS has become a crucial factor in the enterprise networking world. Why? Because of the amount of queries comprising the keyword 'Qos' our esteemed users were kind enough to run on the Community since the beginning to this day. Let us thus find below an introduction on Quality of Service!
BACKGROUND INFORMATION
As networks rapidly develop, services on the Internet become increasingly diversified. Apart from traditional applications such as WWW, email and File Transfer Protocol (FTP), the Internet has expanded to encompass other services such as IP phones, e-commerce, multimedia games, e-learning, telemedicine, videophones, videoconferencing, video on demand (VoD) and online movies. In addition, enterprise users use Virtual Private Network (VPN) technologies to connect their branches in different areas so that they can access each other's corporate databases or manage remote devices through Telnet.
Diversified services enrich users' lives, but also increase the risk of traffic congestion on the Internet. In the case of traffic congestion, services can encounter long delays or even packet loss. As a result, services deteriorate or even become unavailable. Therefore, a solution to resolve traffic congestion on the IP network is urgently needed.
CONTEXT OF QoS
The best way to resolve traffic congestion is actually to increase network bandwidths. However, increasing network bandwidths is not practical in terms of operation and maintenance costs.
The quality of service (QoS) that uses a policy to manage traffic congestion at a low cost has been deployed. QoS aims to provide end-to-end service guarantees for differentiated services and has played an overwhelmingly important role on the Internet. Without QoS, service quality cannot be guaranteed.
INDICATORS OF QoS
The factors that affect the network service quality need to be learned to improve network quality. Traditionally, factors that affect network quality include:
link bandwidth - also called throughput, it refers to the maximum number of transmitted data bits between two ends within a specified period (1 second) or the average rate at which specified data flows are transmitted between two network nodes;
packet transmission delay - it refers to the time required to transmit a packet or a group of packets from the transmit end to the receive end, consisting of of the transmission delay and processing delay;
jitter - if network congestion occurs, the delays of packets over the same connection are different, so the jitter is used to describe the degree of delay change, that is, the time difference between the maximum delay and the minimum delay;
packet loss rate - it refers to the ratio of lost packets to total packets.
SERVICE MODELS OF QoS
How are QoS indicators defined within proper ranges to improve network service quality? The QoS model is involved. The QoS model is not a specific function, but an E2E QoS scheme. For example, intermediate devices may be deployed between two connected hosts. E2E service quality guarantee can be implemented only when all devices on a network use the same QoS service model. International organizations such as the IETF and ITU-T designed QoS models for their concerned services. The following describes three main QoS service models:
Best-Effort - the default service model for the Internet and applies to various network applications, such as the File Transfer Protocol (FTP) and email;
Integrated Service (IntServ) - an application uses a signaling protocol to notify the network of its traffic parameters and apply for a specific level of QoS before sending packets;
Differentiated Service (DiffServ) - classifies packets on a network into multiple classes and takes different actions for each class.
COMPONENTS OF DiffServ MODEL
The DiffServ model consists of four QoS components:
classification and marking - classification classifies packets while keeping the packets unchanged, whereas traffic marking sets different priorities for packets and therefore changes the packets;
policing and shaping - restricting the traffic rate to a specific value, especially when traffic exceeds the specified rate - traffic policing drops excess traffic, while traffic shaping buffers excess traffic;
congestion management - places packets in queues for buffering when traffic congestion occurs and determines the forwarding order based on a specific scheduling algorithm;
congestion avoidance - monitoring network resources so that when network congestion intensifies, the device proactively drops packets to regulate traffic so the network is not overloaded.
PROCESSING ORDER OF QoS
The above figure depicts the order the four QoS components are performed in.
THE BOTTOM LINE
An important factor within routing and switching, QoS always comes in handy whenever it is 'called upon' to be operated. Stay tuned to our weekly blog digest by subscribing to the Community blog and don't forget - we're here to help you solve any QoS-related issue: https://forum.huawei.com/enterprise/en/Switch/forum/861.
