QoS Functionality
QoS can be used to give certain traffic priority over other traffic. Without QoS, all traffic in a network has the same priority and chance of being delivered on time. If congestion occurs, all traffic has the same chance of being dropped. With QoS, specific network traffic can be prioritized to receive preferential treatment. In turn, a network performs more predictably, and utilizes bandwidth more effectively.
QoS is based on DiffServ architecture, which stipulates that individual packets be classified upon entry into a network. Classification information can be carried in the Layer-3 IP packet header or the Layer-2 frame. IP packet headers carry the information using 6-bits from the deprecated IP type of service (TOS) field. Layer-2 802.1Q frames carry the information using a 2-byte Tag Control Information field. All switches and routers accessing the Internet depend on class information to give the same forwarding treatment to packets with the same class information, and give different treatment to packets with different class information. A packet can be assigned class information, as follows:
• End hosts or switches along a path, based on a configured policy
• Detailed packet examination, expected to occur nearer to the network edge, to prevent overloading core switches and routers
• A combination of the above two techniques
Class information can be used by switches and routers along a path to limit the amount of allotted resources per traffic class. Per-hop behavior is an individual device’s behaviour when handling traffic in the DiffServ architecture. An end-to-end QoS solution can be created if all devices along a path have consistent per-hop behavior.
Quality of Service (QoS) provides preferential treatment to specific traffic, possibly at the expense of other traffic. Without QoS, Qumran offers best-effort service to each packet, however, this may cause unpredictable network behavior. Implementing QoS in a network makes performance more predictable and bandwidth utilization more effective.
QoS design in Qumran complies with IETF-DiffServ and IEEE 802.1p standards. A typical QoS model deployment is based on the following elements:
• The packet received on customer edge port will be assigned to a QoS service. The service is assigned based on the packet header information.
• The QoS service defines the packet's internal QoS handling (i.e. traffic class/queue and drop precedence/color) and optionally the packet's external QoS marking, through either the IEEE 802.1p User Priority or the IP header DSCP field.
• Qumran provides end-to-end QoS behavior by providing consistent QoS treatment to the traffic within the network core based on packet's IEEE 802.1 or DSCP marking.
• Qumran can modify the assigned service of the packets if a packet stream exceeds the ingress configured rate by marking drop precedence and remarking packet's IEEE 802.1p or DSCP at the egress.
• Qumran incorporates the required QoS features to implement network-edge, as well as, network-core devices.
• Qumran provides flexible mechanisms to classify packets into different service levels.
• Service application mechanism is based on eight egress priority queues per port.
• The packet Priority fields can be remarked to reflect the QoS assignment on L2 and L3 networks.
Note: Packet priority remarking on an MPLS network is not supported.
Last modified date: 10/20/2023