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Quality of Service (QoS) is defined as mechanisms deployed in order to apply differentiated service levels or more efficient link utilisation. Another general definition is: The ability of a network to provide differentiated services to selected network traffic. From an Optus marketing point of view, QoS allows our customers to be offered additional chargeable options based on their service requirements, such as ensuring that urgent data or voice packets can be prioritised and delivered with guarantees before non-urgent data. The same QoS options should be able to be offered to our customers irrespective of the access methods used. The customer’s service is guaranteed based on the following QoS indicators:

QoS Indicator	Definition
Network Availability	The fraction of time that network connectivity is available between an ingress point and a specified egress point.
Service Availability	The fraction of time that service is available between a specified ingress point and a specified egress point within the bounds of a defined Service Level Agreement (SLA).
IP Packet Loss	A comparative measure of packets faithfully received to the total number of packets transmitted. Loss is expressed as the percentage of packets that were dropped.
Round Trip Time (RTT) or Delay or Latency	The finite amount of time it takes a packet to reach the receiving end point after being transmitted from the sending end point.
Jitter (or Delay Variation)	The difference in the end-to-end delay between packets. For example, if one packet required 100 milliseconds (ms) to traverse the network and the following packet required 125 ms to make the same trip, then the jitter would be calculated as 25 ms.

 

Optus Private IP QoS will be implemented through two main components:
1. Traffic Packet Classification
2. QoS Options >==Traffic Packet Classification == To be able to identify the priority of a packet as it passes through the network, each packet is classified or marked.<br />Currently, Optus uses a subset of the Differentiated Services Code Point (DSCP) classification model to mark each packet. Within each packet, the three IP Precedence bits within the Type of Service (ToS) field are set to one of four values representing a different traffic class or colour (see Table 6 below).<br />The existing Optus network configurations utilise the IP Precedence QoS model, but to align with the Lean IP-VPN program the DiffServ Code Point QoS model is now being proposed to be implemented (see Appendix B.7 below for more details on the DSCP model).<br />In addition, Optus currently utilises a label-swapping paradigm known as Multiprotocol Label Switching (MPLS) for forwarding IP packets within the MSC core. On ingress into the PE router on the edge of the core, a 23-bit label (the MPLS header) is added to each IP packet. This label specifies the packet’s path and priority for the next hop in its journey across the core. On egress of the final PE on the edge of the core, the MPLS header is stripped. Optus will utilise the three-bit Experimental (EXP) field within the MPLS header to support QoS options within the core.<br />The current SLA performance targets for OPI with ATM or Frame Relay services are given in the below table [see Reference 6 for further details]. Engineering are to recommend changes to the SLA performance targets if necessary.<br />

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Traffic Class	IP Precedence	Delay (packet delay between customer facing PE router interfaces)	Jitter (90 Percentile)	Packet Loss
Gold real time (Gold-rt)	5	<40ms one way	<10ms	<1%
Gold non-real time (Gold-nrt)	4	<40ms one way	<10ms	<1%
Silver	3	<60ms	<100ms	<2%
Bronze	0	<60ms one way	No limit	2%

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  QoS Options

 

  QoS options define how the marked traffic is sent and received by routers along each leg of the network journey using particular tuning and configuration settings.
Depending on the product, grade, access method and speed configurations purchased, the customer can select a particular profile that defines the mechanisms to be used in the event of network congestion. The QoS options define the type of profiles that a customer can select. These profile types are known as QoS Classes of Service (CoS).

The following summarises the different QoS options available to the customer as part of this Program:

 

Class of Service	CoS Description
No CoS	This term is to no longer be used, replaced instead by the term: Transparent CoS.
Transparent CoS	Any QoS markings made by the customer are preserved. For unmanaged services (where the customer owns and manages the CE router), the customer can set the IP Precedence bits within the Type of Service (ToS) field in each IP address header at either the CE router or within their LAN, prior to sending them to the CE router. For managed services, customers can still set the IP Precedence within their LAN but the CE router will not change these values. At the PE router, Optus will preserve the IP Precedence bits but will add a MPLS header with the EXP bits set to Bronze. First In First Out (FIFO) or Weighted Fair Queuing (WFQ) is applied to the IP packet within the core and at the final PE router when the MPLS header is stripped off (i.e. no class-based queuing is applied). On egress of the final PE router, the IP Packet will be delivered to the CE router with all bits preserved.
Single CoS	Customer selects a single class for all traffic (e.g. all traffic will be treated as Silver (Assured Forwarding 1 Class)). The IP Precedence / DSCP bits are set at the CE router (either by the customer if the CE is unmanaged or by Optus if managed). At the PE router, Optus will mark the MPLS EXP bits based upon the IP Precedence bits. If the traffic is classed as real-time (i.e. single class selected is “Gold-rt”) and within the agreed bandwidth threshold (i.e. under the agreed Committed Information Rate (CIR)), then the MPLS EXP bits are set to “Gold-rt”. If the Gold-rt threshold is exceeded, the packet is discarded. All IP packets that are not marked “Gold-rt” will have their MPLS EXP bits remarked as “Bronze”. If the single class selected is not real-time, once the threshold is exceeded, the MPLS EXP bits are remarked to “Bronze”.
Multi-CoS Standard	Traffic can be classed using all four classes with bandwidth allocated at set percentages (set by Optus). The IP Precedence bits are set at the CE router (either by the customer if the CE is unmanaged or by Optus is managed). At the PE router, Optus will mark the MPLS EXP bits based upon the IP Precedence bits. Within the core, packets are treated based on their MPLS EXP bit values and, if the agreed percentages are exceeded, the packets are dropped (if real-time) or remarked to Bronze (if not real-time). For reference, the existing egress percentages used for Frame Relay are: Gold-rt 33% Gold-nrt 36%  Silver 12% Bronze 4% Network 5% The existing egress percentages used for ATM are: Gold-rt 25% Gold-nrt 27% Silver 9% Bronze 3%  Network 3% The Multi-CoS Standard egress percentages for other access methods in scope for this Program are to be recommended by Networks IPND.
Multi-CoS Custom	As for Multi-CoS Standard, traffic can be classed using all four classes except bandwidth is allocated based on customer-defined rules.