Guidance

PSN Quality of Service (QoS) testing and reporting

Published 27 October 2015

Both GCN service providers and DNSPs will demonstrate that their service meets the PSN network Quality of Service (QoS) requirements. For GCN service providers, an active probing open standard, the IETF IP Performance Metrics (IPPM) Two-Way Active Measurement Protocol (TWAMP) RFC5357, has been selected.

Performance Measurement

Obligation QOS.12: mandatory for GCNSPs

Service providers must support IETF ‘IP Performance Metrics (IPPM)’ Two-Way Active Measurement Protocol ‘TWAMP’ as the QoS performance measurement protocol standard for PSN.

Obligation QOS.11: mandatory for GCNSPs and DNSPs

Any active probing solution must not adversely impact PSN consumer traffic, either through excessive link load from measurement probes or as the result of load placed on infrastructure by the measurement processes such as generating and responding to probes.

Obligation GCN.17: mandatory for GCNSPs

All GCNSPs must deploy logical and/or physical probes on all GCN PoCs where the GCNSP provides service, to enable measurement of GCN service level performance metrics.

The provision of probes is required to be included in the NNI solution design. Demonstration of probe capability is required prior to completion of the delivery of GCN service at a PoC.

Test requirements

Obligation QOS.20: mandatory for GCNSPs

GCNSPs must:

• provide active probing functionality on all their respective PoC NNIs at each of their PoC locations
• ensure all other GCNSPs can probe their respective PSN NNI probes
• ensure that active probing test streams transit their respective IP infrastructure connected to the PoC/ PoI NNI eg ASBR(PE)
• measure - and report to the PSN team - actual performance against the GCN requirements for each service class defined in QOS.4 from each of its edge nodes to all other GCNSP edge nodes, across the GCN including GCN to DNSP NNI

Obligation QOS.21: mandatory for DNSPs

DNSPs must identify a representative set of pairs of nodes at the edges of their PSN Diffserv domain which will be used for performance reporting. Each pair must include one of the DNSPs customer edge nodes and one of the DNSP’s GCN edge nodes. The set of pairs must be representative both in terms of geographic reach and loading for the DNSP.

DNSPs must also:

• measure - and report to the PSN team - actual performance against the DNSP requirements for each service class defined in QOS.4 for these pairs of nodes
• use the PSN shared services VPN for performance measurement

Obligation QOS.17: mandatory for GCNSPs and DNSPs

Service providers must:

• send test messages of 200 packets for each of the test PSN classes every 15 minutes, for each pair of end-points being monitored
• send 19200 packets in a 24-hour period for each pair of end-points being monitored combine their own results for each PSN service class over a 24-hour period to provide figures for two-way latency, jitter and packet loss for that 24-hour period
• initiate the measurement at a random point in each 15 minute window

Probe management and clock synchronization

PSN service providers do not permit inter-provider probe device management access. All PSN service providers are responsible for management and security of their own measurement infrastructure.

Obligation QOS.16: mandatory for GCNSPs and DNSPs

Service providers must synchronise:

• all MPLS and routing infrastructure elements to UTC (time of day) to within (+/-)10 ms for 99% of measurement instances per month
• all GCN probe infrastructure to (+/-) 4ms from UTC time of day
• all DNSP probe infrastructure to (+/-) 5ms from UTC time of day

Configuration

Obligation QOS.19: mandatory for GCNSPs and DNSPs

Service providers must:

• use packet sizes appropriate to the class of service for all classes of service (eg the PSN real-time service class must use a payload of 60 bytes to simulate the G.729 VoIP codec; all other PSN service class probes shall be based on 400 byte IP datagrams)
• (this bullet has been removed from the obligation)
• have a last packet timeout of 500 milliseconds

Reporting

Obligation QOS.24: mandatory for GCNSPs and DNSPs

Each service provider must provide QoS reports:

• that contain a record for every 24-hour period to the PSN team
• monthly, or - where possible - they may be uploaded daily direct to the GOV.UK performance platform

Obligation QOS.14: mandatory for GCNSPs and DNSPs

Provide the information in the table below in your QoS reports:

• for each service class
• between each pair of end-points
• for each 24 hour period

Time	Time of measurement: the start point of the 24-hour period
SLA	Type of SLA the measurement applies to: eg GCN supplier 1 to GCN supplier 2 or intra-DNSP
Guaranteed service	Type of service: eg GCN or DNSP
Service identifier	Specific service being monitored: to include the class of service and the names of the end-points
Verifier	Name of verifier initiating the measurement
Average round-trip latency	The mean (50th percentile) of all the latency figures for all packets (for this service identifier) in the 24-hour period. – measured in microseconds
Latency 95th percentile	The latency of the best 95% of packets. The 95th percentile of all the latency figures for all packets (for this Service Identifier) in the 24-hour period. – measured in microseconds
Lost packets	Number of lost packets: this can later be converted into a percentage using the knowledge that there are 19200 packets sent per 24-hour period
Sender to Reflector average jitter	The mean (50th percentile) of all the jitter figures for all packets (for this service identifier) in the 24-hour period. – measured in microseconds
Sender to Reflector average maximum jitter	The mean (50th percentile) of all the maximum jitter figures from each test, across all tests (for this service identifier) in the 24-hour period. – measured in microseconds
Reflector to Sender average jitter	The mean (50th percentile) of all the jitter figures for all packets (for this Service Identifier) in the 24-hour period. – measured in microseconds
Reflector to Sender average maximum jitter	The mean (50th percentile) of all the maximum jitter figures from each test, across all tests (for this service identifier) in the 24-hour period. – measured in microseconds

Exception reporting

Obligation QOS.30: mandatory for GCNSPs and DNSPs

Service providers must review their QoS reports and explain any sustained instances of any service operating outside the requirements defined in QOS.4.