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TD0612:  FRU_PRS_EXT.1.2 Testing

Publication Date
2021.10.05

Protection Profiles
EP_SBC_V1.1

Other References
FRU_PRS_EXT.1.2

Issue Description

In the SBC EP, FRU_PRS_EXT.1.2 and Test 2 specify the use of R-factor.  “R-Factor” is a measurement based on jitter and delay of packets that yields a value that reports/reflects call quality.  The SFR states “mediated on the basis of …and R-factor”, but “R-Factor” is not used to mediate traffic. COS/TOS marking differentiate traffic types, and as a result can be used to mediate traffic, but “R-Factor” is a computed value that measure traffic flow for RTP, but is not used to mediate/change/affect that traffic.

Resolution

Extended Package for Session border Controller v1.1 is modified as follows:

FRU_PRS_EXT.1.2 is modified as shown below, with strikethrough denoting deletion:

FRU_PRS_EXT.1.2 The TSF shall ensure that each access to [network bandwidth] shall be mediated on the basis of the subject’s assigned priority and R-factor.

Test 2 is modified as shown below, with strikethrough denoting deletion and underline denoting addition:

Configure the TOE to support QoS. Set QoS tags for media and signaling traffic flows. Configure one remote endpoint to act as a calling party that sends a continuous stream of VVoIP traffic (media and signaling) to another endpoint that is connected to the TOE via a different external interface.  Using a tool of choice, create a data stream of non-VVoIP (no media and no signaling) traffic that ingresses one interface, passes through the TOE, and egresses on the TOE. These shall be the same interfaces used by the VVoIP traffic. Verify using packet captures that traffic between the TOE and the callee is tagged with appropriate QoS markings, and that the QoS R-factor is being updated as the traffic persists VVoIP and non-VVoIP traffic packets are passed through the TOE.  Change the TOE QOS configuration to rate-limit, or police, non-VVoIP traffic. Verify either using packet captures that VVoIP traffic passes through the TOE while non-VVoIP traffic is rate-limited (egress packets are less than ingress traffic) OR that Rating factor (R-Factor) and/or Mean Opinion Score (MOS) values signal mediation.

Justification

The goal of this requirement was to ensure VoIP traffic could be prioritized over other traffic traversing the interface. The submitter was correct that the R-factor is a measured value based on jitter and packet delay, packet loss is also factored into it. The spirit of including the R-factor in testing was in an attempt to measure that delay, jitter, and packet loss in the voip traffic was decreasing when QoS mechanisms were in place. It's true the R-factor does not mediate traffic. It's merely a tools that helps to gauge if mediation needs to take place and if mediation efforts are effective.

 
 
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