Packet Loss & RTT Calculation Method
Banjarmasin June 1, 2017
NOKIA PACKET LOSS CALCULATION METHOD 1. Nokia uses Two Way Active Protocol Measurement Protocol (TWAMP) based on RFC5357, and further simplified to TWAMP Light. 2. TWAMP is a way to have an indication of quality and performance of the IP MOBILE BACKHAUL by exchange test packets between two TWAMP entities, further known as TWAMP Sender and TWAMP Reflector 3. Measures Round Trip Time (RTT), Packet Loss Rate (PLR) and additionally Packet Delay Variation (PDV). 4. Since User Plane is the traffic for end user, Nokia set the TWAMP parameters that reflect U-Plane traffic (IP Address of TWAMP Sender and Reflector, Packet Size, DSCP) 5. In 3G network, use NodeB as TWAMP Sender and RNC as TWAMP Reflector that will indicate the performance of the IP MOBILE BACKHAUL of an IuB interface. Nokia set 3 sessions to imitate RT Traffic, NRT Traffic and HSPA Traffic.
NodeB
Sent TWAMP Messages (vrf IuB)
Reflected TWAMP Messages (vrf IuB)
Access Router
RNC
NOKIA PACKET LOSS METHOD 5. For LTE Network, to better reflect the condition of IP MOBILE BACKHAUL for S1-U interface, it is suggested to have TWAMP Reflector or UDP Echo at SGW site. Since still does not have TWAMP Reflector at SGW site yet, it is agreed to use RNC that co-located with Access Router to indicate performance of ACCESS IP MOBILE BACKHAUL. Note that we can not measure the quality of end-to-end transport (eNB to SGW) performance because of that, only up until Access Router only.
eNB
Sent TWAMP Messages (vrf lte-uplane)
Reflected TWAMP Messages (vrf lte-uplane)
Access Router
RNC
TWAMP Packet Loss Measurement
1.
2.
Since test packets contain sequence numbering, it is possible to measure Packet Loss Rate by TWAMP Sender Session Reflector copies the sequence number from received test packet to the packet that is to be transmitted back
TWAMP RTT Measurement 1. RTT Measurement if use TWAMP Reflector RTT = (RTSS-TTSR) + (RTSR-TTSS) T S G
T S G
TWAMP Sender
TTSS
RTSR TWAMP message containing TTSS
T S G
Reflected TWAMP message containing TTSS, RTSR,and TTSR
T S G
RTSS
TTSR TSG: TTSS : RTSR: TTSR: RTSS:
TWAMP Reflector
Time Stamp Generator Transmit TimeStamp at Sender Receive TimeStamp at Receiver Transmit TimeStamp at Receiver Receive TimeStamp at Sender
2. RTT Measurement if use UDP Echo RTT = RTSS-TTSS T S G
TWAMP Sender
T S G
TTSS TWAMP message containing TTSS
Reflected TWAMP message containing TTSS RTSS TSG: TTSS : RTSS:
Time Stamp Generator Transmit TimeStamp at Sender Receive TimeStamp at Sender
UDP Echo Server
NOKIA 3G TWAMP FORMULA IP TWAMP Packet Lost Ratio (%)
=
100 * lostTwampMessages txTwampMessages
Round Trip Time (miliseconds)
=
maxRTT_15Min 1000
Packet Delay Variation (miliseconds)
=
(maxRTT_15Min – avgRTT_15Min) 1000
NOKIA 4G TWAMP FORMULA IP TWAMP Packet Lost Ratio (%)
=
100 * lostTwampMessages txTwampMessages
Round Trip Time (miliseconds)
=
maxRTT_15Min 1000
Packet Delay Variation (miliseconds)
=
(maxRTT_15Min – avgRTT_15Min) 1000
ERICSSON 3G PACKET LOSS FORMULA 1. Ericsson uses counters related to frame loss to monitor High Speed data service in the downlink direction. Packet Loss SpiXX (%)
=
100 * IuBDataStreams.pmHsDataFramesLostSpiXX IuBDataStreams.pmHsDataFramesReceivedSpiXX+IuBDataStreams.pmHsDataFramesLostSpiXX
RBS
RNC MAC-d
With the use of Sequence Number in MAC PDU, receiver can detect if there’s a frame loss that can be an indication that there’s packet loss in the transport network
ERICSSON 3G RTT FORMULA 2. Ericsson uses maximum dynamic delay between RNC and RBS on the radio network layer based on Node synchronization. RTT (miliseconds)
=
2 * pmIubLinkDynamicDelayMax
RNC 15. CCH FP (FACH): DL Node Synchronisation (T1)
sampleIntervalSup
16. CCH FP (FACH): UL Node Synchronisation (T1, T2, T3)
RBS
ERICSSON 4G PACKET LOSS & RTT FORMULA 1. Ericsson uses counters related to SCTP of X2-MME logical connection between eNB and MME
SCTP Data Chunk Retransmission Rate (%) =
100 * pmRtChunks pmRtChunks + pmOutDataChunks
eNB
MME S1-MME
SCTP will retransmit data if there’s a packet loss indication
X2-AP Adj eNB
2. No RTT measurement method
Summary
ERICSSON Items to be Measured
Protocol
Remarks
NOKIA Protocol
Remarks
Similar Measurement with Ericsson
HSUPA congestion rate in Iub = 100*SUM (IUB_DELAY_CC_DELAY_IND +HW_OVERL_CC_DELAY_IND +IUB_LOSS_CC_FRAME_LOSS_IND 3G Packet Loss Rate
Frame Protocol of Only measures packet loss HSPA rate of HSPA Traffic
TWAMP Light based on RFC5357 3G RTT
4G Packet Loss Rate
4G RTT
Node Synchronization (over FACH)
Only measures delay of node synchronization
SCTP of S1-MME interface
Only measures SCTP traffic (Control Plane). Since SCTP is for Signaling, it will be given higher priority than User Plane Traffic. No measurement
+IUB_DELAY_CC_FRAME_LOSS_IND Strength : Parameters can be set to imitate +HW_OVERL_CC_FRAME_LOSS_IND) the traffic that wanted to be ------------------------------measured (RT, NRT, HSPA, NBAP, SUM (MISSED_EDCH_FRAMES S1-MME, S1-U, X2-AP etc) +DELAYED_EDCH_FRAMES +SUCC_REC_EDCH_FRAMES) Dependency : Need peers that is set as TWAMP N/A Reflector or UDP Echo S1 interface SCTP unsuccessful transmission ratio = 100 - (100* sum(SCTP_S1CHSNT) / sum(SCTP_S1CHSNT+SCTP_S1CHRS NT))
