Xena Networks – Global Price/Performance Leaders in Gigabit Ethernet Testing - Elexo -
[email protected]
x x
x
x
t0
t1
packet
packet
ingress
egress D U T/SU T
t0
packet ingress
t1
packet
D U T/SU T
egress
t0
t1
packet ingress
D U T/SU T
packet egress
t1
t0 tA 0
tA 1
packet ingress
tB 0
packet egress
D U T/SU T A
tB 1
packet ingress
tC 0
packet
D U T/SU T B
egress
packet ingress
t1 ± t0 = (tA 1 ± tA 0)+ (tB 1 ± tB 0)+ (tC 1 ± tC 0)
t0
t1
packet
packet
ingress
egress D U T/SU T
ܶൌ
ܮ ܴ
tC 1
D U T/SU T C
packet egress
ܶ
ܮ
ܶൌ
ܴ
ͷͳʹܾ݅ݏݐ ൌ ͷͳʹ݊ݏ ͳͲଽ ܾݏ
Table 1. Summary of four different latency measurement methods
ȁܦାଵ െ ܦ ȁ ܦ
݅
(RFC 4689)
ݎ݁ݐݐ݅ܬ ൌ ȁܮାଵ െ ܮ ȁ
(Xena)
ܮ ݅
x
ܶݔ
x
ܴݔ
ܶݔ
ܴݔ
ࡶ࢚࢚ࢋ࢘ ൌ ȁሺࡾ࢞ା െ ࢀ࢞ା ሻ െ ሺࡾ࢞ െ ࢀ࢞ ሻȁ ൌ ȁሺࢀ࢞ା െ ࢀ࢞ ሻ െ ሺࡾ࢞ା െ ࡾ࢞ ሻȁ (Xena) ݅
Start
Fram e arrives?
Yes
Firstin stream ? No
No
In sequence? Yes
C alculate Jitteri = |(Txi+1 ² Txi) ² (Rxi+1 - Rxi)|
U pdate min,max,and avg jitterstatistics
IFG histogram
IFG histogram
IFG
IFG
packet
packet
IFG
packet
packet ingress
egress D U T/SU T
IFG
packet
packet
Testport Testport
Testport
Testport
1
2
3
1
3
2
4
4
Input0
0ĺ1
0ĺ0
1ĺ0
0ĺ0
O utput0
Input1
1ĺ0
1ĺ1
0ĺ1
1ĺ1
O utput1
Input2
2ĺ3
2ĺ2
3ĺ2
2ĺ2
O utput2
Input3
3ĺ2
3ĺ3
2ĺ3
3ĺ3
O utput3
Latency = t1 ± t0 t1
t0
ĺ ĺ
ĺ
ĺ ĺ
ĺ ĺ
ĺ ĺ
Input0
ĺ
ĺ
Input1
ĺ
ĺ ĺ
O utput0
ĺ
O utput1
Input2
ĺ
ĺ
ĺ
ĺ
O utput2
Input3
ĺ
ĺ
ĺ
ĺ
O utput3
ǻt
ǻt
TestportTX clock drift/skew
W aiting tim e of
t1
t0
Packetĺ
Latency = t1 ±t0 + ǻt
ĺ Input0
ĺ
ĺ
Input1
ĺ
Input2
ĺ
ĺ
ĺ
ĺ
O utput2
Input3
ĺ
ĺ
ĺ
ĺ
O utput3
ĺ
ĺ ĺ
ĺ
ǻt
O utput1
ǻt
Packetsize difference
O utput0
W aiting tim e of
t0 Latency = t1 ±t0 + ǻt
t1
Packetĺ
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Xena Networks – Global Price/Performance Leaders in Gigabit Ethernet Testing - Elexo -
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