Communication Systems Engineering Episode 1 Part 1 pps
Communication Systems Engineering Episode 2 Part 1 pptx
... = 011 111 10
• They all use a 16 -bit CRC for error detection
• They all use Go Back N ARQ with N = 7 or 12 7 (optional)
SDLC packet
flag address control data CRC flag
Multipoint SN,RN
communication ... Back 7 ARQ
SN
0 3 4 5
t
1
6
RN
0 1 2
3
5
Window (0,6)
(1, 7) (5 ,11 )(2,8) (3,9)
Node A
Node B
2
0 5
Packets
delivered
0
1
2
3
4
5
• Note that packet RN -1...
Communication Systems Engineering Episode 2 Part 3 pps
... (
λ
)
-1
e
Departure rate
ge
-g
1
g
d
– What value of g
dg n
ge
− g
= e
− g
− ge
− g
= 0
()
maximizes throughput?
g
⇒= 1
– g < 1 => too many idle slots
– g > 1 => ... both
sides exceed 1 (for unit duration packets)
– P(success) = e
-g
x e
-g
= e
-2g
– Throughput (success rate) = ge
-2g
– Max throughput at g = 1/ 2, Throughput = 1/ 2e ~ 0 .18
–...
Communication Systems Engineering Episode 2 Part 4 pps
... Token rings were developed by IBM in early 19 80’s
• Token: a bit sequence
– Token circulates around the ring
Busy token: 011 111 11
Free token: 011 111 10
• When a node wants to transmit
– Wait ... attempt) =
i
P (1
−
P)
P(exactly 1 attempt) = P(success) = NP (1- P)
N -1
To maximize P(success),
d
dp
[NP (1- P)
N -1
] = N (1- P)
N -1
− N(N − 1) P (1 P)
N
−
2...
Communication Systems Engineering Episode 2 Part 5 ppsx
... distance from 1 to i using at most h arcs.
– Di (1) = d1i ; i
≠
1 D1 (1) = 0
– Di(h +1) = min {j} [Dj(h) + dji] ;i
≠
1 D1(h +1) = 0
• If all weights are positive, algorithm terminates in N -1 steps. ... in MST.
Eytan Modiano
Slide 16
Slow reaction to link failures
• Start with D3 =1 and D2 =10 0
1
– After one iteration node 2 receives D3 =1 and
D2 = min [1+ 1, 10 0] = 2...
Communication Systems Engineering Episode 2 Part 6 pps
...
Slide 19
TCP Error Control over a GEO Satellite link
EFFICIENCY VS. BER
CHANNEL BER
EFFICIENCY
0
0 .1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1E-07 1E-06 1E-05 1E-04 1E-03 1E-02
SRP
1 ...
EFFICIENCY
0
0 .1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1. 00E-07 1. 00E-06 1. 00E-05 1. 00E-04 1. 00E-03
1, 544
64 KBPS
16 KBPS
2.4 KBPS
KBPS
• TCP assumes dropped pack...
Communication Systems Engineering Episode 2 Part 2 pptx
... customers
in the system
Eytan Modiano
Slide 1
16.36: Communication Systems Engineering
Lecture 17 /18 : Delay Models for Data Networks
Eytan Modiano
Eytan Modiano
Slide 14
Application of little’s Theorem
• ... )
/
/
00
1
1
11
ρρ
ρ
ρ
ρ
ρ
λµ
λµ
λ
µλ
W =
−
−
11
µλ µ
T =
−
1
µλ
NW N
Q
==
−
−=−
λ
λ
µλ
λ
µ
ρ
Eytan Modiano
Slide 6
Inter-arrival times
• Time that elapses between ar...
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