[J] Modeling TCP Reno Performance - A Simple Model and Its Empirical Validation
Tcp periodic modeling
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Transcript of Tcp periodic modeling
TCP MODELING
Submitted by:Varsha Anandani (13MIT0062)
TCP = Transmission Control Protocol Connection-oriented protocol Provides a reliable unicast end-to-end byte
stream over an unreliable internetwork
TCP
1) The sheer scale of systems in which we find
TCP operating is tremendous.
2) There still remain many unknowns in the environment in which TCP is operating.
3) TCP was not designed using optimization.
Motivation for mathematical modeling of TCP
TCP operating scale is very large
Models are required to gain deeper understanding of TCP dynamics
Uncertainties can be modeled as stochastic processes
Drive the design of TCP-friendly algorithms for multimedia applications
Optimize TCP performance
Motivation for TCP Modeling
Link speed the number of bits per second that can be transmitted. Propagation delay, the time it takes the actual electronic, optical, or other
signals to travel from one end of the connection to the other. Window size, the amount of unacknowledged data that can be
outstanding on a TCP connection. Link reliability. Network and intermediate device congestion. Path maximum transmission unit (PMTU).
FACTORS THAT AFFECT THROUGHPUT
TCP Modeling Essentials
Mainly Reno flavors are modeled Two main features are modeled
Window dynamics Packet loss process
Window Dynamics
Linear increase and multiplicative decrease is modelled.
The standard assumption X(t) = W(t)/RTT
Packet Loss Process
Packet loss triggers window decrease Packet loss is uncertain This uncertainty is typically modeled as a
stochastic process E.g. probability p of losing a packet
Gallery of TCP Models
Periodic model Detailed packet loss model Finite state machine Fluid flow model And others…
Periodic Model
Simplest model for TCP No specific
version assumed
Assumes a periodic pattern of congestion window
X(p) = (1/RTT)*Root(3/2p)
P is the packet loss probability
TCP Congestion Control: window algorithm
Window: can send W packets
increase window by one per RTT if no loss, W <- W+1 each RTT
decrease window by half on detection of loss W <- W/2
sender
receiver
W
1 RTT
TCP throughput/loss relationship
Idealized model: W is maximum supportable
window size (then loss occurs)
TCP window starts at w/2 grows to W, then halves, then grows to W, then halves…
one window worth of packets each rtt
to find: throughput as function of loss, RTT
TCPwindow
size
time (rtt)
W/2
W
loss occurs
period
# packets sent per “period”
period
222
8
3
8
1
4
1WWW
Example 1 - Question
If a TCP connection has an average RTT of 200ms, and packet loss probability 0.05, what is the average throughput?