The Time Delay of TCP/IP and
Motivation: why study TCP/IP
It is popular and reliable.
Low cost. (Both software and hardware)
Scalable. (WAN + LAN)
Platform independent. (Wire/Wireless,
Connection/Connectionless, Different OS,
Various of hardware)
Potential applications: LonWorks,
TCP/IP stack layout
TCP/IP vs. OSI
OSI: Open System Interconnection
Figure from A.S. Tanenbaum “Computer Networks” 3ed Edition
For most PC systems
Data link: Ethernet, ISDN/ADSL/Telephone/Internet.
Network: IP, ARP.
Transport: TCP, UDP.
Application: WWW, TELNET, FTP, SMTP, DNS.
Delay of The Ethernet
Data Link layer, Medium Access sublayer.
If there are k stations ready for transmit and the probability for each
station transmits during a contention slot is p. The probability A that some
station acquires the channel in that slot is A=k p(1
A is maximized when p=1/k, with A
> 1/e as k
>Inf, so the mean number
of slots per contention is
Each slot has a duration 2t, the mean contention interval, w, is 2t/A.
Assuming optimal p, the mean number of contention slots is never more than
e, so w is at most .
If the mean frame takes P sec to transmit, when many stations have frames to
Channel efficiency =
Larger frames are more efficient, but others have
to wait longer before they can get access to the
channel. 1024 bytes is a round off between
performance and “fairness”.
The trouble maker for controller: the “mean” not
1024 byte frames
512 byte frames
256 byte frames
128 byte frames
64 byte frames
Number of stations trying to send
Figure from A.S.
Collision of The Ethernet
For a mean interval of 2t/A, collision happens
and Binary Expenential Backoff (BEB) procedure
BEB: after i collisions, a random number between
0 and 2
1 is chosen as the number of slots to
skip. The maximum number of the skipped slots
The possibility of collision after the last round of
BEB is negligible for a LAN, but significant
delay might be introduced.
Go to WAN
ARP: Ethernet address (MAC) to Internet address (IP).
(Defined in RFC826)
Why: Every computer on the Internet has a unique IP address, which is not the address
of Ethernet. So there must be a mechanism to translate between them.
How: Broadcast “Who owns the IP address 18.104.22.168”
Acknowledge “I have, and my MAC address is …..”
Note: ARP is not routable.
The commercial implementations are optimized by
various way, including ARP cache. So the delay of ARP
introduced only once.
ARP is not mandatory. A system with static database does
not need ARP. ARP was designed to reduce the work load
Simple IP routing
The Netmask can judge if a specific IP is in the associate
If (((their_IP ^ my_IP) & netmask) )!=0
use_gateway( ); /* not in this subnet */
go_direct( ); /* on the same wire */
This job would be done by the router, with
unknown delay. Depends on the CPU, software,
load, etc of the router.
More complex routing
The interior gateway routing protocol:OSPF
OSPF represents Open Shortest Path First.
Original Internet interior gateway protocol was a distance vector protocol
(RIP) based on the Bellman
Ford algorithm. It worked well in small systems,
but less well on larger ones. OSPF became a standard in 1990, and it will
become the major interior gateway routing protocol soon.
The exterior gateway routing protocol:BGP
BGP: Border Gateway Protocol
Not just the shortest path, It considers more about politics.
Traffic starting or ending at Netscape should not transit Microsoft.
Congestion Control in The
John Nagle mode.
Congestion Control in IP/TCP
If there are infinite memory on the router, or the
CPU of router is too slow, congestion may
General principle of congestion control: using
“control theory point of view”, “close loop”.
There are many algorithms, such as
Nagle mode, Leaky bucket, Token bucket, etc.
From domain name to IP address
TCP congestion control
TCP updates an estimate of the average
RTT (round trip time) a by
,where g is a ‘gain’ (0<g<1) that
should be related to the signal
noise ratio of m.
Measuring The Delay Is Simple
Consider the worst case for either LAN, such as
Ethernet, or WAN, is very difficult.
There is possibility mathematic model for the
collision of the Ethernet. But some parameters for
the formula cannot be calculated, rather, they are
measured on the real system. Not surprisingly,
different systems might have quite different
The delay is very easy to measure but hard to
The more you know about the delay about other
computers, the easier to predict the delay of your
Though it has not been proved yet, the delay,
even of LAN, must be uncontrollable, if other
computer involved in the same network.
High performance indicates small delay. For a
reliable medium like twist par 100M Ethernet,
large frames will have better performance.
Unfortunately, control systems prefer small
frame. So we should not put heavy load on the
network. Efficiency theory gives us a reference
on selection the working load.
At the beginning, researchers assumes the traffic
of the Ethernet is Poisson, but it now appears the
network traffic is
Paxson and Floyd
Willinger et al
Internet tracking software.
Area Traffic: The Failure of Poisson Modeling
Self Similarity Through High
Variability: Statistical Analysis of
Ethernet LAN Traffic at the Source Level
End Routing Behavior in the Internet
A good presentation
Why is the internet traffic self
Forecasting network performance to support dynamic scheduling
using the network weather service
Papers on 24th Conference on Local Computer Networks
20 October, 1999 Lowell, Massachusetts
Time Series Models for Internet Data Traffic
C. You and K. Chandra
On the Distribution of Round
Trip Delays in TCP/IP Networks
T. Élteto and S. Molnár
Efficient and Accurate Ethernet Simulation
J. Wang and S. Keshav
Case Scenario for Transmission of Synchronous Traffic in an FDDI Network
S. Zhang and E. Lee
Papers on frequency domain.
Modeling Spectral Features in TCP traffic
G. Olowoyeye, B. Kim and K. Chandra 1998
Network traffic modeling using a multifractal wavelets model
series models for Ethernet traffic
K. Chandra, C. You, G. Olowoyeye and C. Thompson , June 1998
Analyzing Stability in Wide
Area Network Performance
Measuring link bandwidths using a deterministic model of packet delay,
Characteristics of wide
area TCP/IP conversations,