Broadband (Cable, DSL, Satellite, Fiber Optics)/PPS & TCP flags


I have two questions:

First question)
How PPS can be estimated in termes of RTT, MSS, WIND Size , Bandwidth

For example if   RRT = 1 sec, MSS=1460, Bandwidth = 512000 bits / sec

WIND Size = Bandwidth * RTT  /8 =  512000 * 1 /8 =  64000Bytes
Nof Segments that can accommodated in in one BDP is 64000 / 1460 = 43.8 = Say  43

Than can I say No.of Packet per Sec (PPS) is 43?

Second question)

We used wireshark to capture TCP data for FTP application. We observed for ACK flag is set both Ack packets & data packets.

Setting ACK flag for acknowledgement packets is OKKK
What is the reason for Setting a ACK flag for even Data packets also??

First question:

When you are talking with an HONEST vendor that is on the up-and-up, PPS figures are always calculated with the minimum packet size.  For example Cisco rates the Cisco ASR 1000 Series Router, as capable of forwarding packets at up to 16 Mp/s with services enabled.  Thus, it can support the processing of the equivalent of 10 Gb/s of traffic at line rate, with services, even for small packets.

See the following for example:

Note at the beginning of the document:

"Numbers are given with 64 byte packet size, IP only"

The RTT really has nothing to do with anything, to be honest.

Second question:

In a TCP connection basically all packets sent after the first packet with the SYN flag set, have the ACK flag set.   I am wondering if you are asking is the ACK flag set on the ACK packets?  Perhaps the following explanation will help:

Keep in mind FTP can be passive or active.  Passive uses the same channel for data and control, active does not.  Read up on the differences and read the above explanation and then look at your setup and capture again.

Broadband (Cable, DSL, Satellite, Fiber Optics)

All Answers

Answers by Expert:

Ask Experts


Ted Mittelstaedt


I will answer questions on the following kinds of High Speed Internet connectivity; ISDN, Frame Relay, dedicated T1, higher speeeds such as DS3/OC3, wireless such as 802.11 and DSL. No questions on dialup V90 or Cable access. I can also answer questions on many types of Cisco routers, and a number of other brands of business routers as well.


I am the technical manager of Internet Partners Inc. an ISP.

I've written a book titled "The FreeBSD Corporate Networker's Guide" published by Addison Wesley

©2017 All rights reserved.