TCP Data Flood

TCP Data Flood

Last updated: January 16, 2009

This section is only applicable to the lab application.

This topic details the following:

8960 TCP Data Flood Overview

Testing the throughput of an IP-based packet switched data connection typically requires both a data source and a data sink. The requirements on the data source are usually straightforward and can often be summarized as "send data as fast as the air interface will allow". Most test environments use a generic PC or Linux server connected to the test set's LAN. This PC is colloquially referred to as the "server", because it is often running an FTP server. Sometimes the data sink will be the phone itself or another PC, often referred to as the "client" PC connected to the DUT and using the DUT as a modem.

The internal Data Generator functionality in the 8960 lab applications can be used to simplify your test environment by removing the need for an external "server" PC for simple throughput testing. As well as shortening test environment setup time this simplification typically results in more repeatable results as the configuration of Windows PCs, and their data throughput capabilities, can vary widely from one PC to another.

The two standard use-cases for throughput testing involve sending either UDP or TCP data as fast as the air interface will allow.

UDP does not impose any throughput restrictions of its own. UDP is a protocol which does not require any acknowledgements of the received data from the recipient of the transmission for retransmission of missed / bad blocks. It is therefore a good mechanism for testing the data throughput capable to almost theoretical limits but may not be completely representative of the end user experience.

TCP is used by common protocols like HTTP and FTP so is a good choice for measuring throughput that an actual user will experience, however end-to-end throughput can be restricted by TCP mechanisms in the server PC (such as receive window size and congestion control) that are not related to over-the-air capacity.

8960 TCP Data Flood Generator

The TCP data generator is an implementation of the RFC 864 CHARGEN service that runs on port 19 on the test set's protocol processor. Please note that a Special High Data Rate hardware test set is required (or a test set with the equivalent hardware upgrades). To use this feature, you simply establish a TCP connection with the test set on port 19 and the generator will start streaming data over the link as fast as possible for as long as the connection exists. The format of the transmitted data is the example described on page 3 of RFC 864 (http://www.ietf.org/rfc/rfc0864.txt). Any user data received over the TCP connection is discarded by the test set.

There are no user-settable configuration parameters associated with this feature.

Using the Character Generator and Discard Functions

Operating Considerations

Data Throughput Monitor and WPA

All traffic transmitted or received by the TCP data generator will be recorded as part of the IP and OTA lines on the Data Throughput Monitor and all IP traffic will also be logged to WPA under the IP logging point.

LAN and Internal Ping Functionality Interactions

Although the intention of the TCP generator is to keep the air interface link fully loaded with data the LAN port and internal ping functionality that is normally used to send data to the DUT are not disabled while either generator is active. This means that you can activate a data generator and still send packets to the DUT through either the external LAN port or internal ping functionality. However those packets have to compete with the active data generator for buffer space in the transmit queue so will likely experience high packet loss rates and possibly higher than normal latencies.

2-box Environment Interactions

In a two-box environment any traffic going to/from the data generators will follow the phone as it moves between boxes. This means that if you establish a connection to the TCP traffic generator on a particular box and then hand the phone over to the other box the TCP traffic generator will remain active.