Improving a Traffic Generator and Analyzer Test-tool for

Media Gateway- Support for Real-time Transfer Protocol (RTP) and RTP Control

Protocol (RTCP) added

Aino Aarni

Objectives and research questions• Study RTP and RTCP protocols and their usage in Media

Gateway• Investigate which features of RTP and RTCP should be

tested in a specific test phase• Study the traffic generator and analyzer test-tool used in

the test phase• Investigate how the test-tool must be improved in order to

be able to use it also for RTP and RTCP testing• Investigate how the features should be implemented in the

test tool• The implementation of sufficient RTP/RTCP support in the

test-tool

Media Gateway

Media Gateway is the connecting node between 2G and 3G networks and other networks (e.g. PSTN, other

Mobile Networks and IP networks)

Core Network

Acces Network

Functions of Media Gateway

• Signaling functions

• Traffic control functions

• Operation and Maintenance functions

• Speech processing functions

Speech processing in Media Gateway

– Speech encoding and decoding (for example AMR to PCM and PCM to AMR)

– Voice quality enhancement– Termination of transfer protocols (Iu-protocol

for 3G termination)

RTP and RTCP in Media Gateway• Speech transfer over IP is replacing the

traditional speech transfer over ATM inside 3G mobile networks

• It must be possible to establish connections between mobile networks and external IP-networks utilizing Voice-over-IP (VoIP)

RTP is needed for carrying speech over IP

RTCP is needed for ensuring the Quality of Service in RTP connections

Therefore full Support for RTP and RTCP was implemented in Media Gateway. This also evoked a need to improve the test environment of Media Gateway with support for RTP and RTCP

Real-time Transfer Protocol (RTP) and RTP Control Protocol (RTCP)• RTP is a data transport protocol for real-time

applications• Used especially for audio and video transfer• RTP is carried on top of UDP/IP/Ethernet

protocols• No Quality-of-Service –functions

• RTCP provides QoS-services for RTP connections by sending periodic RTCP messages on side on RTP data

• RTCP messages contain statistical information about the RTP connection, for example the number of sent packets, received packets, lost packets etc.

• RTCP messages are sent in compound RTCP packet which may contain

– Receiver Report (information about received data)– Sender Report (information about sent and received

data)– Source Description (name of the source)– Bye message (indicates ending the RTP connection)

UDP = User datagram protocol

IP = Internet Protocol

Testing the Speech Processing functions of Media Gateway• Smart testing is done in several phases and as early as possible• Media Gateway is tested in several phases one of which is testing the

speech processing functions as one• Testing a part of a device requires special test environment and test tools• Test environment where the speech processing functions of Media

Gateway are tested:

Guidelines in Test-tool Development• Purpose of testing is to: [1]

1. Ensure the software does what it is supposed to do2. Reveal faults in the software3. Ensure the software does not do anything that it is not supposed to do4. Have confidence that the system performs sufficiently well for its purpose5. Understand how far the software can be pushed before failing or crashing6. Understand the risk in releasing the software– The first three are most important in low-level testing which is the case here

• Testing should be as complete as possible. [2]• It may, however, not be wise (or possible) to test everything in every test phase [2]

• Properties of a good test tool: [3]– Suitable for its purpose– Re-usable– Reliable– Easy to use

1. Watkins, J. 2001, “Testing IT: An Off-the-Shelf Software Testing Handbook”. Port Chester, NY, USA: Cambridge University Press.

2. Gao, J. 2003 “Testing and Quality Assurance for Component-Based Software” Norwood, MA, USA: Artech House

3. Spillner, A. & Rossner, T. & Winter, M & Linz, T. 2007. “Software Testing Practise: Test Management” Santa Barbara, USA: Rocky Nook.

What should be tested about RTP and RTCP

Speech processing parts in Media Gateway must handle:

• Sending and receiving RTP traffic

• Sending and receiveing RTCP packets

• Updating statistical values describing an RTP connection

• Using the above mentioned values correctly when forming RTCP packets

• Peer alivenes supervision ( = noticing a situation in which the peer has not sent anything for 15 seconds)

The Implementation – What was included in the test-tool• Adding RTP-header on top of outgoing data and sending

the frames• Removing RTP-header from incoming data before analyzing

the received frames• Forming and sending RTCP Sender Reports in five seconds

interval• Forming and sending RTCP Receiver Reports in five

seconds interval• Collecting, updating and storing six statistical values about

the RTP connection for forming RTCP packets• Separating incoming RTCP packets from RTP-data and

printing the data in received RTCP packets for the user

The Implementation –What was excluded from the test-tool• Sending RTCP Source Description messages

– These are ignored and not utilized by Media Gateway• Sending RTCP Bye messages

– Sending these was tested in an earlier test phase and nothing new was added

– (Would also have required changes in the other test environment)

• Collecting, updating and storing ten statistical values about the RTP connection for forming RTCP packets– The values in the RTCP messages could be replaced by zeros

or other static value as Media Gateway does not utilize these values anyhow

– No purpose to use much memory for saving and updating these

• Automatic analysis of incoming RTCP packets– Would have required a heavy algorithm running DSP although

this can be done elsewhere in the test environment as well

The Implementation

• Implemented using standard C• Tested in a simulated environment before

taking into use• The improved tool and the support for RTP

and RTCP in it are in use• Future improvements of the test-tool

depend on the improvements in Media Gateway and RTP / RTCP utilization

Thank you!

Questions?