Testing Sip Testcomm 2003 Slides

8/8/2019 Testing Sip Testcomm 2003 Slides

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Testing SIPUsing XML Protocol Templates

M. RanganathanOlivier Deruelle

Doug Montgomery Advanced Networking Technologies Division,

National Institute of Standards and Technology,Gaithersburg, MD 20899, USA.

http://www-x.antd.nist.gov/index.html


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Introducing SIP

Peer-to-peer Signaling Protocol used for IPTelephony, Conferencing and InstantMessagingIntroduced in 1999

9 revisions and 2 RFCs since then!

Widely deployed - Microsoft RTC Server,IM Client, Cisco gateways etc.


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Introducing SIP

Text basedunlike H.323

Stateless Protocol state encoded in message

ExtensibleMany extensions exist.

Can run over unreliable or reliable transportsOut of order / dropped signaling messages.


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Simple SIP Call Flow

INVITE

100 Trying

180 Ringing200 OKACK

OK

UASUAC

UAS User AgentServer

UAC User AgentClient

There can be intermediateSignaling nodes (Proxy Servers

that keep call state).

RTP Media Stream

BYE


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Protocol Complications

Protocol is robust and extensible:SIP keeps enough state in the Messages to deal withall these complications.

Correct implementation is tricky.Signaling may have to go through multiple hops.Proxy servers may go down without warning.

Peers may go down without warning.Sessions can move without prior planning.Network can fail without warning.


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SIP Testing

Load TestingGenerate 100s of simultaneous sessions.

Call Flow TestingUnit testing the SIP Protocol Implementationby generation of scenarios.Primary mode of testing during SIPinteroperability test events.


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Generating SIP Test Cases

Exhaustive testing generates too many testcases.

End-to-end testing is feasibleprotocol state and causality is encoded in theMessages/Call Flows.

Understanding implementationcomplexities results in good test cases.


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SIP Application Structure

Application

Network (Raw Bytes)

Parser Encoder

ReqReq Res

SIP Stack

T r a n s a c t i o n

T r a n

s a c t i o n

T r a n s a c t i o n

Req Res

Dialog DialogMessages

Events

Messages

Events

Messages

Events


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Constructing Test Cases For SIP

Layer the Test Cases like Applications/Stacks are layeredMessage Layer, Transaction Layer and DialogLayer testsThis prunes the number of tests and makes

the tests more meaningful.


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SIP Messages

Protocol encodes all the state it needs in themessage.HTTP/Mail like headers and a Request Line or aStatus Line.

SIP Components use Messages to Identify protocolabstractions.Protocol State is encoded in

Request URI, From, To, Via, CSeq, CallId, Max-ForwardsStateless components built directly on MessageLayer.


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Message Layer

Handle Incoming Requests/ResponsesRead Raw messages from Network.

Output Parsed Messages to Transaction layer.

Dispatch outgoing messagesInput Parsed Messages from TransactionLayer.Encode Parsed Messages and send out on

Network.


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Message Layer

Grammar is context sensitive and defined using ABNFGrammar has changed between RFCs

Grammar is compositional (mail, URL, HTTP)Parser generators have trouble with RFCgrammar

usually hand coded parsers are usedSome tools are available antlr

Headers are Text (Body can be Binary)


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Transaction Layer

SIP Applications are transaction orientedand usually interact directly with atransaction layer.Primary duties of the Transaction Layer

Request Response matchingRetransmission handling for unreliable media.Timeout handling


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Transaction Layer: Common Bugs

Implementations do not implement theTransaction State Machine correctly

Implementations have difficulty keepingbackward compatibilityIn RFC 3261 the branch ID of the topmost

Via header identifies the TransactionRFC 2543 used a hash over From, To, RequestURI and Via headers


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Transaction Layer TestingTesting the State Machine

Simulate lost messagesDrop Requests/Responses

Simulate timing variationsDelay Responses

Generate out of order responses Simulate stray messagesCANCEL messages for Server Transactions that do notexist.

Late CANCELS

Late ACKsDuplicate ACKsOut of Sequence messages.


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Transaction Layer TestingTransaction matching / identification

Via Header branch parameter variationsRFC 3261 relies on this for matching

Variations in From / To, Request URI andCSeq Sequence Number and CSeq MethodRFC 2543 relies on this for matching.


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Dialog Layer

Dialog is a peer-to-peer association betweencommunicating SIP endpointsDialogs established by Dialog creating Transactions.

Not all transactions create Dialogs. A Transaction may belong to exactly one Dialog.

SIP messages carry enough state to identify theDialog directly from the message


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Dialog Layer

Manages Dialog Creation/TeardownDialogs created by transaction completion

Manages Route SetsTest agent must test for expected Route / Record-Route headers in requests

Manages Sequence NumbersTest agent must test for sequence number assignmentManages the Request URI


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Dialog Layer: Common Bugs

Dialogs are identified by portions of amessage:CallID, From, To tags in RFC 3261CallID, From, To addresses RFC2543Stacks try to keep backward compatibility

Bugs are frequently caused by tagmanagement problems.


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Testing the Dialog Layer

Requests/Responses within and outsideDialogRequests/Response for Spurious Dialogs

Variation in From/To Headers and TagsGenerate Requests for Dialogs that do notexist.

CSeq Header Sequence number variationsOut of sequence message arrivals


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Call Flow Testing Approach

Test the causal sequence of messagesrequired to establish and release SIP CallsSIP Protocol Template an XML patternfor a SIP Call Flow.XML Pattern input to a customizable useragent which can run the Call Flow(Responder)


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Motivation

XML is hierarchical good way to represent SIP protocolabstractions

Interoperability testing with controlTypically components are tested in call flowscenariosTypically operating in an un-controlledenvironment

Reproducing complex scenarios is difficult


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XML representation of SIP

Define a set of XML tags to represent therequired headers in a SIP messageDefine XML tags to express call flow statemachineInput to Event Engine that can run the call

flowGenerate variations of the call flow bymodifying the XML script


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Test Scripting Architecture

Call Flow Testing Protocol Template

Event Engine

NIST-SIP Stack

Service Function

Service Script a callout toa service function at transitionpoints in the call flow.

Service ContainerXML Engine + Java/Jythoninterpreter

Network

XML Tags Mirror Protocol


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XML Tags Mirror ProtocolStructure


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Test Script

Pattern matching, timer events and transitions used fortriggering transitions in test script.Test script is represented by a set of Transactions thatmay be nested within a dialog.

The entire transaction state machine is exposed anddefined using XML.

Timing can be varied and controlled errors can be created.

Service code can be called when messages arrive,transactions are started, transactions complete, dialogsare created or dialogs complete.


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Why Do It?

Simple, clear expression of test scenariosProtocol maps to XML script one to oneCan generate multiple scenarios based onsmall variations for the same call flow.Can simulate common end-point (User

Agent) behavior.Can generate controlled errorconditions/timing variations.


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Test Log File Collection

Log file is a diagnostic tool to help debugprotocol problems.Stack generates log files using XML format.

Distributed traces are collated at test proxyTrace viewer pairs arcs by Transactions

Proxy Trace viewer (Java Applet)

Responder UALocal Trace

Local Trace RMI


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Visualizing the Trace

Java Appletcollects andvisualizesdistributed callflow trace files.

Augmented withXML script stateinformation.Enables

debugging callflows & testscripts.


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Related work

TTCN testing of SIPProcedural test casesNot explicitly tailored to SIP

Using our approachSimplifies logical designXML tools can be used for test case design.

http://www-x.antd.nist.gov/proj/iptel


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Extensions and Future Work

Standardize XML representation of the SIPprotocolOff line protocol verification

Generation of Call flows based on message logs Verification of traces based on message logs

Customizable test scriptsExtensions to service creation.

Integration with other distributed scriptingtechnologiesJXTA, SOAP

Testing Sip Testcomm 2003 Slides

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