8-Designing and Deploying a VoIP Network

8/8/2019 8-Designing and Deploying a VoIP Network

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Designing and deployingDesigning and deploying

a VoIP network a VoIP network When ITU meets IETF When ITU meets IETF

Thomas(at)Kernen.Net Thomas(at)Kernen.Net


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A quick VoIP recap A quick VoIP recapDi rectory Gatekeeper ( D GK): Performs call rout ing search atDi rectory Gatekeeper ( D GK): Performs call rout ing search athighest level (ex: country code distrib utes). Country codeshighest level (ex: country code distrib utes). Country codesamong other D GKs Forward LRQ (locat ion request) to aamong other D GKs Forward LRQ (locat ion request) to apartner D GK if call doesn't term inate in local SP D GK partner D GK if call doesn't term inate in local SP D GK Gatekeeper (GK): Performs call rout ing search at intermed iateGatekeeper (GK): Performs call rout ing search at intermed iatelevel (ex: NPAlevel (ex: NPA--NXX). Di strib utes NPA among other GKs.NXX). Di strib utes NPA among other GKs.Prov ides GW resource management (Ressource Ava ilabi lty Prov ides GW resource management (Ressource Ava ilabi lty Ind icator, gw Ind icator, gw--priority, ....)priority, ....)Gateway (GW): Acts as interface b etween the PSTN and IP.Gateway (GW): Acts as interface b etween the PSTN and IP.Normal iz es numb ers from PSTN b efore enter ing IP. Normal iz esNormal iz es numb ers from PSTN b efore enter ing IP. Normal iz esnumb ers from the IP b efore enter ing the PSTN. Conta ins thenumb ers from the IP b efore enter ing the PSTN. Conta ins thedialdial--peer conf iguration. Reg isters w ith the GK.peer conf iguration. Reg isters w ith the GK.


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Gatekeeper A Gatekeeper B

RRQ/RCF

ARQ

RRQ/RCF

LRQ

IP Network

Phone A

Gateway A Gateway B

H.225 (Q.931) Setup

H.225 (Q.931) Alert and ConnectH.245

RTP

ACF

LCF

VV

B asic H.323 CallB asic H.323 Call

VV

ARQ

ACF

Phone B


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Various Codec B andwidth Various Codec B andwidthConsumptionsConsumptions

E ncoding/Compression

ResultBit Rate

G.711 PCMA-Law/ u -Law

64 kbps (DS0)

G.726 ADPCM 16, 24, 32, 40 kbps

G.727 E -ADPCM

G.729 CS-AC E LP 8 kbps

G.728 LD-C E LP 16 kbps

G.723.1 C E LP 6.3/5.3 kbpsVariable

16, 24, 32, 40 kbps

StandardTransmissionRate for Voice


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Cisco Encoding ImplementationCisco Encoding Implementation

= Sample

8 kHz (8,000 Samples/Sec)

= 0010110101

IP QoS WAN

E ncode Decode

20 Byte packet every 20ms (50pps)

8kbps Data RateNote - This 8bkps for Voice Payload only!!

Add on 40 bytes of IP/UDP/RTP and you now have 24kbps!RTP Header Compression will take this down to 11.2kbps


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Voice Quality of Service (QoS) Voice Quality of Service (QoS)RequirementsRequirements

Loss

Delay

Delay Variation (Jitter)

Avoiding The 3 Main QoS Challenges


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L oss and Delay SourcesL oss and Delay Sources

Input queuing

Jitter buffer

COD E C (Decode)

Access (up) link transmission

Backbone network transmission

Access (down) link transmission

COD E C ( E ncode)

Packetization

Output queuingVoice Path

Loss+

Delay+

Delay

Variation


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DelayDelay How Much Is Too Much?How Much Is Too Much?Cumulative Transmission Path Delay

Time (msec)

0 100 200 300 400

CB ZoneCB Zone

Satellite QualitySatellite QualityFax Relay, BroadcastFax Relay, BroadcastHigh QualityHigh Quality

Delay Target

500 600 700 800

ITUs G.114 Recommendation = 0 150msec 1-way delay


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F ixed Delay ComponentsF ixed Delay Components

PropagationPropagations ix microseconds per k ilometersix microseconds per k ilometer

Serializ ationSerializ ation

Processing Processing Coding/compress ion/decompress ion/decod ing Coding/compress ion/decompress ion/decod ing

Packetiz

ationPacket

izat

ion

Processing Delay

Propagation DelaySerialization DelayBuffer to Serial Link


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Variable Delay Components Variable Delay Components

Queu ing delay Queu ing delay D ejitter b uffersD ejitter b uffers

Var iab le packet siz es Var iab le packet siz es

Dejitter Buffer

QueuingDelay

QueuingDelay

QueuingDelay


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56kb WAN

L arge Packets F reeze OutL arge Packets F reeze Out

Voice Voice

Large packets can cause play b ack b ufferLarge packets can cause play b ack b ufferunderrun, result ing in slight voice degradationunderrun, result ing in slight voice degradation

Jitter or play b ack b uffer can accommodate Jitter or play b ack b uffer can accommodatesome delay/delay var iationsome delay/delay var iation

~ 214ms Serialization Delay

10mbps E thernet 10mbps E thernet

Voice Packet60 bytes

E very 20ms

Voice 1500 bytes of Data Voice


E very >>214ms


E very >214ms>214ms




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RTP Controlling Dejitter B ufferRTP Controlling Dejitter B uffer

RTP Timestamp From Router AInterframe gap of 20ms

CC

Sender Receiver

IPNetwork

VV VV

BB AA

RouterA RouterB

10 30 50

20ms 20ms

RTP Timestamp From Router AVariable Interframe Gap (Jitter)

CC BB AA10 30 50

20ms 80ms

RTP Timestamp From Router ADelitter Buffer removes Variation

CC BB AA10 30 50

20ms 20ms


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Calculate Delay B udgetCalculate Delay B udget -- Worst Case Worst Case

PropagationDelay8 ms

Coder Delay25 ms

Serialization Delay2 ms

Dejitter Buffer 50 ms

QueuingDelay4 ms

Site A Site B

(128kbps Frame Relay)

Total 89 msecDejitter Buffer 50 msec

Min 8 msecNetwork Delay (e.g.,Public Frame Relay Svc)

Serialization Delay 128 kbps Trunk 2 msec4 msecQueuing Delay 128 kbps Trunk

5 msec

Packetization DelayIncluded in Coder Delay

Coder Delay G.729 (5 msec look ahead)

Propagation Delay (Private Lines)

FixedDelay

VariableDelay

Coder Delay G.729 (10 msec per frame) 20 msec


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F ragmentation and InterleavingF ragmentation and Interleaving

Serializ ation delay for 64K b ps link w ith an MTUSerializ ation delay for 64K b ps link w ith an MTUof 1500 b ytesof 1500 b ytes

(1500b

ytes x 8bi

ts/b

yte) / (64000bi

ts/sec) =(1500b

ytes x 8bi

ts/b

yte) / (64000bi

ts/sec) =187.5ms187.5msFragmentat ion siz e: design for 10ms fragmentsFragmentat ion siz e: design for 10ms fragments

(0.01 sec x 64000b

ps) / (8bi

ts/b

yte) = 80b

ytes(0.01 sec x 64000b

ps) / (8bi

ts/b

yte) = 80b

ytesIt takes 10 ms to send an 80 b yte packet orIt takes 10 ms to send an 80 b yte packet or

fragment over a 64k b ps link.fragment over a 64k b ps link.


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F ixed F rame Serialization DelayF ixed F rame Serialization DelayMatrixMatrix

Frame Size

LinkSpeed

56kbps

64kbps

128kbps

256kbps

512kbps

768kbps

1536kbs

1Byte

143us

125us

62.5us

31us

15.5us

10us

5us

64Bytes

9ms

8ms

4ms

2ms

1ms

640us

320us

18ms

128Bytes

16ms

8ms

4ms

2ms

1.28ms

640us

36ms

256Bytes

32ms

16ms

8ms

4ms

2.56ms

1.28ms

72ms

512Bytes

64ms

32ms

16ms

8ms

5.12ms

2.56ms

144ms

1024Bytes

128ms

64ms

32ms

16ms

10.24ms

5.12ms

1500Bytes

46ms

214ms

187ms

93ms

23ms

15mss

7.5ms


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Multilink PPP withMultilink PPP withF

ragmentation and InterleaveF

ragmentation and Interleave

E lastic Traffic MTUReal-Time MTU

64 kbps Line

E lastic MTU Real-Time MTUE lastic MTU E lastic MTU

Addendum to PPP Specification

187ms Serialization Delayfor 1500 byte Frame at 64 kbps

64 kbps Line


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Media L ink L ayer OverheadMedia L ink L ayer Overhead

Layer 2 Media Layer 2Header Size

E thernet 14 bytes

PPP/MLPPP 6 bytes

Frame Relay

ATM (AAL5) 5 bytes + waste5 bytes + waste

MLPPP over FR 14 bytes

MLPPP over ATMMLPPP over ATM 5 bytes for every ATM cell5 bytes for every ATM cell+ 20 bytes for MLPPP/AAL5+ 20 bytes for MLPPP/AAL5

6 bytes6 bytes


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RTP Header CompressionRTP Header Compression

2 0ms@8k b /s y ields 2 0 b yte2 0ms@8k b /s y ields 2 0 b ytepayloadpayloadIP header 2 0; UD P header 8; RTPIP header 2 0; UD P header 8; RTP

header 12

header 12

2 X payload!!!!!!!!2 X payload!!!!!!!!

Header compress ion 40Bytes to 2Header compress ion 40Bytes to 2 --4 much of the t ime4 much of the t ime

HopHop--b y b y--HopHop ononslow links


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RTP Header compression detailsRTP Header compression details

Can save a lot of b andw idth (>50%) per flow.Can save a lot of b andw idth (>50%) per flow. Works on ser ial links b etween 2 routers Works on ser ial links b etween 2 routers

CPU intens i ve, might overk ill the routersCPU intens i ve, might overk ill the routersLimited to 2 56 sessions (12 8 calls) over FR Limited to 2 56 sessions (12 8 calls) over FR Limited to 1000 sessions (500 calls) over HD LCLimited to 1000 sessions (500 calls) over HD LC

(checked in 12 .2 (8)T)(checked in 12 .2 (8)T)Not recommend on l inks w ith data rates ab oveNot recommend on l inks w ith data rates ab oveE1E1


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Silence suppressionSilence suppression

VA D (Vo ice Acti v ity D etection) (Cisco) VA D (Vo ice Acti v ity D etection) (Cisco)Codec b uiltCodec b uilt--in silence suppressionin silence suppression

(G.729

a/G.723

.1b )(G.7

29a/G.7

23.1

b )

Should not b e taken into account for c ircuitsShould not b e taken into account for c ircuitscarry ing less than 2 4/ 3 0 calls since b ased oncarry ing less than 2 4/ 3 0 calls since b ased onaggregate volume, not indi v idual calls.aggregate volume, not indi v idual calls.Should not b e taken into account whenShould not b e taken into account wheneng ineering the network.eng ineering the network.


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IP Precedence/DSCPIP Precedence/DSCP

D SCPD SCP -- Di fferent iated Serv ices Code Po intDi fferent iated Serv ices Code Po int(RFC 2 474(RFC 2 474--2 475)2 475)

Set IP Precedence/D

SCP higher for VoIP.Set IP Precedence/

DSCP h

igher for VoIP.Usually set to 5/101000Usually set to 5/101000

Set at source (gateway) if possib le for less hassle.Set at source (gateway) if possib le for less hassle.


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Queuing mechanismsQueuing mechanisms(in Ciscos world)(in Ciscos world)

FIFO, F irst In F irst OutFIFO, F irst In F irst OutPackets arri ve and leave the queue in exactly the same orderPackets arri ve and leave the queue in exactly the same orderSimple conf iguration and fast operat ionSimple conf iguration and fast operat ionNo Pr iority serv icing or b andw idth guarantees poss ib leNo Pr iority serv icing or b andw idth guarantees poss ib le

WFQ, We ighted Fair Queu ing WFQ, We ighted Fair Queu ing A hash ing algorithm, places flows into separate queues where A hash ing algorithm, places flows into separate queues where weights are used to determ ine how many packets are serv iced at weights are used to determ ine how many packets are serv iced ata time. You def ine weights b y setting IP Precedence and D SCPa time. You def ine weights b y setting IP Precedence and D SCP

values. values.Simple conf iguration.Simple conf iguration.No pr iority serv icing or b andw idth guarantees poss ib le.No pr iority serv icing or b andw idth guarantees poss ib le.


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Queuing mechanisms (2)Queuing mechanisms (2)CQ, Custom Queu ing CQ, Custom Queu ing

Traff ic is classif ied into mult iple queues w ith conf igurab le queue limits. Traff ic is classif ied into mult iple queues w ith conf igurab le queue limits.Has b een availab le for a few years and allows approximate b andw idthHas b een availab le for a few years and allows approximate b andw idthallocation for d ifferent queues.allocation for d ifferent queues.No pr iority serv icing possib le. Bandw idth guarantees are approx imate andNo pr iority serv icing possib le. Bandw idth guarantees are approx imate andthere are a limited numb er of queues. Conf iguration is relati vely diff icult.there are a limited numb er of queues. Conf iguration is relati vely diff icult.

PQ, Pr iority Queuing PQ, Pr iority Queuing Traff ic is classif ied into h igh, medium, normal and low pr iority traff ic is Traff ic is classif ied into h igh, medium, normal and low pr iority traff ic isserv iced f irst, then med ium pr iority traff ic, followed b y normal and low serv iced f irst, then med ium pr iority traff ic, followed b y normal and low priority traff ic.priority traff ic.Has b een availab le for a few years and prov ides priority serv icing.Has b een availab le for a few years and prov ides priority serv icing.H igher priority traff ic can starve lower priority queues of b andw idth. NoH igher priority traff ic can starve lower priority queues of b andw idth. Nob andw idth guarantees poss ib le.b andw idth guarantees poss ib le.


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Queuing mechanisms (3)Queuing mechanisms (3)CBWFQ, Class Based Weighted Fair Queu ing CBWFQ, Class Based Weighted Fair Queu ing MQC is used to classify traff ic. Classif ied traff ic is placed into reservedMQC is used to classify traff ic. Classif ied traff ic is placed into reservedb andw idth queues or a default unreserved queue.b andw idth queues or a default unreserved queue.Similar to LLQ except there is no pr iority queue. Simple conf iguration andSimilar to LLQ except there is no pr iority queue. Simple conf iguration andabi lity to prov ide b andw idth guarantees. No pr iority serv icing possib le.abi lity to prov ide b andw idth guarantees. No pr iority serv icing possib le.

PQPQ--WFQ, Pr iority queue WFQ, Pr iority queue--Weighted Fair Queu ing (IP RTP Pr iority) We ighted Fair Queu ing (IP RTP Pr iority)Single interface command is used to prov ide pr iority serv icing to all UD PSingle interface command is used to prov ide pr iority serv icing to all UD Ppackets destined to even port num b ers w ithin a specif ic range.packets destined to even port num b ers w ithin a specif ic range.Simple, one command conf ig. Prov ides priority serv icing to RTP packets.Simple, one command conf ig. Prov ides priority serv icing to RTP packets.

All other traff ic is treated w ith WFQ. RTCP traff ic is not pr ioritiz ed. No All other traff ic is treated w ith WFQ. RTCP traff ic is not pr ioritiz ed. Noguaranteed b andw idth capabi lity.guaranteed b andw idth capabi lity.

Note: MQC = Modular QoS CLINote: MQC = Modular QoS CLI


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Queuing mechanisms (4)Queuing mechanisms (4)Low Latency Queueing (LLQ) = Pr iority Queue (PQ)+ ClassLow Latency Queueing (LLQ) = Pr iority Queue (PQ)+ ClassBasedBased--Weighted Fair Queue (CB We ighted Fair Queue (CB--WFQ). WFQ).

Allows a strict Pr iority Queue to handle a def ined class of packet Allows a strict Pr iority Queue to handle a def ined class of packetto b e prioritiz ed over all other traff ic.to b e prioritiz ed over all other traff ic.

Simple conf ig, abi lity to prov ide pr iority to mult iple classes of Simple conf ig, abi lity to prov ide pr iority to mult iple classes of traff ic and g i ve upper b ounds on pr iority b andw idth ut iliz ation.traff ic and g i ve upper b ounds on pr iority b andw idth ut iliz ation.Can also conf ig b andw idth guaranteed classes and a default class.Can also conf ig b andw idth guaranteed classes and a default class.

All priority traff ic is sent throught the same pr iority queue which All priority traff ic is sent throught the same pr iority queue whichcan introduce j itter.can introduce j itter.

Note: C isco appears to b e work ing on improv ing LLQ and th is isNote: C isco appears to b e work ing on improv ing LLQ and th is iscurrently the #1 queu ing mechanism according to SEs, TAC andcurrently the #1 queu ing mechanism according to SEs, TAC andupdated documentat ion.updated documentat ion.


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Traffic Traffic EngineeringEngineeringBusy Hour (BH) = Num b er of lines required to support theBusy Hour (BH) = Num b er of lines required to support the

worst hour of the day worst hour of the day Grade of serv ice (GOS) = Percentage of l ines that w illGrade of serv ice (GOS) = Percentage of l ines that w illexperience a b usy tone on the 1st attempt dur ing the BHexperience a b usy tone on the 1st attempt dur ing the BH

A GOS of 0.05 means 5 out of 100 callers m ight get a b usy tone A GOS of 0.05 means 5 out of 100 callers m ight get a b usy toneErlang B, most w idely used traff ic model to est imate the num b erErlang B, most w idely used traff ic model to est imate the num b erof lines required for a spec if ic GOS and BH of traff ic.of lines required for a spec if ic GOS and BH of traff ic.Based on various traff ic assumptions such as call queueing,Based on various traff ic assumptions such as call queueing,arri val rate, etc...arri val rate, etc...

1 trunk in use for 1 hour = 1 Erlang = 3 6 CCS of traff ic1 trunk in use for 1 hour = 1 Erlang = 3 6 CCS of traff ic1 Centrum Call Seconds (CCS) = 100 call seconds1 Centrum Call Seconds (CCS) = 100 call seconds1 hour = 3 600 seconds or 3 6 CCS = 1 Erlang 1 hour = 3 600 seconds or 3 6 CCS = 1 Erlang


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Traffic Traffic Engineering (2)Engineering (2)

Step1: Ob tain voice traff ic dataStep1: Ob tain voice traff ic dataSources of traff ic informat ion: CD Rs (Call D etailSources of traff ic informat ion: CD Rs (Call D etailRecord) or carrier bi lls, carrier stud ies, traff ic reportsRecord) or carrier bi lls, carrier stud ies, traff ic reportsD ata needs to b e adjusted for call processing since aD ata needs to b e adjusted for call processing since atrunk in use = Di aling + Call setup + R ing ing +trunk in use = Di aling + Call setup + R ing ing +

Talk ing + Releasing Talk ing + Releasing

Other sources: R ing No Answer, Busy S

ignal, etcOther sources: R

ing No Answer, Busy S

ignal, etc

Add 10% to 16% to all call lengths/total t ime estimates. Add 10% to 16% to all call lengths/total t ime estimates.


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Traffic Traffic Engineering (3)Engineering (3)

Step 2 : Convert to ErlangsStep 2 : Convert to Erlangs Adjusted total hours a month / b usiness days * Adjusted total hours a month / b usiness days *% of traff ic in b usy hour% of traff ic in b usy hourStep 3 : Calculate the numb er of vo ice linesStep 3 : Calculate the numb er of vo ice linesBased on stat istical model for the # of l ines vsBased on stat istical model for the # of l ines vsthe grade of serv ice desiredthe grade of serv ice desired

Step 4: Calculate the data network b andw idthStep 4: Calculate the data network b andw idth(Codec + protocol overhead) * num b er of vo ice(Codec + protocol overhead) * num b er of vo icelines = requ ired b andw idthlines = requ ired b andw idth


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POPPOP SizingSizing

Calculate the numb er of gateways (GW) required toCalculate the numb er of gateways (GW) required tohandle ant icipated call volumehandle ant icipated call volumeUse Busy Hour Call Attempts (BHCA) metr icUse Busy Hour Call Attempts (BHCA) metr ic

Calculate the numb er of ( Di rectory) GatekeepersCalculate the numb er of ( Di rectory) Gatekeepersrequired to process the GW s ignaling required to process the GW s ignaling GWs = max E1s per GW, BHCA, CPS (Calls perGWs = max E1s per GW, BHCA, CPS (Calls perSecond)Second)

GKs = max CPS (check w ith vendor, not an o b v iousGKs = max CPS (check w ith vendor, not an o b v iousf igure to get, varies w ith eachf igure to get, varies w ith eachchassis/conf iguration/software release/ D SP rev)chassis/conf iguration/software release/ D SP rev)


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Tips & tricks Tips & tricks

Build GK redundancy b y mak ing sure all GWsBuild GK redundancy b y mak ing sure all GWshave multiple GKs to reach. HSRP can b e very have multiple GKs to reach. HSRP can b e very useful in conjunct ion w ith mult iple GW useful in conjunct ion w ith mult iple GW-->GK >GK destinations.destinations.Make sure the GWs normal iz e the format of theMake sure the GWs normal iz e the format of thecalled numb ers so the VoIP core deals w ith acalled numb ers so the VoIP core deals w ith asingle call format (E.164 = country+c ity+local).single call format (E.164 = country+c ity+local).


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Inter provider VoIP servicesInter provider VoIP services

What happens when you want to extend the reach What happens when you want to extend the reachof your VoIP serv ices b y interconnect ing w ithof your VoIP serv ices b y interconnect ing w ithother ITSP?other ITSP?

Tandem cod ing (VoIP Tandem cod ing (VoIP-->PSTN>PSTN-->VoIP)>VoIP)Open Settlement ProtocolOpen Settlement Protocol


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Tandem Coding Tandem Coding

In the case where a call is passed b ack from the VoIPIn the case where a call is passed b ack from the VoIPnetwork to the PSTN and then resampled &network to the PSTN and then resampled &compressed the call has b een sampled and compressedcompressed the call has b een sampled and compressedtw ice and therefore the call quality w ill degrade very tw ice and therefore the call quality w ill degrade very rapidly.rapidly.

Examples:Examples: VoIP to GSM v ia the PSTN. VoIP to GSM v ia the PSTN. VoIP to the PSTN v ia another carr ier w ith compress ion VoIP to the PSTN v ia another carr ier w ith compress ion

gear.gear.Other VoIP carr ier doesnt want to r isk interconnectsOther VoIP carr ier doesnt want to r isk interconnects

over VoIP ( interover VoIP ( inter--ITSP QoS management issues)ITSP QoS management issues)


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OpenOpen Settlement ProtocolSettlement Protocol (OSP)(OSP)Open Settlement Protocol (OSP), cl ientOpen Settlement Protocol (OSP), cl ient--server protocol def ined b y the ETSIserver protocol def ined b y the ETSI

TIPHON standards organ iz ation. D esigned to offer bi lling and account ing TIPHON standards organ iz ation. D esigned to offer bi lling and account ing record consol idation for vo ice calls that traverse ITSP b oundar ies. It alsorecord consol idation for vo ice calls that traverse ITSP b oundar ies. It alsoallows serv ice prov iders to exchange traff ic w ith each other w ithoutallows serv ice prov iders to exchange traff ic w ith each other w ithoutestab lishing multiple bi lateral peering agreements b y using a 3 rd party estab lishing multiple bi lateral peering agreements b y using a 3 rd party clearinghouse to ena b le extending the reach of the ir network.clearinghouse to ena b le extending the reach of the ir network.

3 rd party clearinghouse w ith an OSP server w ill allow serv ices such as route3 rd party clearinghouse w ith an OSP server w ill allow serv ices such as routeselection, call authoriz ation, call accounting, and interselection, call authoriz ation, call accounting, and inter--carrier settlements,carrier settlements,including all the complex rating and rout ing tab les necessary for eff icient andincluding all the complex rating and rout ing tab les necessary for eff icient andcostcost--effecti ve interconnect ions. The OSP b ased clearinghouses prov ide theeffecti ve interconnect ions. The OSP b ased clearinghouses prov ide theleast cost and the b est routeleast cost and the b est route--selection algorithms b ased on the a w ide variety selection algorithms b ased on the a w ide variety of parameters.of parameters.


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How How it worksit worksStep 1: customer places call v ia the PSTN to a VoIP Gateway, wh ichStep 1: customer places call v ia the PSTN to a VoIP Gateway, wh ichauthent icates the customer b y communicating w ith a RAD IUS serverauthent icates the customer b y communicating w ith a RAD IUS serverStep 2 : The orig inating VoIP gateway attempts to locate the term ination po intStep 2 : The orig inating VoIP gateway attempts to locate the term ination po int

w ithin it's own network b y communicating w ith a gatekeeper using H.323 w ithin it's own network b y communicating w ith a gatekeeper using H.323 RAS. If there's no appropr iate route, the gatekeeper tells the gateway toRAS. If there's no appropr iate route, the gatekeeper tells the gateway to

search for a termi

nati

on poi

nt elsewhere.search for a termi

nati

on poi

nt elsewhere.Step 3 : The gateway contacts an OSP server at the 3 rd party clearinghouse.Step 3 : The gateway contacts an OSP server at the 3 rd party clearinghouse. The gateway estab lishes an SSL connection to the OSP server and sends an The gateway estab lishes an SSL connection to the OSP server and sends anauthor iz ation request to the clear inghouse. The author iz ation request conta insauthor iz ation request to the clear inghouse. The author iz ation request conta inspertinent informat ion ab out the call, including the dest ination num b er, thepertinent informat ion ab out the call, including the dest ination num b er, thedev ice ID , and the customer I D of the gateway.dev ice ID , and the customer I D of the gateway.Step 4: The OSP server processes the informat ion and, assum ing the gateway Step 4: The OSP server processes the informat ion and, assum ing the gateway is author iz ed, returns rout ing details for the poss ib le terminating gatewaysis author iz ed, returns rout ing details for the poss ib le terminating gatewaysthat can sat isfy the request of the or ig inating gateway.that can sat isfy the request of the or ig inating gateway.


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How it works (2How it works (2) )

Step 5: The Clearinghouse creates an author iz ationStep 5: The Clearinghouse creates an author iz ationtoken, signs it w ith the cert if icate and pr i vate key, andtoken, signs it w ith the cert if icate and pr i vate key, andthen repl ies to the or ig inating gateway w ith a token andthen repl ies to the or ig inating gateway w ith a token and

up to3

selected routes. The ori

g i

nati

ng gateway usesup to3

selected routes. The ori

g i

nati

ng gateway usesthe IP address suppl ied b y the clearinghouse to setupthe IP address suppl ied b y the clearinghouse to setupthe call.the call.Step 6: The orig inating gateway sends the token itStep 6: The orig inating gateway sends the token itrecei ved from the settlement server in the setuprecei ved from the settlement server in the setupmessage to the term inating gateway.message to the term inating gateway.Step 7: The term inating gateway accepts the call afterStep 7: The term inating gateway accepts the call after

validating the token and completes the call setup. validating the token and completes the call setup.


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Voice Speech Quality (VSQ) Voice Speech Quality (VSQ)MOS: ITU P.800 & P.8 3 0, scale from 1 ( b ad) to 5 (excellent),MOS: ITU P.800 & P.8 3 0, scale from 1 ( b ad) to 5 (excellent),b ased on human percept ion (sub jecti ve), most w idely used b y b ased on human percept ion (sub jecti ve), most w idely used b y

VoIP vendors when compar ing codec quality, the oldest model. VoIP vendors when compar ing codec quality, the oldest model.PSQM (Perceptual Speech Quality Measurement), ITU P.861,PSQM (Perceptual Speech Quality Measurement), ITU P.861,

comparesinput and output speech (automated), developed

by compares

input and output speech (automated), developed

by KPN ResearchKPN Research

PAMS (Perceptual Analysis Measurement System), D evelopedPAMS (Perceptual Analysis Measurement System), D evelopedb y British Telecom, O b jecti vely predict results of sub jecti veb y British Telecom, O b jecti vely predict results of sub jecti vespeech quality testsspeech quality testsPESQ (Perceptual Evaluat ion of Speech Qual ity) ITU P.86 2 ,PESQ (Perceptual Evaluat ion of Speech Qual ity) ITU P.86 2 ,latest standard (January 2 001), currently the most accurate modellatest standard (January 2 001), currently the most accurate modelfor automated vo ice quality perception, improves over PSQMfor automated vo ice quality perception, improves over PSQMand PAMSand PAMS


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Sources of potential VSQ problemsSources of potential VSQ problems

D elay jitter: variance in delay ( z ero, little or excessi ve delay)D elay jitter: variance in delay ( z ero, little or excessi ve delay)Encod ing and decod ing of vo ice (PCM/A D PCM/low bi tEncod ing and decod ing of vo ice (PCM/A D PCM/low bi t--rateratecodecs/CLEP)codecs/CLEP)

Time Time--Clipp ing (Front end cl ipp ing) introduced b y Vo ice Acti v ity Clipp ing (Front end cl ipp ing) introduced b y Vo ice Acti v ity D etectors (VA D )D etectors (VA D )

Temporal s ignal loss and dropouts introduced b y packet less Temporal s ignal loss and dropouts introduced b y packet lessEnv ironmental no ise, including b ackground no iseEnv ironmental no ise, including b ackground no iseSignal attenuation and ga in/attenuat ion variancesSignal attenuation and ga in/attenuat ion variances

Level clipp ing Level clipp ing Transm ission channel errors Transm ission channel errors


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Echo: What makes it a problem?Echo: What makes it a problem?

A n

A n analog leakageanalog leakage path between analog path between analog Tx and Rx paths Tx and Rx paths

SufficientSufficient delaydelay in echo returnin echo return

SufficientSufficient echo amplitudeecho amplitude

When all of the following conditions are true,echo is perceived as annoying:


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How the packet voice impact onHow the packet voice impact on

echo perception ?echo perception ?

B its dont leak B its dont leak - - Echo is not introduced on digital linksEcho is not introduced on digital links The packet segment of the voice connection introduces a The packet segment of the voice connection introduces a

significant delay (typically 30 ms in each direction).significant delay (typically 30 ms in each direction). The introduction of delay causes echoes (from analog tail The introduction of delay causes echoes (from analog tailcircuits) that are normally indistinguishable from side tone tocircuits) that are normally indistinguishable from side tone tobecome perceptible.become perceptible.B ecause the delay introduced by packet voice is unavoidable,B ecause the delay introduced by packet voice is unavoidable,thethe voice gateways must prevent the echo voice gateways must prevent the echo. .

WAN PSTNPSTN

Low delay,potential echo sourcesLarge delay ,no echo sources


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Identify and Isolate the echoIdentify and Isolate the echo

problem problemIdent ify Ident ify the echo pro b lem. Which side hearsthe echo pro b lem. Which side hearsecho? Calls to which numb ers hear echo ?echo? Calls to which numb ers hear echo ?

IsolateIsolate the prob

lem as much as possib

le and try the prob

lem as much as possib

le and try to f ind a scenar io where the echo is reproduc ib le.to f ind a scenar io where the echo is reproduc ib le.Whe n ever I hear ech o, t he pr obl em is a t t he OTHER e nd !! Whe n ever I hear ech o, t he pr obl em is a t t he OTHER e nd !!


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B asic securityB asic security

GWs/GKs w/ACLs w ith source ip (yes, can b eGWs/GKs w/ACLs w ith source ip (yes, can b espoofed) appears to b e the #1 source of protect ionspoofed) appears to b e the #1 source of protect ionagainst unagainst un--author iz ed calls.author iz ed calls.Run your VoIP network isolated from any pub licRun your VoIP network isolated from any pub licnetwork using your prefered flavor (physical seperation,network using your prefered flavor (physical seperation,

VLAN, MPLS, etc..) VLAN, MPLS, etc..) VoIP packets are _not_ encrypted, if th is is an issue VoIP packets are _not_ encrypted, if th is is an issueused IPSec! Beware that software crypto w ill add delay used IPSec! Beware that software crypto w ill add delay

and jitter, use hardware crypto for

better performanceand j

itter, use hardware crypto for

better performance(should add pred ictab le delay and jitter)(should add pred ictab le delay and jitter)

Note: CRTP doesn't work w ith IPSec, rememb er th isNote: CRTP doesn't work w ith IPSec, rememb er th is when des igning the b andw idth b udget. when des igning the b andw idth b udget.


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Documents

8-Designing and Deploying a VoIP Network