Erlang SGSN

8/20/2019 Erlang SGSN

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Functional Programming inFunctional Programming inindustryindustry

ERLANG

Courtesy of Urban Boquist and Christer Nilsson (Ericsson Gothenburg)

Leslaw Lopacki

leslawlopacki!net


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OutlineOutline

" Mobile Telecommunications NetworksMobile Telecommunications Networks

" Packet Core Network – GPRS, MTS ! SGSNPacket Core Network – GPRS, MTS ! SGSN

" se o" #rlang in SGSNse o" #rlang in SGSN

"

SGSN $esign Princi%les "or #rlang&SGSN $esign Princi%les "or #rlang&

concurrencyconcurrency

distributiondistribution

"ault tolerance"ault tolerance

o'erload %rotectiono'erload %rotection

runtime code re%lacementruntime code re%lacement" #rlang basics and e(am%les#rlang basics and e(am%les


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Mobile TelecommunicationsMobile Telecommunications

Networks ) GSMNetworks ) GSM

CS # circuit switched

● $oice● %&%

PS # packet switched● e$erything that is '*● wap + www● e,ail●

&&%

%er$ices in teleco,,unications networks-

G.% / General acket .adio %er$ice


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Packet Core NetworkPacket Core Network.adio Network acket Core Network

" GSN *GPRS Su%%ort Network+ nodes&GSN *GPRS Su%%ort Network+ nodes& SGSNSGSN # # Ser'ing GSNSer'ing GSN GGSNGGSN # # Gateway GSNGateway GSN

" asic t-roug-%ut&asic t-roug-%ut& % to ../ kb%s wit- GPRS% to ../ kb%s wit- GPRS % to 012 kb%s wit- #$G#% to 012 kb%s wit- #$G# # # #n-anced $ata Rates "or GSM #'olution#n-anced $ata Rates "or GSM #'olution


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PCN in 34G5 and 3Turbo)4G5 –PCN in 34G5 and 3Turbo)4G5 –

6C$M7 and 8S$P76C$M7 and 8S$P7" $i9erent Radio Network$i9erent Radio Network" Packet Core Network *almost+ t-e same as t-e one in GPRSPacket Core Network *almost+ t-e same as t-e one in GPRS" #ricsson SGSN is 3dual access5 – GPRS and 6C$M7 in one#ricsson SGSN is 3dual access5 – GPRS and 6C$M7 in one" Muc- -ig-er *end user+ s%eeds&Muc- -ig-er *end user+ s%eeds&

% to 4:1 kb%s "or 4G *6C$M7+% to 4:1 kb%s "or 4G *6C$M7+% to .1;1 Mb%s "or 8S$P7 *later u% to 10 Mbit – #'ol'ed% to .1;1 Mb%s "or 8S$P7 *later u% to 10 Mbit – #'ol'ed8SP7+8SP7+

"

" Streaming 'ideo is PSStreaming 'ideo is PS*T< ?? MMS – Multimedia roadcast Multicast Ser'ice+*T< ?? MMS – Multimedia roadcast Multicast Ser'ice+

" Future& 'oice = 'ideo in PSFuture& 'oice = 'ideo in PS" 33


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#ricsson SGSN Node#ricsson SGSN Node

Capacity0 1 23 k subscribers4 5333

0 1 633 k subscribers4 53350 1 233 k subscribers4 53370 1 6 & subscribers4 53320 ~ 5 & subscribers4 5338


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SGSN – asic Ser'icesSGSN – asic Ser'ices

" aut-enticationaut-entication

" admission controladmission control" Auality o" ser'iceAuality o" ser'ice

" mobilitymobility

" roamingroaming

"

;;;;;;

Control %ignalling ayload transport

" user traBcuser traBc

" c-argingc-arging


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SGSN 7rc-itectureSGSN 7rc-itecture

C CCC

!!!

!!!

Control lane

ayload lane

%witch

&% nternet

soft real time

hard real time


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SGSN 8ardwareSGSN 8ardware" 02)42 Control Processors *boards+&02)42 Control Processors *boards+&

ltraSP7RC or PowerPC CPsltraSP7RC or PowerPC CPs

0 G memory0 G memory

Solaris=Dinu( E #rlang = C = CEESolaris=Dinu( E #rlang = C = CEE

" 02)42 Payload Processors *boards+&02)42 Payload Processors *boards+& PowerPC CPsPowerPC CPs

S%ecial -ardware *FPG7s+ "or encry%tionS%ecial -ardware *FPG7s+ "or encry%tion

P-ysical de'ices& "rame relay, atm, ;;;P-ysical de'ices& "rame relay, atm, ;;;


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SGSN Control SignallingSGSN Control Signalling

" attac- *%-one is turned on+attac- *%-one is turned on+

" israu *routing area u%date, mobility in radio network+israu *routing area u%date, mobility in radio network+

" acti'ation *initiate %ayload traBc+acti'ation *initiate %ayload traBc+

"etc; -undreds o" signalsetc; -undreds o" signals

9eleco, standards are :UGE (see www!;gpp!org)<

=e need a high le$el language # concentrate on

G.%4 not on progra,,ing details<


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#rlang=OTP#rlang=OTP

" @n'ented at #ricsson Com%uter Science Dab in t-e@n'ented at #ricsson Com%uter Science Dab in t-e

.H:2s;.H:2s;

" @ntended "or large scale reliable telecom systems;@ntended "or large scale reliable telecom systems;

"

#rlang isrlang is& "unctional language"unctional language

wit- built)in su%%ort "or concurrencywit- built)in su%%ort "or concurrency

" OTP *O%en Telecom Plat"orm+OTP *O%en Telecom Plat"orm+

?? #rlang E lots o" libraries;?? #rlang E lots o" libraries;


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6-y #rlangI6-y #rlangI

" Good t-ings in #rlang&Good t-ings in #rlang&

built)in concurrency *%rocesses and message %assing+built)in concurrency *%rocesses and message %assing+

built)in distributionbuilt)in distribution

built)in "ault)tolerancebuilt)in "ault)tolerance

su%%ort "or runtime code re%lacementsu%%ort "or runtime code re%lacement a dynamic languagea dynamic language

a dynamically ty%ed languagea dynamically ty%ed language

" T-is is e(actly w-at is needed to build a robust Control Plane in a T-is is e(actly w-at is needed to build a robust Control Plane in a

telecom system>telecom system>

@n SGSN&@n SGSN&

" Control Plane So"tware is not time critical *#rlang+Control Plane So"tware is not time critical *#rlang+

" ser Plane *%ayload+ is time critical *C+ser Plane *%ayload+ is time critical *C+


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#rlang – Concurrency#rlang – Concurrency

" 33Normal5 sync-roniJation %rimiti'es ) sema%-ores or monitorsNormal5 sync-roniJation %rimiti'es ) sema%-ores or monitors

does not look t-e same in #rlangdoes not look t-e same in #rlang

instead e'eryt-ing is done wit- %rocesses and messageinstead e'eryt-ing is done wit- %rocesses and message%assing;%assing;

" Mutual e(clusion&Mutual e(clusion& use a single %rocess to -andle resourceuse a single %rocess to -andle resource

clients call %rocess to get access;clients call %rocess to get access;

" Critical sections&Critical sections&

allow only one %rocess to e(ecute sectionallow only one %rocess to e(ecute section


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#rlang ) $istribution#rlang ) $istribution" General rule in SGSN&General rule in SGSN&

a'oid remote communication or sync-roniJation i" %ossiblea'oid remote communication or sync-roniJation i" %ossible

" $esign algorit-ms t-at work inde%endently on eac- node&$esign algorit-ms t-at work inde%endently on eac- node&


load balancingload balancing" 7'oid relying on global resources7'oid relying on global resources

" $ata -andling&$ata -andling&

kee% as muc- locally as %ossible *ty%ically traBc datakee% as muc- locally as %ossible *ty%ically traBc data

associated wit- mobile %-ones+associated wit- mobile %-ones+ some data must be distributed = s-ared *e;g; using mnesia+some data must be distributed = s-ared *e;g; using mnesia+

many di9erent 'ariants o" %ersistency, redundancy,many di9erent 'ariants o" %ersistency, redundancy,

re%licationre%lication


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Fault ToleranceFault Tolerance" SGSN must ne'er be out)o")ser'ice> *HH;HHHK+SGSN must ne'er be out)o")ser'ice> *HH;HHHK+

" 8ardware "ault tolerance8ardware "ault tolerance

Faulty boards are automatically taken out o" ser'iceFaulty boards are automatically taken out o" ser'ice

Mobile %-ones automatically redistributedMobile %-ones automatically redistributed

" So"tware "ault toleranceSo"tware "ault tolerance S6 error triggered by one %-one s-ould not a9ect ot-ers>S6 error triggered by one %-one s-ould not a9ect ot-ers>

Serious error in 3system S65 s-ould a9ect at most t-eSerious error in 3system S65 s-ould a9ect at most t-e

%-ones -andled by t-at board *not t-e w-ole node+%-ones -andled by t-at board *not t-e w-ole node+

:ow can such require,ents be reali>ed?

E@a,ple- the %= handling one phone goes cra>y and o$erwrites all the

,e,ory with garbage!


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SGSN 7rc-itecture – ControlSGSN 7rc-itecture – Control

PlanePlane

" On eac- CP .22 %rocesses %ro'iding 3system ser'ices5On eac- CP .22 %rocesses %ro'iding 3system ser'ices5 33static workers5static workers5

" On eac- CP /2;222 %rocesses eac- -andling one %-oneOn eac- CP /2;222 %rocesses eac- -andling one %-one 33dynamic workers5dynamic workers5

C C C


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$ynamic workers$ynamic workers

" System %rinci%le&System %rinci%le&

one #rlang %rocess -andles all signalling wit- a singleone #rlang %rocess -andles all signalling wit- a singlemobile %-onemobile %-one

" 6-en a signal recei'ed in %ayload %lane&6-en a signal recei'ed in %ayload %lane&

%ayload %lane translates a 3signal5 "rom t-e mobile %-one%ayload %lane translates a 3signal5 "rom t-e mobile %-one

into an #rlang messageinto an #rlang message

t-en sends it to t-e correct dynamic worker, and 'ice 'ersat-en sends it to t-e correct dynamic worker, and 'ice 'ersa

"

7 worker -as a state mac-ine&7 worker -as a state mac-ine& recei'e a signal – do some com%utation – send a re%lyrecei'e a signal – do some com%utation – send a re%ly

signalsignal

a little bit like an #ntity ean in L0##a little bit like an #ntity ean in L0##


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$ynamic workers cont;$ynamic workers cont;" 7 %rocess cras- s-ould ne'er a9ect ot-er mobiles&7 %rocess cras- s-ould ne'er a9ect ot-er mobiles&

#rlang guarantees memory %rotection#rlang guarantees memory %rotection

" S6 errors in SGSN&S6 errors in SGSN&

lead to a s-ort ser'ice outage "or t-e %-onelead to a s-ort ser'ice outage "or t-e %-one

dynamic worker will be restarted a"ter t-e cras-dynamic worker will be restarted a"ter t-e cras-

" Same "or S6 errors in MS&Same "or S6 errors in MS&

e;g; "ailure to "ollow standards will cras- dynamic workere;g; "ailure to "ollow standards will cras- dynamic worker*o9ensi'e %rogramming+*o9ensi'e %rogramming+


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Su%er'ision and #scalationSu%er'ision and #scalation

" Cras- o" worker is noticed by su%er'isorCras- o" worker is noticed by su%er'isor

" Su%er'isor triggers 3reco'ery action5Su%er'isor triggers 3reco'ery action5

" #it-er t-e cras-ed worker is restarted#it-er t-e cras-ed worker is restartedor or

" 7ll workers are killed and restarted7ll workers are killed and restarted

%uper$isor

=orker6 =orker5 =orker;


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Runtime code re%lacementRuntime code re%lacement" Fact& S6 is ne'er bug "ree>Fact& S6 is ne'er bug "ree>

" Must be able to install error corrections into alreadyMust be able to install error corrections into already

deli'ered systems wit-out disturbing o%erationdeli'ered systems wit-out disturbing o%eration" #rlang can load a new 'ersion o" a module in a#rlang can load a new 'ersion o" a module in a

running systemrunning system

" e care"ul>e care"ul>

Code loading reAuires co)o%eration "rom t-eCode loading reAuires co)o%eration "rom t-erunning S6 and great care "rom t-e S6 designerrunning S6 and great care "rom t-e S6 designer


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O'erload ProtectionO'erload Protection" @" CP load or memory usage goes to -ig- SGSN will@" CP load or memory usage goes to -ig- SGSN will

not acce%t new connections "rom mobile %-onesnot acce%t new connections "rom mobile %-ones

" T-e SGSN must ne'er sto% to 3res%ond5 because o" T-e SGSN must ne'er sto% to 3res%ond5 because o"o'erload, better to ski% ser'ice "or some %-oneso'erload, better to ski% ser'ice "or some %-ones

" RealiJed in message %assing ) i" ODP -its messagesRealiJed in message %assing ) i" ODP -its messages

are discarded&are discarded&

silently dro%%edsilently dro%%ed or a denial re%ly generatedor a denial re%ly generated


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#rlang basic synta(#rlang basic synta(

" Erlang shellErlang shell &&

erlerl

" &odules and Aunctions-&odules and Aunctions-

-module(my_mod).-module(my_mod).-export(double/1).-export(double/1).

double(X) -> 2 * X.double(X) -> 2 * X.

" Calling double+6-Calling double+6-

my_mod:double(4).my_mod:double(4).

" to,s- to,s-

cat, dog, home, a2 ..cat, dog, home, a2 ..

" 9uples -9uples -

1,2,cat,home!1,2,cat,home!

" Lists -Lists -

"1,2,cat,home!,1,2,#$"1,2,cat,home!,1,2,#$

" ariables -ariables -

% & 2,#,hor'e,'table!.% & 2,#,hor'e,'table!. & "1,2,cat,home!,1,2,#$. & "1,2,cat,home!,1,2,#$.

ar & "%$.ar & "%$.

" =riting to output-=riting to output-

+o:ormat(ello orld0).+o:ormat(ello orld0).


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#rlang synta( ) case and#rlang synta( ) case and"unctional clause"unctional clause

" Case clause ) case and %attern matc-ing&Case clause ) case and %attern matc-ing&

oc &oc &

ca'e ar oca'e ar o _,_,cat,X! -> +o:ormat(ello 3at0),X_,_,cat,X! -> +o:ormat(ello 3at0),X _,_,hor'e,X! -> +o:ormat(ello or'e0),X_,_,hor'e,X! -> +o:ormat(ello or'e0),X_ -> +o:ormat(5o e6tra6ce0),6o6e_ -> +o:ormat(5o e6tra6ce0),6o6e

e6d.e6d.

" Function clause&Function clause&

hello(_,_,cat,X!) -> +o:ormat(ello 3at0),Xhello(_,_,cat,X!) -> +o:ormat(ello 3at0),X

hello(_,_,hor'e,X!) -> +o:ormat(ello or'e0),X.hello(_,_,hor'e,X!) -> +o:ormat(ello or'e0),X.

hello(_) -> +o:ormat(5o e6tra6ce0),6o6e.hello(_) -> +o:ormat(5o e6tra6ce0),6o6e.


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#rlang synta( ) Recursion#rlang synta( ) Recursion

" %i,ple-%i,ple-

-module(act).-module(act).-export("act1/1$).-export("act1/1$).

act1(7) ->act1(7) ->11

act1(5) ->act1(5) ->5*act1(5-1).5*act1(5-1).

" Dpti,al / tail recursi$e-Dpti,al / tail recursi$e-

-module(act).-module(act).

-export("act2/1$).-export("act2/1$).

act2(5) ->act2(5) ->act2(5,1).act2(5,1).

act2(7,%) ->act2(7,%) ->%%

act2(5,%) ->act2(5,%) ->

act2(5-1,5*%).act2(5-1,5*%).


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#rlang ad'anced synta(#rlang ad'anced synta(

" $ynamic code&$ynamic code&

8u6 & u6(ar)8u6 & u6(ar)

ca'e ar oca'e ar o

_,_,cat,X! -> +o:ormat(ello 3at0),X_,_,cat,X! -> +o:ormat(ello 3at0),X

_,_,hor'e,X! -> +o:ormat(ello or'e0),X_,_,hor'e,X! -> +o:ormat(ello or'e0),X_ -> +o:ormat(5ot elcome here0),6o6e _ -> +o:ormat(5ot elcome here0),6o6e

e6d.e6d.

Calling Fun&Calling Fun&

8u6(1,2,cat,home!).8u6(1,2,cat,home!).

Passing Fun to anot-er "unction&Passing Fun to anot-er "unction&

call_u6(8u6,"$) -> o9call_u6(8u6,"$) -> o9

call_u6(8u6,"X$) -> 8u6(X), call_u6(8u6,).call_u6(8u6,"X$) -> 8u6(X), call_u6(8u6,).

+'t & "1,2,cat,home!,2,#,hor'e,'table!$.+'t & "1,2,cat,home!,2,#,hor'e,'table!$.call_u6(8u6,+'t).call_u6(8u6,+'t).


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#rlang message %assing#rlang message %assing

sender&sender&

;+d < ='g,;+d < ='g,

recei'er&recei'er&

rece+erece+e='g ->='g ->?act+o6>?act+o6>

e6d,e6d,


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#(am%le cont; ) genser'er#(am%le cont; ) genser'er

sender&sender&

@et & ge6_'erer:call(;+d, ='g),@et & ge6_'erer:call(;+d, ='g),

recei'er&recei'er&

ha6dle_call(='g) ->ha6dle_call(='g) ->ca'e ='g oca'e ='g o

add, 5! ->add, 5! ->

reply, 5 A 1!reply, 5 A 1!

......

e6d.e6d.


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ConclusionsConclusions

Pros&Pros&

" #rlang works well "or GPRS traBc control -andling#rlang works well "or GPRS traBc control -andling

" 8ig- le'el language – concentrate on im%ortant %arts8ig- le'el language – concentrate on im%ortant %arts

" 8as t-e rig-t ca%abilities&8as t-e rig-t ca%abilities&


distributiondistribution ;;;;;;

Cons&Cons&

" 8ard to nd good #rlang %rogrammers8ard to nd good #rlang %rogrammers

" #rlang=OTP not yet a main stream language#rlang=OTP not yet a main stream language

@nsuBcient %rogramming en'ironments *debugging, modelling, etc+@nsuBcient %rogramming en'ironments *debugging, modelling, etc+ Single im%lementation maintained by too "ew %eo%le ) bugsSingle im%lementation maintained by too "ew %eo%le ) bugs

" 8ig- le'el language – easy to create a real mess in ust a "ew lines o"8ig- le'el language – easy to create a real mess in ust a "ew lines o"

code;;;code;;;


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Dinks and Re"erencesDinks and Re"erences

" #rlang siterlang site&

-tt%&==www;erlang;org-tt%&==www;erlang;org

" #rlang ser Con"erence *No' 022:+#rlang ser Con"erence *No' 022:+" #rlang Communityrlang Community&

-tt%&==tra%e(it;org-tt%&==tra%e(it;org

" #rlang grou% on Dinked@n#rlang grou% on Dinked@n

http://www.erlang.org/http://www.erlang.org/http://trapexit.org/http://trapexit.org/http://trapexit.org/http://www.erlang.org/


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ooksooks

" ! r,strong! r,strong

“Programming Erlang” “Programming Erlang”

" ! r,strong4 .! irding4 C! =ikstrF,4! r,strong4 .! irding4 C! =ikstrF,4

&! =illia,s&! =illia,s

“Concurrent Programming in Erlang” “Concurrent Programming in Erlang”


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uestionsIuestionsI

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Erlang SGSN