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PNNI: How it Works

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T h i s p r e s en t a t i o n h a s b e e n g e n e r a t e d b y t h e

A TM F o r u m f o r t h e p u r p o s e o f e d u c at i n g t h e

p u b l i c o n A T M T e c h n o l o g y an d t h e AT MF or u m s a c t i v i t i e s .

T h i s p r e s e n t a t i o n i s t h e p r o p e r t y o f t h e A T M

F o r u m a n d c a n o n l y b e g i v e n t o e x t e r n a l

a u d i e n c e s b y a n a u t h o r i z e d A T M F or u m

A m b a s s ad o r . A TM Fo r u m A m b a s s ad o r s

r e g u l a r l y a t t e n d A T M F or u m m e e t i n g s , s o

t h e y c a n r e l a t e f i r s t h a n d a b o u t F o r u m

a c t i v i t i e s . Th e re a re n o re s t r i c t i o n s o n h o w

t h i s m a t e r i a l i s u s e d f o r e d u c at i o n a l p u r p o s es

t o i n t e r n a l a u d i e n c es .

T o r e q u e st a n A TM F o r u m A m b a s sa d o r t o p r e s en t t h i s m a t e r i a l , p l e a s e vi s i t o u r w e b s i t e ,

h t t p : / / w ww . at m f o r u m . c o m , co n t a c t u s v i a e -m a i l a t i n fo @ a t m f o r u m . c o m o r c o n t a c t o n e o f

o u r r e g i o na l o f f i c es : He ad q u a r t e r s + 1 . 6 5 0 . 9 4 9 . 6 7 0 0 , A s i a -P a c i f i c Of f i c e + 8 1 . 3 . 3 4 3 8 . 3 6 9 4 ,

E ur o p e Of f i c e + 3 2 . 2 . 7 3 2 . 8 5 0 5 .

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Topics

l Introduction

l Background Concepts

l Key Phase 1 Requirements

l PNNI Routingl PNNI Signalling

l Configuring the PNNI Hierarchy

l Future Capabilities

l Summary

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What Is a PNNI ?

l PNNI: Private Network-Network or Network-Node

Interface

l UNI: User Network Interface

U N I P N N I U N I

U N I P N N I U N I

A T M

N e t w o r k

A T M

N e t w o r k

- O R -

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PNNI and Other ATM Interfaces

l UNI User Network Interface

l NNI Network Node Interface

l B-ICI BISDN Inter-Carrier Interfacel DXI Data eXchange Interface

P r i v a t e

U N I

P r i v a t e

N N I

P u b l i c

U N I

A T M

D X I

B - I C I

M e t r o p o l i s D a t a Se r v i c e s

I n c .

C o u n t r y W i d e Ca r r i e r

S e r v i c e s

P u b l i c

N N I

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ATM Layer Specification

NNI Cell Format

UNI and NNI cell header difference:

-NNI: 12-bit VPI field, no GFC-UNI: 8-bit VPI field, 4-bit GFC

L e g e n d

C L P -

G F C -

V P I -

C el l L o s s P r i o r i t y

G en e r i c F l o w C o n t r o l

V i r t u a l P a t h I d e n t i f i er

5 B y t e s

4 8 B y t e s

V i r t u a l P a t h I d e n t i f i e r

V i r t u a l C h a n n e l

I d e n t i f i e r

7 6 5 4 3 2 1 0

P a y l o a d T y p e

I d e n t i f i e rC L P

H e a d e r E r r o r

C h e c k

P a y l o a d

( 4 8 b y t e s )

V i r t u a l P a t h

I d e n t i f i e r

V i r t u a l C h a n n e l I d e n t i f i e r

V i r t u a l C h a n n e l

I d e n t i f i e r

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Simple PNNI Solution:Interim Inter-switch Signalling Protocol

(IISP)

Purpose: Enables Switched Virtual Circuit (SVC)

interoperability in small, static environments.

l Uses UNI 3.0/3.1 Signalling between switches

l Requires manual configuration of static topology and resource tables

l Specification released: 3/95

I I S PI I S P

I I S PI I S PI I S PI I S P

V E N D O R BV E N D O R E

V E N D O R D

V E N D O R C

V E N D O R A

A

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Advanced Solution:

PNNI 1.0

Purpose : Enables extremely scalable, full function, dynamic,multi-vendor ATM networks.

l Designed to support a multi-vendor, global ATM internet.

l Two key protocols:

PNNI Routing:

PNNI Signalling:

l Specification released: 3/96

H ie ra rch i ca l , s t a t e -o f -t h e -a r t r o u t i n g

p r o t o c o l

B a s e d o n Q. 2 9 3 1 , e x t e n d e d a s

n e c e s s a r y .

X. 1X.2

X . 1 . 1X . 1 . 2 X . 2 . 1

X . 2 . 2

U s e r A( A d d r : X . 1 . 1 . A )

U s e r B( A d d r : X . 2 . 2 . B )

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Concept of Topology State

Routing

Each node periodically:

(1) Exchanges Hello packets with directly neighboring nodes.

(2) Constructs PNNI Topology State Elements (PTSEs), describing thenode and listing links to direct neighbors, as shown above.

(3) Floods PTSEs to all other nodes.Each node uses own view of global topology to compute routes.

A hierarchical topology state algorithm is the key to PNNI Routing.

A

S 2

U s e r A U s e r B

S 1 S 2

S 3

S 4

S 5

S 1 S 2

S 1

S 3

S 4

S 4

S 2

S 3

S 5

S 5

B

S 4

S 3

S 3

S 2

S 4

S 5

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Concept of Source Routes

l Ingress nodes choose a complete path to the destination

l Ingress node then adds full path to the message itself

l Transit nodes simply follow the given path

PNNI Signalling uses a hierarchical version of this concept.

U s e r A U s e r B

S 1 S 2

S 3

S 4

S 5

A d d s

S o u r c e

R o u t e

B

B S 1 S 2 S 4 S 5

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Key Phase 1 Requirements

l Support UNI 3.1 capabilities Point-to-point and point-to-multipoint connections

QOS classes

l Support some UNI 4.0 (TM and Signalling) capabilities

ABR Individual QoS parameters

l Support massive scalability

l Support intra- and inter-domain functionality in a single,integrated protocol.

l Leverage existing work

PNNI Signalling: PNNI Routing:

U s e Q. 2 9 3 1 a s b a s e

Bor r ow / ex tend concepts f r om

O SP F, IS - IS , ID R P

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Address Format Used in PNNI

l ATM End System Addresses (AESAs) Based on ISO NSAP

Come in multiple varieties, most notably

DCC (Data Country Code)

ICD (International Code Designator)

E.164 (E.164 address contained in AESA)

Other AESA formats may be supported

l No direct support of native E.164 numbers

May translate to E.164 AESA in PNNI network

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In i t ia l Domain Ident i f ier -

Ident i f ies the author i ty r esponsib le

fo r a l loca t ing s t r uctur e o f DSP

2 0 o c t e t s

AF I ID I H O - D SP E S I S E L

7 oc t e t s

Domain Speci f i c Par t -

St ructured by the au thor i t y

ident i f i ed by IDI

D S P

H O -D S P = H i g h e r O r d e r D S P

E SI = E n d S ys t e m I d e n t i f i e r ( M A C a d d r e s s )

S EL = S el e c t o r ( f o r e n d s y s t e m u s e o n l y )

Author i t y and Format Ident i f ie r -

Ident i f ies what s c h e m e is to fo l low

AESA Format

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ATM Address Prefixes

l Address prefix of length p is first p bits of address

l Prefixes with length 0

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47.0091.8000.1122.0001.0F01.0001.00000C.5BD9A5.00C5.0079.0000.0000.0000.0000.0000.00A03E.000001.00 (LECS)

47.0091.8000.1122.0001.0F01.0001.001011.BAD524.00

47.0091.8000.1122.0001.0F01.0001.00603E.7B190A.00

47.0091.8000.1122.0001.0F01.0001.001011.BAE247.00

Advertised reachable address prefixes:

47.0091.8000.1122.0001.0F01.0001 summaryC5.0079.0000.0000.0000.0000.0000.00A03E.000001

matches summary address

Engineering 1

Reachability Informationl In addition to topology information, each node

advertises list of reachable address prefixes

l PNNI routes to nodes advertising the longest matchingprefix for the destination address

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PNNI Routing Hierarchy

l Each switch is (manually) initialized with a full 20-byte address

l Routing hierarchy is then defined recursively:

Neighboring nodes form Peer Groupsbased on their longest prefix incommon

Each peer group then behaves as a Logical Group Node (LGN), toform (next level) peer group, etc.

CB.1

B.2B.3

B . 3 . 2

B . 3 . 1

B . 1 . 1B . 1 . 2

B . 1 . 3

B . 2 . 1

B . 2 . 2

C .1

C .2

A. 1

A. 2

A. 1 . 1 A. 1 . 2

A . 1 . 3

A . 2 . 1

A . 2 . 2

AB

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Aggregation of TopologyInformation

l Within each peer group, nodes (or LGNs) exchange PNNITopology State Packets (PTSPs)

l A Peer Group Leader (PGL)is elected to represent its peergroup as a single LGN at next level

l SVCs are set up as routing control channelsbetween LGNs atthe same level

= P e e r G r o u p

L e a d e r

A B CA

A. 1 A. 2 B . 1 B . 2 B . 3 C

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Passing Information Downthe Hierarchy

l Problem:

With PTSPs sent among peer group members alone, a switch

would not know how to route to remote peer groups.

+ S o l u t i o n : Peer g roup leaders feed h igher - level t opo logy down in t o peer

group.

+ S o l u t i o n : Peer g roup leaders feed h igher - level t opo logy down in t o peer

group.

A B CA

A. 1 A. 2 B . 1 B . 2 B . 3 C

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Single Nodes Topology View

l Global topology as seen by node A.1.1

A. 1 A

CB . 1 B . 2 B . 3

B . 3 . 2

B . 3 . 1

B . 1 . 1B . 1 . 2

B . 1 . 3

B . 2 . 1

B . 2 . 2

C. 1

C. 2

A. 1A. 2

A . 1 . 1 A . 1 . 2

A . 1 . 3

A . 2 . 1

A . 2 . 2

A

B

A . 1 . 1 A . 1 . 2

A . 1 . 3

A.2 B C

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Advertising QOS-relatedTopology State Parameters

Resource information (e.g. available bandwidth)also needs to be advertised in PTSPs.

l Purpose: Allows better paths to be chosen Makes call admission more efficient

U s e r A U s e r B

S 1 S 2

S 3

S 4

S 5

S e t u p(N e w Ca l l )

W h i c h

P a t h ?

A v a i l a b l e B a n d w i d t h ?

A v a i l a b l e B a n d w i d t h ?

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QOS-Related Information:How Much / How Often to Advertise?

N o Q O S - r e l a t e d s t a t e ex p o s ed

N o a d v e r t i s e m e n t s s e n t

Al l Q O S - r e l a t e d s t a t e ex p o s e d

F r e q u e n t a d v er t i s e m e n t s s en t

Pro:

s imple

no ove rhead

C o n :

high cal l b locking rate

b l ind ret r ies waste bandwidth

low network ut i l i zat ion

Pro:

near zero ca l l b lock ing

h ighest ne twork u t i l i za t ion

opt im al rou tes possib le

C o n :

m o s t c o m p l e x

h i gh overhead

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Call Admission Control

l Generic Call Admission Control (GCAC)

Run by a switch choosing a source route

Determines if a path can (probably) support the call

l Actual Call Admission Control (ACAC)

Run by each switch in the chosen path

Determines whether or not the switch can support the call

U s e r A U s e r B

S 1 S 2

S 3

S 4

S 5

S e t u p

R u n s A C A C

R u n s G C A C

C h o o s e s P a t h

R u n s A C A C

R u n s A C A C

R u n s A C A C

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PNNI Signalling

Key Conceptsl Complete Source Routing across each level

of hierarchy

l Use of Designated Transit Lists

l Crankback and Alternate Path routing

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Complete Source RoutingAcross Each Peer Group

+ Answer :! A t the ingress en t r y swi t ch o f each peer g roup, a comp le tesource rou te across the peer g roup is spec i f i ed .

! Swi t ch spec i f y ing t he sou rce rou t e may o r m ay no t be the pee rgroup l eader .

l Question: How is a call setup progressed across thenetwork?

B .1

B. 2

B. 3

A. 1

A. 2

A . 2 . 2

A . 2 . 3

A . 2 . 1

A . 1 . 2

A . 1 . 1

A

BU s e r X

U s e r Y

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Designated Transit Lists

(DTLs)l New Information Element (IE) appended toSETUP and ADD PARTY messages (to carry

Source Route)

+ A ct u a l l y i m p l e m e n t e d a s a p u s h - d o wn / p o p - of f s t a c k

U s e r A U s e r B

S 1 S 2

S 3

S 4

S 5

S E T U P

D T L

S 1 S 2 S 4 S 5 S E T U P

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B .1

B. 2

B. 3

A. 1

A . 2 . 2

A . 2 . 3

A . 2 . 1

A . 1 . 2

A . 1 . 1

U s e r X U s e r Y

A . 1 . 2

A . 1 . 1

A. 1

A. 2

A

B

A . 2 . 3

A . 2 . 1

A. 1

A. 2

A

B

A . 2 . 3

A . 2 . 1

A. 1

A. 2

A

B

A

B

B . 2

B . 1

B . 3

A

B

B . 2

B . 1

B . 3

A . 1 . 2

A . 1 . 1

A. 1

A. 2

A

B

Designated Transit Lists (Example)

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Crankback and Alternate PathRoutingl Question: What happens when a call fails along a specified

source route (e.g. due to insufficient bandwidth)?

l Answer : Call is cranked back to originator of the top Source

Route DTL

Originator then generates a new Source Route, or

Originator cranks back call to generator of higher-level source route.

B .1

B. 2

B. 3

A. 1

A. 2

A . 2 . 2

A . 2 . 3

A . 2 . 1

A . 1 . 2

A . 1 . 1

AB

U s e r XU s e r Y

1

2

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Configuring the PNNIHierarchy

l Hierarchical address assignment is the key

Minimize configuration

Use first levelbits of switch address to generate peergroup ID

Use prefix of switch address to generate default

summary address prefix

Minimize number of routes

l Planning ahead is important to avoid renumbering

Can run with fewer levels in the beginning

Can add levels of hierarchy without renumbering

l

PGL/LGN configuration also requiredl Lots of other things maybe configured

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Hierarchical AddressAssignment Example

. . .

C or p o r a t e A d d r e s s P r e f i x

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2

L o n d o n M a i n

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 1

L o n d o n S o u t h

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 2

B e r l i n

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 1 0 1

B u i l d i n g A

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 1 . 0 1

B u i l d i n g O

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 1 . 0 F

B u i l d i n g O , 1 s t F l o o r

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 1 . 0 F . 0 1

B u i l d i n g O , 2 n d F l o o r

4 7 . 0 0 9 1 . 8 0 0 0 . 1 1 2 2 . 0 0 0 1 . 0 F . 0 2

l e v e l 5 6

l e v e l 7 2

l e v e l 8 0

l e v e l 7 2l e v e l 7 2

l e v e l 8 8

l e v e l 8 8

l e v e l 8 0

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PNNI 1.0 Addenda - Work InProgress

l Leaf Initiated Join

l Multipoint-to-Point Connections

l Closed User Groups

l Network Call Correlation Identifier

l Rerouting

l

Path and Connection Tracel PNNI Routing Authentication

l Transported Address Stack

l Vendor-Specific Signalling Information

l Soft PVC Interworking with Frame Relay

l Mobility Extension Mobile ATM network linked to fixed ATM infrastructure

e.g., an airplane

B

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PNNI Augmented Routing(PAR)l Allows distribution of information about non-ATM

services via PNNI

l Examples

Automatic establishment of router overlay, e.g.

Discover routers running OSPF in same subnet Establish full mesh of SVCs (in small networks)

Server detection (Classical IP, NHRP, MARS, DNS)

l Edge devices not running PNNI can use Proxy PAR

protocol to interact with PAR capable switches.

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Summary

l

Interim Inter-switch Signalling Protocol (IISP) Minimal functionality; Small, static environments only

l PNNI 1.0

Full functionality; Any-size, static / dynamic environments

l Key PNNI Routing Concepts

Addressing Routing Hierarchy

Topology advertisement and aggregation Resource advertisement and QOS-sensitive routing

l Key PNNI Signalling Concepts

Full source routing across peer groups (via DTLs) Crankback and Alternate Path routing

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This concludes thepresentation provided byThe ATM Forum