axe 30 minutes

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2004-10-18 1

Soft Real Time and High Availability, the AXEapproach

AXE applications

Control system structure Hard real time vs. soft real time

Event driven execution, soft real time and parallel

processes

Fault tolerance and recovery Upgrade

Scalability

Operation under overload (separate presentation)



2004-10-18 2

TR

LIT

MSC

HLR SCP

GMSC

MSC

T

I

SCP

SCPIN

MS BTS

BSCGSM

HLRSCP

GMSC

MSC TDMA

ILRL

AXE

TSPCPP

WPP

AXD

EAR

TMOS/CIF

AN

ADSL

T

CCN

FNR

TeS

MSG

ATM Back bone

AN

RNC

3G

UMTS

GPRSSGSN

GGSN

Internet³MGW´

OSS

CSCF

HSS AS

IPMM/SIP

PCU

AXE Applications in Telecom Networks



2004-10-18 3

AXE Control SystemStructure

Central

Processor

Regional

Processor

Adjunct

Pro,( I/O)

Application Hardware

CentralProcessor

Adjunct

Pro,( I/O)

DP

HDLC/Ethernet

< 1024



2004-10-18 4

AXE Hard Real Time vs. Soft Real Time

Central

Processor

Regional

Processor

Adjunct

Pro,( I/O)


CentralProcessor

Adjunct

Pro,( I/O)

Hard Real Time

Soft Real Time

DP

~1ms



2004-10-18 5

Soft Real Time: Event (Signal) Driven Execution

SW

UnitEvent

Buffer

(Typically

2 us/event)

External

EventsInternal Events

Response

ms level

Subject to

Load control



2004-10-18 6

Each event executes until next event is generated, that is

not processes interrupted by a time sharing system

The execution time is limited by design rules (and checks)

The number of internal events is known at system design

The occupancy level of the event buffer is subject to load

control

All share the same level

Soft Real Time: Event (Signal) Driven Execution



2004-10-18 8

AXE HW Redundancy

Central

Processor

Regional

Processor

Adjunct

Pro,( I/O)


CentralProcessor

Adjunct

Pro,( I/O)

DP

HDLC/Ethernet



2004-10-18 9

AXW HW redundancy

RP: Duplicated with simple fail over, or pooled.

Data loss (only temporary data)

AP(I/O): Duplicated, secure data on RAID disks

CP (classic systems): Duplicated, synchronous mode with

transparent fail-over

CP (modern systems): Duplicated, non synchronous,

warm stand-by with possibility for Soft Side Switch for

maintenance purposes (repair and upgrade)



2004-10-18 10

AXE HW Redundancy, Soft Side Switch

A-side memory B-side memory

Wr iteTransf er all pages

LOOP:

Transf er all

modified pages

UNTIL

Hot area stable;

HALT execution;

Transf er hot area;

RESUME on B-side;

Frequentwr ite



2004-10-18 11

AXE SW Recovery.

SW recovery actions are :

- Selective, depending on severance, possibility to recover

and system state (history)

- Coordinated/consistent all over the system



2004-10-18 12

AXE SW Recovery. Levels and Escalation

No action / register irregularity

Perform low level recovery = single transaction (a call) fails

Suppressed/delayed system restart, raise alarm

Small system restart = transactions in dynamic states are

lost (not established calls are lost,established are checked

Large system restart = all transactions are lost (all calls)

Large system restart with reload from back-up copy

Large system restart with reload from ³old´ back-up copy

Escalation to next restart level if a problem recurs



2004-10-18 13

AXE SW Recovery. Low Level Recovery

An identity (ID) is tied to each resource included in a

µtransaction¶, typically a call or a command.

The processing platform provides support for creation of

ID and linking to application SW.

In case of an execution error, the platform identifies all SW

units concerned and orders release over a standard

interface.



2004-10-18 14

AXE SW Recovery. Low Level recovery

Ix IxIx

Ix

Low level recovery handler

IxIx

IxIx

Low level recovery handler

Link sIx

Transaction

Ix

Execution

Error!

ID=Ix

Release



2004-10-18 15

AXE SW Recovery. The Reality

SW Error

Low Level Recovery

No Action Filter

99,8%

0,1%

System Restart

< 0,1%



2004-10-18 16

AXE SW Upgrade

Two different methods are used for SW upgrade:

- Corrections/patches and

- New SW packages

Corrections/patches are local changes of code inserted at

assembler level when the CP is idle => no disturbance

New SW packages are introduced when major changes

including new data structures are required.

The new version of a SW units inherit data from the old

version and are switched in with a system restart => at

least yearly disturbance of new calls (~1 min. down time)



2004-10-18 17

AXE SW Upgrade, Data Inheritance

Data Change

Inf ormationData Change

Inf ormationData Change

Inf ormation

Old unit New unit

Diff erent upgrade

cases



2004-10-18 18

AXE Scalability

The traditional AXE in scalable only in the RP region.

For the CP only a low-end/high-end option exists.

In modern applications the need for HW related RPscalability is decreasing but the need for CP scalability is

increasing. To achieve better scalability AXE uses two

approaches:

1) Parallel multi-threaded execution with common memory2) Clusters of CPs with network interfaces



2004-10-18 19

AXE Scalability, Multi-threaded Execution

Must be 101% compatible with application SW (includes

fault compatibility!)

The problem is not to make it work

The real problem is to make an efficient implementation

with limited over-head including the cost for cache

coherency => minimize true concurrent execution =>

combine concurrency with functional distribution! =(CMX-FD)



2004-10-18 20

AXE Scalability, Concurrent Multi ExecutionProcessor Core

MemoryProcessor Core

Memory

Processor CoreMemory

Processor CoreMemory

CMX-FD. Simplified View

CMX

FD

CMX

FD

CMX

FD

CMX

FD

Cluster of Application Modules

Cluster of APZ-OSand Platform SW



FD-mode: Functional Distribution, that is each function is allocated to execute on one Processor Core only.

CMX-mode: Concurrent (Multi) eXecution, that is each SW unit is allowed to execute on all Processor Cores, but

only one at a time. Certain sequencing rules must be obeyed in order to make each ³call´ exe-

cute like it would in a single CP system.



2004-10-18 21

AXE Scalability. Cluster Systems

Call

Control

T

Protocol

Term. +

Dis patcher

Network

protocols

N+1

Cluster s address

- scalability

-down t

ime atupgrade

- down time at

node f ailure



2004-10-18 22

AXE 10 Minutes, CP ¶Classicµ vs. µModern¶

HW

MIP

Application SW

APZ-CP OS

HW (Q-processor)

OS (Tru64)

APZ-VMASA-

compiler

Application SW

APZ-CP OSSame Same Same

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