Download - 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)
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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
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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
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AXE Hard Real Time vs. Soft Real Time
Central
Processor
Regional
Processor
Adjunct
Pro,( I/O)
Application Hardware
CentralProcessor
Adjunct
Pro,( I/O)
Hard Real Time
Soft Real Time
DP
~1ms
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Soft Real Time: Event (Signal) Driven Execution
SW
UnitEvent
Buffer
(Typically
2 us/event)
External
EventsInternal Events
Response
ms level
Subject to
Load control
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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
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AXE HW Redundancy
Central
Processor
Regional
Processor
Adjunct
Pro,( I/O)
Application Hardware
CentralProcessor
Adjunct
Pro,( I/O)
DP
HDLC/Ethernet
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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)
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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
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AXE SW Recovery.
SW recovery actions are :
- Selective, depending on severance, possibility to recover
and system state (history)
- Coordinated/consistent all over the system
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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
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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.
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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
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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%
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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)
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AXE SW Upgrade, Data Inheritance
Data Change
Inf ormationData Change
Inf ormationData Change
Inf ormation
Old unit New unit
Diff erent upgrade
cases
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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
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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)
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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
Cluster of Application Modules
Cluster of Application Modules
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.
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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
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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