Enhancing System Capacity and Robustness
by Optimizing Software Architecture
in a Real-time Multiprocessor Environment
Mikko Suominen
S-38.310 Thesis Seminar on Networking Technology
Helsinki University of Technology
01.06.2004
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Mikko Suominen
Basic Information
• Thesis written at Oy L M Ericsson Ab, Finland
• Supervisor: Professor Jorma Jormakka
• Instructors: M.Sc. Ilkka Koskinen and M.Sc. Juha Eloranta
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Contents
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Background
Problem Description
Objectives
Scope
UMTS Release 4 Network
Media Gateway
Architecture Tradeoff Analysis Method
Architecture Optimization and Analysis
Conclusion and Future Research
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Background (1/2)
• The Universal Mobile Telecommunications System
(UMTS) is a third generation mobile network standard
specified by the 3rd Generation Partnership Project
(3GPP).
• The UMTS has been evolved from the GSM (Global
System for Mobile Communications) and the GPRS
(General Packet Radio Service) networks.
• UMTS specifications are divided into multiple releases.
– Each release contains some new functionalities and modifications
to the network architecture.
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Background (2/2)
• The UMTS Release 4 network architecture physically
separates call control from media and bearer control.
• This means that the Mobile Switching Centre (MSC),
which handles these tasks in the GSM network, is divided
into two separate network elements.
– The MSC server handles the call control.
– The Media Gateway (MGW) handles the media and the bearer
control.
– The MSC server controls the MGW via the Gateway Control
Protocol (GCP) interface.
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Problem Description (1/2)
• The Ericsson Media Gateway for Mobile Networks (MMGW) is an existing product that fulfills the specifications
for the MGW.
• The M-MGW is the real-time multiprocessor system this
thesis deals with.
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Problem Description (2/2)
• System properties, such as capacity and robustness, are
highly dependent on the software architecture.
• The research problem of this thesis is to find and analyze
different kinds of distributed software architectures that
could enhance the capacity and the robustness of the MMGW.
– The capacity enhancement increases the possible amount of traffic
carried through the M-MGW.
– The robustness enhancement improves the in-service performance
of the M-MGW.
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Objectives
• The purpose of this thesis is to find a number of software
architectures that would help to solve the research
problem of the thesis.
• Every proposed software architecture optimization will be
shown to work according to the specifications.
• Finally, the proposed architectures will be analyzed in the
light of capacity and robustness improvements.
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Scope
• This thesis deals with the UMTS Release 4, because it is
the first release containing the physical separation
between the MSC server and the MGW functionalities.
• Inside the M-MGW, the software architecture optimization
scope is limited to the User Plane Control Functions
(UPCF), which handles the GCP and controls the actual
User Plane.
• This thesis presents only architectural level solutions.
– More detailed solutions including the implementation have been
left to future research.
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CN
CSMGW
UMTS
Release 4
Network
Mc
GMSC
server
Rev A
Authentication Centre
Base Station Controller
Base Station System
Base Transceiver Station
Core Network
Circuit Switched
Equipment Identity Register
Gateway GPRS Support Node
Gateway Mobile Switching Centre
Home Location Register
Mobile Equipment
Media Gateway
Mobile Station
Mobile Switching Centre
Public Switched Telephone Network
Radio Network Controller
Radio Network Subsystem
Serving GPRS Support Node
Subscriber Identity Module
User Services Identity Module
Visitor Location Register
Gc
HLR
Nc
H
PSTN
AuC
Nb
E
B
MSC server
Gf
F
VLR
Gn
Gr
EIR
D
G
AuC
BSC
BSS
BTS
CN
CS
EIR
GGSN
GMSC
HLR
ME
MGW
MS
MSC
PSTN
RNC
RNS
SGSN
SIM
USIM
VLR
GGSN
C
VLR
Gs
B
SGSN
MSC server
Nc
Gp
Gi
PSTN
PSTN PSTN
Mc
Mc
CS-MGW
CS-MGW
Nb
A
Gb
IuPS
IuCS
RNS
BSS
Iur
RNC
BSC
Abis
BTS
RNC
Iub
BTS
Node B
Node B
cell
Um
Uu
ME
SIM-ME i/f
SIM
or
Cu
USIM
MS
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Media Gateway (1/2)
• The fundamental purpose of the MGW is to connect the
UMTS Core Network to other networks, such as UTRAN
(UMTS Terrestrial Radio Access Network) and ISDN
(Integrated Services Digital Network).
• The MGW transports traffic between different networks
and may support:
– media conversion
– bearer control
– payload processing e.g. with different codecs
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API
CPP
GCP
MGW
Media Gateway (2/2)
Application Programming Interface
Connectivity Packet Platform
Gateway Control Protocol
Media Gateway
GCP
MGW
Application
Signaling Transport Converter
Virtual
MGWs
GCP Termination
API
User Plane
Control
Functions
Connection Coordinators
M-MGW
Software
Architecture
Operation
and
Maintenance
API
Media Stream
Function
Media Framing
Function
API
User Plane
Functions
API
CPP
Bearer Termination
Real-time Routing
Switching Function
External Bearer Control
Signaling Gateway
Physical Interfaces
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Architecture Tradeoff Analysis Method (1/2)
• Architecture Tradeoff Analysis Method (ATAM) is a
technique for analyzing software architectures.
• The ATAM is developed in Software Engineering Institute
of Carnegie Mellon University (CMU/SEI).
• The purpose of the ATAM is to assess the consequences
of architectural decisions in light of quality attribute
requirements.
• The ATAM process consists of nine steps.
– A simplified version of the ATAM is used in this thesis.
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Architecture Tradeoff Analysis Method (2/2)
Quality
Attribute
Scenario
Artifact
Stimulus
Response
Environment
Source of
Stimulus
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Response
Measure
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Architecture Optimization and Analysis (1/5)
• Capacity enhancement
 Increase the possible amount of traffic carried through the M-MGW
 UPCF software architecture optimization so that it is able to
handle more GCP messages simultaneously
 Study, which UPCF tasks can be run in parallel on different
processors
• Robustness enhancement
 Improve the in-service performance of the M-MGW
 UPCF software architecture optimization so that its fault tolerance
is improved
 Study, which UPCF services can be replicated across
multiple processors
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Architecture Optimization and Analysis (2/5)
UE
RNC
MSC server
MGW
SETUP
CALL PROCEEDING
Initial Address
Bearer Information
ADD.request ( CTX$, T$ )
ADD.reply ( CTX1, T2 )
UMTS
Originating
Call
ADD.request ( CTX1, T$ )
RAB ASSIGNMENT REQ
ADD.reply ( CTX1, T1 )
RAB ASSIGNMENT COMPL
Establish Bearer +
Change Through-connection
Prepare Bearer +
Change Through-connection
UP Init
UP Init Ack
Continuity
Address Complete
ALERTING
Answer
MOD.request ( CTX1, T1 )
MOD.reply ( CTX1, T1 )
MOD.request ( CTX1, T2 )
MOD.reply ( CTX1, T2 )
CONNECT
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Change Through-connection +
Activate Inter-working Function +
Activate Voice Processing Function
Activate Inter-working Function +
Activate Voice Processing Function
Mikko Suominen
Architecture Optimization and Analysis (3/5)
MSC server
Signaling
Connection
Failure
MGW
Signaling connection failure
Signaling in service
SEC.request ( MGW Communication Up )
SEC.reply ( MGW Communication Up Ack )
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Architecture Optimization and Analysis (4/5)
• Quality attribute scenario 1
– Capacity  Transaction Throughput  Handling Busy Hour Call Attempts
i.
ii.
iii.
iv.
v.
vi.
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Source of stimulus:
Stimulus:
Environment:
Artifact:
Response:
Response measure:
MSC server
GCP transaction arrivals during the busy hour
Normal operation
UPCF system area
All arrived GCP transactions can be handled
All arrived calls can be established
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Architecture Optimization and Analysis (5/5)
• Quality attribute scenario 2
– Robustness  Software Failure  Handling A Subsystem Crash
i.
ii.
iii.
iv.
v.
vi.
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Source of stimulus:
Stimulus:
Environment:
Artifact:
Response:
Response measure:
Subsystem internal to the UPCF
Subsystem crash
Normal operation
UPCF system area
UPCF system area degraded
No downtime
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Conclusion and Future Research (1/2)
• Three different architecture enhancements were found.
 Enhancement 1
+ Easy to implement
+ Most of the legacy architecture could be re-used
– Does not improve the M-MGW capacity or robustness from a single MSC
server’s point of view
 Enhancement 2
+ Improves notably the M-MGW capacity and robustness
+ Future proof solution (very scalable)
– Harder to implement than the first one
 Enhancement 3
± Might improve the M-MGW capacity, but not robustness
± Can be seen as a further enhancement of the first or the second enhancement
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Conclusion and Future Research (2/2)
• Possible topics for future research:
– Testing and simulating the M-MGW software architecture
enhancements found in this thesis
– Enhancing the user plane functions
– Optimizing the usage of the GCP in the M-MGW
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Thank you for listening!
Questions?
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