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A Review of the Architecture and the Underlying Protocols in the Telephone Network

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Title: A Review of the Architecture and the Underlying Protocols in the Telephone Network


1
A Review of the Architecture and the Underlying
Protocols in the Telephone Network
  • Dipak Ghosal
  • Department of Computer Science
  • University of California at Davis

2
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

3
History
  • Pre-1984
  • ATT
  • 1980s saw rapid deployment of digital technology
    in the core network
  • 1984
  • Breakup of ATT into
  • 7 RBOCs (Regional Bell Operating Companies),
  • ATT, and others
  • Local area carriers (LECs) serving LATA were
    regulated
  • Long distance carrier (IXC) service was opened

4
History (2)
  • Post 1984
  • New Telecom Act in 1996
  • Further deregulation of LECs (ILECs and CLECS)
  • Local area and long distance markets opened
  • Local Number Portability
  • Break-up of ATT
  • ATT
  • Lucent (Bell-Labs)
  • Mergers of RBOCs and CLECs

5
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

6
A Typical Regional POTS Network
7
Network Architecture
8
Circuit Network
  • Central Offices (End Offices)
  • Local aggregation points for phone lines
  • Wire-pair (local loop) to each telephone
  • Tandems
  • Hubs interconnecting Central Offices
  • Connecting to IXCs

9
Circuit Network (2)
  • Hierarchical organization
  • End office
  • Toll Center
  • Primary Center
  • Sectional Center
  • Regional Center

10
End Office
11
Signaling Network
  • Signaling network is the brain
  • Circuit network forms the the muscles
  • All nodes in the signaling network are called
    signaling points
  • SSP -gt Service Switching Points
  • STP -gt Signaling Transfer Point
  • SCP -gt Service Control Point

12
Service Switching Point
  • This is the local exchange in the telephone
    network
  • Interfaces both the circuit network and signaling
    network
  • Generate SS7 messages from signals from the voice
    network
  • Generate SS7 query messages for non-circuit
    related messages
  • LNP has significantly altered the traffic mix

13
Signaling Transfer Point
  • Routers in the SS7 network
  • Route messages between SSPs
  • Support Global Title Translation for non-circuit
    related messages
  • These can be separate stand alone nodes or
    adjuncts to a voice switch
  • Many tandems used to act as STPs
  • Deployed as a mated pair

14
Signaling Transfer Point (2)
  • Hierarchy of STPs
  • Local and Regional STPs
  • International STPs
  • Gateway STPs
  • Interconnect different networks including
    cellular networks
  • Very important node in the SS7 network
  • Many other functions including measurements and
    data mining

15
Service Control Point
  • Interfaces to databases
  • 800/900 databases
  • HLR/VLR databases
  • LIDB (Line Information Databases) for calling
    cards
  • Local Number Portability Database
  • New Advanced Intelligent Network (AIN) services.

16
Types of Signaling Links
17
Types of Signaling Links (2)
  • A-Links are access links between SSP and STP or
    SCP and STP
  • B-Links are bridge links that connect mated STP
    pairs in the same hierarchy
  • C-Links are cross links between an STP and its
    mat
  • D-Links are diagonal links between STPs at
    different levels of the hierarchy
  • E-Links a extended links to connect to remote STP
    pairs
  • F-links are fully associated links

18
Types of Signaling Links (3)
  • Link sets are group of links with the same
    adjacent nodes
  • Route is a collection of link sets required to
    reach a destination
  • Route set is a collection of routes
  • Routing is hop-by-hop
  • A signaling point needs to know which linkset to
    use towards the destination

19
Addressing
  • Each signaling point has a address and it is
    referred to as the Point Code
  • It is a 24-bit address
  • 8 bits network identifier
  • 8 bits cluster identifier
  • 8 bits node identifier
  • Full point code routing
  • Partial point code routing
  • Cluster routing or network routing

20
Requirements
  • Availability objective an unavailability of no
    more than 10 minutes downtime between two SPs
  • Lost message probability 1 in 107
  • Message Out-of-sequence probability 1 in 1010
  • Performance objectives
  • Maximum link utilization must be less than 40
  • Various other requirements on various processing
    delay
  • Maximum message processing delay at an SP is
    200ms

21
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

22
Protocol Stack
23
ISDN User Part (ISUP)
24
ISDN User Part (ISUP)
  • IAM Initial Address Message
  • Message type, Called party number, calling party
    category, forward call indicators, nature of
    connection identifier, user service information
  • ACM Acknowledge Message
  • ANM Answer Message
  • REL Release Message
  • RLC Release Clear Message
  • All these message have a associated circuit
    identification code (CIC)

25
Database Query (TCAP)
26
Signaling Connection Control Part (SCCP)
  • Additional functions over MTP (network) layer to
    support connectionless and connection oriented
    services
  • Very similar to transport layer
  • Address Translations
  • Dialed digits to destination point codes
  • Particularly important for non-routable numbers
    such as 800/900.
  • GTT functionality is supported in the STP to
    determine which database will provide the
    translation.

27
Message Transfer Part (MTP) Layer 3
  • Network Management
  • Link management
  • Traffic management
  • Route Management
  • Message discrimination
  • Message distribution
  • Message routing

28
MTP Layer 3 (2)
  • Message discrimination
  • Determine if the message is destined to the
    receiving node
  • If yes apply message distribution to distributed
    it to the appropriate application
  • Else, route it to the destination using the most
    direct route (I.e., fewest number of hops)

29
MTP Layer 3 (3)
  • Traffic management
  • Link failures
  • Route failures
  • Congestion

30
Transient A-Link Failure
31
Link Failure
  • Level-2 processor sends a link failure message to
    the Level-3 processor
  • Level-3 processor updates its own routing table
  • Level-3 processor sends out routing table update
    message to other Level-3 processors within the
    STP

32
Link Failure (2)
  • Send out Traffic Restricted (TFR) messages to all
    the SPs
  • Send out Traffic Prohibited (TFP) message to the
    mate-STP via the C-link
  • Send change-over message to the corresponding SP
  • Sends changeover signal to the Level-2 processor
    to re-routes messages via the C-link

33
Congestion
34
STP Architecture
35
Key Design Issue
  • What is the best cluster size?
  • Centralized architecture have few Level-3
    processors
  • Fewer number of routing tables hence quicker
    update of failue information within the STP
  • Potential Level-3 processor overload
  • Distributed architectures have large number of
    Level-3 processors
  • Multiple failures can be processed in parallel
  • Large number of routing tables and hence delays
    in updating all copies
  • What is the priority structure for different
    message types in the Level-3 processor?

36
Model of Level-3 Processor
37
Network Model
  • 1, 8, 16, 24 A-link failures
  • All failures to a single STP
  • Simultaneous recovery after 11 seconds

38
Call Throughput
39
Key Results
  • A clustered architecture with 8/16 Level-2
    processors per Level-3 processor performed the
    best
  • Priority of tasks was a very important factor
  • Dynamic priority inversion

40
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

41
Routing in Circuit Network
  • Dynamic Routing
  • Some part of the routing changes over time
  • Adaptive Routing
  • Some part of the routing is a function of the
    network state at the time the decision is made

42
Alternate Routing
  • An ordered set of routes from which the choice is
    made
  • Fixed alternate routing
  • A small subset of fixed route is used
  • The set of alternate route is scanned in some
    predetermined order and the call is connected on
    the first free path that is found
  • There are different methods on how the routing
    control is propagated

43
Alternate Routing (2)
  • There are different methods on how the routing
    control is propagated
  • Originating-office control
  • Spill-forward control
  • Crankback

44
Fixed Hierarchical Routing
  • Hierarchical organization of switches
  • End office
  • Toll Center
  • Primary Center
  • Sectional Center
  • Regional Center
  • There are specific hierarchical fan rules of how
    switches are connected

45
Dynamic Nonhierarchical Routing
  • Deployed in mid 1980s
  • A day is divided in to 10 traffic periods
  • All switches are same no hierarchy
  • Routing is alternate type with the provision that
    alternate paths are limited to atmost two links
  • Long paths can result in knock-on effect and
    make the system highly sensitive to overloads
  • Uses crankback

46
Adpative Routing
  • Residual capacity adaptive routing (RCAR)
  • Uses occupancy information of all trunk groups
    periodically updated by measurements
  • DCR sends calls to paths with the largest
    expected number of free trunks
  • Trunk Status Map Routing
  • Adaptive DNHR

47
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

48
The Problem
  • Media events may stimulate a large number of
    calls to a single number in a very short time
    interval
  • Mass Call-Ins cause focused overloads, denying
    service to customers trying to reach other
    numbers
  • Outages may persist for long period
  • Existing automated network controls protect the
    network, but deny service unnecessarily

49
Example of Mass Callin
50
Choke Network
  • Special exchange which serves many clients (e.g.,
    radio stations) that regularly generate call-ins
  • Small number of trunk to this exchange
  • Not suitable for clients that would like to have
    large number of calls completed (ticket sales)

51
Manual Call Gaps
52
TFC Congestion Control
53
Other Methods
  • Automatic Congestion Control (ACC)
  • Method by which a switch can protect itself if
    overloaded
  • Curtails a percentage of call request on a per
    trunk-group basis
  • Code Blocks
  • Blocks a percentage of calls to specific numbers

54
Call Processing and Signaling
Normal Call
Caller
ACM
IAM
REL
RLC
ANM
Callee
IAM carries called number
Conversation
Call to a Busy Number
Caller
REL
RLC
IAM
Callee
Release-Busy
55
Key Ideas
  • When a Mass Call-In occurs, a very large number
    of Release-Busies messages from the same target
    number are quickly generated
  • Call gaps are an effective method for stopping
    traffic to a particular number
  • Call gaps have almost no effect on traffic to
    other numbers, while squelching traffic to the
    target

56
Example of Mass Callin
57
Algorithm
  • Maintain information on called numbers during
    initial call processing
  • Cache recent Release-Busies using hashing
  • Detect multiple Release-Busies to the same target
    number over a short (2-3 second) interval
  • Insert Call-Gaps into switches generating traffic
    to the busy number
  • Remove Call-Gaps after a period of inactivity
    (5-10 minutes)

58
Implementation Issues
  • Current switch technology does not allow Call
    Gaps to be set quickly
  • Fast Call Gaps assume switches engineering to
    allow Call Gaps to be set within one second
  • Slow Call Gaps assume Call Gaps can be set with
    an 8 second delay plus 700 milliseconds per
    switch (achievable with current switches)

59
Simulation Results
60
Simulation Results (Detail)
61
Operator Utilization (10 Operators)
62
Operator Utilization (100 Operators)
63
Summary
  • Unanticipated Mass Call-In events can be
    effectively and efficiently controlled by a
    simple detection method
  • Fast Call Gaps would reduce the effect of Call-In
    overloads to almost unnoticeable levels
  • Slow Call Gaps would provide an effective method
    for controlling Call-In events without the
    necessity of modification of existing switches

64
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

65
Research Summary
  • Security
  • B. Reynolds and Dipak Ghosal. STEM Secure
    Telephony Enabled Middlebox. IEEE Communications
    Magazine Special Issue on Security in
    Telecommunication Networks. October 2002.
  • B. Reynolds and Dipak Ghosal, Secure IP
    Telephony Using Multi-Layer Protection, to
    appear in Network and Distributed Systems
    Security (NDSS03), San Diego, February 2003.
  • Resource Management
  • M. C. Caesar, D. Ghosal, and R. Katz, Resource
    Management for IP Telephony Networks,''
    International Workshop of Quality of Service
    (IWQoS), Miami, May 2002.
  • Node Architectures
  • Dipak Ghosal, A Comparative Analysis of STP
    Architectures Under Transient Failure and
    Overload Conditions, IEEE International
    Conference on Perfromance and Dependable Systems,
    June 1999.

66
Research Summary (2)
  • Pricing
  • Matthew Caesar, Sujatha Balaraman and Dipak
    Ghosal, "A Comparative Study of Pricing
    Strategies for IP Telephony", IEEE Globecom 2000,
    Global Internet Symposium, San Francisco, USA, --
    I presented my work on Nov. 29, 2000.
  • Traffic Issues
  • J. Burns and D. Ghosal, Automatic Detection and
    Control of Media Stimulated Focused Overloads,''
    Proceedings of the International Teletraffic
    Congress, Washington D.C., June 1997, pp.889-900.
    To appear in Telecommunication Systems
  • A. Mukherjee and D. Ghosal, The Impact of
    Background Traffic on the Effectiveness of FEC
    for Audio over Internet,'' InternationalTeletraffi
    c Congress, Edinburgh, UK 1999.

67
Research Summary (3)
  • Enhanced Signaling Network Architecture
  • Abramson, Xiao-yan Fang, and D. Ghosal. Analysis
    of an Enhanced Signaling Network for Scalable
    Mobility Management in Next Generation Wireless
    Networks. IEEE Globecom. Taiwan, ROC, November
    2002. 
  • T. Sinclair and D. Ghosal, An Enhanced Signaling
    Network Architecture for Replicated HLR
    Prototype Implementation and Performance
    Analysis, ICC 1999, Vancouver
  • J

68
Outline
  • History
  • Network Architecture
  • SS7 Protocol
  • Routing
  • Media Stimulated Focused Overload
  • Overview of Telephony Research
  • Current Efforts

69
Overview
  • Security
  • Security architecture for IP Telephony
  • Sensors to detect DoS attacks
  • Detection algorithm
  • Recovery algorithms
  • Preliminary results from simulation analysis
  • Future work
  • Resource Management in IP Telephony
  • Routing

70
Enterprise Network
71
Call Setup Net-to-Net
SIP IP Phone
72
Call Setup PSTN-to-Net
73
Comparison of Solutions
Method Advantage Disadvantage
All Access Every application will work No perimeter security at all
Traffic Redirection No issues with firewall or NAT Removes advantages of using IP telephony
Application Proxy Firewall does not need to be modified Firewall cant provide protection for proxy
Protocol Tunneling Limited additional filter rules required Large overhead and requires modifying IP telephony clients
Secure Telephony Enabled Middleboxes (STEM) Provides high level of network security and allows dynamic apps Requires new firewall installed
74
Vulnerability Analysis
  • Property oriented approach
  • Access control to use IP telephony service
  • Integrity and authenticity of IP telephony
    signaling messages
  • Resource availability and fairness in providing
    IP telephony service
  • Confidentiality and accountability

75
Access Control
  • Deny unauthorized users access to IP telephony
    service
  • Central authentication servers
  • E.g. RADIUS server
  • Enable various network elements to query
    authentication server

76
Integrity and Authenticity of Signaling Messages
  • Call Based Denial of Service
  • CANCEL messages, BYE message, Unavailable
    responses
  • Call Redirection
  • Re-registering with bogus terminal address, user
    moved to new address, redirect to additional
    proxy
  • User Impersonation

77
Payload Encryption
  • Capture and decoding of voice stream
  • Can be done in real-time very easily
  • Capture of DTMF information
  • Voice mail access code, credit card number, bank
    account
  • Call profiling based on information in message
    headers

78
Resource Fairness and Availability
  • Flood based attacks
  • Network bandwidth between enterprise and external
    network
  • Server resources at control points
  • SIP Proxy Server
  • Voice ports in Media/Signaling Gateway
  • Signaling link between Media/Signaling Gateway
    and PSTN
  • End user

79
Internet Originated Attack
  • Enterprise network connection can be flooded
    using SYN flooding
  • Resources in the SIP proxy server can be
    exhausted by a large flood of incoming call
    request
  • End user can be targeted with a large number of
    SIP INVITE requests in a brief period of time

80
PSTN Originated Attack
  • Voice ports on the M/S gateway are completely
    allocated
  • Signaling link between M/S gateway and PSTN STP
    becomes saturated with messages
  • Large number of PSTN endpoints attempt to contact
    a single individual resulting in a high volume of
    INVITE messages

81
Security Architecture
82
Application Layer Attack Sensor (ALAS)
  • Monitors the number of SIP INVITE requests and
    the SIP OK (call acceptance) responses
  • URI level monitor
  • Aggregate level monitor
  • Detection Algorithm
  • Response Algorithm
  • Proxy or M/S gateway returns temporally busy
    messages

83
Transport Layer Attack Sensor (TLAS)
  • Monitors the number of TCP SYN and ACK packets
  • Traffic is monitored at an aggregate level
  • Upon detection of an attack, throttling is
    applied by perimeter devices (e.g. firewall)
  • If attack persists, traceback technologies can be
    used to drop malicious traffic at an upstream
    point

84
RTP Stream Attack Sensor (RSAS)
  • To detect malicious RTP and RTCP streams
  • Parameters of the RTP streams are known at
    connection setup time
  • Police individual streams
  • Statistical techniques to determine large flows
  • Packets corresponding to the malicious streams
    are dropped at the firewall
  • Need cooperation of upstream routers to mitigate
    link saturation

85
Detection Algorithm for TLAS
  • Monitoring the volume of connection attempts vs.
    volume of complete connection handshakes can be
    used to detect an attack
  • Based on the sequential change point detection
    method proposed by Wang, Zhang and Shin (Infocom
    2002) to detect TCP SYN attacks

86
Algorithm
  • All connection setup attempts and complete
    handshakes are counted during the observation
    period
  • During each sampling period the difference is
    computed and normalized
  • Under normal operation, the resulting value
    should be very close to 0
  • In the presence of an attack, the result is a
    large positive number
  • Apply a cumulative sum method to detect short
    high volume attacks as well as longer low volume
    attacks

87
Recovery Algorithm
  • Linear Recovery
  • This is the default behavior of the detection
    algorithm
  • Exponential Recovery
  • The cumulative sum decreases multiplicatively
    once the attack has ceased
  • Reset after Timeout
  • The cumulative sum decays linearly decays until a
    timer expires at which point it is reset to 0

88
Preliminary Results
  • Types of attack
  • Limited DoS attack
  • Single user targeted by one or more attackers
  • Stealth DoS attack
  • Multiple users targeted by one or more attackers
    each with a low volume of call requests
  • Aggressive DoS attack
  • Multiple users targeted with moderate call
    requests
  • Ability to detect both aggregate level attacks as
    well as attack to individual URIs

89
Preliminary Results
90
Preliminary Results
91
Preliminary Results
92
Results
93
Future Work
  • Detailed analysis
  • Tradeoff between detection time and false alarm
    rate
  • Formal vulnerability analysis
  • Additional vulnerabilities with ENUM
  • Routing layer issues
  • Vulnerabilities of multihomed networks

94
Resource Management in IP Telephony Networks
  • Matthew Caesar, Dipak Ghosal, Randy H. Katz
  • mccaesar, randy_at_cs.berkeley.edu
  • ghosal_at_cs.ucdavis.edu

95
Motivation
  • What is IP Telephony?
  • Packetized voice over IP
  • PSTN access through Internet Telephony Gateway
    (ITG)
  • Benefits
  • Improved network utilization
  • Next generation services (POTS ? PANS)
  • Growth
  • Revenues 1.7 billion in 2001, 6 of
    international traffic was over IP, growing Frost
    2002 Telegeography 2002
  • Standardized, deployed protocols (TRIP, SIP,
    H.323)
  • ? Requires scalable architecture to limit
    congestion.

96
Goals
  • High quality, economically efficient telephony
    over the Internet.
  • Low blocking probability
  • Provide preferential treatment, high QoS
  • Questions
  • How to perform call admission control?
  • How best to route calls through converged network?

97
Approach
  • Mechanisms
  • ITG selection
  • Congestion sensitive call admission control
  • Techniques
  • Awareness of ITG congestion
  • Path quality between important points in network




Distance




Utilization
98
Overview
  • IP Telephony Networks
  • Pricing-based Admission Control
  • Redirection Techniques
  • Experimental Design
  • Results
  • Future Work

99
System Architecture
ITG
ITG
LS
LS
ITG
LS
ITG
LS
ITG
LS
ITG
LS
Admin. Domain (AD)
Example Call Setup
Internet
Example Advertisement
Gateway (ITG)
ITG
IP Terminal
Example Call Session
Location Server (LS)
LS
100
Scope of Study
  1. All calls are net-to-phone
  2. ADs cooperate to provide service.
  3. Use IETFs TRIP architecture to support
    interoperability.
  4. Disregard degradation in access network.
  5. Prices determined at start of call.
  6. ITGs offer equal PSTN reachability.

101
Pricing
  • PSTN
  • distance pricing
  • time of day pricing
  • IP Telephony
  • richer user interface
  • allows for more dynamic pricing schemes
  • Baseline Flat-rate Admission Control (FAC)

102
Congestion Sensitive Call Admission Control (CAC)
  • Goal prevent system overload and generate
    revenue
  • Price of call
  • function of number of voice ports in use
  • rises when highly utilized
  • More dynamic than PSTN

103
Price-Congestion Function
  • Used M/M/m/m (m-server loss system)
  • responsive server
  • loss system
  • discouraged arrivals
  • Found price-congestion function that maximized
    revenue with respect to a

104
Congestion Pricing Analysis
  • Exponential function generates most revenue
  • Stepwise linear function almost as good
  • Maximum system price charged early
  • Approximation to function minimizes price
    fluctuations

105
Redirection
  • Problem finding the best ITG
  • Approach tradeoffs between quality and load
  • Method LS maintains
  • Average measured path quality
  • Number voice ports in use
  • Algorithms
  • Random Redirection (RR) (baseline)
  • QoS Sensitive Redirection (QR)
  • Congestion Sensitive Redirection (CR)
  • Hybrid Scheme (CQR)

106
Redirection Schemes
  • QoS Sensitive Redirection (QR)
  • Different paths provide different service
  • Technique
  • Use RTCP RRs to monitor path congestion
  • Route over best paths
  • Congestion Sensitive Redirection (CR)
  • Unbalanced load causes call blocks
  • Technique
  • Use TRIP advertisements to estimate ITG
    utilization
  • Route to least utilized ITG

107
Hybrid Redirection (CQR)
  • Choosing nearby ITG improves call quality, but
    can unbalance load.
  • Algorithm
  • Compute Rdm ? Mi(1-?)Qi
  • Mi is utilization, Qi is loss rate
  • Select randomly from k ITGs with lowest Rdm
  • Tradeoffs
  • Use ? to trade off call quality and load balance
  • Use k to vary flash crowd protection
  • Price Sensitive CQR (PCQR)
  • Decrease ? for higher bids

108
Overview
  • IP Telephony Networks
  • Pricing-based Admission Control
  • Redirection Techniques
  • Experimental Design
  • Results
  • Future Work

109
Experimental Method
  • Modified ns-2
  • Ran for 1.5 simulated hours
  • Eliminated first half-hour
  • User Model
  • Bid uniformly distributed
  • Voice traffic on-off Markov process
  • Pareto cross-traffic
  • Data points stable across several time scales

110
Evaluation Metrics
  • Blocking Probability
  • Average call QoS
  • Used Mean Opinion Score (MOS) based on RTP loss
    rate
  • Economic efficiency
  • Ratio of service tier to QoS achieved
  • Stability Variance in ITG utilization
  • Over time
  • Over the set of ITGs

111
Admission Control Blocking Probability
  • Flat pricing unnecessarily blocks many callers
  • Congestion pricing changes system price
    dynamically with load

112
Redirection Blocking Probability
  • Congestion sensitivity decreases blocking
    probability
  • Small k ? few blocked calls
  • Congestion Sensitive Redirection (CR) improves
    balance over Random Redirection (RR)

113
Redirection Load Balance
?
  • More congestion sensitivity improves balance
  • Load imbalance blocks calls

114
Redirection Background Traffic Effects
  • QoS sensitivity minimizes effects of cross
    traffic
  • Small amount of sensitivity vastly improves call
    quality

115
Summary
  • Admission Control Schemes
  • Congestion sensitive pricing decreases
    unnecessary call blocking, increases revenue, and
    improves economic efficiency
  • Derived exponential price-congestion function
    that maximizes revenue
  • Redirection Schemes
  • Hybrid scheme achieves best of both worlds
  • Price sensitivity improves economic efficiency

116
Future Work
  • Realistic workload
  • Improve user model
  • Develop price-congestion function for real users
  • Study flash-crowd effects
  • ITG Placement
  • Competitive Network

117
Routing in IP Telephony Networks
  • Brian Liao, Matthew Caesar, Dipak Ghosal

118
Problem
  • Finding suitable Gateway to balance resource,
    enhance QoS.
  • Select best path to lower blocking probability,
    decrease delay.

119
Finding The Appropriate Gateway
  • Performing matrix
  • ßMi(1-ß)Qi
  • Mi voice port in use in gateway i
  • Qi Audio Quality in gateway I

120
Finding Suitable Path (I)
  • Blocking Probability Delay are two keys
    selection criteria
  • Multi-constraints shortest path problem is NP

121
Finding Suitable Path (II)
  • Finding K-shortest paths for primary constraint.
  • From the K-shortest paths, select the best path
    with respect to secondary constraint.
  • Feasible in Polynomial Time.

122
Proposed solution
  • Base on location, select the best gateway nearby.
  • Using K shortest path to select path and fulfill
    multi-constraint.

123
Reference
  • Canhui (Sam) Ou, Keyao Zhu, Hui Zang, Laxman H.
    Sahasrabuddhe, and Biswanath Mukherjee, Traffic
    Grooming for Survivable WDM Networks -- Shared
    Protection
  • David Eppstein, Finding the K shortest paths.
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