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1
A Review of the Architecture and the Underlying Protocols in
the Telephone Network
Dipak GhosalDepartment of Computer ScienceUniversity of California at Davis
April 10, 2023 2
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 3
History Pre-1984
AT&T 1980’s saw rapid deployment of digital
technology in the core network 1984
Breakup of AT&T into 7 RBOCs (Regional Bell Operating Companies), AT&T, and others
Local area carriers (LECs) serving LATA were regulated
Long distance carrier (IXC) service was opened
April 10, 2023 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 AT&T AT&T Lucent (Bell-Labs)
Mergers of RBOCs and CLECs
April 10, 2023 5
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 6
A Typical Regional POTS Network
April 10, 2023 7
Network Architecture
April 10, 2023 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
April 10, 2023 9
Circuit Network (2) Hierarchical organization
End office Toll Center Primary Center Sectional Center Regional Center
April 10, 2023 10
End Office
April 10, 2023 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 -> Service Switching Points STP -> Signaling Transfer Point SCP -> Service Control Point
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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.
April 10, 2023 16
Types of Signaling Links
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 20
Requirements Availability objective: an unavailability
of no more than 10 minutes downtime between two SPs
Lost message probability: 1 in 10**7 Message Out-of-sequence probability: 1
in 10**10 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
April 10, 2023 21
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 22
Protocol Stack
April 10, 2023 23
ISDN User Part (ISUP)
April 10, 2023 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)
April 10, 2023 25
Database Query (TCAP)
April 10, 2023 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.
April 10, 2023 27
Message Transfer Part (MTP) Layer 3 Network Management
Link management Traffic management Route Management
Message discrimination Message distribution Message routing
April 10, 2023 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)
April 10, 2023 29
MTP Layer 3 (3) Traffic management
Link failures Route failures Congestion
April 10, 2023 30
Transient A-Link Failure
Level3
L2
Level3
STP1
STP2
LinkFailure
SP1 SP2
L2
SPn
L2
L2
April 10, 2023 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
April 10, 2023 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
April 10, 2023 33
Congestion
Level3
L2
Level3
STP1
STP2
SP1 SP2
L2
SPn
L2
L2
SP3
TFCMessages
April 10, 2023 34
STP Architecture
April 10, 2023 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?
April 10, 2023 36
Model of Level-3 Processor
April 10, 2023 37
Network Model 1, 8, 16, 24 A-link
failures All failures to a
single STP Simultaneous
recovery after 11 seconds
April 10, 2023 38
Call Throughput
April 10, 2023 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
April 10, 2023 40
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 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
April 10, 2023 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
April 10, 2023 43
Alternate Routing (2) There are different methods on
how the routing control is propagated Originating-office control Spill-forward control Crankback
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 47
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 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
April 10, 2023 49
Example of Mass Callin
April 10, 2023 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)
April 10, 2023 51
SSP
STP
Call
Attempt
SSP
XXX-XXX-XXXX 60XXX-XXX-XXXX 60XXX-XXX-XXXX 120XXX-XXX-XXXX 30XXX-XXX-XXXX 10XXX-XXX-XXXX 100XXX-XXX-XXXX 30XXX-XXX-XXXX 3XXX-XXX-XXXX 60XXX-XXX-XXXX 60XXX-XXX-XXXX 120XXX-XXX-XXXX 30XXX-XXX-XXXX 10XXX-XXX-XXXX 100XXX-XXX-XXXX 30XXX-XXX-XXXX 3XXX-XXX-XXXX 60
Call Gap Table
Manual Call Gaps
April 10, 2023 52
SSP
STP
Call
Attempt
SSP
Block all calls
to target DPC
TFC
CongestionDetected
TFC Congestion Control
April 10, 2023 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
April 10, 2023 54
Caller
Caller
Callee
Callee
Normal Call
Call to a Busy Number
IAM
IAM
ACMANM REL RLC
REL RLC
Release-Busy
IAM carries called number
Conversation
Call Processing and Signaling
April 10, 2023 55
• 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
Key Ideas
April 10, 2023 56
Example of Mass Callin
April 10, 2023 57
• 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)
Algorithm
April 10, 2023 58
• 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)
Implementation Issues
April 10, 2023 59
Simulation Results
April 10, 2023 60
Simulation Results (Detail)
April 10, 2023 61
Operator Utilization (10 Operators)
April 10, 2023 62
Operator Utilization (100 Operators)
April 10, 2023 63
• 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
Summary
April 10, 2023 64
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 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.
April 10, 2023 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,'' InternationalTeletraffic Congress, Edinburgh, UK 1999.
April 10, 2023 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
April 10, 2023 68
Outline History Network Architecture SS7 Protocol Routing Media Stimulated Focused Overload Overview of Telephony Research Current Efforts
April 10, 2023 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
April 10, 2023 70
Enterprise Network
PSTN
Enterprise DMZ
SIPRedirect
Proxy
SIPRegistrar /LocationServer
WebServer
DNSServer
EdgeRoute
rExternal
Firewall
Internal
Firewall
Softphone IP Phone
EnterpriseLAN
Authentication Server
Media /Signal
Gateway
Internet
April 10, 2023 71
SIP IP Phone
SIP IP Phone
Location Service
SIP Proxy
SIP Proxy/LS
DNS Server
Media Transport
1
2
3
4
5
6
A request is sent (SIP INVITE) to
ESTABLISH a session
DNS Query for the IP Address
of the SIP Proxy of the
Destination Domain
The INVITE is forwarded
The Location Service is queried to check that the
destination IP address represents a valid
registered device, and for its IP Address
The request is forwarded to the End-Device
Destination device returns its IP Address to the
originating device and a media connection is
opened
Call Setup – Net-to-Net
April 10, 2023 72
Call Setup – PSTN-to-Net
April 10, 2023 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 can’t 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 81
Security Architecture
Internet
Enterprise DMZ
SIPRedirect
Proxy
SIPRegistrar /LocationServer
WebServer
DNSServer
External
Firewall
EdgeRoute
rInterna
lFirewal
l
Transport LayerAttackSensor
ApplicationLayerAttackSensor
PSTN
Media /Signal
Gateway
ApplicationLayerAttackSensor
Softphone IP Phone
EnterpriseLAN
Authentication Server
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 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
April 10, 2023 89
Preliminary Results
April 10, 2023 90
Preliminary Results
April 10, 2023 91
Preliminary Results
April 10, 2023 92
Results
April 10, 2023 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}@cs.berkeley.edughosal@cs.ucdavis.edu
April 10, 2023 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.
April 10, 2023 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?
April 10, 2023 97
Approach Mechanisms
ITG selection Congestion
sensitive call admission control
Techniques Awareness of ITG
congestion Path quality
between important points in network
Dis
tance
Utilization
**
**
*
* *
April 10, 2023 98
Overview IP Telephony Networks Pricing-based Admission Control Redirection Techniques Experimental Design Results Future Work
April 10, 2023 99
System Architecture
ITG
LS
Example Call SetupExample AdvertisementGateway (ITG)
IP TerminalLocation Server (LS)
InternetAdmin. Domain (AD)
Example Call Session
ITGITG
ITG
ITG
ITG
ITG
LS
LS
LS
LS
LS
LS
1 2
3
4
5
6
April 10, 2023 100
Scope of Study 1. All calls are net-to-phone2. ADs cooperate to provide service.3. Use IETF’s TRIP architecture to
support interoperability.4. Disregard degradation in access
network.5. Prices determined at start of call.6. ITGs offer equal PSTN reachability.
April 10, 2023 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)
April 10, 2023 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
April 10, 2023 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
0
1
2
m-1
m
...
m-1
m
April 10, 2023 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
fluctuationsPrice-congestion Function Used in this Study
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60Utilization [voice ports]
No
rmal
ized
Pri
ce C
har
ged
Revenue-maximizing Price-congestion Function
00.10.20.30.40.50.60.70.80.9
1
0 10 20 30 40 50 60Utilization [voice ports]
No
rma
lize
d P
ric
e C
ha
rge
d
April 10, 2023 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)
April 10, 2023 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
April 10, 2023 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
April 10, 2023 108
Overview IP Telephony Networks Pricing-based Admission Control Redirection Techniques Experimental Design Results Future Work
April 10, 2023 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
April 10, 2023 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
April 10, 2023 111
Admission Control: Blocking Probability
Flat pricing unnecessarily blocks many callers
Congestion pricing changes system price dynamically with load
Call Blocking Probability
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.2 0.4 0.6 0.8 1Offered Load
Blo
ckin
g P
rob
ab
ilit
y
QR+FAC
QR+CAC
April 10, 2023 112
Call Blocking Probability
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Beta
Blo
ckin
g P
ro
bab
ilit
y
CQR+NAC k=1CQR+NAC k=3CQR+NAC k=6RR+NAC
Redirection: Blocking Probability
Congestion sensitivity decreases blocking probability Small k few blocked calls Congestion Sensitive Redirection (CR) improves balance over
Random Redirection (RR)
April 10, 2023 113
System Stability
0
50
100
150
200
250
300
0 0.2 0.4 0.6 0.8 1Beta
Va
ria
nc
e in
Uti
liza
tio
n [
po
rts
/se
c]
CQR+NAC k=1
CQR+NAC k=3
CQR+NAC k=6
RR+NAC
Redirection: Load Balance
More congestion sensitivity improves balance
Load imbalance blocks calls
April 10, 2023 114
Redirection: Background Traffic Effects
Effects of Background Traffic
0
1
2
3
4
5
6
0 1 2 3 4 5Background Traffic Multiplier
Qo
S [
MO
S]
CQR+NAC Beta=0
CQR+NAC Beta=0.9
CQR+NAC Beta=1
RR+NAC
QoS sensitivity minimizes effects of cross traffic Small amount of sensitivity vastly improves
call quality
April 10, 2023 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
April 10, 2023 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
April 10, 2023 118
Problem: Finding suitable Gateway to
balance resource, enhance QoS. Select best path to lower blocking
probability, decrease delay.
April 10, 2023 119
Finding The Appropriate Gateway Performing matrix =
βMi+(1-β)Qi
Mi: voice port in use in gateway iQi: Audio Quality in gateway I
April 10, 2023 120
Finding Suitable Path (I) Blocking Probability & Delay are
two keys selection criteria Multi-constraints shortest path
problem is NP
April 10, 2023 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.
April 10, 2023 122
Proposed solution Base on location, select the best
gateway nearby. Using K shortest path to select
path and fulfill multi-constraint.
April 10, 2023 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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