R. Koodli, Fast Handovers for Mobile IPv6 [RFC 4068], Jul 2005 K. Taniuchi, IEEE 802.21: Media Independent Handover , Comm Mag, Jan 09 A. Dutta et al, A Framework of Media-Independent Pre-Authentication (MPA), 2008 I. Ali et al, Network based mobility management in the EPC Network, Comm Mag., Feb 09
Design and Optimization of Authentication, Authorization, and Accounting (AAA) Systems in Mobile Telecommunications Networks Said Zaghloul Technical University Carolo Wilhelmina of Braunschweig, Germany PhD Defense 27.04.2010 Braunschweig, Germany
Background: Evolution Trends Evolution of Service Requirements Evolution of Cellular Systems
Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2009-2014
Background: How an all-IP Network Looks Like ? RNC CAS DPI Rating Server Billing Server AAA Internet Acronyms RNC: Radio Network Controller AGW: Access Gateway CAS: Content Adapt. Server DPI: Deep Packet Inspection IMS: IP Multimedia Subsystem PCRF: Policy & Charging Rules Function CSCF: Call Session Control Function AS: Application Server HSS: Home Subscriber Subsystem Users Database AS AS Radio Access Network PCRF HSS AS CSCF AGW IP Transport Network 3 rd Parties IMS Network Authentication & Billing WiFi Access Car-2-X Services Service/Content Aggregation Network Transport Billing Provider Location Info. Broker Content Provider Wireless Access Subscribers Operator Centric Revenue Streams Adapted from Eliot Weinman, Harnessing the Mobile Internet, Yankee Group
Background: The AAA Systems Role (1) RNC CAS P-GW Rating Server Billing Server AAA Internet Users Database AS AS Radio Access Network PCRF HSS AS CSCF AGW IP Transport Network 3 rd Parties IMS Network Authentication & Billing WiFi Access Car-2-X Services AAA systems are central elements that enable service offerings in emerging cellular networks.
Background: The AAA Systems Role (2) AGW AAA Diameter or RADIUS IP Backbone 1 2 Radio Access Network IP Domain Authenticate Authentication and Accounting Network Access Server (NAS) Call Detail Record (CDR) SQL or LDAP Users DB Billing Systems
Topology: gateway arrangement, roaming, different technologies
Dimensioning and evaluating design options
Testing : to predict the steady state AAA signaling rate for a test
Cost Analysis: to get the cost per user session ($$ per session)
Planning: Models and Analytical Tools Probability and stochastic analysis Probability and stochastic analysis Probability and stochastic analysis Renewal theoretic concepts Renewal theoretic concepts Transient Markov chains theory Analytical Tools Fixed Model Basic Model Distributed Model Control Plane Planning Analytical Toolbox
No lost Response/Answer messages [Response packets are usually smaller than requests]
No blocking at the AGW [AGW capacities are usually large (thousands)]
No fragmentation [Packet sizes are usually of similar sizes are not large]
Planning: Fixed Model (1): Mean Interims Interim Interval Signaling Rate Authentication/ Authorization Accounting Interim Reauth Authorization Lifetime Interim Interval Session Time ( S ) Accounting Start Accounting Stop A message can be transmitted f times Accepted session with probability ( ) Retransmissions Factor Proportion of Received Accepts Let k be the number of transmissions, p be the packet loss probability, and N be the maximum number of retransmissions.
Planning: Fixed Model (2): Mean Interims f J (2) is the service session duration (R.V.) is the accounting interim interval (const.) E[S] / T Error (E[S]/ T , Model) > 3 < 5% 2-3 30% - 5% 1-2 72% - 30% 0.5 219% 0 T 2 T 3 T 4 T 5 T f S (s) f J (j) 0 1 2 3 4 5
Planning – Fixed Model (3) Under exponential assumptions for the session duration, the signaling rate is Parameters: p a = 100%, p=1%, 95% confidence
The interim interval (similarly the authorization lifetime) can largely affect the signaling rate and in a non-linear manner
Holding time ( H ): The random time a user spends in an area during an active session.
Residence Time ( R ) : The random time that a user spends in an area regardless of his session activity .
4 5 H Tr H T H O Given session initiation and termination points, Special case In fixed networks: S = H F Area 1 Area 2 H T 3 H O 2 Holding Time Type Full = H F Originating = H O Terminating = H T Transiting = H Tr 1 H F
Generic (e.g., Gamma) distributed residence times ( R )
The residence time in the initial area R 0 where the session starts is given by its residual since the instant users enter an area and the instant they start their sessions are not necessarily aligned.
The residual lifetime of a random variable is given as
Session ( S ) H T H Tr H Tr H O
Planning – Basic Model (4) t Session Start T ACR (Stop) Case 3 Handoff Event Handoff Event ACR (Stop) Case 2 Handoff Event ACR (Stop) Case 1 T T T T Case 1 no handoffs S H F T T T Case 2 one handoff S H O H T T T T Case 3 multiple handoffs S H Tr H T H Tr H O Accounting Starts and Authentications Accounting Stop Accounting Interims Session Duration
Planning – Basic Model (5) Recall that Break by E [ K ] Combine using E [ K ], p 0 Get E [ I ]
Planning – Basic Model (6) * * Basic Model Fixed Model * 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 200 400 600 800 1000 1200 Mean residence time to mean session time ratio (E[R]/E[S]) Signaling Rate (Messages/sec) Session Arrival Rate Parameters: =100 req/s, M = T = 0.5 E[S] Accounting (Mobile) Accounting (Fixed) Auth (Mobile) Auth (Fixed) Context Transfer
Mobility makes a difference when mean session duration > mean residence time.
Fixed model: Lower bound for the basic model and an upper bound for Auth signaling in cases of context transfers.
Exponential session duration assumption results in approx. 15% error.
Planning – Distributed Model (2) 15 27 21 9 8 26 20 14 1 2 6 0 7 13 19 25 . . . 12 18 24 32 5 Areas 6 Areas We overlay the a transient Markov chain model to describe the mobility pattern between areas or AGW regions.
The Optimization Mechanisms: Delay (2) Policy System Application Server Gateway 1 Gateway 2 Home Agent I am NOT paying for this anymore Delay > 1000 ms Target is 70 ms !!
Mobility management (FMIP, MIH, MPA) does NOT cover QoS maintenance
Only recently , such issues where raised in the context of emerging LTE networks.
I. Ali et al, Network based mobility management in the EPC Network, Comm Mag., Feb 09
The Optimization Mechanisms: Delay (3) RNC: Radio Network Controller PCRF: Policy and Charging Rules Function AAA: Authentication, Authorization, and Accounting Signal to Noise Ratio TIME Current Cell Candidate Cell Hysteresis Margin Handoff D 1 D 2 Trg2 Trg1 Handoff Prediction Proactive QoS Authorization Service Delay Estimates RNC PCRF AAA AAA PCRF
Optimization Mechanisms: Reliability (2) Load almost independent of the interim interval AAA Server Capacity Limit Potential Loss Min Loss Max Load Max Loss Min Load AAA Load Loss Upper Bound Optimization Region 0 0.5 1 1.5 Interim Interval/Mean Session Duration ( T /E s ) AAA Signaling Load (message/sec)
Interim Interval Estimation Block Mean Service Arrival Rates Mean Service Session Durations ( i ) ( E [ S i ] , Var [ S i ]) ,
The loss is given as,
Statistics Collection Block
For each service,
Session arrival rate
Interim Intervals for all services T Session Type Acct Start Message [Begin-of-Session AVP] Acct Stop Message [Session-Continue AVP] H F true false H O true true H T False or N/A true H Tr False or N/A false