Static Call Admission Control and Dimensioning of Media Gateways in IP based Mobile Core Networks

1. Static Call Admission Control and Dimensioning of Media Gateways in IP based Mobile Core Networks Mika Isosaari Supervisor: prof Jorma Virtamo Instructor: Harri Lehtomäki, M.Sc.

2. Contents • Introduction • General Structure of UMTS Release 5 Network • Media Gateway • Multiservice IP Transport Network • Network Dimensioning • Quality of Service • Mechanisms to Guarantee QoS • Static Admission Control • Simulations • Conclutions and Future Work

3. Introduction • Background • VoIP vs. ToIP • How telecom grade speech can be transferred in connectionless IP network? • Multiservice IP network: speech only one of the services • Objectives • To study how circuit-switched speech can be transferred in an IP multiservice network so that a certain Quality of Service (QoS) level can be sustained • How static admission control methods work and what is their influence on network dimensioning

4. Research methods • Literature study • ITU, 3GPP, IETF recommendation and specifications • Books and articles to get a more comprehensive picture of the subject • Numerical evaluation • Used in comparing different static admission control methods and their effect on dimensioning • Simulations • Show how the traffic intensity affects the utilization and resource demand

5. General Structure of UMTS Release 5 Network • Three domains: Circuit-Switched (CS), Packet-Switched (PS) and IP Multimedia Subsystem (IMS) • This thesis focuses on CS domain

6. Layered Architecture • Application layer • Network control layer • Connectivity layer • MGW • Backbone

7. Media Gateway • PSTN/PLMN transport termination point • May support media conversion, bearer control and payload processing (e.g. transcoders and echo cancellers) • Nb User Plane traffic between MGWs is transported either over ATM or IP bearer • Logically resides at the border of the backbone, physically part of site configuration • Basic site infrastructure: Local Area Network (LAN) switches and site routers

8. Multiservice IP Transport Network

9. Telephony services in multiservice IP network • Strict requirements for Telephony over IP (ToIP) • when international telecommunication networks interwork with IP-based networks, the QoS experienced by the users should, as far as practicable, be the same as if there had been no interworking involved • Data Conversions and Protocols • MPLS, IP/UDP/RTP/NbUP, AMR/PCM…

10. Network Dimensioning • The whole planning process is influenced by the UMTS architecture and IP backbone when compared to traditional GSM network • overall architecture is very different • multiservice network • information is transferred in a form of packets in a connectionless network • Dimensioning Challenges • every traffic flow has an effect on all the other traffic flows and a wrongly configured service can lead to degradation of speech quality, which is not acceptable • when the speech is packet-based everything comes in practice a matter of probabilities

11. Quality of Service • Quality of Service (QoS) is the quality of a requested service as perceived by the customer and always meant end-to-end • Information Quality Parameters: delay, jitter, BER, PLR, data rate • QoS Architecture in UMTS Networks vs. QoS in Internet • Mapping of different quality classes important • E.g. with DiffServ: EF  conversational, AF  streaming / interactive, BE  background • Internet QoS: IntServ, DiffServ, MPLS(?), traffic engineering

12. Mechanisms to Guarantee Quality of Service • Network Level Mechanisms • Dimensioning • Overprovisioning • Architecture • Flow Level Mechanisms • Static Admission Control • Dynamic Admission Control • Packet Level Mechanisms

13. Static Admission Control • Basic idea: permanently allocated resources in the backbone network set by the service provider • MGW is in practice the most logical choice in the CN for the implementation (may work together with routers in the backbone) • Main advantage of static methods is their simplicity • Downside is the inefficient usage of network resources • Two most important models: pipe model and hose model

14. Static Admission Control • Pipe model • traditional model how provisioning has been performed in private networks • point-to-point connection with a given pre-allocated capacity • destination-specific: large number of configuration parameters • Implementation: MGW or MGW / edge router • Hose model • first proposed as a flexible model for resource provisioning in VPNs • no individual pipes between nodes but “hoses”, which contain all incoming or outgoing traffic • Advantages: flexibility, ease of specification, multiplexing gain and characterization

15. Simulations • What is the actual gain of statistical multiplexing when the traffic is handled as an aggregate rather than as individual pipes? • Simulations were performed with the NS2 network simulator • PCM: CBR UDP application • AMR: two Exp on/off UDP apps.

16. Simulations - results • Bandwidth limit for link • PLR 10-4 • Jitter <5ms • Utilization: gained link bw divided with average bw

17. Simulations - results

18. Conclusions • Although various mechanisms exist for guaranteeing some QoS level in an IP network there is no particular mechanism that alone could sustain a certain QoS  available mechanisms should be used together so that different mechanisms on packet, flow, and network level complement each other • Justifies also the use of static admission control methods, with which a permanent limit can be set for the traffic that a site can offer to a backbone network

19. Conclusions • Pipe vs. hose • flexibility and easy implementation are clearly characteristics of the hose model • overprovisioning factor related to configuration parameters can with high probability be kept under 2 for the hose model • simulations show clearly that the utilization improves when the traffic intensity is increased, but… • Already 250 Erl traffic has utilization rate of ca. 80 % • gain is not necessarily that significant and does not alone make a clear difference between the two models

20. Future work • measurements from a real network are needed to validate any simulation results • edge router based pipe model • dynamic resource allocation • optimal routing method for the hose model • domain model: combine best features from pipe and hose models

21. Questions?