Issues in a VoIP Network - Issues in a VoIP Network There...

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Issues in a VoIP Network There are several issues that need to be addressed in order to provide a toll-quality, PSTN equivalent end-to-end VoIP network. These include: •Service set to be offered, and the types of end user terminal supported. 1. Choice of signaling protocol(s). 2. Security. 3. Quality of Service (QoS). 4. Reliability / availability. 5. Regulatory Issues 6. Lawful Interception 7. Emergency and Operator Services 8. Call routing and Number Plans. 9. DTMF and Other Tones and Telephony Events 10. Firewall and NAT traversal. 11. Billing and Reconciliation. 12. Network Interconnection. 13. Migration Path. 14. OSS support. 15. Bandwidth Utilization. 16. Fax, Modem, and TTY support. 17. Auto-configuration. 1 Service set A crucial decision facing an operator looking to deploy a VoIP network is the service set that needs to be supported. This could range from a minimal set of services for a “cheap teen line” offering possibly alongside broadband data services, through to full PSTN equivalence and advanced services for carriers wishing to replace their current infrastructure with a new converged network for all subscribers. Another important part of the service design is the choice of end user terminals that are to be supported by the service offering, possible choices include: •POTS “black phones” •IP phones.
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•PBXs and key systems •PC soft-clients (including web-based applications) This whitepaper and the MSF work program is aimed at providing PSTN equivalence service, but does not explicitly limit the choice of terminals. This decision does effectively define much of the problem space that the network designer will have to work with. This can be seen from the fact that many of the issues discussed below are fundamentally affected by the decisions made in regard to services and terminals. 2 Choice of Signaling Protocols Numerous different signaling protocols have been developed that are applicable to a VoIP solution. They include •Device control protocols such as H.248 (Megaco), MGCP, NCS, etc •Access services signaling protocols such as SIP, H.323, etc •Network service signaling protocols such as SIP, SIP-T, BICC, CMSS, etc The choice of which protocol to use in a service provider network is dependent upon both the service set being offered and the equipment available to provide these services. For example a network must support SIP in order to provide access to SIP phones. 3 Security The PSTN has been very resistant to security attacks and has not suffered from significant problems since the introduction of SS7 out-of-band signaling. VoIP Next- Generation network is much more susceptible to security attacks and must address three key security issues. 3.1 Denial of Service A denial of service attack prevents legitimate users of a network from accessing the features and services offered by that network. Denials of service attacks are extremely difficult in the PSTN but all too common in IP networks. There have been several successful attacks on web servers on the Internet, even including the high security government sites. In a complex network, there are many possible denials of service
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attacks. Some examples include sending false signaling messages so that a call agent is
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