Issues in a VoIP Network (part 5)

There are several issues that need to be addressed in order to provide a toll-quality, PSTN equivalent end-toend VoIP network. These include: 

• Service set to be offered, and the types of end user terminal supported.
• Choice of signaling protocol(s).
• Security.
• Quality of Service (QoS).
• Reliability / availability.
• Regulatory Issues
• Lawful Interception
• Emergency and Operator Services

• Call routing and Number Plans.
• DTMF and Other Tones and Telephony Events
• Firewall and NAT traversal.
• Billing and Reconciliation.
• Network Interconnection.
• Migration Path.
• OSS support.
• Bandwidth Utilization.
• Fax, Modem, and TTY support.
• Auto-configuration.

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: 

1.  POTS “black phones”
2.  IP phones.
3.  PBXs and key systems 
4. 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. 

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.