nd changing the configuration in the network. You can manage your seasonal spikes in call volumes with most of the service providers. They might not charge you anything extra for this service; rather, you can negotiate a better price when you buy more from a single vendor. Cost of Security When you take any service over the IP network, you need to take some security meas- ures. This is one of the main differentiators between TDM trunks and SIP trunks. For a TDM trunk, an intruder needs access to your physical wire to do any harm to your net- work or play with your privacy. But for a SIP trunk, your network is accessible from any- where on the Internet. With that in mind, your network is subject to the following threats: Denial of service (DoS) threats, call hijacking, or spoofing the call control system Losing privacy to eavesdropping, man-in-the-middle attacks, or media tampering SPAM attacks with unsolicited or malicious messages such as SPIT or phishing Fake identity threats that result in toll fraud, impersonation, and illegal modem calls 54 SIP Trunking Your service provider provides some degree of protection. However, in reality, most intruders try to access a network through the Internet or SP network. Do not depend solely on the service provider to ensure the security of your network. To ensure security, you might want to deploy firewalls in the middle of the SIP call flow. You can do this before the SBC, after the SBC, or both. Some SBCs (or Border Elements) support native firewalls. You might think your data firewall will perform well enough for your voice/video network; however, this might not occur when you receive SIP INVITES from anyone in the cloud. You might need to upgrade your firewall (or features) to secure your UC. Whether you use a native firewall within SBC or a separate firewall box, you need to budget for this. Cost of Expertise/Knowledge A SIP trunk is a new trunking solution. Service providers have just started offering SIP trunks for enterprises, and deploying a successful SIP trunk is