 to handle the concurrent calls. You might have an interbranch calling facility already in place over the MPLS net- work. If this is the case, you just need to add extra bandwidth for other calls that are made to locations outside the organization. Bandwidth between headquarters and the service provider: You also need to in- crease the bandwidth at your central SBC location, which is connected externally to the service provider. This location can handle hundreds of concurrent calls. However, you might not see a significant increase in bandwidth (compared to your existing data bandwidth to support a large organization). Therefore, depending on the number of SIP trunks purchased and the amount of excess Internet connectivity, a business should consider purchasing more Internet access. However, it's important to know that when a SIP trunk is not used, the bandwidth other- wise allocated to a SIP trunk is freed up for use in less-intensive applications, such as email and general web use. This dynamic allocation of bandwidth is yet another feature of SIP trunks versus more traditional technologies, such as analog or PRI circuits. Although you can increase your bandwidth, the cost might not be significantly higher. Although bandwidth increase is not substantial for large deployments, it is still high on the Small and Medium Business (SMB), especially because a G.711 or wideband call on a SIP trunk takes 80 Kbps whereas a TDM takes only one T1 channel of 64 Kbps. Service Level Agreement Charge Quality is a big issue in the case of VoIP. In the case of TDM circuit (such as T1 PRI), a call takes the full channel of 64 kbps, which is always guaranteed for that specific call. But, in the case of VoIP, the service provider might need to sign up a service level agree- ment (SLA) with the customer to ensure the following parameters: Link quality: Measures the downtime of the system and the link. Some service providers offer you 99.999 percent uptime. Equipment quality: If your SBC and IP-PBX is managed by the service provider,