Xerox 3100MFPX 3100 MFP Guide to Faxing over IP Networks - Page 2

What is Fax over IP (FoIP)? In FoIP, the fax data is sent in its raw digital form across the IP network. As with all IP data, it is divided into a packet structure. Because the fax data is in its raw state it uses less bandwidth and can employ redundancy (data duplication) or Forward Error Correction to improve reliability. Sometimes the fax data rate is reduced to further limit bandwidth usage. It is thus normal that SuperG3 is not supported, and so it should be disabled on the Phaser 3100MFP to avoid compatibility issues. FoIP is sometimes called Fax Relay. There are proprietary versions (e.g. Cisco) but the cross-vendor standard from the International Telecommunications Union is called T.38 (which is supported by the Sagem Fax ATA 101S). It is possible to enable the Phaser 3100MFP for FoIP operation using an IP terminal interface. This interface recognizes the signals from the fax machine and decodes them back to the raw fax data, in real time. A similar interface may be required at the other end of the communication. The interface must also convert fax data received from the network back into analogue signals that the machine will understand. To ensure successful faxing, it is important that all network elements are configured correctly. Quality of Service Requirements What is Quality of Service? Quality of Service (QoS) is a prioritized or guaranteed level of service for a particular network user or application (e.g. VoIP or FoIP). QoS places demands on characteristics such as available bandwidth and the level of network impairments. Network impairments can sometimes be controlled by Service Level Agreements with private network providers, but are generally impossible to control over public internet-wide communications. For this reason, fax communications across the internet are not recommended. Bandwidth and communications protocols, such as FoIP, can be more easily managed by the end to end capabilities (and configuration) of the network interfaces What Are Network Impairments? Data in an IP network is divided up into packets. As each packet of data moves through the network it can be subject to various impairments that can affect some, all, or none of the packets at any given time. These are: Packet Loss: This is the most serious impairment and means that the data stream cannot be fully recombined at the other end. FoVoIP is very sensitive to this and a small level can often lead to failure. If FoIP is configured with redundancy, relatively large levels of loss can be accepted. Packet Delay: Some delay in the packet stream is unavoidable; the level will depend on the length of the network path and the level of congestion within the network. Again, FoVoIP is sensitive to this, since the underlying fax protocol has strict timing requirements. FoIP uses methods to work around this, avoiding failure of the fax communication. Packet Jitter: Jitter is a variation of delay between packets. Above a certain level the affected packet(s) will be considered lost and FoVoIP audio will be broken, resulting in fax failure. FoIP reliability will be better due to lower bandwidth demands against the buffer memory available. dc09cc0449 Customer Support Page 2