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Okidata 5980 Fax Machine with Internet Connectivity
Image courtesy of Mytour ShopperFax over Internet Protocol (FoIP), also known as IP faxing, has existed for several years. If you’ve ever faxed from a computer, you’ve used a variation of FoIP. Previously, IP faxing lacked the familiar sounds of a regular fax session—the reassuring beeps signaling a connection to the recipient’s machine and the confirmation message for each successful transmission. However, the newest FoIP systems merge the reliability of traditional faxing with the cost-effective advantages of Internet-based transmission.
In this article, we’ll explore the various types of IP faxing, review a standard FoIP setup, and examine the hurdles involved in achieving seamless faxing over the Internet.
Understanding the Fundamentals
FoIP, or IP faxing, is a technique for sending faxes via the Internet. It alters the way faxes are transmitted, similar to how VoIP (Voice over Internet Protocol) changes how phone calls are made. In both cases, data travels through a packet-switched network (usually the Internet) rather than the circuit-switched telephone network, bypassing traditional long-distance phone lines (see How VoIP Works for an explanation of packet vs. circuit switching). This setup reduces transmission costs and can be more efficient for businesses already using Internet bandwidth.
The "IP" in FoIP stands for Internet Protocol, a set of standards that governs how data is transmitted over the Internet to the correct destination. Rather than sending fax data as analog signals over phone lines, the information is sent as "IP packets" across the Internet. An IP packet is a data unit formatted so that Internet routers and receiving machines can interpret and decode its contents. (Learn more in What's a packet? and How Routers Work: Transmitting Packets.)
You don’t need to buy a new fax machine to use FoIP. Traditional (or 3G) fax machines can transmit data over the Internet with the help of gateways that bridge the phone lines and the Internet. If you prefer to bypass phone lines completely, you can use an IP fax machine that connects directly to the Internet. When sending faxes between two IP fax machines, the cost is comparable to that of sending an email, and the transmission is faster because it relies entirely on broadband channels.
Setting up FoIP is similar to setting up VoIP, and it’s even possible to send IP faxes via a VoIP server. However, because faxing requires more bandwidth than voice calls, a standard VoIP server may not work smoothly for fax transmission. Typically, some adjustments are needed, such as installing additional software. There are also specialized servers designed to handle both VoIP and FoIP needs.
FoIP can be implemented in various ways. In the following section, we’ll take a look at what a basic IP faxing system looks like.
- Install software to turn your computer into an IP fax machine
- Install software to add faxing features to your existing VoIP server
- Purchase a dedicated FoIP/VoIP server
- Subscribe to an IP fax service to use with your G3 fax machine (similar to using VoIP with your current home phone)
- Buy an IP fax machine
A Basic FoIP System
FoIP relies on two main transmission methods:
- In the store-and-forward method, fax data is sent from a fax server (or gateway) to another fax server as email attachments. This method uses a lower-level Internet protocol (like SMTP). If you’ve been faxing from your PC for several years, you’ve probably used the store-and-forward method. It’s like sending an email to a fax machine instead of an inbox. However, this process doesn’t allow real-time communication between the machines, so it doesn’t feel like a traditional fax experience. The machines can’t verify their capabilities (for example, if the sender uses a color fax machine and the receiver is black and white, one will be disappointed), and the sender won’t get instant confirmation of page delivery.
- With real-time IP faxing, fax data is transmitted from one fax server to another as IP data packets using a high-level Internet protocol like TCP or UDP. These protocols establish real-time connections that allow fax machines to exchange information during the transmission (see How OSI Works to understand protocol layers). A real-time IP fax operates just like a fax sent over a phone line.
The real-time approach is currently the most popular trend in FoIP. There are several configurations available for a real-time IP faxing system, with a few common ones including:
- Traditional G3 fax machine to G3 fax machine
- Fax-enabled PC to G3 fax machine
- IP fax machine to G3 fax machine
- IP fax machine to IP fax machine
Regardless of the method you choose, IP addresses play a role somewhere in the transmission process. An IP address is the unique identifier for any device connected to the Internet. When sending a fax between two IP fax machines, the phone number you dial is essentially an alias. It is quickly translated into the relevant IP address of the receiving machine. When sending a fax from an IP fax machine to a G3 fax machine, the IP fax machine uses the phone number to determine the IP address of the nearest fax server to the destination. Proximity is key — choosing a local fax server ensures that no costly long-distance lines are used when transmitting the fax from the server to the receiving machine.
Let's dive deeper into a simplified, real-time FoIP session between an IP fax machine (acting as the sender) and a G3 fax machine (acting as the receiver):
A real-time IP fax session mirrors the exchanges that happen in a traditional fax session.On the surface, this seems like all there is to an IP fax transmission. However, behind the scenes, there’s a complex conversion process between phone-line faxing, which follows the T.30 protocol, and real-time IP faxing, which operates under the T.38 protocol. In the next section, we'll explore this process in greater detail.
FoIP Protocols
To grasp the steps of an IP fax session, it’s useful to examine the different phases of a fax. If you’ve read How Fax Machines Work, you know that when you place a document in a fax machine and dial a number, the machine sends a signal over the phone lines to the receiver to initiate the fax session. If the receiving machine responds with the familiar series of tones we associate with faxing, the sender knows the connection has been made. At this stage, the two machines exchange control signals to communicate details like supported paper sizes, color capabilities, and compression types.
It’s essential to understand that fax machines are inherently digital. They produce and comprehend digital signals. However, phone lines are analog. To bridge this gap, G3 fax machines use the T.30 protocol, which encodes digital data into analog signals when sending and decodes analog signals back into digital data upon receiving.
Once the machines understand each other's capabilities, the sending machine scans the document, converting it into a series of bits (1s and 0s) representing the black-and-white areas in digital form. It then converts these bits into analog signals to transmit over the phone line. On the receiving end, the machine decodes the signals back into digital form, interprets the bits, and prints the document based on those instructions.
In a fax session, timing plays a crucial role. Phone lines are particularly reliable in this aspect, providing consistent timing throughout each phase of the fax process—connecting, exchanging control signals, transmitting and confirming page data, handling multipage alerts, and ending the session. Throughout, the machines communicate with each other to ensure everything is proceeding smoothly. As discussed earlier, a real-time fax session over the Internet follows these same phases and confirmations. FoIP uses the same method of compressing and interpreting image data as G3 faxing but employs a different protocol for transmission. The protocol that allows real-time faxing over the Internet is T.38.
T.38 takes traditional fax data and adapts it for Internet use. It’s essentially a way to wrap T.30 fax signals into IP packets on the sending side and convert those IP packets back into T.30 signals at the receiving side. Let’s take a closer look at the conversion process during a single phase of an FoIP session between two G3 fax machines:
As demonstrated, faxing over the Internet demands extensive data conversion. From an efficiency standpoint, it might make sense to completely replace the old T.30 protocol with something that’s purely digital and packet-based throughout. However, since faxing originated as a phone-line technology, T.30 is the universally accepted protocol that all fax machines understand. FoIP cannot discard it entirely. But achieving a successful real-time session with all the traditional T.30 phases requires precise timing, which the Internet can't always guarantee. This presents one of the many challenges FoIP faces. In the next section, we’ll explore some of the obstacles to achieving a seamless IP faxing experience.
FoIP Challenges
There are several operational challenges when it comes to sending a fax over the Internet. One major hurdle is protocol conversion. With around 250 million fax machines globally that only recognize T.30, FoIP needs to convert T.30 data into T.38 for transmission and then convert it back into T.30 upon reception. This conversion takes place at the fax server/gateway.
A software package within the fax server functions as a translator between the two protocols. The fax/modem component converts analog fax signals into digital data at the sending end and the reverse at the receiving end. The fax/network component packages the digital data into IP packets for transmission and unpacks them on the receiving side. The fax/protocol component ensures that T.38 timing aligns with the expected T.30 timing—this might involve sending a signal to prevent the receiving fax machine from timing out if a packet experiences a delay.
Another challenge in IP faxing is network timing. Unlike phone lines, which have fairly standardized timing, transmission times over an Internet network are much more variable. If the timing is off, fax machines may fail to understand one another, leading to corrupted or unsuccessful transmissions. In IP faxing, delays can occur due to:
- Processing - The fax gateway needs time to perform T.30/T.38 conversions and assemble the fax data into IP packets for transmission.
- Network delays - If any segment of the network is congested, a packet might arrive later than expected.
- Jitter buffers - The fax gateway may hold back packets on the receiving side to account for timing variations in packet arrival, ensuring they’re delivered in the correct order and at the right intervals.
Jitter buffers are designed to correct timing issues, but they can add some delay in the process. Typically, when there are timing difficulties, the gateway can communicate with the receiving fax machine to keep the connection open until the transmission finishes. If a packet arrives out of order, the gateway can reorder it by referencing the sequence number that’s included in the packet.
If a packet is lost, there won’t be a sequence number available to correct the order. And in the unpredictable environment of the Internet, packet loss is a common occurrence. To handle lost packets, FoIP uses several error-correction techniques. One method involves redundant packets used with the UDP/IP protocol. Each packet contains both its own data and a copy of the previous one, so it would take two consecutive lost packets to result in data loss. Additionally, TCP/IP protocols implement an error-correction scheme where TCP requires confirmation for each sent packet, and if no confirmation is received, the packet is resent. (To learn more about these protocols, refer to searchNetworking: TCP/IP and searchNetworking: UDP.)
FoIP still has a long way to go before it matches the reliability of traditional phone-line faxing, but the introduction of real-time IP faxing has made it an appealing option for those who frequently send long-distance faxes. The benefits of cost savings and network integration with FoIP typically outweigh the occasional inconvenience of needing to resend a fax that didn’t go through.
