Xerox AltaLink B8045, AltaLink B8055, AltaLink B8065, AltaLink B8075, AltaLink B8090 Faxing Over IP Networks Customer Tip

Faxing Over IP
Networks

Customer Tip

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BR27567
Document Version: 1.0 (October 2019). dc08cc0439

A Guide to Faxing Over IP Networks − Customer Tip i

Preface

This guide is intended for network administrators, or service providers, with the responsibility for
configuring settings within an IP network expected to provide telephony service to a Xerox fax
device.

A Guide to Faxing Over IP Networks − Customer Tip ii

Contents

Preface ................................................................................................................................................ i

Communication Protocols ............................................................................................................... 1

What is Voice over IP (VoIP)? ............................................................................................................ 1

What is Fax over VOIP (FoVoIP)? ...................................................................................................... 1

What is Fax over IP (FoIP)? ................................................................................................................ 1

What Fax Protocol does Xerox Use? .................................................................................................. 1

Quality of Service Requirements ..................................................................................................... 2

What is Quality of Service? ................................................................................................................. 2

What are Network Impairments? ........................................................................................................ 2

What Service Level is Required for Fax? ............................................................................................ 2

Recommended Network Configuration Settings ................................................................................. 3

Network Setups ................................................................................................................................. 4

IP Exchanges, Access Devices and Terminal Adapters ..................................................................... 4

Providers & Protocols .......................................................................................................................... 4

A Guide to Faxing Over IP Networks − Customer Tip 1

Communication Protocols

What is Voice over IP (VoIP)?

Internet Protocol (IP) networks carry data in a digital packet format. Voice signals
must be encoded into this digital format before being transmitted over IP. This
encoding also compresses the data to reduce the load (bandwidth) on the
network. This function is provided by an access device that supplies the
conversion interface.

What is Fax over VOIP (FoVoIP)?

FoVoIP is often called Fax Pass-through. The fax is connected to the VoIP
interface on the network and is treated like a standard voice call. The analogue
fax signals are encoded into a digital format, just as for a voice call. The voice
encoding compression severely limits the fax speed, and network quality
issues that are acceptable to voice calls usually cause the fax to fail.

What is Fax over IP (FoIP)?

FoIP is sometimes called Fax Relay. 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 for the fax performance to be degraded and SuperG3 not supported. There
are proprietary versions (e.g. Cisco) but the cross-vendor standard from the International
Telecommunications Union is called T.38. For additional information refer to:

https://en.wikipedia.org/wiki/T.38.

It is possible to configure the Xerox devices 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.

What Fax Protocol does Xerox Use?

The fax module is capable of standard G3 (v.17) fax operation (maximum data rate 14400 bps) or
Super G3 (v.34) fax (maximum data rate 33600 bps). It is designed to connect to analogue
telephone lines that carry audible frequencies (i.e. speech). Fax data is converted into audible
signals for transmission through the Public switched telephone network using a modem.

Please refer to the Customer Expectation Document, for the desired product to determine if the
Xerox product you are using supports this functionality. Please note that for certain Xerox products
a separate Fax Kit needs to be purchased to support this functionality.

Analogue Voice

Digital Fax Data

Analogue Modulation

A Guide to Faxing Over IP Networks − Customer Tip 2

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.

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.

What Service Level is Required for Fax?

This table gives an approximate guide to the maximum levels of impairments that can be present
and still support a successful fax call between supported products, for each configuration of
VoIP/FoIP service used:

Telephony/Fax Service

Bandwidth

Loss

Delay

Jitter

G.729 Pass-through → G.711*

84 Kbps‡

0.01%

500 ms

50 ms

G.711 Pass-through

84 Kbps‡

0.10%

300 ms

30 ms

Cisco Fax Relay (7200 or 14400)†

55 Kbps‡

0.50%

500 ms

25 ms

T.38 (no redundancy; ls & hs=0)†

25 Kbps‡

0.30%

100 ms

10 ms

T.38 (redundancy; ls=5, hs=2)†

52 Kbps‡

10%

800 ms

50 ms

† Voice codec configuration: G729
‡ Bandwidth measured during image data at a fax rate of 14400 bps.

* With “Upspeed” (G.729→G.711) Note: If a pure G.729 channel is used, the fax call is likely to fail.

A Guide to Faxing Over IP Networks − Customer Tip 3

Recommended Network Configuration Settings

It is recommended that for reliable faxing the network should be configured for T.38

with redundancy.

However, some network setups may not support it; those that do may fix the redundancy at a
set level. For instance, with a Cisco IOS configuration, this is set in the dial-peers with the
command below. It is not recommended to disable fax Error Correct Mode (ECM), since any
quoted improvements are questionable and not guaranteed.

fax protocol t38 ls-redundancy 5 hs-redundancy 2

A Guide to Faxing Over IP Networks − Customer Tip 4

Network Setups

IP Exchanges, Access Devices and Terminal Adapters

For some installations, it may not be appropriate to provide VoIP access by using a full-scale IP
exchange (IP PBX). In these cases, multi-port access devices can provide a more localized
service. For small or unusual network setups an Analogue Terminal Adapter (ATA) provides
ultimate flexibility on a per machine basis. Many include two phone ports allowing connection of
two fax machines, or one machine and one phone. Each ATA connects to an existing network point
and so is convenient where phone points are not available.

IP PBXs usually provide a centralized configuration utility. But each access device or ATA must be
set up individually and are generally configured to work with a VoIP registry/gatekeeper or service
provider.

Accurate and consistent configuration across the network is very important – the wrong
configuration is often the cause of fax failure.

Providers & Protocols

Service providers and registry/gatekeeper servers supply directory services (called number to IP
address translation), call initiation, handling and sometimes other telephony features, such as
voicemail. ATAs and other access devices communicate with these servers using standardized
protocols, the most common of which are SIP and H.323. Each access device and registrar/
gatekeeper must understand (and be configured for) the same protocol, as must any two end-point
devices trying to initiate a fax call. For example, all parties must support SIP (or H.323) and T.38 to
achieve the recommended FoIP service.