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Adtran
Enterprise Network Series
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ATLAS Frequently Asked Questions
General
Now that there's an ATLAS 800PLUS, is the ATLAS 800
going to be phased out?
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No. The ATLAS 800 and the ATLAS 800PLUS are two members
of the ATLAS family, and we will continue to enhance and maintain both
products, along with any future ATLAS family members. The ATLAS 800, with
its support of TDM bandwidth management up to T3 rates, PRI/BRI access
switching, and remote access, is a good fit for applications that do not
require frame relay support. The ATLAS 800PLUS provides a
step up in its support for frame relay, including voice over frame and IP
routing.
How can I upgrade from an ATLAS 800 to an ATLAS 800PLUS?
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Customers who purchased an ATLAS 800 system before the ATLAS 800PLUS
was available may be eligible to upgrade to an ATLAS 800PLUS
for only the price of the frame relay software. The requirement is that the
customer use the ATLAS 800PLUS for a frame relay
application to co-exist with the original application for which the ATLAS
800 was purchased. In these situations, ADTRAN will replace their ATLAS 800
chassis with an ATLAS 800PLUS chassis at no charge.
Note that this policy applies only to customers who purchased an ATLAS
800 before the ATLAS 800PLUS is available. ADTRAN will
still offer an upgrade from the ATLAS 800 to the ATLAS 800PLUS
after the ATLAS 800PLUS is released, but it will be a
different program, the details of which are not yet available.
What redundancy is built into ATLAS?
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ATLAS can be equipped with a redundant, load-sharing power supply that
automatically takes over powering the ATLAS system if the main power supply
fails.
While there are currently no redundant modules in ATLAS, there are a
number of measures implemented that will minimize downtime in the event of a
failure, including:
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Hot-swappable Modules
Any ATLAS module can be installed or removed without turning off power
to the chassis.
Off-line Configuration Download
You can completely configure a spare ATLAS chassis while it's off-line,
so that when you bring it into access service, all that's required is
moving the cables over. You can transfer the configuration of your
active ATLAS system to a PC, and then download it to your spare system
so that it's ready to go when you need it.
Can ATLAS operate with more than one clock source?
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The answer to this is YES, but if the clock sources are not synchronous,
controlled data slips will occur.
T1 is a synchronous data format which does not have any spare bit times
nor is it possible to insert any filler bits. This means that just like a
water bucket with a hole in the bottom, if you are not taking data out
exactly as fast as you are putting it in, eventually the data will either
overflow or run empty. In the case of T1, we are "filling" ATLAS
at 1.536 (±) Mbps per T1. If the rate of the composite data
"leaving" ATLAS (through V.35 ports or T1 ports) is not precisely
equal (synchronous) to the composite incoming data rate, there will
eventually be a data slip. This is true for ATLAS or any system
terminating multiple T1s.
In the majority of ATLAS applications, the network connections will be
referenced to the same timing hierarchy, and will therefore be synchronous.
If the sources are not from the same timing hierarchy and are not precisely
synchronous, this would be called a plesiochronous network. (Plesiochronous
is derived from Greek and means almost synchronous). In the past, all
of the major carriers derived their timing from AT&T and, as a result,
were synchronous to each other. Today more carriers are providing their own
timing sources which are becoming more and more GPS timing sources. In all
cases, in order to meet ANSI quality of service objectives, the major
carriers' timing sources are precise, typically ± 1 x 10-11
or better (± .000015 bits / second for a T1 or ±1 bit every 18 hours).
ATLAS derives its internal timing from one source. In cases where
multiple circuits are brought in from plesiochronous carriers, frame slips
will eventually occur on those links not being used as the timing source.
With this in mind, ATLAS is designed with controlled slip buffers at each of
the T1 interfaces, allowing ATLAS to operate in a controlled and predictable
manner. With the slip buffers, when a slip occurs, a frame of data is
dropped or duplicated without any loss of T1 frame synchronization.
Other systems likely behave in precisely the same way, if designed
properly. As stressed earlier, T1 is a synchronous data format without any
spare time, and, as a result, any device terminating multiple T1s with
different timing sources will experience slips, but with slip buffers, the
rate of occurrence and the severity of the disruption can be minimized. In
the real world, multiple timing sources from different carriers will not be
a problem. As the table below shows, the rate is once every 72 days for two
stratum 1 sources.
Probability of Slips in a Plesiochronous Network
|
| |
|
SOURCE 1 |
| |
Stratum 1 |
Stratum 2 |
Stratum 3 |
Stratum 4 |
| SOURCE 2 |
Stratum 1 |
72 days |
2 hours |
27 seconds |
4 seconds |
| Stratum 2 |
2 hours |
65 minutes |
27 seconds |
4 seconds |
| Stratum 3 |
27 seconds |
27 seconds |
13 seconds |
3 seconds |
| Stratum 4 |
4 seconds |
4 seconds |
3 seconds |
2 seconds |
Based on the use of stratum 1 sources, which the carrier should be using, the
rate of slips should be so low that it is not an issue.
What processor does ATLAS use?
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ATLAS distributes the processing among the various modules for
applications that require it, so consequently several ATLAS modules have
their own on-board processor. The ATLAS Base Unit uses an Intel i960 RISC
microprocessor.
Does ATLAS support inverse multiplexing?
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Currently ATLAS does not support inverse multiplexing. In many
video-conferencing applications, ATLAS is installed in a central location
and is connected to the output of various inverse multiplexers such as
ADTRAN's ISU 512 installed throughout the complex. In these situations,
inverse multiplexing support internal to ATLAS would not be a benefit. Other
applications, such as dial backup, do benefit from inverse multiplexing
internal to ATLAS, which will be supported in a future release.
Back to the top of the page.
Frame Relay
What kind of frame relay support has been added to ATLAS?
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With the latest member of the ATLAS family, the ATLAS 800PLUS,
ATLAS now supports transporting voice, data, and LAN traffic over public or
private frame relay networks. Up to four T1 frame relay circuits are
supported by a single ATLAS system.
Does ATLAS support voice over frame relay?
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Yes. ADTRAN is introducing the Voice Compression module for the ATLAS 800PLUS,
available in 8, 16, 24, and 32 channel versions. This module uses the
G.723.1 algorithm to compress voice traffic down to 6.3 kbps. In addition,
the module automatically detects fax transmissions and converts them back to
their baseband component for transmission over the frame relay link.
How many voice ports can a single ATLAS system support?
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A single ATLAS system can support 64 compressed voice channels
simultaneously.
Do I need an ATLAS system at both ends of the link to support voice
compression?
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No. Voice compression support in ATLAS will also interoperate with
ADTRAN's desktop frame relay device, the FSU 5622 ESP.
What is the MOS score for voice compression in ATLAS?
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The MOS for voice compressed using the G.723.1 algorithm that ATLAS uses
is 3.9. For reference, G.726 voice compression (32 kbps ADPCM) achieved an
MOS rating of 4.2.
What is a MOS?
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The Mean Opinion Score (MOS) is an opinion rating frequently employed
to assess the speech quality of communication systems. Numerical values
are calculated using the numbers 5 to 1, (5=excellent, 1=bad). The
score, averaged over a number of words and listeners, is called the Mean
Opinion Score (MOS).
Back to the top of the page.
Switching/ISDN
How is ATLAS different from a PBX?
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There are so many differences, it's probably better to ask, "How is
ATLAS similar to a PBX?"
ATLAS performs several functions that a PBX does:
- ATLAS connects with switched services, such as Robbed-bit T1, Primary
Rate ISDN, and Basic Rate ISDN.
- For incoming calls, ATLAS is able to decode information that indicates
what number was dialed.
- ATLAS implements a dial plan, allowing the customer to configure which
port(s) calls are to be placed, based on the number that was dialed.
- On the subscriber side, client devices can be connected to ATLAS via
BRI, PRI, or Robbed-bit T1.
- When a subscriber goes "off-hook," ATLAS will provide dial
tone for robbed bit trunks, or the appropriate D Channel response for
PRI or BRI connections.
- ATLAS can decode the telephone number that is being dialed, and direct
that call to the appropriate port, based on the user-configured dial
plan.
- ATLAS can perform local switching, allowing one subscriber to call
another without having to access the wide area network.
- ATLAS will present the user with a fast-busy signal, should there not
be an available trunk to place the call.
There are many other features that a PBX implements that are not
supported by ATLAS, including call forwarding, call transfer, voice mail,
and others.
If ATLAS has PBX functionality, but is not a PBX, what is this
functionality used for?
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There are many applications, particularly in data networking, that
require basic switching functionality, but not the full complement of bells
and whistles that a PBX would provide.
ATLAS' Access Switching functionality is valuable in converting between
technologies (e.g. PRI to T1 conversion). It also allows bandwidth to be
used more efficiently by dynamically allocating bandwidth to the application
that requires it versus a static mapping.
With what switches is ATLAS compatible?
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For PRI, ATLAS is compatible with Lucent 4ESS Custom and 5ESS®
Custom, Nortel DMS-100 Custom, and National ISDN-2. ATLAS can emulate a
Lucent 4ESS or 5ESS switch in PRI mode.
For BRI, ATLAS is compatible with Lucent 5ESS Custom, Nortel DMS-100
Custom, and National ISDN-1. ATLAS can also emulate any of these
switch/protocol types.
ATLAS has been tested with and found to be compatible with the GTD-5
switch in PRI mode. ATLAS must be configured for National ISDN-2 when
operating with the GTD-5.
ATLAS is compatible with Nortel's DMS-250 switch also. Setting ATLAS for
DMS-100 Custom mode will allow it to work with the DMS-250 as well.
Can you hook an ISDN telephone up to ATLAS?
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Technically you can, but you must be sure that you are not expecting any
features such as call transfer, call hold, call conferencing, etc. ATLAS
does not currently support any of ISDN special features beyond Caller ID and
called party numbers.
Can you assign a priority to calls? For example, can you guarantee that
the CEO never gets a busy signal?
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No. ATLAS was designed to never interrupt a call in progress in order to
service a higher priority client. If you require that the CEO always have
network capacity available, you will need to configure the system to
allocate bandwidth just for that particular client.
Does ATLAS support H0 or H11 service?
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No. H0 and H11 refer to a specific method for combining ISDN B Channels
to get a higher throughput. They are services that you would subscribe to
with your ISDN service provider: H0 is a 384 kbps service (6 B Channels) and
H11 is a 1.536 Mbps service.
Back to the top of the page.
T3
Why did ADTRAN develop T3 support in ATLAS?
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There are many situations where a host location may require T1 or
Fractional T1 circuits to connect with each of its remote locations. It is
often the case that a single T3 circuit, which transports the equivalent of
28 T1 circuits, costs less per month than as few as eight or nine T1
circuits. T3 support was developed in ATLAS to give customers the
flexibility of accessing the network with a more economical T3 circuit
instead of multiple T1 circuits, should circuit tariffs justify going this
way.
Is T3 support in ATLAS the same as an M13 Multiplexer?
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No. An M13 multiplexer interfaces to a T3 circuit and breaks it into 28
short haul (DSX-1) T1 interfaces. While it is possible to configure an ATLAS
system to emulate an M13 multiplexer, ATLAS does more than that. ATLAS with
T3 support can operate on traffic down to the DS0 level, functioning as what
is sometimes known as a "3/1/0 DACS". T3 support in ATLAS is the
equivalent of an M13 multiplexer and a T1 Bandwidth Manager combined into
one platform.
ATLAS as an M13 multiplexer will have value for applications requiring a
CSU interface on the 28 T1 ports. The T1 CSU is typically not included on
standard M13 multiplexers and must be supplied with external equipment; the
T1 CSUs are built-in with ATLAS.
Why doesn't the ATLAS T3 module have an HSSI port?
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A High-Speed Serial Interface (HSSI) port provides an interface between
Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE)
at speeds up to 52 Mbps. It is generally not used at speeds below 2 Mbps.
Since T3 support in ATLAS is for channelized DS-3 circuits, where the
payload is channelized into 28 T1 circuits, there is generally no
application that will call for ATLAS to provide a DTE interface greater than
T1 speeds.
One exception is when ATLAS is configured as a frame relay concentrator.
In this application, ATLAS could be combining frame relay traffic from
multiple T1 circuits onto a single DTE port. ATLAS provides V.35 port
connectivity operating at speeds up to 2.048 Mbps.
What applications can take advantage of T3 support in ATLAS?
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The simple answer is that any application that could benefit from
multiple T1 circuits terminating in ATLAS might find T3 access beneficial.
These applications include school district networking, health care
facilities connectivity, call centers, distance learning, and other
multimedia, wide area applications. The choice of whether to go with
individual T1 circuits or a single T3 circuit for network access will be
determined by tariffs and other considerations.
What's the difference between ADTRAN's new T3SU 300 and T3 support in
ATLAS?
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The T3SU 300 works on unchannelized T3 circuits, while the T3 module in
ATLAS works on channelized T3 circuits. An unchannelized T3 circuit operates
as one big, fast "pipe", and is often used to connect an Internet
Service Provider to an Internet Network Access Point. A channelized T3
circuit is organized as a combination of 28 T1 circuits, each of which is
comprised of 24 channels, or DS0s. A channelized T3 circuit would typically
be used to transport voice, data, and video from many remote locations to a
host location.
What's the overall capacity of ATLAS with T3 support?
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ATLAS can process up to 60 T1 circuits worth of bandwidth. With T3
access, a system can be configured that reaches this upper limit. With
individual T1 access, the physical characteristics of the ATLAS chassis and
modules will restrict the maximum capacity to 34 T1 or PRI circuits.
Can users implement a T3 application in ATLAS and then use other available
slots for something completely different?
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Yes - this is one of the major benefits that ATLAS provides. As a
modular, highly scalable platform, ATLAS gives its customers the flexibility
to mix and match applications in a single system, reducing training
requirements and permitting network growth and technology migration at the
pace that the customer dictates.
Back to the top of the page.
Remote Access
Why did ADTRAN develop remote access support in ATLAS?
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ATLAS is designed to meet all the wide area networking requirements of
medium to large networks, and to provide its customers with the flexibility
to choose the right service or technology for the application.
Many industries require a mix of services. Frame relay may be appropriate
for connecting offices around the country with their headquarters, while
point-to-point T1 circuits may be desirable for regional locations. These
same industries often require dial-up access for their employees who may
work out of their homes or need to connect from their hotel rooms while
traveling. Remote access support in ATLAS allows a single platform to
address the dedicated, frame relay, and dial-up requirements of an
organization.
When would you use asynchronous RS-232 ports in a remote access
application, instead of coming out the Ethernet port?
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There are many large applications deployed today that are not
client-server based, and are not directed to LAN-attached resources.
Examples include credit card authorization, electronic benefits transfer
(electronic distribution of food stamps), some home banking networks, and
others. Often the applications to which the remote users are calling into
are large, several years old, and do not warrant porting to a LAN-based
platform. These applications require access via asynchronous EIA-232 ports.
The more popular remote access applications, such as accessing the
Internet or telecommuting, use Ethernet as the interface, and not EIA-232
ports.
Back to the top of the page.
Management
Can I manage ATLAS using T-Watch? If so, can I also manage my downstream
TSUs?
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Revision 6.3 and later of T-Watch PRO™ offers support for ATLAS, by
automatically launching a Telnet session when the ATLAS unit is selected.
The GUI interface presented when T-Watch PRO is managing a TSU is not
maintained when managing ATLAS.
You can manage downstream TSUs via T-Watch PRO from an ATLAS system. Two
methods of reaching the remote TSU are supported:
Back to the top of the page.
Compatibility/Compliance
Does ATLAS offer TR-303 (GR-303) or TR-008 compatibility?
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No. Support for these specifications is being investigated.
Back to the top of the page.
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