OBSOLETE OsmoNITB User Manual

My deep thanks to everyone who has contributed to Osmocom. The list of contributors is too long to mention here, but I’d like to call out the following key individuals and organizations, in no particular order:

May the source be with you!

— Harald Welte, Osmocom.org and OpenBSC founder, January 2016.

This version of the manual is endorsed by Harald Welte as the official version of the manual.

While the GFDL license (see [licenses-gfdl]) permits anyone to create and distribute modified versions of this manual, such modified versions must remove the above endorsement.

If you are new to FOSS, please try to understand that this development model is not primarily about “free of cost to the GSM network operator”, but it is about a collaborative, open development model. It is about sharing ideas and code, but also about sharing the effort of software development and maintenance.

If your organization is benefiting from using Osmocom software, please consider ways how you can contribute back to that community. Such contributions can be many-fold, for example

We’re looking forward to receiving your contributions.

Some of the founders of the Osmocom project have established sysmocom - systems for mobile communications GmbH as a company to provide products and services related to Osmocom.

sysmocom and its staff have contributed by far the largest part of development and maintenance to the Osmocom mobile network infrastructure projects.

As part of this work, sysmocom has also created the manual you are reading.

At sysmocom, we draw a clear line between what is the Osmocom FOSS project, and what is sysmocom as a commercial entity. Under no circumstances does participation in the FOSS projects require any commercial relationship with sysmocom as a company.

We have prepared this manual in the hope that it will guide you through the process of installing, configuring and debugging your deployment of cellular network infrastructure elements using Osmocom software. If you do find errors, typos and/or omissions, or have any suggestions on missing topics, please do take the extra time and let us know.

Please note that even while the capital expenses of running mobile networks has decreased significantly due to Osmocom software and associated hardware like sysmoBTS, GSM networks are still primarily operated by large GSM operators.

Neither the GSM specification nor the GSM equipment was ever designed for networks to be installed and configured by anyone but professional GSM engineers, specialized in their respective area like radio planning, radio access network, back-haul or core network.

If you do not share an existing background in GSM network architecture and GSM protocols, correctly installing, configuring and optimizing your GSM network will be tough, irrespective whether you use products with Osmocom software or those of traditional telecom suppliers.

GSM knowledge has many different fields, from radio planning through site installation to core network configuration/administration.

The detailed skills required will depend on the type of installation and/or deployment that you are planning, as well as its associated network architecture. A small laboratory deployment for research at a university is something else than a rural network for a given village with a handful of cells, which is again entirely different from an urban network in a dense city.

Some of the useful skills we recommend are:

If you do have a support package / contract with sysmocom (or want to get one), please contact support@sysmocom.de with any issues you may have.

If you don’t have a support package / contract, you have the option of using the resources put together by the Osmocom community at https://projects.osmocom.org/, checking out the wiki and the mailing-list for community-based assistance. Please always remember, though: The community has no obligation to help you, and you should address your requests politely to them. The information (and software) provided at osmocom.org is put together by volunteers for free. Treat them like a friend whom you’re asking for help, not like a supplier from whom you have bought a service.

If you would like to obtain professional/commercial support on Osmocom CNI, you can always reach out to sales@sysmocom.de to discuss your support needs. Purchasing support from sysmocom helps to cover the ongoing maintenance of the Osmocom CNI software stack.

OsmoNITB is one particular version of the OpenBSC software suite. Unlike classic, distributed, hierarchical GSM networks, OsmoNITB implements all parts of a GSM Network (BSC, MSC, VLR, HLR, AUC, SMSC) in the box, i.e. in one element.

The difference between classic GSM network architecture and the OsmoNITB based GSM network architecture is illustrated in [fig-gsm-classic] and [fig-gsm-nitb].

OsmoNITB contains a variety of different software components, which we’ll quickly describe in this section.

osmo-nitb [-h|-V] [-d DBGMASK] [-D] [-c CONFIGFILE] [-s] [-T] [-e LOGLEVEL] [-l DATABASE] [-a] [-P] [-m] [-C] [-r RFCTL]

Running multiple instances of osmo-nitb is possible if all interfaces (VTY, OML) are separated using the appropriate configuration options. The IP based interfaces are binding to local host by default. In order to separate the processes, the user has to bind those services to specific but different IP addresses.

The VTY and the control interface can be bound to IP addresses from the loopback address range.

The OML interface also needs to be separated by binding it to different IP addresses. Usually it is not possible to use addresses from the loopback address range here since the OML interface needs to be reachable by an external BTS. If only one ethernet interface is available, sub-devices with different IP addresses can be created.

Modify (or add if missing) subscriber entry with the give IMSI, MSISDN, Ki and algorithm (valid values are "none", "xor" and "comp128v1"). The subscriber is automatically marked as authorized.

Delete the subscriber with the given IMSI. Returns "Removed active subscriber" or "Removed" depending on the subscriber’s use status.

The following variables are only available over control interface of osmo-bsc_nat program.

Add given regular expression for matching IMSI(s) to allowed access list A.

This TRAP event notifies all connected clients about IMSI which was rejected by BSC N.

The VTY of a given Osmocom program is implemented as a telnet server, listening to a specific TCP port.

Please see [port-numbers] to check for the default TCP port number of the VTY interface of the specific Osmocom software you would like to connect to.

As telnet is insecure and offers neither strong authentication nor encryption, the VTY by default only binds to localhost (127.0.0.1) and will thus not be reachable by other hosts on the network.

The VTY by default has the following minimal nodes:

The VTY features an interactive help system, designed to help you to efficiently navigate is commands.

Each sub-system of the program in question typically logs its messages as a different category, allowing fine-grained control over which log messages you will or will not see. For example, in OsmoBSC, there are categories for the protocol layers rsl, rr, mm, cc and many others. To get a list of categories interactively on the vty, type: logging level ?

For each of the log categories (see [log_categories]), you can set an independent log level, controlling the level of verbosity. Log levels include:

The log levels are inclusive, e.g. if you select info, then this really means that all events with a level of at least info will be logged, i.e. including events of notice, error and fatal.

So for example, in OsmoBSC, to set the log level of the Mobility Management category to info, you can use the following command: log level mm info.

There is also a special command to set all categories as a one-off to a desired log level. For example, to silence all messages but those logged as notice and above issue the command: log level set-all notice

Afterwards you can adjust specific categories as usual.

A similar command is log level force-all <level> which causes all categories to behave as if set to log level <level> until the command is reverted with no log level force-all after which the individually-configured log levels will again take effect. The difference between set-all and force-all is that set-all actually changes the individual category settings while force-all is a (temporary) override of those settings and does not change them.

The logging system has various options to change the information displayed in the log message.

The default behavior is to filter out everything, i.e. not to log anything. The reason is quite simple: On a busy production setup, logging all events for a given subsystem may very quickly be flooding your console before you have a chance to set a more restrictive filter.

To request no filtering, i.e. see all messages, you may use: log filter all 1

In addition to generic filtering, applications can implement special log filters using the same framework to filter on particular context.

For example in OsmoBSC, to only see messages relating to a particular subscriber identified by his IMSI, you may use: log filter imsi 262020123456789

Each of the log targets represent certain destination for log messages. It can be configured independently by selecting levels (see [log_levels]) for categories (see [log_categories]) as well as filtering (see [log_filters]) and other options like logging timestamp for example.

Osmo counters are the oldest type of counters added to Osmocom projects. They are not grouped.

Rate counters count rates of events.

The control interface command to get a counter (group) is:

rate_ctr.per_{sec,min,hour,day,abs}.<group_name>.<idx>.[counter_name]

It is possible to get all counters in a group by omitting the counter name

Stat items are a grouped replacement for osmo counters.

There are three levels on which a statistic can be aggregated in Osmocom projects: globally, per-peer and per-subscriber.

The stats reporter periodically collects osmo counter, rate counter and stat item values and sends them to a backend. Currently implemented are outputting to the configured log targets and a statsd connector.

libosmocore provides features to monitor the status of TCP connections. This can be a helpful source of information when the links between network components are unreliable (e.g. satellite link between BTS and BSC).

Like everything else, the core network related parameters are configured using the VTY. The respective parameters are underneath the network config node.

You can get to that node by issuing the following commands:

A full reference to them can be found in the OsmoNITB VTY reference manual [vty-ref-osmonitb]. This section will only introduce the most commonly used settings in detail.

The key identities of every GSM PLMN is the MCC and MNC. They are identical over the entire network. In most cases, the MCC/MNC will be allocated to the operator by the respective local regulatory authority. For example, to set the MCC/MNC of 262-89, you may enter:

The MM INFO procedure can be used after a successful LOCATION UPDATE in order to transmit the human-readable network name as well as local time zone information to the MS.

By default, MM INFO is not active. You can activate it, and set its configuration using the VTY. An example is provided below.

The time information transmitted is determined by the local system time of the operating system on which OsmoNITB is running. As BTSs attached to one OsmoNITB can reside in different time zones, it is possible to use the timezone command at each BTS node to set different time zone offsets in hours and quarter hours.

NECI (New Establishment Cause Indication) is an optional change of the definition for establishment cause in the RACH burst. Among other things, in a network with NECI, a MS can explicitly indicate its TCH/H capability while asking for a dedicated radio channel.

It is strongly recommended to use NECI. You can do so by issuing the following command: .Enabling NECI

As opposed to cell re-selection in idle mode, handover refers to the explicit transfer of a MS dedicated channel from one radio channel to another. This typically happens due to a MS moving from one cell to another while in an active call.

OsmoNITB has a number of hand-over related parameters by which the hand-over algorithm can be tuned. Logically, those settings are settings of the BSC component, but for historic reasons, they are also configured under the network VTY node.

The GSM specification specifies a variety of timers both on the network as well as on the mobile station side.

Those timers can be configured using the timer tXXXX command.

GSM provides a full-duplex voice call service. However, in any civilized communication between human beings, only one of the participants is speaking at any given point in time. This means that most of the time, one of the two directions of the radio link is transmitting so-called silence frames.

During such periods of quiescence in one of the two directions, it is possible to suppress transmission of most of the radio bursts, as there is no voice signal to transport. GSM calls this feature Discontinuous Transmission. It exists separately for uplink (DTXu) and downlink (DTXd).

Downlink DTX is only permitted on non-primary transceivers (!= TRX0), as TRX0 must always transmit at constant output power to ensure it is detected during cell selection.

Uplink DTX is possible on any TRX, and serves primarily two uses:

possible on any TRX, and serves primarily two uses:

DTS for both uplink and downlink is implemented in the BTS. Not all BTS models support it.

The Osmocom BSC component can instruct the BTS to enable or disable uplink and/or downlink DTX by means of A-bis OML.

In order to view the status and properties of a BTS, you can issue the show bts command. If used without any BTS number, it will display information about all provisioned BTS numbers.

You can also review the status of the TRXs configured within the BTSs of this BSC by using show trx:

The output can be restricted to the TRXs of one specified BTS number (show trx 0) or even that of a single specified TRX within a specified BTS (show trx 0 0).

Furthermore, information on the individual timeslots can be shown by means of show timeslot. The output can be restricted to the timeslots of a single BTS (show timeslot 0) or that of a single TRX (show timeslot 0 0). Finally, you can restrict the output to a single timeslot by specifying the BTS, TRX and TS numbers (show timeslot 0 0 4).

In order to provision BTSs, you have to enter the BTS config node of the VTY. In order to configure BTS 0, you can issue the following sequence of commands:

At this point, you have a plethora of commands, in fact an entire hierarchy of commands to configure all aspects of the BTS, as well as each of its TRX and each timeslot within each TRX. For a full reference, please consult the telnet VTY integrated help or the respective chapter in the VTY reference.

BTS configuration depends quite a bit on the specific BTS vendor and model. The section below provides just one possible example for the case of a sysmoBTS.

Note that from the configure terminal command onwards, the telnet VTY commands above are identical to configuration file settings, for details see [vty].

Starting with network as above, your complete sysmoBTS configuration may look like this:

A GSM BTS periodically transmits a series of SYSTEM INFORMATION messages to mobile stations, both via the BCCH in idle mode, was well as via the SACCH in dedicated mode. There are many different types of such messages. For their detailed contents and encoding, please see 3GPP TS 24.008 [3gpp-ts-24-008].

For each of the SYSTEM INFORMATION message types, you can configure to have the BSC generate it automatically (computed), or you can specify the respective binary message as a string of hexadecimal digits.

The default configuration is to compute all (required) SYSTEM INFORMATION messages automatically.

Please see the OsmoBSC VTY Reference Manual [vty-ref-osmobsc] for further information, particularly on the following commands:

Every BTS sends a list of ARFCNs of neighbor cells . within its SYSTEM INFORMATION 2 (and 2bis/2ter) messages on the BCCH . within its SYSTEM INFORMATION 5 messages on SACCH in dedicated mode

For every BTS config node in the VTY, you can specify the behavior of the neighbor list using the neighbor list mode VTY command:

In the case of BTS models using Abis/IP (IPA), the GPRS PCU is located inside the BTS. The BTS then establishes a Gb connection to the SGSN.

All the BTS-internal PCU configuration is performed via A-bis OML by means of configuring the CELL, NSVC (NS Virtual Connection and NSE (NS Entity).

There is one CELL node and one NSE node, but there are two NSVC nodes. At the time of this writing, only the NSVC 0 is supported by OsmoBTS, while both NSVC are supported by the ip.access nanoBTS.

The respective VTY configuration parameters are described below. They all exist beneath each BTS VTY config node.

But let’s first start with a small example

A dynamic timeslot is in principle a voice timeslot (TCH) that is used to serve GPRS data (PDCH) when no voice call is active on it. This enhances GPRS bandwidth while no voice calls are active, which is dynamically scaled down as voice calls need to be served. This is a tremendous improvement in service over statically assigning a fixed number of timeslots for voice and data.

The causality is as follows: to establish a voice call, the MSC requests a logical channel of a given TCH kind from the BSC. The BSC assigns such a channel from a BTS' TRX’s timeslot of its choice. The knowledge that a given timeslot is dynamic exists only on the BSC level. When the MSC asks for a logical channel, the BSC may switch off PDCH on a dynamic timeslot and then assign a logical TCH channel on it. Hence, though compatibility with the BTS needs to be ensured, any MSC is compatible with dynamic timeslots by definition.

OsmoBSC support two kinds of dynamic timeslot handling, configured via the network / bts / trx / timeslot / phys_chan_config configuration. Not all BTS models support dynamic channels.

The OsmoBTS Abis Protocol Specification [osmobts-abis-spec] describes the non-standard RSL messages used for these timeslot kinds.

OsmoBSC offers several configuration options to fine-tune access to the BTS. It can allow only a portion of the subscribers access to the network. This can also be used to ramp up access to the network on startup by slowly letting in more and more subscribers. This is especially useful for isolated cells with a huge number of subscribers.

Other options control the behaviour of the MS when it needs to access the random access channel before a dedicated channel is established.

If the BTS is connected to the BSC via a high-latency connection the MS should wait longer for an answer to a RACH request. If it does not the network will have to deal with an increased load due to duplicate RACH requests. However, in order to minimize the delay when a RACH request or response gets lost the MS should not wait too long before retransmitting.

Authorization determines how subscribers can access your network. This is unrelated to authentication, which verifies the authenticity of SIM cards that register with the network.

OsmoNITB supports three different authorization policies:

The currently active policy can be selected using the auth policy (closed|accept-all|token) at the network configuration node of the VTY.

When a Location Update Request is to be rejected by the network (e.g. due to an unknown or unauthorized subscriber), the Location Update Reject message will contain a Reject Cause.

You can configure the numeric value of that cause by means of the location updating reject cause <2-111> command at the network node.

Information about a specific subscriber can be obtained from the HLR by issuing show subscriber command.

For example, to display information about a subscriber with the IMSI 602022080345046, you can use the following command:

Subscribers don’t have to be identified/referenced by their IMSI, but they can also be identified by their extension (phone number), their TMSI as well as their internal database ID. Example alternatives showing the same subscriber record are:

or

A subscriber can be added to the network in different ways:

Once a subscriber exists in the HLR, his properties can be set interactively from the VTY. Modifying subscriber properties requires the VTY to be in the privileged (enable) mode.

All commands are single-line commands and always start with identifying the subscriber on which the operation shall be performed. Such identification can be performed by

There is a smpp vty node at the top level of the OsmoNITB configuration. Under this node, the global SMPP configuration is performed.

Use the local-tcp-ip command to define the TCP IP and port at which the OsmoNITB internal SMSC should listen for incoming SMPP connections. The default behaviour is to listen on all IPs (0.0.0.0), and the default port assigned to SMPP is 2775.

Use the system-id command to define the System ID of the SMSC.

Use the policy parameter to define whether only explicitly configured ESMEs are permitted to access the SMSC (closed), or whether any ESME should be accepted (accept-all).

Use the smpp-first command to define if SMPP routes have higher precedence than MSISDNs contained in the HLR (smpp-first), or if only MSISDNs found not in the HLR should be considered for routing to SMPP (no smpp-first).

Under the smpp vty node, you can add any number of esme nodes, one for each ESME that you wish to configure.

Use the esme NAME command (where NAME corresponds to the system-id of the ESME to be configured) under the SMPP vty node to enter the configuration node for this given ESME.

Use the password command to specify the password (if any) for the ESME.

Use the default-route command to indicate that any MO-SMS without a more specific route should be routed to this ESME.

Use the deliver-src-imsi command to indicate that the SMPP DELIVER messages for MO SMS and the SMPP ALERT should state the IMSI (rather than the MSISDN) as source address.

Use the osmocom-extensions command to request that Osmocom specific extension TLVs shall be included in the SMPP PDUs. Those extensions include the ARFCN of the cell, the L1 transmit power of the MS, the timing advance, the uplink and dwnlink RxLev and RxQual, as well as the IMEI of the terminal at the time of generating the SMPP DELIVER PDU.

Use the dcs-transparent command to transparently pass the DCS value from the SMS Layer3 protocols to SMPP, instead of converting them to the SMPP-specific values.

Use the route prefix command to specify a route towards this ESME. Using routes, you specify which destination MSISDNs should be routed towards your ESME.

The following example configuration snippet shows a single ESME galactica with a prefix-route of all national numbers stating with 2342:

Osmocom has implemented some extensions to the SMPP v3.4 protocol.

These extensions can be enabled using the osmocom-extensions VTY command at esme level.

The TLV definitions can be found in the <osmocom/gsm/protocol/smpp34_osmocom.h> header file provided by libosmocore.

When the internal MNCC handler is enabled, OsmoNITB will switch voice calls between GSM subscribers internally and automatically based on the the subscribers extension number. No external software is required.

When the external MNCC handler is enabled, OsmoNITB will not perform any internal call switching, but delegate all call-control handling towards the external MNCC program connected via the MNCC socket.

If you intend to operate OsmoNITB with external MNCC handler, you have to disable the internal MNCC handler and specify the MNCC socket path in the configuration file.

At the time of this writing, there are only two known open source applications implementing the MNCC interface compatible with the Osmocom MNCC socket:

In mobile networks, the signaling of DTMF tones is implemented differently, depending on the signaling direction. A mobile originated DTMF tone is signaled using START/STOP DTMF messages which are hauled through various protocols upwards into the core network.

Contrary to that, a mobile terminated DTMF tone is not transferred as an out of band message. Instead, in-band signaling is used, which means a tone is injected early inside a PBX or MGW.

When using OsmoNITB with its built in MNCC functionality a mobile originated DTMF message will not be translated into an in-band tone. Therefore, sending DTMF will not work when internal MNCC is used.

For external MNCC, the network integrator must make sure that the back-end components are configured properly in order to handle the two different signaling schemes depending on the signaling direction.

The protocol follows the primitives specified in 3GPP TS 04.07 Chapter 7.1. The encoding of the primitives is provided in the mncc.h header file in OsmoNITB’s source tree, which uses some common definitions from osmocom/gsm/mncc.h (part of libosmocore.git).

However, Osmocom’s MNCC specifies a number of additional primitives beyond those listed in the 3GPP specification.

The different calls in the network are distinguished by their callref (call reference), which is a unique unsigned 32bit integer.

The control interface protocol is a mixture of binary framing with text based payload.

The protocol for the control interface is wrapped inside the IPA multiplex header with the stream identifier set to IPAC_PROTO_OSMO (0xEE).

Inside the IPA header is a single byte of extension header with protocol ID 0x00 which indicates the control interface.

After the concatenation of the two above headers, the plain-text payload message starts. The format of that plain text is illustrated for each operation in the respective message sequence chart in the chapters below.

The fields specified below follow the following meaning:

There are several variables which are common to all the programs using control interface. They are described in the following table.

Those read-only variables allow to get value of arbitrary counter using its name.

For example "rate_ctr.per_hour.bsc.0.handover:timeout" is the number of handover timeouts per hour.

Of course for that to work the program in question have to register corresponding counter names and groups using libosmocore functions.

In the example above, "bsc" is the rate counter group name and "0" is its index. It is possible to obtain all the rate counters in a given group by requesting "rate_ctr.per_sec.bsc.*" variable.

The list of available groups can be obtained by requesting "rate_ctr.*" variable.

The rate counter group name have to be prefixed with interval specification which can be any of "per_sec", "per_min", "per_hour", "per_day" or "abs" for absolute value.

The old-style counters available via "counter.*" variables are superseded by "rate_ctr.abs" so its use is discouraged. There might still be some applications not yet converted to rate_ctr.

In the osmo-python-tests repository, there is an example python script called scripts/osmo_ctrl.py which implements the Osmocom control interface protocol.

You can use this tool either stand-alone to perform control interface operations against an Osmocom program, or you can use it as a reference for developing your own python software talking to the control interface.

Another implementation is in scripts/osmo_rate_ctr2csv.py which will retrieve performance counters for a given Osmocom program and output it in csv format. This can be used to periodically (using systemd timer for example) retrieve data to build KPI and evaluate how it changes over time.

Internally it uses "rate_ctr.*" variable described in [ctrl_common_vars] to get the list of counter groups and than request all the counters in each group. Applications interested in individual metrics can request it directly using rate_ctr2csv.py as an example.

Cell Broadcast was used for various different use cases primarily in the 1990s and early 2000s, including

More recently, SMS-CB is seeing some uptake by various disaster warning systems, such as

The GSM Operation & Maintenance Link (OML) is specified in 3GPP TS 12.21 and is used between a GSM Base-Transceiver-Station (BTS) and a GSM Base-Station-Controller (BSC). The default TCP port for OML is 3002. The connection will be opened from the BTS to the BSC.

Abis OML is only specified over E1 interfaces. The Abis/IP implementation of OsmoBTS and OsmoBSC extend and/or deviate from the TS 12.21 specification in several ways. Please see the OsmoBTS Abis Protocol Specification [osmobts-abis-spec] for more information.

The GSM Radio Signalling Link (RSL) is specified in 3GPP TS 08.58 and is used between a GSM Base-Transceiver-Station and a GSM Base-Station-Controller (BSC). The default TCP port for RSL is 3003. The connection will be opened from the BTS to BSC after it has been instructed by the BSC.

Abis RSL is only specified over E1 interfaces. The Abis/IP implementation of OsmoBTS and OsmoBSC extend and/or deviate from the TS 08.58 specification in several ways. Please see the OsmoBTS Abis Protocol Specification [osmobts-abis-spec] for more information.

We can use a tool called abisip-find to be able to find BTS which is connected in the network. This tool is located in the OsmoBSC project repository under: ./src/ipaccess

A tool called ipaccess-config can be used to configure a new ip.access nanoBTS.

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A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section [licenses-gfdl-section-4].

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires [cover-texts], you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-[cover-texts] on the front cover, and Back-[cover-texts] on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable [transparent] copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete [transparent] copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this [transparent] copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

You may copy and distribute a [modified-version] of the Document under the conditions of sections 2 and 3 above, provided that you release the [modified-version] under precisely this License, with the [modified-version] filling the role of the Document, thus licensing distribution and modification of the [modified-version] to whoever possesses a copy of it. In addition, you must do these things in the [modified-version]:

If the [modified-version] includes new front-matter sections or appendices that qualify as [secondary-section] and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of [invariant-sections] in the [modified-version]'s license notice. These titles must be distinct from any other section titles.

You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your [modified-version] by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of [cover-texts] in the [modified-version]. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any [modified-version].

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the [invariant-sections] of all of the original documents, unmodified, and list them all as [invariant-sections] of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical [invariant-sections] may be replaced with a single copy. If there are multiple [invariant-sections] with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of [invariant-sections] in the license notice of the combined work.

In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s [cover-texts] may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing [invariant-sections] with translations requires special permission from their copyright holders, but you may include translations of some or all [invariant-sections] in addition to the original versions of these [invariant-sections]. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

If you have [invariant-sections], Front-[cover-texts] and Back-[cover-texts], replace the “with…Texts.” line with this:

If you have [invariant-sections] without [cover-texts], or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.