Base transceiver station

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An actual BTS device (Siemens BS11µBTS)

A typical BTS tower which holds the antenna. The tower is quite widely misinterpreted as the

BTS itself. The shelter which houses the actual BTS can also be seen.

A mobile BTS

A BTS mounted on a building

A base transceiver station (BTS) or cell site is a piece of equipment that facilitates wireless

communication between user equipment (UE) and a network. UEs are devices like mobile

phones (handsets), WLL phones, computers with wireless internet connectivity, WiFi and

WiMAX gadgets etc. The network can be that of any of the wireless communication

technologies like GSM, CDMA, WLL, WAN, WiFi, WiMAX etc.

BTS is also referred to as the radio base station (RBS), node B (in 3G Networks) or, simply, the

base station (BS). For discussion of the LTE standard the abbreviation eNB for enhanced node B

is widely used.

Contents

[hide]

1 BTS in Mobile Communication

2 General Architecture

3 Important terms regarding a mobile BTS

4 See also

5 Further reading

6 External links

7 References

[edit] BTS in Mobile Communication

A GSM network is made up of three subsystems:

The Network and Switching Subsystem (NSS) – comprising an MSC and associated

registers.

The Base Station subsystem (BSS) – comprising a BSC and several BTSes

The Operations support system - for maintenance of the network.

Though the term BTS can be applicable to any of the wireless communication standards, it is

generally and commonly associated with mobile communication technologies like GSM and

CDMA. In this regard, a BTS forms part of the base station subsystem (BSS) developments for

system management. It may also have equipment for encrypting and decrypting communications,

spectrum filtering tools (band pass filters) etc. antennas may also be considered as components

of BTS in general sense as they facilitate the functioning of BTS. Typically a BTS will have

several transceivers (TRXs) which allow it to serve several different frequencies and different

sectors of the cell (in the case of sectorised base stations). A BTS is controlled by a parent base

station controller via the base station control function (BCF). The BCF is implemented as a

discrete unit or even incorporated in a TRX in compact base stations. The BCF provides an

operations and maintenance (O&M) connection to the network management system (NMS), and

manages operational states of each TRX, as well as software handling and alarm collection. The

basic structure and functions of the BTS remains the same regardless of the wireless

technologies.

[edit] General Architecture

A BTS in general has the following parts:

Transceiver (TRX)

Quite widely referred to as the driver receiver (DRX). DRX are either in the form of

single (sTRU), double(dTRU) or a composite Double Radio Unit (DRU). It basically

does transmission and reception of signals. Also does sending and reception of signals

to/from higher network entities (like the base station controller in mobile telephony)

Power amplifier (PA)

Amplifies the signal from DRX for transmission through antenna; may be integrated with

DRX.

Combiner

Combines feeds from several DRXs so that they could be sent out through a single

antenna. Allows for a reduction in the number of antenna used.

Duplexer

For separating sending and receiving signals to/from antenna. Does sending and receiving

signals through the same antenna ports (cables to antenna).

Antenna

This is also considered a part of the BTS.

Alarm extension system

Collects working status alarms of various units in the BTS and extends them to

operations and maintenance (O&M) monitoring stations.

Control function

Control and manages the various units of BTS including any software. On-the-spot

configurations, status changes, software upgrades, etc. are done through the control

function.

Baseband receiver unit (BBxx)

Frequency hopping, signal DSP, etc.

[edit] Important terms regarding a mobile BTS

Diversity techniques

To improve the quality of the received signal, often two receiving antennas are used,

placed at an equal distance to an uneven multiple of a quarter of wavelength (for

900 MHz the wavelength it is 30 cm). This technique, known as antenna diversity or

space diversity, avoids interruption caused by path fading. The antennas can be spaced

horizontally or vertically. Horizontal spacing requires more complex installation, but

better performance is obtained in this configuration.

Other than antenna or space diversity, there are other diversity techniques such as

frequency/time diversity, antenna pattern diversity, and polarization diversity.

Splitting

The flow of power within a particular area of the cell, known as sector. Every field can

therefore be considered like one new cell. By using directional antennas, the co-channel

interference is reduced. A typical structure is the trisector, also known as clover, in which

there are three sectors, each one served by separate antennas. Every sector has a separate

direction of tracking of 120° with respect to the adjacent ones. If not sectorised, the cell

will be served by an omnidirectional antenna, which radiates in all directions. Bisectored

cells are also implemented with the antennas serving sectors of 180° separation to one

another.

GSM Means Global System for Mobile Communications

GSM

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Jump to: navigation, search

For other uses, see GSM (disambiguation).

The GSM logo is used to identify compatible handsets and equipment

GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a

standard set developed by the European Telecommunications Standards Institute (ETSI) to

describe technologies for second generation (or "2G") digital cellular networks. Developed as a

replacement for first generation analog cellular networks, the GSM standard originally described

a digital, circuit switched network optimized for full duplex voice telephony. The standard was

expanded over time to include first circuit switched data transport, then packet data transport via

GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is

succeeded by the third generation (or "3G") UMTS standard developed by the 3GPP. GSM

networks will evolve further as they begin to incorporate fourth generation (or "4G") LTE

Advanced standards. "GSM" is a trademark owned by the GSM Association.

The GSM Association estimates that technologies defined in the GSM standard serve 80% of the

global mobile market, encompassing more than 1.5 billion people across more than 212 countries

and territories, making GSM the most ubiquitous of the many standards for cellular networks.

Contents

[hide]

1 History 2 Technical details

o 2.1 GSM carrier frequencies o 2.2 Voice codecs o 2.3 Network structure o 2.4 Subscriber Identity Module (SIM) o 2.5 Phone locking o 2.6 GSM service security

3 Standards information 4 GSM open-source software

o 4.1 Issues with patents and open source 5 See also 6 References 7 Further reading 8 External links

[edit] History

Early European analog cellular networks employed an uncoordinated mix of technologies and

protocols that varied from country to country, preventing interoperability of subscriber

equipment and increasing complexity for equipment manufacturers who had to contend with

varying standards from a fragmented market. The work to develop a European standard for

digital cellular voice telephony began in 1982 when the European Conference of Postal and

Telecommunications Administrations (CEPT) created the Groupe Spécial Mobile committee and

provided a permanent group of technical support personnel, based in Paris. In 1987, 15

representatives from 13 European countries signed a memorandum of understanding to develop

and deploy a common cellular telephone system across Europe. The foresight of deciding to

develop a continental standard paid off, eventually resulting in a unified, open, standard-based

network larger than that in the United States. [1][2][3][4]

France and Germany signed a joint development agreement in 1984 and were joined by Italy and

the UK in 1986. In 1986 the European Commission proposed to reserve the 900 MHz spectrum

band for GSM. By 1987, basic parameters of the GSM standard had been agreed upon and 15

representatives from 13 European nations signed a memorandum of understanding in

Copenhagen, committing to deploy GSM. In 1989, the Groupe Spécial Mobile committee was

transferred from CEPT to the European Telecommunications Standards Institute (ETSI).[3]

Phase I of the GSM specifications were published in 1990. Finnish mobile network operator

Radiolinja completed the first GSM telephone call in July, 1991.[5]

1992, the first short

messaging service (SMS or "text message") message was sent and Vodafone UK and Telecom

Finland signed the first international roaming agreement. Work had begun in 1991 to expand the

GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became

operational in the UK in 1993. Also in 1993, Telecom Australia became the first network

operator to deploy a GSM network outside of Europe and the first practical hand-held GSM

mobile phone became available. In 1995, fax, data and SMS messaging services became

commercially operational, the first 1900 MHz GSM network in the world became operational in

the United States and GSM subscribers worldwide exceeded 10 million. In this same year, the

GSM Association was formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide

GSM subscribers passed 100 million in 1998.[3]

In 2000, the first commercial GPRS services were launched and the first GPRS compatible

handsets became available for sale. In 2001 the first UTMS (W-CDMA) network was launched

and worldwide GSM subscribers exceeded 500 million. In 2002 the first multimedia messaging

services (MMS) were introduced and the first GSM network in the 800 MHz frequency band

became operational. EDGE services first became operational in a network in 2003 and the

number of worldwide GSM subscribers exceeded 1 billion in 2004.[3]

By 2005, GSM networks accounted for more than 75% of the worldwide cellular network

market, serving 1.5 billion subscribers. Also in 2005 the first HSDPA capable network became

operational. The first HSUPA network was launched in 2007 and worldwide GSM subscribers

exceeded two billion in 2008.[3]

The GSM Association estimates that technologies defined in the GSM standard serve 80% of the

global mobile market, encompassing more than 1.5 billion people across more than 212 countries

and territories, making GSM the most ubiquitous of the many standards for cellular networks.[6]

[edit] Technical details

GSM cell site antennas in the Deutsches Museum, Munich, Germany

GSM is a cellular network, which means that mobile phones connect to it by searching for cells

in the immediate vicinity. There are five different cell sizes in a GSM network—macro, micro,

pico, femto and umbrella cells. The coverage area of each cell varies according to the

implementation environment. Macro cells can be regarded as cells where the base station antenna

is installed on a mast or a building above average roof top level. Micro cells are cells whose

antenna height is under average roof top level; they are typically used in urban areas. Picocells

are small cells whose coverage diameter is a few dozen metres; they are mainly used indoors.

Femtocells are cells designed for use in residential or small business environments and connect

to the service provider’s network via a broadband internet connection. Umbrella cells are used to

cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and propagation

conditions from a couple of hundred meters to several tens of kilometres. The longest distance

the GSM specification supports in practical use is 35 kilometres (22 mi). There are also several

implementations of the concept of an extended cell,[7]

where the cell radius could be double or

even more, depending on the antenna system, the type of terrain and the timing advance.

Indoor coverage is also supported by GSM and may be achieved by using an indoor picocell base

station, or an indoor repeater with distributed indoor antennas fed through power splitters, to

deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna

system. These are typically deployed when a lot of call capacity is needed indoors; for example,

in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also

provided by in-building penetration of the radio signals from any nearby cell.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-

phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first

smoothed with a Gaussian low-pass filter prior to being fed to a frequency modulator, which

greatly reduces the interference to neighboring channels (adjacent-channel interference).

[edit] GSM carrier frequencies

Main article: GSM frequency bands

GSM networks operate in a number of different carrier frequency ranges (separated into GSM

frequency ranges for 2G and UMTS frequency bands for 3G), with most 2G GSM networks

operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the

850 MHz and 1900 MHz bands were used instead (for example in Canada and the United

States). In rare cases the 400 and 450 MHz frequency bands are assigned in some countries

because they were previously used for first-generation systems.

Most 3G networks in Europe operate in the 2100 MHz frequency band.

Regardless of the frequency selected by an operator, it is divided into timeslots for individual

phones to use. This allows eight full-rate or sixteen half-rate speech channels per radio

frequency. These eight radio timeslots (or eight burst periods) are grouped into a TDMA frame.

Half rate channels use alternate frames in the same timeslot. The channel data rate for all 8

channels is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1

watt in GSM1800/1900.

[edit] Voice codecs

GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 5.6 and 13 kbit/s.

Originally, two codecs, named after the types of data channel they were allocated, were used,

called Half Rate (5.6 kbit/s) and Full Rate (13 kbit/s). These used a system based upon linear

predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it

easier to identify more important parts of the audio, allowing the air interface layer to prioritize

and better protect these parts of the signal.

GSM was further enhanced in 1997[8]

with the Enhanced Full Rate (EFR) codec, a 12.2 kbit/s

codec that uses a full rate channel. Finally, with the development of UMTS, EFR was refactored

into a variable-rate codec called AMR-Narrowband, which is high quality and robust against

interference when used on full rate channels, and less robust but still relatively high quality when

used in good radio conditions on half-rate channels.

[edit] Network structure

The structure of a GSM network

The network is structured into a number of discrete sections:

The Base Station Subsystem (the base stations and their controllers). the Network and Switching Subsystem (the part of the network most similar to a fixed network).

This is sometimes also just called the core network. The GPRS Core Network (the optional part which allows packet based Internet connections).

The Operations support system (OSS) for maintenance of the network.

[edit] Subscriber Identity Module (SIM)

Main article: Subscriber Identity Module

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM

card. The SIM is a detachable smart card containing the user's subscription information and

phone book. This allows the user to retain his or her information after switching handsets.

Alternatively, the user can also change operators while retaining the handset simply by changing

the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only

a SIM issued by them; this practice is known as SIM locking.

[edit] Phone locking

Main article: SIM lock

Sometimes mobile network operators restrict handsets that they sell for use with their own

network. This is called locking and is implemented by a software feature of the phone. Because

the purchase price of the mobile phone to the consumer is typically subsidized with revenue from

subscriptions, operators must recoup this investment before a subscriber terminates service. A

subscriber may usually contact the provider to remove the lock for a fee, utilize private services

to remove the lock, or make use of free or fee-based software and websites to unlock the handset

themselves.

In some territories (e.g., Bangladesh, Hong Kong, India, Malaysia, Pakistan, Singapore) all

phones are sold unlocked. In others (e.g., Finland, Singapore) it is unlawful for operators to offer

any form of subsidy on a phone's price.[9]

[edit] GSM service security

See also: UMTS security

GSM was designed with a moderate level of service security. The system was designed to

authenticate the subscriber using a pre-shared key and challenge-response. Communications

between the subscriber and the base station can be encrypted. The development of UMTS

introduces an optional Universal Subscriber Identity Module (USIM), that uses a longer

authentication key to give greater security, as well as mutually authenticating the network and

the user - whereas GSM only authenticates the user to the network (and not vice versa). The

security model therefore offers confidentiality and authentication, but limited authorization

capabilities, and no non-repudiation.

GSM uses several cryptographic algorithms for security. The A5/1 and A5/2 stream ciphers are

used for ensuring over-the-air voice privacy. A5/1 was developed first and is a stronger

algorithm used within Europe and the United States; A5/2 is weaker and used in other countries.

Serious weaknesses have been found in both algorithms: it is possible to break A5/2 in real-time

with a ciphertext-only attack, and in February 2008, Pico Computing, Inc revealed its ability and

plans to commercialize FPGAs that allow A5/1 to be broken with a rainbow table attack.[10]

The

system supports multiple algorithms so operators may replace that cipher with a stronger one.

On 28 December 2009 German computer engineer Karsten Nohl announced that he had cracked

the A5/1 cipher.[11]

According to Nohl, he developed a number of rainbow tables (static values

which reduce the time needed to carry out an attack) and have found new sources for known

plaintext attacks. He also said that it is possible to build "a full GSM interceptor ... from open

source components" but that they had not done so because of legal concerns.[12]

In January 2010, threatpost.com reported that researchers had developed a new attack that had

"broken Kasumi" (also known as A5/3), the standard encryption algorithm used to secure traffic

on 3G GSM wireless networks, by means of a sandwich attack (a type of related-key attack),

allowing them to identify a full key. It reported experts as saying that this "is not the end of the

world for Kasumi."[13]

(Paper[14]

) The researchers noted that their attack failed on its predecessor

algorithm MISTY1, and observed that the GSM Association's change of standard from MISTY

to KASUMI resulted in a "much weaker cryptosystem". This was followed between December

2010 and April 2011 by an announcement from other researchers that they had reverse

engineered the GSM encryption algorithms, and demonstrated software capable of real-time

interception of GSM voice calls.[15][16]

New attacks have been observed that take advantage of poor security implementations,

architecture and development for smart phone applications. Some wiretapping and

eavesdropping techniques hijack[17]

the audio input and output providing an opportunity for a 3rd

party to listen in to the conversation. At present such attacks often come in the form of a Trojan,

malware or a virus and might be detected by security software.[citation needed][original research?]

[edit] Standards information

The GSM systems and services are described in a set of standards governed by ETSI, where a

full list is maintained.[18]

[edit] GSM open-source software

Several open source software projects exist that provide certain GSM features:

gsmd daemon by Openmoko[19] OpenBTS develops a Base transceiver station OpenBSC is developing a minimalistic, self-contained GSM network[20][21] The GSM Software Project aims to build a GSM analyzer for less than $1000[22] OsmocomBB developers intend to replace the proprietary baseband GSM stack with a free

software implementation[23]

[edit] Issues with patents and open source

Patents remain a problem for any open source GSM implementation, because it is not possible

for GNU or any other free software distributor to guarantee immunity from all lawsuits by the

patent holders against the users. Furthermore new features are being added to the standard all the

time which means they have patent protection for a number of years.[citation needed]

The original GSM implementations from 1991 are now entirely free of patent encumbrances and

it is expected that OpenBTS will be able to implement features of that initial specification

without limit and that as patents subsequently expire, those features can be added into the open

source version. To date there have been no law suits against users of OpenBTS over GSM

use.[citation needed]

4.3. E1/T1 Cards

1. Introduction

Most of the E1 and T1 cards supported by asterisk are capable of carrying both voice and data.

For now, we only have tutorials on how to do the audio part, the data tutorials might be available later.

So what is this E1 or T1 all about ?

1.1. E1 / T1

E1 is a physical layer protocol, like ethernet. It defines a 2Mbps link between two endpoints.

T1 is similar to E1. It is used in North America and is 1.544Mbps

A more in depth difference between the two can be found here

A J1 card is the Japanse version of a T1. (the tiny differences between T1 and J1 can be found here

Both T1 and E1 can be used to transmit data or voice, or a mixture of both.

For example: if an E1 is reserved for voice channels only, the 2mbit will be split into 32 64Kbps telephone channels. 30 of these channels can carry one telephone conversation

each, and 2 carry signalling and timing information.

A t1 could carry 24 telephone channels, each of which can carry a telephone conversation.

Please note that in the states, its a common practice for carriers to offer fractional T1s, these have only some of the 24 channels provisoned.

Lets have a look at the supported audio operating modes:

1.2.: Supported Audio Modes on E1/T1:

There are a number of protocols which can run on top of E1.

These protocols are grouped into 3 big subgroups, CAS, CCS, RBS.

(a detailed difference between these subgroups can be found here)

Lets have a closer look on these subgroups:

a) CAS signalling

CAS stands for Channel Associated Signalling. Examples are FXS

loop start and E&M wink start. These protocols provide information such as the number that was called, and what state the call is in. They're limited in what information they can

carry, and are slow to set up.

With this kind of signalling, a set of bits is used to replicate opening and closing the circuit (as if picking up the telephone receiver and pulsing digits on a rotary phone), or using

tone signalling which is passed through on the voice circuits themselves

CAS is the original signaling system used by E1. In CAS, channel 16 is reserved for signaling. In recent years, the term RBS has been replaced by CAS which is now used to

refer to bits that are associated with a specific channel whether it is in the T1 or E1 format.

Different subprotocols are:

- E&M

- Wink (this might be only RBS, if you know this for sure, please leave a comment.)

- Feature Group B

- Feature Group D

- FXO & FXS: this seems to only use CAS on E1's

- Ground Start

- Loop Start

- Loop Start with Disconnect Detect

b) CCS signalling

Common Channel signalling: A more recent kind of signalling, which resolves the problems associated with CAS signalling. In this kind of signalling, short messages are sent

over the signalling channel, with more information about the call, including caller ID, type of transmission required, etc. etc.

CCS is used by either T1 or E1 and refers to a system that does not use a specific bit structure for signaling. Instead, all or part of a channel is used to pass messages between

two systems to indicate how a channel is being used.

CCS is used by either T1 or E1 and refers to a system that does not use a specific bit structure for signaling. Instead, all or part of a channel is used to pass messages between

two systems to indicate how a channel is being used. This type of system is commonly found in ISDN which uses a D channel to pass messages.

ISDN signalling and ss7 signalling are a subgroup of CCS signalling.

- ISDN (PRI CPE & PRI NET)

ISDN uses one channel (called the D channel) for signalling call information. On E1, this is one of the 2 signalling channels, leaving 30 channels for voice (called B channels).

On T1, there aren't any spare signalling channels, so one of the voice channels is used, leaving 23 B channels for voice.

A PRI (Primary Rate ISDN) is simply an E1 or T1 with ISDN on top of it. ISDN gives fast, reliable call setup and hangup detection, and detailed information about the call. In the

UK, PRI is also called ISDN30.

An important extension to ISDN is Q.SIG, which provides extra signalling information that is used when connecting PBX systems.

Currently, asterisk has limited support for Q.SIG, it can make and receive calls and retrieve some of the extra information.

- On E1, EuroISDN is the standard for ISDN signalling.

- On T1, there are different standards from different providers:

- NI1

- NI2

- 4ESS (AT&T)

- 5ESS (Lucent)

- DMS100

- SS7

c) RBS: Robbed Bit Signalling

RBS is the original signaling system used by T1 and provides either 2 or 4 signaling bits per channel depending on the multiframe format. In recent years, the term RBS has

been replaced by CAS which is now used to refer to bits that are associated with a specific channel whether it is in the T1 or E1 format.

- E&M

- Wink

- Feature Group B

- Feature Group D

- FXO & FXS: this seems to only use RBS on T1's

- Ground Start

- Loop Start

- Loop Start with Disconnect Detect

1.3. Framing

AMI, B8ZS, and HDB3 are different types of line coding used in T1 and E1 communications systems. AMI stands for alternate mark inversion and is used in both T1 and E1

systems. B8ZS stands for Bipolar with 8 Zeros Substitution and is used in T1 systems while HDB3 stands for High-Density Bipolar 3 and is used in E1 systems.

- HDB3: High-Density Bipolar 3 -> E1 only

- AMI: Aternate Mark Inversion -> E1 and T1, the T1 version exists with both ESF (extended super frame) and SF (super frame)

- B8ZS: Bipolar with 8 Zeros Substitution -> T1 only, exists with both ESF (extended super frame) and SF (super frame)

1.4. What signalling and framing should i ask my carrier?

1.5. Timing or clock sources

A T1/E1 connection needs a timing device on one of both ends.

A T1/E1 line can be clocked internally or can be clocked by the telco.

See more about this in the zaptel E1/T1 howto.

2. Asterisk Compatible E1/T1 cards

2.1 available cards

Digium:

- TE110p: 1 port T1/E1 for use in 3.3 or 5 volt pci slots.

- TE205p: 2 port T1/E1 for use in 5 volt pci slots

- TE210p: 2 port T1/E1 for use in 3.3 volt pci slots

- TE405p: 4 port T1/E1 for use in 5 volt pci slots

- TE410p: 4 port T1/E1 for use in 3.3 volt pci slots

- TE406p: 2nd generation 4 port T1/E1 for use in 5 volt pci slots, with hardware DTMF recognition and echo cancellation. (now discontinued, but still supported)

- TE411p: 2nd generation 4 port T1/E1 for use in 3.3 volt pci slots, with hardware DTMF recognition and echo cancellation. (now discontinued, but still supported)

- TE407p: 3rd generation 4 port T1/E1 for use in 5 volt pci slots, with octasic hardware DTMF recognition and echo cancellation.

- TE412p: 3rd generation 4 port T1/E1 for use in 3.3 volt pci slots, with octasic hardware DTMF recognition and echo cancellation.

- Tormenta 2: Discontinued cards based on the open source project zapatatelephony

These cards were known as: Wildcard T100P, T400P, E100P, E400P

intel

- Dialogic D/41JCT-LS: quad t1/e1 board, requires additional (paid) drivers from digium to make it work.

sangoma

- A101: One port T1/E1 card

- A102 :Two port T1/E1 card

- A104: Four port T1/E1 card

varion

- V400P-E: 4 port E1 card, based on the open source zapata telephony project.

These are the same cards as the discontinued digium cards.

- V400P-T: 4 port E1 card, based on the open source zapata telephony project.

These are the same cards as the discontinued digium cards.

Eikon

- none public available yet.

2.1 What card should you pick ?

I recommend against using cards based on the tormenta project, they are way older and take up a lot more cpu. (and their development seems stalled).

The newest digium cards (TE406p and TE411p) as well as the latest firmware versions of the te405p and te410p are optimized for speed.

Only the digium TE406p and the digiun TE411p have hardware echo cancellation, causing a big difference in cpu usage. But this comes at a slightly higher cost.

If you need the 40% speed gain with on board echo cancellers, go for these cards, otherwise go for the cheaper te410p or te405p. (or the 1 or 2 port versions).

It is said on the mailinglists that the hardware echo canceller also has better quality than the echo cancellation done in software. (I can confirm nor deny this claim - it's based on

a single source).

3. Asterisk E1/T1 channel drivers

There are two ways to get the E1/T1 cards to work:

First one is chan_zap (requires the zaptel kernel modules), this is recommended for all digium + sangoma cards.

The second one is chan_mISDN (requires the mISDN kernel patches)

This is probably only usefull for eicon cards. chan_misdn is written for BRI cards, but also supports some E1/T1 cards.

4. Building, installing and configuring asterisk with E1/T1 cards

We will only discuss using chan_zap for now (its the only recommended thing to do).

First read up on more details for your card,

- TE405 / TE410p tutorial

- the other cards are coming soon

then read the general tutorial on chan_zap.