VoIP GSM Gateway - HG-4000 Series

VoIP GSM Gateway Series supports up to 72 VoIP GSM ports, and provides superior voice technology for connecting legacy PBX systems with IP networks, and new IP-based PBX and devices with Cellular networks.

The VoIP GSM Gateway - HG-4000 series enables inbound and outbound VoIP and Cellular calls - all in one compact box. Given the systems' flexibility, modularity and scalability, the VoIP GSM Gateway - HG-4000 can be pre-configured to meet precise customer requirements. Companies can easily expand the cost-effective systems to meet their evolving telephony needs over time, and establish telephony connectivity between the company and its branches.
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Main Features:

*From 12 to 72 Cellular ports
*Up to 288 SIM Cards
*3G, GSM and CDMA networks
*Advanced LCR & Routing Groups
*IP address & DDI pattern restrictions
*USSD pre-paid SIM cards Top-Up support
*GSM worldwide use (850/1900 or 900/1800)
*Integrated antennas combiner
*WEB management and control
*Embedded VoIP (no need for any external VoIP GW (Cisco, Qunintum and others)
*High quality of voice
*Inbound and Outbound calls
*Redundant power supply - Ready
*Fast and easy installation

Source : http://www.hyperms.com/

Mobile Network Quality

Most of the 2G operators did not get the network performance optimised. Some did not have the knowledge, money, tools or the vendor support. Some operators were not important enough for the vendor to help the network quality process. Some operators concentrated too much on technical details and forgot the big picture, the customers and the operator's revenue flows. Some operators simply decided not to put effort to it or decided that with a dropped call operator gets another call and acquires more revenues from the customer. Some were chasing the wrong target without knowing it. No wonder churn rate is around 30 percent around the world.

RF Planning department's antenna configuration changes and parameter modifications (often incorrectly called as "network optimising") are only a part of the network performance optimising process. When deciding how to optimise the network performance, operators need to take couple of steps back, consider how the network should perform (and what are the real performance targets) from the business point of view and then to have a hard look at the work processes. Once all goals of the network optimisation are set, more detailed performance criteria can be considered. Operators should then understand and define the importance of each type of quality problem. For example: How many call setup failures equals one call drop or one handover failure and why? And also who is responsible of each part of the process. For example: Who is responsible of troubleshooting trivial Phone, BSC or BTS hardware problems?

Several 2G network vendors created famous BTS fault lists, which calculate the priority of which BTSs needed to be investigated. Lists were typically different weighted sums of a collection of system problem indicators based on vendor's opinions and available measurements. Top BTSs on the list were usually sites with multiple time-consuming site design problems that were difficult to solve in as reasonable time. Engineers quickly learned to avoid the top sites and priority lists were not working as intended. Special nomination for the most confusing performance measure goes to call drops per tch channel seizures formula that several vendors were pushing in mid 1990's, hopefully nobody is using that any more.

Four small cells To illustrate the point that it is not easy to prioritise the network improvements with limited resources and time, here is a fundamental network performance problem. The problem looks trivial at first, but is worth a deeper consideration. There are four sectors serving an area. Each of them has different traffic amount, call drop rates and call drops per Erlang figures. To really understand what network performance optimisation is, the solution to this basic dilemma needs to be understood. And this type of situations occurs all the time in the network.

Architecture of the GSM network

A GSM network is composed of several functional entities, whose functions and interfaces are specified. Figure 1 shows the layout of a generic GSM network. The GSM network can be divided into three broad parts. The Mobile Station is carried by the subscriber. The Base Station Subsystem controls the radio link with the Mobile Station. The Network Subsystem, the main part of which is the Mobile services Switching Center (MSC), performs the switching of calls between the mobile users, and between mobile and fixed network users. The MSC also handles the mobility management operations. Not shown is the Operations and Maintenance Center, which oversees the proper operation and setup of the network. The Mobile Station and the Base Station Subsystem communicate across the Um interface, also known as the air interface or radio link. The Base Station Subsystem communicates with the Mobile services Switching Center across the A interface.

Mobile Station

The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to subscribed services irrespective of a specific terminal. By inserting the SIM card into another GSM terminal, the user is able to receive calls at that terminal, make calls from that terminal, and receive other subscribed services.

The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI and the IMSI are independent, thereby allowing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number.

Base Station Subsystem

The Base Station Subsystem is composed of two parts, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). These communicate across the standardized Abis interface, allowing (as in the rest of the system) operation between components made by different suppliers.

The Base Transceiver Station houses the radio tranceivers that define a cell and handles the radio-link protocols with the Mobile Station. In a large urban area, there will potentially be a large number of BTSs deployed, thus the requirements for a BTS are ruggedness, reliability, portability, and minimum cost.

The Base Station Controller manages the radio resources for one or more BTSs. It handles radio-channel setup, frequency hopping, and handovers, as described below. The BSC is the connection between the mobile station and the Mobile service Switching Center (MSC).

Network Subsystem

The central component of the Network Subsystem is the Mobile services Switching Center (MSC). It acts like a normal switching node of the PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. These services are provided in conjuction with several functional entities, which together form the Network Subsystem. The MSC provides the connection to the fixed networks (such as the PSTN or ISDN). Signalling between functional entities in the Network Subsystem uses Signalling System Number 7 (SS7), used for trunk signalling in ISDN and widely used in current public networks.

The Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC, provide the call-routing and roaming capabilities of GSM. The HLR contains all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. The location of the mobile is typically in the form of the signalling address of the VLR associated with the mobile station. The actual routing procedure will be described later. There is logically one HLR per GSM network, although it may be implemented as a distributed database.

The Visitor Location Register (VLR) contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR. Although each functional entity can be implemented as an independent unit, all manufacturers of switching equipment to date implement the VLR together with the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, thus simplifying the signalling required. Note that the MSC contains no information about particular mobile stations --- this information is stored in the location registers.

The other two registers are used for authentication and security purposes. The Equipment Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the network, where each mobile station is identified by its International Mobile Equipment Identity (IMEI). An IMEI is marked as invalid if it has been reported stolen or is not type approved. The Authentication Center (AuC) is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and encryption over the radio channel.

RadioFrame Networks Introduces New S-Series IP Picocell Base Transceiver Station for GSM Networks at 3GSM World Congress

RadioFrame's S-Series Deploys GSM Over IP for Increased Wireless Network Capacity and Coverage in Homes and Small-to-Medium Enterprises

RadioFrame Networks, a leader in modular radio solutions for telecom operators, will introduce its S-Series picocell base transceiver station (S-BTS) for GSM networks in stand C34 at the 3GSM World Congress in Barcelona, Spain, February 13 to 16.

RadioFrame Networks' S-Series is the newest product line in its portfolio of software-controlled RF technology and IP base backhaul, such as DSL or cable modems. Based on 3GPP standards for pico base transceiver stations, the S-Series single-board transceiver integrates mobile voice and data services for GSM/GPRS and EDGE networks for applications in homes to small-to-medium enterprises.

"We are excited to introduce the S-Series to the world at the 3GSM exhibition," said Jeff Brown, President and CEO of RadioFrame Networks. "The S-Series brings the ultimate convergence between the fixed and mobile worlds, helping operators serve home and office users to receive enhanced cellular services."

The S-Series gives network infrastructure providers more efficient and cost-effective capabilities to effectively meet the requirements of their service provider partners. Mobile network operators (MNOs) deploying the S-Series system will now have added flexibility to enhance their customers' voice and data services, while improving both coverage and capacity. More importantly, this can all be accomplished by adding radio resources in very small increments.

The S-Series picocell comes packaged in a very small housing roughly the size of a typical broadband modem that can be branded to a carrier's or OEM's specifications. A combination of innovation and standards-based interface provides outstanding performance, reliability and security.

The S-BTS package includes a single 1-TRX transceiver, all required service logic, and a multiple-switched-ports router with firewall security and Web services to provide the MNO remote fault management and configuration capabilities. The S-Series also provides access-rights controls, authentication and encryption functions within live carrier networks.

The S-Series operates in all four of the primary GSM bands: 850, 900, 1800 and 1900.

RadioFrame Networks is backed by some of the leading voices in wireless communications, including wireless pioneer Craig McCaw, Ignition Partners, VantagePoint Venture Partners, Ericsson Venture Partners, Sprint Nextel, and Samsung Ventures.

About RadioFrame Networks

Headquartered in Bellevue, Wash., RadioFrame Networks Inc., the innovative radio access company, deploys cost-effective radio access via flexible and efficient software-driven base stations. Unlike traditional approaches from vendors offering proprietary, single-technology equipment, RadioFrame Networks offers an agile, multiple-technology, future-proof solution that integrates into existing networks, increases capacity and reduces operating costs and capital expenditures.

Main Topic--2G BTS draws on 3G technologies

Two highlights in the rich development of the 3G networks are advanced technologies and high efficiency. However, the GSM network is the most widely applied network in the world. After a decade of development, the GSM network is still favored and constantly evolves due to the maturity of technical applications and business models.

Reviewing the 2G developments from 3G commercial applications, people may ask: Is it possible to apply the high-efficiency and energy-saving technologies of the 3G systems to the 2G systems? Can we smoothly evolve the 2G systems to the 3G systems? Huawei's new-generation EnerG GSM solution will offer you the best answer.


Multi-carrier technology for 2G

I n the traditional GSM base transceiver station (BTS), a radio frequency unit (RFU) can only process one carrier signal, therefore, a 12-TRX macro BTS needs 12 RFUs. Each BTS is cumbersome when equipped with the necessary combiners and duplexers. With technical innovations, each RFU can now process two radio frequency (RF) signals, and a 12-TRX macro BTS needs only 6 dual transceiver units (DTRUs) and less combiners and duplexers. Compared with the BTS with single-TRX's RFU, the new-generation BTS is smaller, leaner, and offers better radio performance.

Currently, Huawei is the only vendor who has developed a QTRU - a type of RFU based on multi-carrier technology. Each QTRU supports the processing of six RF signals. Digital intermediate frequency (IF) combining technology is also used. Six RF signals are combined in the QTRU, and no independent combiner is required. Power of the six RF signals can be shared to improve radio performance. The QTRU based on the multi-carrier technology is the same size as a DTRU, but has three times the capacity of the DTRU.

Multi-carrier technology can bring noteworthy improvements to 2G networks. Take Huawei's indoor macro BTS3012 for example, since the QTRU and DTRU are the same size, the BTS3012 is able to support both the QTRU and DTRU at the same time. The DTRU-based BTS3012 can support up to 12 TRXs and needs combiners. The QTRU-based BTS3012 can support up to 36 TRXs without combiners. To construct a S12/12/12 site, an operator needs three DTRU-based BTS3012s or only one QTRU-based BTS3012 with no combiner.


High efficiency 3G PA technology for 2G

To deploy a wireless network with overall coverage and good performance, thousands of BTSs may be needed. As a result, the costs of BTSs account for the biggest proportion of overall network construction costs. In each BTS that works as a radio transceiver, the RF power amplifier (PA) is the most important component. The linear PA accounts for about 1/3 of the total cost of each BTS, and the RF PA is a main power consumption unit of BTS.

To cut BTS costs, an effective method is to decrease the costs of the RF PA unit for each BTS. This requires the use of a PA that has wide bandwidth, high linear features, and increased efficiency.

The "DPD + Doherty" high-efficiency digital PA technology does quite well. The digital pre-distortion (DPD) technology enables signal pre-distortion. A pre-distorter is cascaded over a PA. Because the non-linear distortions enabled by the pre-distorter are equivalent to those enabled by the PA in quantity but are opposite in function, thus high linear PA output can be achieved.

The Doherty PA technology has two main parts: the carrier (C) amplifier and the peak (P) amplifier. The carrier PA works constantly, while the peak PA works only at the preset peak. The carrier PA works in a nearly saturated state to get higher efficiency, and it amplifies most signals. The peak PA works only at the peak value, and does not consume power most of the time. The linear area with combined output and input features has been greatly expanded from the linear area of a single amplifier, which enables high efficiency when signals are in the linear area.

Huawei's new-generation GSM RF PA improves efficiency up to 50% while saving over 49% in power consumption when compared with a traditional BTS. This is accomplished by coupling power amplification technology with some innovative PA power consumption management technologies like intelligent shut-off of PA power and dynamic adjustment of PA voltage.

If existing sites are replaced by Huawei's new-generation BTSs that adopt the 3G high-efficiency PA and the multi-carrier technology, a medium-sized city with 2,000 sites can save 33.29 million kilowatts (KW) of electricity each year. The environment is spared 22,000 tons of carbon dioxide (CO2) emissions and the operator saves money too.


Distributed architecture for 2G BTS

To reduce 3G network construction costs, Huawei pioneered in launching 3G Node Bs based on the distributed architecture in 2005. In the distributed architecture, the baseband unit (BBU) and the remote radio unit (RRU) are separated and connected through the standard common public radio interface (CPRI).

The distributed architecture divides the traditional Node Bs into two small modules, BBU and RRU. This facilitates site acquisition, simplifies installation, and drastically cuts 3G network construction costs. Based on its mature design and application experience in 3G distributed Node Bs, Huawei launched the DBS3036, a GSM distributed BTS with large capacity, high integrity and high reliability.

By applying advanced 3G RF technologies like multi-carrier technology and the high-efficiency digital PA to the 2G system, Huawei will soon launch the RRU3036 for new-generation 2G distributed BTSs. Each RRU3036 can support up to 6 carriers. For an S6/6/6 site, only three RRU3036 modules are needed. In the future, big, bulky BTSs with high power consumption will be phased out in 2G network construction.

Fig. 2 Huawei's RRU3036

End-to-end IP technology

The GSM and the WCDMA belong to the same standard system and support smooth evolution. The IP radio access network (RAN) technology used in 3G systems has many similarities to the BSS IP technology used in 2G systems. The IP technologies adopted in 3G systems can all be used in 2G systems and guarantee the sustainable development of 2G systems.

In product platform development, the BSC and BTS of the GSM system are both based on an All-IP platform. This dramatically improves the integration of 2G products, decreases power consumption and maintenance costs, and enables smooth evolution to 3G systems. In the past, 5 to10 cabinets were needed for a BSC that supports 2,000 TRXs, including the packet control unit (PCU) and transcoder (TC). Now only one cabinet is required with Huawei's new-generation BSC6000 designed with the IP platform technology. The BSC6000 and the radio network controller (RNC) are both based on the PARC IP platform. The BSC6000 can be upgraded to a RNC by a simple software upgrade and replacement of a few interface boards.

In networking, Huawei's new-generation distributed BTS provides IP interfaces for 2G networks. The Gb interface, Abis interface and A interface are all designed to support IP connection directly. As a result, the structure of the 2G network is simplified, the transmission expenses in 2G networking are curtailed, and increased requirements for digital services can be accommodated. For example, the 3G network of EMOBILE in Japan has saved up to 95% lease expenses on transmission devices each year after adopting Huawei's IP RAN solution.

When 3G IP technologies are used in 2G product development and IP networking, the reliability and efficiency of 2G networks can be greatly improved. Through IP networking, such functions as the BSC pool or the MSC pool can be conveniently enabled. If a BSC or MSC in the network fails in transmission, another BSC or MSC can take up the services and system services will not be interrupted.

Huawei has diversified and upgraded mobile applications by introducing advanced 3G technologies to the 2G system. By adopting the same technologies, 2G and 3G products will naturally evolve from technical convergence to product convergence.

Link: Huawei's next genaration GSM distributed BTS

By Yin Dongming & Xu Yan

3G distributed Node Bs are maturing and GSM operators have begun to cooperate with telecom vendors to explore the possibilities of applying distributed BTSs in the GSM field. However, many products are simple imitations of 3G distributed Node Bs in appearance, installation features and transmission media. The fact is that GSM networks are significantly different from universal mobile telecommunications system (UMTS) networks, especially in capacity, evolution and environmental impact.


Not mere imitations

GSM distributed BTSs are not mere imitations of the 3G models, but are definitely inheritance and improvement based on the original. Hardware sharing the same platform represents the idea of modular design and product maturity. As the smallest and lightest BTS in the industry, Huawei's next-generation GSM distributed BTS is based on the latest platform that is applicable to UMTS networks and even long-term evolution (LTE) networks.

The next-generation GSM distributed BTS's baseband unit (BBU) inherits high integrity from the 3G distributed Node Bs. Its common public radio interface (CPRI) and board structure are of mature designs, while the remote radio unit (RRU) has been greatly improved. By adopting the natural heat dissipation mode and compact size, the RRU is of higher stability, larger capacity, and greater output power. The distributed BTS' maturity has been shined based on in-depth commercial test data, and the BTS features optimized radio frequency (RF) components, heat dissipation, and antenna system.

A basic requirement for GSM networks is the assurance of smooth evolution to future networks. Huawei's next-generation GSM distributed BTS enables GSM and UMTS systems to share the same platform, fully supporting coexistence of 2G and 3G networks and smooth evolution to future networks. The product also adopts the IP platform design mode and uses IP technologies from the core to interfaces. Based on extensive experience in the IP field, Huawei has pioneered in using the IP clock server to transfer clocks on IP networks and realized IP mobile networking from network elements to the overall network architecture.


Full display of distributed features

Differing from Node Bs in 3G networks, GSM BTSs require larger capacity. At present, many GSM distributed BTSs in the industry support only two carriers due to technical limitations, which seriously limits coverage scenarios. These BTSs can only be used as components for macro BTSs or for small-capacity indoor coverage. To utilize distributed features, the next-generation GSM distributed BTSs must support large-capacity networking and provide the capabilities of macro BTSs in terms of coverage and expansion.

Huawei's next-generation distributed BTS stands out from all the GSM distributed BTSs that can be installed on towers for its support of S4/4/4 configuration and S12/12/12 after upgrades. The application performance with 30W cabinet-top output power is equivalent to that of a macro BTS.

By using Huawei's next-generation GSM BTS, operators can have up to 36 carriers in baseband processing, and can add two BBUs to expand each single BTS to support 12 cells and 72 carriers. This can greatly enrich the application scenarios of GSM distributed BTSs and handle the requirements of heavy-traffic users and highly-integrated services, whether indoors or outdoors. In each sector, a single RRU of Huawei's next-generation GSM distributed BTS can support 4 carriers, and the capacity can be further expanded through cascading. Since the unit supports transmit diversity and 4-antenna receive diversity, the receive sensitivity can be up to -112.5 dBm at normal temperature. Operators can stop worrying about degraded quality of service (QoS) and won't need to construct more sites or plan more networks, while enjoying the features of distributed BTSs.

With the purposes of reducing energy consumption, noise pollution, electromagnetic radiation and interference, Huawei has transplanted a "green" idea into the design of its next-generation GSM distributed BTS. By adopting digital power amplifier and intelligent power control technologies, Huawei's next-generation GSM distributed BTS achieves a power amplification efficiency of more than 40%. As a result, power consumption is further decreased while the same output power is maintained.

Experience promises a bright future

Engineering experience from 3G networks is greatly helpful in deploying GSM distributed BTSs. With its 3G distributed Node Bs, Huawei helped Vodafone Spain migrate the networks in Madrid and Barcelona. By installing RRUs on towers to improve coverage, Vodafone Spain greatly improved its voice quality and high-speed packet access (HSPA) data throughput.

In Hong Kong, where features the most complicated wireless environment and great difficulty in site acquisition, Huawei used the ray-tracing model and 3G distributed Node Bs to build a high-quality network, while saving space and rental costs.

In Singapore, Huawei used distributed Node Bs to realize the coverage of two different scenarios in downtown areas and residential areas. By using fiber extensions and reading directly the original network configuration data, Huawei managed to speed up the network optimization with a record-setting delivery of 100 sites per week.

In Japan, Huawei tailored its distributed Node Bs to meet the operator's rigorous requirements for earthquake resistance, moisture resistance, natural heat dissipation, and reliability, and succeeded in constructing the fastest mobile broadband network nationwide with more than 70% coverage.

Although the mature application of 3G distributed Node Bs have significantly influenced the GSM network deployment, operators are still looking forward to a next-generation distributed BTS solution tailored for GSM networks, rather than equipment that enables simple separation in physical architecture. The next-generation GSM distributed BTS can truly help operators build high efficiency, high quality and quickly operable GSM networks that provide competitive services and products.

Base Transceiver Station BTS

Base Transceiver Station (BTS) is the equipment which facilitates the wireless communication between user equipments and the network.

The term BTS is generally and commonly associated with mobile communication technologies like GSM and CDMA. A BTS forms part of the Base Station Subsystem (BSS) and has the equipments (transceivers) for transmitting and receiving of radio signals, signal processors, signal paths, signal amplifiers, and equipments for system management. It may also have equipments 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. A BTS is controlled by a parent Base Station Controller via the Base station Control Function (BCF).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 BTSs are equipped with radios that are able to modulate layer 1 of interface Um; for GSM 2G+ the modulation type is GMSK, while for EDGE-enabled networks it is GMSK and 8-PSK.

The Base Station Controller (BSC) provides, classically, the intelligence behind the BTSs. Typically a BSC has 10s or even 100s of BTSs under its control. The BSC handles allocation of radio channels, receives measurements from the mobile phones, controls handovers from BTS to BTS. Networks are often structured to have many BSCs distributed into regions near their BTSs which are then connected to large centralised MSC sites.

Although the Transcoding (compressing/decompressing) function is as standard defined as a BSC function, there are several vendors which have implemented the solution in a stand-alone rack using a proprietary interface. This subsystem is also referred to as the TRAU (Transcoder and Rate Adaptation Unit). The transcoding function converts the voice channel coding between the GSM (Regular Pulse Excited-Long Term Prediction, also known as RPE-LPC) coder and the CCITT standard PCM (G.711 A-law or u-law). Since the PCM coding is 64 kbit/s and the GSM coding is 13 kbit/s, this also involves a buffering function so that PCM 8-bit words can be recoded to construct GSM 20 ms traffic blocks, to compress voice channels from the 64 kbit/s PCM standard to the 13 kbit/s rate used on the air interface. Some networks use 32 kbit/s ADPCM on the terrestrial side of the network instead of 64 kbit/s PCM and the TRAU converts accordingly. When the traffic is not voice but data such as fax or email, the TRAU enables its Rate Adaptation Unit function to give compatibility between the BSS data rates and the MSC capability.

However, at least in Siemens’ and Nokia’s architecture, the Transcoder is an identifiable separate sub-system which will normally be co-located with the MSC. In some of Ericsson’s systems it is integrated to the MSC rather than the BSC. The reason for these designs is that if the compression of voice channels is done at the site of the MSC, fixed transmission link costs can be reduced.

BSS interfaces

Um - The air interface between the MS (Mobile Station) and the BTS. This interface uses LAPDm protocol for signaling, to conduct call control, measurement reporting, Handover, Power control, Authentication, Authorization, Location Update and so on. Traffic and Signaling are sent in bursts of 0.577 ms at intervals of 4.615 ms, to form data blocks each 20 ms.

Abis - The interface between the Base Transceiver Station and Base Station Controller. Generally carried by a DS-1, ES-1, or E1 TDM circuit. Uses TDM subchannels for traffic (TCH), LAPD protocol for BTS supervision and telecom signaling, and carries synchronization from the BSC to the BTS and MS.
Link Access Procedures on the D channel (LAPD), is the second layer protocol on the ISDN protocol stack in the D channel.

A - The interface between the BSC and Mobile Switching Center. It is used for carrying Traffic channels and the BSSAP user part of the SS7 stack. Although there are usually transcoding units between BSC and MSC, the signaling communication takes place between these two ending points and the transcoder unit doesn’t touch the SS7 information, only the voice or CS data are transcoded or rate adapted.

Ater - The interface between the Base Station Controller and Transcoder. It is a proprietary interface whose name depends on the vendor (for example Ater by Nokia), it carries the A interface information from the BSC leaving it untouched.

Gb - Connects the BSS to the Serving GPRS Support Node (SGSN) in the GPRS Core Network.