Wireless Local Loop Architecture [ WLL Architecture ]

The Wireless Local Loop Architecture (WLL Architecture) is a system that is responsible for connecting the subscriber to the Public Switched Telephone Network (PSTN) with the help of the wireless technology that utilizes the radio signals and thus providing the standard telephone services to the subscriber. 

The Wireless Local Loop (WLL) was also called the Fixed Radio Access (FRA) and also Radio Local Loop (RLL).

The Wireless Local Loop (WLL) technology came in response to the drawback that was faced by its counterpart i.e. Wireline Local Loop (WLL). The Wireline Local Loop or wired network had some serious disadvantages such as Long Copper Wire has to be installed from the central station to the end-user who had the telephone set, and believe me these copper wires installation were so costly alone that rural areas with a limited budget and isolated geography (such as hilly area) could not think to afford them. The other disadvantage of wired networks was the installation of poles and duct tape essential for wired networks. 

Therefore when the Wireline Local Loop (WLL) came into existence it just reduced the installation cost dramatically and speeded up the installation process. This means now rural and isolated areas can now afford the technology and establish two-way communication. The advantages of Wireline Local Loop (WLL) was that it used the radio system, and the radio systems can be developed rapidly, easily extended, and are distance insensitive.

 

Wireless Local Loop (WLL) & it’s Working

The Wireless Local Loop as the name suggests its technology – ‘Wireless’ describes the use of radiofrequency for communication, ‘Local’ describes a Rural or isolated geographical area (like hilly places), and ‘Loop’ which describes a circuit that connects the subscriber station (telephone) to the line terminating equipment which is a Switch that is located in the central office which connected various distant area networks.

In the Local Loop circuit, the wire trunks start from the central office, and as we move away from the central office these are then broken down into many smaller circuits after some distance. After that, these circuits are then separated into individual drops for the residence houses. The Central Office Switch serves as the point where the traffic concentration occurs initially and then traffic is then forwarded to the individual’s drops of residences in the Local Area. 

When the wires were used in the circuit loops they were known as the Wireline Local Loop, and when the Radio Signals were used in the circuit loops they were known as the Wireless Local Loop. 

The Wireless Local Loop came into use as the implementation of the wired networks was less effective in the rural area as there were fewer users in the area, and also the cost of material used in wired networks was also more. The Wireless Local Loop (WLL) helped to escape the hassle of the copper network cables and the maintenance in wired technology, later on, was a big challenge.

Many problems existed which were removed with the upcoming of the WLL, the labor charges and other investment were not needed anymore. The WLL does not use the copper wire and is also much secure than the previous network and also they were much more scalable than the wired network and hence they were easily adopted by many industries.

 

Wireless Local Loop (WLL) services and facilities

The Closed User Group (CUG) can be supported by the WLL. A close user group is a group of small people mainly for business purposes and they can use the call transfer, conference call facilities which helps the close user group to communicate confidential information securely to each other.

The bandwidth which is offered to the wired technology is limited and the wireless technology is more limited therefore we have to put extra effort into the usage of bandwidth that we have in the wireless technology and the efficient use of bandwidth can be done by reusing the frequency provided.

Some special services are also available in a wireless local loop such as call recording and forwarding facility as well as reminder facility which informs the user if someone called earlier on the telephone and the user missed the call therefore this reminder can help the user to know about the missed call. 

 

Wireless Local Loop Architecture [WLL Architecture]

Wireless Local Loop Architecture Consists of three major components:

1. Wireless Access Network Unit (WANU)
2. Wireless Access Subscriber Unit (WASU)
3. Switch Function (SF)

 

Wireless Access Network Unit (WANU)

The Wireless Access Network Unit (WASU) acts as an interface between the wired side (i.e. PSTN & SF) and the Wireless side (i.e. WANU), this unit is responsible for taking and delivering the data across the wired and wireless domains. 

 

The WANU is responsible for –

1. Air registration and authentication of the Subscriber
2. Privacy via the Air Interface
3. WANU also plays an important role in call management such as:

• Routing & Switching
• Billing Protocol conversion
• transcoding of voice and data
• OAM

 

The Wireless Access Network Unit (WASU) is made of –

1. Many Radio Parts or BST  
2. Radio Port Control Units (RPCU) 
3. Home Location Register (HLR) 
4. Access Manager (AM) that is required for the working of the RPCU

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Wireless Access Subscriber Unit (WASU)

The key role of the Wireless Access Subscriber Unit is translating between the wired and wireless signals. When the data is coming from the wired network then it will find the right encoding to translate the signals to the wireless network and vice versa. 

WASU also ensures that the traditional phones (eg. the dial ring phone) can be used along with the wireless technology in the Wireless Local Loop.

Wireless Access Subscriber Unit provides an interface for UWLL for the network side and the PWLL for the user or subscriber side. 

WASU is responsible for Voice trans-coding as well as authentication and signaling functions.

 

Switch Function (SF)

Switch Function is associated with a switch that can be a digital switch, ISDN switch, MSC. The Switch Function is connected to the WANU with the AWLL interface.

 The transmission that occurs between the WANU and the Switch Function can be made on a leased line, optical fiber, or microwave frequency. The 

 

Wireless Local Loop Architecture [WLL Architecture] & working 

The Public Switching Telephone Network (PSTN) is connected to the switching function (SF). The user can use the PSTN to initiate calls to any number of users that are located within the Wireless Local Loop (WLL) coverage area. 

When the user has initiated the call with help of PSTN then the call will be routed to the Switching Function (SF) via the trunk data, and this Switching Function will then forward the call to the appropriate Wireless Access Network Unit (WANU).

The Wireless Access Network Access Unit (WANU) is made up of many individual components that complete its functions as a whole. They are Base Transceiver Station (BTS), Radio Port (RP), the radio controller (RPCU), an access manager (AM), and Home Location Register (HLR).

The interface that connects the Wireless Access Unit (WANU) and the switch function that is connected to the PSTN is called the AWLL. And the Air Interface that provides the Connection between the WANU and the user side types of equipment is called UWLL. 

The Wireless Access Network Unit (WANU) has to provide for the authentication and the privacy for the air interface between the WANU and the user side these are done with the help of Radio resource management, Limited Mobility Management, and also over the registration of the SUs (Subscriber Units). 

The other facility that is provided in the Operation and Maintenance (OAMP), routing, and billing and switching necessary functions. The WANU also provides other functions such as transcoding of the voice and the data and the protocol conversion.

The WANU acts as a medium between the wired network (PSTN) and the wireless network (WASU). The call is then forwarded via WASU over the Wireless Access Subscriber Unit (WASU) and then the call over the wired channel to the phone.

The Wireless Access Subscriber (WASU) is responsible for providing an air interface for the network and to serve the traditional Interface (TWILL) to the subscriber. This interface also includes authentication functions, OAMP, dual-tone Multiple Frequency (DTMP), protocol conversion and transcoding, dial tone.

In the WLL reference model, the Switch Function (SF) can be with a digital switch which may or may not have Advanced Intelligent Network (AIN) capacity, an ISDN switch, or a mobile switching center (MSC).