OVERVIEW & ARCHITECTURE OF CORDECT WLL

Introduction

The corDECT Wireless Access System (WAS) is designed, to provide simultaneous circuit- switched voice and medium-rate Internet connectivity at homes and offices. The Access System model, which corDECT emulates.

Conceptual Access System

In this conceptual model, there is a Subscriber Unit (SU) located at the subscriber premises. The SU has a standard two-wire interface to connect to a telephone, fax machine, PCO (Public Call Office), speakerphone, cordless phone, or modem. it also provides direct (without a modern) Internet connectivity to a standard PC, using either a serial port (RS-232 or USB) or Ethernet. The Access System allows simultaneous telephone and Internet connectivity. The SU's are connected to an Access Centre (AC) using any convenient technology like wireless, plain old copper, DSL on copper, coaxial cable, optical fibre, or even power lines.

The AC must be scalable, serving as few as 200 subscribers and as many as 2000 subscribers. In urban areas, the AC could be located at a street corner, serving a radius of 7OO m to 1 km. This small radius in urban areas is important for wireless access, in order to enable efficient re- use of spectrum. When cable is used, the small radius ensures lower cost and higher bit rate connectivity However in rural areas, the distance between the AC and the SU could easily be 10 km and even go up to 25 km in certain situations.

The AC is thus a shared system catering to multiple subscribers. The voice and Internet traffic to and from subscribers can be concentrated here and then carried on any appropriate backhaul transport network to the telephone and lnternet networks respectively.

At the AC, the telephone and Internet traffic is separated. The telephone traffic is carried to the telephone network on El links using access protocols such as V5.2. The Internet traffic from multiple subscribers is statistically multiplexed, taking advantage of the bursty nature of Internet traffic, and carried to the Internet network. As use of Voice-over-IP (VOIP) grows, voice traffic from SU's could also be sent to the Internet, gradually making connectivity to the telephone network redundant. However, for connecting to the legacy telephone network.

The AC may be required for some time to come. An AC could also incorporate switching and maintenance functions when required. Futher, It is possible to co- locate internet servers with the AC.

corDECT Wireless Access System

Following the conceptual model, the corDECT Wireless Access System uses a similar architecture to provide telephone and Internet service to a subscriber, as shown The subscriber premises equipment, Wallset IP (WS-IP)

could also incorporate switching maintenance functions when required. Further, is possible to co-locate lnternet servers with Ea AC.

The subscriber premises equipment, Wallset IP (WS-IP) or Wallset (WS), bias a wireiess Connection through a Compact Base Station CBS) to an Access Switch, called a DECT Interface Unit (DIU). The air interface is compliant c) the DECT standard specified by ETSI. The )IU switches the voice traffic to the telephone I network using the V5.2 protocol to connect to in exchange. The DIU also switches the Internet built-in Remote Access Switch(which then routes the traffic to the Int network. The Ras has an Ethernet into which is connected to the Internet using suitable routing device.

The CBS is normally connected to the DIU three twisted-pair wires, which carry sign well as power from the DIU to the Alternatively, it can be connected to through a Base Station Distributor (BSD BSD is remote unit connected to the DIU a standard E1 interface ( on radio, fibre, A BSD can sup to four CBS’s.

The long range communication, a WS is can also be connected to the CBS using hop DECT wireless link, one between V WS and a Relay Base Station (RBS) and between the RBS and CBS, The wireless range supported be WS 0 Ip or WS and the CBS or RBS is

line-of-Sight (LOS)'conditions. The range supported between a CBS and RBS is 25 km in LOS conditions.

A typical system consists of one DIU with one or two RAS units, up to 20 CBS'S, and up to a 1 000 WS-IP's or WS's. The BSD and RBS units are used as required by the deployment scenario.

Sub-systems of the corDECT Wireless Access System

Before we get into more details at the system level, we take a breif look at each of the subsystems.

Wallset IP and Wallset

The Wallset with Internet Port (WS-IP) provides voice connectivity to the subscriber using a RJ-11 interface, enabling one to connect a standard DTMF or decadic telephone, G3 tax machine, PCO (battery reversal and 12/16 kHz metering are standard features), speakerphone, cordless phone, or modem. In addition, the WS-IP has a RS-232 port to directly connect to a PC (obviating the need for a telephone modem). The PC establishes a dial-up PPP (Point-to-Point Protocol) Internet connection using a standard dial-up utility. Internet access is supported at 35 or 70 kbps. In fact, the WS-IP can support simultaneous voice and 35 kbps Internet connections.

Besides these two user interfaces, the WS-IP has an antenna port where either a whip antenna, or an externally mounted antenna (through cable), can be connected. The power to the WS-IP is provided by a 12V adaptor connected to the AC mains and optionally by a solar panel which can be connected in parallel. The WS-IP has a built-in battery and battery charger. The built-in-battery provides 16 hours stand-by time and more than 3 hours talk time for voice calls.

A Wallset (WS) is a similar terminal without the Internet Port.

Multiwallset

The Multiwallset (MWS), provides simultaneous voice service to four subscribers. It has all the features of the WS, but at a significantly lower per-line cost.

The Multiwallset has a DECT Transceiver Module (DTM), which is an outdoor unit with a built-in antenna with 7.5 dB gain. It is connected to an indoor Subscriber Interface Module (SIM), which has four RJ-11 ports for telephones. Each port supports all the terminals a WS supports.

The connection between the DTM and the SIM uses a single twisted-pair wire, obviating the need for RF cable and connectors. The MWS has a built-in-battery for backup and is powered through the AC mains.

Multiwallset IP

The Multiwallset with Internet Port (MWS-IP) is a MWS with four telephones and an additional Ethernet Interface to provide dial-up Internet connectivity. Multiple PC’s can be connected to the Ethernet port and provide a shared 35/70 kbps Internet connection. The PPP-over-Ethernet protocol is used to set up individual connections it is to be noted that at any time, either four simultaneous telephone calls with no Internet connection, or three telephone calls and a 35kbps shared Internet connection, or two telephone calls and a shared 70 kbps Internet connection, can be made. Depending on usage, this may introduce some blocking for voice calls.

Compact Base Station

The Compact Base Station (CBS), provides the radio interface between the DIU and the corDECT subscriber terminal. It supports up to 12 simultaneous voice calls. It is a small, unobtrusive, weatherproof unit that is remotely powered from the DIU or a BSD.

The CBS has two antennas for diversity. A directional antenna with significant gain can be used when coverage is required to be confined to certain directions. For example, if the coverage area is divided into sectors, each sector can be covered by a different Base Station with directional antennas. For 360 degrees coverage using a single CBS, omni-directional antennas are used. More than one CBS can be deployed to serve a single sector or a cell.

The maximum LOS range between a subscriber unit and a CBS is 10 km. An isolated CBS supports approximately 5.8 E of traffic with a Grade of Service (GOS) of 1%, typically serving 30-70 subscribers. Multiple CBS’s serving the same sector or cell increase the traffic handled by each CBS (see Chapter 6).

The CBS is conencted to a DIU or a Base Station Distributor (BSD) with three twisted-pair copper wires, each of which carry voice/data traffic, signalling and power. The maximum loop length, with a 0.4 mm diameter wire, can be 4 km between the DIU and the CBS and 1km between the BDS and the CBS.

DECT Interface Unit

The DECT Interface Unit (DIU) shown in 3.8, implements the functions of a Switch (or a Remote Line Unit), Base Station Controller, and the Operation and Maintenance Console (OMC). System reliability is guaranteed by redundant, hot stand-by architecture. The OMC allows exhaustive real-time monitoring and management of the entire corDECT system. A fully cond DIU with an in-built Remote Access Switch (RAS) only occupies a single 28U, 19’’ cabinet and consumes less than 600w.

Up to 20 CBS’s can be supported by a DIU, directly or through the BSD. The DIU provides up to eight E1 links to the telephone network and/or RAS. The signaling protocol used is either V5.2, which parents the DIU (as a RUL) to an exchange, or R2-MF, in which case the DIU acts as a 1000-line exchange. There is a third option, wherein the corDECT system, using additional equipment, appears to an exchange simply as a number of twisted-pair lines.

Multiple DIU’s are managed through a centralized Network Management System (NMS).

iKON Remote Access Switch

The iKON Remote Access Switch (RAS),, is a 19” 1U unit normally integrated within the DIU cabinet. It terminates the PPP connections from Internet subscribers using corDECT WS-IP or MWS-IP. It is connected to the DIU using up to two E1 ports and does IP-based routing for up to 60 simultaneous corDECT Internet calls. The RAS has a 10Base T Ethernet port to connect to the Internet. It supports RADIUS for accounting and authentication, PAP for user authentication and is managed using SNMP.

Base Station Distributor

The Base Station Distributor (BSD) is a compact, remotely located, locally powered, rack-mountable unit that supports up to four CBS’s (with power feed). The E1 interface between DIU and the BSD can be on copper, fibre, or and link distance depends only on the linkd.

The BSD is designed to extend cord coverage to ppockets of subscribers located away from the DIU.

Relay Base Station

A Relay Base Station (RBS), extends the range of the corDECT system by relaying DECT packets between the CBS subscriber units. The RBS can handle 11 simultaneouslys.

The RBS consists of two units. The RBS A is typically monted on a tower/mast and on the baseband and the RF sub-system. The Ground Unit supplies power and produce maintenance support to the Air Unit at mounted at the bottom of the tower/mast.

The RBS uses three antennas. One and (usually a directional antenna with high ) refererd to as the RBSWS antenna, towards the CBS with which the RBS communicating. The other two antennas RBSBS antennas are used for communication with the subscriber units (two antennas are used for diversity). These antennas are similar to those used by the CBS.

The maximum LOS range between a CBS and a RBS is 25 km, while the maximum LOS range between the RBS and corDECT subscribers is 10 km.

Network Management

CorDECT provides comprehensive operation and maintenance through the corView OMC console. Its repertoire includes hardware and software configuration, subscriber administration, accounting, fault notification, and traffic management. 3.12 depicts the corView GUI for configuring the DIU. Commands range from a bird’s-eye view of the operational status of a network of corDECT systems to probing the internals of an individual Wallset.

This easy-to use, menu-driven console can be run either locally or remotely. When used remotely, a single corView workstation serves as the NMS for a number of corDECT systems. CorView can also be used with the CygNetNMS to provide integrated management of a network of corDECT and other systems.

CorView supports the SNMP protocol and can be connected to the corDECT system by any IP network. In the future, corView will also supportTMN/Q3. When the DFIU is used as a Switch, detailed billing records are maintained and can be exported to the billing centre via several media.

corDECT Access Centre Functionality and Interfaces

The corDECT Access Centre, consisting of a DIU and iKON RAS, is designed to provide interfaces to the telephone network and to the Internet.

The Telephone Connection

The telephone connection provided to a corDECT subscriber is a circuit-switched one. The DIU switches the connection to the telephone network. The interface to the telephone network is provided in three different ways:

1. RLU mode, with V5.2 protocol on E1 interfaces to a parent exchange and

2. Transparent mode, with two-wire interface to a parent exchange and

3. Switch mode, with R2-MF protocol on E1 interfaces to the telephone network.

RLU Mode

The DIU has up to six E1’s that can be connected to a parent exchange using V5.2 signaling. The DIU in this case works as a 1000-line RLU of the parent exchange, as shown in 3.13. Even calls between two corDECT subscribers belonging to the same DIU are switched by the parent exchange.

The numbering and all subscriber facilities are provided by the exchange and billing too is carried out at the exchange. The DIU does some limited subscriber administration, such as authenticating a subscriber (as per the DECT standard). The DIU console, however, provides management functions for managing the DIU, CBS, RBS, BSD, WS, WS-IP, MWS and MWS-IP, and also carries out wireless traffic monitoring. The management functions canalso be carried out centrally for multiple DIU’s,.

Transparent Mode

In this mode, the DIU is parented to an exchange using two-wire interfaces. Each subscriber line is mapped to an unique two-wire port on the exchange. Hook status and digits dealed at the WS/WS-IP/MWS are mapped by the DIU to reflect at the corresponding exchange port. All services of the exchange are available to the subscriber. Billing is carried out at the exchange. However, as in the RLU mode, the DIU carries out subscriber authentication and system management functions.

To provide two-wire interfaces at the DIU, a Concentrating Subscriber Multiplexer (CSMUX) is used. Each SMUX, housed in one 6U 19” rack, can provide up to 240 two-wire ports (grouped as 2 x 120 two-wire ports). The CSMUX is connected to the DIU typically using two E1 ports, providing 4:1 concentration. Thus, using eight E1’s and four CSMUX units and a DIU integrated in two cabinets, one can serve up to

Subscribers in transparent mode a concentration of 4:1 is normally acceptable since wireless channels are anyway shared. Sharing an E1 port among 120 subsceibers, one can serve nearly 0.2 erlang per subscriber at 1% GOS. However, it is to avoid concentration at the CSMUX connect eight E1’s to a signle CSMUX rack. This case, one DIU will be limited to serve a minimum of 240 subscribers.

The transparent mode is the quickset way to reconnect corDECT to an existing telephone work. However, it is not a preferred mode for concetration. In order to serve 960 subscribers, 960 wire ports are required on the exchange side connected to four CSMUX units. In contrast, only to six E1 ports are required at the exchange the RLU mode and use of the CSMUX is sided. Thus, in the RLU mode, the sixe of the exchange as well as the DIU is much smaller the power required is also less when prepared to the transparent mode.

A more serious problem in the transparent mode comes froma signalling anomaly that can emerge in some specific situations. For example, when an incoming call comes to the exchange for a subscriber, the exchange signals ring-back to the calling subscriber if it finds from its database that the called subscriber if free. The exchange simultaneously feeds ring to the corresponding two-wire port. This is detected by the CSMUX in the DIU and the DIU then attempts to page the corresponding WS/WS-IP and ring the subscriber. However as wireless channels are shared, it is possible that sometimes the DIU finds no free channel and fails to feed ring to the subscriber. The anomaly develops when the called port gets ring-back tone, but the called party does not get a ring. Such a situation can sometimes become problematic. The transparent mode is therefore not the most desirable mode of operation. Nevertheless, it is the quickest way to integrate a wireless system to the existing telephone network anywhere in the world.

Switch Mode

The DIU is designed to be a 1000-line, full-fledged, medium-sized exchange for corDECT wireless subscribers. It interfaces to the telephone network on up to six E1-lines using R2-MF protocol. all the exchange functions, including subscriber administration, billing, and management, are carried out at the DIU itself. The advantage of this mode is that the cost of an exchange is totally saved.

The DIU can also serve as a Direct In-Dialing (DID) PBX.

Internet Connection

A corDECT subscriber connects to the WS-IP using a PPP dial-up connection on the RS-232 port. The port is programmed at 38.4 kbps rate for a 35kbps Internet connection and at 115.2kbps rate for a 70kbps Internet connection. The PC connected to the RS-232 port on the WS-IP dials a pre-designated number using a standard dial-up routine. The DIU sets up a circuit-switched connection between the Ws-IP and the iKON RAS connected to the DIU on an E1 port.

The Internet connection employs the wireless link between the WS-IP and the CBS and the wired links between the CBS and the DIU and between the DIU and the RAS. Since the BER on the wireless link could occasionally be high, the PPP packet is fragmented and transmitted with an error detection code on the link from the WS-IP to the DIU. ARQ is performed on this link to obtain error-free fragment transmission. The PPP packets are re-assembled from these fragments before transmitting it to the PC (on the WS-IP side) and to the RAS (on the DIU side).

The connection between the WS-IP and the DIU is at 32kbps or 64kbps (using one or two DECT slots on air). The start/stop bits received at the RS-232 port are stripped before transmission on air. This enables 35kbps Internet throughput between the user PC and the RAS on the 32 kbps connection in an error-free situation. Similarly, 70kbps Internet throughput is possible between the user pC and the RAS on the 64kbps connection. Bit errors on the link will temporarily bring down the throughput.

Each RAS has tow E1 ports for connecting to the DIU and thus can support Internet connections for up to 60 subscribers at a time. The PPP connections are terminated at the RAS and IP packets are routed to the Ethernet port of the RAS for onward transmission to the Internet. The Ethernet ports from multiple RAS’s would normally be connected to an Ethernet switch. The Ethernet switch in turn would be connected to an Internet router, completing the connection to the Internet.