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.
