Chapter 16, NEW TECHNOLOGY FAMILIARIZATION

Managed Leased Line Network

Chapter 16

MANAGED LEASED LINE NETWORK (MLLN)

Contents:

Overview of MLLN

Structure of MLLN

MLLN Network Management System

Digital Cross connect

Network Terminating Units

Tellabs 8100 System Overview

Objectives:

After completion of this module, the participants will be able to know

What is MLLN

What is the structure of MLLN

How a digital cross connect works

What are the network terminating units

236 Prepared by RGM TTC, Chennai


MANAGED LEASED LINE NETWORK (MLLN)

16.1 ScopeThis Module is to familiarize with the newly developed technology of managed leased

lines, its advantages, usage, basic configuration, equipments involvement, etc.

16.2 General

16.2.1 Leased Line.

A leased line is basically dedicated pair/pairs of copper wire connecting between two

points that is available 24 hours a day for use by a designated user (Individual or

Company). A synonym is non-switched line (as opposed to switched or dial up line).

A leased line can be a physical path owned by the user or rented from a telephone

company like BSNL/MTNL/VSNL. In earlier days these leased line equipment used to

be the same as that of the telecomm transmission equipment as the requirement of leased

line networks were low. With the burgeoning need for the leased line, now a days

Managed Leased Line Networks (MLLN) are being used

16.2.2 Managed Leased Line Network.

The MLLN is an integrated, fully managed, multi-service digital network platform

through which service provider can offer a wide range of services at an optimal cost to

Business Subscribers. Backed by a flexible Network Management System with powerful

diagnostics and maintenance tools, the MLLN can be used to provide high-speed leased

lines with improved QoS (Quality of Service), high availability and reliability. The

Network Management System also supports Service Provisioning, Network

Optimization, Planning and Service Monitoring. The system offers features such as end

to end circuit creation and monitoring, Circuit Loop Test and fault isolation, Alternate re-

routing of traffic in case of trunk failure, Software programmability of NTUs, etc. Due to

its wide range of applications in various sectors like banking, financial institutions, stock

markets, newspaper industry, broadcasting houses and Internet Service Providers, this



managed leased line equipment will benefit all sections of people by way of faster

Internet access, accessibility of bank accounts from anywhere, instant news coverage

etc.Various organizations like banks, ATM operators, IT companies will be using this

flexible leased line solution. The following are the few features, which are the beneficial

for the customers.

1. Customers need not to buy 2 pairs of Modems.

2. Modems will be supplied and maintained by Service Provider.

3. 24 Hours performance monitoring of the circuit.

4. Circuit fault reports generated proactively.

5. On demand the bandwidth can be increased.

6. Low lead-time for new circuit provisioning.

7. Protection against the failure of the circuit.

8. Long drive on single pair copper.

9. Centrally managed from Network Management System.

The MLLN also supports enhanced features such as Corporate Internet Access, Point to

Point Data, Point to Multipoint Data, LAN-IC, Hotline, EPABX Inter-connect, EPABX

Remote Extension and ISDN Line Extension, Virtual Private Network, etc.



16.3 TYPICAL STRUCTURE OF MLLN SYSTEM.

The MLLN is planned as three-tier structure of consisting of aggregation and

connectivity at two different levels:

A. Central Node: It will provide following functionality:

(i) NMS Center.



(ii) Connectivity to second stage nodes.

(iii) Leased line aggregation.

B. Second stage Node: It will be located at major cities of a Telecom Circle, where

demand for leased line is high. It will provide following functionality:

(i) Connectivity to third stage nodes.

(ii) Leased line aggregation.

C. Third Stage Node: It will be located at smaller cities / towns of a Telecom Circle,

where demand for leased line is lower (near 10).

It will provide Leased Line aggregation.

16.3.1 Functional Requirements.

The MLLN system is able to provide the following functionality:

(i) Speedy end-to-end service provisioning.

(ii) Round-the-clock end-to-end performance monitoring.

(iii) Automated alarm / fault management.

(iv) Easy re-routing and configuration.

(v) Accounting and Security management.

(vi) On-demand bandwidth availability up to 2 Mbps.

16.3.2 Technical Requirements.

The various components of the MLLN shall be:

a) Network Management System (NMS).

b) Digital cross Connect (DXC).

c) Versatile Multiplexer (VMUX).



d) Network Termination Unit (NTU).

16.4 Network Management System.

The NMS of MLLN is centrally managing all the elements of MLLN viz. Digital Cross

Connect, VMUX and NTUs. This NMS shall be built using the open architecture

_utilizing an industry standard commercially available operating system and relational

data base management system.

The Network Management System shall allow the Network operator to configure,

Provision, manage and monitor all aspects and parameters of the remote elements of the

MLLN without the need of local intervention. It is possible to manage the entire network

from any single location.

16.4.1 The NMS is able to perform the following:

• NMS auto recognize any change of configuration of any network element. The change

of configuration or other settings locally at NTUs shall not be provided. All local settings

on VMUX and DXC shall be password protected.

• Re-initialisation of the network element shall be possible from NMS. This shall be

equivalent to manual start-up (physical jack-out and jack-in) of the network element. This

might be required in case of a complete or partial 'network element' stoppage due to

hardware/software failures.

• NMS has the capability to configure the bandwidth on demand of any leased line for

specified time of the day. This bandwidth on demand is configurable to all possible

programmable bandwidths of NTUs.



• NMS has the capability to assign priority to the leased line at the time of configuration.

This allows the high priority customer lines to be routed first to the standby route, in case

of failure of the main route.

• The configuration of the various network elements like building, viewing, and changing

is possible remotely from the central NMS. The configurations of the network elements

are stored at some place in NMS from where it can be retrieved in case of failure.

• It supports macro command facility to carry out the same kind of operation on a group

of interface by a single command.

• The NMS is capable of placing the Network elements In or Out of service.

16.4.2 Route Management.

A predefined routing schedule is supported by NMS enabling the MLLN to route

automatically. It is possible to perform fast re-establishment of circuits within the

network across alternative paths totally automatically, in the event of failure. Point-to-

point and point-to- multipoint channel routings on an end-to-end basis.

16.4.3 Fault Management.

• It is able to inform the operator about the problems occurring in the network elements

and their modules.

• The fault events are logged in a fault log file and are accessible when required through

database style facilities for information retrieval.

• The fault information provided contains type of network element, the time at which

fault occurred, time when it corrected.

• In addition to the fault information, it provides a brief explanation of the cause of the

fault and proposed corrective action to be taken to rectify the fault.

• The printout of active faults and fault log file is possible.

• It is possible to list:



(i) total number of active faults in the network.

(ii) Number of active faults in a specified network element.

(iii) Number of active faults in each of the faulty network elements.

• The equipments of MLLN is capable of reporting to a pre-specified destination on

detection of an alarm condition. Faults in the network elements, links & system generate

audible alarms also. The activation / inhibition of the audible alarm is controlled by the

Network Manager.

16.4.4 Performance Management.

• It supports the end –to- end performance-monitoring functionality as per ITU-T

recommendation G.821 for links and circuits.

• The information provided includes Total time, Unavailable time, Errored seconds,

SeverelyErrored seconds and degraded minutes.

• It is possible to configure the interval when this performance data is to be collected by

the NMS

• It provides information about the percentage bandwidth usage of the network elements

like VMUX, DXC for a specified period. Performance management module supports

collection, processing & presentation of the performance related data from all the

Network elements. Facility is provided for collection of the network data continuously.

• All the VMUX and DXC must be polled at least once in 5 minutes at Primary NMS

level. All other network elements must be polled at least once in every 5 minutes at

Primary NMS level. It is possible to collect network data periodically; and for definite

interval of time, as required.

• These are configurable by the Network operator through NMS. Further it is possible to

configure collection of network data for specific or all network elements. The network

data for NMS includes following information from the Network elements.

A. Status.

B. Control parameters.

C. Performance parameters.



D. Alarm information.

E. Configuration parameters.

F. Accounting and billing information.

• Data base hard disk memory is sufficient to store all the information in para above and

any other necessary system information for at least one month duration. This information

is auto backed up (or backed up by operator action) to secondary memory devices (off

line storage devices) before deleting / overwriting any portion of this information, on

completion of one complete month. Minimum, of 16 Gb of configured secondary storage

space (secondary hard disk / cartridges / tapes etc) is supplied.

16.4.5 Security Management

• It supports the user identification and operator passwords with various privileges for

giving commands. It records all the login and logout operations done on the NMS. It is

able to set the time of expiry of the operator passwords. It supports password protection

for the for the network elements in the MLLN.

• Network Manager is able to create the operators' passwords. Network Manager is also

be able to control and limit operator's authorizations, rights and privileges. (Here

Network Manager is an account in NMS will full control, rights and privileges. Operator

created accounts by Network Manager for other personnel to help him in controlled way.)

• NMS allows changing of the password by the Network Manager for all accounts. NMS

allows Operator to change their own password. Change of password shall not required

system

• NMS provides for validation of source addresses of all the data that are coming from

the network elements. The data transport mechanism from network elements to NMS

centre has necessary in built facility for error checking and correction.

16.5 DIGITAL CROSS CONNECT (DXC or DACC).



DACC or DXC is a large capacity cross connect device and is installed at different main

sites for providing VMUX connectivity. DACC is made up of Cluster Master control

subrack and slave subracks. Single Subrack (RXS-S) is used as slave subrack and its

units depend on the port capacity ordered. In addition to multiplexing and demultiplexing

the signal, the node takes also care of crossconnecting the signal. (The signal is first

demultiplexed into a lower level after which it is cross-connected and then multiplexed

again). A digital corss-connect (DXC) is a device used in transmission networks. It

separates channels coming from other devices and rearranges them into new channels for

output. A digital cross-connection means that the connection is set up and released by the

network operator, but not through subscriber, which is the case in switching.

16.5.1 DXC NOMENCLAUTRE:

(a) DXCs at metros (Delhi, Mumbai, Kolkata & Chennai) for maintenance regions will

be designated as Regional DXCs (R-DXC).

(b) DXCs of maintenance regions apart from Regional DXCs as above will be called

subregional DXCs (SR-DXC).

(c) DXCs in the SSAs will be called SS-DXC.

The DXC comes in the following configurations.

• DXC-256 = 256 E1 ports.

• DXC-128 Expandable to 256 = Equipped with 128 Ports.



• DXC- 16 Expandable to 64

DXC SS-DXC TO SR-DXC :

The DXCs of the SSA will also be connected to the subregional DXC initially by 2 E1

for each SS-DXC, for the circuit going out of the city. Additional E1s to meet the demand



shall be connected to those SS-DXC under whose coverage area demand has grown, if

there are more than one SS-DXCs at a station.

SR-DXC to SR-DXC

Sub-Regional DXC to Sub-Regional DXC in the same region may initially be connected

by 1 E1 each.

REGIONAL NETWORK.

Multiple R-DXCs at the same station:R-DXC at metro stations consist of multiple DXCs.

Connectivity among these DXCs should be in mesh configuration of 2 E1s each to meet

the requirement of switching the time slots from a station connection at one DXC to the

destination connected on the other DXC.

Core Network of R-DXCs:

All four regional DXC stations will be connected to each other with 8E1s each. The links

may be distributed among multiple DXCs. The no. of links may increase as the demand

increases.

R-DXC to SR-DXC:

• DXCs are to be connected to SR-DXCs in the same region by 3E1s each.

• R-DXCs are to be connected to all SR-DXCs in the distant regions also by 2E1s each to

start with.

• SR-DXC links are to be distributed among multiple DXCs at the metro stations to

MIinimize use of inter-DXC links at that station. At the start up it will not be possible to

connect SR-DXC to all of such DXCs. It may be done as and when additional links are

justified in future.

R-DXCs to SS-DXCs:

SS-DXC may also be connected directly to Regional DXC if the bandwidth consumed by

the circuits from the SSA to concerned Regional is more than 8 Mb. The E1s may be



optimally distributed among DXCs at SS-DXC side as well as R-DXC side such that the

use of inter DXC connectivity at the same station is minimized.

16.5.2 REDUNDANCY REQUIREMENT

MLLN has to provide high reliability service and it is proposed to offer SLA for 99.5%

or better efficiency. Therefore, all the E1 links should be provided as rings wherever

available. In long distance network, E1, between same stations can be split into alternate

physical path of rings to the extent feasible. This will also save on port capacity required

for providing alternate path within MLLN.

16.6 VERSATILE MULTIPLEXER (VMUX)

Versatile Multiplexer (VMUS) is a small capacity cross connect device and is installed at

different sites for providing user connectivity. VMUX is made up of Basic Node, which

is the building block of the MLLN system. The VMUX is provided with two types of

interfaces to connect STU-160 ( SDSL product family used for point- to- point

connections) and CTU-S (HDSL product family modem , with line connection rate up to

4640 Kbit/s ) modems. The number of interfaces depends on the type of VMUX

configuration supplied. There are Four types of VMUXs supplied Viz. VMUX-Type I,

VMUX-Type-II, VMUX-Type-III/DC operation, VMUX-Type-III AC operation.

• The V-MUXs also have a digital cross connect capability and additional E1 ports have

been provided in the V-MUXs. Therefore inter-connectivity among V-MUXs in the same

city can be established using the spare E1 ports for extending local circuits.

• Initially one V-MUX should be connected to a maximum of 2 other V-MUXs in the

same city directly with one E1 each. As the demand for circuits in the areas served by V-

MUXs grows, more E1 links can be directly established among the V-MUXs.



• If there are more than one VMUXs in one exchange area, then depending upon

justification, one of the VMUXs can be dedicated to provide local circuits through direct

route to other VMUXs in the city. This will save DXC ports. However, SS-DXC

connectivity, where SS-DXC is available, shall also be maintained for setting up leased

circuits to VMUXs with which direct route is not available.

• Efforts should be made that no circuit should pass through more than three VMUXs.

However, use of more than four VMUXs in tandem for one circuit must be avoided.

• Routes shows as ‘standby’ are to be used for meeting incremental requirements of long

distance circuits from other V-MUXs if the direct routes are full and the other link has

spare capacity. This is done with the intention of saving port capacities. Protection path

can also be provided against failure of other links to SS/SR-DXC.

V-MUX to SS-DXC in the same City / SDCA.

• V-MUX to DXCs connectivity in the same city/SDCA will serve two purposes: first to

set up circuits to other V-MUXs in the city and second to set up circuits going out of the

city.

• Direct V-MUX to V-MUX connectivity should be utilized for local circuits as per the

plan indicated above. However, for local circuits to other V-MUX areas where the

requirement is, say, less than 10 in the beginning, the circuits can be routed via the E1

link established with the DXC.

• Each V-MUX site in the city should be connected by at least two E1s to the SS DXC.

This connectivity may be distributed in case of multiple SS-DXCs. Number of E1s can be

increased as the requirement grows.

• If there are more than one VMUXs in the same exchange area, DXC connectivity may

be distributed on each of them.



16.7 NETWORK TERMINATING UNITS (NTUs)

• Base band modems (Network Terminating Units = NTUs) are usually customer

premises equipment (CPE). They are typical “last mile equipment.”

• NTUs can also be used for standalone point-to-point connections without the NMS.

• NTUs allow use of the existing telecom copper cables (twisted pair) for digital traffic

with medium distances (~5 km) and high speeds.

• NTUs must be capable of being managed from the centralised NMS for the following

essential parameters:

(i) Speed

(ii) Line loop testing

(iii) Diagnostic

• NTU on the DTE side must support the V.35/V.24/V.28/V.36/ V.11/G.703 data

interfaces.

• NTU must be functionally compatible for all features with the integrated Line drivers of

the VMUX ports.

• NTU should work with the line side interface, which is a built-in feature of the VMUX

and shall support the end to end manageability with NMS of the Managed Leased Line

Network.

• NTU must perform internal self-tests on power-up and provide a visual indication if an

internal failure is detected.



• After power-up, the NTU configurations shall be automatically downloaded from the

connected node.



MLLN developed by M/s. Tellabs 8100

The services in the Tellabs 8100, managed by an access system can be divided into two

categories; business and mobile services. The Tellabs 8100 system provides network

elements for accesss, consolidation and backbone levels. The service can be provided

efficiently through Tellabs8100 customer Nodes and high speed NTUs (Network

Terminating Units). Each service and the entire network are controlled by the network

management system known as the Tellabs 8100 network manager. The network

management system also supports service provisioning, network optimization, planning

and service monitoring. The system offers features such as end to end circuit creation and

monitoring, circuit loop test and fault isolation , alternate re-routing of traffic in case of

trunk failure,software programmability of NTUs etc.. It also support enhanced features

such as Corporate internet access,point to point data, point to multipoint data, LAN-IC

hotline, EPABX interconnect, EPABX remote extension and ISDN line extension ,

Virtual private network etc.

Manageability

The concept of manageability is at present not a novelty, but rather a need. Today’s

leased line network is unmanaged. TRAI had advised the mandatory need of Service

Level Agreements (SLA), for every service being provided. This SLA is achieved with

statistics on an end to end status by MLLN. Today a degradation/disruption in service is

made known to the service provider on a subscriber notification. But in MLLN the

service provider can proactively detect and take corrective measures. In such an above

faulty status, MLLN feature of automatic re-routing of traffic ensures customer

satisfaction and also prevent a likely loss of revenue. Tomorrow, if the network customer

is to demand the service flexibility in SLA, the negotiable bandwidth during the different

time of the day, it can only be provided through MLLN.

DXC ( DACC ) – DIGITAL CROSS CONNECT

DXC is a large capacity cross connect device and is installed at different main sites for

providing VMUX connectivity. DXC is made up of Cluster Master control sub rack and



Slave sub racks. The Basic Node is used as Slave sub rack to build the Cluster Node in

the MLLN system. The DXC comes in the following configurations.

Configuration Master sub rack Fully equipped

Slave sub rack

Bare single sub

rack

DXC 32 Ports 1 1 0

DXC 64 Ports 1 2 0

DXC 64 Expandable to 128 Ports 1 2 2

DXC 96 Expandable to 128 Ports 1 3 1

DXC 128 Ports 1 4 0

DC 128 Expandable to 256 Ports 1 4 4

DXC 160 Ports 1 5 0

DXC 192 Ports 1 6 0

DXC 224 Ports 1 7 0

DXC 256 Ports 1 8 0

The block diagram of DXC 256 Ports is shown below:-

Power Requirement

DXC operates on –48 Volts DC Power supply.

Power requirement for Cluster Master = 10 Amp.

Power requirement for each Slave sub rack = 5 Amp Max.



Each sub rack power supply unit receives –48 Volts DC through individual MCB placed

at the top rear side of each rack.

The list of cards equipped in the Cluster Master rack is as shown.

Configuration

64 Ports 96 Ports 128 Ports

Unit

Expandable to Expandable toExpandable to 256 Ports

128 Ports 128 Ports 256 Ports

RXS-CD 1 1 1 1

PFU-A 2 2 2 2

PFU-B 2 2 2 2

CCU 1 1 1 1

CXU-M 2 2 2 2

CXU-S 2 2 2 2

CXU-A 4 6 8 16

The E1 Cables are connected from QMH / G.703 – 120Q units in the Slave sub racks and

terminated on the DDF

VMUX (Versatile Multiplexer )



VMUX is a small capacity cross connect device and is installed at different sites for

providing user connectivity. VMUX is made up of Basic Node, which is the building

block of the MLLN system. It is provided with different types of interfaces to connect

STU-160 and CTU-S modems. The number of interfaces depends upon the type of

VMUX configuration supplied. The different types of VMUXs are shown in the table

below.

The block diagram and power requirement of a VMUX rack is given below.

VMUX

Item

Type – I Type – II Type – III DC Type – III AC

RXS-S 1 1 1 1

XCG 1 1 1 1

PFU-A 1 1 1 0

PAU-10T 0 0 0 1

IUM-8 4 2 1 1



OMH 1 0 0 0

QMH / HCQ 0 1 1 1

QMH / G.703 2 0 0 0

N.B: The DXC and VMUX systems are installed in standard 19” coms rack with the

following dimensions.

Height: 2.048 m

Width: 0.596 m

Breadth: 0.325 m

DXC and VMUX equipments are designed to operate in a controlled environment. The

standards those are met by these equipments are as per ETSI 300019-1-3. The

environmental conditions that are required are:

1) Dust free clean environment.

2) A/c with temperature and humidity control.

3) A/c failure being exemptible for a maximum period of 2 hours at a time.

4) Operating temperature: 20 to 30C.

Network Terminating Unit (NTU)

The NTUs are located at customer premises and work on 230 Volt AC. Copper pair

connects the NTUs to the respective VMUX. The NTUs compatible with this network is

given below.

• 64 / 128 Kbps NTU with V.35 interface.

• 64 / 128 Kbps NTU with G.703 interface.

• 64 / 128 Kbps NTU with ether net interface.

• N * 64 Kbps NTU with V.35 interface.

• N * 64 Kbps NTU with G.703 interface.

• N * 64 Kbps NTU with Ethernet interface.








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Chapter 16, NEW TECHNOLOGY FAMILIARIZATION