An Introductory Handbook on IP MPLS Technology - RDSO

An Introductory Handbook on IP MPLS Technology

केवल कार्ाालर्ीन उपर्ोग हेतु For Official Use Only

भारत सरकार, रेल मंत्रालय GOVERNMENT OF INDIA, MINISTRY OF RAILWAYS

केमटेक/एस/प्रोज/2021-22/एसपी 37A नवम्बर 2021

CAMTECH/S/PROJ/2021-22/SP 37A November 2021

i

Foreword

Indian Railways is presently relying on legacy Synchronous Digital Hierarchy (SDH) network

to meet Railway backbone telecommunication requirements. However off late, lot of

applications like E-Office, IPAS, MMIS, FOIS etc. along with real time applications like

Charting, COIS, CCTV & IPIS etc. are being deployed to improve the system of working. All

the above applications require huge bandwidth for real time operation and monitoring. The

existing SDH setup is a traditional network which has the limitations such as requirement of

dedicated circuits for each site, wide spread outages in case of failure of head end terminal, low

bandwidth per site, poor scalability and costly etc.

Multiprotocol label switching (MPLS), also known as IP-MPLS is a routing mechanism within

a telecommunications network. Based upon the committee reports and RDSO’s comments and

recommendations, Railway Board has approved the Use of IP-MPLS technology/standards for

telecommunication backbone for Indian Railways.

CAMTECH has prepared this handbook, which covers Introduction and Overview of IP-MPLS

technology, System Architecture, Components & Implementation of IP-MPLS technology in

Indian Railways.

I hope that this handbook will be useful to S&T engineers and maintenance staff of Indian

Railways to get them acquainted with the IP-MPLS technology, MPLS Network & its

applications in Indian Railways.

I wish them all the success.

CAMTECH Gwalior Jitendra Singh

Principal Executive Director

ii

Preface

Indian Railways is using Synchronous Digital Hierarchy (SDH) Network for operational

communication (section control, traction power control, emergency control, block, LC Gate

control etc.), administration communication (VoIP exchanges etc.), data communication (UTN,

FOIS, SCADA, Wi-Fi etc.). The existing SDH setup is a traditional network which has various

limitations and hence Railways has decided to replace SDH network with IP-MPLS network.

Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications

networks that directs data from one node to the next based on short path labels rather than long

network addresses, thus avoiding complex lookups in a routing table and speeding traffic flows.

MPLS has features like efficient & dynamic bandwidth utilization, robust & high resiliency,

better network security feature and Quality of service.

CAMTECH has prepared this handbook with an objective to disseminate the information on

IP-MPLS technology, MPLS network & its applications in Indian Railways among S&T

engineers and maintenance staff of S&T department who deal with communication.

This handbook covers Introduction and Overview of IP-MPLS, Why IP MPLS required & SDH

Technology & Network, Disadvantages of SDH and IP MPLS technology, System architecture,

Implementation & Deployment of IP MPLS in Indian Railways and other important aspects.

We are sincerely thankful to Telecom Directorate/ RDSO/ Lucknow, Railtel Corporation India

Ltd. and M/s Team Engineers Pvt. Ltd. who have provided valuable inputs for preparing this

handbook. Since technological upgradation and learning is a continuous process, you may feel

the need for some addition/modification in this handbook. If so, please give your comments on

email_id: [email protected] or write at Director (S&T), CAMTECH, Indian Railways,

In front of Adityaz Hotel, Airport Road, Maharajpur, Gwalior (M.P.) - 474005. We welcome

all suggestions in this regard.

CAMTECH Gwalior Vijay Garg

Director (S&T)

https://en.wikipedia.org/wiki/Telecommunications_network

https://en.wikipedia.org/wiki/Telecommunications_network

https://en.wikipedia.org/wiki/Node_(networking)

https://en.wikipedia.org/wiki/Routing_table

mailto:[email protected]

iii

Table of Contents

Foreword ..................................................................................................................................... i

Preface ....................................................................................................................................... ii

Table of Contents ...................................................................................................................... iii

Abbreviations .............................................................................................................................. v

Disclaimer ................................................................................................................................ vii

1 Chapter ............................................................................................................................... 1

Introduction and Overview of IP MPLS Technology .............................................................. 1

1.1 Communication in Railways ................................................................................................ 1

1.2 Introduction to IP MPLS Technology ................................................................................ 2

2 Chapter ............................................................................................................................... 4

Why IP MPLS? .......................................................................................................................... 4

2.1 Existing Technology (SDH) .................................................................................................. 4

2.2 Circuit switching and packet switching .............................................................................. 5

2.3 Why IP MPLS? ..................................................................................................................... 5

2.4 What IP MPLS Offers? ........................................................................................................ 6

2.5 IP MPLS benefits .................................................................................................................. 6

3 Chapter ............................................................................................................................... 8

SDH Technology & Network .................................................................................................... 8

3.1 SDH - Overview .................................................................................................................... 8

3.2 SDH Network Architecture ................................................................................................. 9

3.3 Synchronous Transport Module (STM) ............................................................................. 9

3.4 Advantages of SDH ............................................................................................................. 12

3.5 Disadvantages of SDH ........................................................................................................ 13

4 Chapter ............................................................................................................................. 14

IP MPLS Technology .............................................................................................................. 14

4.1 IP MPLS Technology ......................................................................................................... 14

4.2 Evolution of MPLS Technology ........................................................................................ 15

4.3 Technology & Terminology ............................................................................................... 15

4.4 MPLS Operation ................................................................................................................ 17

iv

4.5 MPLS Services .................................................................................................................... 18

4.6 MPLS Application .............................................................................................................. 20

4.7 Advantages and disadvantages ......................................................................................... 20

Advantages ................................................................................................................................................... 20

Disadvantages ............................................................................................................................................... 21

5 Chapter ............................................................................................................................. 22

Implementation of IP MPLS Technology .............................................................................. 22

5.1 Option No.1: ........................................................................................................................ 23

5.2 Option No. 2: ....................................................................................................................... 24

5.3 Comparison Option 1 vs Option 2 ..................................................................................... 24

5.4 The Architecture and components .................................................................................... 25

5.5 Site Deployment of IP MPLS Technology ........................................................................ 27

References ................................................................................................................................ 36

CAMTECH Publications ......................................................................................................... 37

Our Objective ............................................................................................................................. 1

v

Abbreviations

ATM Asynchronous Transfer Mode

AU Administrative Unit

AUG Administrative Unit Group

BGP Border Gateway Protocol

CCITT International Telegraph and Telephone Consultative Committee

CS Circuit Switching

CWDM Carrier Wavelength Division Multiplexing

EMS Element Management System

FEC Forwarding Equivalence Class

IETF Internet Engineering Task Force

IP Internet Protocol

ITU(T) International Telecommunication Union,

L2 Layer 2

L3 Layer 3

LAN Local Area Network

LDP Label Distribution Protocol

LDP Label Distribution Protocol

LER Label Edge Router

LFIB Label Forward Information Base

LSC Label Switch Controller

LSC Label Switch Controller

LSP Label Switched Path

LSR Label Switch Router

MAN Metropolitan Area Network

MPLS Multi-Protocol Label Switching

MPLS TE MPLS Traffic Engineering

NMS Network Management System

NNI Network Node Interface

NOC Network Operation Centre

OFC Optical Fiber Cable

OSI Open Systems Interconnection

OSPF Open Shortest Path First

PDH Plesiochronous Digital Hierarchy

PDMUX Primary Digital Multiplexer

PRS Passenger Reservation System

PS Packet Switching

PSN Public Switched Network

https://en.wikipedia.org/wiki/European_Telecommunications_Standards_Institute

vi

QoS Quality of Service

RSVP Resource Reservation Protocol

SDH Synchronous Digital Hierarchy

SONET Synchronous Optical Network

STM Synchronous Transport Module

TDM Time Divisional Multiplexing

TU Tributary Unit

TUG Tributary Unit Group

UTS Unreserved Ticketing System

VC Virtual Container

VLAN Virtual Local Area Network

VoIP Voice over Internet Protocol

VPN Virtual Private Network

WAN Wide Area Network

WDM Wavelength Division Multiplexing

vii

Disclaimer

It is clarified that the information given in this handbook does not

supersede any existing provisions laid down in the IR Telecom

Engineering Manual, Railway Board and RDSO publications. This

document is not statuary and instructions given are for the purpose

of learning only. The diagrams and figures given in the handbook are

indicative only. If at any point contradiction is observed, then Signal

Engineering Manual, Telecom Engineering Manual, Railway

Board/RDSO guidelines may be referred or prevalent Zonal Railways

instructions may be followed.

viii

Issue of correction slips

The correction slips to be issued in future for this report will be numbered as follows:

CAMTECH/S/PROJ/2021-22/SP37A XX date .......

Where “XX” is the serial number of the concerned correction slip (starting from 01

onwards).

CORRECTION SLIPS ISSUED

Sr. No. of

Correction

Slip

Date of issue Page no. and Item

No. modified

Remarks

CAMTECH/S/PROJ/2021-22/SP37A 1

An Introductory handbook on IP-MPLS Technology November 2021

1 Chapter

Introduction and Overview of IP MPLS Technology

1.1 Communication in Railways

A. Operational Communication

These circuits are provided for safe and punctual operation of trains.

Section Control

Traction Power control

Traction Loco Control

Emergency Communication

Block Communication

LC Gate communication

BPAC

Data Logger

Driver/Guard to Station

B. Administrative Communication

Exchanges (Existing & Future Inter-connectivity) Railway telephony network

that spans across all the zones and divisions.

Many of these exchanges are already VoIP exchanges and many are being

replaced by the VoIP exchanges.

Remote subscribers at various stations are connected using Primary Drop-Insert

(PD) Muxes which in turn are networked through SDH equipment.

B. Data Communication

Unified Ticketing Network (UTN)

Freight Operation Information System Network (FOIS)

RC/SCADA

Video Surveillance/CCTV

Railnet

Railway Display Network

Wi-Fi Service



These services have the requirement from bandwidth intensive, latency sensitive, real-time

application (CCTV, VSS, WIFI, etc.) to low bandwidth, latency tolerant applications (E-

Tender, E-Office, Email, etc.).

1.2 Introduction to IP MPLS Technology

Multi-Protocol Label Switching (MPLS) is a packet forwarding Technology used on network

Router and Switches allow for the virtualization of routing and forwarding table. MPLS

provides a Layer 2 transport method (SDH/SONET, Ethernet and TDM (E1/T1) etc.) for various

protocol over packet switching network (PSN) i.e., it can be said that MPLS-TP operates

between Layer 2 and Layer 3 in the OSI model → thus is often referred as” LAYER 2.5

Protocol” & IP – MPLS operates at Layer 2 & Layer 3.

MPLS uses the concept of label switching to forward the traffic based on the labels as opposed

to the network addresses. There are many different features available under the MPLS umbrella

to carry forward the real time applications. MPLS overcomes many limitations of the traditional

networks by allowing the shared hardware to be used by multiple independent clients. MPLS

was the next evolution of networking after hub and spoke technology. MPLS has two main

components which takes care of all functions of the MPLS connectivity. Label Switching

Router (LSR) is the core router in the MPLS cloud which only does switching in the Label

switching path (LSP- essentially a unidirectional tunnel between the pair of routers, routed

across the MPLS cloud) and Label Edge router (LER) which first encapsulate the packets inside

the MPLS LSP and also make the initial path selection.

Figure 1: OSI Model for MPLS



Figure 2: Network Components for MPLS

MPLS delivers IP and Internet Services enabling the core and edge network to act much like a

TDM transport network but with a greater level of efficiency. Due to increased bandwidth

capacity requirement for applications like CCTV, WIFI, Mobile Video, VOIP, Auto signaling,

CTC, e-Office, IPAS, AIMS, ETCS – Level 2, IRATP, LTE etc., MPLS offers optimum

bandwidth when compared with circuit switching methods.

By employing MPLS pseudo-wire, which is an encapsulation solution that can support native

TDM and packet traffic in the aggregation and access network it is possible to converge

backhaul traffic without compromising services. Optimizing the use of network capacity is

achieved by more granular increments of 10MB, 100MB, 1GE, 10GE, 40 GE or even 100 GE.

MPLS has evolved into a mature and rich set of features available on network infrastructure.

MPLS is used to transport Ethernet frames over a provider’s backbone network with pseudo-

wire (PWE) acting as an emulated point to point connection over a packet switch networking

providing the interconnection to two nodes. An important feature of pseudo-wire technology is

that the service - specific functions are locations only on the edge of the background networking

while only MPLS label switched paths LSPs are established in the core. Increases the stability

of the services and reduces the complexity of the core routers.



2 Chapter

Why IP MPLS?

2.1 Existing Technology (SDH)

Railways has adopted SDH technology on OFC for it short haul (managed by Railways)

and long haul communication (managed by RailTel) requirements.

STM-1 equipment is provided at all the stations with:

i) Drop/Insert E1 circuits for PD Mux, WAN interfaces for UTN/FOIS networks.

ii) Fast Ethernet (IEEE 10 BASE-T) circuits to cater to Ethernet end users e.g.

DSLAMs to extend Railnet at remote stations.

Control comm., TPC, TLC etc. are derived from dropped E1s.

At every station auto phone of the divisional exchange is also provided.

The bandwidth requirement in the future for various applications are tabulated below.

S.

No.

Application Bandwidth at

Major Stn. Jn. Station Wayside Stn.

1 UTN 10 Mbps 2 Mbps 2 Mbps

2 FOIS 10Mbps 2 Mbps 2 Mbps

3 RC/SCADA 10 Mbps 2 Mbps 2 Mbps

4 Surveillance 600 Mbps 500 Mbps 200 Mbps

5 Railnet 100 Mbps 50 Mbps 20 Mbps

6 RDN 500 Mbps 200 Mbps 100 Mbps

7 WiFi at Station 300 Mbps 300 Mbps 100 Mbps

8 Approx. Req. 2 Gbps 1 Gbps 512 Mbps



2.2 Circuit switching and packet switching

Since the invention of the telephone, circuit switching has been the dominant technology

for voice communications.

Since 1970, packet switching has evolved substantially for digital data communications.

It was designed to provide a more efficient facility than circuit switching.

Circuit switching

A dedicated path needs to be established before data transfer

designed for continuous communication like voice service

channel capacity is dedicated for the whole duration of connection. If no data, capacity

is wasted

Inflexible as data packets are sent along the same paths

Packet switching

Does not require dedicated path thus lesser delay

Data are transmitted in short packets hence better utilization of channel.

Each packet contains a portion of user data plus some control info like error

detection/correction etc.

Flexible as data packets are routed dynamically

2.3 Why IP MPLS?

IPMPLS has a great advantage in any-to-any connectivity environment presently an essential

requirement for Indian Railways for communication needs modernization. IPMPLS has a clean

& homogenous separation of control plane, Management plane and date plane operations

throughout the network.

Attribute IP MPLS

Service Support Full

Maturity Proven with 10+ years of deployment in

broadband application / Banking / BSNL

(other service providers)

Standardization Fully Standardized



Attribute IP MPLS

Services Richness L2, L3 VPNs, P2P, P2MP, MP2MP, IP

Multicast

VPNs

Multi-Vendor Interoperability Optimized & Efficient

Protection & Restoration Both

Traffic Engineering Dynamic

Convergence Common NMS, Training & Sparing for

L2/L3

OAM Single platform for L2 & L3

Operational Challenges Lower because L2 & L3 services e2e

supported on same platform / Solution

QoS capabilities for broadband applications High with 1000s of hardware queues per port

support

2.4 What IP MPLS Offers?

1. Efficient and Dynamic Bandwidth utilization

2. Optimizes Network capacity by granular increments of 10MB,100MB,1GE

3. Better Network security features.

4. Robust and high resiliency

5. Deterministic QoS

6. Improves packet performance and controls traffic

7. Support any to any type of connectivity

8. Support both legacy TDM and packet Traffic: CWDM Plane built in

2.5 IP MPLS benefits

1) Elimination of redundancies: MPLS eliminate the need of multiple costly desperate

networks and long lead time turn up-activities.

2) Improved efficiency

a) Pool resources for efficient bandwidth and network hardware



b) Provides ability to activate, modify and decommissioning will be faster

c) Application can operate at maximum capacity without affecting functioning of

other applications

d) Reduced cost: MPLS eliminate many dedicated router and WAN circuits.

3) Improved scalability: The traditional network is unable to respond quickly to meet the

demand of new applications and services. MPLS allows the networks to grow, change

and reduce without purchasing a new hardware and additional WAN circuits.

4) Improved reliability: MPLS network has new features which make the network more

reliable as compared to the traditional network by the way of redundant route, bandwidth

utilization and scalable etc.

5) Core MPLS - IP network will also allow in future to integrate with SDN devices at the

access devices providing further robustness / flexibility and ease of access for

connectivity or to applications in the cloud and also reduce the cost of access devices.



3 Chapter

SDH Technology & Network

3.1 SDH - Overview

The goal of worldwide telecommunication is free exchange of information throughout the

global community. North America, Europe, Japan and India all have different

communication standards and hierarchies. Digital networks of these nations cannot be

freely connected. The technology of these nations competes with each other and remains

incompatible. This not only obstructs telecommunications from one country to the other

but also slows down the development.

On a little closer look at the long-distance network, it is evident that the present system

of independent point to point transmission needs adequate network management

capabilities and On-Line Control of network configuration, so that the transport layer is

strengthened to match the future requirements of the customers as well as operators.

The solution perhaps, lies in the concept of Synchronous Digital Hierarchy (SDH), which

can be termed as transport backbone of the broadband era. The Network Node Interface

(NNI) operating in Synchronous Digital Hierarchy (SDH) recommended by ITU (T) /

CCIR offers a clear solution and sets an international standard for high-speed digital

transmission.

Current public telecommunication networks are based on the long established ITU (T)

Plesiochronous Digital Hierarchy (PDH) of transmission which is not well suited to

support the advanced signal processing and control techniques now possible and

increasingly demanded by the telecom. The SDH is designed to overcome the limitations

of PDH.

ITU (T) adopted SDH in 1988. The original version was known as SONET (Synchronous

Optical Network) that was in use in North America 2 or 3 years prior to ITU (T) adopted

it and changed the name as SDH. SDH (Synchronous Digital Hierarchy) is a standard for

telecommunications transport formulated by the International Telecommunication Union

(ITU) previously called the International Telegraph and Telephone Consultative

Committee (CCITT).



SDH was first introduced into the telecommunications network in 1992 and has been

deployed at rapid rates since then. It is deployed at all levels of the network

infrastructure,

including the access network and the long-distance trunk network. It is based on

overlaying a synchronous multiplexed signal onto a light stream transmitted over fiber-

optic cable.

SDH is also defined for use on radio relay links, satellite links, and at electrical interfaces

between equipment. The comprehensive SDH standard is expected to provide the transport

infrastructure for worldwide telecommunications for at least the next two or three decades.

3.2 SDH Network Architecture

3.3 Synchronous Transport Module (STM)

An STM is the information structure. It consists of information payload and overhead

bits in block frame structure, which repeats at every 125 microseconds. The information

Figure 3: SDH network Architecture



is suitably conditioned for serial transmission on the selected media at a rate, which is

synchronized to the network.

STM followed by an integer, which indicates the level of SDH.

STM 1 is the first level of SDH bit rates.

Higher SDH bit rates are obtained as integer multiples.

Higher rate levels are denoted by the corresponding multiplication fraction of the

first level. STM 1 with 155.520 Mbps is the basic rate. STM 4 indicates that it contains

4 STM 1s’ and each STM 1 is independent in all respects. Similarly, STM 16 means 16

No’s of STM 1s and STM 64 is 64 No’s of STM 1s.

SDH Multiplexing Structure: As per ITU (T)’s recommendation G.709 (Fig 2.1) the

inputs to SDH system are PDH bit streams. ITU (T) has standardized E1, E3, E4 of E

hierarchy and T1, T2 and T3 of T hierarchy as inputs into SDH. The block diagram of

SDH multiplexing structure shown in figure 2.1, shows the making of STM1 or STM N

where N indicates the integer of the SDH level.

Figure 4: SDH multiplexing structure



Container(C): The first entry point of the PDH signal. It is the basic packing unit for

tributary channels, is filled with the information from a Plesiochronous signal. The process

is called as mapping. Justification facilities are provided to adapt Plesiochronous tributaries

to the synchronous network clock. Each container is suitable for the rate of the signal

inputted into it and for the structure of the synchronous frame. Fixed stuffing bits are

inserted for synchronous tributaries. Signal is prepared so as to enter into the next stage i.e.

virtual container. Containers are Basic Containers and Higher Order Containers. As per

recommendation G.709, C-11, C-12, C-2, C-3 & C-4 are the containers for PDH bit rates

of 1.544 mbps, 2.048 mbps, 6.312 mbps,34 mbps or 45 mbps and 140 mbps respectively.

Virtual Container (VC=C+POH): Each container is added with control information

known as Path Over Head (POH), which helps the service provider to achieve end-to-end

path monitoring. The container and the path overhead are together called as Virtual

Container (VC). The POH is 1 column X 9 rows. In Virtual Container the POH fields are

organized in a block frame structure either in 125 microseconds or in 500 microseconds.

Two types of virtual containers have been identified

» Basic virtual containers: VC11, VC12.

» Higher order virtual containers: VC3, VC4

Tributary unit (TU = VC + Pointer): This unit is an information structure, which provides

adaptation between the lower order path layer and the higher order path layer. It consists of

information payload of virtual container and the tributary unit pointer. TU-2 for VC-2,

TU-3 for VC-3 etc.

Tributary unit group (TUG): One or more tributary units are grouped or multiplexed by

byte interleaving to form higher bit stream rate as part of multiplexing structure. TUG-

2 is a group of 3 TU-12s or 4 TU11s or 1 TU2. TUG-3 consists of homogenous assembly

of TUG-2s or TU- 3, either seven TUG-2s or one TU-3.

Pointer: It is an indicator whose value defines frame offset of a virtual container with

reference to the frame reference of transport entity on which it is supported. It indicates the

phase alignment of the virtual containers (VC-n) with respect to the POH of the next



higher-level VC in which it resides. The tributary Unit Pointer location is fixed with

respect to this higher level POH.

Administrative Unit: It is the information structure, which provides adaptation between

higher order path layer and the multiplex section layer. It consists of information payload

and AU pointer, which indicates the offset of the payload frame start relating to the

multiplex section frame start. AU location is fixed with respect to STM-frame.

Administrative Group Unit: It consists of a homogenous assembly of AU-3s or AU-

Network Node Interface (NNI): It is the interface at a network node, which is used to

interconnect another network node. The NNI is the most important interface. This

interface is defined in ITU (T)’s Rec.G.708 and allows interconnection of network

components (e.g., network nodes and multiplex systems) via cable or radio links.

Multiplexing Principles of SDH: 1.5 mbps, 2.048 mbps, 6.312 mbps enter their

respective containers C-11, C-12 & C-2. These signals are prepared and inserted into their

respective VCs and to the tributary unit pointers. TUG-2 can be either four C-11s with

TU-11 or three VC-12s with TU-12 or one VC-2 with TU-2. The C-3 container input

may be 34 mbps or 44.7 mbps. VC-3 container with AU-3 can directly go to AUG and

enter STM frame. Similarly, seven TUG-2s can be mapped into one TUG-3; otherwise

one VC-3 with one TU-3 can be mapped into one TUG-3. Three TUG-3s can be

mapped into VC-4. VC-4 with AU-4 go to AUG and then to STM frame. 3 AU-3s also

can go to AUG and then to STM frame.

3.4 Advantages of SDH

• Network Simplification: Orders of MUX - DEMUX is not required. The direct

extraction of tributary reduces equipment cost and power consumption &

increases reliability.

• Network Management System: NMS is fully software controllable because of

the provision of sufficient number of bits in the SDH frame structure. The

functions are like performance monitoring, configuration management, network

security etc.

• Survivability: Using self-healing ring architecture, the Network will be



automatically reconfigured and traffic instantly re-routed in case of a fault over a

section. This facilitates the repair of faulty section.

• Bandwidth on demand: It is possible to allocate bandwidth on demand to users

anywhere in the network at a short notice can be done by NMS.

• Future proof networking: SDH is an ideal platform for services ranging from

telephone service to ISDN, from mobile radio to WAN etc.

• Standardization: SDH is highly standardized system with regards to optical

interface, frame format etc. The standardization of equipment interfaces enables

the use of multi-vendor end equipment’s.

3.5 Disadvantages of SDH

• Lower bandwidth utilization: It offers lower bandwidth utilization ratio compare

to PDH due to many OH bytes used for OAM.

• Complexity: Direct adding/dropping of lower-rate signal is achieved using

pointers. This increases complexity of the system.

• Vulnerability: Software is used largely in SDH system. Hence it is vulnerable to

computer viruses.

• Complexity: It requires complicated SDH equipment due to variety of

management traffic types and options.

• It cannot carry E2 due to unavailability of container.



4 Chapter

IP MPLS Technology

4.1 IP MPLS Technology

Multiprotocol label switching (MPLS) also known as IP-MPLS (IP- MPLS is one type of

MPLS which primarily uses IP-routers) is a routing mechanism within a telecommunications

network. The routers direct data from one node to another based on the short path labels

instead of the relatively longer network addresses. It avoids the need for complex lookups in

the routing table, so communications tend to be faster. Since it also encapsulates the protocols

of the individual streams which are diverse, into the packets with its own protocol, it is called

the “multiprotocol” routing technique.

MPLS is an “Internet Engineering Task Force” (IETF) specified framework that provides

efficient forwarding, routing and switching of traffic flow through the network. MPLS belongs

to the family of packet switching networks and was designed to overcome the limitations of

IP based forwarding for VPN. In a traditional IP network each router performs an IP lookup,

determines the next hop based on its routing table and forwards the packet to the next hop

thereby creating a lot of overhead at each routers interface. However, MPLS on the other hand

makes packet forwarding decisions which are based entirely on the label of the packet without

the need to examine the packet itself.

MPLS works in between OSI data link layer and network layer and is summarized as Layer 2.5

networking protocol. MPLS is an innovative approach that uses a label based forwarding model.

Out of the three major technologies viz. IP-MPLS, MPLS-TP and Carrier Ethernet, IP-MPLS

has been chosen as the choice of future transport technology for Indian Railways. The basic

advantage of IP- MPLS is its support for L2 and L3 services that is essential for Railways.

Besides this, it also services the requirement of core, aggregation and access network

and can work on a common NMS for OAM (Operations, Administration and

Management/Maintenance) of all the three parts of a Network. The advantage of IP-MPLS is

that it supports IP routing as well as network-oriented connections. The forwarding is done

through hardware with the introduction of MPLS and hence is much faster than normal routing.



The paths are unidirectional and the forward and return paths are usually different. For serving

the requirement of Transport, congruent bidirectional paths can be defined. SD-WAN (software-

defined networking in a wide area network) with IP-MPLS simplifies the management and

operation of a WAN by decoupling the networking hardware from its control mechanism.

4.2 Evolution of MPLS Technology

Evolved from tag switching in 1996 to full IETF standard, covering over 130 RFCs

Key application initially were Layer-3 VPNs, followed by Traffic Engineering (TE),

and Layer-2 VPNs

Figure 5: Evolution of MPLS Technology

4.3 Technology & Terminology

MPLS is not associated with any specific technology, rather it is an overlay technique that

aims to improve performance and efficiency. When a packet enters the MPLS network, a

forwarding equivalence class (FEC) value is assigned to it by adding a small label to the

packet. Every router within the network knows how to handle different FEC labels, so there

is no need to do a header analysis each time. Instead, every router uses the label as an index

to identify a new FEC for that packet. MPLS creates a predetermined path to route traffic in

the most efficient way possible based on the FEC label. This mechanism gives routers the

option to choose low-latency routes for certain applications like live video streaming so it is

delivered faster to the destination when compared to the traditional routing mechanism.



Label: The label is a part of MPLS header. It is placed between the data-link and IP headers.

It identifies the path a packet should traverse. The MPLS header is composed of 32 bits out

of which 20 bits are allocated to the label also called label stack, 3-bits are experimental

bits often used for specifying class of service. One bit is reserved for the bottom of the

stack bit and is set if no label follows. 8-bits are used for time-to-live (TTL) used in the

same way like IP headers.

Label Forwarding Information Base: A table is created by a label switch-capable device

that indicates where and how to forward frames with specific label values.

Figure 6: MPLS Header

Label Switched Path (LSP): It is a unidirectional tunnel between a pair of routers routed

across MPLS network.

Label Edge Router/Ingress router (LER): It is a router that first encapsulates the packet

inside an MPLS LSP and also makes initial path selection.

Label Switched Router (LSR): A router which only does MPLS switching in the middle of

an LSP.

Egress Router: The final router at the end of LSP which removes the label.

Label switched: When an LSR makes forwarding decisions based upon the presence of a

label in the frame.

Label Switch Controller (LSC): An LSR that communicates with an ATM switch to

provide and provision label information within the switch.

Label Distribution Protocol (LDP): It is one of the primary signaling protocols for

distributing labels in MPLS network. It is a set of procedures and messages by which Label

Switched Routers (LSR) establish Label Switched Path (LSP) through a network by mapping

network layer routing information directly to data link layer switched paths. By Label

Distribution Protocol, LSR can collect, distribute and release label binding information to



other LSRs in the MPLS network thus enabling hop-by-hop delivery of packets in the

network along routed paths.

Forwarding Equivalence Class (FEC): It is a group of IP packets that are forwarded. Packets

within an FEC are equivalent in terms of forwarding, such as same destination, same path and

same class of service. A LSP is assigned to each FEC that is defined using IP interior routing

protocols.

Figure 7: MPLS network

4.4 MPLS Operation

MPLS relies on two principal components i.e., Control Plane and Data Plane.

Control Plane: Essential to MPLS is the notion of binding between a label and network layer

routes. The control plane is responsible for the routing information exchange and label

distribution between adjacent devices. It uses standard dynamic routing protocols, such

OSPF routing, IS-IS and BGP, to exchange information with other routers to build IP

forwarding table or label forwarding information base. The control component creates label

bindings and then distributes the label- binding information among LSRs using a Label

Distribution Protocol (LDP).

Data Plane: The data plane is responsible for forwarding packets according to the destination

IP address or label using Label Forward Information Base (LFIB) managed by the control

plane. The Data plane is a simple label based forwarding engine i.e., independent of the type



of routing protocol or label distribution protocol running on the control plane.The network

automatically builds routing tables as MPLS capable routers participate in interior gateway

protocols (OSPF, IS-IS) throughout the network.

Label distribution protocol (LDP) establishes label to destination network mappings. Label

distribution protocol (LDP) uses the routing topology in the tables to establish label values

between the adjacent devices. This operation creates Label Switching Paths (LSP) pre-

configured maps between destination end points. A packet enters the ingress edge label

switching router (LSR) where it is processed to determine which layer-3 service it requires,

such as quality of service (QoS) and bandwidth management. The edge LSR selects and

applies a label to the packet header and forwards it.

The LSR reads the label on each packet, replaces it with a new one as listed in the table and

forwards the packet. The Egress Edge Router strips the label, reads the packet header and

forwards it to its final destination.

4.5 MPLS Services

MPLS Traffic Engineering (MPLS-TE): Traffic Engineering is the process of routing data

traffic in order to balance the traffic load on various links, routers and switches in the network.

It has the ability to control specific routes across a network to reduce congestion and improves

the cost of efficiency of carrying IP Traffic. MPLS is capable of full traffic engineering.

In MPLS TE, a Label Switched Path (LSP) is established for carrying traffic along an explicit

traffic-engineered path, which can be different from the normal destination-based routing

path. IP networks typically have multiple pathways that traffic can take to reach its

destination. Relying solely on routing protocols such as Open Shortest Path First (OSPF) some

of the paths may become congested while others are under-utilized.

MPLS can specify an explicit route for certain traffic flows such as Voice over IP (VoIP)

to take less optimal but less congested routes and avoid packet loss while maintaining very

high link utilization.

MPLS and Quality of Service (QoS): Some types of traffic, such as video, place specific

demands on a network for successful transmission. QoS in an IP network gives devices the

intelligence to preferentially handle traffic as dictated by each subscriber’s network policy.

QoS is defined as those mechanisms that give network managers the ability to control the



mix of bandwidth, delay, jitter and packet loss in the network.

At the ingress of the MPLS network, Internet Protocol (IP) precedence information can be

copied as Class of Service (CoS) bits or can be mapped to set the appropriate MPLS CoS

value in the MPLS label. This is the distinction between IP QoS that is based on IP precedence

field in the IP header and MPLS QoS that is based on the CoS bits in the MPLS label.

MPLS CoS information is used to provide differentiated services and MPLS CoS enables end-

to-end IP QoS across the network.

MPLS VPNs: Virtual Private Networks (VPNs) are a method of interconnecting multiple

sites belonging to a customer using a Service Provider (SP) backbone network in place of

dedicated leased lines. each customer site is directly connected to the SP backbone. The SP

can offer a VPN service more economically than dedicated private WANs built by each

individual customer because the SP can share the same backbone network resources

(bandwidth, redundant links) between many customers.

The customer also gains by outsourcing the complex task of planning; provisioning and

managing a geographically distributed network to the SP.

MPLS-enabled IP VPNs are connectionless IP networks with the same privacy as frame relay

and multiple IP service classes to enforce business-based policies.

MPLS-based VPNs make operations much more efficient than the traditional overlay VPN

solutions which requires tunnelling or encryption deployed over a frame relay, ATM or IP

network. This mesh solution is built point-to-point, requiring separate configuration of each

tunnel or Virtual Circuit (VC). Moreover, since traffic is tunnelled or overlaid, the circuit does

not know which kind of traffic it carries. By contrast if the customer traffic can be classified

by application type, such as voice, mission-critical applications or e-mail, the network can

easily assign traffic to the appropriate VPN, without configuring complex , point-to-point

meshes.

Compared to a VPN overlay solution, an MPLS-enabled VPN network can separate traffic

and provide privacy without tunnelling or encryption. Using labels, MPLS enabled networks

provide privacy on a network-by-network basis much as frame relay provides it on a

connection-by-connection basis.

The frame relay VPN offers transport while MPLS-enabled network supports services. MPLS

is the technology that brings VPN awareness to switched or routed networks.

It enables quick and cost-effective deployment of VPNs of all sizes- over the same



infrastructure. MPLS provides a flexible and elegant VPN solution based on the use of LSP

tunnels to encapsulate VPN data.

4.6 MPLS Application

4.7 Advantages and disadvantages

Advantages

In order to upgrade the existing telecom infrastructure, MPLS can be an excellent option.

It can help with enhanced flexibility, more bandwidth, and better performance.

Scalable: MPLS provides a highly scalable mechanism. It ensures high-performance

telecommunication networks. Networks can easily be engineered and maintained for

bandwidth optimization.

Inter-Connectivity Growth: MPLS allows growth of the inter- connectivity of the network

by using the minimal addition of hardware.

Common applications: MPLS can be used for interconnecting data centres with branch



offices and branches at other locations.

Remote connections: MPLS allows adding new remote connections without using any

additional hardware system at the primary site. Being fully cloud-based, it doesn’t require the

point-to-point connectivity.

WAN routing: With the MPLS link, WAN routing is left to the service provider and employs

fewer staff for WAN.

Quality of service: MPLS comes with the quality of service (QoS) options, which empowers

to treat latency-sensitive traffic like VoIP etc.

WAN protocol: MPLS is the perfect mode to manage any-to-any connectivity, including

video and voice.

Service level agreements: MPLS services are deliverable SLAs (service-level agreements).

These SLAs include delivery guarantees unlike consumer broadband, etc.

Enhanced bandwidth: The technology allows accessing multiple traffic types.

Improved up-time: MPLS allows having an alternative network, thus improves up-time.

Lower congestion: With MPLS, there is an option to use alternative paths and avoid high

traffic congestion, thus reduced network congestion.

Disadvantages

Lack of Total Control: The service provider has to configure the overall networks. And

we will need to work along with service provider in routing MPLS traffic while using

dynamic routing. MPLS does not allow having total control of the network.

Expensive: Since MPLS is an advanced way of networking, it can cost more than the

Ethernet. However, the cost is less than T1 lines.



5 Chapter

Implementation of IP MPLS Technology

At present the following Time Divisional Multiplexing (TDM) circuit switching

communications are being extended through SDH & PDH network:

Data based circuits like PRS / UTS / FOIS /COIS / Crew Management / Data logger

connectivity / Predictive analysis etc.

Voice based circuits like Control Communication, Block communication directly

related to train operations.

Emergency Communication for disaster management.

Last mile Railway telephone communication, Auto phones, Hot line etc.

LC communication through separate Quad.

PBAX Connectivity interlinking on PRI port (NON {IP) or IP (Ethernet).

Circuits for Auto Signaling (EI/BPAC / SSBPAC / UFSBI) etc.,

RAILNET, various internal applications like IPAS/ e- office / SPARROW / Internet etc.

Wi-Fi to Stations (GPON) & Rly Quarters

SCADA Connectivity, Surveillance, TMS / Train Indicative System.

Magneto Phone connectivity in LC gates and Yard, EC / SPT / Selective call phones

etc.,

Any other data applications

Further, bandwidth requirements are ever increasing and the network should handle the safe

signalling data without loss of integrity at higher data speeds. The network should cater the

following IP based data networks

VOIP communication

High speed data applications like CCTV, Wi-Fi and Railnet/Internet etc.,

The future signaling applications like CTC/TMS, ETCS/TCAS (IRATP) etc.,

If SDH/PDH equipment's are replaced with new IP-MPLS switches, the above legacy

communication circuits functioning cannot be transferred directly. Also, Railway Board has

given directives that, the telecom backbone of all future works/replacement of Data networks

such as PRS/UTS/FOIS/SCADA shall be with IP-MPLS equipment's, by providing VPN



network. In this scenario, there shall be following options to achieve IP MPLS based

communication network for these legacy TDM based voice/data communications. Since it will

not possible to introduce the new system immediately considering various type of real time

application prevailing at present in the field at Divisional Head Quarters, Stations and LC

Gates/SSP/SP etc. There are 2 options available in the proposal as briefed below

5.1 Option No.1:

Provide the modular and scalable IP MPLS routers with Ethernet, E1 ports and replace the

existing TDM based end/interfacing communication equipment with IP based equipment's. i.e.

it involves replacing of existing ISDN exchange with IP based exchange, provision of IP based

control communication equipment's, replacing serial communication interfacing equipment's of

SCADA system and existing LC gate communication Equipment’s with IP based end

equipment’s. The above proposal requires complete change of ISDN Exchanges into IP

exchanges, voice Control circuits into VOIP circuits and similarly other relevant circuits etc.

Since it will take some more time, this option is NOT taken up immediately. Hence the existing

SDH equipment and PD-Mux equipment will be retained as it is and the core network will be

IPMPLS circuit. All the existing data circuits from SDH equipment will be shifted into IP-

MPLS circuits.

Figure 8: Integrating IPMPLS & SDH (Gracefully): Option I



5.2 Option No. 2:

Provide the Modular and scalable IP MPLS Router with Ethernet, E1, CWDM ports to transfer

the SDH network to Router Based network and continue with PDH equipment for legacy

communication network, till the replacement of end equipment with IP based equipment’s. In

addition, a modular and scalable IP MPLS Service Aggregator Routers which is not available

on the shelves and to be developed by the vendors which caters Ethernet, E1, Subscriber

(FXS/FXO), E&M modules at all stations and small-scale routers/ integrated hybrid

equipment's at LC gates/IBS/SP/SSPs etc., for migration. Hence option 2 has been identified

for implementation and also it complies to the Railway Board guide lines vide Railway Board

vide letter No.2011/Tele/9(2)/1 ated.25.02.2020 has issued following policy guidelines for

provision of \IP-MPLS technology for Unified Communication Backbone on Indian Railways"

Figure 9: Option by taking additional optical fiber: Option II

5.3 Comparison Option 1 vs Option 2

Option 1

NO additional optical fiber is needed

Seamless integration of STM / PDMUX &

IPMPLS – We can go section wise migration

Scalable bandwidth which can be used as network and need grows



Being a backbone network it is very essential that a device which is scalable is

provided

Multiple options available on down link (copper, Single fiber, Dual Fiber), & uplink

(Scalable: 10G, 25G, 100G, WDM)

Option 2

Additional optical fiber is required – which might be a challenge

Additional optical fiber additional cost to be factored

Parallel network might look very realistic but issues such as:

Bandwidth scalability will be challenge

Higher bandwidth initially might put strain on the costing

5.4 The Architecture and components

The MPLS backbone will support the bandwidth from 10Mb to 6.8 Tb/s on 10 slot equipment.

Considering the bandwidth requirement, scalability and funds availability it is proposed to go

for 120Gbps full duplex i.e. 240Gb backbone loaded with 120Gb cards so at to meet the present

and future requirements. The way stations will be catered with 10Gb bandwidth which can be

integrated with present SDH equipment. The required details as below. The MPLS backbone

will support the bandwidth from 10Mb to 6.8 Tb/s on 10 slot equipment. Considering the

bandwidth requirement, scalability and funds availability it is proposed to go for 240Gb

backbone loaded with 80Gb cards so at to meet the present and future requirements. The way

stations will be catered with 10Gb bandwidth which can be integrated with present SDH

equipment. The required details as below.

1. For Way station: Supply of rack mountable modular aggregator router for wayside station

with minimum switching speed of 120 Gbps full duplex i.e., 240Gbps, unit to supports

L2VPN / L3 VPN / MPLS {TP & IP MPLS and shall be scalable or upgradable. This unit

should be capable of supporting minimum of 2x10Gbe, 12 Gbe, 32xE1s. It is advisable to

have supporting facility to interface with STM1/4 equipment. This shall support all routing

protocols and Tunnel Engineering such as OSPF, ISIS, BGP & MP-BGP, LDP and RSVP-

TE to dynamically establish MPLS tunnels & PW service. The equipment design shall

support dual main control card redundancy and hot redundant power supply card.



2. For Junction stations: Supply of rack mountable modular core router for Major/Junction

station with minimum switching speed of 300 Gbps full duplex or higher, unit to supports

L2VPN / L3 VPN / MPLS {TP & IP MPLS and shall be scalable or upgradable. This unit

should be capable of supporting minimum of 12 x10Gbe, 24 GbE, 32xE1s (optional).

Additional chassis with cards will be provided to take care of multiple directional routes

and protocol as above.

Chassis bundle including with one main control card providing console and

SNMP interface, FAN module and Redundant 48V DC power supply modules.

2/4- 10GE SFP+ and 8/16- GE SFP Ethernet optical interface modules.

16/32- E1 Channel cards, Colored SFP for 10G interfaces/STM interface, SFPs

for 1GE RJ45 ports

3. NMS system for monitoring of IPMPLS network at Division and HQs.

4. Firewall for entire network at Divisional HQ level.

5. MDF, Rack with all termination and accessories.

6. Modular power supply with battery arrangements.

7. Installation and interfacing with existing system.

The equipment shall broadly consist of the following features are required for Indian railways

(IP-MPLS) migration

Interfacing: Support all the features of L2/L3 (IP MPLS standards and as required). It can also

support SDH network (STM 1/ 4/ 16) of existing Indian Railways without additional Optical

Fibre through CWDM module, NMS for mapping and monitoring are required

OSPF (Open Shortest Path First): Used within the MPLS cloud, it has to auto-discover all

other Core and Edge routers. Re-routes traffic in case of failure of any link.

LDP (Label Distribution Protocol): The protocol that facilitates exchange of label

information.

RSVP (Resource Reservation Protocol): The protocol that allows for the use of Traffic

Engineering and also used to exchange labels.



BGP (Border Gateway Protocol): The protocol that exchanges customer routes, of special

significance in L3 VPN, Supports the configuration of VPN through route-distinguisher RD and

route-target RT, Facilitates exchange of labels.

5.5 Site Deployment of IP MPLS Technology



















References

1. IR Telecom Manual 2021

2. Generic Requirements No.: TEC/GR/IT/CEN-004/03/MAR-17

3. RDSO Draft of Implementation of IP MPLS Technology for unified communication

backbone on Indian Railways, Version 1.0 (Draft) (July 2020).

4. Pilot project for Implementation of IPMPLS Technology and Graceful Migration of

Existing Legacy TDM Equipment, Southern Railways

5. Technical literature from IRISET/SC

6. Generic Requirements No.: TEC/GR/IT/CEN-004/03/MAR-17(www.tec.gov.in)

7. Gyandeep Technical Magazine, Nov 2020 IRISET

8. Technical literature from STTC, Podanur, Southern Railways

9. Technical literature from RailTel Corporation India Limited (RCIL)

10. Technical literature from M/s Team Engineers Enterprises

11. Technical literature from M/s Cisco Enterprises



CAMTECH Publications

CAMTECH is continuing its efforts in the documentation and up-gradation of information on

maintenance practices of Signalling & Telecom assets. Over the years a large number of

publications on Signalling & Telecom subjects have been prepared in the form of handbooks,

pocket books, pamphlets and video films. These publications have been uploaded on the internet

as well as Railnet.

For downloading these publications

On Internet:

Visit www.rdso.indianrailways.gov.in

Go to Directorates → CAMTECH Gwalior → Other Important links → Publications for

download - S&T Engineering

or click on link

https://rdso.indianrailways.gov.in/view_section.jsp?lang=0&id=0,2,17,6313,6321,6326

On Railnet:

Visit RDSO website at 10.100.2.19

Go to Directorates → CAMTECH → Publications → S&T Engineering

Or click on the link

http://10.100.2.19/camtech/Publications/CAMTECH%20Publications%20Online/SntPub.htm

A limited number of publications in hard copy are also available in CAMTECH library which

can be issued by deputing staff with official letter from controlling officer. The letter should be

addressed to Director (S&T), CAMTECH, Gwalior.

For any further information regarding publications please contact:

Director (S&T) – 0751-2470185 (O)(BSNL)

SSE/Tele - 9755549287 (CUG)

Or

Email at [email protected]

Or

FAX to 0751-2470841 (BSNL)

Or

Write at

Director (S&T)

Indian Railways Centre for Advanced Maintenance Technology,

In front of Hotel Adityaz, Airport Road, Maharajpur,

Gwalior (M.P.) 474005

http://www.rdso.indianrailways.gov.in/

https://rdso.indianrailways.gov.in/view_section.jsp?lang=0&id=0,2,17,6313,6321,6326

http://10.100.2.19/camtech/Publications/CAMTECH%20Publications%20Online/SntPub.htm




Quality Policy

“We at RDSO Lucknow are committed to maintain and update transparent

standards of services to develop safe, modern and cost effective railway

technology complying with statutory and regulatory requirements, through

excellence in research, designs and standards by setting quality objectives,

commitment to satisfy applicable requirements and continual improvements

of the quality management system to cater to growing needs, demand and

expectations of passenger and freight traffic on the railways through periodic

review of quality management systems to achieve continual improvement

and customer appreciation. It is communicated and applied within the

organization and making it available to all the relevant interested parties”.

Our Objective

To upgrade Maintenance Technologies and Methodologies and achieve

improvement in Productivity and Performance of all Railway assets and

manpower which inter-alia would cover Reliability, Availability and

Utilisation.

If you have any suggestion & any specific comments, please write to us:

Contact person : Director (Signal & Telecommunication)

Postal Address: Centre for Advanced Maintenance Technology, Opposite

Hotel Adityaz, Near DD Nagar, Maharajpur,

Gwalior (M.P.) Pin Code – 474 005

Phone : 0751 - 2470185

Fax : 0751 – 2470841

Email : [email protected]


INDIAN RAILWAYS

Centre for Advanced Maintenance Technology

Maharajpur, Gwalior (M.P.) – 474 005

An Introductory Handbook on IP MPLS Technology - RDSO

Documents