This document provides an overview of MPLS (Multi-Protocol Label Switching) including: 1) It describes the need for MPLS arising from limitations in traditional IP forwarding and issues running one statmux technology over another. 2) It explains basic MPLS concepts like label switching, label distribution protocols, label edge and switch routers, label switching paths, and forwarding equivalence classes. 3) It outlines the basic working process of MPLS including label encapsulation, lookup, and processing functions like push, pop and swap.

1. DIT
Dar es Salaam institute of Technology (DIT)
ETU 07420
Switching Systems
Ally, J
jumannea@gmail.com

2. DIT
MPLS Fundamentals

3. DIT
MPLS Contents
 Data networking and need for MPLS
 Basic concepts and working of MPLS
 Label - Allocation and Distribution
 MPLS Forwarding

4. Traditional Data Networks
DIT

5. Data Network Concept
 A data network is a set of nodes connected by
links.
 Nodes could be Routers, Switches,
Multiplexers connected by links from 64 kbps
till 10 gigabit ethernet.
 Fundamental property of data networks is
multiplexing.
 Two main types of multiplexing are - Time
Division Multiplexing ( TDM ) Statistical
Multiplexing ( StatMux)
 Others are FDM , WDM etc.
DIT

6. Data Network Concept
 TDM is practice of allocating certain amount of
time on a physical circuit for a particular
connection. This translates to bandwidth
allocation as the circuits are fixed rate.
 Examples for TDM being E1 (2Mbps circuit) ,
SDH
 Bandwidth permanently allocated for a
connection whether connection used ( carrying
traffic) or not.
 No traffic congestion issues, bandwidth
guaranteed
DIT

7. Data Network Concept
 Statmux - is the practice of sharing available
bandwidth between all users.
 Examples are : IP , Frame Relay, ATM & now
MPLS.
 It works by way of dividing traffic (data) into
discrete units which are handled separately. IP
units are Packets, ATM units are Cells, Frame
Relay units are Frames.
 Better utilisation of bandwidth, allows
oversubscription.
DIT

8. Data Network Concept
 Introduces resource contention.
 Therefore statmux technologies have to deal with
 Buffering of data units
 Queuing of data units
 Dropping of data units
 Running one statmux technology over other eg. IP
over ATM . Mechanisms available in one
technology to deal with contention does not
translate properly into another.
 Requirement of translating Layer 3 contention
controls mechanisms to Layer 2.
DIT

9. Data Network Concept
DIT

10. Traditional IP Forwarding
DIT

11. Traditional IP Forwarding
DIT

12. Virtual Connection
DIT

13. Virtual Connection
DIT

14. ATM Switching Process
DIT

15. MPLS Origin
DIT

16. MPLS Origin
 To bring advantages of connection oriented
protocols to packet switched networks.
 Faster switching - Replace IP header with
short and fixed-length labels as forwarding
basis.
 To substitute ATM & Frame Relay & provide
Integrated services with QoS without the
overhead of call segmentation.
DIT

17. MPLS Origin
 Technology combining the advantages of
ATM and IP
Layer 3 routing – Scalable and Flexible
Layer 2 switching – Reliable and Traffic
Engineering capability
 MPLS - Multi-Protocol Label Switching
DIT

18. Multiple Protocol Support
DIT

19. MPLS
 MPLS is the binding of the control plane at the bottom
of the network layer with the data forwarding plane at
the top of data link layer.
 MPLS is a hybrid of a traditional network layer-3
routing protocols and layer-2 switching technologies
 MPLS is not a new network layer protocol because it
does not have its own routing capabilities and
addressing schemes
 MPLS is designed to work over many of the data layer
technologies that provides requisite layer-2
addressing and functionality
 MPLS is a “Layer 2.5 Technology”
DIT

20. MPLS Data Encapsulation
DIT

21. Label Position in Packet
DIT

22. Basic Working Process of MPLS
DIT

23. MPLS Label
DIT

24. MPLS Devices
 MPLS uses Label Switched Path (LSP) for layer-2
forwarding.
 The path is setup using signaling protocols like Label
Distribution Protocol (LDP) and routing protocols.
DIT

25. MPLS Terminology
 LER -Label Edge Router
 Examines inbound IP packets and assigns them to an FEC
 Generates MPLS header and assigns initial label i.e Ingress
& Egress
 LSR - Label Switch Router
 Forwards MPLS packets using Label swapping
 Table lookup in Label Information Base (LIB)
 LSP - Label Switch Path
 Path thro’ MPLS network setup by signaling protocol (LDP)
 LSP’s are unidirectional , roughly equivalent to VC
 LSP setup is based on FEC criteria
 LSP may be different from IGP path
DIT

26. MPLS Terminology
 Forwarding Equivalence Class (FEC) is a stream of
IP packets that are forwarded over the same path,
treated in the same manner and mapped to the
same label. ( Same QoS ; Same Next Hop; Same
Path)
 LDP ( Label Distribution Protocol) associates a set of
destinations with each LSP
 Packets could be assigned to a LSP based on
 Combination of destination address and
application type
 Combination of destination address and source
address
DIT

27. Label Processing
 Push
 Add a new label to the top of the packet
 The TTL, stack and CoS fields are derived from the IP packet
header
 Can be performed on an existing MPLS packet-Label
Stacking
 Pop
 Remove the label
 TTL is copied from the label to the IP header
 IP packet is forwarded as a native IP packet
 Swap

Replace the label at the top of the label stack with a new label
 The TTL, stack and CoS fields are copied from the previous label
DIT

28. MTNL MPLS Network - Mumbai
DIT

29. DIT
Thanks!
Technology changes but communication lasts.