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MPLS label Switching vs IP packet switching | difference between label switching and IP switching

This page compares MPLS label switching vs IP packet switching and mentions difference between label switching and IP switching. It provides links to difference between circuit switching, packet switching and message switching. It also mentions benefits (advantages) of MPLS label switching.

Label switching uses labels instead of IP addresses for switching and routing the packets. It works at Layer 2.5 which resides between layer 2 (data link layer) and layer 3 (network layer).

MPLS Label Switching

Generic MPLS label format

MPLS Label is used for label switching. It is placed between L2 header and L3 header. It is 4 octets in size. It consists of following fields.
MPLS Label = { Label (20 bits) , EXP or TC (3 bits), S (1 bit), TTL (8 bits) }
Label : Used for switching. Values from 0 to 15 are reserved.
EXP: Experimental, indicates QoS or priority of label.
S: indicates whether label is the last one in the stack or not. Value of 1 indicates label is bottom label.
TTL: Time to Live
Refer MPLS tutorial for more information.

Label Stacking

The figure-2 depicts label stacking. As shown there are two labels. Label near to L2 header is known as 'top label' and label near to L3 header is known as 'bottom label'.

MPLS operations

There are three basic operations used in MPLS label switching. These operations are Push, Swap and Pop. At the start, push operation is used as ingress CE router assigns label to the packet. In between across LSPs (Label Switching Paths), swap operation is used. At the end, pop operation is used to take out label from the packet as it is no longer needed as destination has been arrived or reached.

MPLS Label Switching

The figure-3 depicts simple MPLS network consisting of different types of routers used for providing switching and routing of MPLS packets between two end systems i.e. hosts. The routers are CE routers, PE routers and P routers.
Refer MPLS and BGP working for control flow and data flow between the hosts.

Label Switching Example

Figure-4 and table below mentions label switching example between station-A and station-B.


Router Designation Incoming Label Incoming Interface Destination network Outgoing interface Outgoing Label
R1 - e0 172.16.1 S1 6
R2 6 S0 172.16.1 S2 11
R3 11 S0 172.16.1 S3 7
R4 7 S1 172.16.1 e0 -

LER (Label Edge Router) and LSR (Label Switching Router) maintains tables known as FEC table and LIB table. LSR combines functionalities of a switch as well as router.
FEC table: {Label In, Destination IP Address, Label Out, Interface}
LIB table: {Label In, Label Out, Interface }

Benefits or Advantages of MPLS Label Switching

Following are the benefits of MPLS Label Switching:
• MPLS forwards any data across network. It is not based on destination IP address but it is based on tags or labels.
• It can be used to transport any types of protocols e.g. ATM, SONET, Ethernet etc.
• Both voice and data can be transported on same network.
• It uses bandwidth very effectively.
• It is network resilient with MPLS fast re-route feature.

IP Packet Switching

circuit switching vs packet switching fig2

Refer Circuit switching vs Packet switching and Packet switching vs Message switching.

Difference between label switching and IP switching

Following table summarizes difference between label switching and IP switching.


MPLS Label Switching IP Packet switching
Routes packet based on 20 bit label. Routes packet based on 32 bit IP address
Established dedicated path known as LSP (Label Switching Path) before data flow. Do not establish dedicated path , just transmit data gram which will be routed based on IP addresses.
Each router builds LFIB (Label Forwarding Information Base) table using LDP protocol. Stores IP routing table.


What is Difference between Circuit switching, packet switching and message switching and more

Circuit switching vs Packet switching
Packet switching vs Message switching
difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD
Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
OFDM vs OFDMA
CDMA vs GSM
Bluetooth vs zigbee
Fixed wimax vs mobile
wibro vs mobile wimax
Microcontroller vs microprocessor
circuit switching Vs. packet switching
Difference between soft handover and softer handover

Useful Links

• Basics of OSI and TCP-IP Layers
• Circuit Switched Call vs Packet Switched Call
• LAN vs WAN vs MAN
• What is an IP address
• What is MAC Address
• What is Hub
• What is Switch
• What is Bridge
• What is Router
• What is Gateway
• Firewall basics
• TCP-IP Packet format
• ARP Protocol format


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