MPLS (Multi-Protocol MPLS (Multi-Protocol Label Switching)Label Switching)

Eric DonnellyEric Donnelly

EEL6785EEL6785

6/19/036/19/03

OverviewOverview

BackgroundBackground

HistoryHistory

Components, DefinitionsComponents, Definitions

OperationOperation

Performance MeasurementsPerformance Measurements

SummarySummary

BackgroundBackground

Standard being developed by IETF (Internet Engineering Standard being developed by IETF (Internet Engineering Task Force) since 1997Task Force) since 1997Integrates key features of Layer 2 and 3 technologies w/o Integrates key features of Layer 2 and 3 technologies w/o limitation to a particular protocollimitation to a particular protocolPackets labeled and sent through network on paths Packets labeled and sent through network on paths rather than hop-to-hop as in IP datagramsrather than hop-to-hop as in IP datagrams

Courtesy of [4]

Basic IdeaBasic Idea

MPLS is a hybrid model adopted by IETF to MPLS is a hybrid model adopted by IETF to incorporate best properties in both packet incorporate best properties in both packet routing & circuit switchingrouting & circuit switching

Forwarding:Label Swapping

Control:

IP Router Software

Control:

IP Router Software

Forwarding:Longest-match Lookup

Control:

ATM Forum Software

Forwarding:Label Swapping

IP Router MPLS ATM Switch

Courtesy of [1]

What about GMPLS?What about GMPLS?

GMPLS (Generalized Multi-Protocol Label GMPLS (Generalized Multi-Protocol Label Switching)Switching)

Previously Multi-Protocol Lambda Switching Previously Multi-Protocol Lambda Switching (another MPLS)(another MPLS)

GMPLS is deployed from MPLS (Label)GMPLS is deployed from MPLS (Label)Apply MPLS control plane techniques to optical Apply MPLS control plane techniques to optical switches and IP routing algorithms to manage switches and IP routing algorithms to manage lightpaths in an optical networklightpaths in an optical network

We will focus on MPLS in this presentationWe will focus on MPLS in this presentation

HistoryHistory

In Mid-90s, many ISPs migrated from router In Mid-90s, many ISPs migrated from router based cores to IP-over-ATM, this provided:based cores to IP-over-ATM, this provided: Greater BandwidthGreater Bandwidth Deterministic forwarding performanceDeterministic forwarding performance Traffic engineering supportTraffic engineering support

Courtesy of [4]

History (Cont.)History (Cont.)

No specific Internet backbone networking equipment available for No specific Internet backbone networking equipment available for ISPs.ISPs.Equipment needed to be adapted—ATM best solution at timeEquipment needed to be adapted—ATM best solution at timeHowever, Continued Internet growth increased stress on ATM However, Continued Internet growth increased stress on ATM networks:networks:

Bandwidth limitationsBandwidth limitations 20 percent “cell tax”20 percent “cell tax” Designed for different tasks (IP—conncectionless, ATM—connection-Designed for different tasks (IP—conncectionless, ATM—connection-

oriented)oriented)Late 1996, proprietary multilayer solutions emerged with integrated Late 1996, proprietary multilayer solutions emerged with integrated ATM switching and IP routing:ATM switching and IP routing:

IP Switching—Ipsilon/NokiaIP Switching—Ipsilon/Nokia Tag Switching—Cisco SystemsTag Switching—Cisco Systems Aggregate Route-Based IP Switching (ARIS)—IBM Aggregate Route-Based IP Switching (ARIS)—IBM IP Navigator—Cascade/Ascend/Lucent TechnologiesIP Navigator—Cascade/Ascend/Lucent Technologies Cell Switching Router (CSR)—ToshibaCell Switching Router (CSR)—Toshiba

--These were all similar technologies, but were --These were all similar technologies, but were NOTNOT interoperable interoperable

History (Cont.)History (Cont.)

Each multilayer switch ran standard IP routing software Each multilayer switch ran standard IP routing software (OSPF, BGP-4)(OSPF, BGP-4)Different label binding approachesDifferent label binding approaches

Data-driven modelData-driven modelLabel bindings created when data packets arrive.Label bindings created when data packets arrive.Labels created either when first packet in a flow or after a number Labels created either when first packet in a flow or after a number of packets in a flow have arrived.of packets in a flow have arrived.IP Switching and CSR used this technique.IP Switching and CSR used this technique.

Control-driven modelControl-driven modelLabel bindings created when control information arrives.Label bindings created when control information arrives.Assigned in response to processing of protocol traffic, control traffic Assigned in response to processing of protocol traffic, control traffic (such as RSVP), or static configuration.(such as RSVP), or static configuration.

--Control-driven model used in MPLS!--Control-driven model used in MPLS!Note: OSPF-Open Shortest-Path First

BGP-Border Gateway Protocol

RSVP-Resource Reservation Protocol

MPLS emergesMPLS emerges

IETF creates MPLS working group to create IETF creates MPLS working group to create unified standard able to operate on any media unified standard able to operate on any media infrastructures (Frame Relay, PPP, SONET), not infrastructures (Frame Relay, PPP, SONET), not just ATM.just ATM.Uses Control-driven model.Uses Control-driven model.Defines new standard-based IP signaling and Defines new standard-based IP signaling and label distribution protocols, as well as existing label distribution protocols, as well as existing protocol extensions (this supports multivendor protocol extensions (this supports multivendor interoperability).interoperability).Does not implement any of the ATM forum Does not implement any of the ATM forum signaling or routing protocols (eliminates signaling or routing protocols (eliminates coordinating of 2 protocol architectures).coordinating of 2 protocol architectures).

Terminology/ComponentsTerminology/Components

FEC (Forwarding Equivalence Class)-Group of FEC (Forwarding Equivalence Class)-Group of packets sharing the same type of transport.packets sharing the same type of transport.LSR (Label Switched Router)-Swaps labels on LSR (Label Switched Router)-Swaps labels on packets in core of network.packets in core of network.LER (Label Edge Router)-Attach Labels to LER (Label Edge Router)-Attach Labels to packets based on a FEC.packets based on a FEC.LSP (Label Switch Path)-Path through network LSP (Label Switch Path)-Path through network based on a FEC (simplex in nature).based on a FEC (simplex in nature).LIB (Label Information Base)- MPLS equivalent LIB (Label Information Base)- MPLS equivalent to IP routing table, contains FEC-to-Label to IP routing table, contains FEC-to-Label bindings.bindings.

MPLS OperationMPLS Operation1a. Routing protocols (e.g. OSPF-TE, IS-IS-TE) exchange reachability to destination networks

1b. Label Distribution Protocol (LDP) establishes label mappings to destination network

2. Ingress LER receives packet and “label”s packets

IP

IP 10

3. LSR forwards packets using label swapping

IP 20IP 40

4. LER at egress removes label and delivers packet

IP

Courtesy of [1]

FECs- Group of packets sharing the same FECs- Group of packets sharing the same type of transporttype of transport

All packets in such a group are All packets in such a group are provided the same treatment provided the same treatment en route to the destination. en route to the destination. Can be partitioned by:Can be partitioned by:

Source-to-Destination AddressSource-to-Destination Address ApplicationApplication Bandwidth RequirementBandwidth Requirement

Conventional Routing=>packet Conventional Routing=>packet assigned to FEC at each hop assigned to FEC at each hop (Layer 3 lookup).(Layer 3 lookup).MPLS=>done only once (at MPLS=>done only once (at egress).egress).

[9]

LSRs and LERsLSRs and LERs

The devices used for MPLS can be classified into label edge routers The devices used for MPLS can be classified into label edge routers (LERs) and label switching routers (LSRs). (LERs) and label switching routers (LSRs). A LSR is a high-speed router device in the core of an MPLS A LSR is a high-speed router device in the core of an MPLS network. network.

Participates in the establishment of LSPs, using the appropriate label Participates in the establishment of LSPs, using the appropriate label signaling protocolsignaling protocol

Does high-speed switching of the data traffic based on the established Does high-speed switching of the data traffic based on the established paths. paths.

A LER is a device that operates at the edge of the access network A LER is a device that operates at the edge of the access network and MPLS network.and MPLS network.

Supports multiple ports connected to dissimilar networks (such as frame Supports multiple ports connected to dissimilar networks (such as frame relay, ATM, and Ethernet)relay, ATM, and Ethernet)

Forwards this traffic on to the MPLS network after establishing LSPs, Forwards this traffic on to the MPLS network after establishing LSPs, using the label signaling protocol at the ingress and distributing the using the label signaling protocol at the ingress and distributing the traffic back to the access networks at the egress. traffic back to the access networks at the egress.

Plays important role in the assignment and removal of labels, as traffic Plays important role in the assignment and removal of labels, as traffic enters or exits an MPLS network. enters or exits an MPLS network.

Inside a LSRInside a LSR

1.1. Data PlaneData Plane

2.2. Control PlaneControl Plane

FEC Protocol  Port  

192.168.10.1 06 443guaranteed no packet

loss

192.168.10.2 11 69 best efforts192.168.10.3 06 80 controlled load

FEC DATAFEC Label in Label out

192.168.10.1 1400 100

192.168.10.2 500 101

192.168.10.3 107 103

LIB

Label in Label out

1400 100

500 101

107 103

NHLFE

Figures Courtesy of [10]

LabelsLabels

The MPLS forwarding component is based The MPLS forwarding component is based on the label-swapping algorithm.on the label-swapping algorithm.Label encapsulated in MPLS header, Label encapsulated in MPLS header, which is “sandwiched” between the Layer which is “sandwiched” between the Layer 2 and IP header.2 and IP header.If Layer 2 technology supports labels If Layer 2 technology supports labels (ATM VPI/VCI, Frame Relay DLCI), MPLS (ATM VPI/VCI, Frame Relay DLCI), MPLS label and header encapsulated in the label and header encapsulated in the Layer 2 label field.Layer 2 label field.

Why Label Swap?Why Label Swap?Label swapping provides a significant number of operational Label swapping provides a significant number of operational benefits when compared to conventional hop-by-hop network layer benefits when compared to conventional hop-by-hop network layer routing.routing.Gives an ISP flexibility in the way that it assigns packets to FECs. Gives an ISP flexibility in the way that it assigns packets to FECs.

Destination address (like conventional IP routing)Destination address (like conventional IP routing) Source address.Source address. Application type.Application type. Point of entry/exit to/from the label-swapping network.Point of entry/exit to/from the label-swapping network. CoS conveyed in the packet header.CoS conveyed in the packet header. Any combination of the above.Any combination of the above.

ISPs can construct customized LSPs that support specific ISPs can construct customized LSPs that support specific application requirements (for instance, VPNs). LSPs can be application requirements (for instance, VPNs). LSPs can be designed to:designed to:

minimize the number of hopsminimize the number of hops bandwidth requirementsbandwidth requirements bypass points of congestionbypass points of congestion

Offer ISPs precise control over the flow of traffic in their networks. Offer ISPs precise control over the flow of traffic in their networks.

……For InstanceFor Instance

If network core runs conventional longest-match IP If network core runs conventional longest-match IP forwarding:forwarding:

Data from Host A and B follow path 1 since it is the shortest-path Data from Host A and B follow path 1 since it is the shortest-path computed.computed.

With MPLS, network administrator could split traffic:With MPLS, network administrator could split traffic:Host A traffic over path 1Host A traffic over path 1Host B traffic over path 2Host B traffic over path 2

Courtesy of [4]

MPLS headerMPLS headerLabel field- Actual MPLS label (20bits).

CoS field- “Class of Service” can effect queuing and discard algorithms applied to packets (3 bits).

S (Stack) field- supports a hierarchical label stack (1 bit).

TTL field- “Time-to-live” provides conventional IP TTL functionality (8 bits).

Courtesy of [4]

…Frame Relay

…PPP/Ethernet

…In ATM

Figures Courtesy of [5]

Label CreationLabel Creation

topology-based methodtopology-based method—uses normal —uses normal processing of routing protocols (such as processing of routing protocols (such as OSPF and BGP) OSPF and BGP)

request-based methodrequest-based method—uses processing —uses processing of request-based control traffic (such as of request-based control traffic (such as RSVP) RSVP)

Note: OSPF-Open shortest-path firstBGP- Border Gateway Protocol

Label SpacesLabel Spaces

Labels used by an LSR for FEC-label Labels used by an LSR for FEC-label bindings are split into 2 categories: bindings are split into 2 categories: Per platform-label values are unique across Per platform-label values are unique across

an entire LSR.an entire LSR. Per interface-label values are associated w/ Per interface-label values are associated w/

interfaces. Label values provided on different interfaces. Label values provided on different interfaces could be the same.interfaces could be the same.

Label DistributionLabel Distribution

No single method of signaling requiredNo single method of signaling required Enhancements of existing routing protocols (to allow Enhancements of existing routing protocols (to allow

piggybacking of label information) include:piggybacking of label information) include:Border Gateway Protocol (BGP)Border Gateway Protocol (BGP)

Resource Reservation Protocol (RSVP)Resource Reservation Protocol (RSVP) LDP (Label Distribution Protocol)- Defined by IETF for LDP (Label Distribution Protocol)- Defined by IETF for

signaling and management of label space.signaling and management of label space.

--Extensions have been defined to support explicit --Extensions have been defined to support explicit routing based on QoS and CoS requirements.routing based on QoS and CoS requirements.

Label Distribution schemes Label Distribution schemes

LDPLDP—maps unicast IP destinations into —maps unicast IP destinations into labels labels

RSVP, CR–LDPRSVP, CR–LDP—used for traffic —used for traffic engineering and resource reservation engineering and resource reservation

BGPBGP—external labels (VPN)—external labels (VPN)

Signaling Mechanisms (general)Signaling Mechanisms (general)

1.1. label requestlabel request—An LSR requests a label from its downstream —An LSR requests a label from its downstream neighbor so that it can bind to a specific FEC. This mechanism can neighbor so that it can bind to a specific FEC. This mechanism can be employed down the chain of LSRs up until the egress LER (i.e., be employed down the chain of LSRs up until the egress LER (i.e., the point at which the packet exits the MPLS domain). the point at which the packet exits the MPLS domain).

2.2. label mappinglabel mapping—In response to a label request, a downstream —In response to a label request, a downstream LSR will send a label to the upstream initiator using the label LSR will send a label to the upstream initiator using the label mapping mechanism. mapping mechanism.

Courtesy of [5]

Distribution and Signaling ProtocolsDistribution and Signaling Protocols

Protocol Routing Traffic engineering

     LDP Implicit NO

     BGP Implicit NO

     IS-IS Implicit NO

     CR-LPD Explicit YES

     RSVP-TE Explicit YES

     OSPF-TE Explicit YES

•Implicit routing- labels are set-up and torn-down (like telephone calls), also known as hard state.

•Explicit routing- allows for better traffic engineering, traffic tunnels are created based on overall view of topology. More dynamic.

Courtesy of [10]

Label Distribution Protocol (LDP)Label Distribution Protocol (LDP)Four message classes

1. Discovery-Announce and maintain presence of an LSR.

2. Session-establish, maintain, terminate sessions b/w LDP peers.

3. Advertisement-create, change, delete label mappings.

4. Notification-advisory and error info.

•Discovery: Runs over UDP

•All others run over TCP

[9]

Message StructureMessage Structure

All LDP messages have a common message All LDP messages have a common message structure (Type-Length-Value encoding scheme)structure (Type-Length-Value encoding scheme)

For specifics on this frame see http://www.networksorcery.com/enp/protocol/LabelDistributionProtocol.htm#Glossary

•Type: Type of message[11]

DiscoveryDiscovery

LSR multicasts HELLO message to well-known UDP port LSR multicasts HELLO message to well-known UDP port on “all routers on this subnet” multicast group.on “all routers on this subnet” multicast group.All routers listen to this group to learn all LSRs with All routers listen to this group to learn all LSRs with direct connection.direct connection.When an LSR is detected, a TCP LDP connection is When an LSR is detected, a TCP LDP connection is established.established.

The HELLO message can also be sent to a well-The HELLO message can also be sent to a well-known UDP port at the IP address of a router if the IP known UDP port at the IP address of a router if the IP address is known through static configuration. address is known through static configuration.

Some Important MessagesSome Important Messages

INITIALIZATION- label allocation mode, timer values, range ofINITIALIZATION- label allocation mode, timer values, range oflabels to be usedlabels to be usedKEEPALIVE- respond to Initialization of parameters areKEEPALIVE- respond to Initialization of parameters areacceptable. Connection is terminated if timely keepalives are notacceptable. Connection is terminated if timely keepalives are notreceivedreceivedLABEL MAPPING – Advertise a binding between address prefixLABEL MAPPING – Advertise a binding between address prefixand labeland labelLABEL WITHDRAWEL – reverse LABEL MAPPING, can occurLABEL WITHDRAWEL – reverse LABEL MAPPING, can occurbecause of routing changesbecause of routing changesLABEL RELEASE– Used in Conservative Label Retention modeLABEL RELEASE– Used in Conservative Label Retention modeLABEL REQUEST– Used for down-stream-on-demand mode toLABEL REQUEST– Used for down-stream-on-demand mode torequest label mappingrequest label mappingLABEL REQUEST ABORT – If next hop changes so that the priorLABEL REQUEST ABORT – If next hop changes so that the priorlabel request is invalid, this cancels the previous requestlabel request is invalid, this cancels the previous request

Slide courtesy of [9]

Performance MeasurementsPerformance Measurements•Computers: Pentium II 300 128 MB RAM

Fast EthernetFreeBSD 4.1

•LERs and LSRs:Juniper Networks M40TM routers (MPLS and RSVP-TE).

• Interconnect:OC-12 (ATM 80 Mbps ATM (PVC) connections for experiment.) •Physical distance:

• LSR 1-LSR 3, LSR 2 -LSR 3 =40km•LSR 1-LSR 2 =5km

Courtesy of [8]

ResultsResults

Path from A to C (TCP stream) Throughput of both MPLS paths (TCP streams)

Courtesy of [8]

ResultsResults

Latency from A to C for TCP stream Latency from A to C for UDP stream

Courtesy of [8]

SummarySummaryImproves packet-forwarding performance in the network Improves packet-forwarding performance in the network

MPLS enhances and simplifies packet forwarding through routers using Layer-2 switching MPLS enhances and simplifies packet forwarding through routers using Layer-2 switching paradigms. paradigms.

MPLS is simple, which allows for easy implementation. MPLS is simple, which allows for easy implementation. MPLS increases network performance because it enables routing by switching at wireline MPLS increases network performance because it enables routing by switching at wireline

speeds.speeds.

Supports QoS and CoS for service differentiation Supports QoS and CoS for service differentiation MPLS uses traffic-engineered path setup and helps achieve service-level guarantees. MPLS uses traffic-engineered path setup and helps achieve service-level guarantees. MPLS incorporates provisions for constraint-based and explicit path setup.MPLS incorporates provisions for constraint-based and explicit path setup.

Supports network scalability Supports network scalability MPLS can be used to avoid the NMPLS can be used to avoid the N22 overlay problem associated with meshed IP–ATM overlay problem associated with meshed IP–ATM

networks.networks.

Integrates IP and ATM in the network Integrates IP and ATM in the network MPLS provides a bridge between access IP and core ATM. MPLS provides a bridge between access IP and core ATM. MPLS can reuse existing router/ATM switch hardware, effectively joining the two disparate MPLS can reuse existing router/ATM switch hardware, effectively joining the two disparate

networks.networks.

Builds interoperable networks Builds interoperable networks MPLS is a standards-based solution that achieves synergy between IP and ATM networks. MPLS is a standards-based solution that achieves synergy between IP and ATM networks. MPLS facilitates IP–over-synchronous optical network (SONET) integration in optical MPLS facilitates IP–over-synchronous optical network (SONET) integration in optical

switching. switching. MPLS helps build scalable VPNs with traffic-engineering capability.MPLS helps build scalable VPNs with traffic-engineering capability.

……HoweverHowever

Some Internet Purists complain that MPLS Some Internet Purists complain that MPLS breaks some critical Internet architectural breaks some critical Internet architectural principles:principles: MPLS supports tunneling, which breaks the MPLS supports tunneling, which breaks the

transparency paradigm.transparency paradigm. MPLS supports sessions, it breaks the MPLS supports sessions, it breaks the

datagram model.datagram model.

But MPLS provides great value to ISPs, But MPLS provides great value to ISPs, such as lower operating costs and ability such as lower operating costs and ability to provide QoS to businesses.to provide QoS to businesses.

Questions???Questions???

ReferencesReferences1.1. Yin, Li, PowerPoint Presentation: “MPLS and GMPLS,” University of California, Berkeley, Yin, Li, PowerPoint Presentation: “MPLS and GMPLS,” University of California, Berkeley,

Summer 2002.Summer 2002.2.2. R. Ramaswami and K. N. Sivarajan, R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical PerspectiveOptical Networks: A Practical Perspective 2 2nd nd Ed., Ed.,

Morgan Kaufmann Publishers.Morgan Kaufmann Publishers.3.3. Nortel Networks, “MPLS—An introduction to multiprotocol label switching,” 2001, Nortel Networks, “MPLS—An introduction to multiprotocol label switching,” 2001,

http://www.nortelnetworks.com/corporate/technology/mpls/collateral/55053.25-04-01.pdfhttp://www.nortelnetworks.com/corporate/technology/mpls/collateral/55053.25-04-01.pdf..4.4. Semeria, Chuck, Juniper Networks, “Multiprotocol Label Switching: Enhancing Routing in Semeria, Chuck, Juniper Networks, “Multiprotocol Label Switching: Enhancing Routing in

the New Public Network,” 2000.the New Public Network,” 2000.5.5. International Engineering Consortium, “Multiprotocol Label Switching (MPLS),” 2003, International Engineering Consortium, “Multiprotocol Label Switching (MPLS),” 2003,

http://www.iec.org/online/tutorials/mpls/http://www.iec.org/online/tutorials/mpls/ 6.6. Farkas, K. et al. “IP Traffic Engineering of OMP Technique,” Technical University of Farkas, K. et al. “IP Traffic Engineering of OMP Technique,” Technical University of

Budapest, Hungary, 2000.Budapest, Hungary, 2000.7.7. Johnson, J., “Despite criticism, MPLS is here to stay,” Network World, April 2002. Johnson, J., “Despite criticism, MPLS is here to stay,” Network World, April 2002.

http://www.nwfusion.com/columnists/2002/0408eye.htmlhttp://www.nwfusion.com/columnists/2002/0408eye.html 8.8. Bayle, T. et al. “Performance Measurements of MPLS Traffic Engineering and QoS,” Bayle, T. et al. “Performance Measurements of MPLS Traffic Engineering and QoS,”

Hiroshima University, Hiroshima University, http://www.isoc.org/isoc/conferences/inet/01/CD_proceedings/T43/http://www.isoc.org/isoc/conferences/inet/01/CD_proceedings/T43/ . .

9.9. Nortel Networks, “MPLS Tutorial,” May, 1999, Nortel Networks, “MPLS Tutorial,” May, 1999, http://www.nanog.org/mtg-9905/ppt/mpls/http://www.nanog.org/mtg-9905/ppt/mpls/ . .10.10. Gallaher, R, “Advanced MPLS Signaling,” December 2001, Gallaher, R, “Advanced MPLS Signaling,” December 2001,

http://www.convergedigest.com/tutorials/mpls3/page1.htmhttp://www.convergedigest.com/tutorials/mpls3/page1.htm . .11.11. Network Sorcery Inc., “LDP,” Network Sorcery Inc., “LDP,”

http://www.networksorcery.com/enp/protocol/LabelDistributionProtocol.htm#Glossaryhttp://www.networksorcery.com/enp/protocol/LabelDistributionProtocol.htm#Glossary . .

Simulation (EXTRA)Simulation (EXTRA)

Courtesy of [6]

Lines studied in simulation

Results (EXTRA)Results (EXTRA)

MPLS Simulation OSPF Simulation

Courtesy of [6]

Results (EXTRA)Results (EXTRA)

OSPF-OMP MPLS-OMP

Courtesy of [6]

These simulations were done using an OMP (Optimized Multipath) extension to their existing protocols.

History (Extra)History (Extra)

Control-driven model benefitsControl-driven model benefits Labels are assigned and distributed before arrival of data traffic. Labels are assigned and distributed before arrival of data traffic.

This means that if a route exists in the IP forwarding table, a label This means that if a route exists in the IP forwarding table, a label has already been allocated for the route, so traffic arriving at a has already been allocated for the route, so traffic arriving at a multilayer switch can be label swapped immediately.multilayer switch can be label swapped immediately.

Scalability is significantly better than in the data-driven model. Scalability is significantly better than in the data-driven model. Number of label switched paths proportional to the number of Number of label switched paths proportional to the number of entries in the IP forwarding table, not to the number of individual entries in the IP forwarding table, not to the number of individual traffic flows. Label assignment based on prefixes, rather than traffic flows. Label assignment based on prefixes, rather than individual flows, permits a single label to represent a highly individual flows, permits a single label to represent a highly aggregated FEC.aggregated FEC.

In a stable topology, the label assignment and distribution In a stable topology, the label assignment and distribution overhead is lower than in the data-driven model because label-overhead is lower than in the data-driven model because label-switched paths are established only after a topology change or switched paths are established only after a topology change or the arrival of control traffic, not with the arrival of each “new” the arrival of control traffic, not with the arrival of each “new” traffic flow.traffic flow.

Every packet in a flow is label switched, not just the tail-end of Every packet in a flow is label switched, not just the tail-end of the flow as in the data-driven model.the flow as in the data-driven model.