An introduction to MPLS and GMPLS (and briefly T-MPLS)Anne-Grethe Kåråsen, Telenor R&I

Modified by Steinar Bjørnstad NTNU

Two slides on T-MPLS added by Norvald Stol NTNU 2007

Why was MultiProtocol Label Switching (MPLS) designed?

• To enhance the performance of the traffic forwarding mechanisms (compared to traditional IP forwarding)

• To provide a traffic engineering (TE) capability in IP networks

What is Traffic Engineering (TE)?

• TE is concerned with performance optimization of operational networks.

• Traffic performance: A major goal of Internet TE is to facilitate efficient and reliable network operations while simultaneously optimizing network resource utilization and traffic performance.

• QoS: Traffic oriented performance objectives include the aspects that enhance the QoS of traffic streams.

• Resource utilization: Resource oriented performance objectives include the aspects pertaining to the optimization of resource utilization.

The resource problem to solve:

• Conventional IGP path computation is selected based upon a simple additive metric.

– Bandwidth availability is not taken into account

• Some links may be underutilized while others are congested.

A solution to the resource problem

Path for R1 to R3 traffic

Path for R2 to R3 traffic

MPLS - some main concepts

• Uses label switching to forward data

– A label is a short fixed length physically contiguous identifier which is used to identify a FEC, usually of local significance.

• MPLS path = Label Switched Path (LSP)

• Forwarding Equivalence Class (FEC)

– A group of IP packets that are forwarded in the same manner

– FEC – label mapping in ingress MPLS node

– Criteria for assigning packets to FECs are configurable

• Next Hop Label Forwarding Entry (NHLFE)

– Packets next hop + label operation (swap, push, pop)

The MPLS shim header

• The EXP Field is "Experimental" though it is proposed use is to indicate Per Hop Behavior of labeled packets traversing Label Switching Routers. (QoS)

• The Stack (S) Field indicates the presence of a label stack.

• The Time to Live Field is decremented at each LSR hop and is used to throw away looping packets.

LSP route determination

• An LSP must be set up and labels assigned at each hop before traffic forwarding can take place.

• There are two kinds of LSPs, based on the method used for determining the route:

– control-driven LSPs (hop-by-hop LSPs)

– explicitly routed LSPs (ER-LSPs)

• A control-driven LSP follows the path that a packet using default IP routing would have used.

• An ER-LSP may be specified and controlled so that the network traffic follows a path independent of what is computed by IP routing.

Constraint-based routing• Types of constraints:

– Resource related (e.g. bandwidth)

– Administrative (e.g. include/exclude certain links)

• Resource related and policy related attributes are associated with links.

• Link attributes are flooded by the routing protocols along with topology information.

• A constraint-based path computation process uses this information when finding paths that satisfy given constraints.

• Most used algorithm is Constraint Shortest Path First (CSPF):

– Excludes all links that fail to meet constraint

– Chooses shortest path that meets constraint

– Convenient for online path selection, one LSP at a time

ER-LSPs

• Explicit LSP: route is determined at the originating node. When we explicitly route an LSP, we call it an LSP tunnel or a traffic-engineering tunnel.

• Explicit route information is carried only at the time of LSP setup, not with each packet forwarded on the LSP.

• LSP tunnels are uni-directional.

• Can be set up manually or by the use of a signaling protocol.

ER-LSP setup example using RSVP-TE

RSVP Path message carried EExplicit RRoute OObject (ERO)

RSVP Resv message carries Label information (L)

LSR8

LSR2

LSR6

LSR3

LSR4

LSR7LSR1

LSR5

LSR9

ERO=(2, 6, 7, 4, 5)

ERO=(6, 7, 4, 5)

ERO=(7, 4, 5)

ERO=(4, 5)

ERO=( 5)

L=21

L=10

L=21

L=14L=5

MPLS Label Forwarding Example

LABEL SWITCHINGIP Forwarding IP Forwarding

IPPacket

Label 1

IPPacket

IPPacket

Label 2

IPPacket

Label 3

IPPacket

Label-Switched Path (LSP)

LERLERLSRLSRLSRLSR

LERLER

Label stacking

Protocols for MPLS routing and signaling

Routing:

• Open Shortest Path First (OSPF) & Intermediate System –Intermediate System (IS-IS) with TE extensions

Signaling:

• Label Distribution Protocol (LDP) [RFC 3036]

• Constraint based LDP (CR-LDP) [RFC 3212]

• Extensions to Resource Reservation Protocol (RSVP) for LSP tunnels [RFC 3209]

• Border Gateway Protocol (BGP) [RFC 3107]

MPLS references

• Multiprotocol Label Switching Architecture, RFC 3031, Jan 2001

• Requirements for traffic engineering over MPLS, RFC 2702, Sept 1999

• Traffic engineering extensions to OSPF version 2, RFC 3630, September 2003

• Traffic Engineering Extensions to OSPF version 3, Internet Draft <draft-ietf-ospf-ospfv3-traffic-07>, April 2006

• IS-IS extensions for traffic engineering, RFC 3784, June 2004

• LDP specification, RFC 3036, Jan 2001

• Constraint-based LSP setup using LDP, RFC 3212, Jan 2002

• RSVP-TE: Extensions to RSVP for LSP tunnels, RFC 3209, Dec 2001

• Carrying label information in BGP-4, RFC 3107, May 2001

Generalized MultiProtocol Label Switching (GMPLS)

• GMPLS is an enhanced version of the MPLS-concept.

• GMPLS related work is coordinated by the IETF Common Control and Measurement Plane (ccamp) working group.

• In data networks, MPLS covers both the control plane (label binding, label distribution, etc.) and the data plane (packet forwarding).

• In circuit switched networks there is no packet forwarding.

• Only MPLS control plane components are applicable to circuit switched networks.

• GMPLS assumes IP-based routing and signaling protocols, and IP addresses. (IP-centric)

GMPLS (former MPS) – mapping to OTN

Main features applicable to OTN (Optical Transport Network)

• MPLS control plane is implemented in each OXC

• Constraint-based routing and signaling provide control plane for OXCs

– to discover, distribute, and maintain relevant state information associated with the OTN

– to establish and maintain OCh trails

• Each OXC is considered an equivalent of a Label Switched Router (LSR)

• Lightpaths (OCh trails) are considered similar to Label Switched Paths (LSPs)

• Lambdas and switch ports are considered similar to labels

GMPLS – new set of LSP interfaces• Packet Switch Capable (PSC) interfaces:

– Recognize packet boundaries and can forward data based on the content of the packet header (IP header, MPLS shim header).

• Layer-2 Switch Capable (L2SC) interfaces:

– Recognize frame/cell boundaries and can forward data based on the content of the frame/cell header (Ethernet MAC header, ATM VPI/VCI).

• Time-Division Multiplex Capable (TDM) interfaces:

– Forward data based on the data’s time slot in a repeating cycle (SDH/SONET, G.709 TDM, PDH).

• Lambda Switch Capable (LSC) interfaces:

– Forward data based on the wavelength on which the data is received (wavelength, waveband).

• Fiber-Switch Capable (FSC) interfaces:

– Forward data based on a position of the data in the real world physical spaces (port, fiber).

GMPLS control plane – functional components• Resource discovery and link management

– The transaction that establishes, verifies, updates and maintains the LSR adjacencies and their port pair association for their transport (data) plane.

– LSR level resource table: resource map that includes attributes, neighbor identifiers, and real-time operation states.

• Routing

– Topology information dissemination

– Path selection

• Signaling

– LSP creation, modification, deletion, restoration, and exception handling

GMPLS – LSR level resource discovery and link management• Self resource awareness/discovery

– As a result, the LSR resource table is populated with local ID, physical attributes, and logical constraints parameters

• Neighbor discovery and port association

– The process of discovering the status of local links to all neighbors by each LSR in the network, The up/down status of each link, link parameters, and the identity of the remote end of the link must be determined (periodical operation) [LMP].

• Resource verification and monitoring

– Neighbor operation state detection and configuration verification (continuous operation).

• Service negotiation/discovery

– Covers all aspects related to service rules/policy negotiation between neighbors.

GMPLS - Routing

• Topology information dissemination

– Distribution of topology information through the network to form a consistent network level resource view among LSRs.

– What type of information is required?

– How is the information disseminated?

– Triggering mechanisms for information update?

• GMPLS assumes that an IP-based routing protocol is used for topology information dissemination.

• GMPLS extensions have been defined for the TE extended versions of OSPF and IS-IS.

GMPLS – Routing cont.

• Path selection

– Usually a constraint-based computation process, resulting in an explicit route or source route.

– Hop-by-hop routing is also possible.

• Specific constraints on optical layer routing

– Re-configurable (but blocking) network elements such as OADMs

– Transmission impairments

– Absence of wavelength conversion

– Path diversity

GMPLS - IGP Extensions

OSPF and IS-IS extensions to carry additional information:

• switching capabilities of link (PSC, L2SC, TDM, LSC, FSC)

• link encoding (e.g. SONET, SDH, GbE, etc.)

• grouping of links that share same fate (SRLG)

• protection capabilities of link

• incoming and outgoing interface ID

• CSPF extensions:

– take into account new constraints (e.g. link encoding, multiplexing capabilities, etc.)

– compute diverse paths

– compute bi-directional paths

GMPLS - Signaling

• GMPLS inherits all signaling functions from MPLS-TE:

– LSP creation

– LSP deletion

– LSP modification

– LSP exception handling

• Additional GMPLS signaling protocol requirements:

– Creation of bi-directional LSPs

– Support of unnumbered links

– Rapid failure notification

– LSP fast restoration

GMPLS – signaling extensions• Generalized label request

– Supports communication of characteristics required to support the LSP being requested, including LSP encoding, switching type, and LSP payload

– LSP bandwidth encoding values, carried in a per protocol specific manner (e.g. in the CR-LDP Traffic Parameters TLV)

• Generalized label

– Extends the traditional label by allowing the representation of labels that identify time-slots, wavelengths, or space division multiplexed positions, or “anything that is sufficient to identify a traffic flow”.

– Non-hierarchical label.

• Support of waveband switching

– A waveband represents a set of contiguous wavelengths that can be switched together to a new waveband.

– Waveband label contains 3 fields: waveband ID, start label, end label.

• Suggested label

– Is used to provide a downstream node with the upstream node's label preference.

– May reduce latency of LSP setup

GMPLS – signaling extensions cont.• Label set

– Is used to limit the label choices of a downstream node to a set of acceptable labels.

• Explicit label control

– Ingress LSR may specify the label(s) to use on one, some or all of the explicitly routed links for the forward and/or reverse path.

• Bi-directional symmetric LSP

– A symmetric bi-directional LSP has the same traffic engineering requirements including fate sharing, protection and restoration, LSRs, and resource requirements in each direction.

– Downstream and upstream data paths are established using a single set of signaling messages.

– New Upstream Label Object/TLV

• Rapid notification of failure and events

– Acceptable Label Set for notification on label error

– Expedited notification (RSVP-TE only)

• Link protection

– Protection Information Object/TLV indicates:

– The desired link protection for each link of an LSP

– Whether the LSP is a primary or secondary LSP

GMPLS – LSP Protection and restoration

• So far, only intra-area, intra-layer P&R mechanisms for handling single failure scenarios are being discussed.

• Protection schemes:

– 1+1 link protection

– 1:N or M:N link protection

– Enhanced protection

– 1+1 LSP protection

• Restoration schemes:

– End-to-end LSP restoration with re-provisioning

– End-to-end LSP restoration with pre-signaled recovery bandwidth reservation and no label pre-selection

– End-to-end LSP restoration with pre-signaled recovery bandwidth reservation and label pre-selection

– Local LSP restoration

GMPLS extensions to the MPLS control plane – a summary

• Support of devices that perform switching in the time, wavelength and space domain.

• Use of label stacking and the resulting LSP interface hierarchy

• The concept of link bundling

• The new Link Management Protocol (LMP) for automatic link configuration and control

• Computation of physically disjoint paths by use of Shared Risk Link Group (SRLG).

• The establishment of bi-directional symmetric LSPs

GMPLS - LSP hierarchy

• Nesting LSPs enhances system scalability

• LSPs always start and terminate on similar interface types

• LSP interface hierarchy

– Packet Switch Capable (PSC) Lowest

– Layer 2 Switch Capable (L2SC)

– Time Division Multiplexing Capable (TDM)

– Lambda Switch Capable (LSC)

– Fiber Switch Capable (FSC) Highest

LSC

TDMPSC

BundleBundleFiber nFiber n

Fiber 1Fiber 1

FSC CloudLSC

CloudTDMCloud

PSCCloud

LSCCloud

TDMCloud

PSCCloud

ExplicitLabel LSPs

Time-slotLSPs Fiber LSPsLSPs

ExplicitLabel LSPs

Time-slotLSPsLSPs

(multiplex low-order LSPs) (demultiplex low-order LSPs)

GMPLS - Link Bundling

• Allows multiple parallel links between nodes to be advertised as a single link into the IGP

• Enhances IGP and traffic engineering scalability

• Component links must have the same:

– Link type

– Traffic engineering metric

– Set of resource classes (colors)

– Link multiplex capability (packet, TDM, λ, port)

• (Max bandwidth request) (bandwidth of a component link)

• Admission control is applied on a per-component link basis

Bundled Link 1

Bundled Link 2

GMPLS references• Optical Network Service Requirements, Internet Draft <draft-

ietf-ipo-carrier-requirements-05>, December 2002

• Generalized Multi-Protocol Label Switching (GMPLS) Architecture, RFC 3945, October 2004

• Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description, RFC 3471, January 2003

• Routing extensions in support of generalized MPLS, RFC 4202, October 2005

• LSP hierarchy with generalized MPLS TE, RFC 4206, October 2005

• Requirements for Generalized MPLS (GMPLS) Signaling Usage and Extensions for Automatically Switched Optical Network (ASON), RFC 4139, July 2005

• Requirements for Generalized MPLS (GMPLS) Routing for Automatically Switched Optical Network (ASON), RFC 4258, November 2005

GMPLS references cont.

• OSPF extensions in support of generalized MPLS, RFC 4203, October 2005

• IS-IS extensions in support of generalized MPLS, RFC 4205, October 2005

• Generalized Multi-Protocol Label Switching (GMPLS) signaling – Constraint-based routed label distribution protocol (CR-LDP) extensions, RFC 3472, January 2003

• Generalized Multi-Protocol Label Switching (GMPLS) signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) extensions, RFC 3473, January 2003

• Link management protocol (LMP), RFC 4204, October 2005

• Impairments and other constraints on optical layer routing, RFC 4054, May 2005

• Shared risk link groups inference and processing, Internet Draft <draft-papadimitriou-ccamp-srlg-processing-02>, June 2003

GMPLS technology specific references

• Framework for GMPLS-based control of SDH/SONET networks, RFC 4257, December 2005

• Generalized Multi-Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control, RFC 3946, October 2004

• Generalized MPLS (GMPLS) signaling extensions for G.709 optical transport networks control, RFC 4328, January 2006

• Traffic engineering extensions to OSPF for Generalized MPLS control of Sonet/SDH networks, Internet Draft <draft-mannie-ccamp-gmpls-sonet-sdh-ospf-01>, February 2003

• Traffic engineering extensions to OSPF for Generalized MPLS control of G.709 optical transport networks, Internet Draft <draft-gasparini-ccamp-gmpls-g709-ospf-00>, November 2002

ITU-T Recommendations

• G.8080 Architecture for the Automatic Switched Optical Network (ASON) (06/2006)

• G.7712 Architecture and Specification of Data Communication Network (03/2003)

• G.7713 Distributed Call and Connection Management (DCM) (05/2006)

– G.7713.1 Distributed call and connection management (DCM) based on PNNI (03/2003)

– G.7713.2 Distributed Call and Connection Management: Signaling mechanism using GMPLS RSVP-TE (03/2003)

– G.7713.3 Distributed Call and Connection Management: Signaling mechanism using GMPLS CR-LDP (03/2003)

• G.7714 Generalized automatic discovery for transport entities (08/2005)

• G.7715 Architecture and Requirements for Routing in the Automatic Switched Optical Networks (06/2002)

– G.7715.1 ASON routing architecture and requirements for link state protocols (02/2004)

Optical Internetworking Forum (OIF) Implementation agreements

• User Network Interface (UNI) 1.0 Signaling Specification, October 2001

• User Network Interface (UNI) 1.0 Signaling Specification, Release 2: Common Part, February 2004

• RSVP Extensions for User Network Interface (UNI) 1.0 Signaling, Release 2, February 2004

• Intra-carrier E-NNI Signaling Specification, February 2004

Transport-MPLS (T-MPLS)

• Standardized by ITU-T for application in transport part of network only.

• Simplified MPLS: all features not necessary for connection-oriented applications are removed, i.e. less complex operation and more easily managed than MPLS.

• Management principles are adopted from existing standards/practice, e.g. from SONET/SDH.

• Supports - engineered point-to-point bi-directional LSPs, - end-to-end LSP protection, and - advanced OAM.

• Goal is to provide reliable packet-based technology (MPLS) in a form that is aligned with circuit-based transport networking.

T-MPLS (2)

Differences from MPLS:

• Use of bi-directional LSPs traversing the same links and nodes.

• No LSP merging option. (Multipoint-to-point is allowed in MPLS, as in IP). Not allowed in pure connection oriented network.

• No Equal Cost Multiple Path (ECMP) option. Not needed in connection-oriented network.

• No Penultimate Hop Popping (PHP) option. Label must be present in last node.

• (See whitepaper by TPACK: ”Transport-MPLS A New Route to Carrier Ethernet” for overview – or standards).