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).