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Multiprotocol Label Switching (MPLS)

Multiprotocol Label Switching (MPLS). References: Juniper white papers on MPLS and DiffServ at: http://www.juniper.net/solutions/literature/white_papers/. Outline. General concepts ATM LSR Ships-in-the-night DiffServ-MPLS architecture Resource provisioning High availability.

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Multiprotocol Label Switching (MPLS)

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  1. Multiprotocol Label Switching (MPLS) References: Juniper white papers on MPLS and DiffServ at: http://www.juniper.net/solutions/literature/white_papers/

  2. Outline • General concepts • ATM LSR • Ships-in-the-night • DiffServ-MPLS architecture • Resource provisioning • High availability

  3. MPLS: General Concepts Outline: • Historic perspective • MPLS basics • ATM LSR

  4. A historical Perspective What happened in mid-90’s? • The problems with overlay models reveal themselves: • Overlay models create bottleneck from the lack of segmentation and reassembly (SAR) functionality on interfaces faster than OC-48 • Overlay models increase complexity by requiring providers to manage two separate control planes and two fundamentally different types of networking equipment • Overlay model results in an inefficient use of network bandwidth due to the traditional ATM cell tax • No QoS for LANE and the IP Diffserv approach to CoS does not map well to the existing ATM QoS mechanims • LANE requires a client-server model in place, e.g., LEC, LECS, LES, and BUS • Classical IP over ATM requires the deployment of n-squared routing adjacencies.

  5. A Historical Perspective (cont’d) • Multi-layer switching solutions in the spotlight: • IP switching by Ipsilon/Nokia • Tag switching by Cisco • Aggregate routing-based IP switching (ARIS) by IBM • IP Navigator by Cascade/Ascend/Lucent • Cell Switching Router (CSR) by Toshiba • All ATM based solutions

  6. IP ROUTER ATM SWITCH ATM-LSR IP Routing Software IP Routing Software ATM Routing & Signaling Software CONTROL Signaling & label binding Longest Prefix Match Label Switching FORWARDING Label Switching MPLS Basics • MPLS switching concept:

  7. ROUTING CONTROL PLANE MPLS CONTROL DATA PLANE SWITCHING CONTROL MPLS Basics (cont’d) • Separation of control functions from forwarding functions:

  8. Ingress LER LSR Egress LER Routing Routing CONTROL PLAN CONTROL PLAN CONTROL PLAN Signaling Signaling LAYER-2 TRANSPORT LABELED SWITCHING LABELED SWITCHING LABELED SWITCHING LAYER-2 TRANSPORT Frames 13 20 MPLS Basics (cont’d) • Label distribution and label swapping:

  9. 0 LAYER-3 0 LAYER-2 1 20 3 1 8 Label exp s TTL MPLS Basics (cont’d) • Generic label and label stacking:

  10. MPLS Basics (cont’d) • ATM Based label and label stacking: 0 0 + VPI/VCI LAYER-3 0 LAYER-2 1 20 3 1 8 Label exp s TTL

  11. MPLS Basics (cont’d) • MPLS signaling protocols: distribute labels and maintain connectivity of an LSP • Topology driven: • LDP: • distributes labels based on routing topology, i.e., label to FEC binding where FEC = IP prefix. • Using TCP and maintaining “hard state”. • No QoS. • Policy driven: • RSVP-TE: Widely deployed • distributes labels based on source routing • Using raw IP and maintaining “soft state” • Designed for QoS • CR-LDP: not well accepted • Distributes labels based on source routing • Using TCP and maintaining “hard state” • Designed for QoS

  12. MPLS Basics (cont’d) • Label distribution mechanisms: • Downstream-on-demand (RSVP-TE, CR-LDP, LDP) • Unsolicited-downstream (LDP) Label Request Downstream LSR Upstream LSR Label Response Next Hop to FEC Downstream LSR Upstream LSR Unsolicited Label Response Next Hop to FEC

  13. MPLS Basics (cont’d) • Label retention modes: • Conservative label retention: • an upstream LSR maintains the received label binding for an FEC only if the label binding is received from the downstream LSR that the upstream LSR has selected as the next-hop for that FEC • Liberal label retention: • An upstream LSR maintains the received label binding for an FEC even if the label binding is received from a downstream LSR that the upstream LSR has not selected as the next-hop for that FEC • Pros and Cons of the two modes?

  14. MPLS Basics (cont’d) • Routing for MPLS • Traditional shortest path based IP routing protocols provide enough information for LDP signaling • Policy driven signaling protocols set up an LSP based on the policy: • A policy may enforce a manually configured route • A policy may use a route found by a constraint-based routing protocol • A policy may use a route found by a shortest-path based routing protocol • Constraint-based routing protocols: • Find “best” routes meeting multiple criteria • Pre-calculate or calculate on-demand

  15. MPLS Basics (cont’d) • MPLS eliminates the potential for SAR bottlenecks by not using ATM as a transport • MPLS eliminates the complexity of managing two separate control planes and two fundamentally different types of networking equipment. • MPLS eliminates the cell tax by not using ATM as a transport • MPLS can support DiffServ CoS. • The peer-to-peer nature of IP routed MPLS eliminates the need to manage a complex logical topology (n-squared PVCs) • MPLS provides flexible traffic engineering features

  16. MPLS Related Research Topics • MPLS multicasting • Pseudo-wire over MPLS • MPLS VPN • MPLS high availability • MPLS Traffic engineering Useful Resources: Go to: http://www3.uta.edu/library/ejournals/ and click on: ACM Digital Library IEEE Xplore

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