Multiprotocol Label Switching (MPLS) References: Juniper white papers on MPLS and DiffServ at: white_papers/

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

MPLS: General Concepts Outline: Historic perspective MPLS basics ATM LSR

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.

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

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

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

MPLS Basics (cont’d) Label distribution and label swapping: CONTROL PLAN LAYER-2 TRANSPORT LABELED SWITCHING CONTROL PLAN LABELED SWITCHING CONTROL PLAN LAYER-2 TRANSPORT LABELED SWITCHING Frames 1320 Routing Signaling Ingress LEREgress LER LSR

MPLS Basics (cont’d) Generic label and label stacking: LAYER-2 LAYER-3 Label expsTTL

MPLS Basics (cont’d) ATM Based label and label stacking: LAYER-2 LAYER-3 Label expsTTL VPI/VCI +

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

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

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?

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

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

MPLS Related Research Topics MPLS multicasting Pseudo-wire over MPLS MPLS VPN MPLS high availability MPLS Traffic engineering Useful Resources: Go to: and click on: ACM Digital Library IEEE Xplore