What is MPLS? Its a high performance method for forwarding packets through a network. Its a multi protocol because it can work with protocols like OSPF,RSVP,LDP, BGP etc. It uses label (a short fixed length) with packet. All packets with same label use the same path - a so- called label switched path (LSP). Because labels refer to paths and not endpoints, packets destined for the same endpoint can use a variety of LSPs to get there.
Why MPLS? Fast forwarding Traffic Engineering Virtual Private Networks It combines the scalability and flexibility of routing with performance of layer 2.
MPLS Label Format
Label Distribution Protocol Request 56.2 Mapping 0.40Mapping Intf In DestIntf out Label out Intf In Label in DestIntf out Intf In Label In DestIntf out Label out Network X.X /
MPLS Operation Label creation and distribution LFIB table at each router Label switching path and table lookup Forwarding of packet through the network
MPLS Traffic Engineering Optimizes the routing of IP traffic. Routes traffic flows across the network based on resources the flow requires and the resources available. Employs Constraint-based routing Recovers to link or node failures that change the topology. Routing protocol used must be a link state protocol.
ATM ATM is a ITU-T standard for a cell relay wherein information for services is conveyed in small, fixed size cells. ATM is a cell switching and multiplexing technology that combines the benefits of circuit switching with those of packet switching. The cell size in ATM is 53 bytes where the payload is of 48 bytes and the 5 bytes constitutes for the header information. Its a connection oriented duplex communication network.
Why ATM ? Integrated Services High speed Scalable Quality of service Well established industry standard Faster more efficient switching
Cell Header VPI/VCI - Used to route cell to destination 24 bit information, routing significance only CLP - Cell Loss Priority 1: discard first; 0: try not to discard PT - Payload Type Data or OAM (Operation, Administration, Maintenance) Congestion indication End of AAL5 packet GFC - Generic Flow Control (UNI only) local functions
Types of ATM Connections PVC (Permanent Virtual Connections) SVC (Switched Virtual Connections) Fundamental Connections Point-to-point Point-to-multipoint ATM CoS Constant Bit Rate (CBR) Variable Bit Rate- Real time (VBRrt) Variable Bit Rate- Nonreal time (VBRnrt) Unspecified Bit Rate (UBR) Available Bit Rate (ABR)
Connection setup through ATM Connects to B OK Signaling request Connection routed – setup path Connection accepted /rejected Data flow- along same path Connection tear down End system A End system B
ATM Switching Operation InputOutput Receives cell across a link on a known VCI or VPI value Translation table lookup takes place to determine the outgoing port and new VPI / VCI value is assigned. Retransmits cell on that outgoing link with appropriate identifiers
Phase 1: MPLS TE over ATM ( NRT) ATM LSR Edge LSR LC-ATM Interfaces Pagent on R6 R5 ATM 1 Pagent on R2 R1 R4 R7 ATM 2 R8 R3 ATM 3 Pagent Path LSR: Label Switch Router LC-ATM: Label Controlled ATM Links used : OC-3 ( Mbps) 2.1 P a t h 1 P a t h 2 P a g e n t p a t h Path 1 Path 2
Result of Phase 1 Result of Phase 1 MPLS forwarding table with TE configured: MPLS forwarding table with TE configured:
rack7r5#trace Type escape sequence to abort. Tracing the route to [MPLS: Label 27 Exp 0] 92 msec 204 msec 160 msec msec 112 msec * Route taken before change of Tunnels (with Label info): Route taken before change of Tunnels (with Label info): Ping traffic showing packets drop: Ping traffic showing packets drop: rack7r5#ping Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to , timeout is 2 seconds:...!! Success rate is 40 percent (2/5), round-trip min/avg/max = 28/28/28 ms Result of Phase 1: Result of Phase 1:
Result of Phase 1 Result of Phase 1 Ping showing 100% success after change of Tunnels: Ping showing 100% success after change of Tunnels: Route taken after change in Tunnels (with label info): Route taken after change in Tunnels (with label info): rack7r5#ping Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to , timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 28/34/60 ms rack7r5#trace Type escape sequence to abort. Tracing the route to [MPLS: Label 29 Exp 0] 36 msec 36 msec 36 msec msec 16 msec *
Phase 2: MPLS TE over ATM ( RT) Phase 2: MPLS TE over ATM ( RT) Pagent on R6 R5 ATM 1 R4 ATM 2 R8 R3 Path 1 Path 2 ATM 3 Pagent Path R7 T1 Link Callgen R1 Callgen R2 Pagent on R2 PSQM Server R1 GW
Result of Phase 2 Result of Phase 2 Route taken before starting the call: Route taken after change the call: Route taken after change the call: rack7r5#trace Type escape sequence to abort. Tracing the route to [MPLS: Label 16 Exp 0] 152 msec 76 msec 80 msec msec 248 msec * rack7r5#trace Type escape sequence to abort. Tracing the route to [MPLS: Label 32 Exp 0] 36 msec 36 msec 36 msec msec 20 msec *
Results of Phase 2:
During congestion MPLS automatically switches the path to the other path that is under utilized. LS1010 is not working as LSR when configured along with the 3600 series routers with the existing IOS, hence we cannot use SVCs. The success rate of the call increased by increasing the PCR value of the switch. Due to the configuration done codecs G.729 and G.723 also yielded better results when compared to other codecs inspite of their lower bit rate Observations
Goals Effects of link loading and link failure on an ATM network running MPLS Traffic Engineering (TE) Behavior of Non-Real Time Traffic Behavior of Real Time Traffic
Conclusions The PSQM scores obtained were better for all scenarios by configuring MPLS TE with ATM TM. Recovery of links is faster when MPLS TE with ATM TM is used. G.723 inspite of lower bit rate yielded comparably equivalent scores hence for our scenario we would recommend using it.
Future Work MPLS QoS can be implemented on the existing scenario by replacing 3600 series with 7200 series routers. ATM QoS can be implemented by replacing LS1010s with that of MGX 8500 series switches. Implement VPN extending our existing network scenario. Behavior of real time traffic with more number of calls. Measure parameters such as jitter, echo, delay etc.
References MPLS Technology and Applications – Bruce David & Yakov Rekhter Cisco ATM Solutions – Cisco Press RFC 3031
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