Link and Multilink Services Overview

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The Multilink Protocol (MP) enables you to split, recombine, and sequence datagrams across multiple logical data links. The goal of multilink operation is to coordinate multiple independent links between a fixed pair of systems, providing a virtual link with greater bandwidth than any of the members.

The JUNOS software supports several MP-based services PICs: the Multilink Services PIC, the Link Services PIC, and the link services intelligent queuing (IQ) and voice services configured on the Adaptive Services (AS) and MultiServices PICs. For more information about link services IQ, see Link Services IQ Interfaces Configuration Guidelines. For more information about voice services, see Voice Services Configuration Guidelines.

Note: The ml- interface type is used to configure interfaces on the Multilink Services PIC and does not support class-of-service (CoS) features. The ls- interface type is used for limited CoS configurations on the Link Services PIC (except on J-series Services Routers), and the lsq- interface type is used for full CoS configurations on the Adaptive Services and MultiServices PICs.

For link services IQ (lsq) interfaces, JUNOS CoS components are fully supported and are handled normally on M-series and T-series routing platforms, as described in the JUNOS Class of Service Configuration Guide. There are some restrictions on J-series Services Routers; for more information on link services IQ configuration, see Link Services IQ Interfaces Configuration Guidelines.

The Link Services and Multilink Services PICs support the following MP encapsulation types:

Multilink Point-to-Point Protocol (MLPPP)
Multilink Frame Relay (MLFR)

MLPPP enables you to bundle multiple PPP links into a single logical link. MLFR enables you to bundle multiple Frame Relay data-link connection identifiers (DLCIs) into a single logical link. MLPPP and MLFR provide service option granularity between low-speed T1 and E1 services and higher-speed T3 and E3 services. You use MLPPP and MLFR to increase bandwidth in smaller, more cost-effective increments. In addition to providing incremental bandwidth, bundling multiple links can add a level of fault tolerance to your dedicated access service, because you can implement bundling across multiple PICs, protecting against the failure of any single PIC.

Note: Even if the PIC can support up to 4xDS3 total throughput, each aggregate can only run a volume of traffic equal to one DS3 in bandwidth. Aggregating DS3 links is not supported.

At the logical unit level, the Multilink Services and Link Services PICs support the MLPPP and MLFR Frame Relay Forum (FRF) 15 encapsulation types. At the physical interface level, the Link Services PIC also supports the MLFR FRF.16 encapsulation type.

MLPPP and MLFR FRF.15 are supported on interface types ml-fpc/pic/port, ls-fpc/pic/port, and lsq-fpc/pic/port. For MLFR FRF.15, multiple permanent virtual circuits (PVCs) are combined into one aggregated virtual circuit (AVC). This provides fragmentation over multiple PVCs on one end and reassembly of the AVC on the other end.

MLFR FRF.16 is supported on a channelized interface, ls-fpc/pic/port:channel, which denotes a single MLFR FRF.16 bundle. For MLFR FRF.16, multiple links are combined to form one logical link. Packet fragmentation and reassembly occur on a per-VC basis. Each bundle can support multiple VCs. Link Services PICs can support up to 256 DLCIs per MLFR FRF.16 bundle. The physical connections must be E1, T1, channelized DS3-to-DS1, channelized DS3-to-DS0, channelized E1, channelized STM1, or channelized IQ interfaces. When you bundle channelized interfaces using the link services interface, the channelized interfaces require M-series Enhanced Flexible PIC Concentrators (FPCs).

Note: When running MLPPP or MLFR on a non-QPP interface, you cannot mix logical units that are members of an aggregate with logical units configured using other families, such as inet. For example, the following configuration is not valid:


                           
                              interface e3-0/0/0 {
                              encapsulation frame-relay;
                              
                                 
                                    unit 99 {
                                    dlci 99;
                                    
                                       
                                          family mlfr-end-to-end {
                                          bundle ls-0/0/0.1;
                                          }
                                       
                                    
                                    }
                                 
                              
                              
                                 
                                    unit 100 {   ## mixes mlfr with family inet
                                    dlci 100;
                                    
                                       
                                          family inet {
                                          address 192.168.164.53/30;
                                          }
                                       
                                    
                                    }
                                 
                              
                              }

The standards for MLPPP, MLFR FRF.15, and MLFR FRF.16 are defined in the following specifications:

RFC 1990, The PPP Multilink Protocol (MP)
FRF.15, End-to-End Multilink Frame Relay Implementation Agreement

FRF.16.1, Multilink Frame Relay UNI/NNI Implementation Agreement

Note: Endpoint Discriminator Class compatibility checking is enabled on MLPPP interfaces. Prior to JUNOS Release 8.0, when a Juniper Networks router received an unsupported Endpoint Discriminator Class message from an MLPPP session peer, it returned an ACK response.

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