Enterasys Networks X-PeditionTM manual Multi-Class Mlppp

PPP Features

•Fragmentation/reassembly

•Detection of fragment loss

•Optimal buffer usage

•MTU size determination

•Management of MLPPP bundles

•MIB support for network management

•Up to four T1/E1 lines can be aggregated running MLPPP

•Multi-class MLPPP for up to five multiple sequence number streams over one MLPPP bundle

Multi-Class MLPPP

The Multi-Class extension to Multi-link PPP, as defined by RFC-2686, provides a means of transmitting multiple sequence traffic streams over one Multi-link PPP bundle on a Multilink or Dialer interface. Multi-Class offers best-effortQuality of Service (QoS) to minimize delay and fully utilize bandwidth over each member link ensuring that high priority traffic such as real-time voice and video packets is transmitted with minimum delay. The XSR’s implementation of Multi-Class MLPPP supports the following features:

•Multilink Maximum Received Reconstructed Unit (MRRU). This non-configurable feature is set to 1500 bytes by default.

•Multilink Short Sequence Number Header Format is non-configurable but allows lower priority traffic classes to be suspended in favor of higher priority classes when necessary. The XSR defaults to the long sequence number header format but is passive - if a peer requests the short format the router provides a short sequence number. The Suspendable (class) level for negotiation is defaulted to 5. The XSR will accept any lower Suspendable (class) level negotiation and reject any larger levels.

•Endpoint Discriminator is configurable to specify a class with the ppp multipoint endpoint command.

•Multilink Header Format is enabled with the ppp multilink multi-classcommand.

The benefits of operating Multi-Class MLPPP are as follows:

•Fragment interleaving with different classes (priorities).

•Multiple suspension (class) layers to accommodate multiple priority classifications and packet interleaving.

•Full bandwidth utilization across the bundle since all fragments with different priorities can be sent over any member link without violating the order of packets sharing the same classification.

Multi-Class is limited in that it does not provide a method for packet classification, relying on an external method - QoS - to prioritize the output packet stream with certain criteria. QoS currently supports up to four types of classification via ACLs. While MLPPP supports sending packets outside MLPPP with no fragmentation and no MLPPP header by default, the total level of prioritization supported is five for QoS, the same as that (four suspendable levels) available in Multi-Class MLPPP.

If the negotiated Multi-Class level is less than the number of classes set by QoS, MLPPP will fit the QoS class type into the MLPPP Multi-Class number according to the principle that the higher priority QoS class type will fit into a higher Multi-Class class until the Multi-Class number 0, which will contain any remaining QoS low priority classes.

XSR User’s Guide 8-5