Link aggregation (LNW170 LAN ports)

Overview

Alcatel-Lucent 1665 DMX supports link aggregation on an unprotected LNW170 for any two LAN ports of the same rate (i.e. 100 or 1000 Mbps), operating in switched mode.

When a slot pair is equipped with LNW170 circuit packs, provisioning the slot to the protected state sets the packs to be equipment protected and assigns certain corresponding ports on the companion circuit packs to the same fixed link aggregation groups. When the slot is provisioned to the unprotected state, if the NE is equipped with VLF MAINs, the LNW170 circuit packs are unprotected and the corresponding ports on the companion packs operate independently. If the NE is equipped with non-VLF MAINs, the LNW170 in the slot is unprotected and any circuit pack in the companion slot is alarmed.

Description

Ordinarily, multiple Ethernet links between two bridges form loops (unless a spanning tree blocks all but one) so they can't be used to increase bandwidth. Link Aggregation causes defined groups of links to be treated as a single logical link, making multiple LAN ports appear as one. In this way, Bandwidth may be increased without requiring an upgrade to a higher rate link.

Link aggregation can also remove failed links automatically, thereby providing a means of facility protection. When a link fails, traffic is shifted to the remaining links in that Link Aggregation Group (LAG). More links than are needed can be added to the group and each is active until it fails (similar to utilizing LCAS protection for SONET tributaries). When two links are on different packs they can provide both, facility and equipment protection.

Active/Standby LAG

In Active/Standby LAG, one link of the LAG is designated as the protection link and the other is the working link. Only the working link carries MAC client traffic when none of the links fails. When the working link fails, the traffic switches to the protection link. The protection switching is bidirectional and revertive.

Link aggregation example

The figure below depicts link aggregation on two LNW170 LAN ports functioning at 100Mbps. The top portion of the figure shows two ports receiving separate 100 Mbps inbound flows. The bottom portion depicts the same two flows being equally split across the two outbound ports in the LAG. In this example, no failure has occurred and both ports comprising the LAG are in-service.

Traffic entering incoming ports is aggregated into a LAG. While both ports are in-service, outgoing traffic is split between working ports.

Figure 3-10: Link aggregation at 100 Mbps (all ports in-service)

The instance pictured above represents the ideal case, in which there are at least 2 flows, each a maximum of 100Mbps. In this case they can be equally split over the two ports comprising the LAG. The ability to split two or more flows across multiple ports depends on the distribution of MAC or IP addresses used to identify the flows.

Link aggregation employs an algorithm that assigns traffic flows to member ports to prevent mis-ordering. A given flow can be assigned to only one port and cannot be split across multiple ports in the same LAG. To increase flexibility, Alcatel-Lucent 1665 DMX allows a flow to be defined by either a MAC source and destination address pair or an IP source and address pair. The algorithm uses the XOR of the least significant bits of the address pairs to assign a port/link. Therefore, the actual load balancing achieved depends on the distribution of MAC/IP addresses.

Application advantage

Link Aggregation provides a means of supporting facility protection and bandwidth increases/decreases on LAN ports. Link Aggregation causes defined groups of links to be treated as a single logical link and removes failed links automatically, thereby enabling bandwidth changes and facility protection on 2 paired links comprising a LAG. When the two ports of a LAG are on separate packs, the active-WAN pack (the one selected to send and receive on the SONET network side) is protected against failure by the selection of the second pack. The LNW170 supports this combination of facility and equipment protection.