Basic Operations Flow for LEC

Figure 9-10 Classical IP over ATM operation flow.

III. Multi-Protocol over ATM MPOA

It can be safe to say that MPOA is the next stage in the evolution of ATM based LAN networking. It is a result of experience gained from LANE and CLIP. The experience with LANE and CLIP revealed some significant deficiencies in the way the standard bodies approached the problem of transition from legacy LAN to ATM-based LAN environment. One of the key deficiencies of LANE and CLIP was the fact that it was still necessary to use classical routers to carry traffic between the logical subnetworks created by these protocols even if the logical subnetworks resided over the same ATM network. As mentioned earlier, these routers cause excessive latency and become the bottleneck points, since every packet has to be individually processed by these routers. In addition, since these routers have to regenerate the packets from ATM cells in order to interpret the packet header for routing purposes, this creates additional Figure 9-11 Communication between two LIS domains. The router concept worked well in the traditional LAN environment when the traffic generated in the LAN segments was IP-based and the amount of traffic that had to go through the routers was a relatively small percentage of the traffic in the LAN environment, i.e., only 20 of the traffic had to go through The solution provided with MPOA eliminates the bottleneck and overhead created by the classical routers by setting up a VC connection shortcut between two end-stations once a traffic flow is detected between them. In other words, the routing function and the physical path are separated from each other to take advantage of the efficiency of ATM-based transport. MPOA allows seamless networking between ATM and non-ATM subnetworks. The authors of this book believe that MPOA will allow ATM to make significant inroads into the traditional LAN world. The key factor in this progress is the fact that MPOA eliminates the problems associated with the classical routers such as excessive latency and bottleneck for traffic flow by separating switching from routing. The power of MPOA comes from the fact that it not only replaces classical routers but provides significant improvements over them. MPOA also addresses another problem associated with CLIP which is the lack of multicast capability. It also extends the LANE’s multicast capability beyond the ELAN boundaries. MPOA provides multicast capability at Layer-3. MPOA is a combination of LANE, NHRP, Multicast Address Resolution Server MARS and Multicast Server MCS. MPOA relies on LANE for Layer-2 bridging between ATM-based LAN segments and traditional LAN segments based on Ethernet or Token Ring within an ELAN logical subnetwork. It relies on NHRP for Layer-3 routing between the logical subnetworks. MPOA also provides a very efficient VLAN platform on an ATM network which may cover large geographical distances. Previous Table of Contents Next Copyr ight © CRC Pr ess LLC