What are the proc and cons of having a SP network with multi ASs (IP/MPLS core in AS #1 and regional Carrier Ethernrt Aggregation networks in different ASs: AS#2,3....) vs. single AS (multi area with OSPF)? What are the criterion for this selection? What is the impact on the aggregation (IP/VPN, Internet, Voice) from Access Gateways (MSANs and DSLAMs), WiMAX BTSs, Node Bs and end to end delivery of VLL and VPLS services accross multi ASs with dual homing?

udunuwara - 13 July 2009 05:18 AM

What are the proc and cons of having a SP network with multi ASs (IP/MPLS core in AS #1 and regional Carrier Ethernrt Aggregation networks in different ASs: AS#2,3....) vs. single AS (multi area with OSPF)? What are the criterion for this selection? What is the impact on the aggregation (IP/VPN, Internet, Voice) from Access Gateways (MSANs and DSLAMs), WiMAX BTSs, Node Bs and end to end delivery of VLL and VPLS services accross multi ASs with dual homing?

it is all about tradeoffs in your network to do with scale and protocols.

A multiarea topology will scale better - whether that is relevant depends on how many nodes will be in the topology, what kit you use and so on.

However some protocols do not work well across multi area topologies - RSVP-TE is one that has caused problems before, so it matters how you plan to structure your network core. If bandwidth is plentiful and cheap to scale up (ie you have your own lambda transmission) then you might just over provision the network rather than use more complex protocols.

And finally IS-IS is often thought to scale better than OSPF within a single area - but i do not have any real numbers to back that up.

Stephen

I think it mostly depends on the network size and if the provider network span multiple operator networks. If it spans multiple operator networks, obviously, it needs to span multiple AS. Otherwise, it's only a scalability issue. Although it's possiable that the provider apply different routing policy in aggregation and core, it seems to me that's infrequent. But I still would like to know if there is really such case, for some other reasons, the provider deploy multiple AS. Anybody comments it?