Purpose of MER on Sky Fibre VDSL2 service

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Purpose of MER on Sky Fibre VDSL2 service

Post by embleton » Tue Aug 21, 2018 5:11 pm

Multiprotocol Encapsulated Routing (MER) is a bridge between the customer modem, DSLAM and Sky's backend from my understanding. And it allocates, in fact, multiple Digital Subscriber Line Access Multiplexor (DSLAM) ports to Sky in a network bridge between DSLAM onwards to Sky to reduce the number of virtual circuits on the internet backbone. This is done to reduce the cost.

When a circuit connection is made to the router it is different than that established to DSLAM and Sky which is 1500 bytes on a bridge to Sky. The traffic between the router modem and DSLAM is Pulse Time Modulation (PTM) a variable length packet size that only passes traffic when the link is passing traffic between modem and DSLAM and even to Sky.

This is important to know because the complete Media Acess Control (MAC) of the router isn't passed between traffic between router and DSLAM to route traffic completely along the path between router and destination at Sky during each packet.

The complete MAC routing over ethernet is built at the router modem and at Sky and is NOT passed between those points, but is passed at the modem WAN and at Sky's end to the final destination, it de-encapsulates the MAC at Sky. And can be seen it is not a route but a complete network bridge between Sky and router, but it is virtual. This is done to reduce cost. But the bridge is virtual and only exists when traffic is passing between WAN and Sky.

On establishing a connection to DSLAM and router a circuit is built to DSLAM using MER; the purpose of Multiprotocol Encapsulated Routing (MER) is to increase the efficacy reducing the overhead between Sky and router modem by not using the MAC address in each packet to route individually packets. But to establish a transparent circuit that does NOT require an ethernet MAC address between the router modem and remote system at Sky. Again this is done for cost.

The Media Access Control (MAC) address data field encapsulates the traffic ROUTING so encoding the routing within the header MAC address between the router and Sky. There is NO authentication between the router and Sky's backend, it is actually at the DSLAM to Sky. The ID is at DSLAM for the customer, all the other information is at Sky's end.

If somebody was to hijack the twisted pair to DSLAM then they have access to the internet...

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