 If you recall, in traditional networking, when we teach you computer networks at the undergraduate level, we introduce the concept of network as either a local area network or a metropolitan area network or a wide area network. And so far, we actually thought about Ethernet as a technology that was meant to be at the local area. But the concept of Metro Ethernet is to scale up the overall coverage of Ethernet to metropolitan and it's known as Metro Ethernet or the carrier Ethernet. So in this module, we'd look at the need which governs Metro Ethernet adoption, some interesting issues which emerge and the unique characteristics which are expected out of Metro Ethernet. And this would certainly be achieved through adopting certain modifications to Ethernet as such. First of all, when we look at IEEE 802.3 and Ethernet, these two medium access control technologies are quite similar and these have been around for a very long time on the access side. But on the core side, most of the infrastructure that the telecom operators provided both at the core and the long haul transport networks was the SDH synchronous digital hierarchy. It was TDM based multiplexing technique that allowed the different users to aggregate their traffic. Certainly, there was a requirement to achieve certain bitrate by using bit stuffing and padding and certain other means. But anyways, TDM based multiplexing technique was performing very good and it had its own advantages. But since Ethernet basically is a technology that has been there on the on the on the access side for a very long time. So the Metro Ethernet forum as mandated by the by the ITUT started working on the development of Ethernet as the last mile or couple of last miles technology. So it means now the scope is no more restricted to 100 meters or 200 meters that we typically assume in a local area network, but it had to now be considered for such large geographical coverage. The benefits surely which were expected out of Metro Ethernet adoption were that it is already there on the on the core network. Different service providers have their internal architecture based on Ethernet. And the equipment is low cost and the Ethernet technology requires minimum maintenance and operational cost. So with these benefits, Metro Ethernet is now all set to be adopted. However, there are certain issues and certain desirable characteristics which are expected out of Metro Ethernet. First of all, Ethernet is a probabilistic medium access control scheme. So the Ethernet end users always envy the performance of TDM based networks. So once Metro Ethernet had to be provided over large geographical area and as a probable replacement to the time division multiplex technologies like SDH. So Ethernet users actually were expecting that we'd be given same level of performance that our past technology was like SDH. So actually Ethernet had to be rehashed and it had to be rethought altogether. And the network which is covering an area of few miles is Metro Ethernet network or the carrier Ethernet. So it is equivalently known as MEN or carrier Ethernet CE. The required characteristics of Metro Ethernet are that it has to support scalability. As we know that Ethernet is a probabilistic scheme and the efficiency of Ethernet is directly dependent upon the total number of users which are active in LAN. So now that lots and lots of customers had to be accommodated and the customers are enterprises, each enterprise with its own internal network. The network operators had to think to provide broadband access to many subscribers in a given metropolitan or a geographical area. The next concern is providing quality of service. Surely comparing it to a deterministic scheme Ethernet is not very good in providing quality of service. So the expectation that naturally emerges is that the carrier Ethernet should now provide the same performance guarantees in terms of throughput and delay. Incidentally throughput and delay are never guaranteed in Ethernet as such because it depends on the user occupancy and the user traffic. So now it had to be thought. So the TDM based access was the gold standard. So the quality of service actually had to be brought closer to and if not better to the TDM based lease lines on the on the access side. Because when a certain corporate or an enterprise subscribes to a service through certain service level agreement or SLA then the expectations of user are quite high. So providing quality of service commensurate to those expectations is a challenge. Then comes reliability. Typically in telecom sector the core and the access network equipment that is on the central office is there with some redundancy to achieve a very high availability. So five nights availability actually means a downtime of five minutes a year. That actually means that if you want to provide the same level of reliability to the to the metropolitan Ethernet network then it actually has to be compared to how SDH provides reliability. And if if at all there is a link breakage then some kind of link redundancy has to be provided and the recovery time from that failure that is the mean time to repair should should not be deviating much from the 50 milliseconds benchmark. Then we have the service management service management actually implies that once a certain contract has been signed between a service provider and service consumer then continuous monitoring of service provisioning has to be ensured to determine the quality of experience. So there are certain tools which are needed to monitor the performance live. There are certain parameters as we earlier agreed on throughput delay jitter packet loss etc. So these services are observed and monitored against these parameters for the end users. So it means that the service management has to be done now on the exercise. And lastly backward compatibility that we term as the emulation of TDM service since the leads lines are still around which are based on the time division multiplexing. And these leads lines are still an option for some of the corporates and enterprises. So it means that the metro ethernet network or the carrier ethernet actually has to integrate in a very transparent manner with these leads lines. So the service should not be affected end to end whether it is being provisioned between two endpoints one on the on the metro ethernet network and the other one on a lead line.