Transmission Trends - Greater deployment of optic fibre networks
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What are the key new transmission technologies being adopted by your organisation?
Vijoy Kumar
Some of the key transmission technologies/media include optic fibre, microwave and satellite. In the case of optic fibre cable (OFC), we are using the latest technologies like DWDM, which provides high bandwidth. Once OFC is laid we can later add electronics at both ends to avail of high bandwidth speeds. Meanwhile, microwave media is now being increasingly preferred by operators as microwave links eliminate the cost of digging up roads for fibre and resolve the issues that arise in getting the requisite clearances from the municipal departments. More importantly, network deployment is faster using microwave. It also leads to reduced capex for operators since the latter have to erect a tower to install a BTS. So it is easier and more cost effective to install an antenna on the same tower. Various technologies can be deployed on top of the microwave to avail of higher bandwidth. Finally, satellite technologies like VSAT are a cost-effective way of providing connectivity in areas with difficult terrain like hilly regions and forests.These are also used to connect rural areas.
Kuldip Singh
Mahanagar Telephone Nigam Limited (MTNL) was the first telecom operator to deploy IP over multi-protocol label switching (MPLS) in the city. The technology permits the transmission of various signals within a given quality of service on the IP network, which is carried over MPLS at the MPLS core. So, we have deployed a core and an edge router where various equipment requiring backhaul can be connected in the core. This is converted into IP and is then carried over IP with an MPLS core.
This enables us to provide the quality of service required for real-time video signals or audio communication. It also provides backhaul for data. Backhaul is common within voice, video and data; so one can provide services to the end-user. This is the advantage of this technology.
The only problem is that of synchronisation, which arises since conventional time-division multiplexing (TDM), which requires synchronisation, cannot be used. For this, we are looking at alternative technologies.
Arun Sur
Reliance Communications has 165,000 km of OFC. In my opinion, the national network should be built on fibre optic photonic technology. As a step in this direction, we started our implementation on fibre optic only with SDH in 2001-02. Gradually, we evolved to DWDM technologies to avail of high bandwidths (each lamda is 10G). We have already implemented DWDM throughout the national express ring network intervening with high definition technology and high capacity density cross connects. On an average, each ring has 10 lambdas which can go up to 40 lambdas. We have got these cross connects located at very strategic nodes so that we can route the network traffic in the event of a fibre optic disruption. In the case of DWDM technology too, we have an evolved version known as common photonic layer (CPL) technology, which can tolerate slightly more loss in fibre optic communications. We experience 10-12 cable cuts in the long distance network. With each cable cut, there is a loss in the cable because of splicing and jointing. But all DWDM technology is very loss sensitive. Sometimes, over the years, the loss gets accumulated and it becomes difficult to communicate from one point to the other when the loss is above 24 or 25 db. CPL technology has a method of overcoming this problem. We have SDH, DWDM and CPL technologies in the TDM domain but we are now evolving to all-IP technology even on long distance voice communication. With the evolution of technology, the core switching is gradually evolving to new generation networks with large-scale introduction of soft switches paving the way for an IP path for bothGSM and CDMA voice communication.
We have introduced an RDN network, which has two layers. One layer deals with voice as well as with the VPN of enterprises. The second layer, the RIN network, carries the data traffic of the internet and is the base for carrying 3G/4G traffic like HSDPA or LTE. We have implemented a very robust, high capacity national backbone network on fibre optic on DWDM/CPL/high definition technology on multi-lamda bandwidth. We are carrying the voice through our RDN network technology.
What are the key trends in transmission?
Vijoy Kumar
With the movement towards IP, the transmission architecture required will remain largely unchanged. However, different types of equipment will be required to transmit IP. In addition, there is likely to be a movement towards greater deployment of optic fibre networks as operators trial technologies like LTE and accelerate the rollout of 3G networks. This is because with these technologies, the speed requirements will result in a demand for higher bandwidths which technologies like VSAT cannot support. For instance, while VSATs provide speeds of up to 2 Mbps, in LTE speeds are upwards of 36 Mbps. Even in the case of microwave links, there will be bandwidth limitations. Only optic fibre networks and technologies like DWDM that ride on it will be able to support these speeds.
Kuldip Singh
There are primarily two evolving technologies. One is based on carrier Ethernet and the other is based on MPLS transport. Both technologies address difficulties in legacy systems, such as synchronisation. Carrier Ethernet and MPLS both address the problems of synchronisation.
Arun Sur
Every transmission space is going for metro Ethernet technology. In this respect, we are in the right direction. We have adopted metro Ethernet technology for serving enterprise and retail customers. We have adopted a soft switch new-generation network capable of carrying cellular voice and data traffic on IP.
The government has allowed sharing of transmission systems.What are the developments on this front and how has the move impacted operators?
Vijoy Kumar
Sharing any type of resource, whether passive infrastructure like towers or active infrastructure like transmission media, is always welcome. It is a win-win situation for all operators as it leads to substantial reductions in capex. However, the government will need to address regulatory issues to ensure that backhaul transmission sharing can yield the requisite benefits.
Kuldip Singh
We are open to sharing our transmission network with anybody, but we have so far not received any enquiries from interested operators. This is a good opportunity for operators. I do not know why sharing has not taken off yet, because in Delhi and Mumbai, it is very difficult to lay fibre and create a backhaul because of the difficulty in digging and laying cables. I think that if you have the capacity in the backhaul, operators can utilise it and this can be an opportunity for both newcomers as well as operators who have backhaul, since they can derive revenues from it.
Arun Sur
Any new operator entering the market finds it very difficult to launch services. Consequently, what is happening is that new operators are not building infrastructure, instead, they are going in for infrastructure sharing, which involves sharing of the active infrastructure, the power, the tower and the shelter. At the same time, they are sharing the transport systems of various existing operators. Every new operator is relying on someone else's transport system.
What are the key issues as far as the performance of core transmission networks is concerned?
Vijoy Kumar
First, the stability of transmission media is important. Stability is determined by parameters like bit error rate. Second, synchronisation is always a key issue in the case of transmission media. With most transmission now being digital, as opposed to analog earlier, the networks of all operators need to be synchronised. Kuldip Singh Any transmission network requires that the operator should be able to give the requisite quality of service to different signals. For example, if you have data applications – there being an inherent difference between data and voice – you cannot afford to miss any data, as nothing will work. In the case of voice, it does not make as much of a difference. But voice has to be real time and cannot be delayed. When I talk, you have to hear me immediately to make sense. Thus, the requirements are different. Data can wait but it has to be 100 per cent correct. Voice can do if a certain number of words go missing, but it cannot wait, it has to be in real time. So any transmission network should be able to support correction in data and lose no packets while providing the requisite priority to the real-time action required for voice.
An MPLS IP network is able to do both things. We have deployed this in Delhi and Mumbai. We were the first to deploy the technology four years back and we are carrying video and voice signals from that.
The only difficulty is that the technology cannot be used for last mile backhaul for the legacy network, which requires TDM synchronisation. For this, we need carrier Ethernet or MPLS-based transport.
Arun Sur
India is at a stage of rapid road infrastructure development. All the fibre optic cables were laid on the side of the national and state highways. These roads are now being dug up for increasing the number of lanes. This is causing 10 to 14 cuts of cable every day. To ensure that communication does not suffer, resiliency in the network in the form of various protection mechanisms is implemented. This includes SNCP and BLSR technology, which allows the traffic to flow in spite of fibre cuts.
The power situation in India is also not good. All the transport nodes need DG back-up and many have DG back-up in addition to battery back-up. In many places, usable power is available only for a few hours. However, the present-day electronics technology is quite robust and component failures are few and far between.
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