Tejas XTN Solutions for Mobile Backhaul
Introduction
In addition the legacy services still bring a large share of revenue for brown-field service providers and must be supported on newer architectures. Service providers must continuously launch new revenue generating data services and these must be supported by the transport infrastructure. All these challenges and how Tejas provides solutions to address these requirements are discussed in this paper.
Key Operator Challenges
Fast 3G roll out: The operators who win 3G service licenses want the 3G services to be launched as soon as possible. Every month of delay causes them to lose potential revenue and also pay interest on the spectrum licensing fee. Their existing 2G infrastructure is TDM based and leveraging it to deliver the data services is key for this, and yet a major challenge.
No Disruption of the existing 2G traffic: The launching of the 3G services through the existing infrastructure should ensure that there is no disruption of the 2G services since 2G services form the major part of the service providers revenue. It is estimated that even by 2015, 60% of the mobile connections will be running on 2.5G (Source: Ovum).
Capex Optimization: Since the operators spend substantial capital for their 3G licenses, they may not be able to spend heavily on the network upgrades for 3G services. In addition operators are not sure about how much revenue will come from 3G and investing heavily on 3G infrastructure puts that capital at risk.
Legacy 2G Infrastructure: Traditional (2G/2.5G) systems did not assume any data support from the backhaul infrastructure, and relied on encapsulating data traffic into ATM which were carried by E1 circuits. However this approach is not suitable for 3G firstly due However this approach is not suitable for 3G firstly due bursty nature of data traffic. A statistical multiplexing based packet transport solution is needed.
Smooth Migration from Voice to Data: The universal trend in telecom is the migration from voice to data based services. This transition will happen slowly, and managing the transition phase is really important. Building two parallel networks, one for voice and one for data is not efficient both in terms of capex and opex. Also even if two parallel networks are run, integration is a major challenge as at some places data is carried over TDM and in other parts of the network TDM has to be carried over Data.
Support for new 3G/4G Data Services: A lot of new data services are being launched by service providers, which services are being launched by service providers, which base. However these services require certain network parameters to be met, if the user has to get a satisfactory or good quality of experience. For eg, a gaming user, although his bandwidth requirement is not high, he’ll expect an extremely low latency. Similarly a VOIP or Video Call user will require a bandwidth guarantee and low jitter for a good quality of experience. These different parameters should be supported and configurable on a per service basis from the underlying network, in order to give a good Quality of Experience to the end-user.
Tejas Solutions for 3G Backhaul
This section addresses how each of the operator challenges have been addressed by Tejas.
2G Network Optimization Suite for Fast 3G rollout: The Key to fast 3G rollout is leveraging the existing infrastructure and optimizing it for bandwidth use. This can easily help delay the 3G upgrades by 2 to 4 quarters and help the operator buy more time to scale up. Tejas brings the following innovative features on it’s platforms to help leverage the existing TDM infrastructure:
2G Network Optimization Suite for Fast 3G rollout
1. Ethernet Over PDH (EoPDH): Most of the BTS to RNC connectivity is over microwave and out of this a major part is
over PDH radio. 3G NodeBs typically handoff data traffic as Ethernet. Tejas supports EoPDH aggregation to carry this data traffic over PDH microwave Several such lines will reach the the RNC and the Ethernet traffic will be extracted from these E1 lines and handed to the next level of transport in the Ethernet form. EoPDH line cards can aggregate upto 128 EoPDH links into a single GigE handoff at the hub location. The aggregation cards can be run in a 1+1 redundant configuration for higher reliability. This solution saves the operator from upgrading the microwave links from PDH microwave to EthernetMicrowave on day one.
2. Double bandwidth Protected Ring (DBPR): The cell sites/BTS have point to point microwave links that carry the PDH traffic which are protected by dedicated links. As the bandwidth crunch increases due to the introduction of the 3G
services, it would be of great value addition if the protected bandwidth could be used for carrying extra traffic. Since
data traffic is bursty and can withstand a graceful degradation, a solution of dedicating only a few protected TDM circuits to data traffic and carrying the rest as extra traffic on the protection bandwidth would offer very high value to the operator. DBPR does exactly this, by being able to run a shared protection bandwidth ring between the nodes. This ring can be used to carry data traffic when work path is up, but will be used for TDM traffic in case of a failure. This
effectively doubles the bandwidth available on the ring by making the protection bandwidth available for extra low priority (mostly data) traffic.
3. Ethernet Ring Protection Scheme (ERPS): Existing 2G network provide support SNCP and MSSPRING protection for 50ms protection of data traffic. A similar protection is needed for data traffic. ERPS provides the ability to build 50ms protected Ethernet rings in the network. Tejas integrates it with TDM so that these protected rings can run over bandwidth carved out of TDM capacity (either dedicated VC12s or from DBPR). Deploying ERPS in the network has many advantages:
a. 50ms protection : Provides 50ms protection on packet rings
b. Doubles Bandwidth: Since ERPS can use both sides of the ring to carry traffic, it effectively doubles the bandwidth available on the ring. Thus a 21xVC12 bandwidth carved out of SDH will give a total ring capacity of 84Mbps ( 42Mbps on each side).
c. Shared Bandwidth: Enables sharing of ring bandwidth between different nodes in a ring. If one BTS was pumping lots of traffic while other BTSes are idle, then the entire packet ring bandwidth (84Mbps in the above example) is available to this BTS.
d. Dual Homing: Tejas enables the ERPS ring to be terminated onto two different gateway nodes, without having to close the ring. This helps protect against a single gateway failure by switching the traffic to the second gateway.
Tejas POTP Technology for Smooth TDM to Data Migration
Tejas provides a hybrid platform which supports both 2G and 3G services. The 3G services can be provided through
additional Ethernet blades in the platform which supports Ethernet services by EoSDH through the existing fibers without
affecting the existing 2G traffic. As the density of the Ethernet traffic increases, in the future, separate Ethernet links
can be subtended through these cards and run along the TDM fibers. Further when a phase where the majority of the
traffic is data traffic, the traditional TDM services can be transported through Ethernet links with features like SYNC-E
and CES (Circuit Emulation Service).By this the existing TDM links can be reclaimed for Ethernet traffic.
The various stages of network evolution are shown below
Phase 1: Ethernet traffic from base stations is mapped into existing TDM links with GFP, VCAT and LCAS. Tejas provides all key packet processing to efficiently utilize these links.
Phase 2a: As data traffic increases client ports on ELAN cards are commissioned as aggregate links. These are connected on new pair of fiber or additional CWDM/ DWDM wave and add capacity to the network. For this stage, no hardware upgrades are necessary and no existing services are disrupted
Phase 2b: As the network capacity gets exhausted, a few more client interfaces can be commissioned over yet more
fibers/CWDM/DWDM waves. These new links work in a load sharing manner and meet the growing demands of the market.
Phase 3: Major part of the traffic is data and very little legacy Voice traffic exists. Major part of even 2G services have
been moved to VOIP and the requirement for TDM is minimal. In this case, the TDM fiber capacity can be reclaimed and
used for more data traffic. The few TDM circuits are supported through circuit emulation.
Key Benefits
Capex Optimization: Tejas understands that in today’s environment of tough competition, operators try to keep their capex small and prefer to finance their capex from their existing revenues. Tejas provides the modularity and flexibility required for a service provider to deply the POTP family as a primarily TDM platform today, but as data services grow, he can add more modules to the same chassis to scale the data services. Also, the POTP platform uses a distributed switching architecture, so that the operator does not have to buy the entire switching capacity at one go, but can add packet switching modules, which together can work as a larger capacity switch. Thus Tejas provides a build as you grow model and reduces the risk on the 3G capex.
Carrier Class Data capabilities: Several advanced capabilities and features are required to meet the challenges of Transport Networks. Tejas supports best in class packet capabilities on it’s POTP platforms, like 50ms protection in ring and mesh topologies, hierarchical QoS, connection oriented Ethernet, traffic engineering and SLAs, advanced OAM and security features. These features are key to the transport network meeting the required SLAs and to scale up to support millions of services.
Seamless Integration of TDM & Packet: Tejas POTP platform is built in such a way that the operator no longer has to worry about how much TDM and how much packet to configure on his network element. With support for EoS, any excess TDM capacity can be used for carrying data traffic. Similarly with support for Circuit emulation, any excess data capacity can be used to carry TDM traffic. This also offers flexibility to the service provider since he can build heterogeneous TDM or packet based networks (from the same platform), and many times a TDM circuit or a data service can be traversing many TDM and packet subnets in the network.