Schematic view of TDM-based RAN
Schematic view of MPLS-based RAN
The traditional sets of network segments from the access to the edge and core layers
The comparatively simple management of an end to end seamless MPLS architecture
About 1.2 billion active mobile broadband subscribers worldwide, according to ITU data, are using bandwidth-intensive applications such as cloud computing and video telephony, placing significant demands on network reliability and profitability — no surprise to service providers the world over.
But how can the paradox between demands on legacy platforms and cost pressures be overcome effectively?
Convergence and network simplification have been hallmark trends in general for service providers in recent years — one common platform for business, residential and mobile subscribers. Access networks could also benefit from consolidation, but this has remained a challenge due to the disparate technologies developed for mobile, residential, and business access.
Instead of relying on separate access devices to connect customers, operators want to converge access networks to deliver both a more predictable experience to users and better economics to shareholders.
The varieties of network access have evolved over time, from circuits to packets, TDM to IP/ethernet, and from wireline to wireless. So it is only natural that there are multiple access networks for different applications with many touch points, but this reality leaves operators with an obvious management challenge.
Many of the responses — also logical, given the choices available — have focused on adding capacity in the form of point-to-point bandwidth from access to aggregation, with the only innovation being to replace TDM with ethernet. Truck rolls are typically required for minor operational changes, and there is inconsistent quality in telephone calls — jitter, dropped calls — and internet access connections.
As more and more access connections require wireless support, the challenges facing mobile operators have become a paramount concern. These challenges range from the rising tide of packet traffic, to the underlying transport technology and the management of the end-to-end network.
Challenges for mobile operators
The main challenges in optimising backhaul have to do with the multiple network layers at Layers 1-3; there are many transport technologies and protocols, and access infrastructures that span multiple generations.
The movement from voice-oriented TDM technology towards data-centred IP/ethernet is part of this trend, as is the presence of many generations of mobile equipment, from voice-oriented TDM technology to data-oriented IP/ethernet, including 2G and 3G legacy as well as 4G and LTE adoption.
In addition to the traditional cellsites, there are many small cell network deployments, and peak backhaul capacities for all locations will increase significantly over the next couple of years, including urban and non-urban macrocells, as well as both indoor and outdoor small cell access deployments.
Other large issues include the need to handle diversion of traffic that can be offloaded to either WLAN or wifi public networks, and maintenance of the strong financial and strategic balance that is needed in building access networks. The balance is tipping to IP/ethernet, as well as to MPLS in the access layer.
In fact, according to Infonetics Research’s Small Cell and LTE Backhaul Strategies: Global Service Provider Survey, published in November 2011, by 2013 a majority of mobile operators and transport providers will have over 90% of their cell sites connected with IP/ethernet and 70% of mobile operators plan to use MPLS at their cell sites.
Furthermore, all mobile operators plan to extend MPLS from the provider edge to the access layer. Clearly, there is a recognized requirement to have more intelligence in the access segment of the provider network. Convergence is a major driver here — with explosive traffic growth, independent solutions for mobile, residential and business are too costly and difficult to manage.
Against this backdrop, the rise of packet-oriented data traffic continues at a rapid pace, overloading the existing mobile network infrastructure and causing major bottlenecks in mobile backhaul. The existing architecture will not scale, which leads to the desire for more intelligence in the access layer, especially in mobile backhaul.
Role of management in the access layer
Access networks are inherently difficult to design and manage, because they are very dependent on geography and there are many choices of locations and the need for many “satellites” in the field, away from central hub locations that can aggregate the traffic.
A key consideration in the design of access networks is how to manage all of these devices. One solution is to have a single point (hub device) for operating, provisioning, monitoring, logging and maintenance of the “satellite” devices (which may number into the thousands). This can occur on either the control plane (network element operating system), management plane (an NMS), or a hybrid.
To get an idea of the topological advantages of MPLS intelligence in the access layer, consider a mobile access example. In the existing TDM RAN shown in the diagram, the base stations do not connect to each other at all; dozens of these base stations would be “homed” — or assigned — to an existing controller.
In particular, the mobile RAN has a wide range of interface and protocol types, and there are new network elements introduced with each generation of mobile specifications — 2G, 3G, 4G/LTE and so on.
There are similar, although not as diverse, disparities in residential access — ATM and ethernet. Still, the flexibility of MPLS is attractive in the access network, as it allows a simpler and more flexible end-to-end provisioning model than any previous solution, whether based on TDM or point-to-point ethernet.
The second diagram demonstrates that it is more bandwidth efficient and cost effective to have an MPLS-based network aggregate traffic from multiple base stations and transport it to the controller. That way, if base stations have to be reassigned to a controller, a configuration change can handle the re-homing task.
The role of seamless MPLS
MPLS has long been the transport architecture of choice in both core and edge networks — in the core with high capacity transport label switched paths (LSP) and in the edge with Layer 2 and Layer 3 VPN services, including VPLS and point to multipoint LSPs. The access network, however, is more complicated than the core in both size and complexity.
The third diagram illustrates service provisioning in a traditional network; there are two different segments provisioned in the access and aggregation layers, and another one in the core. There are multiple control planes controlling these network segments. Even if these segments were all LSPs, they still might be separately provisioned LSPs held within the boundaries of the regions (clouds) shown within the diagram—multiple provisioning points, more difficult to maintain.
In a seamless MPLS network, all forwarding of packets within the network, from the time a packet enters the network until it leaves the network, is based on MPLS.
As shown in the fourth diagram, there is a single provisioning point per connection with the notion of a single LSP across the access nodes in a network-wide single MPLS domain. Minimising the number of service provisioning points further enables decoupling of services architecture from the underlying topology and transport.
With seamless MPLS, the idea is to provision the service end-to-end to minimise the number of provisioning points. The service provisioning is aligned with the network architecture, and maintains simplicity in the access network.
Achieving this relies on increased capabilities and intelligence on the service nodes (traditional PE routers); at the same time, it also simplifies operations and makes efficient use of network resources by reducing the number of provisioning points and relying on a single MPLS-based domain forwarding in the data plane.
For service providers it is all about improving the user’s total experience while also improving the economic viability of the mobile network through a combination of improved revenue generation and lowered operating costs. GTB
David Noguer Bau is head of service provider marketing EMEA at Juniper Networks
For more information, see the papers entitled Seamless MPLS and Building Multi-Generation Scalable Networks with End-to-End MPLS (www.juniper.net )