Better backhaul with MPLS to the cell site

2011 has left the North American mobile operators breathless. A wide adoption of smart phone, exponential increase in smart devices (phones , tablets, game consoles), and rapid growth of smartphone applications have compounded to make the mobile economy very dynamic.  Mobile data usage and the LTE deployment trials have driven operators’ to address bandwidth shortages for mobile backhaul.

More importantly, carriers are now faced with the realization that there is true need for network change to support the troika of the new mobile economy tsunami:  How to manage and adapt their networks to support the convergence of Mobile broadband, smart device growth and applications adoption.

The first quarter of 2012 was no different, with exciting applications like Instagram being added to Android (later acquired by Facebook) or Apple announcing iPad3 with LTE connectivity.  The rapid rise of smart devices and applications acceptance has been staggering

Other markets are also following, some with slightly different characteristics, for example the Asia Pacific market where in many countries the mobile device is the only broadband access device used. In Western  Europe we see similar to North America all of the tier 1 players gearing up for the challenge with frequent announcements on LTE trails and new networks deployments, all boosting up  the demand to the amazing predicted 92% CAGR in 5 years.

Change is expected in almost all aspects of the network (maybe beside the OSS / BSS) as a result of this massive growth and convergence of smart device technology, mobile broadband, applications and content acceptance.

To address the mobile broadband arena, carriers are adapting their networks through a number of mechanisms:

RAN technology is moving forward with HSPA+, progressing to LTE and later LTE Advanced to accommodate up to 1Gig downlink bandwidth. It is ironic that the needs are changing so fast that while LTE is hardly commercialized, the next gen “advanced” generation is already being introduced.  The fast pace of the changing technologies may cause some operators to skip some technological generations while others will have even bigger mix of technologies in their network.

Mobile architecture is changing, with new concepts entering the market, such as “small cell” and “Cloud RAN.” The Evolved Packet Core (EPC) concept of flat, all-IP-based network also has caught on as LTE offerings mandate an end-to-end IP service. Such architecture will enable easier introduction and creation of new services to support new business models, partnerships, and deployment options .

As a result, the mobile backhaul space is going through considerable change, but as oppose to the RAN and Packet core, which has been well defined by the 3GPP standard body, mobile backhaul wasn’t defined at all, leaving the operators with multiple technological options each offer different values and disadvantages.

Two standard bodies are addressing the mobile backhaul technology space: the Metro Ethernet Forum (MEF) with MEF 22.1 and the new CE 2.0 initiative which promotes assured services, OAM, and network to network interconnection for Carrier Ethernet as the transport technology, and the Broadband Forum’s TR-221 specification for MPLS use in mobile backhaul networks.

Why operators are looking for change of backhaul technology?

The rising data use forces many mobile operators to massively invest in the network infrastructure in order to remain competitive, despite the fact that they can’t link this capital investment to increase of revenues to minimize churn. Since data traffic is taking the higher share of the operator networks, there is a need to migrate the backhaul links to technologies that are more efficient in delivering these services as well and supporting the exponential growth in the demand.

Competition is fierce not only with the mobile operators traditional competitors but also with new types of competition.  Over-The-Top (OTT) applications providers (GoogleVoice, Skype, texting applications) threaten their traditional services (Voice, SMS and video conferencing). As competition is moving into the mobile operator playfield, some operators are looking outside of their traditional market and taking advantage of their infrastructure to offer fixed connectivity services to business customers.

The combination of these two elements has driven the backhaul providers to offer improved backhaul offerings with various new characteristics to assure bandwidth is managed more efficiently and judiciously for customer based SLA agreements

Today, mobile backhaul is provided not only by the mobile operators but rather a combination of the mobile operators and other service providers providing services to the mobile operators. These operators or carrier’s carriers, have networks based on variety of physical transport such as cable, copper, fiber, wireless as well as multiple technologies such as DOCSIS, ActiveE, xDSL, xPON. Some new players have joined this market (Utilities  and pure wholesale providers) utilizing  their existing network footprint to change the costs models for new service offerings as a result of   implementing FMC (Fixed Mobile Convergence) based networks.

What are the mobile backhaul technology requirements?

The mobile network combines multiple technology generations including 2G, 3G and 4G –which may co-exist in the same cell or in different cells. Any technology that is selected must offer a seamless migration path from TDM to packet based transport as well as to support maintenance of carrying TDM over the packet network. As each mobile macro cell serves large amounts of customers and some aggregation points may even serve multiple base stations, operators and cell sites must implement transport protocol(s) that can provide high resiliency support with sub 50 ms recovery time.

While there are many technological options, there is one common denominator, and that is that all options are packet based technologies. As mobile backhaul evolves together with the mobile network, and new application requirements are presented, operators need to choose their next generation mobile backhaul networking solution. For the most part, there are two main mature options, IP/MPLS solution and L2 Carrier Ethernet network.

As the network grows with more mobile cells (big and many new small cell technologies), scalability can become a limiting factor in the use of L2 Ethernet E-Line, tree, or E-LAN connections  as large numbers of cells may become difficult to manage and maintain . In this article we will focus on the use and benefits of IP/MPLS to the cell site for mobile backhaul.

Why extend MPLS to the cell site?

MPLS was created to combine the best of two worlds: ATM switching and IP routing. MPLS decouples the data plane from the control plane; it is a connection-oriented technology, so the connection has to be established prior to the data’s delivery. The MPLS control plane establishes the connection by signaling through each hop along the path.

MPLS has significant traffic engineering capabilities that can be used to provide end-to-end service-level-agreement (SLA) assurance. The MPLS data plane switches the packets based on MPLS labels that  are carried inside a 32-bit MPLS header.

IP/MPLS is the de-facto standard in the core today and while most edge and access networks will be L2, rapid changes due to the dynamic nature of mobile connectivity have forced operators to understand that MPLS needs can be extended to the access and aggregation layers for easier control, resiliency, redundancy, and scalability of their overall networks.

Offering MPLS at the edge of the network for mobile backhaul service provides multiple advantages:

Maximize Scalability – MPLS is highly scalable.  The 20-bit label allows for over one million LSPs per node.  With each node changing the label and reusing labels, practically infinite LSP numbers can be supported. By using VPWS or VPLS (virtual private wire/line services) such a network can support thousands of customers and each customer can have a different logical topologies. H-VPLS technology further increases the scalability by segmenting the network into several partitions each concentrating into the VPLS hub that are fully meshed between themselves.

In contrast, Ethernet’s 12-bit VLAN tags allow for 4K VLANs per switch.  VLAN stacking (Q-in-Q) allows for 4K customer VLANs to be carried in 4K provider VLANs.  Since each customer is likely to use multiple VLAN IDs, the number of customers that can be supported is quite limited.

Dynamic Path Creation – MPLS is a connection oriented technology. Which means that the path between two points has to be established prior to the traffic passing. The path creation is handled by control plane protocols (namely LDP and RSVP variants), starting from the source LER (Label Edge Router), traversing the LSR (Label Switch Routers) all the way through the destination LER.

These protocols base their path creation on the dynamic routing information exchange between peers. The dynamic nature of MPLS minimizes the service creation time while increasing the network scalability, as most of the work is done by dynamic protocols. This will ease the manageability of the network as path creation if done by configuration only the end devices.

Additional resources

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