Introduction

One of the most important growth engines for mobile operators is their ability to offer any type of content. Massive delivery of internet and TV content is impacting the mobile backhauling infrastructure that was originally built to handle voice traffic. The roadmap to fulfill the clear needs and vision includes technical challenges such as how to deliver significantly more data while preserving the synchronous nature of the network and how to perform phased migration from a TDM network to a packet-based network. MPLS and MPLS-TP technologies that are adopted by fixed-line service providers are offering a field-proven and cost effective basis for Packet Transport Network (PTN) based mobile backhauling.

Next-generation mobile backhauling is all about data
Fixed-line mature network solutions are suitable for the new mobile arena

Five years ago CDMA technology enabled SMS with few kpbs, than HSPA technology enabled web and email surfing with bandwidth limitation of ~ 100kbps. Next-generation mobile broadband technologies, such as LTE, enable real-time multimedia with bandwidth requirements of more than 1000kbps.
The movement from the voice era with its TDM backhauling to the data era decoupled the network costs from its revenues. As a result, scaling up bandwidth over the existing PDH/SDH infrastructure cannot satisfy mobile operator’s business case.

The data and Ethernet potential at mobile networks is well described by industry analysts, for example:

• Traffic measurement company Comscore find out that iPhone users consume two to four times as much network data volume as other smartphone users
• Analyst firm OVUM expects Ethernet to capture 50% of wireless backhaul technology at 2013
• Analyst firm HeavyReading expects mobile backhauling application to capture 17% of Carrier Ethernet infrastructure market at 2011
• Analyst firm Infonetics expects Ethernet copper and fiber to capture 32%, or $3B at 2011 from mobile backhauling equipment revenues

Mobile backhauling evolution steps
Transforming a TDM network to a Packet Transport Network

Metro Ethernet Forum (MEF) is providing guidelines for implementing mobile backhauling network that is based on PTN. The mobile backhaul network is placed between the radio Network Controllers (NC) and the radio access Base Station (BS).
MPLS / MPLS-TP based PTN with circuit emulation technologies for the delivery of TDM leased-line services over packet are successful implementation.

Scenario 1a: legacy split access

In the basic use-case there are two parallel networks that transport different types of mobile traffic: the MPLS / MPLS based PTN role is to carry all the new data traffic and the legacy TDM network is remained untouched.
This is appropriate in cases where the mobile operator intends to offload low priority, high bandwidth traffic from the legacy network.

Figure #1: Legacy split access

Scenario 1b: legacy backhaul

When the Packet Transport Network is stable and reliable, an upgrade to the PTN eliminates the need to maintain the legacy TDM network. Radio access nodes with legacy interfaces transport all traffic over the PTN that is using circuit emulation technologies in order to deliver TDM over packet services.
The outcome is a unified mobile backhauling that is using GIF that interconnects all the legacy equipment to the PTN.

Figure #2: Legacy backhaul

Scenario 2a: split access

This use case is similar to the “legacy split access” use case in the way the Packet Transport Network is used to offload certain traffic, such as low priority high bandwidth traffic, from the legacy network. The overlay legacy network transport voice and delivers synchronization.
Here, the radio access network nodes are equipped with both Ethernet and legacy interfaces. Therefore they can be connected directly to the UNI via an Ethernet interface (eliminating the need for a GIF) and split the traffic: TDM traffic to the legacy network and Ethernet traffic to the PTN.

Figure #3: Split access

Scenario 2b: pure packet

When the Packet Transport Network is stable and reliable, an upgrade to the radio access network nodes eliminates the need to maintain the legacy TDM network.
The new RAN nodes send all the traffic (now everything is over Ethernet) over the PTN.
The outcome is a pure-packet mobile backhauling that is very similar to the classic usage of Carrier Ethernet and MPLS / MPLS-TP by fixed-line service providers.

Figure #4: Pure packet

Mobile backhauling using MPLS / MPLS-TP
Delivering a future proof, scalable, and cost effective solution

MPLS and MPLS-TP technologies were originally built for service provider’s need to deliver large amount of connection-oriented traffic with different QoS types. Today, MPLS is the de-facto technology at metro aggregation networks and it enables voice, video and data services. Leveraging mature and scalable MPLS / MPLS-TP solutions from the fixed-line domain to the mobile networks is lowering risks and costs.

Cell Site Gateway (CSG) usage: when fixed-line infrastructure reaches the cell site, the mobile operator place a CSG that receives all the traffic from the antennas and send it to an access network. The CSG is a multi-service access switch and the gateway functionality means that number of E1 or Ethernet services are encapsulated to Ethernet packets. From this point the data packets need specific QoS and the network needs to preserve synchronization.
At the other side of the mobile backhauling network, the controller needs to receive and handle all the services that came from the antennas. Therefore, another gateway, called Aggregation Site Gateway (ASG) is needed to de-encapsulate all the Ethernet traffic and send it to the controller.
Figure #5 demonstrates the CSG/ASG scenario over PTN:

Figure #5: CSG/ASG usage in PTN mobile backhauling

Hub Site Gateway (HSG) usage: CSG or even a switch is not always placed at the cell site location. In some cases few access networks carry PDH traffic (normally E1 services) and Ethernet traffic till the demarcation point where the MPLS / MPLS-TP aggregation begins. In such cases, a relatively small aggregation device is having a gateway functionality to encapsulate PDH/SDH traffic and deliver it over the PTN. Therefore, such network element is called Hub Site Gateway (HSG). The Ethernet traffic doesn’t need the gateway functionality and is simply being carried over MPLS / MPLS-TP PW towards the controller.

At the aggregated PTN, MPLS / MPLS-TP based data packets need specific QoS and the network needs to preserve synchronization.

At the other side of the mobile backhauling network, the controller needs to receive and handle all the services that came from the antennas. Therefore, another gateway, called Aggregation Site Gateway (ASG) is needed to de-encapsulate all the PTN traffic and send it to the controller.

Figure #6 demonstrates the HSG/ASG scenario over PTN:

Figure #6: HSG/ASG usage in PTN mobile backhauling

The CSG and HSG scenarios demonstrate how MPLS / MPLS-TP with its proven abilities to serve different types of services in PTN can be used easily for mobile backhauling. The network scheme and services handling are typical, and the powerful QoS, protection and OAM mechanisms are also typical to classic aggregation networks. Therefore, the solution is robust, scalable and cost effective.

Orckit-Corrigent PTN solution enables MPLS / MPLS-TP based mobile backhauling
A cost optimized, standard and interoperable MPLS solution with E1 till STM-n services over packet

Orckit-Corrigent PTN solution is build from the CM-4000 small/medium/large switching capacity switches for metro aggregation networks, CM-401x PTN access switches, and CM-View network and services management system.
The carrier grade solution is based on standard Layer 2 MPLS and MPLS-TP technologies, interoperable capabilities, a wide set of transport features and cost optimization.

Figure #7: E2E mobile backhauling solution

For the specific needs of mobile backhauling, the solution includes:

• A dense mixture of GE, 10GE and PDH/SDH interfaces that enables a scalable and affordable solution 
• Synchronization technologies, including Synchronous Ethernet and IEEE 1588v2 that are required to deliver TDM services 
• TDM emulation protocols including CEP, SAToP and CESoP that enables E1 services till STM-n services over MPLS network 
• ATM over packet and ATM cross-connect

 Figure #8: PTN solution traffic flow

Orckit-Corrigent PTN products enable MPLS / MPLS-TP based mobile backhauling
CM-4140 PTN switch: a mobile backhauling HSG and ASG
CM-401x PTN access switches: a mobile backhauling CSG

Orckit-Corrigent CM-4140 is a PTN switch positioned for aggregation networks. It is a standard Layer 2 MPLS / MPLS-TP and interoperable product with a wide set of transport features, including Ethernet and TDM over packet services and transport-class availability, synchronization and management. The CM-4140 offers high switching capacity at small footprint with low power consumption.The CM-4140 ideally fits in 2G/3G/4G mobile networks as HSG and ASG due to its cost point and abilities to deliver Ethernet services as well as low rate and high rate TDM services over MPLS aggregation network.

Photo #1: Orckit-Corrigent CM-4140 PTN switch 

• HSG and ASG for mobile backhaul solution
• Standard and interoperable Layer 2 MPLS / MPLS-TP
• E1, STM-1/4/16 over packet
• CEP, SAToP, CESoP
• STM1/4 ATM
• Synchronous Ethernet, IEEE 1588v2
• 168G switching capacity at 3RU footprint with 250W of power consumption

Orckit-Corrigent CM-401x PTN portfolio is a complete access solution for mobile backhaul, legacy SDH and PDH migration, and enterprise CLE and pre-aggregation applications. The CM-401x portfolio includes CM-4011, CM-4012 and CM-4013 products and is fully compatible with the company’s metro aggregation products that include the CM-4140, CM-4206, and CM-4314T/4314 chassis based PTN products, and the company’s CM-View NMS product. All CM-401x products deliver 16G of non blocking switching capacity and are packed only in 1RU fixed configuration size. The CM-401x portfolio is equipped with a broad mixture of Ethernet, PDH and SDH interfaces and therefore fits to various networking scenarios and increases network scalability. As packet transport solution, Ethernet, IP/MPLS and MPLS-TP technologies are implemented in the CM-401x portfolio, as well as standard and interoperable packet synchronization and circuit emulation technologies.
 

Photo #2: Orckit-Corrigent CM-401x PTN access portfolio

Summary

The vision for truly broadband and real-time content on mobile devices is clear and the technical and economical challenges to fulfill this vision are changing the mobile backhauling infrastructure. At the end of the road a typical Packet Transport Network based on MPLS and MPLS-TP technologies will carry all the traffic, and the phased migration from TDM based network to a packet based network is achievable with synchronization and circuit emulation technologies.
Orckit-Corrigent is offering a standard and interoperable PTN portfolio including CSG/HSG/ASG products that are cost optimized and having the capabilities to deliver both E1 and STM-n services over the aggregation network. Implementing HSG and ASG is a single product simplifies the solution and reducing costs. And implementing Layer 2 MPLS and MPLS-TP with circuit emulation and synchronization technologies brings a complete, field-proven and cost optimized solution for mobile backhauling networks that need to deliver broadband content and services.