4G Wireless Backhaul

The telecommunications industry is evolving rapidly. Wireline carriers are
making significant investments in fiber infrastructures to deliver business,
transport and residential services, and carrier Ethernet is emerging as an
important access and backhaul technology around the globe.

Wireless carriers are scrambling to keep pace with a growing demand for
mobile Internet services, and wireless equipment vendors are developing fourth
generation or 4G technologies that can provide IP-based, high-speed broadband
services for fixed, nomadic and mobile users.

As wireless carriers move to 4G mobile technology, huge demands are being
placed on carrier backhaul infrastructure. The multiple, high-bandwidth,
quality-sensitive services that carriers have planned for 4G require an
infrastructure that is packet-based, scalable and resilient, as well as
cost-effective to install, operate and manage.

An innovative, connection-oriented Ethernet technology Provider Backbone
Bridging-Traffic Engineering (PBB-TE) 802.1Qay, is emerging as a key solution
for addressing the enormous 4G backhaul infrastructure challenge. Currently
being standardized by the IEEE, PBB-TE promises to provide the resiliency,
scalability and operational efficiency that wireless carriers require.

Evolving to 4G

First generation (1G) mobile systems were analog and focused only on voice
traffic. Second generation (2G) marked the transition from analog to digital
systems. Third generation (3G) mobile systems evolved to support more
bandwidth-hungry services, such as email, text messaging and image sharing.

Typically, 3G mobile networks require two parallel backbone
infrastructures-one consisting of circuit-switched nodes and the other
consisting of packet-based nodes. This network infrastructure doubles the
capital and operational expenses associated with deploying, maintaining and
operating 3G mobile networks.

4G mobile networks require a single, all-IP, packet-based backhaul
infrastructure, providing carriers with a significant cost advantage. However,
the number of mobile devices and multitude of services such as traditional
voice, voice conferencing, image sharing, video, and high-speed data, strains
the infrastructure.

All about 4G

Several 4G network characteristics have been established by international
standards development organizations and forums. Generally, 4G standards are
characterized by superior bandwidth, which sacrifices some of the mobility
attributes.

While most target 4G characteristics directly relate to the family of air
interface standards, many directly influence the backhaul infrastructure
requirements. These include:

• Scalability
• Resiliency
• Topological flexibility
• Improved economics

Scalability Requirements

Improved customer scalability: Each successive wireless generation has
experienced significant customer growth. Some early 4G network markets have seen
end-station counts (measured in Media Access Control addresses) that are
two to five times higher than initial estimates. Therefore, the 4G wireless
backhaul infrastructure must be able to support tens to hundreds of thousands of
MAC addresses per market.

IP transport: IPv6 is an important network layer technology for 4G networks
given the number of wireless and mobile devices moving to IP based services. A
Layer 2 transport backhaul infrastructure using IPv4 for management enables use
of IPv6 network layer scalability without requiring Network Address Translation
(NAT).

Base stations: Markets require diverse numbers of base stations/towers. The
4G wireless backhaul infrastructure must be able to handle growing base station
counts while retaining address and customer scalability.

Resiliency Requirements

Stability: As 4G networks are deployed and expanded, the stability during
backhaul infrastructure expansion and maintenance is a critical issue. Current
stopgap implementations are prone to mis-configuration, causing traffic storms
and costly network outages. There must be resilient, reliable backhaul
infrastructure stability.

Predictable low-latency data transmission: Voice and other services reliant
on fixed circuit-switched network delay require packet-based, low-latency,
predictable data transmission.

Multi-vendor interoperability: Legacy Ethernet implementations often use
vendor-specific proprietary control plane protocols to attempt to solve diverse
backhaul architectures.

Optimized bandwidth plan: Traditional Ethernet backhaul technologies use loop
prevention control plane protocols such as IEEE 802.1w Rapid Spanning Tree (RST).
Often, half of the backhaul capacity/paths are disabled when these protocols are
used. In order to maximize backhaul utilization, enhanced techniques to manage
redundant paths and overall bandwidth engineering are required.

Deterministic bandwidth guarantees: Some network redundancy schemes result in
overloaded paths during fault conditions. To provide deterministic bandwidth, 4G
wireless backhaul infrastructure must have predictable failover and resiliency
schemes.

Pre-defined failover actions: Legacy Ethernet's connectionless nature weakens
bandwidth and Quality of Service (QoS) configurability.

Topological Flexibility Requirements

Base station site interconnect technology: Wireless and mobile operators
face myriad challenges when interconnecting base stations. In some cases, copper
or fiber access is available. In many instances, microwave links are more
economical and readily deployable. 4G mobile backhaul infrastructure must have
the flexibility to accommodate wireline copper, fiber, or wireless microwave and
free space optical connectivity.

Economic Requirements

Cost effective: Given the competitive nature of wireline and wireless
operators, the backhaul infrastructure solution must be cost effective to
deploy, maintain and operate.

Simplified provisioning: Since mobile networks are constantly evolving
through expanding markets, growing numbers of base stations, and customers,
network and service provisioning must be simple yet powerful.

Automated network monitoring: While many legacy technologies like TDM contain
extensive monitoring capabilities, traditional ethernet lacks troubleshooting
and fault detection. 4G wireless backhaul infrastructure requires network and
service monitoring, as well as fault detection, isolation, repair, and
verification capabilities.

Using PBB-TE in 4G Wireless Backhaul Networks

In early 2007, IEEE 802.1 commissioned a project to standardize Provider
Backbone Transport (PBT) as PBB-TE. Known as IEEE 802.1Qay, The effort was made
to produce a standard that defines enhanced Ethernet-based techniques for
transporting services across diverse network topologies using MAC header
encapsulation.

PBB-TE eliminates the need for non-edge switches to perform MAC address
learning and unknown address flooding. Instead, point-to-point tunnels are
provisioned using a comprehensive management platform. (Rather than using
conventional ethernet control plane protocols such as IEEE 802.1w RSTP and IEEE
802.1s MSTP to prevent loops and provide resiliency, the management platform
traffic engineers the operator's network. This which utilizes more capacity,
pre-defines failover scenarios and optimizes service performance and assurance).

Base station traffic is forwarded along the primary tunnel. Each primary
tunnel is protected by one or more backup tunnels. Multiple techniques are used
to provide efficient tunnel failover and service restoration in the event the
backhaul infrastructure links become unreliable or inoperable.

Tunnel Resiliency Techniques

PBB-TE provides a variety of tunnel resiliency techniques. One technique
involves IEEE 802.1ag Connectivity Fault Management (CFM) frames, which are
known as Continuity Check Messages (CCMs). CFM provides network, path and
service-level in-band management capabilities. Primary and backup tunnels are
monitored using CFM CCM frames. Each tunnel endpoint sends CCMs at preconfigured
intervals to monitor the status of the tunnel. A disruption in the reception of
CCMs causes tunnel failover to occur. Base station traffic is then automatically
switched to the backup tunnel.

Another technique involves ITU-T Recommendation G.8031/Y.1342, which defines
Ethernet Protection Switching (EPS). This recommendation defines point-to-point
Virtual Local Area Network (VLAN)-based protection schemes including 1+1 and 1:1
protection switching architectures. The 1+1 protection scheme implies the base
station traffic is permanently sent across the primary and backup tunnels. The
tunnel endpoint discards the backup tunnel traffic until detection of a primary
tunnel failure. The Automatic Protection Switching (APS) protocol synchronizes
the two tunnel endpoints. The 1:1 protection scheme signifies that the base
station traffic is only sent across the backup tunnel upon detection of a
failure.

Relevant 4G Mobile Standards

The following 4G mobile standards will benefit from utilizing IEEE 802.1Qay
PBB-TE as a component of the wireless backhaul infrastructure:

IEEE 802.16 Worldwide Interoperability for Microwave Access (WiMax):

• Fixed, nomadic, portable, and mobile wireless broadband connectivity
  without the need for direct line-of-sight to a base station

HiperMAN:

• WiMax variation created by the European Telecommunications Standards
  Institute (ETSI) Broadband Radio Access Networks (BRAN) group
• Operates in the 2-11GHz range and is seamlessly interoperable with subset
  of IEEE 802.16a-2003

iBurst:

• Uses technology known as High Capacity Spatial Division Multiple Access
  (HC-SDMA), recently standardized by Alliance of Telecommunications Industry
  Solutions (ATIS)
• Long Term Evolution (LTE) also known as UMTS release 8
• UMTS-based wireless broadband Internet system with voice and other
  services added

Ultra Mobile Broadband:

• Improved CDMA2000 mobile phone standard for next generation applications
  and requirements

WiBro:

• Service name for mobile WiMax in Korea market

Wireless carriers around the globe are faced with increasing demands for new
mobile Internet services. These growing service demands are driving a move to
IP-based, high-speed broadband services that only new 4G technologies can
provide. However, wireless carriers implementing 4G mobile technologies are
realizing these new technologies place huge demands on their backhaul
infrastructure. Carrier Ethernet's innovative new connection-oriented
technology, PBB-TE, is emerging as the ideal solution for meeting the demands of
4G technologies. With PBB-TE, 4G mobile operators can create a robust,
packet-based backhaul infrastructure that is scalable, resilient and more
cost-effective to install, operate and manage.

Neeraj Gulati,

The author is vice president and managing director, Ciena India

vadmail@cybermedia.co.in