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Introduction

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 (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 technology 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, isemerging 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.

Wireless Evolution 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

infrastructuresone consisting of circuit-switched nodes and one

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. The generations of wireless standards

are shown in Figure 1.

Figure 1. Wireless standards evolution

4G Network Characteristics and Requirements

Several 4G network characteristics have been established by

international standards development organizations and forums.

These requirements and performance targets are shown in

Figure 2, along with their impact on air interface and/or

infrastructure equipment. Generally, 4G standards are

characterized by superior bandwidth, which sacrifices some ofthe mobility attributes.

Figure 2. 4G requirements and performance targets

While most of the 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

4G Wireless BackhaulInfrastructure Using Carrier EthernetTransport Technologies

10K 100K 1M 10M 25M 50M 100M0K

10K

100K

1M

10M

25M

50M

100M

1G

2G

3G

4G

DOWNLINK

UPLINK

UMB

LTE

WiMAXiBurst

WiBro

UMTS-TDD

HSPA+

HSDPA/HSUPA

1xEV-DO

UMTS/W-CDMA

PHS

CDMA2000

EDGE/EGPRS

GSM

D-AMPSIS-95

WiDENiDEN

GPRS

HSCSD

PDC

CDPDDataTAC

Mobitex

AMPSNMT

CSD

TD-SCDMA

GAN/UMA

HIPERMAN

MOBILITY

SPEED

802.11

4G

2G1G

3G

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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 [MAC]

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 andcustomer 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-switchednetwork 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 aredisabled 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 Ethernets 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 provisioningSince 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 NetworksIn early 2007, IEEE 802.1 commissioned a project to standardize

Provider Backbone Transport (PBT) as PBB-TE. Known as IEEE

802.1Qay, the effort will produce a standard that defines

enhanced Ethernet-based techniques for transporting services

across diverse network topologies using MAC header

encapsulation. PBB-TE, shown in Figure 3, has emerged to

address current Layer 2 bridging limitations that relate to

resiliency and scalability.

Figure 3. Mobile Backhaul using IEEE 802.1Qay PBB-TE

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4G Wireless Backhaul

POP

Internet

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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 operators network,

which utilizes more capacity, pre-defines failover scenarios and

optimizes service performance and assurance.

Figure 4 depicts PBB-TE equipment located at the Point of

Presence (POP) and at each base station location. Redundant

PBB-TE tunnels take divergent paths back to the POP to provide

deterministic, reliable failover.

Figure 4. Redundant PBB-TE tunnels

The topological flexibility associated with PBB-TE enables 4G

cells to grow and expand as market penetration and customer

acquisition dictates. A logical view of the same 4G market is

shown in Figure 5. In this example, each base station has a

primary and backup tunnel configured back to the POP.

Figure 5. Redundant 4G PBB-TE tunnels

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)

3

4G Wireless Backhaul

Benefit

No customer MAC addresslearning in backhaul infrastructure

No flooding of unknown MACaddresses

Reduced likelihood of traffic stormStandards-based control plane =IEEE 802.1ag CFM, ITV-T Y.1731

Explicit primary and backuppaths

Enables fast and predictablefailover

Switches at each base station onlylearn attached customer MACaddresses and backhaul addresses(not transiting customer MACs)

Only the POP-located backboneedge bridge, which terminatesPBB-TE tunnels, learns all customer

MACs

True traffic engineering

Since 4G networks haveconfigurable channel bandwidth,PBB-TE tunnels can accommodate awide range of service types andbandwidth plans

Configurable bandwidth forservices and tunnels

Committed Information Rate,Excess Information Rate

Improves network utilization

Optimized paths minimizeframe delay

Data plane = IEEE 802.1Qay PBB-TE

Control plane = IEEE 802.1agCFM, ITV-T Y.1731

Eliminates use of proprietary,vendor-specific protocols

UNIQUE FEATURES AND BEN EFI TS O FC IENA WIRELESS BACK HAUL SOLUTIONS

Ciena Feature

Improved resiliency

Improved scalability

Improved servicepredictability

Interoperable,standards-based

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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.

Again, the APS protocol synchronizes the tunnel endpoints.

While this recommendation is useful for basic point-to-point

topologies, it is not intended for more complex topologies like

multiple rings or mesh architectures and will have limitedapplicability in 4G mobile backhaul infrastructures.

While the CFM resiliency technique has advantages, such

as the ability to work across multiple rings and mesh

architectures, its inherent scalability is often challenged. In order

to achieve rapid failover in the 50-100 ms range, the CCM

interval must be ~10 ms. Depending on the number of tunnels

and services, a small CCM interval may overwhelm some

networking equipment. Some implementations, in

order to satisfy a given CCM interval demanded by the failover

requirement, may sacrifice management plane responsiveness,

such as provisioning, traffic statistics collection and otherimportant tasks. Derivations of the CFM CCM approach include

path-based failure detection and propagation. Such schemes

may improve failover determinism without causing undue stress

on the networking equipment.

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

Summary

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 Ethernets

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.

4G Wireless Backhaul

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Ciena may from time to time make changes to the products or specifications contained herein without notice. All rights reserved. IEEE is a registered trademark of the IEEE. WiMax and WiBro are trademarks of the WiMAXForum. 2008 Ciena Corporation. WP058 7.2008