Backhaul

page twenty two www.csimagazine.com Cable & Satellite International july-august 2007

Acellular network needs to

backhaul traffic from its base

stations back to a central point,

such as a base station controller (BSC),

mobile switching centre (MSC) or central

server. A wide range of potential solutions

exist to enable this but one approach that is

seeing greater attention is using cable

networks. Cable cell tower backhaul has been

a sideline for the cable industry but it is now

getting prominence in the US as cable

companies expand their business service

offerings, of which backhaul is a subset.

This is an opportunity that most

operators have identified and it's becoming

an increasingly visible part

of their strategies. “What I'm seeing

is the landscape changing a little,

with a growing number of cable operators

starting corporate initiatives to address

business services, including backhaul,

starting in 2007 and moving forward,

a little like the next frontier,” says Bill

Dawson, VP of access strategy at C-Cor.

Some small regional deployments have

already occurred, and the shift is now

moving towards a broader level, where

Multiple Service Operator (MSOs) are

engineering a solution that can be

deployed in multiple locations. Indeed,

most vendors active in this space predict

large scale deployments within the next

year or so.

The market is coming to the forefront

in terms of visibility in the MSO space

on a nationwide scale in the US. Comcast,

Time Warner, Cable Vision, Charter and Cox

are all said to be actively pursuing the

business opportunity in terms of R&D and

are receiving a lot of encouragement out of

the traditional cell carriers. But while the

large Tier 1 cable operators are leading the

market, vendors point to a large number of

smaller regional players also pursuing it to

various extents.

Why cable, and why now?Figures from market researchers Heavy

Reading suggest cellular backhaul was a

$2.3bn market opportunity in 2006, rising

to $4bn in 2008 and close to $7bn by

2010. The cellular network is experiencing

significant growth in its backhaul

requirements, primarily because

of the evolution from traditional voice

services to bandwidth intensive data

services thanks to the deployment

of faster networks, such as HSPA

and EV-DO. In addition, voice traffic

itself is experiencing growth.

Nortel recently conducted a business

case study in North America, which

looked at traffic growth and what the

demand means for mobile traffic backhaul.

It estimated that wireless backhaul traffic

was growing at a rate greater than

30%, much of it attributable to data

services, which are expected to account

for more than 35% of all wireless traffic

by 2010. Simply put, capacity

requirements are beyond those

of the current connected network.

Mobile network operators (MNOs) today

generally have two to four T1s per cell

tower, and it's a market dominated by the

Local exchange Carriers (LECs). The

forecasts vary, but generally demand is seen

as rising from current numbers to around

five to seven T1s per tower for voice alone

over the next five-ten years. “On top of that,

you are also looking at adding somewhere

in the vicinity of 10-30Mbps of broadband

to that tower site. The current copper

bundle delivering T1 service to that tower

site has a maximum capacity of 27Mbps.

So if you have two customers, you are very

likely going to blow the capacity of the

current access network very soon,” says

Michael Collette, CEO, PhyFlex Networks

(formerly Narad Networks).

“All in all, whereas one or two T1s were

sufficient to handle voice traffic, growth

is driving those numbers up towards

eight to ten T1 per tower, with an

expectation in most cellcos' planning for

the need for at least 16 T1s/tower in the

future,” says Bob Scott, director of

business development, transmission access

networks, at Scientific-Atlanta.

Exacerbating the problem is the fact

that MNOs need to increase capacity

while at the same time reducing the cost

per megabit because currently their total

cost for backhaul is a very large part

of their total operating expense - some

estimates put this at around 20-30%

of OpEx. Extrapolating this to across

the approximately 200,000 cell sites

in North America, this puts a tremendous

cost burden onto the cellcos, motivating

them to look for alternatives.

These cost and availability drivers

could potentially play into cable's hands

as cable operators are well positioned,

particularly in the US, to take advantage

of this opportunity because of their

proximity to cell sites. In North America,

cable fibre access points are typically

much closer to cell towers compared

to telco access points. This proximity

Cable's new frontierGoran Nastic examines the marketopportunity for cable to act as a transport mechanism for backhauling cellular traffic and the network architectureoptions open to cable operatorswanting to engage in this space.With North America leading theway, what can Europe learn?

“What's happeningfrom a technologyperspective is thatthe tools arebeing assembledinto the toolkit tobe able to providecellular backhaulon a wide scale.”

Backhaul

Cable & Satellite International july-august 2007 www.csimagazine.com page twenty three

makes cable economically more viable

for building a new access network

to that tower.

According to the Nortel study, the

average extension from the last fibre node

which cable would have to provide to reach

out the cell site was less than a mile

(typically 1-1.5km distance). Nortel claims

its business case shows that because

cablecos are investing in leveraging their

infrastructure and using Ethernet as the

transport mechanism, they are able to offer

equivalent T1 to wireless operators at an

approximately 33% discount and still get

a positive return on investment (ROI). The

attraction is that they can offer equivalent

T1 services at a lower cost than what the

local exchange provider would be offering

to the mobile operator.

It also found that a large percentage

(60+) of the total aggregate traffic was

being originated from suburban cell site

areas. This is significant because much

higher capacity exists at those cell sites

in terms of the number of megabytes

required for backhaul. That's where the

opportunity lies for the cable operators

coming into play, given that they have

huge investments in cable going out to

residential users in the suburban area and

their fibre is already deployed there. “It

becomes very attractive for them to look at

the fibre plant and the extension to provide

a backhaul service,” notes Geoffrey Spencer,

marketing manager of Carrier Ethernet

business development EMEA at Nortel.

The potential ROI then accelerates where

cell sites are shared by multiple wireless

operators, as is often the case in both

North America and Europe. Moreover,

targeting the top three or four wireless

carriers in the US or any European market

accounts for 85% of the cell backhaul

opportunity. In Nortel's calculations,

if the MSO was just to backhaul one

operator, the payback would be around two

years, yet if they could sign up two or

more operators per cell site, that breakeven

would fall to six to 12 months, making it

more attractive to extend the infrastructure

to the cell site and, in parallel, sign up

multiple mobile operators for backhaul.

Fibre vs HFCCox was an early mover in this space,

and the indications are that it has made a

good business model out of cell backhaul.

According to Scientific-Atlanta's Scott,

Cox has a network that currently provides

60-65% of total cell backhaul transport

in one of the top 50 cities in North

America, meaning that it has actually

supplanted the telephone company

as the major supplier for cell site backhaul.

Cox is using an IP-based transport for

wireless backhaul that Scientific-Atlanta

is providing, namely the company's PRISMA

IP platform, which is able to do timing over

packet. This forms one part of Cox's

backhaul solutions, which are all market

specific. Currently, Cox and many MSOs

tend to use either IP transport systems

or SONET-based solutions to support it,

mainly because they desire to have ring

topologies, which the PRISMA IP can

do in the IP transport layer, as can the

Cisco 15454in the SONET space. Both

products feature low latency and jitter,

which are critical for the voice component

of cell backhaul.

“MSOs are using both IP and SONET

because of the ability of these

technologies to manage the network.

IP transport systems allow them to migrate

from T1 service towards an IP-based

network very easily. This would coincide

with the IP-centric evolution occurring

in the cellular network, as higher data

rates and new technologies are

introduced,” says Scott.

A new solution introduced by Cisco

allows for cellular networks to support

legacy systems as they upgrade to pure

IP. Specifically, the company has introduced

a circuit emulation over packet (CEOP)

card that plugs into the Cisco 7600 router,

which is widely deployed in the MSO

and MNO space, and - like the PRISMA

IP - is MEF-compliant. It is based on the

new pseudowire over IP standard, which

allows for the creation of TDM services

over Ethernet, essentially creating a handoff

between the cell site and cell base station.

Choices available to cable operators

include pseudowire solutions, T-1 over

HFC, Ethernet over Coax/DOCSIS,

as well as a variety of plant topologies.

Pseudowires (or TDMoIP) are a way

of emulating T1 performance using

Ethernet, a T1-to-Ethernet conversion

strategy. Located at the tower site, these

boxes convert back to T1 or equivalent

format somewhere over the network,

although the exact point where that

conversion takes place varies significantly.

Whatever the backhaul solution,

it must meet the four key performance

indicators of wireless traffic, including

delay (as low as 8ms to ensure good voice

quality); frame loss rate (keeping that up

to 10 to minus 8); synchronisation

(especially for carrying GSM traffic,

which has strict requirements in terms

of jitter, traceability etc); and high

availability (meeting four to five nines

depending on the access infrastructure).

For the most part, backhaul is deployed

by SONET-based technology, but there

is a migration to leverage circuit emulation

technology as defined by the Metro

Ethernet Forum (MEF), which has defined

a framework for technologies and

performance measurements. The MEF has

been working to provide a low cost

reliable backhaul solution that can support

pseudowires and data and voice over

a carrier Ethernet solution. Proponents

of Ethernet argue that the main variable

for lowering cost is to migrate from a

traditional TDM SONET circuit switched

architecture to Ethernet, which is less

expensive to implement. They claim there

will be an eventual move to Ethernet-

based wireless handoffs, so the wireless

backhaul will soon migrate over to

Ethernet worldwide.

Others aren't as convinced. “The issue

we see with Ethernet is that the

performance of the T1 link is very

dependent on the quality of the medium

used to transmit it. In an Ethernet situation,

you have packet loss, you have to do

retransmit, and what this translates into

is roundtrip delay,” says Tee Harton,

VP of marketing at Vyyo.

Vyyo has a product line that delivers

T1 over HFC using DOCSIS as its basis,

albeit a slightly modified version of

DOCSIS, which it has deployed in China

and North America. The XMTS is placed

inside the cable headend, and it's a

platform that Harton claims can deliver

as many as 56 T1s to individual tower

sites within that cable serving area.

A standard has recently been published

for performing circuit emulation or T1

services over DOCSIS, but this will take

Source: Cisco/Scientific-Atlanta

WWiirreelleessss ooppeerraattoorr

Sprint

Cingular

T Mobile

Verizon Wireless

Alltel

Others

TOTAL

CCeellll ssiitteess

45,000

43,000

24,000

22,000

8,000

33,000

175,000

Backhaul

page twenty four www.csimagazine.com Cable & Satellite International july-august 2007

time to catch on. This is because of the

bandwidth issue, which is still precious

within the HFC plant, so this requires

further digitisation and freeing up more

spectrum, as well as bandwidth expansion.

The question of providing TDM reliability

over DOCSIS also remains to be resolved

despite the recent CableLabs standard.

“Some of the emerging technologies like

circuit emulation and eventually Ethernet

will eventually have many of the network

measurement capabilities required by

MNOs, in terms of reporting loopbacks

and other variables. However, exactly when

Ethernet is in a position to offer these

network management and reporting

capabilities is open to debate,” says Mike

Emmendorfer, senior director of solution

architecture and strategy at Arris.

TDM over IP running over fibre will see

the most significant initial rollout, according

to Scientific-Atlanta’s Scott, who adds that

as services move towards pure IP, coax will

begin to play a bigger role for backhaul,

especially with DOCSIS 3.0.

As Reza Vaez-Ghaemi, product line

manager, Telecom Field Services at JDSU,

argues, “TDMoIP can potentially offer better

scalability and performance, but the

advantage of T1 over HFC lies with the

installed base of HFC plants.”

The HFC/fibre debate, therefore, isn’t so

clear cut. “MSOs are looking at the

situation on an ROI basis and if you blindly

choose to deliver fibre everywhere you

perform backhaul you will cost yourself a

lot of money, especially in situations where

an HFC-based solution to a few towers

would be a lot cheaper. HFC is generally

viable as a transport mechanism for

backhauling both voice and data wireless

traffic, but it does depend on the amount

of data. If a particular tower needs a GigE

link, HFC isn't the right choice. But if the

data component is in the region of 10-

20Mbps plus a TDM element, then HFC

makes sense and is suitable for this

purpose,” says Vyyo’s Harton.

What cablecos should consider is there

are a lot of different options for delivering

cellular backhaul services, and not any one

alone fits every application cleanly. They

will have to consider several different

delivery options given the circumstances on

the ground. HFC and fibre can all play a

role in certain situations, so MSOs should

be open to a mixed technology for

delivering these kinds of services.

“What's happening from a technology

perspective is that the tools are being

assembled into the toolkit to be able to

provide cellular backhaul on a wide scale.

A few interfaces have to be worked out -

perhaps standardised - but the basic

technology is becoming mainstream,” says C-

COR's Dawson. This includes technology that

provides more bandwidth and more capacity

in existing fibre by supporting DWDM and

TWDM wavelengths.

Transmission lines, both coax and fibre, are

costly to build, in some cases prohibitively

costly, so the trick, according to Dawson, is

to take existing infrastructure and run more

traffic through it, whether by upgrading the

bandwidth, adding wavelength to the fibre

through xWMD or service group

segmentation. “Over time, cable operators

will do all three of these - even in one

system. We're still setting the baseline

technology, and specific details like what the

interfaces will look like will be adapted to

individual customer needs,” says Dawson.

Dawson argues that ultimately proximity is

more important than capacity because it is

easier to overcome capacity that the

proximity. “Cable operators need to

understand that proximity is more important

than capacity because we can fix capacity

with technology, but you have to fix proximity

with shovels,” he says.

PhyFlex's Collette claims his company's

Ethernet over coax doesn't take spectrum

away from bandwidth hungry applications

such as HD or VOD as it operate in higher

frequencies where there is no competition for

spectrum. “We're essentially opening up new

capacity for applications.”

The general consensus is that in the

medium- to long-term, coax will have a

greater role to play in one way or another.

If both bandwidth and the technology are

available, in some markets it will make sense

to use the coax in certain applications. A

combination of both fibre and coax will exist

- it's not an 'either/or' solution.

Vendors are also optimistic that in five

years time MSOs could be either the

dominant carrier for cell site backhaul or

close to being the largest, at least

in North America. There is some

movement in Europe, although it

varies widely from region- to-region

and evidence is strictly anecdotal. In

the UK, a number of mobile operators

are in discussion to share cell sites and

backhaul infrastructure or backhaul leases,

and this consolidation in terms of radio

access networks may stimulate the market.

In terms of cable operators with the

requisite infrastructure, this again varies

across Europe, but in regions where cable

penetration is very high, such Belgium and

the Netherlands, the infrastructure is very

close to the cell site, according to Nortel's

Spencer. The same scenario exists in parts

of the UK, for instance, especially inside the

main cities, meaning that the opportunity

exists in these markets to exploit the

infrastructure.

In Europe, cable systems are almost

entirely built to provide residential services,

but as MSOs upgrade to 1GHz, bandwidth

could be dedicated to business services.

“One of the motivations to increase the

capacity of the network is to provide extra

capacity for services beyond residential

services, and cellphone backhaul can be

included in this. In Europe, the return path

already goes up to 65Mhz and typically

nowhere close to being filled to capacity,

so there will be enough capacity for both

directions if the network is upgraded to

1GHz,” says C-Cor’s Dawson.

The additional opportunity in the region

centres on the fact that a number of wireless

operators are looking to offload their HSDPA

traffic from a data perspective via some

wholesale service. The top priority of

European MSOs, however, remains the triple

play residential market, with wireless

backhaul viewed as an opportunity above

and beyond this market.

What is certain in that as cable looks

to its next growth, backhaul is capable

of being one of the next growth engines

that most of the MSOs are looking for.

For the cable company, it seems the time

is right to make the move, or at least carefully

evaluate the options. CSI