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
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