OTN accelerates metro networking
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By Dong Qibing
FTTH can provide all the bandwidth a home needs for the foreseeable future, yet user
experience can hardly be assured if the metro network fails to ensure bandwidth
integrity..
OTN for the metro broadband network
In a metro broadband network, a broadband remote access server (BRAS) with a
limited number of network nodes is typically located at the core metro equipment
room, while numerous OLT/DSLAM sites exist in a legacy metro network, which
connects to the core equipment rooms through long-distance wiring that may go
through both access and convergence rings. In addition, legacy networks use metro
Ethernet to transport GE traffic from OLT/DSLAM, which has a high transmission
efficiency and saves fiber, yet delivers limited bandwidth.
Many operators are trying to enhance their broadband access rate from 2Mbps to
8-20Mbps, which requires n*GE ports to carry DSLAM uplink traffic. Legacy
networks converge traffic layer-by-layer, while their high convergence rate can hardly
provide sufficient bandwidth. With OTN, each DSLAM access node can enjoy an
independent ODUk signal to transport traffic directly to the core convergence nodes,
which greatly enhances metro network efficiency as layered convergence and high
convergence rates are eliminated.
Without OTN/WDM introduction, flattening the metro Ethernet is challenging as it
consumes large amount of fiber as well as pipe resources. OTN can provide sufficient
wavelength during the metro Ethernet flattening process; it also provides L0/L1
protection to enhance network security. With sufficient overhead, OTN can help
operators monitor networks in real time and supply switchover protection for faulty
services within 50ms.
OTN for private line services
Enterprise private line services are shifting from pure text & voice to electronic
whiteboard, video conferencing, remote visualization, remote business
presentation/demonstration, and remote team cooperation. Their remote
implementation will reduce travel costs, thus reducing an enterprise’s carbon footprint,
but it will mean a dramatic increase in bandwidth.
Existing enterprise private lines are mostly based on SDH/MSTP networking, which
is insecure and hardly suitable for GE or other bandwidth-hungry services of its ilk.
E2E OTN network wavelengths and subwavelengths can satiate enterprise needs for
QoS, security, and isolation of their private line services.
OTN for mobile backhaul
Though fixed broadband is expanding rapidly, access ubiquity is impossible without
mobile broadband. For a certain city with 6,000 base stations, 750 10GE access rings
and 50 100GE convergence rings are in place. Currently, 100GE line cards require
support from high-end routers and 100GE-ready OTN/WDM networking, which
means costly network construction and power consumption. In addition, the use of
packet equipment to build 100GE convergence layers will be primarily oriented
around data transmission transparency, instead of increasing the convergence rate, as
it will be more costly and consume more power.
In IP RAN, operators can use OTN to replace 100GE rings with flattened network
architecture. Traffic can be carried through 1-n (n<4) 10GE wavelengths, which is
then transported through OTN (as opposed to 100GE rings) to the backbone network.
Each mobile network needs a low-convergence transport network to ensure security
and QoS. Packet-based IP RAN delivers E2E and high-QoS transmission, but its
CAPEX/OPEX and power consumption are high and more equipment room space is
needed.
OTN makes for a viable alternative, as the convergence layer can use it to connect
10GE IP RAN and large-scale Layer-3 equipment at the backbone layer. By flattening
the packet network, operators need not deploy 100GE packet equipment at the
convergence layer, which reduces power consumption, removes bandwidth
bottlenecks, and enhances QoS.
Building metro OTN
The accelerated fixed, mobile, and enterprise private line services are gobbling up
legacy fiber/pipe resources. Deploying new fiber is becoming increasingly difficult as
it may involve complicated application or negotiation for land usage. Metro OTN is
emerging as a practical choice for operators.
Metro OTN construction should start with the convergence layer to help flatten the
metro Ethernet networks, and then proceed to the access layer to ensure enhanced data
transmission for OLT/DSLAM uplink traffic. Finally, the IP RAN and OTN access
must be improved so that GE, C-RAN, private line, site services, and enterprise
private services all are facilitated.
As of the end of 2011, more than 200 metro networks in China have had OTN
introduced to enhance both fixed and mobile data transmission. Metro OTN has also
delivered enhanced enterprise private line services, enabling operators to gain a
competitive edge in a crowded landscape.
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