This document discusses a mini-fiber node (mFN) technology for upgrading cable networks to support two-way broadband services in a more cost-effective way than traditional approaches. The mFN architecture uses low-cost fiber optic nodes connected to small sections of the existing coaxial cable network to provide clean bandwidth and simplify medium access control protocols. Local contention resolution at each mFN improves efficiency and quality of service support compared to existing centralized standards. The mFN approach provides abundant high-speed bandwidth while radically simplifying service provisioning and enabling standard-compatible MAC protocols for mixed asynchronous and synchronous transmission.

1. Providing QoS Over Mini-Fiber Node Cable Networks, X. Qiu and X. Lu
Providing QoS Over Mini-Fiber Node Cable Networks
Xiaoxin Qiu and Xiaolin Lu
AT&T Labs-Research
100 Schulz Dr.
Red Bank, NJ 07701
(732)345-3217 (voice), (732)345-3040 (fax)
xl@research.att.com
One of the challenges facing the cable industry today is to cost-effectively
upgrade a conventional cable network, which was originally designed for one-way
broadcast services, to a two-way broadband digital platform for emerging services.
Following the traditional upgrade strategy, the industry has been feverishly restructuring
coax plants for more bandwidth, and enabling two-way capability with low-frequency
(5-40 MHz) upstream technology. However, the small upstream bandwidth and ingress
noise limit service opportunities, and the required complex signal processing results in
higher operation and terminal cost. Further, the tree-and-branch architecture with many
users sharing the coax bus forces the industry to standardize complex head-end mediate
access protocols (MCNS, IEEE802.14), which rely on central contention resolution and
resource reservation for all types of traffic with large collision domain. They may work
well in lightly loaded systems, but incur low efficiency, large delay, and difficulties to
guarantee QoS.
To solve those limitations, we proposed and demonstrated a mini-fiber node
(mFN) technology that overlays existing networks with an economically viable fiber-to-
the-bridger architecture, as shown in Fig.1. The mFNs, each contains a low-cost laser
diode and a low-cost PIN diode, couple directly into the passive coax legs after each
distribution coax amplifier, and is connected to the head-end with separate fiber. While
the existing systems still operating within the bandwidth defined by coax amplifiers, the
mFNs subdivide the serving areas into small cells (50 home-pass/mFN) and exploit the
clean and large bandwidth above amplifier limitation for bi-directional transmission. This
therefore simultaneously resolves both upstream and downstream limitations without re-
engineering embedded coax plants. The use of clean spectrum and robust digital
subcarrier signals also allows us to use low-cost, low power consumption and space-
saving optical and RF components in the mFN and also at the HE, resulting in a low-cost
cable network upgrade.
The unique position of each mFN enables a considerable simplification in
defining medium access control (MAC) protocols. Each mFN can do local policing, and
resolve upstream contention within its serving area without involving other parts of the
networks. This can be accomplished by incorporating a simple out-of-band signaling
loopback scheme over the mFN. Active users contend in the upstream signaling channel
and monitor the channel status and contention results over the downstream signaling
channel facilitated by the mFN. This therefore enables the use of standard, but full-
duplex, Ethernet protocol (CSMA/CD), and therefore the use of standard and low-cost
terminals (modified Ethernet transceiver, etc). No ranging is needed, and the head-end
becomes virtually operation-free for contention resolution. The relative small round-trip
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2. Providing QoS Over Mini-Fiber Node Cable Networks, X. Qiu and X. Lu
delay between each user and the mFN (~2000ft) also substantially increases bandwidth
efficiency and reduces contention delay (Fig.2).
To provide higher-standard QoS, the headend need to manage certain scheduling/
reservation for synchronous type of transmission. Nevertheless, the contentions for
sending reservation requests and transmitting asynchronous data are still resolved locally
using out-of-band signaling. The headend dynamically partitions the transmission and
signaling frames into synchronous and asynchronous parts. For asynchronous
transmission, users are only allowed to contend in the asynchronous part of the frame and
transmit when contention succeeds. For synchronous transmission, users can content in
any part of the signaling frame to send requests to the headend. When succeed, the users
will wait for the headend to grand the requests in the downstream data channel. Because
the de-coupling of reservation (out-of-band requests) from the real upstream data
transmission, users can make reservation in the signaling channel, while others with pre-
permission can transmit data in the data channel at the same time. This therefore further
increases transmission efficiency, reduces overall delay, and satisfies different service
needs.
In summary, the mFN strategy cost-effectively upgrades a cable network with
abundant ingress-free bandwidth. By resolving the architecture limitations, it radically
simplifies service provisioning, and enables simple and standard-compatible MAC
protocols. The combination of local contention resolution and central resource allocation
enables efficient mixed synchronous and asynchronous transmission to support both
VBR-type of services and CBR-type of services with guaranteed QoS.
1000
100
CO/HE
Average delay (ms)
Analog video FN mFN mFN
10
mFN
New MCNS
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Services
0.1
New Services TV
Analog video Modem
0.01
5 50 500 750 1G
10 30 50 70 90
Number of active users
Fig. 2. Upstream delay comparison between mFN based NAD and MCNS standard based
cable modem. It was assumed that the average data rate is 120 kbps/user, with total
Fig. 1. Mini-Fiber Node (mFN) for cable upgrade
speed of 10Mbps. The assumptions for MCNS modem will change in real
implementation.
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