mFN Based Access Protocol


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First publication of mFN-based access protocols: 1998 GlobalComm

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mFN Based Access Protocol

  1. 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) One of the challenges facing the cable industry today is to cost-effectivelyupgrade a conventional cable network, which was originally designed for one-waybroadcast services, to a two-way broadband digital platform for emerging services.Following the traditional upgrade strategy, the industry has been feverishly restructuringcoax plants for more bandwidth, and enabling two-way capability with low-frequency(5-40 MHz) upstream technology. However, the small upstream bandwidth and ingressnoise limit service opportunities, and the required complex signal processing results inhigher operation and terminal cost. Further, the tree-and-branch architecture with manyusers sharing the coax bus forces the industry to standardize complex head-end mediateaccess protocols (MCNS, IEEE802.14), which rely on central contention resolution andresource reservation for all types of traffic with large collision domain. They may workwell in lightly loaded systems, but incur low efficiency, large delay, and difficulties toguarantee 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 laserdiode and a low-cost PIN diode, couple directly into the passive coax legs after eachdistribution coax amplifier, and is connected to the head-end with separate fiber. Whilethe existing systems still operating within the bandwidth defined by coax amplifiers, themFNs subdivide the serving areas into small cells (50 home-pass/mFN) and exploit theclean and large bandwidth above amplifier limitation for bi-directional transmission. Thistherefore simultaneously resolves both upstream and downstream limitations without re-engineering embedded coax plants. The use of clean spectrum and robust digitalsubcarrier 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-costcable network upgrade. The unique position of each mFN enables a considerable simplification indefining medium access control (MAC) protocols. Each mFN can do local policing, andresolve upstream contention within its serving area without involving other parts of thenetworks. This can be accomplished by incorporating a simple out-of-band signalingloopback scheme over the mFN. Active users contend in the upstream signaling channeland monitor the channel status and contention results over the downstream signalingchannel 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-costterminals (modified Ethernet transceiver, etc). No ranging is needed, and the head-endbecomes virtually operation-free for contention resolution. The relative small round-trip 1
  2. 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 100CO/HE Average delay (ms) Analog video FN mFN mFN 10 mFN New MCNS 1 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. 2