spaper06_slides - To support quality-of-service(QoS for...

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To support quality-of-service (QoS) for real- time data communications such as voice, video and interactive services using Hybrid Fiber Coaxial (HFC) networks.
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Higher transmission capacity compared to xDSL. Bidirectional hybrid fiber coaxial (HFC) networks can support interactive broadband applications, including video-on-demand, tele- conferencing, telephony, and Internet access. Attractive for the installed residential coax network's extensive coverage area.
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Uses a hierarchical tree-and-branch topology. The coaxial wire portion of the network extends from a fiber- optic interconnected node to the subscribers' homes.
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The fiber node has a fiber connection to the so-called head-end, which terminates the HFC network. All data coming from the subscribers is directed to the head- end.
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The frequency spectrum on the coax wire portion of the network is divided into a downstream region and an upstream region. Range of Downstream - 50 to 750 MHz, divided into channels of fixed width. Range of Upstream - 5 to 40 MHz with variable size channels. Data rates on the channels are 3 Mbps and 30 Mbps in the upstream and downstream directions.
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Each upstream channel is a multi-access channel, and collisions occur when multiple subscribers, transmit simultaneously on the channel. All downstream channels are collision-free.
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To transmit on the upstream channel, it first sends a transmission request to the head- end. With multiple stations transmitting a request at the same time, the requests collide, and a collision resolution protocol (CRP) is activated to ensure successful retransmission of the request.
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On successful transmission: o The head-end acknowledges the successful request. o Schedules a time slot on the upstream channel for data transmission. o Sends the station a grant message to inform the station when it can transmit. Since the grant message never allocates the same time slot to more than one station, all transmission of data is collision-free.
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MAC Operation: o An HFC upstream channel is divided into discrete time slots, called mini-slots. o The head-end designates some of the mini-slots as contention slots (CS) and some as data slots (DS). o Contention slots, which are one mini-slot long, are used to transmit requests for bandwidth. o Data slots, which are several mini-slots long, are used to transmit data.
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MAC Operation: o Only CS are prone to collisions, which occur when more than one station attempts to transmit a request in the same slot. o Data slots are explicitly allocated to a specific station by the head-end and are collision-free. o
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spaper06_slides - To support quality-of-service(QoS for...

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