Configuring
Next, the Cisco uBR900 series performs a series of
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Table 40 | Cable Access Router Initialization Sequences and Events |
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Sequence |
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1. |
| Scan for a downstream channel |
| The Cisco uBR900 series acquires a downstream |
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| and establish synchronization |
| channel by matching the clock sync signal that is |
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| with the CMTS. |
| regularly sent out by the CMTS on the downstream |
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| channel. The cable access router saves the last |
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| operational frequency in nonvolatile memory and tries |
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| to reacquire the saved downstream channel the next |
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| time a request is made. |
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| Note | An ideal downstream signal is one that |
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| synchronizes QAM symbol timing, FEC |
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| framing, and MPEG packetization, and |
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| recognizes downstream sync MAC layer |
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| messages. |
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2. |
| Obtain upstream channel |
| The cable access router waits for an upstream channel |
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| parameters. |
| descriptor (UCD) message from the CMTS and |
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| configures itself for the upstream frequency specified |
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| in that message. |
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3. |
| Start ranging for power |
| The cable access router waits for the next upstream |
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| adjustments. |
| bandwidth allocation map message (MAP) from the |
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| CMTS to find the next shared request timeslot. The |
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| router then sends a ranging request message on the |
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| next available shared request timeslot, communicating |
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| its UID (its unique MAC address) using a temporary |
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| SID of 0 (zero) to indicate it has not yet been allocated |
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| an upstream channel. |
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| In reply to the cable access router ranging request, the |
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| CMTS sends a ranging response containing a |
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| temporary SID to be used for the initial router |
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| configuration and bandwidth allocation. As needed, |
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| the router adjusts its transmit power levels using the |
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| power increment value given by the CMTS in its |
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| ranging response message. |
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| Note | At this point, the cable access router has |
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| established connectivity with the CMTS but is |
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| not yet online. The next steps allocate |
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| “permanent” upstream and downstream |
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| frequencies, and the configuration required for |
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| IP network connectivity. |
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| Cisco IOS Multiservice Applications Configuration Guide |
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