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2013年5月14日 星期二

2013年1月24日 星期四

[Network] Bridge & Router operational Mode

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[Network] Bridge & Router operational Mode 



Selecting Bridge & Router operational Mode


The operational mode of the wireless device should be selected according to the requirements and applications. The table below gives a brief outline of the pros and cons of each operational mode.













































Bridge Mode


Router Mode


  • Does not block any broadcast or multicast


  • Blocks and provide protection against broadcast storms


  • Transparent bridge and can pass Non-IP protocols


  • Only IP protocol is supported


  • PPPOE protocol Pass-through


  • No PPPOE protocol pass-through


  • Able to transport VLAN tagging


  • Doesn't supports VLAN


  • No network segmentation. One broadcast domain


  • Network segmentation (Clients can be on different IP subnet)


  • Can only relay the DHCP client's request to the external DHCP server


  • Can Act as DHCP server & relay which Prevents IP conflict & DHCP Injection


  • Bridges maintains bridging table (Mac) & STP can be used to avoid loops


  • No STP feature; maintains routing table


  • External bandwidth Controller can be used to control the speed of the clients by Mac or IP address


  • External bandwidth Controller can be used to control the speed of the clients by IP only


  • In client device, it uses MAC address to associate which requires WDS compatible AP


  • Use SSID to associate, work with any 802.11a/b/g AP

Bridge mode



  • Device will act as a transparent bridge and will operate in Layer 2 - Mac layer


  • Bridge mode association is based on channel and MAC authorization only. SSID will not be used for the setting up a link.


  • If the remote is configured in a bridge mode and channel needs to be changed then channel needs to be changed at both the radios.



Router mode



  • Device will operate in Layer 3 to perform routing. It is pure routing and network provider has to take care of proper routing as there is no NAT feature in airHaul.


  • Association is based on SSID.




  • Remote configured in a Router mode will automatically follow the Root Bridge for any change in channel. Due to this, Remote Router mode is preferred for selecting a channel with low interference for setting up a link in the beginning


Reference :


2011年12月2日 星期五

[Dosis Cable Modem] DOCSIS 101: T1,T2,T3, & T4 Timeout Descriptions

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This is a handy summary of the various timeout errors you will find in a DOCSIS network.  T3 and T4 timeouts are described in much more detail elswhere in this blog, however this post provides a high level overview of the various timeouts as a reference.  Thanks to baranek110 for the tutorial located on Cable-Modem’s Blog.



T1 ( No UCD’s received )



Explanation: The cable modem has not received any periodic Upstream Channel Descriptor (UCD) messages from the CMTS within the timeout period. This error message is DOCSIS event message is U01.0, Upstream Channel Descriptor.



T2 ( No Maintenance Broadcasts for Ranging opportunities received )



Explanation: The cable modem did not receive a broadcast maintenance opportunity in which to transmit a Ranging Request (RNG-REQ) within the T2 timeout period (approximately 10 seconds). The cable modem is resetting its cable interface and restarting the registration process. This error message is DOCSIS event message is R01.0, Ranging Request.



T3 ( Ranging Request Retries Exhausted )



Explanation: The cable modem has sent 16 Ranging Request (RNG-REQ) messages without receiving a Ranging Response (RNG-RSP) message in reply from the CMTS. The cable modem is therefore resetting its cable interface and restarting the registration process. This typically is caused by noise on the upstream that causes the loss of MAC-layer messages. Noise could also raise the signal-to-noise ratio (SNR) on the upstream to a point where the cable modem’s power level is insufficient to transmit any messages. If the cable modem cannot raise its upstream transmit power level to a level that allows successful communication within the maximum timeout period, it resets its cable interface and restarts the registration process. This error message is DOCSIS event message is R03.0, Ranging Request.



T4 ( Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received )



Explanation: The cable modem did not received a station maintenance opportunity in which to transmit a Ranging Request (RNG-REQ) message within the T4 timeout period (30 to 35 seconds). The cable modem is resetting its cable interface and restarting the registration process. Typically, this indicates an occasional, temporary loss of service, but if the problem persists, check for possible service outages or maintenance activity on this particular headend system. This error message is DOCSIS event message is R04.0, Ranging Request.



T6 ( Cable Interface Reset )



Explanation: The cable modem has sent 3 Registration Requests (REG-REQ) to the CMTS without receiving a Registration Response (REG-RSP) within the T6 timeout period (3 seconds). The cable modem is therefore resetting its cable interface and restarting the registration process



This problem can also occur if the DOCSIS configuration file is corrupt, or if it contains a large number of vendor-specific information fields (VSIF). If the configuration file contains a large amount of VSIF information, the cable modem might generate a Registration Request (REG-REQ) that exceeds the maximum size of DOCSIS MAC-layer management messages (1514 bytes plus the header). The CMTS considers this an invalid MAC-layer management message and drops it, without replying.



 



Reference :



DOCSIS 101: T1,T2,T3, & T4 Timeout Descriptions

2011年10月25日 星期二

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