Docsis contention slots

If your network is live, make sure that you understand the potential impact of any command.Telephony communication has requirements over and above those needed for data.If you are pushing TCP traffic, use multiple PCs through one CM.The theoretical peak US rate you can get with A-TDMA is about 27 Mbps or so (aggregate).

The industry is also looking to serve commercial customers and add voice services.Dynamic Map Advance is an algorithm that automatically tunes the look-ahead time in MAPs based on the farthest CM that is associated with a particular US port.

TCP, on the other hand, requires an acknowledgment to prove that the sent packet was correctly received.Performance Characterisation of the MCNS DOCSIS 1.0 CATV Protocol with Prioritised First. Figure 1 The MCNS DOCSIS 1.0 system. the contention slots,.The goal of this document is to explain how to optimize throughput and availability in a DOCSIS environment and to explain the inherent protocol limitations that affect performance.When a CM is transmitting a large block of data US (for example, a 20 MB file), it will piggyback bandwidth Requests in data packets rather than use discrete Requests, but the modem still has to do the Request-and-Grant cycle.10-Specific_system_DOCSIS +. DOCSIS Overview, Ajay. 1023 A packet arrives R = 11 Next MAP has 6 contention slots 6<11 so keep waiting Next MAP has 2 contention.There is always a trade-off and compromise relationship between throughput, complexity, robustness, and cost.Keep in mind, however, that you will disconnect all modems on the system temporarily, when you make this change.

Issue the show cable modem phy command to see the physical layer attributes of the modem.Because this large total packet will take some time to transmit from the CM to the CMTS, the PPS will decrease accordingly.

As technology becomes more advanced, ways will be found to compress more efficiently or to send information with a more advanced protocol that either is more robust or is less bandwidth intensive.It does no good to decrease the homes per node if you just combine them again in the headend (HE) anyway.It is also advantageous to have different amounts of FEC associated with the type of burst.The DOCSIS specifications are intended to define the behavior of Cable.1. A method of testing an upstream DOCSIS channel with a test signal transmitted within mini-slots allocated for contention transmission or data PDUs during normal.In an attempt to minimize the affect of burst errors, a technique known as interleaving is used, which spreads data over time.Therefore, you might want to adjust your MSS to 1380, to reflect the maximum useful data in each packet.More channel BW means more US bps, which means more modems can be supported.

If admission control is used on the US, it will make some modems not register when the total allocation is used up.Set the DOCSIS configuration file for no minimum, but with a maximum of 20 MB up and down.Many modems can be active for the initial polling, but only one modem can be active in the US at any given instant in time.Fragmentation is also supported in DOCSIS 1.1. Concatenation allows several smaller DOCSIS frames to be combined into one larger DOCSIS frame, and be sent together with one request.

Also keep in mind that modems must be rebooted, for the changes to take effect.To help alleviate this bottleneck problem, Telco Return takes advantage of Point-to-Point Protocol (PPP) and makes the acknowledgments much smaller.This document is not restricted to specific software or hardware versions.The cable default-phy-burst command overrides the DOCSIS configuration file setting of 0, and the lower of the two numbers takes precedence.It then transfers control to a CGI script that does the actual analysis and displays the results.The CMTS provides time slots and controls the usage for each upstream interval. The CMTS sends regular mappings of minislot structure in downstream broadcast MAP messages. The CMTS allocates contention broadcast slots that all CMs can use, and allocates upstream minislots for unicast or noncontention data from specific CMs.Extreme caution should be used before you change the DS modulation.

Remember that the US is a TDMA-based, slotted contention medium where time slots are granted by the CMTS.The packet size, referred to as MTU, is the greatest amount of data that can be transferred in one physical frame on the network.It could be more than 4 ms, which will be every other MAP opportunity.Max Concat Burst affects 1.1 modems that can also fragment, so they can concatenate many frames with one request but still fragment into 2000-byte packets for VoIP considerations.Greater spectral efficiency with 64-QAM creates better use of existing channels and more capacity.

Understanding the limitations will aid in expectations and optimization.There was an older Broadcom issue where it would not concatenate two packets, but it could do three.This could entail the use of DOCSIS 1.1 QoS provisioning, payload header suppression (PHS), or DOCSIS 2.0 features.The problem of allocating bandwidth on the upstream channel of an HFC cable network for contention-based. in DOCSIS contention slots in a shared.If typical packets made up of 1518-byte Ethernet frames are sent at 250 PPS, that would equal about 3 Mbps because there are 8 bits in a byte.Toshiba also sends the next Request in front of a grant, to achieve a higher PPS.The total number of simultaneous users is based on a Poisson distribution, which is a statistical probability algorithm.Traffic engineering, as a statistic used in telephony-based networks, signifies about 10 percent peak usage.That is a secondary effect, and it is that effect which can cause a decrease in peak US data throughput.

This might have something to do with setting the Max Traffic Burst the same as the Max Concat Burst, so more testing might be warranted.

Patent US8134921 - CMTS upstream channel bandwidth

The DS can be severely hampered, if the acknowledgments are not concatenated on the US.This payload is further reduced, because it is also shared with DOCSIS signaling.