1、CMTS Load Balance OverviewBy Zhimin ZhangHow LB usually work Each LBG contains some DS/US channel.When modem is registered,it will be assigned to a LBG(except legacy LBG.)CMTS check the balance status periodically,if not balanced,move some modem to lower load channel.How to measure balance status Mo
2、dem count Whether modem number is balanced across channels.Utilization Whether traffic load is balanced.Service flow(not support anymore)Whether service flow number is balanced.The load is counted base on channel,not only within LBG.“show cable load load”Modem move strategy(When and how many times t
3、o move)Static LB Move modem once after registered Dynamic LB Move modem whenever not balanced.Passive LB CMTS ignore the register for modem on overload channelHow to move modem(message send to modem)DCC Move primary DS DBC Move both primary and bonding group.UCC Move upstream only Init tech 0-4,conf
4、igurable.LB Types Legacy Load Balancing(Not supported in new release)Cant differentiate individual modem Docsis Load Balancing D2.0 GLBG(D2.0 modems)D3.0 GLBG(D3.0 modems)RLBG(both 2.0/3.0)Modem will be assigned to a load balance group to take effect.“show cable load-balance”How to create LBG 2.0 GL
5、BG/RLBG use the same command,but RLBG has a restrict keyword cable load-balance docsis-group 1 restricted downstream Modular-Cable 7/1/0 rf-channel 0-7 upstream Cable7/1/0 0-3 3.0 GLBG are created automatically when FN is created.Cant be created by CLI,but parameter can be changed.Legacy Load Balanc
6、ing Cisco private solution.Not process each individual modem after registered.No LBG assignment.Docsis LB Assignment RLBG has the highest priority If a modem does not match the RLBG,then it will be assigned to GLBG base on DOCSIS version and channel set.2.0 modem is assigned to 2.0 GLBG.3.0 modem is
7、 assigned to 3.0 GLBG.RLBG can match tagging,oui,docsis-version,service type,cli GLBG are assigned by channel set.To save the system resource Since there may be tens of thousands of modems.LB will not move modem in real time,it will check the balance status after every specific interval.Default 30s.
8、“interval”.To reduce ping-pong effect(flap)In a platform with unstable modems offline/online,cmts will always found its un-balanced and try to move modem.Traffic statistics has a delay,so CMTS may move to many modems to another channel and have to move it back in next interval.Threshold is used to a
9、ccept somewhat un-balance.So that it will not waste unnecessary resource.“threshold”Treat voice/video different By default,modem that has special service will not be moved by LB.But this can be changed by“policy”command.This is to ensure the service quality.“policy”We dont want a specific modem to b
10、e moved Exclude command“docsis-policy”could be used to disable a modem being moved permanently or for some period.“docsis-policy”Continue For utilization based,move a modem that with high traffic will be more efficient because less modem needs to be moved.But if the traffic is very high,such as 75%o
11、f a channel,then better not to move it,because it may make other channel overload as well.“disable-throughput-lowerbound”to define what is high load modem.Upperbound not support yet.We may want some modems moved first Some modem may have some important service,so if possible,move other modems first.
12、LB priority in modem config file.Dynamic D3.0 LB Currently support static/dynamic LB for NB modems.Currently support static LB for WB/UB modems.Now we are trying to support dynamic LB for WB/UB modems.A lot of exception for LB Case 1：Channel-1 has 15%traffic,channel-2 has 1 percent,threshold is 1%.Modem will be moved from channel-1 to channel-2.But since channel-1 usage is also very low,its not needed to move modem at all.“min-threshold”is used to avoid unnecessary modem move.
