▁traffic ▁burst s ▁occur ▁in ▁the ▁soft ▁pipe , ▁they ▁cannot ▁pre empt ▁hard ▁pipe ▁band width . ▁IP ▁hard ▁pipe ▁res erves ▁band width ▁and ▁ens ures ▁low ▁delay ▁for ▁services , ▁and ▁therefore ▁can ▁be ▁used ▁to ▁carry ▁le ased ▁line ▁services ▁of ▁high - value ▁customers . ▁ ▁Pur pose ▁ ▁As ▁car rier ▁networks ▁are ▁evol ving ▁to ▁IP , ▁customers ▁with ▁strict ▁band width , ▁delay , ▁and ▁security ▁requirements ▁prefer ▁SD H ( S ynchronous ▁Digital ▁Hier archy ) ▁networks . ▁To ▁retain ▁these ▁customers , ▁carri ers ▁must ▁maintain ▁both ▁IP ▁and ▁SD H ▁networks , ▁which ▁inc urs ▁significant ▁maintenance ▁costs . ▁Therefore , ▁carri ers ▁expect ▁to ▁migr ate ▁their ▁customer ▁network ▁to ▁the ▁IP ▁network ▁to ▁reduce ▁maintenance ▁costs ▁and ▁facil itate ▁user ▁management . ▁ ▁IP ▁hard ▁pipe ▁is ▁an ▁IP ▁network - based ▁end - to - end ▁transmission ▁technology ▁that ▁provides ▁band width ▁guarantee ▁and ▁low ▁delay ▁through ▁dedicated ▁hardware ▁and ▁independent ▁pip es , ▁allowing ▁IP ▁networks ▁to ▁provide ▁end - to - end ▁transmission ▁services ▁with ▁SD H ▁service ▁quality . ▁IP ▁hard ▁pipe ▁also ▁provides ▁service - specific ▁S LA ▁( service - level ▁agreement ) ▁monitoring ▁and ▁gran ular ▁O AM , ▁ens uring ▁smooth ▁evolution ▁of ▁SD H ▁networks ▁to ▁IP ▁networks . ▁ ▁Ben ef it ▁ ▁IP ▁hard ▁pipe ▁applies ▁to ▁carri ers ' ▁key ▁services ▁( such ▁as ▁le ased ▁line ▁services ▁of ▁enter pr ises ) ▁and ▁bear er ▁networks ▁for