put router to sleep and wake it up

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Dec 10th, 2008
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Hi,


In past few years, some people were working on developing algorithms and schemes to reducing power consumption of network device. I'm wondering, whether any of the proposed schemes has been realized on any cisco routers/switches?


If it does, can anyone tell me where to find the document about how long it will take a router(e.g., edge router of an AS) to wake up a sleeping line cards? Does it took milliseconds or microseconds?


Thanks a lot.


Joe


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Giuseppe Larosa Thu, 12/11/2008 - 00:08
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hello Joe,

routers usually cannot sleep because they need at least to exchange some messages like L2 keepalives or routing protocols messages.


There are strategies for using on demand ISDN links, and with DDR you can do it logically on PPPoE (or other PPPoX) but I don't know of any power saving feature.

the reason is that being internetworking devices you cannot say when it is an idle period: if one lan client wants to access a remote resource the wan link has to be used.

the more you think to an enteprise solution the more you need the router to be alive and talking with neighbors to be ready to route/forward traffic.


Hope to help

Giuseppe


insert7992 Thu, 12/11/2008 - 01:42
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Hi, Giuseppe,


Thanks for the reply.


Yes, routers usually cannot sleep. However, since not all components work all the time, it's not necessary to keep all parts of the router fully worked. For example, some people propose to put some router line cards to sleep if it didn't receive any packets for an time interval; and re-active the line card if new packets are received. Another scheme is to put line cards to sleep and buffer the receving packet till certain amount and then awake the router and transimit the packets.


I'm interested in the time needed to awake a sleeping line card.


Joe

patrickvanham Thu, 12/11/2008 - 02:16
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having a linecard go to sleep doesn't make much sense since even a few milliseconds may cause problems with time-sensitive data. Buffering data until a certain amount is received makes even less sense, that will only increase load on the total network (TCP retransmits).


There may be a scenario such as scheduled sleep times in small corporate LAN environments that might work, but for serviceproviders and enterprises it would not be useful.

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