Cell Relay Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: IP Switching-TTL
Organization: DECUServe Message-ID: <25NOV199710131296@eisner.decus.org> References: <64uchc$lv3$1@dismay.ucs.indiana.edu> <64vcuc$3q$1@shell6.ba.= best.com> X-Trace: news.decus.org 880470793 19733 HOLDREGE [192.67.173.2] X-Nntp-Posting-Host: eisner.decus.org Date: Tue, 25 Nov 1997 15:13:00 GMT Lines: 38 Xref: news.indiana.edu comp.dcom.cell-relay:12008 In article <64vcuc$3q$1@shell6.ba.best.com>, bannai@best.com (Vinay Banna= i) writes... >In article <64uchc$lv3$1@dismay.ucs.indiana.edu>, >Nafez Aboulibda <nafez@igdv.fh-darmstadt.de> wrote: >>My name is Nafez Aboulibda, I'm doing my MSc project. >>There is some thing relating to the TTL field in the Flow identifier in= >>Ipsilon=92s publications >>"IP switching" that I couldn't understand. >>Since this field is not transmitted within the packet and their issue i= s >>to retain the function of >>TTL. >>My question is : where is the recovery procedure explicitly done to >>decrement the TTL field >>on each node . >>Ipsilon's words" the TTL field is not transmitted in the packet but it >>is recovered from the >>info. stored at the destination" >> >>with regards. >>Nafez Aboulibda >> >> > = >This is something of an issue for all IP switching and tag switching >folks. Since the packets (or the cells of the packets) are switched till= >they hit the egress node, there cannot be any TTL decrements. Tag folks >want to check the TTL value at the ingress point and based on the tag fi= nd >out how many swithing nodes it has to traverse to the egress point and >decrement that value from the TTL at the ingress. I have not been keepin= g >up with the MPLS for a while so I am not sure what their position is rig= ht >now. As far, the IFMP, I think what they do is somehow code the TTL valu= e >into the flow identifier and at the egress point of the switching core >network, they re-introduce the TTL value back into the IP header. I don'= t >think they decrement the TTL value either at the ingress or the egress. = Ascend's IP Navigator which is based on MPLS does decrement the TTL field= =2E It also explicitly prevents routing loops which is obviously important with = the high bandwidth connections used. |
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