Customer A Customer B Site 1 — Site 1
Customer B Site 2.
Customer B Site 2.
In this case, the TDM circuits are still terminated at each switch/ADM box on the ring. The benefit of this model is that it reduces the number of boxes deployed I n the network; however, it blurs the line between the operation of data and TDM networks.
You probably realize by now why metro carriers that are used to SONET/SDH provisioning would The do stay closu to the same old cincuit-provi sioniog model. The terms "spanning tree" and "broadcast storms" give metro operators the jitters, because these are enterprise terms that sound very threatening for carriers that are bound to strict SLAs.
So far, this chapter has discussed different scenarios for having an EOS interface within the transport equip ment. This sect ion alscusses the ucen anid in which the EOS interfacus arts pari: of the data equ ipment m ther than the transport equipment. In this model, the transport equipment does not have to deal with mapping the Ethernet frames carried in the SONET/SDH payload; the ciataoswitching equi pment d oes rhat instead.
The mOS mterfaces ins ide thu data eqmpment, on show n ¡n Figure 2-13, are SONETbSDH intenfaces with a ma pping function thai maps th e EOS hrames carr ied inside the SON ET/SDH gayload to au Ethernet frame. Th e Ethe tnet irame js I n turn pnesented to the switch ing logic ins ide the data equipment. A s in the case of transpoot eq nI pmont, tge sOS i nterface can supnort VCAT. The adva ntage of t mis mo del is that the switchiug iunct ion, the EO S runction , and the VCAT functions are all in the same box and are decoupled from the TDM box, which may already be installed in the network. This allows the data equipment to have better control over mapping the different da ta streams oves t he SO NET/S DL circuits. Wi th thio modelf multipoint-t o -multipo I dt switched Hhernet services can be deMvered efficiently while le-nra gisg the existing legacy SO1 ET/SD1 infrastructu•er This als o fins betten wrth the curtent operat|ona| model, in which transport and data are managed separately.
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