Net II - Wide Area Network
ABC removed the leased T1 lines and went to subcontracted frame relay service from MCI.Subcontracted frame relay is a special type of public switched data network (PSDN). PSDNs aretypically portrayed as clouds on network diagramsbecause the user does not have to know what isgoing on inside the PSDN. The PSDN serviceprovider handles all switching, management, andmaintenance tasks. Overall, PSDNs are easier touse than leased lines, and because of price competition,PSDNs tend to be less expensive than acomparable mesh of leased lines. ABC’s Net II used Cisco routers to switch data frames over the frame relay PSDN. The Cisco routers on ABC’sNet II followed the frame relay protocol whichroutes data according to layer two or the data linklayer protocol. Once the frame is in the PSDN, itis MCI’s responsibility to deliver the frame at theother end of the cloud to the proper Cisco routerof ABC’s Net II.