In customer network architectures, the customer owns and operates the equipment on the ring. In some cases, the customer also owns and operates the fiber or copper facilities that tie together the network elements. ATM/Frame Relay NetworksYou have already learned about the service-provider ATM and Frame Relay networks. The difference between a customer ATM/Frame Relay network and a carrier network is based on who owns the equipment. If the customer decides to lease its own fiber and DS1s or DS3s, the customer could buy the equipment itself and deploy its own private ATM or Frame Relay network. For a large customer with many sites, this might prove more cost-effective than acquiring the ATM or Frame Relay service from a carrier. The customer has a couple of added benefits when privately deploying ATM/Frame Relay:
Customer Synchronous Optical NetworksMany enterprise businesses are deploying their own private SONET networks by leasing dark fiber and "lighting" it themselves with their own capital SONET equipment. They deploy a SONET ring just as a service provider would; however, they are responsible for maintaining the network if it goes down. A disadvantage of the private SONET ring deployment is the troubleshooting process, which can take longer because the customer does not have the expansive trouble history database that a carrier with thousands of rings has. The Technical Assistance Center (TAC) personnel of the carriers see many more issues in a day, and TAC records can identify trends because of the large data pool of trouble tickets. The big advantage, of course, is money. The business case is strong for private ownership of SONET rings, especially because many geographies possess a fiber "glut" and lease fiber relatively inexpensively. Payback periods using legacy SONET equipment are nowhere near that of MSPPs but are still reasonable and justifiable, depending on the time frame. Legacy platforms were more rigid and costly, so there were not many private deployments; as a result, not much expertise was available among customer personnel to deploy legacy private SONET customer rings. Return on investment (ROI) for the SONET capital equipment stemmed from saving monthly SONET service charges from a carrier's service. End users must evaluate whether they have the talent on staff to monitor and maintain the SONET rings. IP and MPLS NetworksAs mentioned in the section on service-provider IP/MPLS, IP MPLS networks enable a global CoS data service across multiple IP VPN backbones to extend the reach and service capabilities for enterprises without purchasing additional customer premises equipment (CPE). The requirement is that each router in the backbone must be MPLS enabled; MPLS adds a label, which is a tag, at the edge of the network to each packet so that they are switched, not routed. This label contains a VPN identifier and a CoS identifier, and allows all packets to follow the same path and receive the same treatment. In a private deployment of IP/MPLS, such as in a carrier deployment, differentiating among customers is not a requirement because only the customer's traffic rides the backbone. However, a private IP/MPLS deployment creates a secure VPN for the customer with the following benefits:
Figure 4-15 shows an example of a customer-deployed IP/MPLS network. Here the customer owns the routers and configures the VPNs. The links between the routers are most often leased from providers; however, some companies, utilities, or public-sector entities own their own fiber or copper facilities, so even the links are privately owned. Figure 4-15. Customer-Deployed IP/MPLS Network Where Links Between Routers Are Leased from Service Providers |