Case Study

Thirty-Seven Incorporated's headquarters is located in Seattle, WA, with virtual connections to regional offices in New York, NY, Miami, FL, and Albuquerque, NM. Buffalo is a supplier depot with a single virtual connection to the New York regional office. Figure 21-7 illustrates this VPN implemented by Thirty-Seven, Inc.

Figure 21-7. Thirty-Seven, Inc. MPLS-enabled VPN

Thirty-Seven, Inc. is using an MPLS-VPN because the NSP has provided SLGs regarding the three Classes of Service provided by the NSP: Gold, Silver, and Bronze. Thirty-Seven, Inc. has several applications requiring WAN connectivity: e-mail, file sharing, file storage and data mining, and multimedia (voice and video applications).

MPLS enables the service provider to provide Thirty-Seven, Inc. the following Classes of Service to meet these application communication requirements (as detailed in the following table, Table 21-2).

Table 21-2. Thirty-Seven, Inc. Application/Class of Service Implementation Chart

Application	Class of Service
E-mail	Bronze
File sharing	Silver
Data mining	Silver
File storage	Bronze
Voice over IP (VoIP)	Gold
Video over IP	Gold

Thirty-Seven, Inc. has configured their Cisco routers with CAR policies to ensure that each CoS is queued in accordance with stated requirements. In this instance, the network service provider does not reclassify, or recolor, ingress traffic. Thirty-Seven, Inc. has decided that the VPN can be made more cost-efficient by recoloring outbound traffic from each site.

This recoloring enables Thirty-Seven, Inc. to take advantage of unused bandwidth in another CoS; for example, in the case Miami has exceeded the configured bandwidth queue for its Bronze connection to Seattle but has available bandwidth in its Gold connection. The Miami CE Router is configured to recolor this "extra" traffic to Gold so that it can be sent across the Gold virtual connection. In the event that Gold traffic is to be sent, the Bronze traffic is immediately dropped or buffered for transmission, depending on available resources in the Miami CE.

NOTE

If packets are dropped, it is up to the upper-layer protocols, such as TCP in the TCP/IP suite, to manage the retransmission of dropped packets.