Enterprises use Service Providers (SPs) to link to other sites. As shown in Figure 1, the SP edge module can include:
- Internet Service Providers (ISPs)
- WAN services such as Frame Relay, ATM, and MAN
- Public Switched Telephone Network (PSTN) services
The SP edge provides connectivity between the enterprise campus module to the remote enterprise data center, enterprise branch, and enterprise teleworker modules.
The SP edge module:
- Spans across large geographic areas in a cost effective manner
- Converges voice, video, and data services over a single IP communications network
- Supports QoS and service level agreements
- Supports security using VPNs (IPsec / MPLS) over Layer 2 and Layer 3 WANs
Click the Service Provider Edge in Figure 1 for more information.
When acquiring Internet services from an ISP, redundancy or failover should be considered. As shown in Figure 2, redundant connections to a single ISP can include:
- Single-homed - A single connection to an ISP
- Dual-homed - Two or more connections to a single ISP
Alternatively, it is possible to set up redundancy using multiple ISPs, as shown in Figure 3. Options for connecting to multiple ISPs include:
- Multihomed - Connections to two or more ISPs
- Dual-multihomed - Multiple connections to two or more ISPs