at interfaces with optical networks 10/100Kbps Ethernet or 1 Gigabit Ethernet* at 10 Gig-E per port** JUNIPER NETWORKS Dual redundant power supplies Four built-in 10 Gig-E uplinks to optical networks** Management ports for administration and software Two ports (clock input/output), updates (console Ethernet, BITS input for clocking on Aux + USB drive connector) protocols such as SONET and Fibre Channel that require exact timing*** Types of ports: * SFP (Small Form-factor Pluggable) ** XFP (10 Gigabit Small Form-actor Pluggable) *** UART (Universal Asynchronous Receiver/Transmitter) Figure 6-1 When routers are used in a network's edges, carriers use the services described in this illustration. These services are not implemented in core, aggrega- tion routers. (Courtesy Juniper Networks) Core, Aggregation Routers Core routers carry the highest concentration of traffic. A single core router connects to multiple edge routers, aggregates traffic from these edge routers, and then sends it to distant cities and countries. If a single router doesn't have the capacity to handle this aggregated traffic, multiple routers can be networked together. When this is done, networked routers function as a single entity with a single management interface. This simplifies the carrier's operations, upgrades, and remote diagnostics. The Internet Networking routers together is commonly done through virtualization. (See Chap- ter 1, "Computing and Enabling Technologies," for information on virtualization.) Vir- tualization enables multiple servers or computers to appear as one device. In addition, traffic is balanced among all of the networked routers. If one router fails, the others absorb its traffic. Ensuring Reliability in the Core and Edge Routers sold to carriers and to large web sites such as Google and Amazon are designed for "five 9s" of reliability. This means that they offer 99.999 percent uptime. They are sold with hot-swappable cards that connect to other services and networks. If a card fails, it can be replaced without tak