1. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–1 IP packets arrive in one door and are packaged together and shipped to their destination through a back door.

2. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–2 Routers interfacing to host devices are referred to as host routers. Routers connected to the network are called network routers if they interconnect to an internal network and core if they interconnect to the outside world’s core network.

3. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–3 Routing between networks requires host routers to interface with end devices. The host router also interfaces with a core or network router to connect to other networks.

4. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–4 Configuring a static route on a Cisco router is fairly simple. The commands needed to set up the route are shown here.

5. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–5 Routing protocols deploying distance vector routing algorithms count the number of hops referring to devices between the initiating router and the terminating router.

6. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–6 The dotted-decimal system is used to define IP addresses. Each decimal value has an equivalent binary value that is used by the device. The decimal value is used by humans as it is easier to understand.

7. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–7 Classless IP addressing such as CIDR improves network efficiency by reducing the number of routes needed across the Internet through a hierarchical domain structure. Route tables are built between Tier 1 ISPs. Lower- level networks communicate only with higher-level Tier 1 ISP.

8. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–8 IP routing within an internal LAN depends on IP addresses attached to the devices hanging off the network.

9. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–9 Packets traveling between Detroit and St. John’s travel on a DS-1 within a frame relay frame within an IP packet. Each router interface has an IP address assigned to it along with a frame relay DLCI.

10. Introduction to Telecommunications, 2/e By M.A.Rosengrant Copyright (c) 2007 by Pearson Education, Inc. All rights reserved. Figure 12–10 The internal router ties to the ISP’s POP. Traffic travels through the interface port on the internal router that is tied to the core router located at the ISP’s POP. The core router ties to the supernet. Traffic is routed between the routers using standard routing protocols such as RIP. Traffic is routed across the internet between Tier 1 ISOs with supernet routing using sophisticated protocols such as BGP. In both instances there are interface ports or doors for traffic to come in and go out.