My book's definition for access network is "a network that physically connects an end system to the first router (also known as the "edge router") on a path from the end system to any other distant end system". However, the figure below(access networks highlighted in blue) seems to indicate that the network extends beyond the first router, which is at odds with the definition at the top of the page. Is the diagram or definition wrong? How can you reconcile the two?
There may be further information about Figure 1.4 in the book itself. There may also be supplementary information in an associated publication such as a study/class guide or downloadable supplemental materials - maybe even in the teaching materials. If not (or you don't have access to them), I see one of two different explanations:
- This is an error. Today, publishers often post errata for books on their website. I would check to see if such exists and if it mentions this issue (and others that may throw you as you work through the book).
- It is intended this way to show that each home has an access network, but those homes are also in themselves ultimately a single client on the ISP access network. Put another way, from the ISP perspective each home is a client attached to their access network.
The blue line is a connection. The home router is connecting to the ISP router. The home router is the first router in the home, so it is the edge router for the home. The router to which it connects is a router at the ISP, and that router is not part of the home network, it belongs to the ISP network. The home router must connect to an ISP to access the Internet. The home network could change to a different ISP, and the line will then connect to a different ISP router. The ISP router is not part of the home network; it is part of the ISP network.