Internet Protocols-1.2 network edge
1.2.1 A closer look at network structure:
network edge:边缘网络
- hosts: clients and servers
- servers often in data centers
- part of the network with the users and computers
边缘网络包括汇聚层网络和接入层网络的一部分或全部， 是接入用户的最后一段网络。
access networks, physicalmedia: wired, wireless communication links
- part of network connecting edge to rest of network
network core:
- the “middle” of the network
- interconnected routers
- network of networks
edge router:边缘路由器
边缘路由器，又称“接入路由器”，是位于网络外围（边缘）的路由器。位于网络中心的路由器叫核心路由器。边缘路由器和核心路由器是相对概念，它们都属于路由器，但是有不同的大小和容量，某一层的核心路由器是另一层的边缘路由器。
1.2.2 Access networks and physical media
Q: How to connect end systems to edge router?
如何连接终端系统到边缘路由器?
- residential access nets
- institutional access networks (school, company)
- mobile access networks
1.2.3 Network basics – packets
- Imagine we want to transmit 10GB of data.
- This may take several hours to send.
- It is useful to split the data down into smaller units (known as
packets). - This “packet” of data can be sent relatively quickly.
- The packet can be, for example, checked for errors.
- The packet could be retransmitted if a problem was detected.
1.2.4 Host: sends packets of data
- takes application message
- breaks into smaller chunks, known as packets, of length L bits
- transmits packet into access network at transmission rate R
- link transmission rate, aka link capacity, aka bandwidth