Networks

f## Components of a network

1. End systems, clients running network apps
2. Communication links: fiber optics, radio
3. Packet switches: forward packets. routers and switches
4. Protocols: TCP, ID, UDP, HTTP, etc.

The internet

A network of networks - Interconnected ISP

Componenets of the Internet

1. Standards (open, free)
   • RFC: Request For Comments
   • IETF: Internet Engineering Task Force
2. Infrastructure that provides services to applications
   • Web, VoIP, email, games
3. Programming interface to apps
   • hooks that allow sending and receiving app programs to connect to the internet
   • provides service options, analogus to postal service
   • Socket APIs

Important Properties for the Internet

1. Interoperability: standard communication protocols (HTTP, TCP, UDP, IP, ARP, whatever-P), conventions.
   • Each P deals with a unit of data called a packet. Each packet has a H: header and a P: payload.
   • protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission and receipt
2. Shared resources: Internet is a shared resource.
   • Time division multiplexing (TDM, eg: RCS)
   • Frequency division multiplexing (FDM, eg: multiprocessors)
   • Data traffic is bursty. Packet switching & statistical multiplexing:
     • 1 Mbps link.
     • Each user 100 Kbps when active.
     • Active 10% of the time.
     • Packet occupies the link on demand only
     • FDM or TDM - fixed dedicated fraction of link
3. Complex interacting components
   • Many pieces to a network: naming, routing, reliability, lots of apps
   • Emergent Behaviour
   • Layering reduces interactions from \(\mathcal{O}(N^2)\) to \(\mathcal{O}(N)\) where \(N\) is the number of modules
   • Internet protocol stack:
     • Application (FTP, HTTP)
     • Transport (TCP, UDP)
     • Network (IP, routing)
     • Link: data transfer b/n neighbouring network elements (Ethernet, Wifi)
     • Physical: Hardware
     • Cascaded headers
4. Scalability