Computer Networks

Basic idea

Spatially separated computers exchanging messages over a shared physical medium according to a layered stack of protocols (link → IP → TCP/UDP → application).

Key facts

• Layered model: physical / link / network (IP) / transport (TCP, UDP) / application.
• Internet: a network of networks linked by ISPs and backbone routers; addresses via IP.
• Intranet: privately administered subnet of the Internet, isolated by firewalls.
• Wireless paradigms enable mobile, ubiquitous and IoT computing.

Common distributed systems based on widely used computer networks

• The internet
• Intranets
• Wireless networks

The internet

Consists of a large number of interconnected collection of computer networks of different types. Features include:

• Computers interacting using a common means of communicating.
• Many different services (applications) (WWW, FTP, SFTP)
• A number of Intranets linked by backbones
• Internet Service Providers (ISPs), that provide access to services on the Internet while providing local services such as email and web hosting.
• A backbone network link with high transmission capacity
• Communication via Satellite, fiber optic cables and other high bandwidth circuits.

Intranets

Is a portion of the Internet that is seperately administrated by organisations. Features:

• A boundary that can be configured to enforce local security policies.
• Several local area connections (LANs) linked by backbone connections.
• A connection to the Internet via a router allowing users within the intranet to acces services on the Internet.
• Firewalls to protect an intranet by preventing unauthorized messages leaving or entering by filtering incoming and outgoing messages.

Wireless networks

Wireless networks allow the intergration of small computing devices (laptops, mobile phones etc)

Three popular paradigms that use wireless networks are:

1. Mobile computing : The mobile computing paradigm allows users to perform computing tasks on the move, while being part of a distributed system.
2. Ubiquitous computing : Where cheap computing devices are embedded in devices that are used in parts of parts of a distributed system.
3. Internet of Things : Everyday objects are addressable and connected to the internet and may be part of a distributed system.

Siblings

• CAP (or more accurately PACELC) theorem
• Challenges of Distributed Systems
• Consistency
• CRDT (Conflict-free Replicated Data Types)
• distributed file systems
• distributed models
• Distributed Systems
• FLP result
• operating systems