General Computer Science 320201 GenCS I & II Lecture ... - Kwarc

computers, connections and services.
The growth of the Internet rests on three design decisions taken very early on. The Internet
1. is a packet-switched network rather than a network, where computers communicate via
dedicated physical communication lines.
2. is a network, where control and administration are decentralized as much as possible.
3. is an infrastructure that only concentrates on transporting packets/datagrams between computers.
It does not provide special treatment to any packets, or try to control the content
of the packets.
The first design decision is a purely technical one that allows the existing communication lines to
be shared by multiple users, and thus save on hardware resources. The second decision allows the
administrative aspects of the Internet to scale up. Both of these are crucial for the scalability of
the Internet. The third decision (often called “net neutrality”) is hotly debated. The defenders
cite that net neutrality keeps the Internet an open market that fosters innovation, where as
the attackers say that some uses of the network (illegal file sharing) disproportionately consume
resources.
Package-Switched Networks
Definition 489 A packet-switched network divides messages into small network packets
that are transported separately and re-assembled at the target.
Advantages:
many users can share the same physical communication lines.
packets can be routed via different paths. (bandwidth utilization)
bad packets can be re-sent, while good ones are sent on. (network reliability)
packets can contain information about their sender, destination.
no central management instance necessary (scalability, resilience)
c○: Michael Kohlhase 339
These ideas are implemented in the Internet Protocol Suite, which we will present in the rest of the
section. A main idea of this set of protocols is its layered design that allows to separate concerns
and implement functionality separately.
The Intenet Protocol Suite
Definition 490 The Internet Protocol
Suite (commonly known as
TCP/IP) is the set of communications
protocols used for the Internet and
other similar networks. It structured
into 4 layers.
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Layer e.g.
Application Layer HTTP, SSH
Transport Layer UDP,TCP
Internet Layer IPv4, IPsec
Link Layer Ethernet, DSL