Local area networks

LAN (local area network)
According to Cisco, a LAN is a network of computers and other components located relatively close together in a limited area.

VLAN (virtual LAN)
According to Cisco, a VLAN is a single broadcast domain.

Switching versus routing

According to Cisco, a switch creates a network and a router connects networks. What is the difference between switching and routing?

Names, addresses and routes

In computer networks, a source process inspects a string of bits in order to make decisions about how to reach a destination process. In this context, the string of bits could be one of the following:

• Names are independent of location. Names continue to be valid regardless of changes to the location of the destination and which source might be attempting to reach that destination. Names are also referred to as identifiers or IDs.
• Addresses are dependent on the location of the destination. An address is valid regardless of which source might be attempting to use that address. But, changes to the location of the destination would change its address.
• Routes are dependent on the location of both the source and the destination. Different sources may have different routes to reach the same destination. A source would likely require different routes to reach different destinations.

Ethernet address vs. IP address

Ethernet addresses use a flat hierarchy design to satisfy the primary design objective of autoconfiguration.

IP addresses use a hierarchical design to satisfy a key design goal of aggregation.

Devices according to complexity of forwarding decisions

Devices at each layer

Repeater – Layer 1 device that regenerates the electrical signal from one network segment to another network segment. This was often used with bus topology networks.

Hub – An improved repeater device with multiple ports which was particularly suited for star topology networks.

Bridge – Layer 2 device that stores and forward frames between different network segments. Key functions of bridges are:

1. Flooding frames
2. Forwarding frames
3. Discarding frames

Router – Layer 3 device that stores and forward packets with consideration for transit hops.

Switch – A device with multiple ports that combined the functions of a hub and a bridge.

Everything is switching

1. Layer 1 switching is performed by repeaters and hubs
2. Layer 2 switching is performed by bridges and switches
3. Layer 3 switching is performed by routers or multilayer switches

The success of computer networks has narrowed the meaning of switching to be fast frame forwarding.

Previously, switching had a more general meaning of making a connection between two endpoints.

Forwarding by broadcast reduces capacity

Forwarding in parallel increases capacity

Service models

Using a connectionless service model, Layer n-1 offers two functions to Layer n above it:

1. accept data from Layer n
2. deliver data to Layer n

Using a connection-oriented service model, Layer n-1 must offer more functions to Layer n above it:

1. connection setup
   1. connection initiated by Layer n
   2. connection initiated by a remote peer
2. accept data from Layer n
3. deliver data to Layer n
4. connection release
   1. connection released by Layer n
   2. connection released by a remote peer