Networking 101

Copyright Priscilla Oppenheimer

Study Topics 1

Fundamentals

Definitions

Protocol: a formal description of a set of rules and conventions that govern how devices on a network exchange information
Protocol suite: a collection of protocols that enable network communication from one computer to another
Bandwidth: the data-carrying capacity of a network
Throughput: a measure of the actual amount of data transferred over a unit of time
Topology: the architecture or layout of a network

Topologies

Bus: connects devices in a linear fashion with the cable proceeding from one device to the next
Ring: connects devices in a circle with no beginning or end that needs to be terminated
Star: includes a central node where all the network segments meet
Extended star: a star of stars
Hierarchy: a tree, similar to a star except that instead of a central node there is a central trunk from which all nodes branch
Mesh: devices are interconnected with multiple paths between nodes so that redundancies exist
Hybrid: different types of topologies connected together

Types of Networks

Local Area Network (LAN)

Operates within a limited geographic area
Allows many users to access high-bandwidth media
Provides full-time connectivity to local services
Connects physically adjacent devices

Wide Area Network (WAN)

Operates over large, geographic area
Connects LANs

Metropolitan Area Network (MAN)

Connects users in a metropolitan area

Storage Area Network (SAN)

Specialized, high-performance network for accessing storage devices

Virtual Private Network (VPN)

A private network that is constructed within a public network, such as the Internet
Example: Connecting remote offices to headquarters over the Internet rather than using a private WAN

Types of Networking Devices

Repeater: regenerates and retimes signal
Hub: multiport repeater; connects individual computers
Bridge: connects LAN segments
Switch: high-speed, multiport bridge; connects individual computers
Router: connects networks, chooses paths
Firewall: protects a private network's resources from outside users

Throughput

Throughput doesn't match bandwidth because of:

PC performance
Server performance
Other users on the network
Routing
Network design
Delay
Etc.

Estimating time to transfer data (best case)

Time = Size of data object being transferred/Bandwidth
Seconds = Gigabits/Gbps
Seconds = Megabits/Mbps
Seconds = Kilobits/kbps

EXAMPLES:

1. What is the best-case estimate of how much time it would take to send a 50 MB JPEG photo to your grandma if you only have a 40 kbps modem line? See if you can work this out and then check your answer here.

2. What is the best-case estimate of how much time it would take to send a CD worth of photos (640 MB) to a server if you have a 10-Mbps Ethernet connection? See if you can work this out and then check your answer here.

Types of Delay

Processing delay: the time it takes for a device (such as a switch or router) to take a packet from an input interface, examine and change it as needed, and place it into the output queue of the output interface (depends on CPU speed/utilization, switching mode, device architecture, configured features on both the input and output interfaces)
Queuing delay: the time a packet resides in the output queue of a router (depends on the number of, and size of, packets already in the queue, the speed of the output interface, and the queuing mechanism)
Serialization delay: the time it takes to serially place bits in a packet onto the medium (depends on the speed of the interface, for example, it takes much longer to place bits at 128 Kbps than it does at 100 Mbps), the size of the packet, and the type of medium; also called transmission delay
Propagation delay: the time it takes for a bit to get from the source to the destination, once on the medium (depends on the type of the medium and the distance travelled)

OSI Model

7	Application	Provides network services to the user's applications; handles file and message transfer, directory lookups, naming, authentication, and other services required by applications
6	Presentation	Ensures that information sent by one system will be readable by the application layer of another system; handles encryption and compression
5	Session	Establishes, manages, and terminates sessions between applications
4	Transport	Provides end-to-end communication, error recovery, and flow control
3	Network	Provides connectivity and path selection between networks
2	Data Link	Provides transit of data across a physical link
1	Physical	Defines the electrical and mechanical specifications for physical links between systems

Five conversion steps for encapsulating data

Build the data
Package the data for end-to-end transport
Append the source and destination Network layer addresses
Append the source and destination Data Link layer addresses
Convert to bits for transmission

Layers, Data, Addressing and Devices

Layer	Type of data this layer sends	Addresses this layer uses	Devices that work at this layer
Application	Data	Names	End-user devices, servers
Transport	Segments	Ports (for example, port 80 for HTTP)	End-user devices, servers, firewalls
Network	Packets	Layer 3 addresses such as IP addresses (192.168.0.1)	Routers, firewalls
Data Link	Frames	Physical, hardware, NIC, Media Access Control (MAC) addresses (00:00:0C:12:23:56)	Switches, bridges, NICs, wireless access points
Physical	Bits	None	Hubs, repeaters

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