Networking Fundamentals

Dr. Alexios Louridas

Computer Networks

Forms Of Networks

Forms Of Networks

Network Technology

PAN

LAN

MAN

WAN

Personal Area Networks (PAN), any device that communicate over the range of a person.

Local Area Network (LAN) standards for devices in single limited area.

Metropolitan Area Network (MAN) connecting user networks within small geographic areas.

Wide Area Network (WAN) connecting user networks over large geographic areas. 

The Internet

Mobile Networks

  • Mobile Station (MS)
    • Mobile Devices
  • Base Station (BS)
    • Radio equipment
  • Mobile Switching Centre (MSC)
    • Connects multiple BS
  • Public Switched Telephone Network (PSTN)
  • Radio Access Network (RAN)
    • Transmission network
  • Core Network
    • Infrastructure Network
    • Internet

Radio Propagation

Designing a Network

Reliability

Dealing with Failures and Errors

Error detection
Error correction
Routing

Resource Allocation

Congestion

Multiplexing
Quality of Service (QoS)

Some Networks are Scalable!!
 

Evolvability

Scaling a network

Addressing
Protocol Layering

Internetworking

Security

Confidentiality

 

Authentication

 

Integrity

Protocol Layering

Abstraction

Protocol

Interface

Physical Medium

To minimise errors and complexity. Layered architecture with each layer having their protocols and algorithms hidden from other layers.

Each layer has a specific communication language/protocol

Communications between each layer is done via a interface. The interface defines which primitive operations and services the lower layer makes available to the  upper one.

At the bottom of all layers a physical layer connects devices together. It is the layer where the true data transmission from one location to another happens

Layers

Distinguishing operations per layer is important to be able to create equipment specific for a layer.

Protocols
Each layer should contain a single protocol. A list of all protocols used in a network architecture is called a protocol stack.
Interfaces
These are not and should not be part of a network architecture

Network Architectures

Example of Layered Network Architecture

A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers?

Problem

The total number of header bytes: n * h
The total packet size: n * h + M
Hence, the fraction of each packet used by protocol header is
[n * h / (M + n * h)]

 

Use n = 7, h=8 and M =56 and M =100

What do you believe is better sending big packets or small packets?

Answer

Communications SERVICES

Connection-Oriented Service

 

Connectionless Service

Network Performance

  • Data rate = Amount of data per time.
     
  • Bandwidth

    • The amount of information that can flow through a network connection in a given time.

      Measured in bits per second (bps)

      Throughput is the actual bandwidth at a specific time of day.

  • Latency
    • Time taken from source to destination. Usually latency is used to devices to show how long it takes for data to enter and the leave a device. Whereas delay is usually used to describe the time taken from source to destination.
  • RTT
    • Round Trip Time for data. Measures in seconds
  • RTTX Bandwidth

    • Bandwidth Delay Product is measured in bits and it signifies the amount of data that are transferred at anytime in through the network.

T_{best} = \frac{S}{BW}, T_{true}=\frac{s}{Throughput}

A normal person (Danny) can carry a bag with 3 data cartridges each containing 10GB of data and can run at a speed of 18km/hour. For what range of distances does Danny have a higher data rate than a transmission line whose data rate (excluding overhead) is 150Mbps? How does your answer change if (i) Danny’s speed is doubled; (ii) each cartridge capacity is doubled; (iii) the data rate of the transmission line is doubled. 

Problem

Danny can carry 3 * 10 = 30GB (240Gb)
Speed = 18 km/hour = 0.005 km/sec
Distance: d km
Time: d / 0.005 = 200*d sec
Hence, 240 / (200*d) Gbps or 1200/ d Mbps.

Solve inequality: 1200/d > 150
For d < 8 km, Seb has higher rate than the communication line.

Answer

i)If Danny’s speed is doubled, then his data rate will also double. Therefore, the range of distances for which Danny has a higher data rate than the transmission line will also double.

 

ii) If each cartridge capacity is doubled, then Danny can carry 60 gigabytes of data. Therefore, redoing calculation in the main question you should find that the distance would double.

 

iii) If the data rate of the transmission line is doubled, then the range of distances for which Danny has a higher data rate than the transmission line will be halved.

Answer

Transmission Control Protocol / Internet Protocol

  1. Network still operational even if some routers are destroyed.
  2. Flexible architecture.
  3. Quick and easily deployable.

TCP/IP

Open System Interconnection.

  1. Each layer should be abstract.
  2. Each layer should perform a well-defined function.
  3. The function of each layer should be chosen with an eye toward  defining internationally standardized protocols.
  4. The layer boundaries should be chosen to minimize the information  flow across the interfaces.
  5. Layers should be large enough do be distinguishable between layers but small enough to be feasible.

OSI

Layered Reference Models

OSI  Reference Model

OSI MODEL

Application

Presentation

Session

Transport

Network

Data Link

Physical

Model Comparison

TCP/IP MODEL

Application

N/A

N/A

Transport

Network

Link

N/A

Physical Layer (OSI)

Physical Cables to connect network nodes


Wireless connection between network nodes


Data packets in raw form are just digital 1 and 0.


Electromagnetic, Electrical and Optical data transfers.

Serial Lines
Ethernet connection

 

Creates Connections
Media Access Control (MAC) addressing

 

Ignored mostly in early TCP/IP
 

Data Link (OSI and TCP/IP)

Network Layer (OSI)
Internet Layer (TCP/IP)

Routing of data
Transporting data from source to destination

Internet Protocols is used in this layer
 

Transport Layer (OSI and TCP/IP)

End to End packet delivery via datagrams or virtual circuits.


Data from a source process to data at a destination process


Error recovery


Retransmission


Two Protocols:

  • TCP (Transmission Control Protocol)
  • UDP (User Datagram Protocol)

Session Layer (OSI)

Authentication
Security
Creation of connection

presentation Layer (OSI)

Protocols that work with the client
Image formats
Video formats

Application Layer (OSI and TCP/IP)

This is the layer that most users interact with and will recognise.

Provides network services to the end user:
HTTP
FTP
SMTP
TELNET

Protocols per layer

Analysis of Reference models

OSI Timing

Bad timing. It was released too late to change the TCP/IP widespread usage.

Political Reasons

OSI 7 layers were more political selected rather than technical. The reason of the session and presentation layer are very thin.
Difficult to implement and probably inefficient.

TCP/IP Layer Separations

Services, interfaces and protocols are not easily differentiated. That makes design of expanding new networks very difficult.
It is more described as protocol stack rather than network architecture.

Bottom Layers undistinguishable

The link layer is used more like an interface between the OSI data link and network layer.
Besides the IP and TCP protocols all others protocols are very loosely defined but because of well spread usage difficult to replace.

ITU

Finding information

International Telecommunications Union
Committed to connecting all the world’s people.
ITU-R – for radiocommunications
ITU-T – for standardisation.
ITU-D – for development.

ISO

International Standards Organisation
Brings together experts to share knowledge and develop voluntary, consensus-based, market relevant International Standards that support innovation and provide solutions to global challenges.

3GPP

3rd Generation Partnership Project 
Unites seven telecommunications standard development organizations (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC), to provide a stable environment to produce the Reports and Specifications of mobile broadband standards.

W3C

World Wide Web Consortium
To develop Web standards, protocols and guidelines to ensure the steady and long-term growth of the Web.