LM7 – Networking

Hello and here we go,

Lecture Capture videos below however please read this entire page  as few if any CISS 100 texts provide this additional information.  Note there is significant content in this page’s submenu and you may optionally access it as necessary. If you are in the System & Network Administration program you should be reading the sub-menu information as well.

Lecture Part 1

Lecture Part 2

Lecture Part 3

 

Network Architecture

A network architecture is a conceptual blueprint that provides the necessary basis to define, build and maintain a physical and logical network and must provide and account for; (1) fault tolerance, (2) Quality of Service (QoS), (3) security, and (4) scalability.

(1) Fault tolerance allows a network to function normally even when components fail.  This is often accomplished through redundancy or duplication of equipment and media.

(2) QoS indicates the level of performance and services offered through a network.  We have recently observed the emergence and explosion of converged and unified communications (VOIP, Video/Web Conferencing, Multimedia Streaming, etc.) and these different technologies require different levels of service.   As an example, we do not want drop outs (i.e. lost or delayed packets) in our VOIP conversations but waiting 6 seconds instead of 5 seconds for a file download/transfer is probably acceptable.  In this capacity QoS determines communications priority decisions in relation to the communications import to an organization.  Networks need a mechanism to manage congested network traffic and QoS can provide a mechanism to mitigate this complexity and provide satisfactory communications.

(3) Security is a critical component of networking since users must have confidence in communication services.  How many times have you heard me state that we think about security first in everything we do. A network must ensure confidence by restricting message access to intended and authorized recipients, processes and devices.  The network must also provide communications integrity by ensuring that information is available and that it has not been accidentally or intentionally altered during transmission (i.e Information Assurance).

(4) Scalability determines a network’s ability to grow and react to future changes.  This includes both internal growth and external growth by joining other networks (e.g. internetworking).  We will see that both the OSI Reference Model and TCP/IP Protocol Model satisfy these core requirements.

 

Networking Elements

To properly understand network architecture and infrastructure (and keep in mind the Internet is a network) it is necessary to understand the 4 network elements comprised of; (1) the communication devices, (2) the messages and their encodings, (3) the mediums, and the (4) the protocols.  For completeness it is also necessary to understand (5) network topologies.

(1) Communication Devices:

We will leave the detailed understanding of the communication devices almost solely to the System and Networking Administration program however as basis, many communications devices may be involved in addition to the hosts or end-devices participating in the communications.  These intermediary devices include: (a) network access devices to connect end-users to network (e.g. hubs, switches, WAP), (b) internetwork devices that connect networks (e.g. routers), (c) communication servers that perform routing services (e.g. DHCP, IPTV, Wireless broadband, etc.), (d) modems that connect users to servers and networks (e.g. cable, telephone) and (e) security devices (e.g. firewalls).  It must be noted these intermediary devices run a multitude of processes that route, regenerate and retransmit data signals and manage the network, its security and QoS.

(2) Messages & Encodings: 

Messages are the units of information that travel between devices (e.g. segmented Web pages, e-mail, Voice over IP, etc.).   Message encodings have several purposes that include security (encryption) and timing.  To understand the need for timing note it is well known that it is impossible to synchronize 2 computers and their clock cycles but it is possible to embed the timing in the signal as Manchester encoding does.  Rather than signal a 1 with a high state and a 0 with a low state (or vice versa), Manchester encoding uses a mid cycle transition from high to low  and low to high to encode the 1’s and 0’s.  The following illustration is from Wikipedia’s entry on Manchester Encoding.

650px-Manchester_encoding_both_conventions

(3)  Mediums:

As previously introduced, historically, interconnections have been a limiting factor in computing power and speed.  The physical layer network media is the foundation of any network and provides the framework for the network architecture.  Choosing and implementing the correct and appropriate type of connection medium is critical to data communications and therefore an organization’s success.

The messages may travel over several different mediums each with their own specific characteristics (fault tolerance, QoS, security, scalability, analog or digital, etc.) and protocols (e.g. Ethernet’s CSMA/CD). To understand networking mediums please read “Physical Layer Media” in the sub-menu structure.

(4) Protocols:

Protocols establish consistent rules for exchanging data between applications, services and layers providing the foundation for communications congruence.  Protocols must necessarily determine: (a) the format of the message, (b) the data segmentation, (c) how intermediary devices share information about paths, (e) the methods to handle update messages between intermediary devices, and (e) the process to initiate and terminate communications between hosts. To understand protocols further, please read “TCP & UDP” in the sub-menu structure.

(5) Network Topologies

Lastly my 5th item necessary for proper understanding: Network Topologies although this not a network element.  Network Topologies are covered in the textbook but should you want a deeper understanding please read “Network Topologies” in the sub-menu.  Every CIS student should understand Ethernet technology so if you have questions following the lecture please read about Ethernet & CSMA/CD in the sub-menu.  System and Network students should also read Wide Area Networking in the sub-menu.

 

Ok, so we established the foundational concepts above however we need a few more items for our basic understanding before we proceed.  As an introduction and overview of networking architectures, please read the “OSI & TCP/IP Models” found in this Networking and Internet’s sub-menu structure.  Also, please review and understand the content below.

 

Analog vs. Digital

Analog is continuous – http://en.wikipedia.org/wiki/Analog_signal

This continuous nature gives ultimate precision but detecting different states is complex and error prone (e.g. what happens if there is insufficient power).

Digital is discrete – http://en.wikipedia.org/wiki/Digital_signal

Digital has fixed intervals (in computing interpreted as, 1/0 or on/off or true/false).

 

Circuit vs. Packet Switching:

Circuit switching maintains the connection path for duration of communication (e.g. landline phones).

Packet switching routes packets dynamically across data networks.

Here is a nice description of circuit and packet switching.

Now to get everyone thinking, we assess everything for security, does the single circuit switching path make it easier to eavesdrop/intercept communications (in contrast to packet switching) since all communication occurs over this single path.

 

Synchronous vs. Asynchronous Transmission vs. Communication:

Many texts present sync vs. async communications from the end user or computer mediated communications standpoint (i.e. synchronous phone call vs. asynchronous email) which is not incorrect but it is important to understand the difference at a more finely granular network level.

In a nutshell synchronous transmissions requires connection management so that the parties know how (predetermined format) and when the transmission is occurring.  An example would be Web Conferencing.

Note this does not mean that an end station knows precisely when a message is arriving only that it is arriving. This can occur at different levels (datalink, TCP, etc.). (Note our present text presents this concept in a misleading way as it seems to imply the end stations know when the message is arriving but it is impossible to know precisely when a synchronous communication will arrive when sent over a network).

In asynchronous transmissions, data is transmitted when it is ready to send and the receiver must determine the timing inherent in or built into the signal.

Here is a more detailed description from InetDaemon.com.

 

Simplex, Half-Duplex & Full Duplex:

Simplex – one direction only: http://en.wikipedia.org/wiki/Simplex_communication

Half-Duplex – one direction at a time (e.g. walkie-talkie)

Full Duplex – both directions concurrently (phone): http://en.wikipedia.org/wiki/Duplex_(telecommunications) (link also contains multiplexing description)

Now which one requires the most protocols?  Think about the phone, what would happen if you didn’t provide courtesy (protocol) and just continually spoke interrupting the other speaker?

 

Connection Oriented vs. Connectionless

Here is a nice presentation on Connection vs Connectionless communications with excerpts below. Please see  the TCP/IP resources in the sub-menu for a more complete presentation on the TCP 3-way connection setup handshake.

Connection-Oriented means that when devices communicate, they perform handshaking to set up an end-to-end connection.

Connectionless means that no effort is made to set up a dedicated end-to-end connection.

 

Wireless

To provide a foundational understanding please read about Microwaves that range from .3 GHz to 300 GHz: http://en.wikipedia.org/wiki/Microwave.

Business-IT-Society Analysis

In additon to security we assess everything with respect to the Business-IT-Society triangle and what is rarely discussed about wireless in CIS texts is: are these microwaves effecting us from a health standpoint?   A significant portion of medicine is based on statistical evidence.    We have only been immersed in environmental microwaves for 20 years and the  present environment  may even be saturated with microwaves.   We may not know,  detect or diagnose the effects of these microwaves on our bodies for many years.

 

Multiplexing

Recall we introduced Multiplexing in Operating Systems and defined it as the creation of several logical resources from a single physical resource.  In OS we further discriminated between space division and time division multiplexing. Networking multiplexing refers to the ability to transmit several signals over the same channel simultaneously and this can be done using time division multiplexing (e.g. packet switching) and frequency division multiplexing where different frequencies can be placed on a medium concurrently (e.g. DSL & WiFi).

 

Bandwidth

Bandwidth is a measure of the difference between the lowest and highest frequencies a media can transmit and is expressed in hertz (Hz).  Higher frequencies can transmit more data in a given period of time since they accommodate more transitions.

Business-IT-Society – I posed the question above concerning wireless health concerns so let’s assess this further. We introduced that medicine research is in some part statistical. Let’s consider the accelerating increase and evolution of both carrier waves and bandwidth (e.g. increase in number or wireless signals and evolution of technologies bandwidth such as 1G -> 2G -> 3G etc., Bluetooth is now 4.0, Wireless is now 802.11x, etc.).

 

Throughput

Throughput is defined to be the amount of effective data that a network can accommodate during a given time and is usually measured in megabits per second (Mbps). Throughput is determined by the physical nature the media, the network’s physical and logical configuration and the network’s management protocols.

 

WANs

Lastly, every CIS student should understand the Internet so please read “Wide Area Networking & Internet” in the sub-menu.  For your reference, note that Wide Area Networking also presents multiplexing, circuit switching and packet switching.

 

IPV4 & IPV6

Now we should also be aware that IPV6 has arrived and facilitates the IoT due to its increased address space: http://en.wikipedia.org/wiki/IPv6

IPV4 used 32 bit (4 byte addressing e.g. 187.56.201.125

IPv6 uses a 128-bit address, allowing 2128, or approximately 3.4×1038 addresses (facilitating IoT among other things

 

Physical/Logical Address Resolution

At some point the system must resolve the logical to physical address mapping.  TCP/IP does this with the Address Resolution Protocol (ARP).

 

TCP/IP  3-way Handshake

In the submenu is a complete writeup of TCP/IP but here is a nice succinct description: http://www.slashroot.in/understanding-tcp-three-way-handshake

 

TCP/IP Protocols List

Now to see almost everything that runs on TCP/IP please see here:

http://www.w3schools.com/tcpip/tcpip_protocols.asp

 

Networking Access Resources

Research & White Paper Resources

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