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The following report analyse the process of what happens when the laptop powers on and points to an address using its browser, the address which resides on the web server. The report itself will be divided into separate sections to further breakdown what happens at each link of the network as well as each layer of the OSI model. Each section will contain its own specific point of interest, which will reflect that of the network provided.
The four sections that we have divided up are as follows:
Student A- Addressing (Looking at the entire network in terms of Addressing throughout)
Student B- Security (Looking at the entire network in terms of Security throughout)
Student C- Protocols (Looking at the entire network in terms of Protocols throughout)
Student D- Graphical analysis/Maths (Looking at the entire network in terms of Graphical analysis/Maths throughout)
Process of communication from start to finish throughout the network.
The laptop powers on and starts the POST process (Power on Self Test), then proceeds to boot the Operating System.
Initially the laptop must request a transmission slot before it can start communicating with the network, this is done through CSMA/CA. After a sot has been allocated then authorisation must take place using WPA2.
Once full boot sequence is complete; and the O.S. is running, user takes control and runs the browser. The user then points towards a destination website. The laptop then communicates through its NIC (network interface card) then connects via a wireless link (AP) using any necessary drivers and software. Once a connection is made to start the local area network, the first router that the laptop is connected to must communicate with the next router within the network once traffic starts to flow. The Client (laptop) must carry out a ping in order to retrieve a MAC address from the router, firstly its checks NetID and its ARP table/server for MAC address. It must then frame the ping packet with the MAC address of the router in the destination field and the clients MAC address in the source field. It will then issue an ARP request to capture the MAC address of the remote client, it will then retrieve said MAC address and proceed to frame the ping packet with the MAC address of the router in the source field and client MAC address in destination field.
The above process is carried out until the website address information is back with the client (laptop).
Protocols Throughout the Network-Section 1
OSI Layers Explained
The OSI model is split into 7 separate layers. Each layer is responsible for carrying out functions used to transmit data from one network to another. The OSI model is separated into two sets, the Application Set and the Transport Set. The Application Set uses all three upper layers (Layers 5, 6 and 7); The Transport Set uses the lower layers (Layers 1, 2, 3 and 4). The diagram below outlines these stages:
The OSI model works by starting at the application layer which carries out its function then passes control to the next layer till it reaches the bottom. It then passes its way over the network connection and starts the process all over again starting from the bottom layer (Physical Layer) and working its way up the hierarchy till it reaches the required destination.
The Upper Layers of the OSI are responsible for all application functions such as managing the connection, formatting an encryption.
Layer 7 Application: This layer allows the user to communicate with the OS and provides application services such as SMTP, browsing the internet, network data sharing, allowing file and data transactions etc.
Layer 6 Presentation: This layer translates data into a format. It encrypts/decrypts data, compresses/decompresses data and handles graphics.
Layer 5 Session: Controls the timing of each session of user application processes.
The Lower Layers of the OSI are mainly used for network based functions such as addressing, routing and flow control.
Layer 4 Transport: This layer controls error recognition and recovery of lost or corrupted data.
Layer 3 Network: This layer decides which routing path is best for data transmission between nodes. All hardware devices such as routers and switches are used at this stage.
Layer 2 Data: This layer decides which physical protocol is to be used depending on what type of network and it also splits the data into frames for transmitting.
Layer 1 Physical: This layer manages all physical hardware such as physical connections, voltages etc. (Janssen, n.d.)
The model below shows the comparison and relationship between both the TCP/IP model and the OSI model. Both models are very similar in which they both use a layered structure. The TCP/IP model splits up into four layers as you will see below, each layer has specific protocols. TCP/IP model is used to allow computers to communicate over various networks.
Host to Host
Protocols of Each OSI Layer
DNS : Changes the domain name e.g. glasgow.com into an IP address 22.214.171.124 which makes it simpler for a computer to understand. DNS server works by matching all domain names to IP addresses which are held within a massive database. This protocol uses standard RFC 0974.
HTTP : This protocol is a request - respond protocol. It is divided into 4 different sections; connection, request, response and close.
Connection - To determine whether a connection has been established. A message will be displayed on the connection as to whether it has been successful or not.
Request - The user makes a HTTP request which is passed to the server.
Respond - If the connection to the Web server has been successful it will allow Web pages to be downloaded. If it has been unable to connect an error message will be displayed.
Close - Once all requested information has been successfully delivered, the connection can then closed.
HTTP is used for all communications over the WWW (World Wide Web) to exchange information. It is known as a stateless protocol as it does not need previous knowledge of which stage was run before it. This protocol uses standard RFC 2616. (Rock-Evans, 1998)
DHCP: DHCP assigns IP addresses to devices on a network by determining whether the IP is static or dynamic.
Static Addresses: This is an address that is manually applied and does not change.
Dynamic Addresses: This is the opposite of a static address which means that addresses are automatically applied and will automatically change in accordance to the network.
This protocol uses standard RFC 3131.
POP3: A method used in order to retrieve emails from a remote server. This protocol uses standard RFC 1939.
SMTP: Used to send emails to remote server. This protocol uses standard RFC 1869.
This layer provides several different functions these include:
Data conversion which helps decipher image, video, sound and audio formats.
Translation from different character codes such as RTF and ASCII, among others.
PAP: is known to use a two way process for authentication. A username and password is requested and sent. A response is then sent determining whether it has been a successful attempt or a failed attempt. (Andrew J. Whitaker, 2008)
TCP: TCP is known as a 'suite' of protocols as it is used within IP, UDP, ARP etc. TCP transmits data in the correct order between a point to point connection. Although if the connection fails then the server will get send the lost part of the file or message. TCP allows communication between an IP and an application. This protocol uses standard RFC 0793. (NixCraft, 2007)
UDP: Unlike TCP, UDP is connectionless which means there is a greater chance data packets may get lost or corrupted while being transferred to its destination. It does not provide a correct order delivery and does not track connections. Although there is a greater chance of packets being lost UDP allows for each individual packet to arrive whole. This protocol uses standard RFC 0768. (NixCraft, 2007)
IPSec: IPSec offers improved security which means it is offers a secure network connection. IPSec transmits data safely and securely making it completely confidential due to the authentication process. IPSec is commonly used within L2TP tunnelling as is supports data encryption.
IPv4: IPv4 is an Ethernet based protocol that sends packets of data across the network and routes traffic over the internet or in other words it is a packet switched link layer protocol. IPv4 is known as a connectionless protocol, this means that data sent has only one intention and that is to reach its destination and not taking into account duplication, security and integrity of data. (Pc.net, n.d.)
(For IPv4 In-depth refer to - Section 2)
IPv6: IPv6 is more or less and upgrade to its earlier predecessor IPv4. IPv6 has the same feature as IPv4, just not as faulty and with fewer limitations. IPv6 has some additional features such as new header formats, larger address space (it has a 128 bit address space), configuration settings for stateless and stateful addressing, IPSec header support and is improved for prioritised delivery. (Davies, 2009)
RIPv2: RIPv2 is a distance vector protocol and is an improved version of RIP as it provides features such as authentication for routing updates and also includes the subnet mask of the network address. RIPv2 has become a popular choice of protocol for routing. RIPv2 is not used for large networks as is it limited to only 15 hops maximum. This protocol uses standard RFC 1058. (Orbit Computer Solutions, 2013)
ICMP: ICMP is used for error information and error messages. For example when a node is overloaded ICMP reports the problem by sending a message. This protocol uses standard RFC 0792. (Fairhurst, 2010)
ARP: ARP is used to convert IP addresses into physical addresses such as a MAC address. This protocol uses standard RFC 0826.
IEEE802.11: Has two modulation techniques DSSS and FHSS. DSSS uses different Phase shift keys dependant of the speed, 1Mbps uses Differential Binary Phase Shift Keying and for 2Mbps it uses Differential Quadrature Phase Shift Keying. FHSS is an entirely popular modulation technique when compared to its counterpart DSSS, mainly due to speculation on whether or not FHSS adds to the quality of security or not but no proof has been provided as to say it does. As the years progressed IEEE 802.11 standard has seen improvements upon the system such as 802.11a, 802.11b and 802.11g; among others. (Danielyan, 2001)
WPA2: This standard is a method of authentication and security for a WLAN, one the most important aspect of WPA2 lies in its encryption algorithm known as AES (Advance Encryption Standard) which outdone the DES (Data Encryption Standard). In terms of security, WPA2 has two modes in which it can implement, Personal and Enterprise. (Bing, 2008)(Page 139)
PPP: Used for communicating between two points. PPP is commonly used for a fast connection needed for broadband communications. PPP handles three main components; link control protocol, protocol encapsulation and network control protocols. (Kozierok, 2005)
CHAP: CHAP is part of PPP. CHAP works by sending a challenge message to the requestor which then returns a response using a value using a one-way hash function. Both PPP and CHAP use standard RFC 1661, RFC 1662 and RFC 1663. (Rouse, 2005)
FDDI: FDDI transmits data at a speed of 100 mbps which means it can manage high traffic networks. FDDI uses a physical ring in order to transmit data, this means that if one ring goes down then a secondary ring is there to provide backup. Fibre optic connections transmit data by sending pulses of light which creates a wave through the optical fibre. This protocol uses standard ANSI. (Drew Bird, 2003)
10BASE-T: Twisted pair telephone cable also known as twisted pair Ethernet. It runs at a speed of 10Mbps which makes it a suitable speed. This protocol uses standard IEEE 802.3.
100BASE-TX: 100 BaseTX is a fast Ethernet standard which uses a twisted pair cable media system to receive and transmit data signals. This protocol uses standard IEEE 802.3. (Spurgeon, 2000)
100BASE-FX: Uses fibre optic cabling which operates at 100 Mbps. It uses two strands of fibre; one for data transmission and the other for reception. This protocol uses standard IEEE 802.3. (Dean, 2009)
V.34 Modem: Allows for data to be sent and received across telephone lines.
The table below shows the process of the individual segments within the network provided to us.
POTS: POTS uses modems to send transmissions from one point to another. POTS is limited to the amount of data that can be transferred across a medium and sits at 56Kbps transfer speed. This speed is reduced if both end of the connection use a modem to send transmissions, this happens by conversion from an analog signal to a digital signal. This result being a maximum of 33Kbps.
Laptop To Access Point
Layer 1 Protocol
802.11 (Wireless connection)
Layer 2 Protocol
Layer 3 Protocol
Layer 7 Protocol
Access Point to Router 1
Layer 1 Protocol
10Base-T (Twisted Pair Cable)
Layer 2 Protocol
Layer 3 Protocol
Layer 7 Protocol
Router 1 to Router 2
Layer 1 Protocol
V.34 (Telephone Connection)
Layer 2 Protocol
Ethernet and PPP (CHAP is used for Authentication)
Layer 3 Protocol
Layer 4 Protocol
Router 2 to Switch
Layer 1 Protocol
100Base-FX (Fibre Optic Cable)
Layer 2 Protocol
Layer 3 Protocol
Layer 7 Protocol
Switch to DNS and Web Servers
Layer 1 Protocol
100Base-TX (Unshielded Twisted Pair)
Layer 2 Protocol
Layer 3 Protocol
Layer 7 Protocol
The above table defines what protocols are used at each step of the within the network. Form the laptop accessing the access point to the resulting web request.
Addressing Throughout the Network - Section 2
ARP is the process of retrieving the MAC address using a destination IP address or the next IP address in line along the network. In terms of the network provided, the process of an ARP request is explained in Section 4.
(We have assumed that IPv4 is being used within the network)
IPv4 is used in Networks to assign a logical address to a physical device through the communication of each devices network interface. Both devices A and B must know each other's Ethernet address through the use of ARP which was previously mentioned above. Essentially Ipv4 identifies a device using a specific logical address which then can be translated by using ARP and then communication between the two devices can begin. With assistance from DHCP, IPv4 addresses are automatically assigned from a DHCP server along with the subnet mask.
IPv4 works using 32 bit address otherwise known as dotted decimal notation.
For example let's take the address 172.16.10.0 and show it in the dotted decimal form(working provided).
256 128 64 32 16 8 4 2 1
0 1 0 1 0 1 1 0 0 =172 (the first octet)
The above example shows how we get 172 using 8 bits. The below diagram represents a Class B address divided into 4 octets.
172 16 0 0
1st 2nd 3rd 4th
There are various addresses with differing characteristics, each representing a 32 bit address. A Class D is a Unicast address and Class E being an anycast address.
(J.D Wegner, 2000)(pages 4 - 9)
RIP version 2 is in one word or another, an upgraded version of its predecessor RIPv1 and is known as a distance vector protocol. RIPv2 was implemented to overcome some of the issues presented in version 1. some of the new additions to RIPv2 is VLSM(Variable Length Subnet Masking), Multi-casting and route authentication and supports Classless Inter-Domain Routing(CIDR). Some unchanged features include the update time and hop count limit which are still set to 30 seconds and a maximum 15 hop limit; respectively. As well as those features it still uses UDP (User datagram Protocol) port 520. However RIPv2 isn't appropriate for large networks due to its low convergence.
RIPv2's authentication helps prohibit any unwanted use of the network with devices that don't have permission to use it.
(Anthony Bruno, 2003)
DHCP is a service that can be installed onto a server to automatically assign IP addresses to connected clients and servers. These IP addresses stem from a pool of addresses given to the DHCP server by the user that installed this service, these ranges are usually given out in pools of one hundred give or take, but can be any given number i.e. 172.16.0.1 - 172.16.0.100. These "ranges" are also known as scopes. The request is authorised then an IP from the IP address pool is allocated to that machine. If there is no server then an APIPA address is allocated instead. The following describes a DHCP request:
Firstly - a DHCP node sends a DHCPDISCOVER message
Secondly - the first router reply's with a DHCPOFFER message
Thirdly - the Client (laptop) sends a DHCPREQUEST message
Lastly - the first router reply's with a DHCPACK message
Other features such as Reservations allow for specific IP addresses to be assigned to a select Client/server. (Rand Morimoto, 2006) (pages 289 -296)
DNS was introduced to battle the need to memorize difficult to remember IP addresses. The DNS is a bank of domain names which are updated and regulated throughout its domain forest. A DNS is comprised of two separate parts, one being the client and the other the server. The server side of DNS contains Forward and Reverse lookup zones, which are used to resolve IP addresses into an FQDN and vice versa.
Example of a FQDN; www.google.com
The client side is much simpler in that all it does is request results from the DNS server in the form of a recursive query to a forwarder; this only takes place if the client has exhausted all other options i.e. checking its local cache. Once the query reaches the DNS server, the DNS server sends a reply back to the querying machine with the correct information if it has been authorized and none if it hasn't been authorised. Primary and Secondary DNS servers can be implemented to combat redundancy issues.
(Morimoto, 2004)(pages 188 - 191)
Security Throughout the Network - Section 3
PAP uses a password and is used by Point to Point protocol (PPP). PAP is considered as unsecure as it passes information using ASCII which is easily readable. CHAP and EAP are better protocols are they are more secure, this is the reason that PAP is only used as a last resort. Gregg (2006)
CHAP (also used by PPP) provides protection against replay attacks ,authenticates a user on a network to an authenticating entity like an internet service provider and validates an individual computers characteristics at random stages and does this by using a method called a three-way-handshake (this is done using a password), this happens automatically. Shown below are the steps then followed to carry this task out. Panek (2011)
When the link establishment phase is completed, the authenticator omits a challenge note to the receiver
The receiver should respond with a value determined through using a one-way-hash function which will be a mixture of the challenge and the password.
The value is checked by the authenticator to make sure it has the same value and if they are the same authentication is granted. If the value is not the same then the whole process will be terminated.
Steps 1 through to 3 are repeated on several occasions and when the authenticator sends new challenges to the receiver.
EAP provides the use of relevant information for transportation over the network. It is not a wired key (only works on wireless devices). Hooper (2010)
WPA/WPA2 are protocols are protocols used for security purposes. WPA overtook the place of WEP, an encryption key must be manually entered on a wireless device and does not change, the act of doing so is referred to as using TKIP. Malicious attacks are well known to TKIP and so it will dynamically generate a brand new 128-bit key for every packet sent through the medium. WPA2 has subsequently replaced WPA, the design for this was made to also work with older devices that may have used WEP or WPA. Briere (2011)
FCS points to the extra checksum qualities that may be additional to a communication protocol and looks out for errors. Upper-layer and user application data is sent with the use of frames, more bytes may be added for the purpose of frames as they need to have a minimum length for timing reasons. Hall (2010)
CRC for frame checking allows for use of a polynomial algorithm which calculates a CRC number for any data that is being transmitted, the calculation is also stored in the FCS field and the end point to which the data is being transmitted, does the same calculation to the data once received. (Juniper, 2013)
In IEEE standard data field's and frames are LLC bytes. The LLC sub-layer receipts the network protocol information that comes in the form of an IP packet, additionally adding control info that will aide transport of the packet to the endpoint connection. Through the use of LLC, layer 2 can get through to the upper layers. (OSI model) (Heartpence 2011)
RADIUS is a protocol sourced by networks for authentication, authorization and accounting management for devices connecting to and having the use of a network facility. The protocol runs in the Application layer residing inside the OSI and sources UDP as transport. A Radius server conducts validation on the endpoints that are linked to any network it is connected with. Morimoto (2008)
Allows its self to believe through proper checks that there is no malicious incoming threats, Carrier Sense Multiple Access (CSMA) will try to determine another incoming transmission before sending data
CSMA is based on the principle "sense before contention" or "listen before talk".
CSMA/CA (carrier sense multiple access /collision avoidance) vs. CSMA/CD (carrier sense multiple access /collision detection)
In CSMA/CA collisions are escaped due to signals being sent for each node to be sent prior to the sending actually happening, it is not the most popular way of doing things due to decrease in performance and unnecessary operating costs.
In CSMA/CD outlines what will take place when two devices detect a clear networking passage, then try and send out a signal at identical moments. A pile-up happens and the two devices immediately stop transmitting. The two devices will then retransmit after an unplanned amount of time has passed. Performance will drop at a really high rate if this keeps happening with the collisions. Shiner (2001)
To check that data has been transmitted properly, parity bits are used by parity checking. A parity bit is added (seven or eight bits) to every data unit that is transmitted over a network. The reason for this is to make sure that all bytes have either an even or odd number of set bits. This is to enable a sent bit with the number 0 (even) and 1 (odd. If even parity checking is enabled and bits are to be sent then this is the way it is done. Here's an example, as a transmitting machine sends data it counts each group of bits and if there is seven (as it is odd) it will set the parity to 1, if the number is even then the parity will be 0, this is to make sure that each byte has even numbers of set bits.
The sender and receiver must both conform to using Parity Checking
If the two side are not enabled with the same Parity Sense then communication is impossible
Parity Checking is also used to test memory storage devices
Point-to-Point protocol resides on the Data link layer. It works over asynchronous serial (dial up) or synchronous serial (ISDN) media. Combined together with LCP. Its purpose is to construct and uphold data link connections. Network Control Protocol is also sourced to permit several network layer protocols (routed) to be used on a point-to-point link. The basic purpose of PPP Is to transfer Layer 3 packets across a Point-to-Point link. Authentication is established using PAP and CHAP. Lammie (2007)
Internet Protocol Security
Otherwise referred to as IPsec is basically a bundle of protocols that are used to keep network connections secure. Originally with IPv4 there was no security built in, there seemed to have been little emphasis on security as compared to that of today. To provide peace of mind in the form of security for internet communications, IPsec was developed as an add-on to IPv4, however has been added to IPv6 as a native part of the protocol. Together with a suite of protocols it is designed for securing all IP communications. It has many features including ease of implementation and purpose, supporting most Operating Systems. IPsec will abide anywhere it can be used with L2TP tunnelling protocol and also supports DES.
Whilst using IPsec rapidly helps to maintain security, confidentiality and authentication of data, we also must know that there is no safeguard measures to check this and ensure security, and that this internet protocol is safe for information to be passed over it.
Every computer requires a firewall. A Firewall is essentially a mechanism that we use to filter out unwanted access items to servers and networks like malicious attacks from hackers. Rhee (2013)
Mathematical Discussion & Graphical Diagrams - Section 4
IEEE 802.11 Standard (Diagram)
Looking at the very beginning of the networking model provided for us we see that once the laptop is fully powered on its next step will be to acquire a signal via a access point. This process is first started with help from the user, once the user pinpoints a website for the browser to acquire a signal to send a request to, the network interface card then acts through the use of a wireless access point which in turn initiates the LAN connection. The wireless protocol used in the connection is 802.11.
Between 1 - 2 Mbps
The standard and first form of 802.11 protocol
Maximum of 54 Mbps
Higher resistance when it comes to interference/collisions, High Frequency, lacks signal strength.
Used mainly in home, office and community areas (internet café)
Maximum of 54 Mbps
Pretty much similar to 802.11b but with a higher bandwidth of 54 Mbps.
Maximum of 600 Mbps
2.4GHz - 5 GHz
Unlike 802.11a and 802.11g. 802.11n allows for channel bonding and multiple input and multiple output.
Given that the speed is 2Mbps for the network provided, then the network must be using the outdated standard 802.11 giving it very little signal distance.
The above diagram demonstrates 802.11a vs 802.11b vs 802.11g. Both 802.11a and 802.11g appear to have a very low Range in when the capacity of data transmitted increases leaving them with a high data rate when sending 54Mbps but range increases rapidly for 802.11g when there is less data being transmitted allowing for over 300 feet travelled. On the other hand 802.11b can achieve the same range but only get a maximum output 0f 11Mbps.
In the network provided there is a 2 Mbps data rate and assuming that the network is using 802.11 giving the range of wireless connectivity very low travel distance. (National Insturments, 2008)
Wi-Fi protected Access 2 essentially allows for secure data transfer and protection between to end points and is the successor to WPA and its wired counterpart WEP. WPA2 is just an upgrade from WPA in which it has a much higher form of encryption AES. It is assumed that the WPA2-Personal is being used as it uses pre-shared keys and is much easier to set up for smaller organisations, the network provided in the task hints that it is a small network in use hence the use of WPA2-Personal. (Charlie Russel, 2009)
Address resolution protocols main job is to point the physical hardware address of a network node to its corresponding IP address. A cache is present to store these physical address locations and this is called the address resolution cache, this is a short-cut to prevent another ARP request being sent to locate the physical address again. An Ethernet uses a 48 bit MAC address.
(Groth, 2001) (pages 165 -167)
The above diagram depicts how an ARP request works. An ARP request is sent from Node one and is sent through the hub to reach Node two. Once the ARP request is received by Node two, it is then stored and saved within the cache, this allows for faster communication between nodes as future ARP requests will not have to be sent as it is stored within the cache as a reference. Once information is retrieved from the ARP reply then the first Nodes cache will then be updated. The ARP process will then be finished as all the information needed from the opposite Node will be held within in each nodes ARP cache, allowing for communication with one another.
This is a form of traffic that is deemed important over all other manner of traffic. Interesting traffic takes priority when sent via a router to its destination, once the traffic arrives all other uninteresting traffic is drop; safe for the interesting traffic. (Syngress, 2003)
OSI layer one; the Physical layer, incorporates anything that is real/tangible to the user. For example, hardware such as cabling and hubs, switches, routers are all considered to be physical but mainly focuses on transmission of data through the wires used within the network.
The network design provided consists of various cabling components that each have their own traits.
10BaseT - A very standard form of Ethernet cable used mainly back in the 1990's for use in networking Local Area Networks, and phone cabling. 10baseT runs at a transmission speed of 10Mbps over a Cat3 twisted pair cable and connects using an RJ45 8-pin connector. 10BaseT Signal encoding allows for transceivers to receive and send information(signals) over a four wires which is is divided into two pairs, one set for receiving signals and the other for sending signals. (Spurgeon, 2000)(pages 125 -126)
100BaseFX - Unlike 10baseT with its Twisted Pair and UTP cabling, 100BaseFX uses fibre-optic cabling with a baseband transmission speed of 100 Mbps. While 100BaseFX is using half duplex mode its properties are similar to that of 10BaseT in which one wire is used for receiving signals and the other of course for sending them but again unlike 10BaseT, it has a full duplex mode which changes the operation of each strand to match one another, in this mode both wires are used for sending and receiving signals. In this mode a potential 2000 meters segment length is capable but only 412 meters if half duplex mode is used, just under 1/5 of that of full duplex.
Other forms of Fast Ethernet exist such as 1000BaseT and 100BaseTX but neither have anywhere near a maximum potential distance as 100BaseFX however 1000BaseT has 10 times the transmission speed as that of 100BaseFX (1000 Mbps with only 100 metre segment distance.) (Dean, 2010) (pages 212 -213)
Max Transmission Speed (Mbps)
Max distance (Metres)
http://www.cisco.com/en/US/i/Other/Software/S3501-4000/s3983.jpg (Cisco, n.d.)(100Base-FX)
Parity Checking (Example/Diagram)
Parity checking allows for an additional bit to be added to a piece of data to ensure that the total 8 bit (now 9 bit) data piece remains and odd parity or an even parity. The extra bit is added to the string of binary digits can either be a 0 or a 1. The number of 1's within a binary code of a piece of data add up to and odd or even number then a 1 or zero can be added as a parity bit to keep both the odd and even numbers in check. (Gupta, 2006)
0 1 2 3 4 5 6 7 + (parity(8)) 0 1 2 3 4 5 6 7 + (parity(8))
1 0 1 0 1 0 0 1 + 1 1 1 0 0 0 1 1 0 + 0
TCP Re-Transmission is a simple method of sending data segments a second, or even multiple times again. When a transmission is sent, the system gives the sent transmission a pre-determined amount of time to reach its destination. In a sense it's a timer that goes off when an anomaly occurs or if a period of time has passed while a transmission is in progress. There are several reasons that an anomaly could occur such as data corruption, congestion or possibly hardware failure. (Kozierok, 2005) (Chapter 49)
In the diagram above a simple transmission is taking place where Host A sends 8 bytes of data to Host B. once Host B receives the data sent from Host A it must then send an acknowledgement back to Host A to confirm to Host A that the data has reached its destination. During the transmission an anomaly occurs (hardware failure or data corruption) and the acknowledgement doesn't reach its destination; Host A (marked by the red X). After the predetermined amount of time Host A sends a second segment to Host B in hopes for better results. (Edu.cn, n.d.)
Checksum Error Detection(Diagram)
Checksum essentially is a mathematical way to ensure the data being transmitted is free of errors, checksum does this by making sure each piece of data or "word" adds up to a numerical value that can be cross checked by the receiving device. So in turn if a piece of data has specific value and that value is altered in some way that the receiving devices corresponding checksum algorithm doesn't match the original then the device will know that the data has been altered or is corrupt. (Kundu, 2008)(pages 53 -55)
Checksum allows for the transmitted and received data to be compared against one another in-case there is any dissimilarity's. Each bit of data sent adds up to a total value and that total is displayed at the bottom of the diagram provided. The binary digits highlighted in red are alterations made to the original transmitted data, due to corruption or some other failure. These anomalies are detected and the checksum error detection produces an error report.
Signal encoding is the process of interpreting transmitted data sent from an electronic device through a physical medium, such as an Ethernet cable. "Encoding" is a term used when electronic data is converted to a different format, this is so that this data can be properly transmitted from one place to another. There are many types of encoding such as Digital to Digital, Digital to Analog, Analog to Digital and Analog to Analog. Along with encoding types there are various different encoding techniques, these being NRZ-L(Non-Return to Zero - Level) encoding, NRZ-I(Inverted) encoding, and Manchester encoding; among others. (Diane. Barrett, 2005) (pages 11 -20)
cis67776x | | | | | | | | | | | | |0 |1 |0 | 0 | 1 |1 |0 |0 | 0 | 1 |1 | | |---| | |---|---| | | |---|---| | | | | | | | | | | | | |---| |--|---| | |---|--|---| | | | | | | | | | | | | | |
Low voltage = 1
High Voltage = 0
changes in polarity only happen if the signal changes. Retains its polarity if signal is constant.
cis67778x | | | | | | | | | | | | |0 |1 |0 | 0 | 1 |1 |0 |0 | 0 | 1 |1 | | |---|--|---| |---|---|--|---| |---| | | | | | | | | | | | | |---| | | |---| | | | |---| | | | | | | | | | | | | |
Low voltage = 1
High Voltage = 0
similar to that of NRZ-L but when a change in voltage happens (low voltage) then polarity changes.
cis67781x | | | | | | | | | | | | |0 |1 |0 | 0 | 1 |1 |0 |0 | 0 | 1 |1 | |-| | --|| |-| | --| --|-| |-||-| | --| --| | | | | || | | | | | | | | | || | | | | | | | --|-| ||-| --|-| |-| | --| -| --|-| |-| | | | | | | | | | | | | |
Low/High voltage = 1
High/Low Voltage = 0
whenever there is a low voltage that is immediately followed by a high voltage and vice versa.
cis67782x | | | | | | | | | | | | |0 |1 |0 | 0 | 1 |1 |0 |0 |0 | 1 | 1 | | --|-| |-||-| | --|-| |-| |-|||| | --|-| | | | | | | || | | | | | | | | |||| | | | | | |-| | --| -| --|-| | --| --| -||--|-| | --| | | | | | | | | | | | |
Low/High voltage = 1
High/Low Voltage = 0
Again similar to Manchester except the start of the signal is represented by a 0 and is altered at the middle of each bit period.
CSMA/CD is an acronym for Carrier Sense Multiple Access Collision Detect and is essentially a method for allowing fast and efficient access for the Ethernet cable. CSMA/CD is in place to help deal with lost packets of data, sending the same signal again and again after a randomized amount of time. CSMA/CD was intentionally designed to send signals at random intervals because if two system were to do this at the same predetermined time then the signals would just collide and create and infinite loop of signal sending.
CSMA/CD can be broken down into separate parts for easier explanation, CS-MA-CD:
The Carrier Sense(CS) is a method of listening to how busy the traffic on a network/Ethernet cable is, if there is no traffic on an Ethernet cable the Carrier Sense will detect this and know that now is an appropriate time to send the signal.
Multiple Access (MA) this signify's that multiple computers can begin to transmit data on the network simultaneously.
Collision Detection(CD) is exactly as it sound, when two transmissions happen at the same time then a collision will occur and (CD) will recognise this. When a collision is detected then the randomly set signals come into play, essentially racing to be the first one to take priority over the cable. (Shinder, 2002) (pages 122 -123)
csmacd CSMACD Flowchart
The Flowchart above shows the processes of CSMA/CD where data can be fully acknowledge or collide with other data. Data will loop indefinitely until it is successful or stated to stop otherwise.
(Andrew Mallett, n.d.)
Finalised Discussions regarding the provided network i.e. Links, Protocols, Addressing, Security and Graphical Diagrams.
Sectioned every area of the report in terms of components/Mechanisms used within the network and this document has Links to each section for easier marking/traversal. Layers are described appropriately, Addressing, Security and Graphical section allow for an IN-depth look into these protocols.