Ethernet Standards and Encapsulation

Most widely used technology in networking is Ethernet. As we say in the early lesson that Ethernet work both in the data link layer(Layer 2) and the physical layer (Layer 1). there are different Ethernet standards that support different band of data.

• 10 Mb/s


• 100 Mb/s


• 1000 Mb/s (1 Gb/s)


• 10,000 Mb/s (10 Gb/s)


• 40,000 Mb/s (40 Gb/s)


• 100,000 Mb/s (100 Gb/s)

Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. For the Layer 2 protocols, as with all 802 IEEE standards, Ethernet relies on the two separate sublayers of the data link layer to operate, the Logical Link Control (LLC) and the MAC sublayers. We also explain MAC and LLC in earlier lessons.

LLC sublayer

As we know that data link has two sublayers. Upper sub-layer is LLC. So LLC communicate with the upper layers of the OSI model. The LLC get the network protocol data, which is usually an IPv4 packet. LLC adds control information to help deliver the packet to the destination. The LLC is used to communicate with the upper layers of the application and transition the packet to the lower layers for delivery.

LLC is implemented in software, and its implementation is independent of the hardware. The driver software of computer NIC and be considered as LLC. The driver is a software program and instruction that interacts directly with the computer NIC and other hardware. Driver software enables communication between the network device,  computer, operating system as well as with other network computers and network devices.

MAC sublayer

MAC is the lower sublayer of the data link layer. It is implemented by computer hardware, typically in the NIC. The specifics are listed in the IEEE 802.3 standards. Figure 4.2 lists common IEEE Ethernet standards.It shows how the data link layer is divided into the LLC and MAC sublayers. The LLC communicates with the network layer while the MAC sublayer allows various network access technologies. For instance, the MAC sublayer communicates with Ethernet LAN technology to send and receive frames over copper or fiber-optic cable. The MAC sublayer also communicates with wireless technologies such as Wi-Fi and Bluetooth to send and receive frames wirelessly.

As we know that Media Access Control (MAC) layer is between the Logical Link Control (LLC) sublayer and physical layers, The MAC sublayer has following key tasks:

• Data encapsulation


• Media access control

Data encapsulation

The data encapsulation process includes frame assembly from transmission node and disassembly on receiving node. In forming the frame, the MAC layer adds a header and trailer to the network layer PDU.

Data encapsulation provides three key functions:

• Data Framing-The framing process provides a sequence of one or more characters that are used to recognize a group of bits that make up a frame. These sequences bits provide synchronization between the transmitting and receiving nodes.


• Addressing -The data link layer is the lowest layer in the OSI model that is concerned with addressing. Data Link Layer receive Layer 3 PDU. The encapsulation process in data link layer provides data link layer address. labeling information with a particular destination location. Every device on a network has a unique number, generally called a physical address or MAC address, that is used by the data link layer protocol to ensure that data intended for a specific machine get to it properly. 

• Error detection –The data link each frame contains a trailer that used to detect any errors in transmissions.

Media Access Control

The MAC sublayer second responsibility is control access to the media. This sublayer is responsible for the placement of frames on the media and the removal of frames from the media. The MAC sublayer communicates directly with the physical layer.

Ethernet

Definition

The Ethernet is both a data link (Layer 2 of OSI Model) and physical layer(Layer 1 of OSI Model) main component for local area networks (LANs). Bob Metcalfe and D.R. Boggs invented this in 1972.Ethernet is a network protocol that controls how data is transmitted over a LAN. Technically it is referred to as the IEEE 802.3 protocol. It is also used in contrast with WAN (wide area network) which spans for much larger geographical areas.

The Ethernet protocol standards describe a lot of aspects of network communication as well as frame format, frame size, timing, and encoding. Ethernet telling, how networked devices can format data for transmission to other network devices on the same network segment, and also describe how to put that data out on the network connection.

The Ethernet is a contention-based method of networking. A contention-based method means that any device can try to transmit data across the shared medium whenever it has data to send. The Carrier Sense Multiple Access/Collision Detection (CSMA/CD) process is used in half-duplex Ethernet LANs to detect and resolve collisions. Today’s Ethernet LANs use full-duplex switches, which allow multiple devices to send and receive simultaneously with no collisions.

The OSI model describes separately both the data link layer function and the physical standards of the media. The Ethernet standard define both the Layer 2 protocols and the Layer 1 technologies. According to specification, It supports different media, bandwidths, and other Layer 1 and 2 variations. The basic frame format and address scheme are the same for all types of Ethernet.

http://fschub.com/network-interface-card-nic/

Lab - Working with Personal Computer NICs

Required Resources

1x PC Installed Windows 7 or 10 with NICs (Wired and Wireless)

Wired Connection and  Wireless Connection

 Identify and Work with PC NICs

Here, you will recognize the Personale Computer NICs. That you can explore in different ways. You will also learn how to disable and enable these NICs. I am performing this lab with my laptop which is Windows 10 installed so you will see the images of windows there is little difference in menu selection in other operating systems like Windows 7, window8, etc

 Step 1: Use the Network and Sharing Center.

• The first step is to open the Network and Sharing Center. The best and easiest way to open it is clicking on Start and typing here network and. This will immediately show you the app in the list.

Network and Sharing Center

• Open the Network and Sharing Center by clicking the Windows Start button > settings > network and internet here you can find network and sharing center

To start Network and Sharing Center from the taskbar notification area

Right-click the Network icon in the taskbar notification area. And click Network and Sharing Center.

system tray Network and Sharing Center

• To start Network and Sharing Center from a command prompt


• Click Start, and write cmd this will show you Command Prompt immediately. Click command prompt or press ENTER command prompt will be open.


• In the command prompt, type the following command, which is not case sensitive, and then press ENTER:


• control.exe /name Microsoft.NetworkAndSharingCenter


• Next click on change adapter setting, here your will see all network connection.

network connections

Wireless NIC

•  Select the Wireless Network Connection option and right-click it to bring up a drop-down list. If your wireless NIC is disabled, you will have an option to Enable If your NIC was already enabled, then Disable would be the first option on this drop-down menu. If your Wireless Network Connection is currently disabled, then click Enable.

wi-fi enabling

• Right-click the Wireless Network Connection, and then click Status

• The Wireless Network Connection Status window displays where you can view information about your wireless connection.

wi-fi status

• Click Details to display the Network Connection Details window.

• 
  

  What to note here?

  
  

• What is the MAC address of your wireless NIC?


• Do you have multiple IPv4 DNS Servers listed?


• What is IPv4 Address?


• Do you have  IPv4 Default Gateway?


• Why would multiple DNS Servers be listed?


• When you have reviewed the network connection detail here now click Close.

• Open a command window prompt and type ipconfig /all.


• You can notice that the information displayed in network connection detail is the same which is will be displayed in the command prompt in result of ipconfig /all

cmd prompt

• Close the command prompt window and the Network Connection Details This should get you back to the Wireless Network Connection Status. Click Wireless Properties. In the Wireless Network Properties window, click the Security tab.

Here you can see which type of security is being used. Click the Show characters. Check out the show character box to display the actual Network security key, instead of the hidden characters, and then click OK.

wi-fi security

• Close the Wireless Network Properties and the Network Connection Status windows. Select and right-click the Wireless Network Connection option at notification area to connect and disconnect a wireless network > click connect. At a pop-up window that appears at the bottom right corner of your desktop that displays your current connections, along with a list of SSIDs and signals strength that are in the range of the wireless NIC of your PC. If a scrollbar appears on the right side of this window, you can use it to display additional SSIDs. Here in this image, you can see two wireless networks.  If you want to connect automatically to the device each time you in range of the device then check out connect automatically

SSID

• If you are connecting first time to a wireless device then you will be asked for a password Enter password and click next make a connection with your wireless device. This will be saved next time you will automatically connect the device.

wi-fi-Password

Work with your wired NIC.

• On the Network Connections window, select and right-click the Local Area Connection or Ethernet option to display the drop-down list. If the NIC is disabled, enable it, and then click the Status To see a status you must have an Ethernet cable attaching your PC NIC to a switch or router otherwise you can't see a status of your wired NIC.

• The Local Area Connection Status or Ethernet status window will open. This window displays information about your wired connection to the LAN. Click Details… to view the address information for your LAN connection just you see before in for wireless NIC.

The System Tray Network Icons

Use the Wireless Network icon.

• Click the system tray Wireless Network icon to view the pop-up window that we already show in above, displays the SSIDs that are in a range of your wireless NIC. When the system tray displays the Wireless Network icon, the wireless NIC is active. If wireless is connected it well show to the internet it will show the icon like below.


• Examine your system tray. What is connected and what is the status of the connection is it connected to the internet or it is limited.


• If your wireless NIC is connected to the wireless device and its also access to the internet, its system tray icon will be about following. 

• If wireless is connected but it has no access to the internet it will show the icon like below. The yellow marks is shown that the connection is limited

• If wireless in available and wireless NIC is active but not connected to any wireless its wireless icon at system tray will be like following

• Now disable the wireless ICON and examine you should see that the  Wireless Network Connection icon has been replaced by the Wired Network icon, which indicates that you are using your wired NIC for network connectivity. Examine the below image it has a red X mark that means that the cable at wired NIC is unplugged or the device which is connected to this NIC is power off. If the cable is unplugged or device is switched off ( may be a DSL Router, Switch or wired port of wireless device) do needful to connect wired NIC.

• Here examine network connection with yellow mark, its mean that NIC is connected somewhere but there is no internet connection or it is a limited connection. If you are working in LAN environment it should be limited.

• Now examine the below image its mean that the network is connected and it has internet access.

Cisco Packet Tracer Introduction

Cisco Packet tracer is a simulator software used to illustrate at a basic level how network work. It is used to create & simulate network virtually. It gives similar situation close to as exists physical. Packet tracer is developed at Cisco Systems. It is a dominant and energetic tool that show the various protocols used in networking.

Cisco Packet tracer includes layer 2 protocols such as Ethernet and PPP, layer 3 protocols such as IP, ICMP, and ARP, and layer 4 protocols such as TCP and UDP. Routing protocols can also be traced. Packet Tracer is a supplement to and not a replacement for experience with real equipment. Click here to download Packet tracer software.

Choosing Devices and Connections 

Here we will begin building our first cisco packet tracer network topology by selecting devices and the media in which to connect them. Several types of devices and network connections can be used. Here in this lab, we will keep it simple by using End Devices, Switches, and Connections. 
Single click on each group of devices and connections you will see the various choices. When we select a device in the left panel, in the right panel we see all the listed devices of that type. 

Adding a Switch

 

Select a switch, by clicking once on the left panel and then click once on any switch at the right panel.

Add the switch by moving the plus sign “+”  and click on the topology area.  It will draw a switch at the topology area of packet tracer

Adding an End Device to Topology 

Select end devices at the left panel, by clicking once and then select a PC

Add the PC by moving the plus sign “+” below  SW0, and click once to place PC in topology. 

Perform the above steps to place 3 more PCs at the topology.

 

Connecting All PCs with Switch

Select a connection at the left panel by clicking once and then select an automatically choose connection type by clicking once.  

After clicking automatically choose connection type click on PC0 and then on switch0. It will connect pc0 to switch0

Perform this process for all other 3 PCs

If you don’t want to use in automatically choose a connection type, then select appropriate connection type and do the following steps.  
Click once on PC0

• Choose Fast Ethernet


• Drag the cursor to Switch0


• Click once on Switch0 and choose FastEthernet0/1


• Notice the green link lights on PC0 Ethernet NIC and amber light Switch0 FastEthernet0/1 port. The switch port is temporarily not forwarding frames, while it goes through the stages for the Spanning Tree Protocol (STP) process.


• After an about 30 seconds the amber light will change to green indicating that the port has entered the forwarding stage. 

You can see the port number moving the cursor over the link light. It will show Ethernet type and number.

Try out more topologies at different scenarios. That will increase your packet tracer skills. 

Lab-Building an Ethernet Crossover Cable, connecting two PCs one to one

Objectives of the lab

Part 1: Analyze Ethernet Cabling Standards and Pinouts

Part 2: Build an Ethernet Crossover Cable

Part 3: Test an Ethernet Crossover Cable

Part 4: IP Address Settings on Computer

Part 5: Testing the Connection using Ping Command

Resources Required

• 2 RJ-45 connectors


• RJ-45 crimping tool


• Category 5 or 5e cable length.


• Wire cutter


• Wire stripper


• Ethernet cable tester (optional)


• 2 PCs (Windows 7 or 10 installed)

Part 1: Analyze Ethernet Cabling Standards and Pinouts

The TIA/EIA has UTP cabling standards for using in LAN environments. TIA/EIA has two standards 568-A and 568-B. These are the two standards which are mostly used in LAN cabling. These standards determine which color wire is to be used on which pin. In straight through cable both ends should be 568A standard but in crossover cable, one end should be 568A and the other end should be 568B. which reverses the send and receive pairs. Crossover cables are normally used to connect same devices like hubs to hubs or switches to switches, but they can also be used to directly connect two hosts to create a simple network.

Step 1: Table for TIA/EIA 568-A standard Ethernet cable.

The following table and diagrams display the color scheme and pinouts, as well as the function of the four pairs of wires used for the 568-A standard.

 

Pin Number	Wire Color	Wire role
1	White/Green	TX +
2	Green	TX -
3	White/Orange	RX +
4	Blue	Not Used
5	White/Blue	Not Used
6	Orange	RX -
7	White/Brown	Not Used
8	Brown	Not Used

Step 2: Table for TIA/EIA 568-B standard Ethernet cable.

 

The following table and diagrams display the color scheme and pinouts, as well as the function of the four pairs of wires used for the 568-B standard.

Pin Number	Wire Color	Wire role
1	White/Orange	TX +
2	Orange	TX -
3	White/Green	RX +
4	Blue	Not Used
5	White/Blue	Not Used
	Green	RX -
7	White/Brown	Not Used
8	Brown	Not Used

Part 2: Build an Ethernet Crossover Cable

                         

In a crossover cable second and third pairs on the RJ-45 connector at one end, reversed at the other

end (see table in step 1 and step 2). The cable pinouts are the 568-A standard on one end and the 568-B

standard on the other end.

 Steps to make a cable

• 
  

  Determine the cable length required. Max length is 100 meter and 91 meters

  
  


• 
  

  Cut off the required piece of cable and using a wire stripper, remove 5.08 cm (2 in.) of the cable jacket from both ends.

  
  


• 
  

  Hold the four pairs of twisted cables forcefully where the jacket was cut away. reorder the cable pairs into the order of the 568-A wiring standard. Refer to the table in step 1, if necessary.

  
  


• 
  

  If possible, maintain the twists in the cable; this provides noise cancellation.

  
  


• 
  

  Flatten, straighten, and line up the wires using your thumb and forefinger and you may be used pencil for this job

  
  


• 
  

  Make sure that the cable wires are still in the exact order for the 568-A standard. Using your wire cutters, trim the four pairs in a straight line to within 1.25 to 1.9 cm (1/2 to 3/4 in.).

  
  


• 
  

  Put an RJ-45 connector on the end of your cable, with the spike on the underside pointing downward.

  
  


• 
  

  Tightly insert the wires into the RJ-45 connector. All wires should be seen at the end of the connector in their proper positions. If the wires are not extending to the end of the connector, take the cable out. Rearrange the wires again, and reinsert the wires back into the RJ-45 connector.

  
  


• 
  

  If everything is correct, insert the RJ-45 connector with cable into the crimper. Crimp down hard enough to force the contacts on the RJ-45 connector through the insulation on the wires, thus completing the Conducting path.

  
  

Part 3: Test an Ethernet Crossover Cable

Many cable testers will test for length and mapping of wires. If the cable tester has a wire map feature, it

verifies which pins on one end of the cable are connected to which pins on the other end.

.Step 2: Connect two PCs together via NICs using your Ethernet crossover cable.

• Set your PCs with following IP address settings. For example, your have a PC-1 and PC-2. Your IP Address should be set according to the table. The default gateway has no need at the same network so it should be empty.  

Device	Interface	IP Address	Subnet Mask	Default Getway
PC-1	NIC	192.168.100.1	255.255.255.0	No Need
PC-2	NIC	192.168.100.2	255.255.255.0	No Need

 

• Using the crossover cable you made before, connect both PCs together via their NICs.

 Part-4: - IP Address Settings on Computer  (windows 7 or 10)

Step-1: - Open Network and sharing center.

 

Step-2: - On the network and sharing center window click on change adapter setting. You will see a network sharing window.

Here your should see “ Local Area connection” or “Ethernet”  right click on that and click on properties

 

Step-3: - In this window select “Internet protocol version 4(TCP/IPv4)” and click Properties

Step-4: - Here click used the following IP Address and fill in your own IP and subnet mask click OK and again click ok Now your PC-1 is ready. Do the same with PC-2

Part-5: - Testing of Connection using Ping Command

1. Go to “windows command prompt”


2. In the command prompt of PC-1 enter the following command “ ping 192.168.100.2


3. Repeat the process and ping from PC-2 to PC-1.


4. assume IP addressing and the firewall does not issue, your pings should be successful if the cables were properly made.


5. Ping statistics for IP Address

            Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)

 Note: The Windows firewall may have to be temporarily disabled for pings to be successful.

 

LAN and WAN Frames - Layer 2 Protocols

In a TCP/IP network, every OSI Layer 2 protocols work with IP at OSI Layer 3. but, the Layer 2 protocol used depends on the logical topology and the physical media.

every protocol performs media access control for specific Layer 2 logical topologies. This means that a number of different network devices can work as nodes that operate at the data link layer while implementing these protocols. These devices contain the NICs on computers as well as the interfaces between routers and Layer 2 switches.

The Layer 2 protocols used for a particular network topology is determined by the equipment used to apply that topology. The technology is, in turn, determined by the size of the network - in terms of the number of hosts and the geographic scope - and the services to be provided over the network.

A LAN usually uses a high-bandwidth technology that is able of supporting huge figures of hosts. A LAN's moderately small geographic area (a single building or a multi-building campus) and its high density of users, make this technology cost-effective.

on the other hand, WANs cover a large geographical area, using a high bandwidth technology is usually not cost-effective for WANs. The cost of the long distance physical links and the technology used to carry the signals over those distances typically results in lower bandwidth capacity. Traditionally, WANs have been implemented using one of two technologies: circuit switching and packet switching. Recently, frame relay and ATM networks have assumed major roles. The differentiation in bandwidth usually results in the use of different protocols for LANs and WANs.

Data link layer protocols

• 
  

  Ethernet

  
  


• 
  

  802.11 Wireless

  
  


• 
  

  Frame Relay

  
  


• 
  

  Point-to-Point Protocol (PPP)

  
  


• 
  

  HDLC

  
  

Click to view LAN and WAN Frame Demo

 

 

Pakistan Super League 2017 Schedule

The second edition of the PSL will start on from February 9 in Dubai. The matches will be played in Sharjah and Abu Dhabi apart from Dubai with the PSL 2017 final to be played in Lahore Insha Allah Ho.There is the schedule of Pakistan Super Leag matches

Date	Local Time	Time (GMT)	PSL Match	Venue
9-Feb	20:00	16:00	Peshawar vs Islamabad	Dubai
10-Feb	15:30	11:30	Lahore vs Quetta	Dubai
10-Feb	20:00	16:00	Karachi vs Peshawar	Dubai
11-Feb	15:30	11:30	Islamabad vs Lahore	Dubai
11-Feb	20:00	16:00	Quetta vs Karachi	Dubai
12-Feb	20:00	16:00	Peshawar vs Lahore	Dubai
15-Feb	20:00	16:00	Islamabad vs Quetta	Sharjah
16-Feb	20:00	16:00	Lahore vs Karachi	Sharjah
17-Feb	15:30	11:30	Peshawar vs Quetta	Sharjah
17-Feb	20:00	16:00	Karachi vs Islamabad	Sharjah
18-Feb	15:30	11:30	Quetta vs Lahore	Sharjah
18-Feb	20:00	16:00	Islamabad vs Peshawar	Sharjah
19-Feb	20:00	16:00	Peshawar vs Karachi	Sharjah
20-Feb	20:00	16:00	Lahore vs Islamabad	Sharjah
23-Feb	20:00	16:00	Karachi vs Quetta	Dubai
24-Feb	15:30	11:30	Peshawar vs Lahore	Dubai
24-Feb	20:00	20:00	Quetta vs Islamabad	Dubai
25-Feb	15:30	11:30	Lahore vs Karachi	Dubai
25-Feb	20:00	16:00	Peshawar vs Quetta	Dubai
26-Feb	20:00	16:00	Karachi vs Islamabad	Dubai
28-Feb	20:00	16:00	Playoff 1: Team 1 vs Team 2	Sharjah
1-Mar	20:00	16:00	Playoff 2: Team 3 vs Team 4	Sharjah
3-Mar	20:00	16:00	Winner Playoff 2 vs Runner Up Playoff 1	Dubai
7-Mar			PSL 2017 Final (Subject to security so time will be announced later)	Lahore

Sports and cricket are not the subjects of this blog I upload these detail only for the interest of my viewer in Pakistan super league. so this will be continued till PSL ending. 

Data Link Layer Frame

In networking, a frame is layer 2 (data link layer of the OSI model) data unit that is transmitted between network points. This frame contains complete addressing, necessary protocol, and control information. The data link layer received layer 3 (Network layer of the OSI model) PDU from layer 3 within the data field and then prepare this PDU as layer 2 frame for carrying across network media. Before transmission, data link layer protocol encapsulates this with trailer and header. There are a lot of different data link layer protocols that describe data link layer frames. At the receiving end again data link layer protocols explain and de-encapsulate this frame. Figure 3.24 Illustrate frame which has three basic parts:-

• 
  

  Header

  
  


• 
  

  Data

  
  


• 
  

  Trailer

  
  

Figure 3.24 Illustrate the layer 2 frame general structure.

The frame fields

The general frame as shown in above mention image but, the structure of the frame contains fields in the header and trailer varies according to the protocol. There is no frame structure that meets the requirements of all data transportation across all type of media. Depending on the background, the size of control information needed in the frame varies to match the access control requirements of the media and logical topology. So frame has no standard size its varies according to the media and environment.

 

Typical frame fields are following:-

• 
  

  Start and stop indicator fields – These fields  explain the start and end restrictions of the frame

  
  


• 
  

  Addressing fields- indicate the source nodes and destination nodes.

  
  


• 
  

  Type  - this field explains layer3 protocols in the data field.

  
  


• 
  

  Control - identify special flow control services like QoS (Quality of Service).

  
  


• 
  

  Data -The frame payload (Network layer packet)

  
  


• 
  

  Error Detection- These frame fields are used for error detection and are included after the data to form the trailer.

  
  

Figure 3.25 Illustrate the frame fields 

Carrier Sense Multiple Access (CSMA)

Carrier Sense Multiple Access is a networking protocol that listens to network signals on the carrier/medium before transmitting any data. CSMA is implemented in Ethernet networks with more than one computer or network device attached to it. CSMA is part of the Media Access Control (MAC) protocol.

Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

Carrier Sense Multiple Access/Collision Detection (CSMA/CD) is the most widely used transmission method used in half-duplex Ethernet networks.  On Ethernet, any device can attempt to send a frame at any time. Each device senses whether the line is idle and therefore available to be used. If it is, the device begins to transmit its first frame. If another device has tried to send at the same time, a collision is said to occur and the frames are discarded. Each device then waits a random amount of time and retries until successful in getting its transmission sent.

Carrier Sense Multiple Access with Collision Avoidance

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is a method for carrier transmission in 802.11  networks. CMSA/CA uses a method similar to CSMA/CD to detect if the media is clear. CMSA/CA also uses additional techniques. This method does not detect collisions but attempts prevent collisions before happen. Each device that transmits includes the time duration that it needs for the transmission. All other wireless devices receive this information and know how long the medium will be unavailable.

In CSMA/CA, when a node receives a traffic that is to be sent, it checks to be sure that the channel is clear (no other node is transmitting at the time). If the channel is clear, then the packet is sent. If the channel is not clear, the node waits for a randomly chosen period of time and then checks again to see if the channel is clear. This period of time is called the backoff factor and is counted down by a backoff counter. If the channel is clear when the backoff counter reaches zero, the node transmits the packet. If the channel is not clear when the backoff counter reaches zero, the backoff factor is set again, and the process is repeated. Carrier sense multiple access with collision avoidance (CSMA/CA) is,  the least popular of the access methods. This access method is now used with WLANs.

Half and Full Duplex Communication

Duplex communication refers to the direction of data transmission between two devices. Half-duplex communications limit the exchange of data to one direction at a time while full-duplex allows the sending and receiving of data at the same time.

Half-duplex communication

In this type of communication where one side can talk at a time. When one side has complete transmitting its data, the other side can reply. Only one node can talk at a time. If both try to talk at the same time, a collision will take place on the network. So both device can transmit and receive on the media but cannot do so at the same time. The half-duplex mode is used in legacy bus topologies and with Ethernet hubs. WLANs also operate in half-duplex. Half-Duplex is used with contention-based access methods. this method of communication is not very efficient and requires more time to send/receive larger amounts of data. Older networks work in half-duplex mode, due to the constraints of the network medium (coax cable) and hardware equipment (hubs). Figure 3.22 illustrate the half-duplex communication.

Full-duplex communication 

Full-duplex is the type of communication where Both devices can transmit and receive on the media at the same time. The data link layer assumes that the media is available for transmission for both nodes at any time. Of this type, there is no danger of a collision and therefore the transfer of data is completed much faster. Ethernet switches operate in full-duplex mode by default but can operate in half-duplex if connecting to a device such as an Ethernet hub. Figure 3.23 shows full-duplex communication.

Today, all networks make use of switches instead of hubs and UTP Ethernet cabling instead of co-axial cabling, which allow full-duplex communication between all connected hosts. It is important that both interconnected interfaces operate using the

Physical LAN Topologies

Physical LAN topologies define how the end systems are physically interconnected. In shared media LANs, end devices can be interconnected using the following physical topologies:

Star topology

In Star topology, all end devices are connected to the central device.Early star topologies interconnected end devices using Ethernet hubs. However, star topologies now use Ethernet switches. The star topology is easy to install, very scalable (easy to add and remove end devices), and easy to troubleshoot.

All the data on the star topology passes through the central device before reaching the intended destination. Hub/Switch acts as a junction to connect different nodes present in Star Network, and at the same time it manages and controls the whole of the network. Depending on which central device is used, “hub” and “Switch”  can act as repeater or signal booster. Central device can also communicate with other hubs and switch of different network.

Extended Star Topology

In an extended star topology, additional Ethernet switches interconnect other star topologies.

Bus Topology

Bus Topology is the simplest of network topologies. All end systems (computers as well as servers)  are connected to each other and terminated in some form on each end. Infrastructure devices such as switches are not required to interconnect the end devices. Bus topologies using coax cables were used in legacy Ethernet networks because it was inexpensive and easy to set up.

Ring Topology

In the ring topology, end systems are connected to a single circle of cable. Unlike the bus topology, the ring does not need to be terminated. The signals travel around the loop in one direction and pass through each computer, which acts as a repeater to boost the signal and send it to the next computer. Ring topologies were used in legacy Fiber Distributed Data Interface (FDDI) and Token Ring networks.

Figure 3.21 illustrate physical LAN topologies

 

Network Topology

The network topology is the arrangement or relationship of the network devices, including its nodes and connecting lines. The network really has two shapes or two types of topology; one is physical and the other is logical.

The physical topology

The physical topology of a network is the actual physical and geometric layout of the network that we can see such as devices like routers, switches, and wireless access points, nodes and cables. There are several common physical topologies like point-to-point, ring, bus, star and mesh topologies. 

The logical topology

A logical topology is how devices appear connected to the user. This topology defines the way a network transfers frames from one node to the next. This topology consists of virtual links between the nodes of a network. These logical paths are defined by data link layer protocols.  The data link layer deals the logical topology of a network when controlling data access to the media. It is the logical topology that influences the type of network framing and media access control used.

Common Physical WAN Topologies

WAN's are generally interconnected using the following physical topologies:

Point-to-Point 

Only two devices are involved in a point-to-point connection, with one wire (or air, in the case of wireless) sitting between them.This is the simplest topology in networking. For this reason, this is a very popular WAN topology. Figure 3.18 illustrated the physical point-to-point topology.

Hub and Spoke

A hub and spoke network is a traditional and widely used topology for all types of networks. It's also called the star topology. In this topology, a central site interconnects branch sites using point-to-point links. The Central site is called a hub and branch site is called spokes. Communication between two spokes always travels through the hub. Figure 3.19 illustrated the physical hub and spoke topology.

Mesh Topology

A mesh network is a network topology in which each node relays data for the network so this topology provides high availability but requires that every end system is interconnected to every other system. Therefore the administrative and physical costs can be very high. Each link is essentially a point-to-point link to the other node. Variations of this topology include a partial mesh where some but not all of the end devices are interconnected. 3.20 illustrated the physical mesh topology.

Next - Common Physical LAN Topologies