Planning and Cabling Networks

Before using an IP phone, accessing instant messaging, or conducting any number of other interactions over a data network, we must connect end devices and intermediary devices via cable or wireless connections to form a functioning network. It is this network that will support our communication in the human network.

When planning the installation of LAN cabling, there are four physical areas to consider:
• Work area
• Telecommunications room, also known as the distribution facility
• Backbone cabling, also known as vertical cabling
• Distribution cabling, also known as horizontal cabling


Total Cable Length

For UTP installations, the ANSI/TIA/EIA-568-B standard specifies that the total combined length of cable spanning three of the areas listed above, excluding the backbone cable, is limited to a maximum distance of 100 meters per channel. This standard also specifies maximum backbone distances, ranging from 90m for UTP to 3000m for single mode fiber cable, based on application and media type.



Work Areas

The work areas are the locations devoted to the end devices used by individual users. Each work area has a minimum of two jacks that can be used to connect an individual device to the network. We use patch cables to connect individual devices to these wall jacks. Allowed patch cable length depends on the horizontal cable and telecommunication room cable lengths. Recall that the maximum length for these three area can not exceed 100m. The EIA/TIA standard specifies that the UTP patch cords used to connect devices to the wall jacks must meet or exceed the performance requirements in ANSI/TIA/EIA-568-B.

Straight-through cable is the most common patch cable used in the work area. This type of cable is used to connect end devices, such as computers, to a network. When a hub or switch is placed in the work area, a crossover cable is typically used to connect the device to the wall jack.


Telecommunications Room

The telecommunications room is where connections to intermediary devices take place. These rooms contain the intermediary devices - hubs, switches, routers, and data service units (DSUs) - that tie the network together. These devices provide the transitions between the backbone cabling and the horizontal cabling.
Inside the telecommunications room, patch cords make connections between the patch panels, where the horizontal cables terminate, and the intermediary devices. Patch cables also interconnect these intermediary devices.
The Electronics Industry Alliance/Telecommunications Industry Association (EIA/TIA) standards specify two different types of UTP patch cables. One type is a patch cord, with a length of up to 5 meters, which is used to interconnect equipment and patch panels in the telecommunications room. Another type of patch cable can be up to 5 meters in length and is used to connect devices to a termination point on the wall.


Horizontal Cabling

Horizontal cabling refers to the cables connecting the telecommunication rooms with the work areas. The maximum length for a cable from a termination point in the telecommunication room to the termination at the work area outlet must not exceed 90 meters. This 90 meter maximum horizontal cabling distance is referred to as the permanent link because it is installed in the building structure. The horizontal media runs from a patch panel in the telecommunications room to a wall jack in each work area. Connections to the devices are made with patch cables.


Backbone Cabling

Backbone cabling refers to the cabling used to connect the telecommunication rooms to the equipment rooms, where the servers are often located. Backbone cabling also interconnects multiple telecommunications rooms throughout the facility. These cables are sometimes routed outside the building to the WAN connection or ISP.

Backbones, or vertical cabling, are used for aggregated traffic, such as traffic to and from the Internet and access to corporate resources at a remote location. A large portion of the traffic from the various work areas will use the backbone cabling to access resources outside the area or facility. Therefore, backbones typically require high bandwidth media such as fiber-optic cabling.


Electromagnetic Interference/Radio Frequency Interference

Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) must be taken into consideration when choosing a media type for a LAN. EMI/RFI in an industrial environment can significantly impact data communications if the wrong cable is used.

Interference can be produced by electrical machines, lightning, and other communications devices, including computers and radio equipment.

As an example, consider an installation where devices in two separate buildings are interconnected. The media used to interconnect these buildings will be exposed to the possibility of lightning strikes. Additionally, there maybe a great distance between these two buildings. For this installation, fiber cable is the best choice.

Wireless is the medium most susceptible to RFI. Before using wireless technology, potential sources of interference must be identified and, if possible, minimized.


Making LAN Connections

Straight-through UTP Cables

A straight-through cable has connectors on each end that are terminated the same in accordance with either the T568A or T568B standards.

Identifying the cable standard used allows you to determine if you have the right cable for the job. More importantly, it is a common practice to use the same color codes throughout the LAN for consistency in documentation.



Use straight-through cables for the following connections:
• Switch to a router Ethernet port
• Computer to switch
• Computer to hub


Crossover UTP Cables

For two devices to communicate through a cable that is directly connected between the two, the transmit terminal of one device needs to be connected to the receive terminal of the other device.

To achieve this type of connection with a UTP cable, one end must be terminated as EIA/TIA T568A pinout, and the other end terminated with T568B pinout.



To summarize, crossover cables directly connect the following devices on a LAN:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router Ethernet port connection
• Computer to computer
• Computer to a router Ethernet port


MDI/MDIX Selection

Many devices allow the UTP Ethernet port to be set to MDI or MDIX. This can be done in one of three ways, depending on the features of the device:

1. On some devices, ports may have a mechanism that electrically swaps the transmit and receive pairs. The port can be changed from MDI to MDIX by engaging the mechanism.

2. As part of the configuration, some devices allow for selecting whether a port functions as MDI or as MDIX.

3. Many newer devices have an automatic crossover feature. This feature allows the device to detect the required cable type and configures the interfaces accordingly. On some devices, this auto-detection is performed by default. Other devices require an interface configuration command for enabling MDIX auto-detection.


Making WAN Connections

By definition, WAN links can span extremely long distances. These distances can range across the globe as they provide the communication links that we use to manage e-mail accounts, view web pages, or conduct a teleconference session with a client.

Wide area connections between networks take a number of forms, including:
• Telephone line RJ11 connectors for dialup or Digital Subscriber Line (DSL) connections
• 60 pin Serial connections

The first cable type has a male DB-60 connector on the Cisco end and a male Winchester connector on the network end. The second type is a more compact version of this cable and has a Smart Serial connector on the Cisco device end. It is necessary to be able to identify the two different types in order to connect successfully to the router.


Data Communications Equipment and Data Terminal Equipment

The following terms describe the types of devices that maintain the link between a sending and a receiving device:

Data Communications Equipment (DCE) - A device that supplies the clocking services to another device. Typically, this device is at the WAN access provider end of the link.

Data Terminal Equipment (DTE) - A device that receives clocking services from another device and adjusts accordingly. Typically, this device is at the WAN customer or user end of the link.



The V35 compliant cables are available in DTE and DCE versions. To create a point-to-point serial connection between two routers, join together a DTE and DCE cable. Each cable comes with a connector that mates with its complementary type. These connectors are configured so that you cannot join two DCE or two DTE cables together by mistake.


Making the Device Management Connection

A terminal emulator is a software program that allows one computer to access the functions on another device. It allows a person to use the display and keyboard on one computer to operate another device, as if the keyboard and display were directly connected to the other device. The cable connection between the computer running the terminal emulation program and the device is often made via the serial interface.

To connect to a router or switch for device management using terminal emulation, follow these steps:

Step 1:

Connect a computer to the console port using the console cable supplied by Cisco. The console cable, supplied with each router and switch, has a DB-9 connector on one end and an RJ-45 connector on the other end. (Older Cisco devices came supplied with an RJ-45 to DB-9 adapter. This adapter is used with a rollover cable that has an RJ-45 connector at each end.)

Many newer computers do not have an EIA/TIA 232 serial interface. If your computer has only a USB interface, use a USB-to-serial conversion cable to access the console port. Connect the conversion cable to a USB port on the computer and then connect the console cable or RJ-45 to DB-9 adapter to this cable.

Step 2:

With the devices directly connected via cable, configure a terminal emulator with the proper settings. The exact instructions for configuring a terminal emulator will depend on the particular emulator. For the purpose of this course, we will usually use HyperTerminal because most varieties of Windows have it. This program can be found under All Programs > Accessories > Communications. Select HyperTerminal.
Open HyperTerminal, confirm the chosen serial port number, and then configure the port with these settings:
• Bits per second: 9600 bps
• Data bits: 8
• Parity: None
• Stop bits: 1
• Flow control: None

Step 3:

Log in to the router using the terminal emulator software. If all settings and cable connections are done properly, you can access the router by pressing the Enter key on the keyboard.

Ethernet

These protocols comprise the TCP/IP protocol stack and since the Internet was built using these protocols, Ethernet is now the predominant LAN technology in the world.

Internet Engineering Task Force (IETF) maintains the functional protocols and services for the TCP/IP protocol suite in the upper layers. However, the functional protocols and services at the OSI Data Link layer and Physical layer are described by various engineering organizations (IEEE, ANSI, ITU) or by private companies (proprietary protocols). Since Ethernet is comprised of standards at these lower layers, generalizing, it may best be understood in reference to the OSI model. The OSI model separates the Data Link layer functionalities of addressing, framing and accessing the media from the Physical layer standards of the media. Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies. Although Ethernet specifications support different media, bandwidths, and other Layer 1 and 2 variations, the basic frame format and address scheme is the same for all varieties of Ethernet.


Ethernet – Layer 1 and Layer 2

Ethernet operates across two layers of the OSI model. The model provides a reference to which Ethernet can be related but it is actually implemented in the lower half of the Data Link layer, which is known as the Media Access Control (MAC) sublayer, and the Physical layer only.
Ethernet at Layer 1 involves signals, bit streams that travel on the media, physical components that put signals on media, and various topologies. Ethernet Layer 1 performs a key role in the communication that takes place between devices, but each of its functions has limitations.



As the figure shows, Ethernet at Layer 2 addresses these limitations. The Data Link sublayers contribute significantly to technological compatibility and computer communications. The MAC sublayer is concerned with the physical components that will be used to communicate the information and prepares the data for transmission over the media..

The Logical Link Control (LLC) sublayer remains relatively independent of the physical equipment that will be used for the communication process.


Logical Link Control – Connecting to the Upper Layers

Ethernet separates the functions of the Data Link layer into two distinct sublayers: the Logical Link Control (LLC) sublayer and the Media Access Control (MAC) sublayer. The functions described in the OSI model for the Data Link layer are assigned to the LLC and MAC sublayers. The use of these sublayers contributes significantly to compatibility between diverse end devices.

For Ethernet, the IEEE 802.2 standard describes the LLC sublayer functions, and the 802.3 standard describes the MAC sublayer and the Physical layer functions. Logical Link Control handles the communication between the upper layers and the networking software, and the lower layers, typically the hardware. The LLC sublayer takes the network protocol data, which is typically an IPv4 packet, and adds control information to help deliver the packet to the destination node. Layer 2 communicates with the upper layers through LLC.


MAC – Getting Data to the Media

Media Access Control (MAC) is the lower Ethernet sublayer of the Data Link layer. Media Access Control is implemented by hardware, typically in the computer Network Interface Card (NIC).

The Ethernet MAC sublayer has two primary responsibilities:
• Data Encapsulation
• Media Access Control


Data Encapsulation

Data encapsulation provides three primary functions:
• Frame delimiting
• Addressing
• Error detection

The data encapsulation process includes frame assembly before transmission and frame parsing upon reception of a frame. In forming the frame, the MAC layer adds a header and trailer to the Layer 3 PDU. The use of frames aids in the transmission of bits as they are placed on the media and in the grouping of bits at the receiving node.

The framing process provides important delimiters that are used to identify a group of bits that make up a frame. This process provides synchronization between the transmitting and receiving nodes.

The encapsulation process also provides for Data Link layer addressing. Each Ethernet header added in the frame contains the physical address (MAC address) that enables a frame to be delivered to a destination node.

An additional function of data encapsulation is error detection. Each Ethernet frame contains a trailer with a cyclic redundancy check (CRC) of the frame contents. After reception of a frame, the receiving node creates a CRC to compare to the one in the frame. If these two CRC calculations match, the frame can be trusted to have been received without error.


Media Access Control

The MAC sublayer controls the placement of frames on the media and the removal of frames from the media. As its name implies, it manages the media access control. This includes the initiation of frame transmission and recovery from transmission failure due to collisions.


Ethernet Collision Management

Legacy Ethernet

In 10BASE-T networks, typically the central point of the network segment was a hub. This created a shared media. Because the media is shared, only one station could successfully transmit at a time. This type of connection is described as a half-duplex communication.



As more devices were added to an Ethernet network, the amount of frame collisions increased significantly. During periods of low communications activity, the few collisions that occur are managed by CSMA/CD, with little or no impact on performance. As the number of devices and subsequent data traffic increase, however, the rise in collisions can have a significant impact on the user's experience.

Current Ethernet

A significant development that enhanced LAN performance was the introduction of switches to replace hubs in Ethernet-based networks. This development closely corresponded with the development of 100BASE-TX Ethernet. Switches can control the flow of data by isolating each port and sending a frame only to its proper destination (if the destination is known), rather than send every frame to every device.



The switch reduces the number of devices receiving each frame, which in turn reduces or minimizes the possibility of collisions. This, and the later introduction of full-duplex communications (having a connection that can carry both transmitted and received signals at the same time), has enabled the development of 1Gbps Ethernet and beyond.


MAC Address Structure

The MAC address value is a direct result of IEEE-enforced rules for vendors to ensure globally unique addresses for each Ethernet device. The rules established by IEEE require any vendor that sells Ethernet devices to register with IEEE. The IEEE assigns the vendor a 3-byte code, called the Organizationally Unique Identifier (OUI).


IEEE requires a vendor to follow two simple rules:
• All MAC addresses assigned to a NIC or other Ethernet device must use that vendor's assigned OUI as the first 3 bytes.
• All MAC addresses with the same OUI must be assigned a unique value (vendor code or serial number) in the last 3 bytes.

The MAC address is often referred to as a burned-in address (BIA) because it is burned into ROM (Read-Only Memory) on the NIC. This means that the address is encoded into the ROM chip permanently - it cannot be changed by software.

However, when the computer starts up, the NIC copies the address into RAM. When examining frames, it is the address in RAM that is used as the source address to compare with the destination address. The MAC address is used by the NIC to determine if a message should be passed to the upper layers for processing.


Hexadecimal Numbering and Addressing

Hexadecimal ("Hex") is a convenient way to represent binary values. Just as decimal is a base ten numbering system and binary is base two, hexadecimal is a base sixteen system.

The base 16 numbering system uses the numbers 0 to 9 and the letters A to F. The figure shows the equivalent decimal, binary, and hexadecimal values for binary 0000 to 1111. It is easier for us to express a value as a single hexadecimal digit than as four bits.



Understanding Bytes

Given that 8 bits (a byte) is a common binary grouping, binary 00000000 to 11111111 can be represented in hexadecimal as the range 00 to FF. Leading zeroes are always displayed to complete the 8-bit representation. For example, the binary value 0000 1010 is shown in hexadecimal as 0A.


Summary:

Ethernet is an effective and widely used TCP/IP Network Access protocol. Its common frame structure has been implemented across a range of media technologies, both copper and fiber, making the most common LAN protocol in use today.

As an implementation of the IEEE 802.2/3 standards, the Ethernet frame provides MAC addressing and error checking. Being a shared media technology, early Ethernet had to apply a CSMA/CD mechanism to manage the use of the media by multiple devices. Replacing hubs with switches in the local network has reduced the probability of frame collisions in half-duplex links. Current and future versions, however, inherently operate as full-duplex communications links and do not need to manage media contention to the same detail.

OSI Physical Layer

Upper OSI layer protocols prepare data from the human network for transmission to its destination. The Physical layer controls how data is transmitted on the communication media.

The role of the OSI Physical layer is to encode the binary digits that represent Data Link layer frames into signals and to transmit and receive these signals across the physical media - copper wires, optical fiber, and wireless - that connect network devices.

The delivery of frames across the local media requires the following Physical layer elements:
• The physical media and associated connectors
• A representation of bits on the media
• Encoding of data and control information
• Transmitter and receiver circuitry on the network devices



At this stage of the communication process, the user data has been segmented by the Transport layer, placed into packets by the Network layer, and further encapsulated as frames by the Data Link layer. The purpose of the Physical layer is to create the electrical, optical, or microwave signal that represents the bits in each frame. These signals are then sent on the media one at a time.

There are three basic forms of network media on which data is represented:
• Copper cable
• Fiber
• Wireless



The representation of the bits - that is, the type of signal - depends on the type of media. For copper cable media, the signals are patterns of electrical pulses. For fiber, the signals are patterns of light. For wireless media, the signals are patterns of radio transmissions.

Different physical media support the transfer of bits at different speeds. Data transfer can be measured in three ways:
• Bandwidth
• Throughput
• Goodput

Bandwidth

The capacity of a medium to carry data is described as the raw data bandwidth of the media. Digital bandwidth measures the amount of information that can flow from one place to another in a given amount of time. Bandwidth is typically measured in kilobits per second (kbps) or megabits per second (Mbps).

Throughput

Throughput is the measure of the transfer of bits across the media over a given period of time. Due to a number of factors, throughput usually does not match the specified bandwidth in Physical layer implementations such as Ethernet.

Many factors influence throughput. Among these factors are the amount of traffic, the type of traffic, and the number of network devices encountered on the network being measured. In a multi-access topology such as Ethernet, nodes are competing for media access and its use. Therefore, the throughput of each node is degraded as usage of the media increases.

Goodput

A third measurement has been created to measure the transfer of usable data. Goodput is the measure of usable data transferred over a given period of time, and is therefore the measure that is of most interest to network users.



As shown in the figure, goodput measures the effective transfer of user data between Application layer entities, such as between a source web server process and a destination web browser device.

Unshielded Twisted Pair (UTP) Cable
Unshielded twisted-pair (UTP) cabling, as it is used in Ethernet LANs, consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.



As seen in the figure, the color codes identify the individual pairs and wires in the pairs and aid in cable termination.

The twisting has the effect of canceling unwanted signals. When two wires in an electrical circuit are placed close together, external electromagnetic fields create the same interference in each wire. The pairs are twisted to keep the wires in as close proximity as is physically possible. When this common interference is present on the wires in a twisted pair, the receiver processes it in equal yet opposite ways. As a result, the signals caused by electromagnetic interference from external sources are effectively cancelled.

This cancellation effect also helps avoid interference from internal sources called crosstalk. Crosstalk is the interference caused by the magnetic field around the adjacent pairs of wires in the cable. When electrical current flows through a wire, it creates a circular magnetic field around the wire.

UTP Cable Types
UTP cabling, terminated with RJ-45 connectors, is a common copper-based medium for interconnecting network devices, such as computers, with intermediate devices, such as routers and network switches.

Different situations may require UTP cables to be wired according to different wiring conventions. This means that the individual wires in the cable have to be connected in different orders to different sets of pins in the RJ-45 connectors. The following are main cable types that are obtained by using specific wiring conventions:
• Ethernet Straight-through
• Ethernet Crossover
• Rollover



Using a crossover or straight-through cable incorrectly between devices may not damage the devices, but connectivity and communication between the devices will not take place. This is a common error in the lab and checking that the device connections are correct should be the first troubleshooting action if connectivity is not achieved.


Fiber Media
Fiber-optic cabling uses either glass or plastic fibers to guide light impulses from source to destination. The bits are encoded on the fiber as light impulses. Optical fiber cabling is capable of very large raw data bandwidth rates. Most current transmission standards have yet to approach the potential bandwidth of this media.

Optical fiber media implementation issues include:
• More expensive (usually) than copper media over the same distance (but for a higher capacity)
• Different skills and equipment required to terminate and splice the cable infrastructure
• More careful handling than copper media

At present, in most enterprise environments, optical fiber is primarily used as backbone cabling for high-traffic point-to-point connections between data distribution facilities and for the interconnection of buildings in multi-building campuses. Because optical fiber does not conduct electricity and has low signal loss, it is well suited for these uses.


Single-mode and Multimode Fiber
Fiber optic cables can be broadly classified into two types: single-mode and multimode.



Single-mode optical fiber carries a single ray of light, usually emitted from a laser. Because the laser light is uni-directional and travels down the center of the fiber, this type of fiber can transmit optical pulses for very long distances.

Multimode fiber typically uses LED emitters that do not create a single coherent light wave. Instead, light from an LED enters the multimode fiber at different angles. Because light entering the fiber at different angles takes different amounts of time to travel down the fiber, long fiber runs may result in the pulses becoming blurred on reception at the receiving end.

It is recommended that an Optical Time Domain Reflectometer (OTDR) be used to test each fiber-optic cable segment. This device injects a test pulse of light into the cable and measures back scatter and reflection of light detected as a function of time. The OTDR will calculate the approximate distance at which these faults are detected along the length of the cable.

A field test can be performed by shining a bright flashlight into one end of the fiber while observing the other end of the fiber. If light is visible, then the fiber is capable of passing light. Although this does not ensure the performance of the fiber, it is a quick and inexpensive way to find a broken fiber.


Wireless Media
Wireless media carry electromagnetic signals at radio and microwave frequencies that represent the binary digits of data communications. As a networking medium, wireless is not restricted to conductors or pathways, as are copper and fiber media.



Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage. In addition, wireless is susceptible to interference and can be disrupted by such common devices as household cordless phones, some types of fluorescent lights, microwave ovens, and other wireless communications.

The Wireless LAN
A common wireless data implementation is enabling devices to wirelessly connect via a LAN. In general, a wireless LAN requires the following network devices:

• Wireless Access Point (AP) - Concentrates the wireless signals from users and connects, usually through a copper cable, to the existing copper-based network infrastructure such as Ethernet.
• Wireless NIC adapters - Provides wireless communication capability to each network host.

As the technology has developed, a number of WLAN Ethernet-based standards have emerged. Care needs to be taken in purchasing wireless devices to ensure compatibility and interoperability.

Standards include:

IEEE 802.11a - Operates in the 5 GHz frequency band and offers speeds of up to 54 Mbps. Because this standard operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures. Devices operating under this standard are not interoperable with the 802.11b and 802.11g standards described below.

IEEE 802.11b - Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mbps. Devices implementing this standard have a longer range and are better able to penetrate building structures than devices based on 802.11a.

IEEE 802.11g - Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps. Devices implementing this standard therefore operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a.

IEEE 802.11n - The IEEE 802.11n standard is currently in draft form. The proposed standard defines frequency of 2.4 Ghz or 5 GHz. The typical expected data rates are 100 Mbps to 210 Mbps with a distance range of up to 70 meters.

The benefits of wireless data communications technologies are evident, especially the savings on costly premises wiring and the convenience of host mobility. However, network administrators need to develop and apply stringent security policies and processes to protect wireless LANs from unauthorized access and damage.

Data Link Layer

To support our communication, the OSI model divides the functions of a data network into layers.

To recap:
• The Application layer provides the interface to the user.
• The Transport layer is responsible for dividing and managing communications between the processes running in the two end systems.
• The Network layer protocols organize our communication data so that it can travel across internetworks from the originating host to a destination host.

For Network layer packets to be transported from source host to destination host, they must traverse different physical networks. These physical networks can consist of different types of physical media such as copper wires, microwaves, optical fibers, and satellite links. Network layer packets do not have a way to directly access these different media.

It is the role of the OSI Data Link layer to prepare Network layer packets for transmission and to control access to the physical media.

The Data Link layer performs two basic services:
• Allows the upper layers to access the media using techniques such as framing
• Controls how data is placed onto the media and is received from the media using techniques such as media access control and error detection

As with each of the OSI layers, there are terms specific to this layer:



Frame - The Data Link layer PDU
Node - The Layer 2 notation for network devices connected to a common medium
Media/medium (physical)* - The physical means for the transfer of information between two nodes
Network (physical)** - Two or more nodes connected to a common medium
The Data Link layer is responsible for the exchange of frames between nodes over the media of a physical network.

The Data Link layer exists as a connecting layer between the software processes of the layers above it and the Physical layer below it. As such, it prepares the Network layer packets for transmission across some form of media, be it copper, fiber, or the atmosphere.



In many cases, the Data Link layer is embodied as a physical entity, such as an Ethernet network interface card (NIC), which inserts into the system bus of a computer and makes the connection between running software processes on the computer and physical media. The NIC is not solely a physical entity, however. Software associated with the NIC enables the NIC to perform its intermediary functions of preparing data for transmission and encoding the data as signals to be sent on the associated media.


The two common LAN sublayers are:

Logical Link Control
Logical Link Control (LLC) places information in the frame that identifies which Network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IP and IPX, to utilize the same network interface and media.

Media Access Control
Media Access Control (MAC) provides Data Link layer addressing and delimiting of data according to the physical signaling requirements of the medium and the type of Data Link layer protocol in use.


Some network topologies share a common medium with multiple nodes. At any one time, there may be a number of devices attempting to send and receive data using the network media. There are rules that govern how these devices share the media.

Contention-based Access for Shared Media
Also referred to as non-deterministic, contention-based methods allow any device to try to access the medium whenever it has data to send. To prevent complete chaos on the media, these methods use a Carrier Sense Multiple Access (CSMA) process to first detect if the media is carrying a signal. If a carrier signal on the media from another node is detected, it means that another device is transmitting. When the device attempting to transmit sees that the media is busy, it will wait and try again after a short time period. If no carrier signal is detected, the device transmits its data.

CSMA is usually implemented in conjunction with a method for resolving the media contention. The two commonly used methods are:

CSMA/Collision Detection
In CSMA/Collision Detection (CSMA/CD), the device monitors the media for the presence of a data signal. If a data signal is absent, indicating that the media is free, the device transmits the data. If signals are then detected that show another device was transmitting at the same time, all devices stop sending and try again later. Traditional forms of Ethernet use this method.

CSMA/Collision Avoidance
In CSMA/Collision Avoidance (CSMA/CA), the device examines the media for the presence of a data signal. If the media is free, the device sends a notification across the media of its intent to use it. The device then sends the data. This method is used by 802.11 wireless networking technologies.


Full Duplex and Half Duplex
In point-to-point connections, the Data Link layer has to consider whether the communication is half-duplex or full-duplex.

Half-duplex communication means that the devices can both transmit and receive on the media but cannot do so simultaneously. Ethernet has established arbitration rules for resolving conflicts arising from instances when more than one station attempts to transmit at the same time.

In full-duplex communication, 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. Therefore, there is no media arbitration necessary in the Data Link layer.


The topology of a network is the arrangement or relationship of the network devices and the interconnections between them. Network topologies can be viewed at the physical level and the logical level.

The physical topology is an arrangement of the nodes and the physical connections between them. The representation of how the media is used to interconnect the devices is the physical topology.

A logical topology is the way a network transfers frames from one node to the next. This arrangement consists of virtual connections between the nodes of a network independent of their physical layout. These logical signal paths are defined by Data Link layer protocols. The Data Link layer "sees" 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.

Logical and physical topologies typically used in networks are:
• Point-to-Point
• Multi-Access
• Ring



A point-to-point topology connects two nodes directly together. In data networks with point-to-point topologies, the media access control protocol can be very simple. All frames on the media can only travel to or from the two nodes. The frames are placed on the media by the node at one end and taken off the media by the node at the other end of the point-to-point circuit.

A logical multi-access topology enables a number of nodes to communicate by using the same shared media. Data from only one node can be placed on the medium at any one time. Every node sees all the frames that are on the medium, but only the node to which the frame is addressed processes the contents of the frame.

In a logical ring topology, each node in turn receives a frame. If the frame is not addressed to the node, the node passes the frame to the next node. This allows a ring to use a controlled media access control technique called token passing.


Data Link Layer Protocols – The Frames

Remember that although there are many different Data Link layer protocols that describe Data Link layer frames, each frame type has three basic parts:
• Header
• Data
• Trailer

All Data Link layer protocols encapsulate the Layer 3 PDU within the data field of the frame. However, the structure of the frame and the fields contained in the header and trailer vary according to the protocol.

The Data Link layer protocol describes the features required for the transport of packets across different media. These features of the protocol are integrated into the encapsulation of the frame. When the frame arrives at its destination and the Data Link protocol takes the frame off the media, the framing information is read and discarded.

Addressing the Network

Addressing is a key function of Network layer protocols that enables data communication between hosts on the same network or on different networks. Internet Protocol version 4 (IPv4) provides hierarchical addressing for packets that carry our data.

Designing, implementing and managing an effective IPv4 addressing plan ensures that our networks can operate effectively and efficiently.

These addresses are used in the data network as binary patterns. Inside the devices, digital logic is applied for their interpretation. For us in the human network, a string of 32 bits is difficult to interpret and even more difficult to remember. Therefore, we represent IPv4 addresses using dotted decimal format.

If you want to know how to convert between 8-bit binary and decimal numbers, go to counting binary.

Within the address range of each IPv4 network, we have three types of addresses:

Network address - The address by which we refer to the network
Broadcast address - A special address used to send data to all hosts in the network
Host addresses - The addresses assigned to the end devices in the network

Network Address:
The network address is a standard way to refer to a network. Within the IPv4 address range of a network, the lowest address is reserved for the network address. This address has a 0 for each host bit in the host portion of the address.

Sample:
10.0.0.0
172.16.0.0
192.168.1.0

Broadcast Address:
The IPv4 broadcast address is a special address for each network that allows communication to all the hosts in that network. To send data to all hosts in a network, a host can send a single packet that is addressed to the broadcast address of the network.
The broadcast address uses the highest address in the network range. This is the address in which the bits in the host portion are all 1s.

Sample:
10.0.0.255
172.16.0.255
192.168.1.255

Host Address:
As described previously, every end device requires a unique address to deliver a packet to that host. In IPv4 addresses, we assign the values between the network address and the broadcast address to the devices in that network.

Sample:
10.0.0.1 to 10.0.0.254
172.16.0.1 to 172.16.0.254
192.168.1.1 to 192.168.1.254

Network Prefixes
The prefix length is the number of bits in the address that gives us the network portion. For example, in 172.16.4.0 /24, the /24 is the prefix length - it tells us that the first 24 bits are the network address. This leaves the remaining 8 bits, the last octet, as the host portion.
Networks are not always assigned a /24 prefix. Depending on the number of hosts on the network, the prefix assigned may be different. Having a different prefix number changes the host range and broadcast address for each network.

Notice that the network address could remain the same, but the host range and the broadcast address are different for the different prefix lengths. In this figure you can also see that the number of hosts that can be addressed on the network changes as well.

See the figure for an example of the address assignment for the 172.16.20.0 /25 network.



In the first box, we see the representation of the network address. With a 25 bit prefix, the last 7 bits are host bits. To represent the network address, all of these host bits are '0'. This makes the last octet of the address 0. This makes the network address 172.16.20.0 /25.

In the second box, we see the calculation of the lowest host address. This is always one greater than the network address. In this case, the last of the seven host bits becomes a '1'. With the lowest bit of host address set to a 1, the lowest host address is 172.16.20.1.

The third box shows the calculation of the broadcast address of the network. Therefore, all seven host bits used in this network are all '1s'. From the calculation, we get 127 in the last octet. This gives us a broadcast address of 172.16.20.127.

The fourth box presents the calculation of the highest host address. The highest host address for a network is always one less than the broadcast. This means the lowest host bit is a '0' and all other host bits as '1s'. As seen, this makes the highest host address in this network 172.16.20.126.

In an IPv4 network, the hosts can communicate one of three different ways:

Unicast - the process of sending a packet from one host to an individual host. It is used for the normal host-to-host communication in both a client/server and a peer-to-peer network.

Broadcast - the process of sending a packet from one host to all hosts in the network. It is used for the location of special services/devices for which the address is not known or when a host needs to provide information to all the hosts on the network.

Some examples for using broadcast transmission are:
• Mapping upper layer addresses to lower layer addresses
• Requesting an address
• Exchanging routing information by routing protocols

Multicast - the process of sending a packet from one host to a selected group of hosts. It reduces traffic by allowing a host to send a single packet to a selected set of hosts.
Some examples of multicast transmission are:
• Video and audio distribution
• Routing information exchange by routing protocols
• Distribution of software
• News feeds

Private Addresses
A networks that are accessible on the Internet, there are blocks of addresses that are used in networks that require limited or no Internet access.
The private address blocks are:
• 10.0.0.0 to 10.255.255.255 (10.0.0.0 /8)
• 172.16.0.0 to 172.31.255.255 (172.16.0.0 /12)
• 192.168.0.0 to 192.168.255.255 (192.168.0.0 /16)

Network Address Translation (NAT)
With services to translate private addresses to public addresses, hosts on a privately addressed network can have access to resources across the Internet.

NAT allows the hosts in the network to "borrow" a public address for communicating to outside networks. While there are some limitations and performance issues with NAT, clients for most applications can access services over the Internet without noticeable problems.

Public Addresses
The vast majority of the addresses in the IPv4 unicast host range are public addresses. These addresses are designed to be used in the hosts that are publicly accessible from the Internet. Even within these address blocks, there are many addresses that are designated for other special purposes.

Assigning Addresses within a Network
As you have already learned, hosts are associated with an IPv4 network by a common network portion of the address. Within a network, there are different types of hosts.

Some examples of different types of hosts are:
• End devices for users
• Servers and peripherals
• Hosts that are accessible from the Internet
• Intermediary devices

Each of these different device types should be allocated to a logical block of addresses within the address range of the network.

Addresses for Servers and Peripherals
Any network resource such as a server or a printer should have a static IPv4 address, as shown in the figure. The client hosts access these resources using the IPv4 addresses of these devices. Therefore, predictable addresses for each of these servers and peripherals are necessary.

Addresses for Hosts that are Accessible from Internet
In most internetworks, only a few devices are accessible by hosts outside of the corporation. For the most part, these devices are usually servers of some type. As with all devices in a network that provide network resources, the IPv4 addresses for these devices should be static.

Addresses for Intermediary Devices
Most intermediary devices are assigned Layer 3 addresses. Either for the device management or for their operation. Devices such as hubs, switches, and wireless access points do not require IPv4 addresses to operate as intermediary devices. However, if we need to access these devices as hosts to configure, monitor, or troubleshoot network operation, they need to have addresses assigned.

Routers and Firewalls
Unlike the other intermediary devices mentioned, routers and firewall devices have an IPv4 address assigned to each interface. Each interface is in a different network and serves as the gateway for the hosts in that network. Typically, the router interface uses either the lowest or highest address in the network. This assignment should be uniform across all networks in the corporation so that network personnel will always know the gateway of the network no matter which network they are working on.


Defining the network and host portions
To define the network and host portions of an address, the devices use a separate 32-bit pattern called a subnet mask, as shown in the figure. We express the subnet mask in the same dotted decimal format as the IPv4 address. The subnet mask is created by placing a binary 1 in each bit position that represents the network portion and placing a binary 0 in each bit position that represents the host portion.

The prefix and the subnet mask are different ways of representing the same thing - the network portion of an address.

a /24 prefix is expressed as a subnet mask as 255.255.255.0 (11111111.11111111.11111111.00000000). The remaining bits (low order) of the subnet mask are zeroes, indicating the host address within the network.

The subnet mask is configured on a host in conjunction with the IPv4 address to define the network portion of that address.

For example, let's look at the host 172.16.20.35/27:

Address
172.16.20.35
10101100.00010000.00010100.00100011

subnet mask
255.255.255.224
11111111.11111111.11111111.11100000

network address
172.16.20.32
10101100.00010000.00010100.00100000

Because the high order bits of the subnet masks are contiguous 1s, there are only a limited number of subnet values within an octet. You will recall that we only need to expand an octet if the network and host division falls within that octet. Therefore, there are a limited number 8 bit patterns used in address masks.

The AND Operation
ANDing is one of three basic binary operations used in digital logic. The other two are OR and NOT. While all three are used in data networks, AND is used in determining the network address. Therefore, our discussion here will be limited to logical AND. Logical AND is the comparison of two bits that yields the following results:
1 AND 1 = 1
1 AND 0 = 0
0 AND 1 = 0
0 AND 0 = 0

An example of AND operation:

OSI Network Layer

We have seen how network applications and services on one end device can communicate with applications and services running on another end device.

Next, as shown in the figure, we will consider how this data is communicated across the network - from the originating end device (or host) to the destination host - in an efficient way.

The protocols of the OSI model Network layer specify addressing and processes that enable Transport layer data to be packaged and transported. The Network layer encapsulation allows its contents to be passed to the destination within a network or on another network with minimum overhead.

The Network layer - provides services to exchange the individual pieces of data over the network between identified end devices.

To accomplish this end-to-end transport, Layer 3 uses four basic processes:
• Addressing
• Encapsulation
• Routing
• Decapsulation

Addressing – the network layer must provide a mechanism for addressing these end devices. If individual pieces of data are to be directed to an end device, that device must have a unique address.

Encapsulation - Not only must the devices be identified with an address, the individual pieces - the Network layer PDUs - must also contain these addresses. During the encapsulation process, Layer 3 receives the Layer 4 PDU and adds a Layer 3 header, or label, to create the Layer 3 PDU. When referring to the Network layer, we call this PDU a packet.

Routing - the network layer must provide services to direct these packets to their destination host. Along the way, each packet must be guided through the network to reach its final destination. Intermediary devices that connect the networks are called routers. The role of the router is to select paths for and direct packets toward their destination. This process is known as routing.
During the routing through an internetwork, the packet may traverse many intermediary devices. Each route that a packet takes to reach the next device is called a hop.

Decapsulation - the packet arrives at the destination host and is processed at Layer 3. The host examines the destination address to verify that the packet was addressed to this device. If the address is correct, the packet is decapsulated by the Network layer and the Layer 4 PDU contained in the packet is passed up to the appropriate service at Transport layer.

The Internet Protocol (IPv4 and IPv6) is the most widely-used Layer 3 data carrying protocol.

IPv4 basic characteristics:
• Connectionless - No connection is established before sending data packets.
• Best Effort (unreliable) - No overhead is used to guarantee packet delivery.
• Media Independent - Operates independently of the medium carrying the data.

Dividing Networks:
Rather than having all hosts everywhere connected to one vast global network, it is more practical and manageable to group hosts into specific networks.

Networks can be grouped based on factors that include:
• Geographic location
• Purpose
• Ownership

Grouping Host Geographically:
We can group network hosts together geographically. Grouping hosts at the same location - such as each building on a campus or each floor of a multi-level building - into separate networks can improve network management and operation.

Grouping Hosts for specific Purposes:
Users who have similar tasks typically use common software, common tools, and have common traffic patterns. We can often reduce the traffic required by the use of specific software and tools by placing the resources to support them in the network with the users.



Grouping Hosts for Ownership:
Using an organizational (company, department) basis for creating networks assists in controlling access to the devices and data as well as the administration of the networks. In one large network, it is much more difficult to define and limit the responsibility for the network personnel. Dividing hosts into separate networks provides a boundary for security enforcement and management of each network.



Common issues with large networks are:
• Performance degradation
• Security issues
• Address Management

Large numbers of hosts connected to a single network can produce volumes of data traffic that may stretch, if not overwhelm, network resources such as bandwidth and routing capability.

Dividing large networks so that hosts who need to communicate are grouped together reduces the traffic across the internetworks.



To be able to divide networks, we need hierarchical addressing.

Hierarchical Address - uniquely identifies each host. It also has levels that assist in forwarding packets across internetworks, which enables a network to be divided based on those levels.

The logical 32-bit IPv4 address is hierarchical and is made up of two parts. The first part identifies the network and the second part identifies a host on that network. Both parts are required for a complete IP address.



This is hierarchical addressing because the network portion indicates the network on which each unique host address is located. Routers only need to know how to reach each network, rather than needing to know the location of each individual host.

Fundamental of routes:
The routing table stores information about connected and remote networks. Connected networks are directly attached to one of the router interfaces. These interfaces are the gateways for the hosts on different local networks. Remote networks are networks that are not directly connected to the router. Routes to these networks can be manually configured on the router by the network administrator or learned automatically using dynamic routing protocols.

Routes in a routing table have three main features:
• Destination network
• Next-hop
• Metric

The router matches the destination address in the packet header with the destination network of a route in the routing table and forwards the packet to the next-hop router specified by that route. If there are two or more possible routes to the same destination, the metric is used to decide which route appears on the routing table.



As shown in the figure, the routing table in a Cisco router can be examined with the show ip route command.

As you know, packets cannot be forwarded by the router without a route. If a route representing the destination network is not on the routing table, the packet will be dropped (that is, not forwarded). The matching route could be either a connected route or a route to a remote network.

Routing is done packet-by-packet and hop-by-hop. Each packet is treated independently in each router along the path. At each hop, the router examines the destination IP address for each packet and then checks the routing table for forwarding information.

The router will do one of three things with the packet:
• Forward it to the next-hop router
• Forward it to the destination host
• Drop it

Static Routing – routing that depends on manually entered routes in the routing table. if the internetwork structure changes or if new networks become available, these changes have to be manually updated on every router. If updating is not done in a timely fashion, the routing information may be incomplete or inaccurate, resulting in packet delays and possible packet loss.

Dynamic Routing - Routing protocols are the set of rules by which routers dynamically share their routing information. When a router receives information about new or changed routes, it updates its own routing table and, in turn, passes the information to other routers. In this way, all routers have accurate routing tables that are updated dynamically and can learn about routes to remote networks that are many hops way.

Dynamic routing protocols are:
• Routing Information Protocol (RIP)
• Enhanced Interior Gateway Routing Protocol (EIGRP)
• Open Shortest Path First (OSPF)

OSI Transport Layer

Data networks and the Internet support the human network by supplying seamless, reliable communication between people - both locally and around the globe. On a single device, people can use multiple services such as e-mail, the web, and instant messaging to send messages or retrieve information. Applications such as e-mail clients, web browsers, and instant messaging clients allow people to use computers and networks to send messages and find information.

Data from each of these applications is packaged, transported, and delivered to the appropriate server daemon or application on the destination device. The processes described in the OSI Transport layer accept data from the Application layer and prepare it for addressing at the Network layer. The Transport layer is responsible for the overall end-to-end transfer of application data.

Transport Layer – segment the data and manages the separation of data for different application. Multiple applications running on device receive the correct data.
Some protocols at the transport layer provide:
•Connection-oriented conversations
•Reliable delivery
•Ordered data reconstruction
•Flow control



Congestion – the state of a network when there is not sufficient bandwidth to support the amount of network traffic.

UDP – (user datagram protocol) a simple, connectionless protocol, described in RFC 768. It has the advantage of providing for low overhead data delivery. The pieces of communication in UDP are called datagrams.

Applications that use UDP include:
•Domain Name System (DNS)
•Video Streaming
•Voice over IP (VoIP)

TCP – (transmission control protocol) a connection-oriented protocol, described in RFC 793. TCP incurs additional overhead to gain functions. Additional functions specified by TCP are the same order delivery, reliable delivery, and flow control.

Applications that use TCP are:
•Web Browsers
•E-mail
•File Transfers

IANA – (Internet Assigned Numbers Authority) assigned port numbers. A standard body that is responsible for assigning various addressing standards.

There are different types of port numbers:
Well Known Ports (Numbers 0 to 1023) - These numbers are reserved for services and applications. They are commonly used for applications such as HTTP (web server) POP3/SMTP (e-mail server) and Telnet.

Registered Ports (Numbers 1024 to 49151) - These port numbers are assigned to user processes or applications. These processes are primarily individual applications that a user has chosen to install rather than common applications that would receive a Well Known Port.

Dynamic or Private Ports (Numbers 49152 to 65535) - Also known as Ephemeral Ports, these are usually assigned dynamically to client applications when initiating a connection. It is not very common for a client to connect to a service using a Dynamic or Private Port (although some peer-to-peer file sharing programs do).

Netstat - an important network utility that can be used to verify connections. It list the protocol in use, the local address and port number, the foreign address and port number, and the state of the connection.

Three-way handshake – a process that establishes a TCP session between two endpoints. The process is as follows:
1.A client wishes to communicate with a server.
2.In response, the server responds with a SYN-ACK.
3.The client then sends an ACK (usually called SYN-ACK-ACK) back to the other end and the session is established.



Within the TCP segment header, there are six 1-bit fields that contain control information used to manage the TCP processes. Those fields are:
URG - Urgent pointer field significant
ACK - Acknowledgement field significant
PSH - Push function
RST - Reset the connection
SYN - Synchronize sequence numbers
FIN - No more data from sender

These fields are referred to as flags, because the value of one of these fields is only 1 bit and, therefore, has only two values: 1 or 0. When a bit value is set to 1, it indicates what control information is contained in the segment.

Window size – to determine the number of segments sent by the sending device before the receiving device sends a confirmation. It is a field in the TCP header that enables the management of lost data and flow control.



Flow control – assists the reliability of TCP transmission by adjusting the effective rate of data flow between the two services in the session. When the source is informed that the specified amount of data in the segments is received, it can continue sending more data for this session.

Application Layer Functionality and Protocols

Most of us experience the Internet through the World Wide Web, e-mail services, and file-sharing programs. These applications, and many others, provide the human interface to the underlying network, enabling us to send and receive information with relative ease. Typically the applications that we use are intuitive, meaning we can access and use them without knowing how they work. However, for network professionals, it is important to know how an application is able to format, transmit and interpret messages that are sent and received across the network.


OSI – (Open System Interconnection) international standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multivendor equipment interoperability. It divides the networking process into seven logical layers, each of which has unique functionality.

Application Layer – uses protocols that are implemented within applications and services. It provides the interface between the applications on either end of the network.

Presentation Layer – ensure that data from the source device can be interpreted by the appropriate application on the destination device.

Session Layer – create and maintain dialogs between source and destination applications. It handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time.

DNS – (Domain Name Service) is used to resolve internet names to IP addresses. It matches resource names with the required IP address.

HTTP – (Hypertext Transfer Protocol) is used to transfer files that make up the web pages of the World Wide Web. It transfer data from a web server to a client.

SMTP – (Simple Mail Transfer Protocol) is used for the transfer of mail messages and attachments.

Telnet – is used to provide remote access to servers and networking devices. But it does not support encryption.

FTP – (File Transfer Protocol) is commonly used to support for file transfer between a client and a server.

Client-server model – the device requesting the information is called a client and the device responding to the request is called a server.
• centralized administration
• security is easier to enforce

Peer-to-peer – two or more computers are connected via a network and can share resources (such as printers and files) without having a dedicated server.
• Act as both a client and server within the same communication.
• Hybrid mode includes a centralized directory of files.
• Can be used in client-server networks



Nslookup – a utility of a computer operating systems that allows the user to manually query the name servers to resolve a given host name. This utility can also be used to troubleshoot name resolution issues and to verify the current status of the name servers.



MTU – (Mail User Agent) allow messages to be sent and places received messages into the clients mailbox, both of which are distinct processes. In order to receive e-mail messages from an email server, the email client can use POP. Sending e-mail from either a client or a server uses message formats and command strings defined by the SMTP protocol. Usually an e-mail client provides the functionality of both protocols within one application.




Protocols operate at application layer of the OSI model:
• DNS
• SMTP
• POP

The e-mail server operates two separate processes:
• Mail Transfer Agent (MTA)
• Mail Delivery Agent (MDA)
The Mail Transfer Agent (MTA) process is used to forward e-mail. As shown in the figure, the MTA receives messages from the MUA or from another MTA on another e-mail server. Based on the message header, it determines how a message has to be forwarded to reach its destination. If the mail is addressed to a user whose mailbox is on the local server, the mail is passed to the MDA. If the mail is for a user not on the local server, the MTA routes the e-mail to the MTA on the appropriate server.

DHCP – (Dynamic Host Configuration Protocol) enables devices on a network to obtain IP addresses and other information from a DHCP server. This service automates the assignment of IP addresses, subnet masks, gateway and other IP networking parameters.

SMB – (Server Message Block) is a client/server file sharing protocol. It describe the structure of shared network resources, such as directories, files, printers and serial ports. SMB file-sharing and print services have become the mainstay of Microsoft networking.

Communicating over the Network

More and more, it is networks that connect us. People communicate online from everywhere. Efficient, dependable technology enables networks to be available whenever and wherever we need them. As our human network continues to expand, the platform that connects and supports it must also grow.

Rather than developing unique and separate systems for the delivery of each new service, the network industry as a whole has developed the means to both analyze the existing platform and enhance it incrementally. This ensures that existing communications are maintained while new services are introduced that are both cost effective and technologically sound.

Channel – consist of the media the provides the pathway over which the massage can travel from source to destination.

Multiplexing – the process used to interleave the pieces of separate conversation together on the network.

Two types of Network Devices:

End device – the network devices that people are most familiar. Examples are computers, printer, voip phones, security camera, mobile handheld.

Intermediary devices – provide connectivity and to work behind the scenes to ensure that data flows across the network. The management of data as it flows through the network is also a role of the intermediary devices.

Examples of intermediary network devices are:
• Network access devices (hubs, switches, and wireless access points)
• Internetworking devices (routers)
• Communication servers and modems
• Security Devices (firewalls)

LAN – an individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure.

WAN – use specifically designed network devices to make the interconnections between LANS. It allow many forms of communication including exchange emails, corporate training, and other resource sharing.

Internetwork – a global mesh of interconnected networks meets these human communication needs. A connection of two or more data networks forms an internetwork.

Intranet – is often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization’s members.

Protocol suite – a group of inter-related protocols that are necessary to perform a communication function. It determines the formatting of messages and the process of encapsulation used to forward data.

IEEE – (Institute of Electrical and Electronics Engineers) a protocol that has been endorsed by the networking industry and ratified by a standards organization. The use of standards in developing and implementing protocols ensures that products from different manufacturers can work together for efficient communications.

Encapsulation – the wrapping of data in a particular protocol header. During the encapsulation process the data is formatted and separated into segments then the server adds the source and destination IP address to each segment header to deliver packets to the destination.

PDU – (Protocol Data Unit) the form that a piece of data takes at any layer.

------------------
TCP/IP Model
------------------
Application – represents data to the user plus encoding and dialog control.

Transport – supports communication between diverse devices across diverse networks.

Internet – determines the best path through the network

Network Access – controls the hardware devices and media that make up the network.

----------------
OSI Model
----------------

Application – provides the end-to-end connectivity between individuals in the human network using data networks.

Presentation – provides for common representation of the data transferred between applications layer services.

Session – provides services to the presentation layer to organize its dialogue and to manage data exchange.

Transport – defines services to segment, transfer, and reassemble the data for individual communications between the end devices.
• Called as Layer 4: port (software). TCP and UDP protocols are associated
• Encapsulate segments

Network – provides services to exchange the individual pieces of data over the network between identified end devices.
• Also called as Layer 3: IP address and logical address
• Encapsulate packets

Data Link – describe methods for exchanging data frames between devices over a common media.
• Also called as Layer 2: MAC and physical address
• Encapsulate frames

Physical – describe the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical-connections for bit transmission to and from a network device.
• Encapsulate bits