Cabling WAN - Part II

Physical Layer Implementations in WAN

Most physical implementation transmits data or traffic across WAN (wide Area Network). The requirement for physical implementation depends on distance of the equipment from the speed and the services itself. The selection of type of physical layer depends on distance. Speed and type of interface required to connect.

Figure below shows the lists of subset of the physical implementation which support most commonly used WAN solutions.

WAN Physical Layer Implementations

 Serial connections are used to support wireless serial such as dedicated leased lines that run point-to-point protocol (PPP), High-Level Data Link control (HDLC) or Frame Relay. The speed of the connection varies from 56kbps to T1/E1 (1.544/2.048 Mbps).ISDN (Integrated Services Digital Network) offer dial-on-demand connections or dial backup services. ISDN BRI (Basic Rate Interface) is made up of two 64kbps Bearer channel (B channel)for data and one 16kbs Delta channel (D channel) for signaling and other link management tasks. Point-to-point protocol is transmit data over B channel.

Difference between WAN serial connections

Long distance communication in WAN is performed using serial transmission. Serial transmission is a process in which bits are sent over single channel. Unlike parallel data transmitted at a time, serial transmission is one-at-a time transmission. This provides more reliably long distance communication. Serial channels employ electromagnetic or optical frequency range to carry bits.

The Frequency defined in terms of cycles per second (Hertz), function as band or spectrum required for communication. For example: the frequency of signals send over voice grade telephone lines is 3 kHz. The size of the frequency is also known as bandwidth.

Various types of physical connection enable to connect to serial WAN services. Depending on the selection of physical implementation given by the service provider, the type of serial cable to be used with router has to be selected.

Figure shows different type of serial connector

WAN Serial Connections Types

For Cisco router, physical connectivity at the customer site is provided by one of the two types of serial connectors. The first type of serial connection is 60-pin connector which is commonly used by Cisco routers. This indicates that the router end of most adapter cable use male 60-pin connector, so the network ends of the adapter cables has to match with particular WAN service hardware.



Bandwidth can also be expressed as bits per second (bps)which indicate the quantity of data in bits transmitted by using two physical layer implementation (EIA/TIA-232 and EIA/TIA-449). Table below shows the physical standards for WAN serial connections.

Cabling Routers for serial connections

In addition to determining cable type, one more factor which is very much essential is to determine whether the device is Data-terminal Equipment (DTE) or Data Circuit-terminating Equipment (DTE) device. These are the two types of devices that can communicate over serial interface. DCE provides physical connection to the network and forwards the data to the service provider.

If the connection is made directly to a service provider or a device that provides signal clocking such as channel or data service unit (CSU/DSU), the router will be data terminal equipment (DTE) and uses a DTE serial cable. Figure below shows DTE/DCE connections. In this example router which is DTE device is connected to CSU/DSU or modem, which are DCE devices. As the serial devices are DCE, DTE cable has to be used to connect router and CSU/DSU or modem.

DTE/DCE Connections

DTE/DCE Connections

In some cases router is required to provide the signal clocking, so it will use data communication equipment (DCE) signal cable. For example when performing back-to-back router scenario in a test environment, one router is DTE and other router is DCE.
When router has to be cabled in a serial connectivity, it may have fixed or modular ports. The type of ports either fixed or modular will have impact on the syntax which will be used to configure each interface.

Cisco 2500 Router

Figure shows an example of 2500 Router with fixed port. Each port is assigned with port type and port number for example “serial 0”. In order to configure fixed interface has to be specified using this convention.

Fixed serial ports on 2500 router

Routers with modular serial ports are also available. Typically, each port is assigned a label of port type, slot number and port number. In order to configure port on modular card, interfaces are specified using this convention:


<Port type><slot number>/<port number>. For example serial 1/0

Note: port designation convention changes with type of router used. For example: 7500 series router has virtual interface processor. The convention of this also include VIP slot

<Port type><slot number>/<port adapter number>/<port number> (serial 1/0/0)

Note: Using label of port type and port number such as serial 0, you can configure 1603 router (which both fixed and modular serial interface) as fixed interface.

Cabling Router for ISDN BRI connection

ISDN BRI standard defines several physical wiring interfaces, but the two common types of interfaces are BRI U-Interface and BRI S/T interface. U-Interface is the 2-wire interface provided by the service provider for connection to the NTI.U-Interface has built- in internal NT-1 devices. The S/T –interface is the 4-wire interface between NT1 and the ISDU networking equipment such as router. An S/ T interface is used when NT1 is a separate device. The type of interface required is determined depending on whether service provider will provide an NT1 device.NT1 refers to network termination type 1 device.

NTI is a simple  device that serves as an interface between router and ISDN equipment and it is used to connect four wire subscribes wiring to two-wire local loop.

Category 5 straight-through cables are required to interconnect ISDN BRI port to the service provider device

Note: cables from ISDN BRI port has to be properly inserted only to ISDN jack or switch. Because ISDN BRI uses high voltage and it may  effect non-ISDN devices



Setting up console  connection                       

To initially configure Cisco device, management connection has to be directly provided to a device. This management attachment is nothing but console port. Console port enables to configure Cisco hub, switch or router. The type of cable used to connect a console port and terminal is rollover or console cable with RJ-45 connector.

Figure below shows connecting device using console cable.

Steps to connect computer to console port:

Step 1: connect the device to the computer using console cable. RJ-45 to DB-9 or RJ-45 to DB-25 adapter may be required for computer or terminal.

Step 2: configure terminal emulation software for computer with above a default COM port settings: 9600bps, 8 data bits, no parity, 1 stop bit and no flow control.

Cabling WAN - Part I

The physical elements of router such as interfaces help to other terminals. In this lesson, you will learn the features of different types of physical interfaces such as console port, auxiliary port, Ethernet interface, serial port and modular interfaces. Ethernet interface is used to connect to Ethernet network and auxiliary ports are used to connect a modem to router. Modular interface allows to add new interface cards without a need to purchase a new router.

A connection between one networks to another some times make use of WAN services. These WAN services utilize various types of connection and cabling methods which is very much different from those of LAVs. So it is very important to understand the type of cabling required to connect to these services. In this lesson, you will learn the process of connecting Cisco devices to a terminal which enables to configure and monitor devices.

Physical Interfaces

A router has several physical interfaces which enables it to connect to different types of network media and terminals. The terms port and interfaces can be used interchangeably. Some of the physical interfaces normally found on Cisco router are listed below.

Console port

Console port is a point where you connect computer or terminal to router to access operating system. While connecting to the router console port is very much essential to configure other interfaces. ASCII terminal is the most commonly used computer running terminal emulation software for example Hyper Terminal in windows 98 can be connected to console port. Console port. Console port provides access to the command interpreter, so that it can be used to configure and maintain router.

Console cable is an asynchronous serial interface which uses RJ-45 connector and looks same phone jack but slightly larger. Adapters are also available which is required for connections to PC terminals, modems and other external communication equipment. RJ-45 crossover or console cable is required to connect computer or a laptop to router. Depending upon the size of the PC serial port, you rewire either RJ-45 to DB-9 female adapter or RJ-45 to DB-25 female adapter.

Cable pinout for: Cisco Console RJ45 to DB9 Pin

Use this cable to configure a Cisco router through the Console port at the router. 

This cable is also suitable to be used with Sun T2000. 

Console cable can be identified by comparing the modular ends of the cable. The wire connected to the pin on the outside of the left connector (pin 1) must have same color as the pin on the outside of the right connector (pin 8).  In Cisco cables, pin 1 is white on one connector and pin8 is white on the other connector.

Table shows the RJ-45 console cable pinouts

The default parameters for the console port are

• 9600 bits per second.
• 8 data bits
• No parity generated or checked.
• 1 stop bits

Auxiliary Port

Auxiliary (AUX) port is an asynchronous serial port which looks same as console port. Auxiliary port is used to connect modem to the router. The main difference between console port and auxiliary port provides hardware flow control enabling synchronized communication between sending and receiving device. When the buffer on receiving device gets full, it sends a message to the sending device asking to stop transmission speeds than terminal devices. Auxiliary port is suitable for high speed modem connection and the maximum speed is 38,400bps.

In order to connect auxiliary port to a modem, RJ-45 crossover cable is required. And RJ-45 to DB-25 male adaptor which is very compatible with the modems can be used.

Ethernet Interface

The Ethernet Interface is used to connect a router to a LAN and it is most common interface on a Cisco router. Ethernet interface uses RJ-45 connector or it may use 15-pin Attachment Unit Interface (AUI) connector Cisco routers are available with either 10 megabit or 100 megabit Ethernet interface. Cisco routers are also available in different configuration with either one or several Ethernet interface.

In some cases, you need to hook Ethernet interface to 10BaseT hub or switch. For this, you require AUI connector to 10BaseT transceiver.

Serial port

Serial port is an interface which is used to connect WAN links either a leased line or T1.Maximum speed at which the Cisco router’s serial port may operate is 115,200kbps. A router’s serial port is different from PC’s serial port. A router’s serial ports are synchronous which operate at higher speed than PC’s serial port.  PC’s serial ports are asynchronous. Serial port can be directly connected to Data communication Equipment for example Channel service Unit/Data Service Unit (CSU/DSU). A CSU/DSU which is required on both the ends of dedicated leased line is a high powered modem. The selection of cable type depends on DCE device. In lab environment, wide Area Network (WAN) can be simulated by directly connecting two serial ports using DCE/DTE cable.

Modular Interfaces

Most of the Cisco routers such as 3600 serial, 2600 serial have modular interface. Modular interface is an empty slot which enables to plug any other type interface. Serial and Ethernet interface can be added. Modular interface are available in various type such as Integrated Services Digital Network (ISDN), Frame Relay any voice interface cards. For T1 and ISDN lines, the modular interfaces have built-on CSU/DSUs and NT1s respectively which eliminates the need of additional router and line.

Note: The devices in synchronous communication synchronize by constantly transmitting bits over a wire or line. In synchronous communication, when there is data devices simply send idle characters to continue the synchronization. In asynchronous communication, a start bit and stop bit are added to each segment. For synchronous communication, both start and stop bits are eliminated, so faster transmission speed is achieved.

Cabling LAN - Part II

Crossover Cables & straight Through Cables

Ethernet cables can be wired in three different ways. The two main ways are straight through and Cross over. The third type is called as Rolled. Straight through cables are generally used to connect different types of equipment; for example, a computer  and a hub. Crossover cables are generally used to connect similar types of equipment like a computer to another computer. Inside the UTP cable there are 8 physical wires. The 8 wires are arranged in pairs: one pair is used to send information and other pair is used to receive information. For computers to communicate, the sending pair of one computer has to be connected to receiving pair of another computer. So crossover cables are required.

T568B Termination T568A Termination

RJ45 Jack

Straight-through Cable

The straight- through cable is used to connect:

• Host to switch or hub
• Router to switch or hub

Straight through Cable

Straight Through Cable

In the above figure you can see only 1,2,3 and 6 pins are used. Connect pin 1 to pin 1,2 to 2,3 to 3 and 6 to 6. Remember this would be an Ethernet cable and it will not work with voice, Token Ring, and ISDN.

Crossover cable

The Crossover cable be used to connect:

• Switch to switch
• Hub to hub
• Host to host
• Hub to switch
• Router direct to host

Same four wires are used in the cable as in the straight-through cable but different pins are connected together. In the  following figure, can see how four wires are used in crossover Ethernet cable. And notice that instead of connecting 1to1, 2to2 etc, pins 1 is connected 3, pin 2 is connected to 6 on each side of the cable.

Crossover cable pinouts

Two pairs crossed, two pairs uncrossed

Certain equipment or installations, including those in which phone and/or power are mixed with data in the same cable, may require that the "non-data" pairs 1 and 4 (pins 4, 5, 7 and 8) remain un-crossed.

T568A  - All Four Pairs Crossed

T568B  - All Four Pairs Crossed

Rolled cable

Roll Over or Console Cable

Rolled cables are not used to connect any Ethernet connections together, but rolled Ethernet cable can be used to connect a host to a router console serial communication port. Rolled cable is also used to connect PC running Hyper- Terminal to the Cisco hardware. Eight wires are used in rolled cable to connect serial devices, although not all eight are  used to send information just as in Ethernet networking. Figure below shows eight cables used in a rolled cable.

Cabling LAN - Part I

In a network, a machine has to be connected to at least other machine, through metal cabling, fiber-optic cabling or radio waves. Even new technologies such as radio based networks and infrared light based networks produce new ways of connecting two devices to each other, but least expensive and most popular medium for networking is still copper wires.

Cables use copper wires to transmit electrical signals or fiber optic to transfer optical light signals. Cabling is also called as wiring because copper wire is used in greater part in the network cables. Electrical signal, which is transmitted through cable, generate magnetic field and radio frequency interfaces. When cables are used, the electrical signal emits radiation, which may interfere with other signals. When this happens it is called as cross talk. In order to overcome this, metallic wires are manufactured in such a way that it reduces the effects of radiation and interference. The wires, which are close to one another, can interfere with the transmission, changing the electrical signal and can cause bit error. Because of interference, cables produce emission and are susceptible to nearby cables. The popular way to reduce these effects of emission is to send the information, through a pair of wires and to twist the pair of wires together, Using an opposite current on each wire generates magnetic field but in opposite

direction. So by twisting the wires, the two magnetic fields cancel each other. Another popular way to reduce emissions of copper cables is to shield the wires by some material which blocks electromagnetic radiation. Shielding the wires makes the cables less flexible and increases material and manufacturing costs. In this lesson, you will learn some of the cable type, its uses and features.

Cabling types

A wide range of cabling types has been used to connect Ethernet systems. Network uses three types of cables: coaxial, twisted and fiber optic cables. Twisted pair is similar to telephone cable. It consists of pairs of cables twisted around each other to reduce electrical interference. For high speed and high secure systems, Fiber optic cables are used. However, it is less commonly used, as the cable is expensive and more difficult to install.

1. Unshielded Twisted Pair (UTP) Cable
2. Shielded Twisted Pair (STP) Cable
3. Coaxial Cable
4. Fiber Optic Cable

Twisted Pair Cables:

Twisted pair cable is a type of cable, which consists of two independently insulated wires around one another. The use of twisted pairs helps to reduce crosstalk and electromagnetic induction. High quality twisted pair cables have 1to 3 twists per inch. Twisted pair cables is the ordinary copper wire which is used to connect most of the home and business computers to Telephone company. Each wire in twisted pair cables has color plastic insulation attached to it. Twisted-pair cables are lighter, thinner, more flexible and easier to install than coaxial and fiber-optic cabled. There are two types of twisted pairs: Unshielded twisted pair and shielded twisted pair.

Shielded Twisted pair (STP):
The twisted pair in STP are individually wrapped in a foil shield and enclosed in an outer braided wire shield. The shielding is designed to minimize electromagnetic radiation and susceptibility to crosstalk. Each pair is surrounded by insulating material, with another insulator covering all pairs together. The extra material makes the cable white bulky and cause lack of flexibility. Shielded twisted pair cables are commonly used on networks using Token Ring topology.

Unshielded Twisted Pair (UTP):
Unshielded Twisted pair cable is the most popular of all the cable types. UTP cables are used not only for networking but also for traditional telephone (UTP) cable consists of four pairs of wires inside the jacket. Each wire has some colored plastic insulation attached to it. As copper wire is smaller in diameter, it may break easily. So, a thin plastic insulation provides more strength to each individual wire. Each pair has different twists per inch, which helps to eliminate interference from adjacent pairs or from other electrical devices.

Unshielded Twisted pairs standards

A great many different cabling standards exist. EIA/TIA (Electronic Industries Association / Telecommunications Information Association) standard  568A is one of several standard that specify “Categories” of unshielded twisted pair cabling systems in terms of data rates that they can carry. Under UTP type of cables for Ethernet wiring, the categories number. For computer networks the most common are category5, category5e and category6

CATI (category1) is typically used for telephone wire. This type of wire is not capable of supporting network traffic and it is twisted. CATI is not suitable to use with Ethernet. Only telephone companies who provide ISDN use it. There fore, the wiring between the customer’s site and Phone Company’s network use CATI cable.

CAT2 is used most commonly used for token ring networks, supporting speeds up to 4 Mbps. For higher speeds (100 Mbps) CAT5 cables are suitable. CAT3, CAT4 andCAT5 cables are generally 4 pairs of twisted copper wires. CAT5 has more twists per inch than CAT3, therefore it can run at higher speeds and greater lengths. CAT3 and CAT4 are also used for token ring networks. Category5e is a new standard that will specify transmission performance, which exceeds CAT5. Like CAT5, it consists of unshielded twisted pair with 100-ohm impudence and electrical characteristics supporting at frequencies up to 100MHz. CAT6 wire was originally designed to support multi gigabyte Ethernet. It is similar to CAT5 but contains a physical separator between the four pairs to further reduce electromagnetic interference. CAT7 is a proposed standard that aims to support transmission at frequencies up to 600MHz over 100 ohm twisted pair.

Most common cable categories

Category	Bandwidth	Applications	Notes
Cat1	0.4 MHz	Telephone and modem lines	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat2	? MHz	Older terminal systems, e.g. IBM 3270	Not described in EIA/TIA recommendations. Unsuitable for modern systems.
Cat3	16MHz	10BASE-T and 100BASE-T4 Ethernet	Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s.
Cat4	20MHz	16 Mbit/s Token Ring
Cat5	100MHz	100BASE-TX & 1000BASE-T Ethernet
Cat5e	100MHz	100BASE-TX & 1000BASE-T Ethernet	Enhanced Cat5. Practically the same as Cat5, but with better testing standards so Gigabit Ethernet works reliably.
Cat6	250MHz	1000BASE-T Ethernet	Most commonly installed cable in Finland according to the 2002 standard. SFS-EN 50173-1
Cat6e	250MHz (500MHz according to some)	10GBASE-T (under development) Ethernet	Not a standard; a cable maker's own label.
Cat6a	500MHz	10GBASE-T (under development) Ethernet	Standard under development (ISO/IEC 11801:2002 Amendment 2).
Cat7	600MHz	No applications yet.	Four pairs, U/FTP (shielded pairs). Standard under development.
Cat7a	1200MHz	Telephone, CATV, 1000BASE-T in the same cable.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.
Cat8	1200MHz	Under development, no applications yet.	Four pairs, S/FTP (shielded pairs, braid-screened cable). Standard under development.

Coaxial cable

Coaxial cable is a type of communication transmission cable in which solid center conductor is surrounded by an insulating medium, which is surrounded by tubular outer conductor (foil). The entire assembly is then surrounded with an insulating and protective outer layer. Coaxial cables are capable of carrying many data, voice and video conversations simultaneously. The two type of coaxial cabling used with Ethernet are.

• Thicket
• Thinnet

Thicket

Thicket coaxial is used with Ethernet 10BASE5 network, which supports a 100Mbps transmission rata and consists of 500 meter segment length. Thick Ethernet consists of mark at every 2.5 meters, which  indicates proper placement of 10Base5 transceivers used to connect  stations to the network Transceiver placed at any multiple of 2.5 meters intervals minimizes signal reflection, which may spoil the transmission quality in the cable. Vampire tap is used to connect  to the segment. Vampire tap is piece of metal, which is cylindrical in shape when tap is closed. When tap is closed around the cable, it is pushed through the shielding to provide the metal in the vampire tap to touch the copper wire inside the cable.

Thinnet

Thinnet coaxial cable is used with Ethernet 10 Base2 networks. Compared to thicknet cables, thicknet are cheaper, Lighter, flexible and easier to install. It consists of 185 meter maximum segment Length. 10Base2 transceiver is connected to the thinnet cable segment through “BNC (British Naval Connector) T” connector. To connect to computer, one end of T connector plugs directly into Ethernet card in the computer station, another end is plugged into cable from upstream cable, and another cable attached to next device downstream.

10Base5 and 10Base2 Connectors

Transceiver is a term formed by combining the terms transmitter and receiver. Instead of Ethernet card, it consists of electronics that send and receive signal on the Ethernet cable.
Disadvantages of coaxial cable includes that are more expensive, heavier and relatively inflexible. Also, when it is used for Ethernet, a single break in cable causes the failure of entire segment.

Fiber-Optic Cable

An optical fiber breakout cable

A multi-fiber cable

Fiber-optic cabling is a technology in which the electrical signal is converted into optical signal that is transmitted through a thin glass fiber and it is converted back into electrical signal. The figure below shows the components of a fiber-optic cable.


Fiber-optic cable is made from fiberglass and it does not break easily. The plastic and Kevlar coating provides more strength to the fiber glass. Kevlar is the material that most of bullet proof vests is made of.

Fiber-optic cable consists of two concentric layers of high-purity silica glass- the core and the cladding. The “core” is the inner part of an optical fiber through which light is transmitted. The “cladding” is the material in the middle layer. The light stays confined to the core because the cladding has lower refractive index than the core, which means that when light hits the outer wall, it is reflected back to core. The outer protective layer serves to protect core and cladding from damage.

The devices such as Ethernet switches, which are at the end of the cable, generate optical light signal. These signals travel through the optical fiber in the canter of cable. Electricity is not used across the cable; only light is transmitted.

Optical fiber connector

FC connector	MIC (FDDI) connector
LC connector	MT-RJ connector
LuxCis connector	SC connector
ST connector

IP Address

Every message and every piece of information sent over any TCP/IP network is sent as an IP packet. IP’s job is to enable data to be transmitted across and between networks. Hence the name: Internet protocol. An IP address is a numeric identifier assigned to each machine on an IP network. It designates the specific location of a device on the network. An IP address is software address not a hardware address and it is used to find hosts on a local network. Before entering into more complicated aspects of IP addressing, you have to learn some of the basics. In this lesson, you will learn some of the fundamentals of IP addressing and its terminology. Then you will learn IP addressing scheme and private IP addresses.

IP addressing definition

Internet protocol address or IP address uniquely identifies every network or host on the Internet. An IP address is a 32 bit binary number usually represented as 4 decimal values, each representing 8 bits. Since each of the 8 positions can have two different states (0 or 1), the total number of combinations per octet is 28or 256.so each octet can contain any value between 0to 255. Each octet is separated by decimal points. For this reason, an IP address is known as “dotted decimal” notation.

For example: 140.179.220.200 is an IP address which is written in dotted decimal format. The actual binary format is 10001100.10110011.11001000.The first octet in this example is 140 and second octet is 179 and so on and the range of decimal number is between 0to 255.

Every IP address consists of two parts, one identifying the network that the computer belongs to known as Network ID and one identifying the host on the network known as Host ID.

Network part of the IP address (Network ID)

Internet is the interconnection of many individual networks. So each network must know its own address on the Internet and that of the other networks with which it communicates. The organization requires a unique network number, which it can request from Network Information center (NIC). This unique network number is added to packet, which is sent from the network onto the Internet.

The Host part of the IP address

In addition to network address or number, information is required to identify which specific host or machine in a network is sending or receiving a message. Therefore, IP address needs unique network number .and this is the part of the IP address.

IP Terminology

It is very important to learn some of the terminology, which is vital to understand Internet protocol. Some of the terms are listed below

• Bit: A bit is one digit; either a 1 or 0
• Byte: A byte is 8 bits.
• Octet: An Octet, mare up of 8 bits, is just an ordinary 8-bit binary number. The terms byte and octet can be used interchangeably.
• Network address: This is the designation used in routing to send packets to a remote network-for example, 10.0.0.0, 172.16.0.0, and 192.168.10.0.
• Broadcast address: The address used by applications and hosts send information to all nodes on a network is called the broadcast address .Examples include 255.255.255.255, which broadcast to all networks, all nodes; 172.16.255.255 which broadcasts to all subnets and hosts on network 10.0.0.0.

Classes of networks

Since networks vary in size, the IP addresses are divided into classes. The most common classes are class A,B and C.The class D(multicast) address and class E (research) addresses exist but end user does not generally use them. The class of an IP address can be identified by looking at its first octet. The size of the host part depends on the size of the network.

The five classes of IP address is shown in the figure

Class	Leading bits	Start	End	Default Subnet Mask in dotted decimal	CIDR notation
A	0	0.0.0.0	127.255.255.255	255.0.0.0	/8
B	10	128.0.0.0	191.255.255.255	255.255.0.0	/16
C	110	192.0.0.0	223.255.255.255	255.255.255.0	/24
D	1110	224.0.0.0	239.255.255.255	not defined	not defined
E	1111	240.0.0.0	255.255.255.254	not defined	not defined

The blocks numerically at the start and end of classes A, B and C were originally reserved for special addressing or future features, i.e., 0.0.0.0/8 and 127.0.0.0/8 are reserved in former class A; 128.0.0.0/16 and 191.255.0.0/16 are reserved in former class B; 192.0.0.0/24 and 223.255.255.0/24 are reserved in former class C.

While the 127.0.0.0/8 network is a Class A network, it is designated for loop-back and cannot be assigned to a network.

CIDR	host bits	Netmask	Hosts in subnet	Classful name	Typical usage
/8	24	255.0.0.0	16777216 = 224	Class A (see this list)	Largest block allocation made by IANA
/9	23	255.128.0.0	8388608 = 223
/10	22	255.192.0.0	4194304 = 222
/11	21	255.224.0.0	2097152 = 221
/12	20	255.240.0.0	1048576 = 220
/13	19	255.248.0.0	524288 = 219
/14	18	255.252.0.0	262144 = 218
/15	17	255.254.0.0	131072 = 217
/16	16	255.255.0.0	65536 = 216	Class B
/17	15	255.255.128.0	32768 = 215		ISP / large business
/18	14	255.255.192.0	16384 = 214		ISP / large business
/19	13	255.255.224.0	8192 = 213		ISP / large business
/20	12	255.255.240.0	4096 = 212		Small ISP / large business
/21	11	255.255.248.0	2048 = 211		Small ISP / large business
/22	10	255.255.252.0	1024 = 210
/23	9	255.255.254.0	512 = 29
/24	8	255.255.255.0	256 = 28	Class C	Large LAN
/25	7	255.255.255.128	128 = 27		Large LAN
/26	6	255.255.255.192	64 = 26		Small LAN
/27	5	255.255.255.224	32 = 25		Small LAN
/28	4	255.255.255.240	16 = 24		Small LAN
/29	3	255.255.255.248	8 = 23		Smallest multi-host network
/30	2	255.255.255.252	4 = 22		"Glue network" (point to point links)
/31	1	255.255.255.254	2 = 21		Rarely used, point to point links (RFC 3021)
/32	0	255.255.255.255	1 = 20		Host route

In common usage, the "host all zeros" address is reserved for referring to the entire network, while the "host all ones" address is used as a broadcast address in the given subnet; this reduces the number of addresses available for hosts by 2. This explains the reference to /31 networks as "Rarely Used," as the only possible addresses on a /31 network are "host all ones" and "host all zeros." RFC 3021 creates an exception to the "host all ones" and "host all zeros" broadcast usage to make /31 networks usable for point-to-point links. In practice, however, point-to-point links are still typically implemented using /30 networks, or occasionally by /32 and point-to-point explicit host routes. There is generally no technical advantage to /31 versus /32, although one or the other may be more convenient based on other issues. A /30 is always wasteful and has as its sole advantage that it behaves "as expected" for any other subnetwork.

Private IPv4 address spaces

The Internet Engineering Task Force (IETF) has directed the Internet Assigned Numbers Authority (IANA) to reserve the following IPv4 address ranges for private networks, as published in RFC 1918:

RFC1918 name	IP address range	number of addresses	classful description	largest CIDR block (subnet mask)	host id size
24-bit block	10.0.0.0 – 10.255.255.255	16,777,216	single class A	10.0.0.0/8 (255.0.0.0)	24 bits
20-bit block	172.16.0.0 – 172.31.255.255	1,048,576	16 contiguous class Bs	172.16.0.0/12 (255.240.0.0)	20 bits
16-bit block	192.168.0.0 – 192.168.255.255	65,536	256 contiguous class Cs	192.168.0.0/16 (255.255.0.0)	16 bits

Classful addressing is obsolete and has not been used in the Internet since the implementation of Classless Inter-Domain Routing (CIDR) starting in 1993. For example, while 10.0.0.0/8 was a single class A network, it is common for organizations to divide it into smaller /16 or /24 networks.

Broadcast Addresses

Four different types of broadcast addresses are

• Layer 2 broadcasts: These are sent to all nodes or hosts on a LAN.
• Layer 3 broadcasts: These are sent to all hosts or nodes on the network
• Unicast: These are sent to single destination host
• Multicast: These are the packets sent from a single source and transmitted to many devices on
• different networks.

Layer 2 Broadcast: 

Layer 2 broadcasts are also known as hardware address. They do not pass the LAN boundary unless they become a Unicast packet. A typical hardware address is 6 bytes and looks something like Oc.43.a4.f3.12.c2. The broadcast would be all 1s in binary and all Fs in hexadecimal, which looks like FF.FF.FF.FF.FF.FF.

Layer 3 broadcast addresses: 

Broadcast message are meant to reach all hosts on a broadcast domain. These are network broadcast that have all host bits on. The network address of 173. 14.0.0.255.255.0.0 Would have a broadcast address of 173.14.255.255 with all host bits on. Broadcast can also be “all networks and all hosts,” as indicated by 255.255.255.255.

Unicast: 

A Unicast is different because it’s broadcast that has an actual destination IP address- in other words, it’s sent to a specific host, most commonly a DHCP server. For example: the host on a network sends out an FF.FF.FF.FF.FF.FF.and 255.255.255.255. destination broadcast looking for a DHCP server on the LAN. The router will see that this is a broadcast sent for the DHCP server, and forward the request to the IP address of the DHCP server on another LAN. So, basically, if the DHCP server IP address is 173.14.10.1, the host just sends out a 255.255.255.255 broadcast, and the router changes that broadcast to the specific destination address of 173.14.10.1, the host just sends out a 255.255.255.255 broadcast to the specific destination address of 173.14.10.1.

Multicast: 

Multicast is point-to-multipoint communication. It is similar to broadcast but this works in a different manner. Multicast works by sending message or data to IP multicast group addesaaes.Routers then forward copies of the packet to every interface that has hosts subscribed to that group address. This is major difference between broadcast and multicast.

TCP/IP Model Introduction

The TCP/IP protocol suite is named for two of its most important protocols Transmission control protocol (TCP) and Internet protocol (IP). The TCP/IP protocol suite establishes the technical foundation of the Internet. The Department of Defense (DoD) developed TCP/IP to ensure and preserve date integrity. TCP/IP model contains a large number of protocols, which helps one computer to communicate with another. Description of each of these protocols is documented by Request for comments (RFC) and it is approved by Internet Engineering Task force (IETF). This model is a condensed version of the OSI model and contains only four layers. They are Application layer, Host-to-Host layer, Internet layer and Network access layer. Each of these layrerwill be discussed in detail in this lesson.

TCP/IP protocol Architecture

Like other networking models, TCP/IP divides the functions of communication protocols into different layers. Most description of TCP/IP defines three to five levels in the protocol architecture. The four level model is based on the three layers(Application, Transport and Network Access) as defined in the DOD protocol model with the addition of Internet layer. The protocols at the internet and transport later: Internet protocol (IP), Transmission control protocol (TCP) and User Datagram Protocol (UDP) is usually called as “core” of the suite which supports to perform a variety of functions at each of the TCP/IP model layer. The layers in TCP/IP Architectural Model are shown in figure.

TCP/IP and the DoD Model

The DoD model is basically a condensed version of the OSI model- it’s composed of four, instead of seven, layers:

• Process/Application layer
• Host-to-Host layer
• Internet layer
• Network Access

OSI-TCP/IP Model

Figure shows a comparison of the DoD model ( TCP/IP Mode ) and the OSI reference model. As you can see, the two are similar in concept, but each has a different number of layers with different names.

How protocol stack works

Two Internet hosts connected via two routers and the corresponding layers used at each hop.

TCP/IP Model and OSI model are quite similar in nature. Data is passed down the stack when it is being sent to the network and up the stack when it is received from the network. Every layer uses control information to keep addressing and other information that is needed by the protocol to deliver the data. These control information is called as header or trailer. Each layer upon receiving the data from the previous layer adds its own header in front of the information. This process of adding control information is known as Data encapsulation. When the data is received from the network, opposite procedure happens. At each layer the headers are the headers are stripped off and discarded before passing it to next layer. The process of removing header or trailer from the data is known as Decapsulation.

Encapsulation of application data descending through the TCP/IP layers

Each layer in TCP/IP model has its own data structure, but a layer will not know the data structure used by the layer below and above it.

Network Devices - Switch

Switches :

A network switch or switching hub is a computer networking device that connects network segments ( i.e different LANs ).

Like network bridge that the Switch processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3 and above) are often referred to as Layer 3 switches or multilayer switches.

When packets are received at the destination, it is checked for the errors and if errors are found, data will be retransmitted. When the packets are arrives, the header is checked to determine which packet is destined for which segment and then it is forwarded to that segment. Switches can be used in heavily loaded network to combine the data flow and improve performance.

Role of switches in networks
Switches may operate at one or more OSI layers, including physical, data link, network, or transport layer. A device that operates simultaneously at more than one of these layers is known as a multilayer switch.

Layer-specific functionality
While switches may learn about topologies at many layers, and forward at one or more layers, they do tend to have common features. Other than for high-performance applications, modern commercial switches use primarily Ethernet interfaces, which can have different input and output bandwidths of 10, 100, 1000 or 10,000 megabits per second. Switch ports almost always default to Full duplex operation, unless there is a requirement for interoperability with devices that are strictly Half duplex. Half duplex means that the device can only send or receive at any given time, whereas Full duplex can send and receive at the same time.

At any layer, a modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as an IP telephone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterrupted power supplies, the connected device can continue operating even when regular office power fails.

Layer-1 hubs versus higher-layer switches
A network hub, or repeater, is a fairly unsophisticated network device. Hubs do not manage any of the traffic that comes through them. Any packet entering a port is broadcast out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions result, which slows down the network.

There are specialized applications where a hub can be useful, such as copying traffic to multiple network sensors. High end switches have a feature which does the same thing called port mirroring. There is no longer any significant price difference between a hub and a low-end switch.

Layer 2

A network bridge, operating at the Media Access Control (MAC) sublayer of the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC address of each connected device. Single bridges also can provide extremely high performance in specialized applications such as storage area networks.

Classic bridges may also interconnect using a spanning tree protocol that disables links so that the resulting local area network is a tree without loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. The older IEEE 802.1D spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while the spanning tree would re-converge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w, but the newest edition of IEEE 802.1D-2004, adopts the 802.1w extensions as the base standard. The IETF is specifying the TRILL protocol, which is the application of link-state routing technology to the layer-2 bridging problem. Devices which implement TRILL, called Bridges, combine the best features of both routers and bridges.

While "layer 2 switch" remains more of a marketing term than a technical term,[citation needed] the products that were introduced as "switches" tended to use micro-segmentation and Full duplex to prevent collisions among devices connected to Ethernets. By using an internal forwarding plane much faster than any interface, they give the impression of simultaneous paths among multiple devices.

Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth method were performance-increasing methods when used on "switch" products with the same input and output port bandwidths:

1. Store and forward: The switch buffers and, typically, performs a checksum on each frame before forwarding it.
2. Cut through: The switch reads only up to the frame's hardware address before starting to forward it. There is no error checking with this method.
3. Fragment free: A method that attempts to retain the benefits of both "store and forward" and "cut through". Fragment free checks the first 64 bytes of the frame, where addressing information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device in Layer 3 or Layer 4 (OSI), typically a router.
4. Adaptive switching: A method of automatically switching between the other three modes.

Cut-through switches have to fall back to store and forward if the outgoing port is busy at the time the packet arrives. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is rarely the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth (e.g., 10/100 Mbit/s) into a higher bandwidth (at least 1 Gbit/s). Alternatively, a switch that provides access to server ports usually connects to them at a much higher bandwidth than is used by end user devices.

Layer 3
Within the confines of the Ethernet physical layer, a layer 3 switch can perform some or all of the functions normally performed by a router. A true router is able to forward traffic from one type of network connection (e.g., T1, DSL) to another (e.g., Ethernet, WiFi).

The most common layer-3 capability is awareness of IP multi-cast. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multi-cast group only to ports where the attached device has signaled that it wants to listen to that group. If a switch is not aware of multi-casting and broadcasting, frames are also forwarded on all ports of each broadcast domain, but in the case of IP multi-cast this causes inefficient use of bandwidth. To work around this problem some switches implement IGMP snooping.

Layer 4
While the exact meaning of the term Layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translation, but then adds some type of load distribution based on TCP sessions.

The device may include a statecraft firewall, a VPN concentrator, or be an IPSec security gateway.

Layer 7
Layer 7 switches may distribute loads based on URL or by some installation-specific technique to recognize application-level transactions. A Layer-7 switch may include a web cache and participate in a content delivery network.

Types of Switches :
Many types of switches exist, including ATM Switches, LAN Switches and WAN Switches.

ATM Switch ( Asynchronous Transfer Mode) :
ATM switch is a high performance, cell oriented technology that utilizes fixed-length information unit known as Cell for high speed transmission, and support voice, video and data applications. ATM allows customers to replace their separate voice and data networks with single network to handle, data and other multimedia contents such as video.

ATM Switch

LAN Switches :

A separate connections for each one in a company's internal network are known as LAN network. Essentially, a LAN creates a series of instant network that contains only two devices communicating with each other at that particular moment. Lan switches are designed to switch data frames at high speed.

LAN Switch

WAN Switches :

A WAN Switch is a multi-port inter-networking device used in carrier networks.Typically these devices switch traffic such as Frame Relay, X.25 and operate at the data link layer of the OSI Reference Model.

WAN Switch