Why use a Network?
we use networks for communication between computers, sharing of data
and peripherals. In the business world we use networks for ease of
administration and to cut costs.
Sharing data example.............. imagine an office with 5 secretaries working on 5
different computers, one requires a file from another computer in a non
networked office this file would have to be written to a portable media
then loaded onto the computer. In a networked office the file could be
accessed via the network from a shared folder.
Sharing peripherals example the same office with 5 secretaries
working on 5 different computers, in order to print their work each
computer would need to have a printer attached. In a networked office
you could have one shared printer, cutting costs.
What you need.
A common language or protocol (TCP/IP IPX/SPX, APPLE TALK) is a
convention or standard that controls or enables the connection,
communication, and data transfer between two computing endpoints.
Cabling BNC,Cat5, fibre optic
Hardware NIC(Network Interface Card), router, switch, hub, modem wireless access point.
Network Service (DNS, WINS, DHCP).
Network Hardware
A network card, network adapter, network interface card or NIC is a
piece of computer hardware designed to allow computers to communicate
over a computer network. It has a MAC address. Every network card has a
unique 48-bit serial number called a MAC address, which is written to
ROM carried on the card. Every computer on a network must have a card
with a unique MAC address. The IEEE is responsible for assigning MAC
addresses to the vendors of network interface cards. No two cards ever
manufactured should share the same address.
Hubs
An Ethernet hub or concentrator is a device for connecting multiple
twisted pair or fibre optic Ethernet devices together, making them act
as a single segment. It works at the physical layer of the OSI model,
repeating the signal received at one port out each of the other ports
(but not the original one). The device is thus a form of multiport
repeater. Ethernet hubs are also responsible for forwarding a jam signal
to all ports if it detects a collision. Hubs also often come with a BNC
and/or AUI connector to allow connection to legacy 10BASE2 or 10BASE5
network segments. The availability of low-priced Ethernet switches has
largely rendered hubs obsolete but they are still seen in older
installations and more specialist applications.
A network switch or switch for short is a networking device that
performs transparent bridging (connection of multiple network segments
with forwarding based on MAC addresses) at full wire speed in hardware.
As a frame comes into a switch, the switch saves the originating MAC
address and the originating (hardware) port in the switch’s MAC address
table. This table often uses content-addressable memory, so it is
sometimes called the “CAM table”. The switch then selectively transmits
the frame from specific ports based on the frame’s destination MAC
address and previous entries in the MAC address table. If the
destination MAC address is unknown, for instance, a broadcast address or
(for simpler switches) a multicast address, the switch simply transmits
the frame out of all of the connected interfaces except the incoming
port. If the destination MAC address is known, the frame is forwarded
only to the corresponding port in the MAC address table.
A hub, or repeater, is a fairly unsophisticated broadcast device. Any
packet entering any port is broadcast out on every port and thus hubs do
not manage any of the traffic that comes through their ports. Since
every packet is constantly being sent out through every port, this
results in packet collisions, which greatly impedes the smooth flow of
traffic. A switch isolates ports, meaning that every received packet is
sent out only to the port on which the target may be found (assuming the
proper port can be found; if it is not, then the switch will broadcast
the packet to all ports except the port the request originated from).
Since the switch intelligently sends packets only where they need to go
the performance of the network can be greatly increased.
A router is a computer networking device that forwards data packets
across a network toward their destinations, through a process known as
routing. A router acts as a junction between two or more networks to
transfer data packets among them. A router is different from a switch. A
switch connects devices to form a Local area network (LAN).
One easy illustration for the different functions of routers and
switches is to think of switches as local streets, and the router as the
junctions with the street signs. Each house on the local street has an
address within a range on the street. In the same way, a switch connects
various devices each with their own IP address(es) on a LAN. Routers
connect networks together the way that on-ramps or major junctions
connect streets to both main roads and motorways. The street signs at
the junctions the (routing table) show which way the packets need to
flow.
Wireless Access Point (WAP) A wireless access point (AP) connects a
group of wireless stations to an adjacent wired local area network
(LAN). An access point is similar to an Ethernet hub, but instead of
relaying LAN data only to other LAN stations, an access point can relay
wireless data to all other compatible wireless devices as well as to a
single (usually) connected LAN device, in most cases an Ethernet hub or
switch, allowing wireless devices to communicate with any other device
on the LAN.
Wireless Routers A wireless router integrates a wireless access point
with an Ethernet switch and an Ethernet router. The integrated switch
connects the integrated access point and the integrated Ethernet router
internally, and allows for external wired Ethernet LAN devices to be
connected as well as a (usually) single WAN device such as a cable modem
or DSL modem. A wireless router advantageously allows all three devices
(mainly the access point and router) to be configured through one
central configuration utility, usually through an integrated web server.
However one disadvantage is that one may not decouple the access point
so that it may be used elsewhere.
Cables Terminology
10BASE2 (also known as cheapernet or thinnet) is a variant of
Ethernet that uses thin coaxial cable. The 10 comes from the maximum
transmission speed of 10 Mbit/s (millions of bits per second). The BASE
stands for baseband signaling, and the 2 represents a rounded up
shorthand for the maximum segment length of 185 metres (607 feet).
10BASE5 (also known as thicknet) is the original “full spec” variant
of Ethernet cable. The 10 refers to its transmission speed of 10 Mbit/s.
The BASE is short for baseband signalling as opposed to broadband, and
the 5 stands for the maximum segment length of 500 metres.
10BASE-T is an implementation of Ethernet which allows stations to be
attached via twisted pair cable. The name 10BASE-T is derived from
several aspects of the physical medium. The 10 refers to the
transmission speed of 10 Mbit/s. The BASE is short for baseband.The T
comes from twisted pair, which is the type of cable that is used
100BASE-T is any of several Fast Ethernet 100 Mbit/s CSMA/CD
standards for twisted pair cables, including: 100BASE-TX (100 Mbit/s
over two-pair Cat5 or better cable). The segment length for a 100BASE-T
cable is limited to 100 metres
Coaxial cable is an electrical cable consisting of a round conducting
wire, surrounded by an insulating spacer, surrounded by a cylindrical
conducting sheath, usually surrounded by a final insulating layer. It is
used as a high-frequency transmission line to carry a high-frequency or
broadband signal.
BNC connectors were commonly used on 10base2 thin Ethernet networks,
both on cable interconnections and network cards, though these have
largely been replaced by newer Ethernet devices whose wiring does not
use coaxial cable.
Category 5 cable, commonly known as Cat 5, is an unshielded twisted
pair cable type designed for high signal integrity. Category 5 has been
superseded by the Category 5e specification. This type of cable is often
used in structured cabling for computer networks such as Gigabit
Ethernet, although they are also used to carry many other signals such
as basic voice services, token ring.
Category 5 cable included four twisted pairs in a single cable
jacket. It was most commonly used for 100 Mbit/s networks, such as
100BASE-TX Ethernet
Cat5 cable uses an RJ-45 (Registered Jack-45) connector at each end
of the cable with a fixed wiring scheme. The ends are then crimped on to
the cable
A protocol (TCP/IP IPX/SPX, APPLE TALK) is a convention or standard
that controls or enables the connection, communication, and data
transfer between two computing endpoints. Sending and receiving systems
need to use the same protocol unless a gateway service sits between
networks and translates from one to the other.
Most protocols specify one or more of the following properties:
- Detection of the underlying physical connection (wired or wireless), or the existence of the other endpoint or node
- Handshaking
- Negotiation of various connection characteristics
- How to start and end a message
- How to format a message
- What to do with corrupted or improperly formatted messages (error correction)
- How to detect unexpected loss of the connection, and what to do next
- Termination of the session or connectio
NetBIOS is an acronym for Network Basic Input/Output System. The
NetBIOS API allows applications on separate computers to communicate
over a local area network. NetBIOS must be enabled for Windows File and
Print Sharing to work.
NetBIOS provides three distinct services:
- Name service for name registration and resolution
- Session service for connection-oriented communication
- Datagram distribution service for connectionless communication.
Name service In order to start Sessions or distribute Datagrams, an
application must register its NetBIOS name using the Name service.
NetBIOS names are 16 bytes in length
Session service Session mode lets two computers establish a
connection for a “conversation,” allows larger messages to be handled,
and provides error detection and recovery. In NBT, the session service
runs on TCP port 139.
Datagram distribution service Datagram mode is “connectionless”.
Since each message is sent independently, they must be smaller; the
application becomes responsible for error detection and recovery. In
NBT, the datagram service runs on UDP port 138.
IPX/SPX (NWLINK)
Internetwork Packet Exchange (IPX) is the OSI-model Network layer
protocol in the IPX/SPX protocol stack. The IPX/SPX protocol stack is
supported by Novell’s NetWare network operating system. Because of
Netware’s popularity through the late 1980s into the mid 1990s, IPX
became a popular internetworking protocol. Novell derived IPX from Xerox
Network Services’ IDP protocol. IPX usage is in general decline as the
boom of the Internet has made TCP/IP nearly universal. Computers and
networks can run multiple network protocols, so almost all IPX sites
will be running TCP/IP as well to allow for Internet connectivity. It is
also now possible to run Novell products without IPX, as they have
supported both IPX and TCP/IP since NetWare reached version 5.
Sequenced Packet Exchange (SPX) is a transport layer protocol (layer 4
of the OSI Model) used in Novell Netware networks. The SPX layer sits
on top of the IPX layer (layer 3 – the network layer) and provides
connection-oriented services between two nodes on the network. SPX is
used primarily by client/server applications.
NWLink is a IPX/SPX-compatible protocol developed by Microsoft and
used in its Windows NT product line.NWLink is Microsoft’s version of
Novell’s IPX/SPX Protocol. The Microsoft version of NWLink includes the
same level of functionality as the Novell Protocol. NWLink includes a
tool for resolving NetBIOS names.NWLink packages data to be compatible
with client/server services on NetWare Networks. However, NWLink does
not provide access to NetWare File and Print Services. To access the
File and Print Services the Client Service for NetWare needs to be
installed.
AppleTalk is a suite of protocols developed by Apple Computer for
computer networking. It was included in the original Macintosh (1984)
and is now used less by Apple in favour of TCP/IP networking.
AppleTalk contains two protocols aimed at making the system
completely self-configuring. The AppleTalk address resolution protocol
(AARP) allowed AppleTalk hosts to automatically generate their own
network addresses, and the Name Binding Protocol (NBP) was essentially a
dynamic DNS system which mapped network addresses to user-readable
names.
For interoperability Microsoft maintains the file services for Macintosh and the print services for Macintosh
The Internet protocol suite is the set of communications protocols
that implement the protocol stack on which the Internet and most
commercial networks run. It is sometimes called the TCP/IP protocol
suite, after the two most important protocols in it: the Transmission
Control Protocol (TCP) and the Internet Protocol (IP), which were also
the first two defined.The Internet protocol suite like many protocol
suites can be viewed as a set of layers, each layer solves a set of
problems involving the transmission of data, and provides a well-defined
service to the upper layer protocols based on using services from some
lower layers. Upper layers are logically closer to the user and deal
with more abstract data, relying on lower layer protocols to translate
data into forms that can eventually be physically transmitted.The OSI
model describes a fixed, seven layer stack for networking protocols.
Comparisons between the OSI model and TCP/IP can give further insight
into the significance of the components of the IP suite, but can also
cause confusion, as TCP/IP consists of only 4 layers.
The four layers in the DoD model, from bottom to top, are:
- The Network Access Layer is responsible for delivering data over the
particular hardware media in use. Different protocols are selected from
this layer, depending on the type of physical network.
- The Internet Layer is responsible for delivering data across a
series of different physical networks that interconnect a source and
destination machine. Routing protocols are most closely associated with
this layer, as is the IP Protocol, the Internet’s fundamental protocol.
- The Host-to-Host Layer handles connection rendezvous, flow control,
retransmission of lost data, and other generic data flow management. The
mutually exclusive TCP and UDP protocols are this layer’s most
important members.
- The Process Layer contains protocols that implement user-level functions, such as mail delivery, file transfer and remote login.
Network Services
DNS (Domain Naming System)
The Domain Name System (DNS) stores and associates many types of
information with domain names, but most importantly, it translates
domain names (computer hostnames) to IP addresses. It also lists mail
exchange servers accepting e-mail for each domain. In providing a
worldwide keyword-based redirection service, DNS is an essential
component of contemporary Internet use.
The DNS pre-eminently makes it possible to attach easy-to-remember
domain names (such as “es-net.co.uk”) to hard-to-remember IP addresses
(such as 270.146.131.206). People take advantage of this when they
recite URLs and e-mail addresses.
WINS (Windows Internet Naming Service)
Windows Internet Naming Service (WINS) is Microsoft’s implementation
of NetBIOS Name Server (NBNS) on Windows, a name server and service for
NetBIOS computer names. Effectively, it is to NetBIOS names what DNS is
to domain names – a central mapping of host names to network addresses.
However, the mappings have always been dynamically updated (e.g. at
workstation boot) so that when a client needs to contact another
computer on the network it can get its up-to-date DHCP allocated
address. Networks normally have more than one WINS server and each WINS
server should be in push pull replication; the favoured replication
model is the hub and spoke, thus the WINS design is not central but
distributed. Each WINS server holds a full copy of every other related
WINS system’s records. There is no hierarchy in WINS (unlike DNS), but
like DNS its database can be queried for the address to contact rather
than broadcasting a request for which address to contact. The system
therefore reduces broadcast traffic on the network, however replication
traffic can add to WAN / LAN traffic.
DHCP (Dynamic Host Configuration Protocol)
The Dynamic Host Configuration Protocol (DHCP) automates the
assignment of IP addresses, subnet masks, default routers, and other IP
parameters. The assignment usually occurs when the DHCP configured
machine boots up or regains connectivity to the network. The DHCP client
sends out a query requesting a response from a DHCP server on the
locally attached network. The DHCP server then replies to the client
with its assigned IP address, subnet mask, DNS server and default
gateway information.The assignment of the IP address usually expires
after a predetermined period of time, at which point the DHCP client and
server renegotiate a new IP address from the server’s predefined pool
of addresses. Configuring firewall rules to accommodate access from
machines who receive their IP addresses via DHCP is therefore more
difficult because the remote IP address will vary from time to time.
Administrators must usually allow access to the entire remote DHCP
subnet for a particular TCP/UDP port. Most home routers and firewalls
are configured in the factory to be DHCP servers for a home network.
ISPs (Internet Service Providers) generally use DHCP to assign clients
individual IP addresses.DHCP is a broadcast-based protocol. As with
other types of broadcast traffic, it does not cross a router.
APIPA (Automatic Private IP Addressing)
If computers are unable to pick an address up from a DHCP server they
use Automatic Private IP Addressing (APIPA). This means the computer
will assign itself a random address between 169.254.0.1 –
169.254.254.254/16, allowing it to communicate with other clients who
are also using APIPA.
Automatic Private IP Addressing (APIPA), this allows unknowledgeable
users to connect computers, networked printers, and other items together
and expect them to work. Without Zeroconf or something similar, a
knowledgeable user must either set up special servers, like DHCP and
DNS, or set up each computer by hand.
Networks
A Local Area Network (LAN) is a computer network covering a small
local area, like a home, office, or small group of buildings such as a
home, office, or college. Current LANs are most likely to be based on
switched Ethernet or Wi-Fi technology running at 10, 100 or 1,000
Mbit/s.The defining characteristics of LANs in contrast to WANs (wide
area networks) are: their much higher data rates; smaller geographic
range; and that they do not require leased telecommunication lines.
A Personal Area Network (PAN) is a computer network used for
communication among computer devices (including telephones and personal
digital assistants) close to one person. The reach of a PAN is typically
a few metres and may use Bluetooth, wireless or USB for connection.
A Wide Area Network (WAN) is a computer network covering a wide
geographical area, involving a vast array of computers. This is
different from personal area networks (PANs), metropolitan area networks
(MANs) or local area networks (LANs) that are usually limited to a
room, building or campus. The most well-known example of a WAN is the
Internet. WANs are used to connect local area networks (LANs) together,
so that users and computers in one location can communicate with users
and computers in other locations.
12:45
Breaking
with its own naming conventions, Microsoft released Windows 2000
(initially called NT 5.0) for the business market. It appeared in 4
models: Professional -which replaced Workstation, Server, Advanced
Server and Datacenter Server catered for differing business
requirements.
