STP

When the design requires some LAN switches, network engineer generally include a redundant LAN segment between these switches.

The goal is simple, the switches are likely to fail in operation, or there is the possibility of the cable was disconnected or unplug redundant so that the existence of this segment, the network service can still be running even though there are obstacles above.

LAN with redundant link that allows the frame looping endlessly in the network.

These looping frames that cause performance problems on the network.

STP is a protocol contained in the OSI layer 2 functions to ensure the absence of loops in the network topology LAN. STP allows a network to include links that are free (extra) to provide automatic backup if the primary link being active failed, without danger of the loop on the bridge, enable or disable this backup link manually. Bridge loops must be avoided. because it could create a network flooding occurs.
Excess Spanning Tree Protocol (STP)
1. Avoiding Traffic with mesegmentasi high bandwidth access through the switch
2. Provides Backup / stand-by path to avoid loops and switches the failed / failing
3. Prevent looping

Common problems can be alleviated by the Spanning Tree Protocol is a broadcast storm. Broadcast storm caused a lot of broadcast (or multicast or unicast-destination unknown) in the loop on the network continuously. This will create a link that is not useful (because of the dual link between the bridge / switch) and will significantly affect the performance of end-user's computer because of too many existing broadcast process.

Broadly speaking, Spanning Tree Protocol work this way:
Determine the root bridge.

Root bridge of the spanning tree bridge ID is a bridge with the smallest (lowest). Each bridge has a unique identifier (ID) and a priority number which can be configured. To compare two bridge ID, priority number than the first time. If the priority number between the two bridges are the same, then that will be compared next is the MAC addresses. For example, if switches A (MAC = 0000.0000.1111) and B (MAC = 0000.0000.2222) have the same priority number, say 10, then switch A which will be selected to be the root bridge. If the network admin to switch B is to become root bridge, then the priority number switch B must be smaller than 10.

Determine the least cost paths to the root bridge.

Spanning tree that has been calculated to have the property that is the message from all devices connected to root bridge with traverse with the lowest cost path, the path of the tool to the root has the lowest cost of all paths of the tool to root.Cost of traversing a path is number of cost-cost of the existing segments in the path. Different technologies possessed a different default cost for the network segments. Administrators can modify the cost to visitor network segment that feels important.

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MikroTik Router

MikroTik RouterOS ™ is a linux operating system that can be used to
making the computer into a reliable network routers, includes various features
made for ip networks and wireless networks, suitable for use by ISPs and
hostspot provider.
There was also fitur2 follows:
* Firewall and NAT - stateful packet filtering; Peer-to-Peer protocol filtering; source and
destination NAT; classification by source MAC, IP addresses (networks or a list of
networks) and address types, port range, IP protocols, protocol options (ICMP type,
TCP flags and MSS), interfaces, internal packet and connection marks, ToS (DSCP)
byte, content, matching sequence / frequency, packet size, time and more ...
* Routing - Static routing; Equal cost multi-path routing; Policy based routing
(Classification done in firewall); RIP v1 / v2, OSPF v2, BGP v4
* Data Rate Management - Hierarchical HTB QoS system with bursts; per IP / protocol
/ Subnet / ports / firewall mark; PCQ, RED, SFQ, FIFO queue; CIR, MIR, contention
ratios, dynamic client rate equalizing (PCQ), bursts, Peer-to-Peer protocol Limitation
* HotSpot - HotSpot Gateway with RADIUS authentication and accounting; true plug-
and-Play access for network users; data rate of Limitation; differentiated firewall; traffic
quotas; real-time status information; walled-garden; customized HTML login pages;
iPass support; SSL secure authentication; advertisement support
* Point-to-Point tunneling protocols - PPTP, PPPoE and L2TP Access concentrators
and clients; PAP, CHAP, and MSCHAPv2 authentication protocols MSCHAPv1;
RADIUS authentication and accounting; MPPE encryption; compression for PPPoE;
Limitation of data rate; differentiated firewall; PPPoE dial on demand
* Simple tunnels - ipip tunnels, EoIP (Ethernet over IP)
* IPsec - IP security AH and ESP protocols; MODP Diffie-Hellman groups 1,2,5; MD5
and SHA1 hashing algorithms: DES, 3DES, AES-128, AES-192, AES-256 encryption
algorithms; Perfect Forwarding Secrecy (PFS) MODP groups 1,2,5
* Proxy - FTP and HTTP caching proxy server; HTTPS proxy; transparent DNS and
HTTP proxying; SOCKS protocol support; DNS static entries; support for caching on
a separate drive; access control lists; caching lists; parent proxy support
* DHCP - DHCP server per interface; DHCP relay; DHCP client; multiple DHCP
networks; static and dynamic DHCP leases; RADIUS support
* VRRP - VRRP protocol for high availability
* UPnP - Universal Plug-and-Play support
* NTP - Network Time Protocol server and client; synchronization with GPS system
* Monitoring / Accounting - IP traffic accounting, firewall actions logging, statistics
graphs accessible via HTTP
* SNMP - read-only access
* M3P - MikroTik Packet Packer Protocol for Wireless links and Ethernet
* MNDP - MikroTik Neighbor Discovery Protocol; also supports Cisco Discovery
Protocol (CDP)
* Tools - ping; traceroute; bandwidth test; ping flood; telnet; SSH; packet sniffer;
Dynamic DNS update tool
Layer 2 connectivity
* Wireless - IEEE802.11a/b/g wireless client and access point (AP) modes; Nstreme
and Nstreme2 proprietary protocols; Wireless Distribution System (WDS) support;
Virtual AP; 40 and 104 bit WEP: WPA pre-shared key authentication; access control
list; authentication with RADIUS server; roaming (for wireless client); AP bridging
* Bridge - spanning tree protocol; multiple bridge interfaces; bridge firewalling, MAC
* VLAN - Virtual LAN IEEE802.1q support on Ethernet and wireless links; multiple
VLANs: VLAN bridging
* Synchronous - V.35, V.24, E1/T1, X.21, DS3 (T3) media types; sync-PPP, Cisco
HDLC, Frame Relay line protocols; ANSI-617d (ANDI or annex D) and Q933a
(CCITT or annex A) Frame Relay LMI types
* Asynchronous - s * r * al PPP dial-in / dial-out; PAP, CHAP, MSCHAPv1 and
MSCHAPv2 authentication protocols; RADIUS authentication and accounting;
onboard s * r * al ports; modem pool with up to 128 ports; dial on demand
* ISDN - ISDN dial-in / dial-out; PAP, CHAP, and MSCHAPv2 MSCHAPv1
authentication protocols; RADIUS authentication and accounting; 128K bundle
support; Cisco HDLC, x75i, x75ui, x75bui line protocols; dial on demand
* SDSL - Single-line DSL support; line termination and network termination modes
Standard installation can be performed on a PC computer. PC that will be used as a router
mikrotikpun not require substantial resources for the use of standards,
for example, just as the gateway.
Following its minimum spec:
 CPU and motherboard - P1 pake ampe P4, AMD, Cyrix origin is not a multiprocessor
 RAM - minimum 32 MiB, maximum 1 GiB; 64 MiB or more highly recommended, if
would all be a proxy, it is recommended 1GB ... comparison, in memory 15MB
there is 1GB in proxy ..
 a minimum of 128MB HDD or Compact Flash ATA parallel, not recommended
using the UFD, SCSI, what else: D S-ATA
 NIC 10/100 or 100/1000
For the purposes of a large load (network of complex, complex routing, etc.)
advised to consider the selection of an adequate resource PC.
More complete can be found at www.mikrotik.com.
However Mikrotik is not free software, means we have to buy licenses
against any facility provided. Free trial is only for 24 hours.
We can buy software on CD mikrotik installed on a hard disk or
disk on module (DOM). If we buy the DOM does not need to install but stay
DOM plug on our PC IDE slot.
The following steps are the basics configured to setup mikrotik
network
simple as a gateway server.
1. The first step is to install RouterOS on a PC or connect the DOM.
2. Log In Mikrotik Routers via console:
MikroTik v2.9.7
Login: admin
Password: (blank)
Until this step we can get in on the machine Mikrotik. The default user is
admin
and without a password, just type admin and press the enter key.
3. To change the default password security
[Admin @ MikroTik]> password
old password: *****
new password: *****
Retype new password: *****
[Admin @ MikroTik]]>
4. Changing the name of the Mikrotik Router, in this step the server name will be changed into
"XAVIERO" (this name does bebas2 wrote mo replaced)
[Admin @ MikroTik]> system identity set name = XAVIERO
[Admin @ XAVIERO]>
5. See the interfaces on Mikrotik Router
[Admin @ XAVIERO]> interface print
Flags: X - disabled, D - dynamic, R - running
# NAME TYPE RX-RATE TX-RATE MTU
0 R ether1 ether 0 0 1500
1 R ether2 ether 0 0 1500
[Admin @ XAVIERO]>
6. Provide the IP address on the interface Mikrotik. Suppose ether1 we will use
for connection to the Internet with IP 192.168.0.1 and ether2 we will use to
our local network with IP 172.16.0.1
[Admin @ XAVIERO]> ip address add address = 192.168.0.1
netmask = 255.255.255.0 interface = ether1
[Admin @ XAVIERO]> ip address add address = 172.16.0.1
netmask = 255.255.255.0 interface = ether2
7. Looking at the IP address configuration we have given
[Admin @ XAVIERO]> ip address print
Flags: X - disabled, I - invalid, D - dynamic
# ADDRESS NETWORK BROADCAST INTERFACE
0 192.168.0.1/24 192.168.0.0 192.168.0.63 ether1
1 172.16.0.1/24 172.16.0.0 172.16.0.255 ether2
[Admin @ XAVIERO]>
8. Provides default gateway, the gateway to the Internet connection is assumed is
192.168.0.254
[Admin @ XAVIERO]> / ip route add gateway = 192.168.0.254
9. Viewing the routing table on the Mikrotik Routers
[Admin @ XAVIERO]> ip route print
Flags: X - disabled, A - active, D - dynamic,
C - connect, S - static, r - rip, b - bgp, o - ospf
# DST-ADDRESS G GATEWAY DISTANCE INTERFACE PREFSRC
0 ADC 172.16.0.0/24 172.16.0.1 ether2
1 ADC 192.168.0.0/26 192.168.0.1 ether1
2 A S 0.0.0.0 / 0 r 192.168.0.254 ether1
[Admin @ XAVIERO]>
10. Ping test to the Gateway to ensure the configuration is correct
[Admin @ XAVIERO]> ping 192.168.0.254
192.168.0.254 64 byte ping: ttl = 64 time <1 ms 192.168.0.254 64 byte ping: ttl = 64 time <1 ms 2 packets transmitted, 2 packets received, 0% packet loss round-trip min / avg / max = 0/0.0/0 ms [admin @ XAVIERO]>
11. DNS setup on Mikrotik Routers
[Admin @ XAVIERO]> ip dns set primary-dns = 192.168.0.10 = allowremoterequests
no
[Admin @ XAVIERO]> ip dns set secondary-dns = 192.168.0.11 = allowremoterequests
no
12. Viewing the configuration control
[Admin @ XAVIERO]> ip dns print
primary-dns: 192.168.0.10
secondary-dns: 192.168.0.11
allow-remote-requests: no
cache-size: 2048KiB
cache-max-ttl: 1w
cache-used: 16KiB
[Admin @ XAVIERO]>
13. Tests for the access domain, for example with ping domain name
[Admin @ XAVIERO]> ping yahoo.com
216 109 112 135 64 byte ping: ttl = 48 time = 250 ms
10 packets transmitted, 10 packets received, 0% packet loss
round-trip min / avg / max = 571/571.0/571 ms
[Admin @ XAVIERO]>
If you've managed to reply means DNS settings are correct.
14. Masquerading setup, if Mikrotik will we use as a gateway server
then to the client computer on the network can connect to the internet we need to
masquerading.
[Admin @ XAVIERO]> ip firewall nat add action = masquerade outinterface =
ether1 chain: srcnat
[Admin @ XAVIERO]>
15. Look at the configuration Masquerading
[Admin @ XAVIERO] ip firewall nat print
Flags: X - disabled, I - invalid, D - dynamic
0 chain = srcnat out-interface = ether1 action = masquerade
[Admin @ XAVIERO]>
After this step can be done to check the connection of local networks. And
if successful means we've managed to install Mikrotik Router as
Gateway server. After connecting to the network can be managed Mikrotik
using Winbox
which can be downloaded from the server mikrotik Mikrotik.com or from us.
Eg Ip address server
mikrotik we 192.168.0.1, via a browser to open http://192.168.0.1 and download the Winbox from
there.
If we want the client to get an IP address automatically then we need
setup dhcp server on mikrotik. Here are the steps:
1.Buat IP address pool
/ Ip pool add name = dhcp-pool ranges = 172.16.0.10-172.16.0.20
2. Add a DHCP Network and gateway that will be distributed to the client in
This example is 172.16.0.0/24 and network gateway 172.16.0.1
/ Ip dhcp-server network add address = 172.16.0.0/24 gateway = 172.16.0.1
3. Add the DHCP server (in this example is applied to the interface dhcp ether2)
/ Ip dhcp-server add interface = ether2 address-pool = dhcp-pool
4. See the status of DHCP server
[Admin @ XAVIERO]> ip dhcp-server print
Flags: X - disabled, I - invalid
# NAME INTERFACE RELAY ADDRESS-POOL LEASE-TIME ADD-ARP
0 X dhcp1 ether2
X stated that the DHCP server is not enabled so necessary enable
advance in step 5.
5. Do not Forget made enable dhcp server first
/ Ip dhcp-server enable 0
then check back to dhcp-server such as step 4, if an X is not there
is already active.
6. From the test client
c: \> ping www.google.com
for bandwidth controller, the system can or can simple queue with
mangle
[Admin @ XAVIERO] queue simple> add name = Komputer01
interfaces = ether2 target-address = 172.16.0.1/24 max-limit = 65536/131072
[Admin @ XAVIERO] queue simple> add name = Komputer02
interfaces = ether2 target-address = 172.16.0.2/24 max-limit = 65536/131072
and so on .

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READ MORE - MikroTik Router

Open System Interconnection

Hierarchical models enable you to design internetworks in layers. To understand the importance of layering, consider the Open System Interconnection (OSI) reference model, which is a layered model for implementing computer communications. Using layers, the OSI model simplifies the tasks required for two computers to communicate. Hierarchical models for internetwork design also use layers to simplify the tasks required for internetworking. Each layer can be focused on specific functions, allowing you to choose the right systems and features for each layer. Hierarchical models apply to both LAN and WAN design.
Benefits of Hierarchical Models

The many benefits of using hierarchical models for your network design include the following:
Cost savings
Ease of understanding
Easy network growth
Improved fault isolation

After adopting hierarchical design models, many organizations report cost savings because they are no longer trying to do it all in one routing/switching platform. The modular nature of the model enables appropriate use of bandwidth within each layer of the hierarchy, reducing wasted capacity.

Keeping each design element simple and small facilitates ease of understanding, which helps control training and staff costs. Management responsibility and network management systems can be distributed to the different layers of modular network architectures, which also helps control management costs.

Hierarchical design facilitates changes. In a network design, modularity allows creating design elements that can be replicated as the network grows, facilitating easy network growth. As each element in the network design requires change, the cost and complexity of making the upgrade is contained to a small subset of the overall network. In large, flat, or meshed network architectures, changes tend to impact a large number of systems.

Improved fault isolation is facilitated by structuring the network into small, easy-to-understand elements. Network managers can easily understand the transition points in the network, which helps identify failure points.

Today's fast-converging protocols were designed for hierarchical topologies. To control the impact of routing overhead processing and bandwidth consumption, modular hierarchical topologies must be used with protocols designed with these controls in mind, such as EIGRP.

Route summarization is facilitated by hierarchical network design. Route summarization reduces the routing protocol overhead on links in the network and reduces routing protocol processing within the routers.

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access point

As an access point, Level One WAP-6010 has a feature that is fairly simple. However, its performance is quite reliable for a small network, home, or even your office.

Forms of Level One WAP-6010 includes a compact and lightweight. All parts of the body Level One WAP-6010 is encased by a black plastic material so it will not attract too much attention.

Level One WAP-6010 has been using 802.11n wireless standard capable of providing a maximum speed of 300 Mbps hinggal. However, if the device is connected with the WAP-6010 is having problems of compatibility, WAP-6010 can also be used to customize standard 802.11b or 802.11g speed is lower.

In the face of the WAP-6010, there are buttons or indicator lights are not too many. Only there are three lights that indicate the activity of a LAN and WAN, and one button to activate the WPS feature. At the back, there is only one RJ45 port which doubles as a LAN port as well as WAN. Two existing antennas on the back is removable plug so that users can be more flexible when it wants to replace it with a more robust transmission power.

Setting the initial Level One WAP-6010 is quite easy. Even in his web interface, there is an option the Setup Wizard to configure easily with existing guidelines. But for users who are more proficient, you can make the necessary arrangements through the various features that exist beneath the menu.

Various features that exist on Level One WAP-6010 somewhat mediocre. There are a variety of standard features that are generally present in the wireless access point. Level One WAP-6010 can operate in various modes such as mode of AP, AP Client, Bridge, WDS (Wireless Distribution System), or even as a repeater. These functions also include safety standards, such as protection with WEP encryption, WPA, WPA2, WPA-PSK, and WPA2-PSK. In addition, Level One WAP-6010 can also perform filtering (filtering) of the MAC address that is banned or allowed to join the network. WPS function can also be activated if you use WPA or WPA2 encryption methods.

Performance Level One WAP-6010 including pretty good. Our test results with NetIQ Chariot test applications (connected to the wireless client adapter class N), showed a fairly good throughput. Average throughput of 67.10 Mbps produced with the highest achievement of 80.00 Mbps. WAP-6010 and the response is in receiving and forwarding data is also quite good. Value of the average response of 1.19 seconds, although some time had touched the figure 3.32 seconds.

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Metropolitan Area Network (MAN)

A Metropolitan Area Network (MAN) is one of a number of types of networks (see also LAN and WAN). A MAN is a relatively new class of network, it serves a role similar to an ISP, but for corporate users with large LANs. There are three important features which discriminate MANs from LANs or WANs:
The network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings or as large as the North of Scotland.
A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a single network provider who sells the service to the users. This level of service provided to each user must therefore be negotiated with the MAN operator, and some performance guarantees are normally specified.
A MAN often acts as a high speed network to allow sharing of regional resources (similar to a large LAN). It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.

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wide area network (WAN)

The electronic device modem is used computers establish communication over long distance through telephone line. A modem converts the digital signals into analog signals and vice versa. The modem enables the computer to send and to receive information over long distance through telephone line or microwave system.

A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN).

Wide area network (WAN) technologies connect a smaller number of devices that can be many kilometers apart. For example, if two libraries at the opposite ends of a city wanted to share their book catalog information, they would most likely make use of a wide area network technology, which could be a dedicated line leased from the local telephone company, intended solely to carry their data.

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Internet

The Internet is a network of computers that could be categorized as a WAN, connecting millions of computers around the world, without borders, where every person who has a computer can join the network by simply connecting to the internet service provider (internet service provider / ISP) such as Telkom Speedy , or Indosatnet. The Internet can be translated as an international networking (international network), for connecting computers internationally, or as internetworking (networking between networks) for network connecting millions around the world.

The Internet started when the U.S. Department of Defense (Department of Defense, USA) built a computer network in 1969, which was named ARPANET (Advanced Research Project Agency Network) in order to connect multiple computers within its universities doing military research, especially to build a network computer communication that is able to withstand nuclear attack. These networks continue to grow, more and more computers are involved, and the research side of software development is also growing. In May 1974, Vinton G. Cerf of Stanford University and Robert E. Kahn of the Department of Defense, USA, published a paper in IEEE Transaction on Communication entitled "A Protocol for Packet Network Intercommunication", the concept was later popular as a TCP / IP , when the ARPANET had adopted the protocol into standard protocols for ARPANET in 1983. The university, especially the University of California at Berkeley and then build the operating system of the Berkeley Software Distribution Unix) or BSD UNIX (known as Free BSD Unix) and the department of defense finance Bolt Baranek and Newman (BBN) for the implementation of the protocol to TCP / IP in BSD Unix to be implemented on the ARPANET, the forerunner of the Internet thus formed.

At the end of 1983, the ARPANET network divided into DARPANET (Defence ARPANET) and MILNET (Military Network). In 1985 the network was formed NFSNET (National Science Foundation Network) to connect the existing supercomputer in various universities in America and is connected to the ARPANET. NSFNET network developed by researchers continue to college. In 1988 the Internet backbone network is only a capacity of 56 Kbps. Although in 1990 the ARPANET officially closed, but the Internet network that has formed forwarded by the university in the United States and enter the university network in the Americas (Canada and South America) and networks in Europe to be part of the Internet. In 1992 the network backbone upgraded to T3 with a speed of 45 Mbps, and around 1995, increased again to OC-3 at a speed of 155 Mbps. Now the high-speed Internet backbone in order Gbps.

Internet topology is basically a mesh-topology, linking many types of networks via packet-switching systems, even if it can be said that the center of its are some of the NAP (Network Access Point) in San Francisco (Pacific Bell), Chicago (Ameritech) , New Jersey (Sprint), and Merit Access Exchange (MAE) in San Francisco (MAE West) and Washington, DC (MAE East) is handled by MFS Datanet.

Although no organization has the internet, but there are many organizations that maintain these networks through the establishment of standardization of protocols, rules, and access methods. Internet Engineering Task Force (IETF) to handle the technical problems that arise on the Internet, such as problems in the protocol, the architecture and operation of the Internet. Internet Research Task Force (IRTF) to handle the technical research, such as the addressing system and other engineering. Internet Assigned Numbers Authority (IANA) controls the distribution of IP address (IP #) to various countries and organizations. Internet Society (ISOC) to handle administrative and organizational structure of the Internet.

Commercial entity then provides access services to provide connections from the user's computer to the Internet, and the agency is called Internet access provider or ISP. Some well-known ISP in the world is America On Line (AOL), Australia OnLine, CompuServe, Genie, and Prodigy. In Indonesia there are TelkomNet, Indosatnet, Wasantara Net, InterNux, and so on. ISPs provide dial-up connection via a modem-telephone, wireless connection through WLAN antenna, or ADSL connection via the telephone. Connection protocol used is SLIP (Serial Line Interface Protocol) or PPP (Point-to-Point Protocol), where the SLIP connection is usually slower than the PPP.

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Client-server

Client-server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients.

A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Client-Server is one of the computer Industries newest and hottest buzzwords. There is no generic definition of client/server as it is used to depist number of nature, developing, and anticipateologies. However the general idea is that clients and servers are separate logical entities that work together Attention over a network to accomplish a task.

Client-server is very fashionable. As such, it might be just a temporary fad; but there is general recognition that it is something fundamental and far-reaching; for example, the Gartner Group, who are leading industry analysts in this field, have predicted that

"By 1995 client-server will be a synonym for computing."
Most of the initial client/server success stories involve small-scale applications that provide direct or indirect access to transactional data in legacy systems. The business need to provide data access to decision makers, the relative immaturity of client/server tools and technology, the evolving use of wide area networks and the lack of client/server expertise make these attractive yet low risk pilot ventures. As organizations move up the learning curve from these small-scale projects towards mission-critical applications, there is a corresponding increase in performance expectations, uptime requirements and in the need to remain both flexible and scalable. In such a demanding scenario, the choice and implementation of appropriate architecture becomes critical. In fact one of the fundamental questions that practitioners have to contend with at the start of every client/server project is - "Which architecture is more suitable for this project - Two Tier or Three Tier?". Interestingly, 17% of all mission-critical client/server applications are three tiered and the trend is growing, according to Standish Group International, Inc., a market research firm.

Architecture affects all aspects of software design and engineering. The architect considers the complexity of the application, the level of integration and interfacing required, the number of users, their geographical dispersion, the nature of networks and the overall transactional needs of the application before deciding on the type of architecture. An inappropriate architectural design or a flawed implementation could result in horrendous response times. The choice of architecture also affects the development time and the future flexibility and maintenance of the application. Current literature does not adequately address all these aspects of client/server architecture. This paper defines the basic concepts of client/server architecture, describes the two tier and three tier architectures and analyzes their respective benefits and limitations. Differences in development efforts, flexibility and ease of reuse are also compared in order to aid further in the choice of appropriate architecture for any given project.

Chapter-2
History & defintion:-
History

The University of Waterloo implemented Oracle Government Financials (OGF) in May of 1996. That moved UW's core accounting systems to a vendor-supported package on a Solaris/Unix environment and away from locally developed package(s) on IBM/VM. Plans at that time were to move more (if not all) business systems to a single vendor and to standardize on a single Data Base platform (Oracle for both). A very large state of the art Solaris system was purchased with the intention of co-locating these other Oracle supplied services on the same system with the OGF. Network security architecture was planned that involved isolating administrative networks, fire walling those networks with protocol filters and active traffic monitoring. Systems were purchased and deployed to implement that security architecture.
Much has changed in the interim. While the OGF now includes more services beyond the 1996 suite the plans to move all business systems has failed. Notably, we require People Soft/HRMS (Human Resources Management System) for Payroll (deployed in fourth quarter 1998) with People Soft/SIS (Student Information Services) to follow some years hence—Oracle was unable to deliver these key components for our business. Also we've discovered, while it's reasonable to require Oracle as the Data Base when other applications are specified, it's unreasonable to expect that they will be certified with the same versions of the Oracle Data Base and/or the underlying operating system. Technology changes quickly too: the state of the art Solaris system is no longer current. Networks were restructured to isolate administrative systems in the "Red Room" and administrative users throughout the campus. However, the administrative firewall and active traffic monitor was never implemented - recently it's been dismantled.

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Plug and Play

Devices (Plug and Play and non-Plug and Play) can be connected to your computer in several ways. Some devices, such as network adapters and sound cards, are connected to expansion slots inside your computer. Other devices, such as printers and scanners, are connected to ports on the outside of your computer. Some devices, known as PC Cards, connect only to PC Card slots on a portable computer.

For a device to work properly with Windows, software known as a device driver must be installed on the computer. Each device is supported by one or more device drivers, which are typically supplied by the device manufacturer. However, some device drivers are included with Windows. If the device is Plug and Play, Windows can automatically detect it and install the appropriate device drivers.

If the device is not automatically installed by Windows, the Found New Hardware Wizard will appear and ask you to insert any media (such as compact discs or floppy disks) that were provided with the device. Non-Plug and Play devices are installed using the Add Hardware Wizard in Control Panel. If you want to manually install device drivers, you must use Device Manager Before manually installing device drivers, you should consult the device documentation provided by the manufacturer.

Important

You must be logged on as an administrator or as a member of the Administrators group in order to install or configure a device if:

The device driver does not have the Designed for Windows Logo or a digital signature
Further action is required to install the device, requiring Windows to display a user interface.
The device driver is not already on your computer.
You need to configure a device using Device Manager.
Your computer is connected to a network; network policy settings may also prevent you from installing hardware.

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RMON

RMON are the functions that monitor the network performance, errors and other summary information. RMON functions can be implemented in a network device (HUB, LAN switch) or a station (PC, Server).

The Remote Network Monitoring (RMON) specification was created. RMON is often called a protocol, and you will sometimes see SNMP and RMON referred to as “the TCP/IP network management protocols”. However, RMON really isn't a separate protocol at all—it defines no protocol operations. RMON is in fact part of SNMP, and the RMON specification is simply a management information base (MIB) module that defines a particular set of MIB objects for use by network monitoring probes. Architecturally, it is just one of the many MIB modules that comprise the SNMP Framework.

RMON (Remote Network Monitoring) provides standard information that a network administrator can use to monitor, analyze, and troubleshoot a group of distributed local area networks (LANs) and interconnecting T-1/E-1 and T-2/E-3 lines from a central site. RMON specifically defines the information that any network monitoring system will be able to provide. It's specified as part of the Management Information Base (MIB ) in Request for Comments 1757 as an extension of the Simple Network Management Protocol (SNMP). The latest level is RMON Version 2 (sometimes referred to as "RMON 2" or "RMON2").

RMON can be supported by hardware monitoring devices (known as "probes") or through software or some combination. For example, Cisco's line of LAN switches includes software in each switch that can trap information as traffic flows through and record it in its MIB. A software agent can gather the information for presentation to the network administrator with a graphical user interface. A number of vendors provide products with various kinds of RMON support.

RMON collects nine kinds of information, including packets sent, bytes sent, packets dropped, statistics by host, by conversations between two sets of addresses, and certain kinds of events that have occurred. A network administrator can find out how much bandwidth or traffic each user is imposing on the network and what Web sites are being accessed. Alarms can be set in order to be aware of impending problems.

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ACEs

Access control in its basic definition can be anything from scanning your work badge for permit into your employment facility to the old fashion way of handing in a movie ticket for theatre access. It’s the idea and process by which people are identified and granted certain access and in most cases privileges.

Furthermore, computerized access control systems can be security devices that monitor and control entry to a house, apartment, or building. Because keys are easily duplicated, these systems are the best way to keep track of who is entering the area.

When it comes to your business, access control can be designed to restrict access to your building complex in order to increase security and control. There are now access control systems that do away with keys all together and provide computerized trails of who and when someone enters your property.

Access control devices can range from simple electronic keypads that secure a single door to large networked security systems for multiple buildings that can include parking lot gates, integration with time and attendance systems, exit controls, telephone entry, and multiple other levels of security. If a business owner implements sophisticated access control, there should be no need to replace lost keys, track down keys from terminated employees, or wonder who has access to which areas.

If you are seriously considering applying electronic access control devices within your business then know that the local and state law likely will require certain standards which will cost you time and money.

Access control is also important when it comes to work computers and programs, as well as personal computers. Any computer that is networked to any outside source is vulnerable. That is why you can now guard computer and program access with passwords, fingerprint identification, and even more means such as voice recognition or even retinal scans.

Meanwhile, access control from a homeowner’s point of view does not have to be costly and can help prevent unauthorized access onto your property and uphold safety once inside. Such access control devices can be applied to locksets, entry and exit control, even TV and computer privileges.

One of the most common access control devices found in the residential area is an electronic entry gate. Even if you have fencing around your home, you should consider installing a security gate in which people must enter an access code in order to gain entry into your driveway and into your home

ACLs can be used to filter traffic for various purposes including security, monitoring, route selection, and network address translation. ACLs are comprised of one or more Access Control Entries (ACEs). Each ACE is an individual line within an ACL.

ACLs on a Cisco ASA Security Appliance (or a PIX firewall running software version 7.x or later) are similar to those on a Cisco router, but not identical. Firewalls use real subnet masks instead of the inverted mask used on a router. ACLs on a firewall are always named instead of numbered and are assumed to be an extended list.

Access Control Entries (ACEs) provide a mapping of user groups to containers. There are five types of ACEs:
User Explicitly identifies an individual user and overrides any other ACE.
Same company Identifies the host organization. This ACE, called People in my company in the Communicator user interface, typically resides in the Company Container. By default, every user in the organization is a member of the Company Container unless the user is explicitly given membership in another container. For example, in Figure 6 above, roy@contoso.com and carl@contoso.com have Team level access
Domain ACE Identifies all users who are members of a specified SIP domain. This ACE is called people in in the Communicator user interface. As shown in Figure 6 above, msn.com is a member of the Public Container, so every member of the msn.com domain can see the user information that is included in the Public Container.
Federation ACE Identifies all users from partner organizations that are federated with the host organization. This ACE is called people in domains connected to my company in the Communicator user interface. For details about federation, see the Microsoft Office Communications Server 2007 Planning Guide.
Public Internet connectivity (PIC) ACE Identifies all users who belong to supported public IM service providers, which can include the MSN network of Internet services, Yahoo!, and AOL. Public Internet connectivity requires a separate license. This ACE is called people in public domains in the Communicator user interface. For details, see the Microsoft Office Communications Server 2007 Planning Guide.

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RJ45

The wires used for a LAN are mostly those headed by an RJ45 jack, which is similar to the jack plugged into your telephone set, but twice as big. Some Ethernet networks use coaxial cables, but that’s rarer, and present in rather large LANs, which span over areas between buildings. If you want to see what a coaxial cable is like, look at the thick cable that links your TV antenna to your TV set.

Ethernet is by far the most popular LAN protocol used today. It is so popular that if you buy a network card to install on your machine, you will get an Ethernet card, unless you ask for something different, if of course that different protocol is available.

Ethernet has evolved over the years. Today, you can get cheap Ethernet LAN cards with speeds up to 100 Mbps; while the fastest Ethernet reaches Gbps (1 Gbps = 1000 Mbps) in speed.

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Switches

Switches allow us to create a "dedicated road" between individual users (or small groups of users) and their destination (usually a file server). The way they work is by providing many individual ports, each running at 10 Mbps interconnected through a high speed backplane. Each frame, or piece of information, arriving on any port has a Destination Address field which identifies where it is going to. The switch examines each frame's Destination Address field and forwards it only to the port which is attached to the destination device. It does not send it anywhere else. Several of these conversations can go through the switch at one time, effectively multiplying the network's bandwidth by the number of conversations happening at any particular moment.

Another analogy which is useful for understanding how switches increase the speed of a network is to think in terms of plumbing. For sake of argument, assume that every PC on a network is a sink, and a 10 Mb/s connection is a 1/2-inch pipe. Normally, a 1/2-inch pipe will allow enough water to flow for one or two sinks to have enough water pressure to fill quickly. However, putting more sinks on that same 1/2-inch pipe will drop the water pressure enough that eventually the sinks take a very long time to fill.

To allow all sinks to fill quickly, we can connect the source of water to a larger (6-inch) pipe, and then connect each sink to the 6-inch pipe via its own 1/2-inch pipe. This guarantees that all sinks will have enough water pressure to fill quickly. See Figure One for an image of this concept.

Most network operating systems now use a "Client-Server" model. Here, we have many network users, or "clients" accessing a few common resources, or "servers." If we look at our previous highway example, an analogy would be to have a hundred roads for individuals all converging at two or three common points. If these common points are the same width as our individual roads, then they cause a major bottleneck, and the end result is exactly the same as if everyone was sharing one small road. This totally defeats the purpose of building all the individual roads in the first place.

The solution is to widen the road to our shared resource so that it can support the full load of most or all of the individual roads at once. In other words, we increase the bandwidth to our servers while connecting our clients at 10 Mbps. This is usually referred to as a High Speed Backbone. In networking slang, it is commonly called a "Fat Pipe."

This layout is splitting our overall network into four subnetworks. From left to right these subnetworks are outlined in Red, Green, Blue, and Violet. The Red subnetwork is a shared 10 Mbps setup, with all of the "Undemanding Users" sharing 10 Mbps of bandwidth. The Green and Blue subnets are dedicated 10 Mbps connections, sometimes referred to as "Private Ethernets." Here, each of the two power users has 10 Mbps of bandwidth dedicated to his or her machine, and this bandwidth is not shared with anyone else. Finally, we have our Violet subnetwork. This one is a Fast Ethernet setup running at a speed of 100 Mbps, and the bandwidth is shared by the two servers.

This is the most common way of setting up a switched network, and almost always results in an optimal price/performance ratio. We limit the amount of expensive Fast Ethernet hardware needed by only using it where its cost is justified by the performance it gives in handling the load at that point in the network, while leveraging an existing investment in 10 Mbps equipment in less demanding parts of the network. As a 10/100 switch is a fairly costly piece of equipment, each port we dedicate to a user is also rather expensive, so again these are only dedicated to individual users where that user's load justifies it. Finally, we can set up shared subnetworks which lump anywhere from two up to 100 users on one switch port.

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DCE

The success of the original Ethernet project lead to a joint development of a 10 Mbps standard in 1980. This time three companies were involved: Digital Equipment Corporation, Intel and Xerox. The Ethernet Version 1 specification that arose from this development formed the basis for the first IEEE 802.3 standard that was approved in 1983, and finally published as an official standard in 1985. Since these first standards were written and approved, a number of revisions have been undertaken to update the Ethernet standard and keep it in line with the latest technologies that are becoming available.

Ethernet standard releases

The Ethernet standard has undergone many releases and updates as a result of the continual development of the technology. In this way, Ethernet has been able to meet the ongoing needs of the industry.

Ethernet terminology

There is a convention for describing the different forms of Ethernet. For example 10Base-T and 100Base-T are widely seen in the technical articles and literature. The designator consists of a three parts:
The first number (typically one of 10, 100, or 1000) indicates the transmission speed in megabits per second.

The second term indicates transmission type: BASE = baseband; BROAD = broadband.

The last number indicates segment length. A 5 means a 500-meter (500-m) segment length from original Thicknet. In the more recent versions of the IEEE 802.3 standard, letters replace numbers. For example, in 10BASE-T, the T means unshielded twisted-pair cables. Further numbers indicate the number of twisted pairs available. For example in 100BASE-T4, the T4 indicates four twisted pairs.


Elements

The Ethernet LAN can be considered to consist of two main elements: the interconnecting media, and the network nodes.

The network nodes themselves fall into two categories. The first is the Data Terminal Equipment (DTE). These devices are either the source or destination of the data being sent. Devices such as PCs, file servers, print servers and the like fall into this category. The second category of devices are known as Data Communications Equipment (DCE). Devices that fall into this category receive and forward the data frames across the network, and they may often be referred to as 'Intermediate Network Devices' or Intermediate Nodes. They include items such as repeaters, routers, switches or even modems and other communications interface units.

The media through which the signals propagate are just as important. Initially coaxial cable with a single inner connector were used. Now either an Unshielded Twisted Pair (UTP) or a Shielded Twisted Pair (STP) are normally used. There are also optical fibre options, and these are often used for the much higher data rate systems.

Network topologies

There are several network topologies that can be used for Ethernet communications. The actual form used will depend upon the requirements.

Point to point - This is the simplest configuration as only two network units are used. It may be a DTE to DTE, DTE to DCE, or even a DCE to DCE. In this simple structure the cable is known as the network link. Links of this nature are used to transport data from one place to another and where it is convenient to use Ethernet as the transport mechanism.

Coaxial bus - This type of Ethernet network is rarely used these days. The systems used a coaxial cable where the network units were located along the length of the cable. The segment lengths were limited to a maximum of 500 metres, and it was possible to place up to 1024 DTEs along its length. This form of network is not used these days, although a very few legacy systems might just still be in use.

Star network - This type of Ethernet network has been the dominant topology since the early 1990s. It consists of a central network unit, which may be what is termed a multiport repeater or hub, or a network switch. All the connections to other nodes radiate out from this and are point to point links.

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STP

Most of the electronics devices we use, such as personal computers and laptops, communicate by sending each other Ethernet packets. They are notated as Ethernet stations. Each such station has a unique address (a globally unique number comprises of 48 bits). This is called a MAC address. Each station has a network interface card (NIC) which is aware of this number and would not let an Ethernet packet with another MAC address to enter the station itself. Also, this MAC address is added to any packet transmitted from this NIC. Eventually, any packet carries the unique source address along its way.

The main component in an Ethernet network is the Ethernet switch (For clarity we discuss here Switched Ethernet, and ignore an older Shared Ethernet scheme, which is almost obsolete). A switch is connected to the stations either by a copper cable or a fiber cable, and can connect to various speed stations. Since all the stations, regardless of the speed itself use the same packet format, the switch enables all stations, regardless of their speed to interconnect.

As defined by the IEEE 802.3 group, the Ethernet switch is designed to detect the Ethernet packet origin (Ethernet Source Address) and the packet destination (Ethernet Destination Address). The destination and the source addresses are the first parameters in an Ethernet packet, and are read by the switch. A table of addresses within the switch constantly learns and keeps records of the addresses that are included in the packets entering the switch over the time, and organizes the address table such that each address is related to the port from which certain source address entered the switch. This table is served to direct each incoming packet to its relevant output port, so that the packet should reach its destination eventually.

The detection of the addresses, learning the addresses, and the decision where to switch the packet to, are all done by hardware means, as fast as possible. This is why Ethernet can reach 100Gbits/second.

The IEEE 802.3 definition of Ethernet includes, of course, some more notions such as Full-Duplex, Flow Control, Cut-Through, Store-and-Forward, MAC, Broadcast and Unicast packets, Auto-negotiation, Spanning Tree (STP), and more. We will discuss these topics in further articles.

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IEEE 802.3

During the 90s of last century, many existing protocols and architectures in social networks. Engineers have developed several types of protocols, each for a specific use of disclosure of information such as the transfer of data, voice, broadcasting, data center, and so on. Among them can be found Token Ring, FDDI, ATM and more.

However, due to the simplicity and low cost of Ethernet components, it has prevailed in the end, and is now the most widely used protocol in local area networks (LAN). Faster Ethernet protocol have been defined that can fit many of the above applications and network.

In reality, Ethernet is a family of protocols, each with a different speed, and all are based on packet transfer, as defined by IEEE 802.3 standards group. Today there are Ethernet protocols and components ranging from 10Mbit/sec (10 million bits per second), a 100Mbit/sec (aka Fast Ethernet), 1 Gbit / sec (1 billion bits per second), 10Gbit/sec, 40Gbit / sec and recently 100Gbit/sec.

Ethernet is a protocol physical layer (layer1 and 2 of the 7 levels of the OSI model). It defines the way in which an Ethernet frame (packet) is transferred to the cable / fiber, Ethernet switch and how long the path may lead the structure to its destination.

Ethernet can run on twisted pair copper cables and fiber cables. Copper cables, usually able to transfer Ethernet packets up to 100 meters, and are mainly used in the creation of internal networks. The fiber can reach tens of kilometers and are used to interconnect between campus and down town.

Being a physical layer protocol, Ethernet is a carrier of data for higher level protocols such as IP (Internet Protocol). In fact, most of the cases in which people discuss the IP protocol, Ethernet protocol assumes discussed as a vector. The IP protocol allows communication between two logically separated networks. That is, Ethernet enables direct communication within a logical network, called the VLAN (Virtual LAN), and you must use the IP protocol to route the packet correctly between the Ethernet VLAN.

Most of electronic devices such as personal computers and laptops, to communicate by sending each Ethernet packet. They are identified as Ethernet stations. Each station has a unique address (a unique number consists of 48 bits total). This is called a MAC address. Each station has a network interface card (NIC) that is aware of this issue and would not let an Ethernet packet with a different MAC address to enter the station. Furthermore, this MAC address is added to any packages sent by this network adapter. In the end, each packet contains the unique address of origin in its path.

The main component of an Ethernet network is the Ethernet switch (For clarity we discuss here Switched Ethernet, and an old pattern of ignoring shared Ethernet, which is almost obsolete). A switch is connected to the remote via a copper wire or fiber cable, and can connect to different stations speed. Since all stations, regardless of the speed using the same packet format, the option is active all stations, regardless of their speed interconnect.

As defined by the IEEE 802.3 group, the Ethernet switch is designed to detect the origin of the Ethernet packets (Ethernet Source Address) and the destination of the packet (Ethernet destination address). The destination and source addresses are the first parameters in an Ethernet packet, and are read by the switch. A table of addresses within the switch is constantly learning and maintaining records of addresses that are included in the packets entering the switch in time, and organizes the address table so that each address is tied to the port from which the source address some joined switch. This table is used to route each incoming packet to its appropriate output port, so that the packet should reach its destination at the end.

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IEEE-488

The IEEE-488 interface bus, also
known as the General Purpose Interface Bus "GPIB" is an 8 bit wide
byte serial, bit parallel interface system which incorporates:
5 control lines
3 handshake lines
8 bi-directional data lines.
The entire bus consists of 24 lines, with the remaining lines occupied by ground
wires. Additional features include: TTL logic levels (negative true logic), the
ability to communicate in a number of different language formats, and no minimum
operational transfer limit. The maximum data transfer rate is determined by a
number of factors, but is assumed to be 1Mb/s.
Devices exist on the bus in any one of 3 general forms:
1. Controller
2. Talker
3. Listener
A single device may incorporate all three options, although only one option may
be active at a time. The Controller makes the determination as to which device
becomes active on the bus. The GPIB can handle only 1 ‘active’
controller on the bus, although it may pass operation to another controller. Any
number of active listeners can exist on the bus with an active talker as long as
no more then 15 devices are connected to the bus.
The controller determines which devices become active by sending interface
messages over the bus to a particular instrument. Each individual device is
associated with a 5 bit BCD code which is unique to that device. By using this
code, the controller can coordinate the activities on the bus and the individual
devices can be made to talk, listen (un-talk, un-listen) as determined by the
controller. A controller can only select a particular function of a device, if
that function is incorporated within the device; for example a ‘listen’
only device can not be made to talk to the controller.
The Talker sends data to other devices.
The Listener receives the information from the Talker.
In addition to the 3 basic functions of the controller, talker, and listener
the system also incorporates a number of operational features, such as; serial
poll, parallel poll, secondary talk and listen addresses, remote/local
capability, and a device clear (trigger).
Device dependent messages are moved over the GPIB in conjunction with the
data byte transfer control lines. These three lines (DAV, NRFD, and NDAC) are
used to form a three wire ‘interlocking’ handshake which controls the
passage of data. The active talker would control the ‘DAV’ line
(Data Valid) and the listener(s) would control the ‘NRFD’ (Not Ready
For Data), and the ‘NDAC’ (Not Data Accepted) line.
In the steady state mode the talker will hold ‘DAV’ high (no data
available) while the listener would hold ‘NRFD’ high (ready for data)
and ‘NDAC’ low (no data accepted. After the talker placed data on the
bus it would then take ‘DAV’ low (data valid). The listener(s) would
then send ‘NRFD’ low and send ‘NDAC’ high (data accepted).
Before the talker lifts the data off the bus, ‘DAV’ will be taken high
signifying that data is no longer valid. If the ‘ATN’ line (attention)
is high while this process occurs the information is considered data ( a device
dependent message), but with the "ATN’ line low the information is
regarded as an interface message; such as listen, talk, un-listen or un-talk.
The other five lines on the bus (‘ATN’ included) are the bus
management lines. These lines enable the controller and other devices on the bus
to enable, interrupt, flag, and halt the operation of the bus.
All lines in the GPIB are tri-state except for ‘SQR’, ‘NRFD’,
and ‘NDAC’ which are open-collector. The standard bus termination is a
3K resistor connected to 5 volts in series with a 6.2K resistor to ground - all
values having a 5% tolerance.
The standard also allows for identification of the devices on the bus. Each
device should have a string of 1 or 2 letters placed some where on the body of
the device (near or on the GPIB connector). These letters signify the
capabilities of the device on the GPIB bus.
C Controller
T Talker
L Listener
AH Acceptor Handshake
SH Source Handshake
DC Device Clear
DT Device Trigger
RL Remote Local
PP Parallel Poll
TE Talker Extended
LE Listener Extended

Devices are connected together on the bus in a daisy chained fashion.
Normally the GPIB connector (after being connected
to the device with the male side) has an female interface so that another
connector may be attached to it. This allows the devices
to be daisy chained. Devices are connected together in either a Linear or Star
fashion.
Most devices operate either via front panel control or HPIB control (REMOTE).
While using the front Panel the device is in the Local state, when receiving
commands via the HPIB, the device is in the Remote state. The device is placed
in the Remote state when ever the System Controller is reset or powered on,; also,
when the system controller sends out an Abort message. In addition, if the
device is addressed, it then enters the Remote state.

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READ MORE - IEEE-488

DTE

Data terminal equipment (DTE) is a term or concept initially developed by IBM to refer to any device that converts information into signals for transmission purposes, or converts received signals to information. In other word, it is a device that is the source or sink of information. Although the term has been applied to multiple layers in the OSI Reference Model (OSI-RM), it is most commonly associated with the Physical Layer and associated with bit transmission.

Although it is possible for two DTE to be directly connected using a null modem cable, the term DTE is most commonly associated with data circuit-terminating equipment (DCE), and a DTE is typically connected to a DCE. The DCE is typically responsible for providing clocking for synchronization purposes, which introduces another defining characteristic of DTE: they typically are not capable of generating a clock signal.

There are many examples of equipment that would be considered DTE. In the age when communication with a minicomputer or mainframe was accomplished using a dumb terminal, the terminal was the DTE on the circuit connecting it to the computer or a terminal server or cluster controller. A computer with terminal emulation software and using the serial interface built into most computers can also be a DTE. Other examples of DTE include:
A computer connected to a modem that it is using for dial access to a network resource (e.g., the Internet)
A router connected to a DSU through which it is connected to a private line, or packet network service
A router or computer connected to an ISDN NT1 through which it is connected to a network resource (e.g., the Internet)

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Computer networks have become the critical part of every business in the world

Computer networks have become the critical part of every business in the world. Networks use the communication devices such as hubs, switches and routers to better manage the traffic between nodes. Modern network use different kind of switching technology to benefit the network with more capacity, scalability, performance and speed. A switch is a centralized network communication device that is used to connect all the computers with each other. It uses to reduce the congestions in the networks and to increase the performance and capacity of the networks.

It can connect different types of the networks or the networks of the same type. Advanced switches offer the high speed links which are used to connect the different switches with each other. Switches determine the Ethernet and IP address of the computers and maintain the switching table.

Circuit Switching Technology

In the circuit switching, caller establishes the connection before making the call. All the network resources are fully allocated during the transmission. The path between the source and destination is determined by the circuit.

Virtual Circuit Packet Switching Technology

It is the combination of the circuit switching and datagram switching technology to make advantages of both technologies. It uses the traffic engineering features of the circuit switching and resources usage efficiency of the datagram packet switching technology.

Switching technology has always been evolved and a new generation known as optical switches is in place to provide the optimal performance, speed, scalability and efficiency to the networks.

In circuit switching, resources remain allocated during the full length of a communication, after a circuit is established and until the circuit is terminated and the allocated resources are freed. Resources remain allocated even if no data is flowing on a circuit, hereby wasting link capacity when a circuit does not carry as much traffic as the allocation permits. This is a major issue since frequencies (in FDM) or time slots (in TDM) are available in finite quantity on each link, and establishing a circuit consumes one of these frequencies or slots on each link of the circuit. As a result, establishing circuits for communications that carry less traffic than allocation permits can lead to resource exhaustion and network saturation, preventing further connections from being established. If no circuit can be established between a sender and a receiver because of a lack of resources, the connection is blocked.

A second characteristic of circuit switching is the time cost involved when establishing a connection. In a communication network, circuit-switched or not, nodes need to lookup in a forwarding table to determine on which link to send incoming data, and to actually send data from the input link to the output link. Performing a lookup in a forwarding table and sending the data on an incoming link is called forwarding. Building the forwarding tables is called routing. In circuit switching, routing must be performed for each communication, at circuit establishment time. During circuit establishment, the set of switches and links on the path between the sender and the receiver is determined and messages are exchanged on all the links between the two end hosts of the communication in order to make the resource allocation and build the routing tables. In circuit switching, forwarding tables are hardwired or implemented using fast hardware, making data forwarding at each switch almost instantaneous. Therefore, circuit switching is well suited for long-lasting connections where the initial circuit establishment time cost is balanced by the low forwarding time cost.

The circuit identifier (a range of frequencies in FDM or a time slot position in a TDM frame) is changed by each switch at forwarding time so that switches do not need to have a complete knowledge of all circuits established in the network but rather only local knowledge of available identifiers at a link. Using local identifiers instead of global identifiers for circuits also enables networks to handle a larger number of circuits.

Virtual circuit packet switching (VC-switching) is a packet switching technique which merges datagram packet switching and circuit switching to extract both of their advantages. VC-switching is a variation of datagram packet switching where packets flow on so-called logical circuits for which no physical resources like frequencies or time slots are allocated. Each packet carries a circuit identifier which is local to a link and updated by each switch on the path of the packet from its source to its destination. A virtual circuit is defined by the sequence of the mappings between a link taken by packets and the circuit identifier packets carry on this link. This sequence is set up at connection establishment time and identifiers are reclaimed during the circuit termination.

We have seen the trade-off between connection establishment and forwarding time costs that exists in circuit switching and datagram packet switching. In VC-switching, routing is performed at circuit establishment time to keep packet forwarding fast. Other advantages of VC-switching include the traffic engineering capability of circuit switching, and the resources usage efficiency of datagram packet switching. Nevertheless, a main issue of VC-Switched networks is the behavior on a topology change. As opposed to Datagram Packet Switched networks which automatically recompute routing tables on a topology change like a link failure, in VC-switching all virtual circuits that pass through a failed link are interrupted. Hence, rerouting in VC-switching relies on traffic engineering techniques.

In practice, major implementations of VC-switching are X.25 [70], Asynchronous Transfer Mode (ATM [6]) and Multiprotocol Label Switching (MPLS [50]). The Internet, today's most used computer network, is entirely built around the Internet Protocol (IP), which is responsible for routing packets from one host to another. Because of the central role of IP in the Internet, we now discuss how ATM and MPLS interact with IP.

You can use a network switching technology to provide LAN segmentation features. LAN switches can assist in increasing bandwidth availability for workstations because LAN switches support simultaneous switching of packets between the ports in the switch.

READ MORE - Computer networks have become the critical part of every business in the world

READ MORE - Computer networks have become the critical part of every business in the world

types of Virtual LANs

There are the following types of Virtual LANs:
Port-Based VLAN: each physical switch port is configured with an access list specifying membership in a set of VLANs.
MAC-based VLAN: a switch is configured with an access list mapping individual MAC addresses to VLAN membership.
Protocol-based VLAN: a switch is configured with a list of mapping layer 3 protocol types to VLAN membership - thereby filtering IP traffic from nearby end-stations using a particular protocol such as IPX.
ATM VLAN - using LAN Emulation (LANE) protocol to map Ethernet packets into ATM cells and deliver them to their destination by converting an Ethernet MAC address into an ATM address.

The IEEE 802.1Q specification establishes a standard method for tagging Ethernet frames with VLAN membership information. The IEEE 802.1Q standard defines the operation of VLAN Bridges that permit the definition, operation and administration of Virtual LAN topologies within a Bridged LAN infrastructure. The 802.1Q standard is intended to address the problem of how to break large networks into smaller parts so broadcast and multicast traffic would not grab more bandwidth than necessary. The standard also helps provide a higher level of security between segments of internal networks.

The key for the IEEE 802.1Q to perform the above functions is in its tags. 802.1Q-compliant switch ports can be configured to transmit tagged or untagged frames. A tag field containing VLAN (and/or 802.1p priority) information can be inserted into an Ethernet frame. If a port has an 802.1Q-compliant device attached (such as another switch), these tagged frames can carry VLAN membership information between switches, thus letting a VLAN span multiple switches. However, it is important to ensure ports with non-802.1Q-compliant devices attached are configured to transmit untagged frames. Many NICs for PCs and printers are not 802.1Q-compliant. If they receive a tagged frame, they will not understand the VLAN tag and will drop the frame. Also, the maximum legal Ethernet frame size for tagged frames was increased in 802.1Q (and its companion, 802.3ac) from 1,518 to 1,522 bytes. This could cause network interface cards and older switches to drop tagged frames as "oversized."

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