Structured cabling is building or campus telecommunications cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems.Structured cabling falls into six subsystems:[1][2]Demarcation Point is the point at which the telephone company network ends and connects with the wiring at the customer premises.Equipment or Telecommunications Rooms house equipment and wiring consolidation points which serve the users inside the building or campus.Vertical or Riser Cabling connects between the equipment/telecommunications rooms, so named because the rooms are typically on different floors.Horizontal wiring can be IW (inside wiring) or Plenum Cabling connects telecommunications rooms to individual outlets or work areas on the floor, usually through the wireways, conduits or ceiling spaces of each floor.Work-Area Components connect end-user equipment to outlets of the horizontal cabling system.Structured cabling design and installation is governed by a set of standards that specify wiring data centers, offices, and apartment buildings for data or voice communications using various kinds of cable, most commonly category 5e (CAT-5e), category 6 (CAT-6), and fibre optic cabling and modular connectors. These standards define how to lay thecabling in various topologies in order to meet the needs of the customer, typically using a central patch panel (which is normally 19 inch rack-mounted), from where each modular connection can be used as needed. Each outlet is then patched into a networkswitch (normally also rack-mounted) for network use or into an IP or PBX (private branch exchange) telephone system patch panel.Lines patched as data ports into a network switch require simple straight-through patch cables at the each end to connect a computer. Voice patches to PBXs in most countries require an adapter at the remote end to translate the configuration on 8P8C modular connectors into the local standard telephone wall socket. No adapter is needed in the U.S. as the 6P2C and 6P4C plugs most commomly used with RJ11 and RJ14 telephone connections are physically and electrically compatible with the larger 8P8C socket. RJ25 and RJ61 connections are physically but not electrically compatible, and cannot be used. In the UK, an adapter must be present at the remote end as the 6-pin BT socket is physically incompatible with 8P8C.It is common to color code patch panel cables to identify the type of connection, though structured cabling standards do not require it, except in the demarcation wall field.Structured cabling standardTIA-526-7 Measurement of Optical Power Loss of Installed Single-Mode Fiber Cable Plant – OFSTP-7 - (February 2002)TIA-526-14-A Optical Power Loss Measurements of Installed Multimode Fiber Cable Plant – OFSTP-14 - (August 1998)Installing Cable - Some GuidelinesWhen running cable, it is best to follow a few simple rules:Always use more cable than you need. Leave plenty of slack.Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.If it is necessary to run cable across the floor, cover the cable with cable protectors.Label both ends of each cable.Use cable ties (not tape) to keep cables in the same location togetherInstallation Factors:Topology - Horizontal cabling should be installed in a star configuration with each work-area outlet connected to a telecommunications closet.Appearance - The horizontal cabling should never be visible. Drop ceilings, raised access floor, conduit, wire raceways, ceiling pathways, cable trays, under carpet raceways, inter-stud wiring methods can all be used to hide the wire.Maximum Distances - The total cable length should not be more than 295 feet (90m) from the work area outlet to the telecommunications closet. The work area patch cable should be no more than 10 feet (3m) and the patch cables and jumpers in the telecommunications closet should not add up to more than 23 feet (7m) for a total maximum of 328 feet (100m). It is recommended that a patch cord should not exceed 16.7 feet (6m) and that a maximum of 2 patch cords per run is used. The above guidelines are provided by the EIA/TIA 568 Commercial Structured Wiring standard.Work Area Outlet - Each work area should have a minimum of two outlets: one for data and one for voice. If there is demand for high-throughput applications in some work areas, you may want to consider installing fiber to one of the outlets.Electromagnetic Interference - When installing horizontal cabling try to avoid running cable close to any electrical facilities that generate high levels of EMI like photocopiers, motors, transformers, and elevators. Never install the horizontal cabling in the same outlet as electrical components. If running the horizontal cable parallel with electrical wiring, keep it at least 15 inches away. If you must cross electrical wiring, do so at a 90 degree angle.Recognized Media:Four pair 100-ohm UTP cableTwo pair 150-ohm shielded twisted pair (STP) cable62.5/125 micron multimode fiber optic cable50-ohm coaxial cableAdvantages of wireless networks:Mobility - With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc. More an more businesses are also offering free WiFi access.Fast setup - If your computer has a wireless adapter, locating a wireless network can be as simple as clicking "Connect to a Network" -- in some cases, you will connect automatically to networks within range.Cost - Setting up a wireless network can be much more cost effective than buying and installing cables.Integrated Services Digital Network (ISDN) is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. It was first defined in 1988 in the CCITT red book.[1] Prior to ISDN, the phone system was viewed as a way to transport voice, with some special services available for data. The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI), Primary Rate Interface (PRI) and Broadband ISDN (B-ISDN).ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions. Channel bonding can achieve a greater data rate; typically the ISDN B-channels of 3 or 4 BRIs (6 to 8 64 kbit/s channels) are bonded.ISDN should not be mistaken for its use with a specific protocol, such as Q.931 whereby ISDN is employed as the network, data-link and physical layers in the context of the OSI model. In a broad sense ISDN can be considered a suite of digital services existing on layers 1, 2, and 3 of the OSI model. ISDN is designed to provide access to voice and data services simultaneously.However, common use has reduced ISDN to be limited to Q.931 and related protocols, which are a set of protocols for establishing and breaking circuit switched connections, and for advanced call features for the user. They were introduced in 1986.[2]ISDN elementsIntegrated services refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people's complete communications needs (apart from broadband Internet access and entertainment television) at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to Integrated Switching and Transmission[3] in that telephone switching and carrier wavetransmission are integrated rather than separate as in earlier technology.ATM is a connection-oriented, unreliable (does not acknowledge the receipt of cells sent), virtual circuit packet switching technology. Unlike most connectionless networking protocols, ATM is a deterministic networking system — it provides predictable, guaranteed quality of service. From end to end, every component in an ATM network provides a high level of control. ATM technology includes:Scalable performance. ATM can send data across a network quickly and accurately, regardless of the size of the network. ATM works well on both very low and very high-speed media.Flexible, guaranteed Quality of Service (QoS). ATM allows the accuracy and speed of data transfer to be specified by the client. This feature distinguishes ATM from other high-speed LAN technologies such as gigabit Ethernet. The QoS feature of ATM also supports time dependent (or isochronous) traffic. Traffic management at the hardware level ensures that quality service exists end-to-end. Each virtual circuit in an ATM network is unaffected by traffic on other virtual circuits. Small packet size and a simple header structure ensure that switching is done quickly and that delays due to high traffic are minimized.Unobstructed speed. ATM imposes no architectural speed limitations. Its pre-negotiated virtual circuits, fixed-length cells, message segmentation and re-assembly in hardware, and hardware-level switching all help support extremely fast forwarding of data.Integration of different traffic types. ATM supports integration of voice, video, and data services on a single network. ATM over Asymmetric Digital Subscriber Line (ADSL) enables residential access to these services.Atm Fixed length cell:Because ATM uses small (53-byte), fixed-length cells that require less logic to process, the network spends no time determining where a particular cell begins and ends. The small cell size ensures that delays in forwarding cells are minimized. Because the cell size is so predictable, buffer usage and analysis algorithms can be simplified and optimized.Traditional LAN technologies, such as Ethernet, have inherent speed limitations Either the underlying infrastructure (the cable) or the segment length must be changed to support fast traffic. However, unlike Ethernet and Token Ring, ATM has no such imposed limitations. If you can invent a faster physical layer — if you can design a quicker method of transmitting data from one place to another over one wire or many wires — ATM can work over that physical layer and at those new speeds. In addition, ATM allows information with different requirements and from different nodes to be transmitted nearly simultaneously without conflict.The User Datagram Protocol (UDP) is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol (IP) network without requiring prior communications to set up special transmission channels or data paths. The protocol was designed by David P. Reed in 1980 and formally defined in RFC UDP uses a simple transmission model without implicit handshaking dialogues for providing reliability, ordering, or data integrity. Thus, UDP provides an unreliable service and datagrams may arrive out of order, appear duplicated, or go missing without notice. UDP assumes that error checking and correction is either not necessary or performed in the application, avoiding the overhead of such processing at the network interface level. Time-sensitive applications often use UDP because dropping packets is preferable to waiting for delayed packets, which may not be an option in a real-time system.[1] If error correction facilities are needed at the network interface level, an application may use the Transmission Control Protocol (TCP) or Stream Control Transmission Protocol(SCTP) which are designed for this purpose.UDP's stateless nature is also useful for servers answering small queries from huge numbers of clients. Unlike TCP, UDP is compatible with packet broadcast (sending to all on local network) and multicasting (send to all subscribers).[2]Common network applications that use UDP include: the Domain Name System (DNS), streaming media applications such as IPTV, Voice over IP (VoIP),Comparison of UDP and TCPMain article: Transport LayerTransmission Control Protocol is a connection-oriented protocol, which means that it requires handshaking to set up end-to-end communications. Once a connection is set up user data may be sent bi-directionally over the connection.Reliable – TCP manages message acknowledgment, retransmission and timeout. Multiple attempts to deliver the message are made. If it gets lost along the way, the server will re-request the lost part. In TCP, there's either no missing data, or, in case of multiple timeouts, the connection is dropped.Ordered – if two messages are sent over a connection in sequence, the first message will reach the receiving application first. When data segments arrive in the wrong order, TCP buffers the out-of-order data until all data can be properly re-ordered and delivered to the application.Heavyweight – TCP requires three packets to set up a socket connection, before any user data can be sent. TCP handles reliability and congestion control.Streaming – Data is read as a byte stream, no distinguishing indications are transmitted to signal message (segment) boundaries.UDP is a simpler message-based connectionless protocol. Connectionless protocols do not set up a dedicated end-to-end connection. Communication is achieved by transmitting information in one direction from source to destination without verifying the readiness or state of the receiver.Unreliable – When a message is sent, it cannot be known if it will reach its destination; it could get lost along the way. There is no concept of acknowledgment, retransmission or timeout.Not ordered – If two messages are sent to the same recipient, the order in which they arrive cannot be predicted.Lightweight – There is no ordering of messages, no tracking connections, etc. It is a small transport layer designed on top of IP.Datagrams – Packets are sent individually and are checked for integrity only if they arrive. Packets have definite boundaries which are honored upon receipt, meaning a read operation at the receiver socket will yield an entire message as it was originally sent.No congestion control - UDP itself does not avoid congestion, and it's possible for high bandwidth applications to trigger congestion collapse, unless they implement congestion control measures at the application level.Data Encapsulation in TCP/IPThe “N-1, N-2” stuff makes this seem more difficult than it really is, so let’s use a real-world (simplified) example instead. The Transmission Control Protocol (TCP)operates at layer 4 of the OSI model. It transmits messages called segments that contain data encapsulated from higher-layer protocols. The layer below TCP is theInternet Protocol (IP) at layer 3. It receives data from TCP and encapsulates it for transmission.So, in the formal language of the OSI Reference Model, TCP segments are created as layer 4 PDUs. When passed to IP, they are treated as layer 3 SDUs. The IP software packages these SDUs into messages called IP packets or IP datagrams, which are layer 3 PDUs. These are in turn passed down to a layer 2 protocol, say Ethernet, which treats IP datagrams as layer 2 SDUs, and packages them into layer 2 PDUs (Ethernet frames) which are sent on layer 1. (Actually, in some technologies further encapsulation even occurs at layer one prior to transmission.)On the receiving device, the process of encapsulation is reversed. The Ethernet software inspects the layer 2 PDU (Ethernet frame) and removes from it the layer 2 SDU (IP datagram) which it passes up to IP as a layer 3 PDU. The IP layer removes the layer 3 SDU (TCP segment) and passes it to TCP as a layer 4 PDU. TCP in turn continues the process, going back up the protocol layer stack. The complete process is illustrated in Figure 16.Count-to-infinity problemThe Bellman-Ford algorithm does not prevent routing loops from happening and suffers from the count-to-infinity problem. The core of the count-to-infinity problem is that if A tells B that it has a path somewhere, there is no way for B to know if the path has B as a part of it. To see the problem clearly, imagine a subnet connected like as A-B-C-D-E-F, and let the metric between the routers be "number of jumps". Now suppose that A is taken offline. In the vector-update-process B notices that the route to A, which was distance 1, is down - B does not receive the vector update from A. The problem is, B also gets an update from C, and C is still not aware of the fact that A is down - so it tells B that A is only two jumps from C (C to B to A) , which is false. This slowly propagates through the network until it reaches infinity (in which case the algorithm corrects itself, due to the "Relax property" of Bellman Ford).