A patch panel or patch bay is a panel, typically rackmounted, that houses cable connections. One typically shorter patch cable will plug into the front side, while the back will hold the connection of a much longer and more permanent cable. The assembly of hardware is arranged so that a number of circuits, usually of the same or similar type, appear on jacks for monitoring, interconnecting, and testing circuits in a convenient, flexible manner.
Patch panels offer the convenience of allowing technicians to quickly change the path of select signals, without the expense of dedicated switching equipment. This was first used by early telephone exchanges, where the telephone switchboard (a massive array of patch panels) and a large room full of telephone operators running it was ubiquitous.
A passive device, typically flat plate holding feed through connectors, to allow circuit arrangements and rearrangements by simply plugging and unplugging patch cables.
CSMA/CD
Short for Carrier Sense Multiple Access / Collision Detection, a set of rules determining how network devices respond when two devices attempt to use a data channel simultaneously (called a collision). Standard Ethernet networks use CSMA/CD to physically monitor the traffic on the line at participating stations. If no transmission is taking place at the time, the particular station can transmit. If two stations attempt to transmit simultaneously, this causes a collision, which is detected by all participating stations. After a random time interval, the stations that collided attempt to transmit again. If another collision occurs, the time intervals from which the random waiting time is selected are increased step by step. This is known as exponential back off.
CSMA/CD is a type of contention protocol. Networks using the CSMA/CD procedure are simple to implement but do not have deterministic transmission characteristics. The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 8802.3.
Difference of CSMA/CA and CSMA/CD
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance): CSMA/CA is the principle medium access method employed by IEEE 802.11 WLANs. It is a "listen before talk" method of minimizing (but not eliminating) collisions caused by simultaneous transmission by multiple radios unlike CSMA/CD that deals with network transmissions once collisions have been detected.
IP address
An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP route messages based on the IP address of the protocol destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.
Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.
MAC address
Short for Media Access Control address, a hardware address that uniquely identifies each node of a network. In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI Reference Model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The MAC layer interfaces directly with the network medium. Consequently, each different type of network medium requires a different MAC layer.
On networks that do not conform to the IEEE 802 standards but do conform to the OSI Reference Model, the node address is called the Data Link Control (DLC) address.
Difference of client and server
A client is an application or system that accesses a (remote) service on another computer system known as a server by way of a network. Client devices normally request and receive information over the network. A server device hosts files, databases, Web sites, or other applications. Server is a computer or software providing services to remote client machines or applications, such as supplying page contents (texts or other resources) or returning query results. Server devices often feature higher-powered processors, more memory, and larger disk drives than clients.
