Host connectivity / Peer-to-peer

Host connectivity
5.1.11 This page will explain how NICs provide network connectivity.


The function of a NIC is to connect a host device to the network medium. A NIC is a printed circuit board that fits into the expansion slot on the motherboard or peripheral device of a computer. The NIC is also referred to as a network adapter. On laptop or notebook computers a NIC is the size of a credit card.

NICs are considered Layer 2 devices because each NIC carries a unique code called a MAC address. This address is used to control data communication for the host on the network. More will be learned about the MAC address later. NICs control host access to the medium.

In some cases the type of connector on the NIC does not match the type of media that needs to be connected to it. A good example is a Cisco 2500 router. This router has an AUI connector. That AUI connector needs to connect to a UTP Category 5 Ethernet cable. A transceiver is used to do this. A transceiver converts one type of signal or connector to another. For example, a transceiver can connect a 15-pin AUI interface to an RJ-45 jack. It is considered a Layer 1 device because it only works with bits and not with any address information or higher-level protocols.

NICs have no standardized symbol. It is implied that, when networking devices are attached to network media, there is a NIC or NIC-like device present. A dot on a topology map represents either a NIC interface or port, which acts like a NIC.

The next page discusses peer-to-peer networks.

Peer-to-peer
5.1.12 This page covers peer-to-peer networks.


When LAN and WAN technologies are used, many computers are interconnected to provide services to their users. To accomplish this, networked computers take on different roles or functions in relation to each other. Some types of applications require computers to function as equal partners. Other types of applications distribute their work so that one computer functions to serve a number of others in an unequal relationship.

Two computers generally use request and response protocols to communicate with each other. One computer issues a request for a service, and a second computer receives and responds to that request. The requestor acts like a client and the responder acts like a server.

In a peer-to-peer network, networked computers act as equal partners, or peers. As peers, each computer can take on the client function or the server function. Computer A may request for a file from Computer B, which then sends the file to Computer A. Computer A acts like the client and Computer B acts like the server. At a later time, Computers A and B can reverse roles.

In a peer-to-peer network, individual users control their own resources. The users may decide to share certain files with other users. The users may also require passwords before they allow others to access their resources. Since individual users make these decisions, there is no central point of control or administration in the network. In addition, individual users must back up their own systems to be able to recover from data loss in case of failures. When a computer acts as a server, the user of that machine may experience reduced performance as the machine serves the requests made by other systems.

Peer-to-peer networks are relatively easy to install and operate. No additional equipment is necessary beyond a suitable operating system installed on each computer. Since users control their own resources, no dedicated administrators are needed.

As networks grow, peer-to-peer relationships become increasingly difficult to coordinate. A peer-to-peer network works well with ten or fewer computers. Since peer-to-peer networks do not scale well, their efficiency decreases rapidly as the number of computers on the network increases. Also, individual users control access to the resources on their computers, which means security may be difficult to maintain. The client/server model of networking can be used to overcome the limitations of the peer-to-peer network.

The next page discusses a client/server network.