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Radio Communication and Networks

Radio communication is usually associated with wireless communication systems like taxicab radios and marine radio, as well as broadcast systems such AM/FM radio and television. Other wireless radio technologies include cordless phones, cellular phones, pagers, garage door openers, walkie-talkies, satellite messaging systems, amateur packet radio, and citizens band radio. Many copper-cable network technologies also operate in the frequency bands allocated to radio. The topic “Electromagnetic Spectrum” has a table that illustrates the most common uses of the radio spectrum.

RADIUS (Remote Authentication Dial-In User Service)

Remote Authentication Dial-In User Service (RADIUS) is a client/serverprotocol and software that enables remote access servers to connect to a central server to authenticate dial-in users and authorize their access to the requested system or service. RADIUS stores user profiles in a central database that all remote servers can share.RADIUS provides enhanced security, letting administrators set up a policy from a single network point. Another advantage of having a central service is the ease of tracking usage for billing and for network statistics. Created by Livingston (now owned by Lucent), RADIUS is a de facto industry standard used by a number of network product companies and is a proposed IETF standard.

RAID (Redundant Arrays of Inexpensive Disks)

RAID defines techniques for combining disk drives into arrays. Data is written across all drives, which improves performance and protects data. The alternative is to use one large drive, which does not have the performance benefits of an array and is a single point of failure.

A RAID appears as a single drive. Data is written evenly across the drives by using a technique called striping. Striping divides data over two or more drives.

RAP (Resource Allocation Protocol)

RAP is not a protocol itself, but the name of an IETF working group that is attempting to develop standards for providing QoS (Quality of Service) for the Internet. Specifically, the Resource Allocation Protocol Working Group is creating a scalable policy control model for RSVP. The working group also developed COPS (Common Open Policy Service) protocol, which is used in policy-based management.

RARP (Reverse Address Resolution Protocol)

RARP is an Internet protocol that performs the opposite task of ARP (Address Resolution Protocol). It translates a MAC (Medium Access Control) address, which is the address hard-wired into network interface cards, into the IP address that has been assigned to the system with the MAC address. The protocol was originally used to obtain an IP address for Ethernet-connected diskless workstations. Since there is no disk on which to store an IP address, a diskless workstation must obtain the IP address from another source and store it in memory while it is running.

RAS (Remote Access Server)

In the world of computer networking, redundant methods are used to

protect systems from failure, to protect data from loss and corruption, and to ensure that communication systems stay online and provide a required amount of performance. Some examples are given here:

* Backup and archiving is the most obvious form of redundancy. You create copies of files on alternate disks or backups.

* CRC (cyclic redundancy check) is a method for detecting errors in transmitted data.

Remote access covers a range of techniques that let home users, mobile users, and remote office users access resources on a corporate network, or the Internet in the case of an ISP. Remote access methods should let remote users access a network as if they are directly attached to it and using the same protocols. Note that this topic discusses access to corporate networks, but there are many similarities to connecting with ISPs to access the Internet.

There are two types of remote operations:

* Remote control : In this mode, the dial-up user remotely controls a computer that is connected to the corporate network. Only keyboard commands and screen updates cross the dial-up connection.

* Remote node : In this mode, the user’s remote computer becomes another node on the network. All requests and responses cross the dial-up connection, usually via PPP links that encapsulate TCP/IP protocols.

Ring Network Topology

Ring network topology is a closed-loop to pology that does not require terminators .The token ring topology forms a logical ring but has the cable layout of a star topology with a central hub. The ring is actually maintained in the hub. When a workstation attaches to the hub, the

ring extends out to the workstation through the cable and back again to the hub. If another hub is attached, the ring is maintained by running cables from the ring-out connector on the first hub to the ring-in connector on the second hub, and from the ring-out connector on the second hub to the ring-in connector on the firsthub.

RIP (Routing Information Protocol)

RIP (Routing Information Protocol) is common protocol used for managing router information within a self-contained network such as a corporate local area network or an interconnected group of such LANs. Using RIP, a gatewayhost (with a router) sends its entire routing table (which lists all the other hosts it knows about) to its closest neighbor host every 30 seconds. The neighbor host in turn will pass the information on to its next neighbor and so on until all hosts within the network have the same knowledge of routing paths, a state known as network convergence. RIP uses a hop count as a way to determine network distance. (Other protocols use more sophisticated algorithms that include timing as well.) Each host with a router in the network uses the routing table information to determine the next host to route a packet to for a specified destination.

RMON (Remote Monitoring)

Remote Monitoring (RMON) is a specification that allows network monitors and console systems to exchange network-monitoring data. RMON provide network administrators with more freedom in choosing network-monitoring probes and consoles with features that meet their particular needs. The RMON specification defines what can be exchanged between RMON-compliant console managers and network probes. As such, RMON provides network administrators with comprehensive network-fault diagnosis, planning, and performance-tuning information. RMON was defined by the user community with the help of the Internet Engineering Task Force (IETF).

Routers are internetworking devices that connect similar and

heterogeneous network segments Into internetworks. Routers are layer 3 networking devices. In contrast, repeaters operate at the Physical layer while bridges (and switches) operate at the data link layer(layer2). The traditional view of a router is a box with two or more interfaces. The interfaces provide connections for networks and/or point-to-point links.

There is usually a serial interface for connecting a management console. This interface allows managers to securely configure a router by avoiding sending management information over the network controlled by the router.

This topic discusses routing protocols and algorithms. (routing switches). A historical perspective on the development of routing on the Internet is referenced under “Routing on the Internet.” Also note that this topic covers IP routing, although other routable protocols such as IPX (Internetwork Packet Exchange) exist .Routing is a packet-forwarding process that takes place on internetworks (i.e., separate networks that are joined by routers). When a host sends a packet, it is either for a local host on the same network or a host on a remote network. If the packet does not have a local IP network address, the host sends the packet to the default router ,which forwards the packet to other networks.

See Multilayer Switching.

Routing on the Internet

The Internet is a massive internetwork of router-connected networks, consisting of thousands of autonomous systems that are each managed by different authorities. These networks share traffic and exchange routing information.

RPC (Remote Procedure Call)

A procedure is a software routine that runs in a computer. A procedure call is a request by one procedure to another procedure for some service. This is relatively easy when both procedures are running in the same computer. A remote procedure call is a request made by a process in one computer to another computer across a network. RPCs are a form of middleware. Other forms of middleware are discussed under “Middleware and Messaging.”

RSTP

)802.1w Rapid Spanning Tree(

The 802.1w Rapid Reconfiguration of Spanning Tree protocol was created as an improvement over the original 802.1D Spanning Tree Protocol. The 802.1w RSTP improves upon STP by providing rapid reconfiguration capability.Both standards maintain the quality of bridged LAN or media access control (MAC) service. However, RSTP offers greater rigidity and availability. The secret to RSTP’s advantage is shorter recovery time. Once a link is lost or the network structure has changed, STP requires 30 to 60 seconds to detect the changes and reconfigure, greatly affecting network performance. RSTP reduces the time it takes to reconfigure and restore service, less than a second, at the same time RSTP remains compatible with STP.