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(1) Address Resolution Protocol (ARP)

The address resolution protocol (arp) is a protocol used by the Internet Protocol (IP) [RFC826], specifically IPv4, to map IP network addresses to the hardware addresses used by a data link protocol. The protocol operates below the network layer as a part of the interface between the OSI network and OSI link layer. It is used when IPv4 is used over Ethernet.

The term address resolution refers to the process of finding an address of a computer in a network. The address is "resolved" using a protocol in which a piece of information is sent by a client process executing on the local computer to a server process executing on a remote computer. The information received by the server allows the server to uniquely identify the network system for which the address was required and therefore to provide the required address.

The address resolution procedure is completed when the client receives a response from the server containing the required address. An Ethernet network uses two hardware addresses which identify the source and destination of each frame sent by the Ethernet. The destination address (all 1's) may also identify a broadcast packet (to be sent to all connected computers). The hardware address is also known as the Medium Access Control (MAC) address, in reference to the standards which define Ethernet. Each computer network interface card is allocated a globally unique 6 byte link address when the factory manufactures the card (stored in a PROM). This is the normal link source address used by an interface. A computer sends all packets which it creates with its own hardware source link address, and receives all packets which match the same hardware address in the destination field or one (or more) pre-selected broadcast/multicast addresses.

(2) Electronic Mail

One of the most prominent uses of networking since the first networks were devised, has been electronic mail. It started as a simple service that copied a file from one machine to another, and appended it to the recipient's mailbox file. Basically, this is still what email is all about, although an ever growing net with its complex routing requirements and its ever increasing load of messages has made a more elaborate scheme necessary.

Various standards of mail exchange have been devised. Sites on the Internet adhere to one laid out in RFC-822, augmented by some RFCs that describe a machine-independent way of transferring special characters, and the like. Much thought has also been given recently to ``multi-media mail'', which deals with including pictures and sound in mail messages. Another standard, X.400, has been defined by CCITT.

Quite a number of mail transport programs have been implemented for systems. One of the bestknown is the University of Berkeley's sendmail, which is used on a number of platforms. The original author was Eric Allman, who is now actively working on the sendmail team again. There are two ports of sendmail-5.56c available, one of which will be described in chapter- . The sendmail version currently being developed is 8.6.5.

The mail agent most commonly used with is smail-3.1.28, written and copyrighted by Curt Landon Noll and Ronald S.-Karr. This is the one included in most distributions. In the following, we will refer to it simply as smail, although there are other versions of it which are entirely different, and which we don't describe here.

Compared to sendmail, smail is rather young. When handling mail for a small site without complicated routing requirements, their capabilities are pretty close. For large sites, however, sendmail always wins, because its configuration scheme is much more flexible.

Both smail and sendmail support a set of configuration files that have to be customized. Apart from the information that is required to make the mail subsystem run (such as the local hostname), there are many more parameters that may be tuned. sendmail's main configuration file is very hard to understand at first. It looks as if your cat had taken a nap on your keyboard with the shift key pressed. smail configuration files are more structured and easier to understand than sendmail's, but don't give the user as much power in tuning the mailer's behavior. However, for small UUCP or Internet sites the work required in setting up any of them is roughly the same.

(3) Error detection and Recovery

The Run Control system is responsible for error logging and it is the central system which should cope in an expeditious manner with various types of failures, including failures attributable to other systems such as the trigger, readout or slow control system, etc. Depending on the type of error, emergency instructions or dedicated recovery procedures can be invoked either automatically or by requesting the operator intervention, for instance, to ignore errors, to try again, to reset the entire system to a well defined state, and so on. The procedures are supposed to be as intelligent as possible to guide the operator to fix problems in a simple manner.

(4) Flow Control Systems

Weatherford’s custom life-of-well Flow Control and Well Servicing Equipment are more than just “as-needed” solutions. When brought in at the front end of a project, these systems can provide long-term savings for a variety of completion applications.

We also offer customers a unique approach to flow control, which includes: 1) Working with them to create an optimized well design that fulfills life of well requirements for flow control and well servicing, and 2) Supplying well-designed, manufactured and supported equipment that allows successful well servicing throughout the field life.

Our range of products and services include:

• Uniset Well Servicing Systems that optimize well completion designs.
• Standard Flow Control products.
• Advanced Flow Control Systems not offered by any of our competitors.
• Heavy-Duty Fishing Services that include world-class operators and cutting edge equipment.
• High-Impact Petroline Wire line Tool string that is the choice of wire line professionals.
• Rolling Systems that increase the operating envelope.
• Petroline Slick plugs for reducing operational costs.

(5) SNMP Background

The Simple Network Management Protocol (SNMP) is an application-layer protocol designed to facilitate the exchange of management information between network devices. By using SNMPtransported data (such as packets per second and network error rates), network administrators can more easily manage network performance, find and solve network problems, and plan for network growth.

Like the Transmission Control Protocol (TCP), SNMP is an Internet protocol. Internet protocols are created by the Internet community, a group of individuals and organizations that developed and/or regularly use a large, diverse international network called the Internet. The Internet derived from the Advanced Research Projects Agency network (ARPANET), which was created by packet switching researchers in the early 1970s.

There are two versions of SNMP: Version 1 and Version 2. Most of the changes introduced in Version 2 increase SNMP's security capabilities. Other changes increase interoperability by more rigorously defining the specifications for SNMP implementation. SNMP's creators believe that after a relatively brief period of coexistence, SNMP Version 2 (SNMPv2) will largely replace SNMP Version 1 (SNMPv1). SNMP is part of a larger architecture called the Internet Network Management Framework (NMF), which is defined in Internet documents called requests for comments (RFCs). The SNMPv1 NMF is defined in RFCs 1155, 1157, and 1212, and the SNMPv2 NMF is defined by RFCs 1441 through 1452.

Today, SNMP is the most popular protocol for managing diverse commercial internetworks as well as those used in universities and research organizations. SNMP-related standardization activity continues even as vendors develop and release state-ofthe-art, SNMP-based management applications. SNMP is a relatively simple protocol, yet its feature set is sufficiently powerful to handle the difficult problems presented in trying to manage today's heterogeneous networks.

SNMP Technology

SNMP is part of the Internet network management architecture. This architecture is based on the interaction of many entities, as described in the following section.

The Internet Management Model As specified in Internet RFCs and other documents, a network management system comprises:

• Network elements -- Sometimes called managed devices, network elements are hardware devices such as computers, routers, and terminal servers that are connected to networks.
• Agents -- Agents are software modules that reside in network elements. They collect and store management information such as the number of error packets received by a network element.
• Managed object -- A managed object is a characteristic of something that can be managed. For example, a list of currently active TCP circuits in a particular host computer is a managed object. Managed objects differ from variables, which are particular object instances. Using our example, an object instance is a single active TCP circuit in a particular host computer. Managed objects can be scalar (defining a single object instance) or tabular (defining multiple, related instances).
• Management information base (MIB) -- A MIB is a collection of managed objects residing in a virtual information store. Collections of related managed objects are defined in specific MIB modules.
• Syntax notation -- A syntax notation is a language used to describe a MIB's managed objects in a machine-independent format. Consistent use of a syntax notation allows different types of computers to share information. Internet management systems use a subset of the International Organization for Standardization's (ISO's) Open System Interconnection (OSI) Abstract Syntax Notation 1 (ASN.1) to define both the packets exchanged by the management protocol and the objects that are to be managed.
• Structure of Management Information (SMI) -- The SMI defines the rules for describing management information. The SMI is defined using ASN.1.
• Network management stations (NMSs) -- Sometimes called consoles, these devices execute management applications that monitor and control network elements. Physically, NMSs are usually engineering workstation-caliber computers with fast CPUs, megapixel color displays, substantial memory, and abundant disk space. At least one NMS must be present in each managed environment.