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Before we describe WAP model, first we would like you to understand how Standard Internet works. The Internet model makes it possible for a client to reach services on a large number of origin servers, each addressed by a unique Uniform Resource Locator (URL). A markup language - the Wireless Markup Language (WML) has been adapted to develop optimized WAP applications. The user selects an option on their mobile device that has a URL with Wireless Markup language (WML) content assigned to it. The phone sends the URL request via the phone network to a WAP gateway using the binary encoded WAP protocol.
The gateway translates this WAP request into a conventional HTTP request for the specified URL and sends it on to the Internet. IP is the primary protocol in the Internet Layer of the Internet Protocol Suite and has the task of delivering distinguished packets from the source host to the destination host solely based on their addresses. File Transfer Protocol (FTP) lives up to its name and provides a method for copying files over a network from one computer to another.
Email requires its own set of protocols and there is a variety, both for sending and for receiving mail.
SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration.
Web pages are constructed according to a standard method called Hypertext Markup Language (HTML). A related protocol is Hypertext Transfer Protocol over Secure Socket Layer (HTTPS), first introduced by Netscape. We are a group of current or aspiring teachers currently studying at Pace University in Westchester County in New York State. This article is a brief overview of the File Transfer Protocol, an FTP site, and an FTP client. This article is the original implementation article from Internet Engineering Task Force (IETF). This article provides an overview of the SNMP and explains the concepts of SNMP manager and SNMP Management Information Base (MIB). Ethernet is not a protocol!  I ranted about this before, way back in 2006: “Why Use Industrial Ethernet?”  So today I’ve counted to ten and will move from rant mode to education mode.
So, when users respond to IMS and VDC and say their Industrial Ethernet protocol is “Ethernet,” what do they mean?  I would not accept this answer if I were a market research company!  So what do they mean?  Do they mean web server? I also find that the term Ethernet as a protocol can be used depending on the control system that person is most familiar with. Unfortunately, several of our friends in the trade press and elsewhere inadvertently perpetuate this myth by asking in surveys which fieldbus are do you presently or plan to use, and then include Ethernet as an option. Good news is that this means job security for those that realize it is the protocol that makes all the difference. James, I also think a lot of it is “I have no idea.” But more realistically it is probably an all of the above. Rowan, I like the point about Ethernet meaning different things to different users depending on their vendor of choice. However, I also agree that it does not go far enough to be considered a network protocol since it is only one part – you have define the data formatting. I tried to direct commenters from the PROFINET Group on LinkedIn to come to the blog to comment so all the comments would be in one place.
A comparison with RS232 is not valid, as RS232 doesn’t even do those things I mentioned above.
Rob and James, I’ve enjoyed this tangent as it refines definitions, but the real point I was trying to make and the answers I was looking for got lost. My (not-so) clever headline was to call attention to the fact that Ethernet by itself does nothing more than move frames from point A to point B. The award for the “Best Analogy” goes to Paul Chapple on the LinkedIn discussion page: “I often use the analogy of a telephone. That being said, when someone calls Grid Connect and says that they have Ethernet in their automation installation, they often say that because they know there are Ethernet cables in their application. The network presents more challenges when it comes to performance monitoring than any other part of your system.
One of the most difficult problems to assess is the effect of network topology on network performance. NOTE:Real World Data sharing on a network is important from several performance perspectives. There isn’t much you can do about certain network performance inhibitors, so we don’t even discuss them in this chapter.
The following four sections don’t provide an in-depth view of network bottlenecks, but they do give you an overview of the kinds of problems you’ll run into. The first aspect you need to understand about Microsoft Windows 2000 is that there are several layers of network-specific software. Since each layer in the networking model is independent, you can mix and match protocols that are compatible within a networking model.
The independence of each network layer means you can tune each layer within the confines of the protocol specification.
Let’s look at the various operating system layers using the Open Systems Interconnection (OSI) reference model for comparison. MORE INFO:There are a lot of Institute of Electrical and Electronics Engineers (IEEE) standards that control the configuration of networks and how they transfer data from one location to another.
There are a lot of acronyms for the Internet model in Figure 8-1, but the vast majority of them should mean something to you if you’ve been working with computers any length of time. It doesn’t take long to figure out that all these data translation layers don’t exist in a vacuum.
You also shouldn’t be too surprised to find out that each of these layers may require some type of tuning.
The previous section helped you understand what the various operating system layers are all about. Flags and Fragmentation OffsetsNetworkThere are actually three fields in this packet element. ProtocolNetworkDetermines which protocol receives the packet when it gets transferred from the network to transport layer. Header ChecksumNetworkAllows the network layer to check the integrity of the packet once it arrives at the destination machine. Destination PortTransportDetermines the software port on the receiver that’s responsible for accessing the data. Acknowledge NumberTransportTells the source that the destination received a certain number of bytes of data.
Urgent PointerTransportThe receiver counts this number of bytes from the beginning of the sequence number field to the point in the data stream where urgent data exists.
DataSession, Presentation, and ApplicationThe information that an application on one node needed to transfer to an application on a second node. The local machine is the one the user uses to gain access to the resources the network can provide. A third source of network bottlenecks for the local machine is the network agent that operates in the background.
The fourth major source of network bottlenecks for the local machine is the application or hardware that’s experiencing some sort of problem. TIP:A sniffer or other form of network packet reader is an indispensable tool in finding errant hardware and software on the network.
Creation and documentation of the Internet Protocol suite closely resemble an academic research project. Type-of-service---Specifies how a particular upper-layer protocol would like the current datagram to be handled.
Total length---Specifies the length of the entire IP packet, including data and header, in bytes. Time-to-live---Maintains a counter that gradually decrements down to zero, at which point the datagram is discarded. Protocol---Indicates which upper-layer protocol receives incoming packets after IP processing is complete. As with all network-layer protocols, the addressing scheme is integral to the process of routing IP datagrams through an internetwork. Class A networks are intended mainly for use with a few very large networks because they provide only seven bits for the network address field. Class B networks allocate 14 bits for the network address field and 16 bits for the host address field. If a network administrator has chosen to use 8 bits of subnetting, the third octet of a class B IP address provides the subnet number. On some media (such as IEEE 802 LANs), media addresses and IP addresses are dynamically discovered through the use of two other members of the Internet protocol suite: the Address Resolution Protocol (ARP) and the Reverse Address Resolution Protocol (RARP). A more recent addition to ICMP provides a way for new nodes to discover the subnet mask currently used in an internetwork.
The ICMP Router Discovery Protocol (IRDP) uses router advertisement and router solicitation messages to discover addresses of routers on directly attached subnets.The way IRDP works is that each router periodically multicasts router advertisement messages from each of its interfaces. Source port and destination port---Identify the points at which upper-layer source and destination processes receive TCP services. Sequence number---Usually specifies the number assigned to the first byte of data in the current message. UDP is a much simpler protocol than TCP and is useful in situations where the reliability mechanisms of TCP are not necessary. Subnet broadcast (defined in RFC 922) supports broadcasting to all the subnets of a particular network number.
Figure 18-12, when Workstation A uses subnet broadcasting to send a packet to each workstation on Subnetwork 2, a duplicate packet also arrives. Routers listen to IGMP messages and periodically send out queries to discover which groups are active on which LANs. The Web browser (the client) reads the .html file, interprets the code and displays the page. To create a page which is dynamic, one that changes constantly, such as a price list or a hotel reservation, you will have to obtain information stored on a database server. We navigate between pages using links, which are usually blue and underlined; each link contains the address (also called URL) of another page. For the client there is not much difference between browsers - it's a question of preferences and features. For the designer there are a few precautions to be taken since the browsers don't all interpret the code in the same way. When you design a website it's important that you test the results with all of the major browsers to make sure that the client is seeing what you expect him to see.
HTML provides the content developer with a means to describe the appearance of a service in a flat document structure. Static content is produced once and not changed or updated very often; for example, a company presentation. In order to save valuable bandwidth in the wireless network, WML can be encoded into a compact binary format. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard. Each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the upper layer protocols based on using services from some lower layers.
For this purpose the Internet Protocol defines addressing methods and structures for datagram encapsulation. This layer architecture is often compared with the seven-layer OSI Reference Model; using terms such as Internet Reference Model in analogy is however incorrect as the Internet Model is descriptive while the OSI Reference Model was intended to be prescriptive, hence Reference Model.
More generally, it provides for some simple file management on the contents of a remote computer.
It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention. An HTML page is transmitted over the Web in a standard way and format known as Hypertext Transfer Protocol (HTTP). Included in this link is a download as well as support, tutorials, and basic knowledge articles.
My experience for so long now is that anyone that says Ethernet is an industrial protocol , just has no idea on the subject.
IT& Controls headbutting is simply as they are standing on each others turf and it is a natural defence mechanism.
I think the part that confuses end users is that unlike Profibus DP, Device or Modbus RTU, you can have multiple protocols running on the same wire. It has defined the electrical signaling, a message format, it has an address format, detection of transmission errors, retries (sometimes), flow control, point-to-point and broadcast capabilities, medium access control, VLAN’s, QoS, autonegotiation, etc. I can call any number in China, but unless the other person can speak English I cannot communicate.
The reason’s simple: You can’t monitor the network’s performance if the amount of traffic isn’t at normal levels.
Any change you make to one machine normally changes the performance characteristics of the network as a whole and each machine on the network. You not only have the operating system and the local hardware to worry about, but there are also other machines to consider.
We’ll divide this conversation into four major components: the operating system, the local machine, remote machines, and other sources. The whole idea of interactions causes some network administrators to dismiss this area of tuning as too difficult to manage, especially on large networks. This is one of those areas where you can’t predict the results because user-oriented solutions depend on the cooperation of the user to work. Given the state of the art, you’ll find that hardware is the most common solution to network performance problems.
This section looks at two major areas of the network: the local operating system and the applications designed to use the network.
In short, the use of a network is supposed to make users more efficient while reducing the cost of performing the work.
Users adamantly protect their right to hide data—no amount of training changes that stance.


Sometimes classifying a network bottleneck is the most difficult problem of all because the problem looks like it can be part of several major subsystems. An application doesn’t send data directly to the NIC, and then through the NIC to another machine.
The operating system implements the various layers that are mandated by various networking standards.
The interdependence of each layer, however, means a change at one layer, of necessity, affects all the other layers in the network model. Originally, it was supposed to be the next big thing in networking, but the original promise of the model fell through as vendors argued for their particular wants or needs in a networking model.
It includes identifying the parties in a communication, defining the anticipated level of service, and specifying any security requirements such as user authentication and any special requirements such as data syntax. The session layer begins and ends the transaction, as well as coordinating the resources of the two parties to keep this conversation from interfering with other conversations that the entity may engage in.
This means it checks the packets for errors and requests copies of packets that get lost in transit. It includes the NIC that converts the data for transmission and the cable that allows actual transfer of data from one machine to the next. This Web site provides a very good overview of the reference model and links to other locations where you can find out more. Notice that the layers don’t match up precisely; but, by comparing the two, you can get some idea of what each layer in the Internet protocol stack does. For example, there are several standards that appear in Figure 8-1 that control the transmission of data on Internet networks. If a Web server does a poor job of creating Web pages for a browser, it’s certain your network sees additional packets to transfer the additional data. For example, at the physical layer, most NICs provide some type of enhanced options (the most common of which is direct memory access (DMA) data transfers) that improve system performance. However, knowing that the operating system processes the network connection in layers doesn’t tell you the whole story.
The first rows of identification information tell where the data fits within the OSI model.
It either contains the length of the remainder of the packet, or more commonly, the packet type. This field prioritizes the packet as a whole and helps network components such as routers deliver the packets according to their importance to the network as a whole. The datagram begins at the very end of the data link layer and ends at the end of any data included within the packet. The packet ID is used to ensure that all the packets arrive at the destination and that the packets don’t end up in another session.
If the network can’t find the destination address in the time allotted, the packet is declared dead and deleted. The example shows a length of 20 bytes, which includes the transport layer, but nothing else. The remaining six bits represent the following flags: urgent, acknowledgment, push, reset, synchronize, and finish. This means working with both operating system-specific applications (Windows Explorer) and user-oriented applications (Microsoft Office). The first is the application that isn’t designed for network use and is hostile to any attempt to use it with the network.
A database application is always designed with network use in mind because the database is normally held on a central machine for everyone’s access. For example, Ethernet NICs can experience a problem where they continuously generate packets even if there isn’t any data to transfer to another node. You can use the packet-sniffing capabilities of these devices to locate the source of packet streams that don’t appear to have any use other than to use up network bandwidth. In addition to internetwork routing, IP provides fragmentation and reassembly of datagrams and error reporting. One bit specifies whether the packet can be fragmented; the second bit specifies whether the packet is the last fragment in a series of fragmented packets. Class C networks provide only 8 bits for the host field, however, so the number of hosts per network may be a limiting factor.
ARP uses broadcast messages to determine the hardware Media Access Control (MAC)-layer address corresponding to a particular internetwork address. Dynamic routing calls for routes to be calculated at regular intervals by software in the routing devices.
All in all, ICMP is an integral part of any IP implementation, particularly those that run in routers. Hosts discover the addresses of routers on the directly attached subnet by listening for these messages. Under certain circumstances, it can also be used to identify an initial sequence number to be used in the upcoming transmission. The UDP header has only four fields: source port, destination port, length, and UDP checksum.
Network File System (NFS), External Data Representation (XDR), and Remote Procedure Call (RPC) combine to allow transparent access to remote network resources. Because many multicast applications are data intense, packet duplication is a significant disadvantage of subnet broadcast.Internet Group Membership ProtocolInternet Group Membership Protocol (IGMP), defined in RFC 1112, relies Class D IP addresses for the creation of multicast groups. However, Notepad++ is an excellent replacement for the original Notepad and it has one really useful feature when you start Javascript and PHP and that is: line numbers.
It's an inexpensive shareware and it has a very useful screen capture utility that will help with your websites.
However, if you can't afford Photoshop there is an open-source software equivalent that will do great work for you. If more advanced features like procedural logic are needed, then scripting languages such as JavaScript or VB Script may be utilised.
Dynamic content is needed when the information provided by the service changes more often; for example, timetables, news, stock quotes, and account information. Today's IP networking represents a synthesis of several developments that began to evolve in the 1960s and 1970s, namely the Internet and LANs (Local Area Networks), which emerged in the mid- to late-1980s, together with the advent of the World Wide Web in the early 1990s. Upper layers are logically closer to the user and deal with more abstract data, relying on lower layer protocols to translate data into forms that can eventually be physically transmitted. The first major version of addressing structure, now referred to as Internet Protocol Version 4 (IPv4) is still the dominant protocol of the Internet, although the successor, Internet Protocol Version 6 (IPv6) is being deployed actively worldwide.
Protocols exist for a variety of different types of communication services between computers. When configuring email clients such as Outlook Express, an Internet address for an SMTP server must be entered.
SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force (IETF). Both side in defence typically do not want to understand the demands and issues on each side of the fence.
I use the analogy that Ethernet is the express service for sending packages while serial is dial-up modem or truck transport. Ethernet refers to the physical layer that many different communications networks can run on. Yet, having the traffic at normal levels means you have to consider the interactions of multiple machines when monitoring performance.
For example, adding a higher performance network interface card (NIC) to one workstation may adversely affect the performance of other machines on the network that have lower performance NICs installed. These four major sources of network bottlenecks are the first place to look for performance problems on the network. However, the gains or losses a network can encounter due to interactions tend to dwarf other areas of network optimization. For example, what happens to network performance if you have 50 people using a word processor all day and they unconsciously hit the Save button every few seconds? If other users also follow this practice, server performance can suffer because users will make redundant data requests from different areas of the server hard disk drive. Topology limitations in effect today are unlikely to disappear tomorrow, no matter how much you’d like to get rid of them.
These sections help you reduce the complexity of the problem by breaking it down to one of four major network areas: operating system, local machine (both hardware and software), remote machine (both hardware and software), and other (like users).
The data goes through several transformation layers before it becomes the packet that eventually gets transferred to another node on the network. Two diplomats (the operating system) interact in a specific way based on a treaty (the protocol). For example, the TCP protocol has requirements that an operating system must meet to ensure interoperability with other operating systems that also implement TCP. In short, you need to consider how a performance change in one layer will affect the other layers around it.
We talk about how the layers fit together from a very generic, standards-oriented, perspective. It helps to look at how the operating system eventually transfers data from one point to another using these various layers to encapsulate the data in a package.
For example, the operating system may have to convert a text stream into meaningful entries in a dialog box. It’s the session layer that defines the two parties in the conversation and ensures that their conversation remains unique. When the network layer receives a packet that belongs to another party, it forwards the packet to the requested destination. Likewise, responses from the browser to the Web server require some sort of data translation, and then transmission. We cover the various hardware and software enhancements that you can make to the various layers in the appropriate sections of the chapter.
When you get to the bottom of whatever network model you’re using, you end up with a data packet that contains a lot of information about how the data should be transferred from one point to another. This helps you correlate the existence of certain data with its purpose in the overall scheme of network data transfer. This value includes both the Version and IHL elements, so you start counting the 20 bytes at the end of the data link layer. The datagram doesn’t include the data link layer or any padding characters used to flesh out the packet to a given transfer size. The sending machine then receives an error message saying the destination address doesn’t exist. All that must happen is that the source and destination need to increment the number at the same interval. How the source and destination nodes handle the data depends on what kind of application is creating and receiving the information.
The methods that these applications employ to gain access to network resources on the user’s behalf determine a number of network performance factors, such as the amount of bandwidth used to service the call. Fortunately, there are few of these applications in use anymore and the vast majority of them are custom applications designed to perform a specific task. For example, an agent can detect potential hardware problems long before the user realizes they exist and allow the network administrator to fix the errant hardware before it becomes a problem. An application that can’t find a desired node may simply keep generating request packets, rather than acknowledge that a problem exists and reporting it to the user.
Once the source of a packet stream is identified, you can usually troubleshoot the local machine and find the source of the problem rather quickly. For example, assume that a network has been assigned a class B address, and all the nodes on the network currently conform to a class B address format.
ARP is sufficiently generic to allow use of IP with virtually any type of underlying media-access mechanism. This contrasts with static routing, where routes are established by the network administrator and do not change until the network administrator changes them. Instead, at each stop, the next destination is calculated by matching the destination address within the datagram with an entry in the current node's routing table.
Hosts can use router solicitation messages to request immediate advertisements, rather than waiting for unsolicited messages. The source and destination port fields serve the same functions as they do in the TCP header. By using a specific Class D address, an individual host dynamically registers itself in a multicast group. With reverse path flooding, on receipt of a packet, the router floods the packet out all paths except the path that leads back to the source of the packet, which insures that a data stream reaches all LANs. Instead of your standard "this is a variable" type training however, Robert teaches you how to actually apply PHP and MySQL in real world scenarios. You use FTP to transfer files from your home computer to the Web server (assuming that you don't have a Web server at home).
It consists of a set of standards for network management, including an application layer protocol, a database schema, and a set of data objects. It really come down to a environment where these potential conflicts are eliminated so that productive mutual cooperation can take place. Since it does define a ‘set of conventions’ for getting the ‘1’s and 0’s’ from point A to point B, I believe that it does fit the formal definition of what a protocol is. In addition, the monitoring you perform today only remains valid as long as the network configuration remains unchanged. Even something as simple as a cable change can affect network performance because cable length affects network timing and, therefore, the rate at which data moves on the cable. The ability to communicate with other users is what makes the network popular, while the interactions and complexity of the network environment is the stuff of nightmares for the network administrator. There are a host of factors that make it impossible to realize the full performance benefits from any network topology. You can’t afford to ignore interactions—they must be managed to optimize data throughput.
Perhaps the answer to a network performance problem isn’t in the operating system or the user, but in creating a new network segment so the users have the additional bandwidth required to get their work done.
Users constantly seek new ways to get the benefits of networks without sharing the data they create with others.
The first performance problem that will occur is due to the loss of hard disk drive space that could be used for temporary files and virtual memory.


However, other network performance inhibitors are actually very easy to remedy and result in massive savings of both time and effort for the network administrator. The purpose of this section is to make network problems easier to resolve by making them easier to see.
Once the data arrives at the other node (possibly another machine or a peripheral device similar to a printer), there are several additional layers that interpret the packet and make it suitable for use on the remote node. These diplomats represent the countries (the physical machine) and their interests (the application software). The same holds true with IP and other protocols you may use in setting up network communications. The protocols used to communicate between nodes must be agreed on in advance and is often dictated by the application in use at the time.
As you can see, the question of tuning a network model that’s implemented by Windows 2000 isn’t an easy issue to discuss. Think of the data as a letter, and the various layers as the envelope used to ensure prompt delivery.
The OSI reference model, however, accurately portrays everything that needs to go on in a data transfer, so many people now use it as a teaching aid. Although this chapter provides a good overview of what OSI is all about, this Web site provides detailed information about which technologies work together to create a complete OSI implementation.
All the layers perform some type of work on every piece of data that gets transferred from one machine to another, which means all these layers affect the performance of your system in some way.
For now, all you really need to understand is that the layers exists and that many of them can be optimized. This flag tells any routers in the path that you don’t want to break the packet into smaller pieces for faster transport. If the client were using HTTP (a browser), the port number would be 80 decimal in most cases. Network hostile applications usually require special handling by the operating system because they don’t provide any resources of their own.
If the database application is designed without any form of buffering, it likely accesses the database server constantly, which means it generates a lot of network traffic. Both of these errors create bottlenecks on the network that can easily be fixed once the network administrator can identify their source.
Subnet addresses are only present if the network administrator has decided that the network should be divided into subnetworks.
RARP uses broadcast messages to determine the Internet address associated with a particular hardware address. Each node's involvement in the routing process consists only of forwarding packets based on internal information, regardless of whether the packets get to their final destination.
IRDP offers several advantages over other methods of discovering addresses of neighboring routers.
The length field specifies the length of the UDP header and data, and the checksum field allows packet integrity checking. If the router is attached to a LAN that does not want to receive a particular multicast group, the router sends a "prune" message back to the source to stop the data stream.
Obviously, you don't want to have to change the date in every page of the website every morning. It can also be used for downloading from the Web but, more often than not, downloading is done via HTTP. For the typical Ethernet response, I usually respond with Ethernet is the Pipe, what is the language that is spoken down the pipe? So, the difficult process of monitoring a network for specific problems occurs on a regular basis. This chapter seeks to reduce the complexity of the network performance monitoring and optimization equation. In fact, this is such a significant problem that we spend time talking about the very problem of theoretical topology performance potential as compared to the real world topology performance potential. Fortunately, there are ways to make the interaction picture easier to see and, more importantly, manage. The problem from the network administrator’s perspective is finding out the source of this nervous twitch, and then finding a remedy for the situation that the user is willing to try. There are also other issues to consider, such as the quality of the hardware you use, the kind of drivers, and the way the hardware and drivers are configured. In other cases, you find that wise use of network resources is the answer to performance problems.
Network bottlenecks cause performance reductions until a company purchases more hardware, which, in turn, reduces the cost savings of using the network.
The second performance problem is that the hard disk drive cache won’t work as it normally would to enhance server performance.
The actual number of layers the data encounters depends on the protocol used to transmit the data and various operating system options such as data encryption. In short, you can view a protocol as the rules of engagement and the language used to communicate between two machines.
You need to consider each layer not only individually, but also as part of the greater whole.
We actually tear a network packet (the envelope used to transfer data from one node to another) apart to see what makes it tick.
Just as the envelope has specific physical characteristics and requires certain information, a network packet needs to help the system identify the sender and receiver of the information you ask it to transmit.
The following list provides a very brief overview of the seven layers of the OSI reference model. The efficiency with which all these layers do their work makes a difference in the overall performance of your network and affects what the user sees in the way of response time. Before we delve into these monitoring utilities, however, it’s a good idea to know what a packet actually looks like as it travels along the cable from one machine to the next. Table 8-1 contains a listing of the various data elements (in the order they appear in the figure) along with a description of their purpose.
According to the TCP specification mentioned earlier, the datagram requires 5 bytes of padding to meet the minimum requirement of 46 bytes. The push flag tells the sending TCP to rush the delivery of data through the rest of the layers. These applications take resources away from other applications when they do require access to the network.
All this traffic eats up network bandwidth and can quickly become a problem if a lot of users are accessing the database at one time. However, agents that run constantly, yet provide only a modicum of information once a week (or even as often as once a day), use network resources without providing much in return. Taken together, the RFCs provide a colorful history of the people, companies, and trends that shaped the development of what is today the world's most popular open-system protocol suite.
Rather than change all the addresses to some other basic network number, the administrator can subdivide the network using subnetting. RARP is particularly important to diskless nodes, which may not know their internetwork address when they boot.Internet RoutingRouting devices in the Internet have traditionally been called gateways---an unfortunate term because, elsewhere in the industry, the term applies to a device with somewhat different functionality.
In other words, IP does not provide for error reporting back to the source when routing anomalies occur. Primarily, it does not require hosts to recognize routing protocols, nor does not it require manual configuration by an administrator.Router advertisement messages allow hosts to discover the existence of neighboring routers, but not which router is best to reach a particular destination. The UDP checksum is optional.Upper-Layer ProtocolsThe Internet Protocol suite includes many upper-layer protocols representing a wide variety of applications, including network management, file transfer, distributed file services, terminal emulation, and electronic mail.
To send a message to all devices connected to the network, a single network device uses a broadcast address. When running DVMRP, routers periodically reflood the network to reach new hosts, using an algorithm that takes into account the frequency of flooding and the time required for a new multicast group member to receive the data stream.To determine which interface leads back to the source of a data stream, DVMRP implements its own unicast routing protocol. So, you create a small program to display the date using information stored in the client computer. Sites that have a lot of downloading (software sites, for example) will often have an FTP server to handle the traffic. Email clients such as Outlook Express require an address for a POP3 server before they can read mail. A solution for this kind of problem can be as easy as setting the word processor to automatically save at given intervals, and then demonstrating that the feature does indeed work. In short, for every benefit you can gain from a network, there are potential problems that reduce or even eliminate the effect of using the network in the first place. When users make shared data requests, the first request moves the data from the hard drive to server memory.
A network that performs well can make users feel as if they’re accessing local resources, when, in fact, those resource reside on another machine and can be physically located in another building. As a result of reading these two sections, you should walk away with a better idea of how the layering of protocols to create a specific kind of network model works and how you can use this information to better tune your system. Currently, the OSI reference model is sponsored by the International Standards Organization. In some cases, you find that agents become more of a network bottleneck and performance inhibitor than a help in making the network run smoothly. This is done by borrowing bits from the host portion of the address and using them as a subnet field, as shown in Figure 18-4.
Gateways (which we will call routers from this point on) within the Internet are organized hierarchically.
This task is left to another Internet protocol, the Internet Control Message Protocol (ICMP). Table 18-1 maps the best-known Internet upper-layer protocols to the applications they support. These two forms of addressing have been sufficient for transferring traditional data (such as files and virtual terminal connections).Now that application developers are trying to deliver the same data (such as the audio and video required for conferencing) to some, but not all, devices connected to the network, another form of addressing is required. Subsequent requests use the cached copy of the data, which results in a performance gain on the server because reading from memory is faster than reading from the hard drive.
I’ve tried to use relatively standard values, but the values you actually see using a network monitoring utility or hardware (such as a sniffer) depend entirely on your network configuration. Some routers are used to move information through one particular group of networks under the same administrative authority and control (such an entity is called an autonomous system). The new form of addressing is called multicast addresses, and it involves the transmission of a single IP datagram to multiple hosts. The path that multicast traffic follows may not be the same as the path that unicast traffic follows.The need to reflood prevents DVMRP (especially early versions that do not implement pruning) from scaling well. Both SMTP and POP3 use TCP for managing the transmission and delivery of mail across the Internet. In addition, caching multiple copies of the same data from different locations on the hard drive wastes server memory.
The OSI reference model is also part of the International Telecommunication Union’s (ITU) X.200 standard.
Routers used for information exchange within autonomous systems are called interior routers, and they use a variety of interior gateway protocols (IGPs) to accomplish this purpose. Since the script is run from the local browser, (the client), we'll refer to "client-side scripting". Routers that move information between autonomous systems are called exterior routers, and they use an exterior gateway protocol for this purpose.
The Simple Network Management Protocol (SNMP) is a network management protocol used for reporting anomalous network conditions and setting network threshold values.
UDP FloodingUDP flooding depends on the spanning tree algorithm to place interfaces in the forwarding and blocking states. It has been used to build the multicast backbone (MBONE) across the Internet.The MBONE is used to transmit conference proceedings and deliver desktop video conferencing. Every time a data modifications occurs, network traffic increases because every user has to modify his or her copy of the data separately, rather than make one change to a single master document.
By placing certain interfaces in the blocking state, the spanning tree algorithm prevents the propagation of duplicate packets. In short, both network and server performance suffer when users fail to share data and treat the network drive as an extension of their local drive. The router sends specific packets (typically UDP packets) out the interfaces that are in the forwarding state. The hosts establish tunnels to each other over the IP Internet and run DVMRP over the tunnels. This technique saves bandwidth by controlling packet flow in topologies that feature redundant routers and alternate paths to the same destination.
The MBONE is a very high consumer of bandwidth both because of the nature of the traffic (audio and video) and because it is implemented with host-based tunnels.
Host-based tunnels tend to result in packet duplication, which the backbone networks transmit unnecessarily.In addition, the MBONE relies on extremely knowledgeable administrators for support. In spite of their efforts, the MBONE has caused significant disruption to the Internet when popular events or multiple events are active.Multicast Open Shortest Path FirstMulticast Open Shortest Path First (MOSPF) is an extension to OSPF. OSPF is a unicast routing protocol that requires each router in a network to be aware of all available links in the network.
Protocol Independent Multicast (PIM) is an Internet draft (under discussion by the IETF Multicast Routing Working Group) that has two modes of behavior for the two traffic types: dense mode and sparse mode.
A router that is running PIM can use dense mode from some multicast groups and sparse mode for other multicast groups.Dense ModeIn dense mode, PIM uses reverse path flooding and is similar to DVMRP.
One significant difference between PIM and DVMRP is that PIM does not require a particular unicast protocol to determine which interface leads back to the source of a data stream.
Instead, PIM uses whatever unicast protocol the internetwork is using.Sparse ModeIn sparse mode, PIM is optimized for environments in which there are many data streams but each data stream goes to a relatively small number of the LANs in the internetwork.
For this type of traffic, reverse path flooding wastes bandwidth.PIM-SM works by defining a rendezvous point.




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