J. Postel, Internet Protocol, Network Information Center, RFC 791, September 1981.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....use the following probe procedure: 1. From a host to be tested, T, select a multi homed host 1 , H, as the destination (see Figure 1) 2. Let the IP address of one interface on H, say A, be the destination address that can be reached by T. 3. From T, open a TCP connection to the discard port [16] of host H via interface A, and start sending data. 4. Login to host H from a control host, C, via another interface, say B. 5. Disable interface A while the communication between host T and host H is in progress 2 . Disabling interface A while host T is sending data to the discard port of ....

J. Postel. RFC-863: Discard Protocol. Request For Comments, May 1983. Network Information Center.

....Generating zero window probes using TCP echo service 4.1 Probing Procedure We use the following simple procedure to study zerowindow probing in various TCP implementations. For each implementation, we conduct five experiments. 1. From a host to be tested, open a TCP connection to the echo port [15] of another host. 2. Keep sending data to the echo port without reading the echoed data. As Figure 6 shows, because the probe program sends data without reading the echo, the receive buffer of TCP A eventually becomes full, causing it to send a zero window ACK segment to TCP B. Because TCP B ....

J. Postel. RFC-862: Echo Protocol. Request For Comments, May 1983. Network Information Center.

....us to probe the network at a specified rate, and collect detailed information. 2.2 Application level measurements We also used two programs, data source and data sink, which run as application processes 4 on any UNIX platform. These processes communicate using User Datagram Protocol (UDP) [2]. UDP is a very simple protocol that has no flow control mechanism and provides unreliable data transfer between two application processes. Data source generates packets at a specified rate. It puts a timestamp and a packet number in each packet and gives it to the network. Data sink saves the ....

J. B. Postel (editor). User Datagram Protocol. Request for Comment: RFC-768, Network Information Center, August 1980.

....over an extended period of time, we used the setup described below. One of the design goals was to ensure that the measurement setup does not cause significant additional load on the network. The user level behavior of a path through the Internet was observed using User Datagram Protocol (UDP) [11]. This allowed us to conduct controlled experiments using application level software, without requiring any modification to the kernel implementation of Internet protocol suite. Since UDP does not define (nor implement) any flow control and transfers packets to IP with minimal processing, we are ....

J. B. Postel (editor). User Datagram Protocol. Request for Comment: RFC-768, Network Information Center, SRI International, August 1980.

....of decentralized naming. Most notably, its name space includes the file systems of several UNIX hosts as subtrees. There is also a server that can make the file system of any host on the DARPA Internet appear as a directory in the V name space, using the Internet s File Transfer Protocol [33] to access the remote files. 6.2 Future Work Decentralized naming appears to be a promising area for continuing work. Most of the work that remains at this point is implementation and experimentation with some of the portions of the design that have not yet been incorporated into the V ....

J. Postel and J. Reynolds. File Transfer Protocol. Technical Report RFC 959, Network Information Center, SRI International, October 1985.

....loads differ from simulated loads. Figure 1 shows hourly samples of HTTP request rates for this service. 2. Characteristics of popular services The most popular server based Internet information services are the World Wide Web, electronic mail (SMTP [16] USENET news (NNTP [8] and FTP [17] archive services. Many people expect server based electronic commerce to become popular in the next few years, but it is not yet clear what technology will be employed. Each of these protocols has its own characteristics. In this paper, for reasons of space, I will focus on the World Wide Web, ....

J. Postel and J. Reynolds. File Transfer Protocol (FTP). RFC 959, Network Information Center, SRI International, October, 1985.

....reaching their ultimate destination, this is called inter network fragmentation. A good discussion of both methods, in more detail, may be found in Shoch [24] In this paper, drawing on experience with a large heterogeneous internetwork, we examine fragmentation in the context of the IP protocol [19]. IP supports the use of inter network fragmentation. Transparent fragmentation may be also be used as long as it is invisible to the IP layer. Fragmentation appears at first to be an elegant solution to the problem, but subtle complications arise in real networks that can result in poor ....

....of datagrams. IP datagrams are encapsulated in network specific packets. Gateways may fragment an incoming packet if it will not fit in a single outgoing packet; in this case, each fragment is sent as a separate packet. The IP header contains several fields that are used to manage fragmentation [19]: Identification: A 16 bit field assigned by the sender to aid in assembling the fragments of a datagram. The tuple (source, destination, protocol, identification) for a given datagram must be unique over all existing datagrams. When a packet is fragmented, the value of the Identification ....

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Jon Postel. Internet Protocol. RFC 791, Network Information Center, SRI International, September, 1981.

.... communication, the IP datagram layer itself (and its partner, the ICMP protocol) It would be a poor idea to put the entire fragmentation avoidance mechanism in, say, the TCP layer, because both the mechanism and any additional protocol would have to be duplicated in parallel layers, such as UDP [18], NETBLT [6] and VMTP [3] and because it would be awkward for a TCP based mechanism to share knowledge with other layers and across connections. This is not to say that layers above IP should be uninvolved in fragmentation avoidance. Architectural layering does not mean that higher layers must ....

Jon Postel. User Datagram Protocol. RFC 768, Network Information Center, SRI International, August, 1980.

....the protocol to be used through a Uniform Resource Locator (URL) In future versions, a virtual file system layer which would provide a uniform naming scheme may be added. 4 The FTP Implementation FTP is the Internet standard for file transfer. Its official specification is given in the RFC 959 [PR85]. The FTP protocol uses two TCP IP connections. The control connection is initiated by the FTP client which connects to a previously defined server port (port 21 is the default) Using this first connection, the client can send requests to the server and receive positive and negative ....

J. Postel and J. Reynolds. File transfer protocol. RFC 959, Network Information Center, SRI International, October 1985. 8

....is in the form of mbufs. Mbufs represent the network buffer abstraction present in most Berkeley derived network implementations. Received packets are placed in mbufs or a linked list of mbufs called an mbuf chain, and may be coalesced as required by protocol processing. Using the IP protocol[Pos81], packet sizes are limited to 64KBytes which is adequate to hold most compressed frames (the largest JPEG compressed images we have encountered is about 20KBytes, with typical values of 7 8KBytes) does not discuss the Berkeley networking implementation which does not perform an upcall all the ....

Jon Postel. Internet Protocol. RFC 791, Network Information Center, September 1981.

.... although measured performance at the network interface (a DEC DEFZA FDDI adapter, which provides no send side DMA) is 56 64 Mbit s [KP93] For the sender employing splice, 12,000 bytes of 8 bit image data are sent per frame, divided into three FDDI packets using the UDP transport protocol [Pos80] to send a sequence of 50 frames (150 FDDI packets) Image data is stored in a statically allocated kernel memory region in the sender, and is passed directly to the network protocol subsystem to be sent. For the user level sender, the same image data is statically allocated in a user process, ....

Jon Postel. User Datagram Protocol. RFC 768, Network Information Center, May 1980.

....them [Comer 91] The well known ports are controlled and assigned by the Internet Assigned Numbers Authority (IANA) Recently, the range of assigned well known ports managed by the IANA has been expanded to 0 1023. Ports in the range 1024 65535 are registered but cannot be controlled by the IANA [Reynolds 92] Table 2.2 shows some frequently used assigned TCP port numbers and their respective applications. Table 2.2: Examples of Assigned TCP Port Numbers. Decimal Protocol keyword Description 20 FTP Data File Transfer Protocol (data) 21 FTP File Transfer Protocol (control) 23 Telnet Terminal ....

J. Reynolds and J. Postel, Assigned Numbers, RFC 1340, Network Information Center, SRI International, Menlo Park, California, 1992.

....have been negotiated the sender SMTP sends the mail data, terminating with a special sequence. If the receiver SMTP successfully processes the mail data it responds with an OK reply and the connection is closed. 2.7. 2 File Transfer Protocol (FTP) FTP is used for transferring files between hosts [Postel 85] The primary function of FTP is to transfer files among hosts efficiently and reliably and allow the convenient use of remote file storage capabilities. User FTP sessions are subdivided into FTP Control and FTP Data connections. The FTP Control connection deals with the transactions related to ....

J. B. Postel and J. K. Reynolds, File Transfer Protocol. RFC 959, Network Information Center, SRI International, Menlo Park, California, 1985.

....can map to any of the host machines in the Department of Computational Science, such as skorpio.usask.ca (shown as the shaded box in Figure 2.6) 2. 4 The Internet Protocol (IP) The Internet Protocol (IP) defines an unreliable, connectionless delivery mechanism for network packets [Comer 91, Postel 81a] It is responsible for defining the basic unit of data transfer called an Internet datagram, finding a route for the datagram and getting it to the other end, and lastly, for providing a set of rules that characterize the unreliable packet delivery. A datagram is divided into header and data ....

J. B. Postel, Internet Protocol, RFC 791, Network Information Center, SRI International, Menlo Park, California, 1981.

....Gopher 79 Finger Finger 80 WWW World Wide Web 113 Ident Identification Protocol 119 NNTP Network News Transfer Protocol CHAPTER 2. BACKGROUND 16 2. 6 User Datagram Protocol (UDP) UDP is a connectionless datagram delivery service that does not guarantee delivery in the transport level [Postel 80] It provides a procedure for application programs to send messages known as user datagrams, to other programs with a minimum of protocol mechanism. Each user datagram consists of two parts, the UDP header and the UDP data area. Figure 2.9 shows the header format of the UDP datagram. 32 bits ....

J. B. Postel, User Datagram Protocol, RFC 768, Network Information Center, SRI International, Menlo Park, California, 1980. REFERENCES 95

.... Although the examples in this paper DATAGRAM ACCESS CONTROLS FOR UNIX BASED GATEWAYS do assume the use of IP, much of the mechanism (especially the kernel support) should be applicable to any similar protocol suite, including OSI [30] All datagrams in an IP internetwork carry an IP header [24], which includes the source and destination host addresses. In general, this is all that an IP gateway may assume about a datagram, so one might choose to restrict access on a host by host basis. Since IP network numbers can be extracted from IP host addresses, and since network numbers can often ....

Jon Postel. Internet Protocol. RFC 791, Network Information Center, SRI International, September, 1981.

....might also restrict datagrams based on source or destination network number. In fact, however, almost all information is carried by transport protocols layered above IP. Primarily, these include TCP [25] for reliable byte stream applications (mail, file transfer, remote terminal access) and UDP [23] for request response protocols (name service, routing, the NFS file access protocol [28] Certain control information is carried by the ICMP protocol [26] One may wish to require or restrict the use of such higher level protocols, which can be done based on information in the IP header. ....

Jon Postel. User Datagram Protocol. RFC 768, Network Information Center, SRI International, August, 1980.

....reduce domain crossing User level access to the data link layer is not universally regarded as a good thing. Some have suggested that user programs never need access to explicit network communication [23] others might argue that all networking should be done within a transport protocol such as IP [19] or the ISO Transport Protocol [15] with demultiplexing done by the transport layer code. Both these arguments implicitly assume a homogeneous networking environment, but heterogeneity is often a fact of life: machines from different manufacturers speak various transport protocols, and research ....

Jon Postel. Internet Protocol. RFC 791, Network Information Center, SRI International, September, 1981.

....for the administrator to express a scheduling policy. It must also allow the administrator to control the flow of information out of the system to support autonomy and security. 3.1 Prior work Several of these problems have been investigated by other researchers. The FTP protocol family (see [35, 40, 29, 11]) provides mechanisms to move files and programs. Efficient implementations of revocation might use checkpointing and process migration mechanisms, such as those as in Emerald [24] Amoeba [30] Sprite [31] Dune [36] Charlotte [1] or the V System [44] These mechanisms can also be used in ....

J.B. Postel and J.K. Reynolds. File transfer protocol. RFC 959, Network Information Center, October 1985.

....[44] These mechanisms can also be used in developing fault tolerance and load balancing schemes. Essick [15] and Shub, et al. 13, 39] have devised architecture independent task representations. XDR [23] and ASN.1 [16, 17] specify machine independent data formats. The User Datagram Protocol [34] and Reliable Datagram Protocol [45, 32] protocols from the DARPA TCP IP protocol suite are message based protocols, and could form the basis for our information exchange prototols. 3.2 New research The remaining components constitute our research. We have designed protocols to exchange ....

J.B. Postel. File transfer protocol. RFC 768, Network Information Center, August 1980.

....control in Transmission Control Protocol (TCP) 4] have been designed based on assumed network dynamics. The goal of this study has been to assess the dynamics of the Internet through experimental observations. Internet provides an unreliable data transfer service using the Internet Protocol (IP) [3]. IP provides no guarantees regarding data transfer. Internet may lose, reorder or duplicate packets. 1 Transit times for the packets may also vary significantly. The end to end This work is supported in part by RADC and DARPA under contract F30602 90 C 0010 to UMIACS at the University of ....

J. B. Postel (editor). Internet Protocol. Request for Comment: RFC-791, Network Information Center, September 1981.

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J. Postel, Internet Protocol, Network Information Center, RFC 791, September 1981.

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Jon Postel and Joyce Reynolds, File Transfer Protocol (FTP), RFC 959, Network Information Center, SRI International, Menlo Park, California, October 1985.

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J. B. Postel. Internet Protocol. RFC: 791, Network Information Center, September 1981.

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J. Postel, Internet Protocol, Network Information Center, Request for Comments, RFC0791, Jan. 91, 45 p.

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