Out-of-band data

Last updated

In computer networking, out-of-band data is the data transferred through a stream that is independent from the main in-band data stream. An out-of-band data mechanism provides a conceptually independent channel, which allows any data sent via that mechanism to be kept separate from in-band data. The out-of-band data mechanism should be provided as an inherent characteristic of the data channel and transmission protocol, rather than requiring a separate channel and endpoints to be established. [1] The term "out-of-band data" probably derives from out-of-band signaling, as used in the telecommunications industry. [2]

Contents

Example case

Consider a networking application that tunnels data from a remote data source to a remote destination. The data being tunneled may consist of any bit patterns. The sending end of the tunnel may at times have conditions that it needs to notify the receiving end about. However, it cannot simply insert a message to the receiving end because that end will not be able to distinguish the message from data sent by the data source. By using an out-of-band mechanism, the sending end can send the message to the receiving end out of band. The receiving end will be notified in some fashion of the arrival of out-of-band data, and it can read the out of band data and know that this is a message intended for it from the sending end, independent of the data from the data source.

Implementations

It is possible to implement out-of-band data transmission using a physically separate channel, but most commonly out-of-band data is a feature provided by a transmission protocol using the same channel as normal data. A typical protocol might divide the data to be transmitted into blocks, with each block having a header word that identifies the type of data being sent, and a count of the data bytes or words to be sent in the block. The header will identify the data as being in-band or out-of-band, along with other identification and routing information. At the receiving end, the protocol looks at the header and routes the data to the normal reception endpoint if it is in-band, and to a separate mechanism if it is out-of-band. Depending on the implementation, there may be some mechanism for notifying or interrupting the receiving application when out-of-band data has arrived.

The most commonly used protocol containing an out-of-band data mechanism is the Internet's Transmission Control Protocol. It implements out-of-band data using an "urgent pointer," which marks certain data in the transmitted data stream as out-of-band. Unfortunately, a long-existing discrepancy between RFC 793 and RFC 1122 limits the usability of this feature of TCP; [3] nonetheless, it is heavily used by certain standard application protocols, notably the Telnet protocol. [4]

On Unix-like computers, out-of-band data can be read with the recv() system call. A process or process group can be configured to receive SIGURG signals when out-of-band data is available for reading on a socket, by using the F_SETOWN command of the fcntl() system call. This is a form of asynchronous I/O.

The Serial Advanced Technology Attachment (SATA) protocol commonly used to connect disk drives to computers implements an out-of-band data protocol. [5]

The Consultative Committee for Space Data Systems' Space Data Link Protocol implements an out-of-band mechanism via the "command" flag. When set, the received data is to be interpreted and acted on by the data link receiver, rather than being telemetry/telecommand information to be passed to the destination. [6]

Issues

Some sources define "out-of-band data" as including the characteristic that out-of-band data should be prioritized ahead of queued in-band data. [7] This is reinforced by TCP's (RFC 793) referring to the out-of-band data mechanism as "urgent data." However, prioritization is neither an essential nor a necessarily desirable characteristic of out-of-band data; moreover, TCP implementations vary greatly on how they treat the urgency of out-of-band data. [1]

See also

Related Research Articles

<span class="mw-page-title-main">HTTP</span> Application protocol for distributed, collaborative, hypermedia information systems

The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can easily access, for example by a mouse click or by tapping the screen in a web browser.

The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when communicating with another IP address. For example, an error is indicated when a requested service is not available or that a host or router could not be reached. ICMP differs from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications.

The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). Early versions of this networking model were known as the Department of Defense (DoD) model because the research and development were funded by the United States Department of Defense through DARPA.

The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telephone systems, as well as mobile phone calling over LTE (VoLTE).

The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.

The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP, which is part of the Transport layer of the TCP/IP suite. SSL/TLS often runs on top of TCP.

Telnet is a client/server application protocol that provides access to virtual terminals of remote systems on local area networks or the Internet. It is a protocol for bidirectional 8-bit communications. Its main goal was to connect terminal devices and terminal-oriented processes.

In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP does not require prior communication to set up communication channels or data paths.

<span class="mw-page-title-main">Email client</span> Computer program used to access and manage a users email

An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email.

<span class="mw-page-title-main">Network address translation</span> Protocol facilitating connection of one IP address space to another

Network address translation (NAT) is a method of mapping an IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device. The technique was originally used to bypass the need to assign a new address to every host when a network was moved, or when the upstream Internet service provider was replaced, but could not route the network's address space. It has become a popular and essential tool in conserving global address space in the face of IPv4 address exhaustion. One Internet-routable IP address of a NAT gateway can be used for an entire private network.

The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data connections between the client and the server. FTP users may authenticate themselves with a plain-text sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that protects the username and password, and encrypts the content, FTP is often secured with SSL/TLS (FTPS) or replaced with SSH File Transfer Protocol (SFTP).

<span class="mw-page-title-main">Transport layer</span> Layer in the OSI and TCP/IP models providing host-to-host communication services for applications

In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end communication services for applications. It provides services such as connection-oriented communication, reliability, flow control, and multiplexing.

Explicit Congestion Notification (ECN) is an extension to the Internet Protocol and to the Transmission Control Protocol and is defined in RFC 3168 (2001). ECN allows end-to-end notification of network congestion without dropping packets. ECN is an optional feature that may be used between two ECN-enabled endpoints when the underlying network infrastructure also supports it.

In computer networking, Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs) or as part of the delivery of services by ISPs. It uses encryption ('hiding') only for its own control messages, and does not provide any encryption or confidentiality of content by itself. Rather, it provides a tunnel for Layer 2, and the tunnel itself may be passed over a Layer 3 encryption protocol such as IPsec.

In computer networking, the Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol. DCCP implements reliable connection setup, teardown, Explicit Congestion Notification (ECN), congestion control, and feature negotiation. The IETF published DCCP as RFC 4340, a proposed standard, in March 2006. RFC 4336 provides an introduction.

A network socket is a software structure within a network node of a computer network that serves as an endpoint for sending and receiving data across the network. The structure and properties of a socket are defined by an application programming interface (API) for the networking architecture. Sockets are created only during the lifetime of a process of an application running in the node.

In computer networking, a port or port number is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of network service. A port at the software level is identified for each transport protocol and address combination by the port number assigned to it. The most common transport protocols that use port numbers are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP); those port numbers are 16-bit unsigned numbers.

<span class="mw-page-title-main">WebSocket</span> Computer network protocol

WebSocket is a computer communications protocol, providing simultaneous two-way communication channels over a single Transmission Control Protocol (TCP) connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011. The current specification allowing web applications to use this protocol is known as WebSockets. It is a living standard maintained by the WHATWG and a successor to The WebSocket API from the W3C.

The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the protocol provides the message-oriented feature of the User Datagram Protocol (UDP), while ensuring reliable, in-sequence transport of messages with congestion control like the Transmission Control Protocol (TCP). Unlike UDP and TCP, the protocol supports multihoming and redundant paths to increase resilience and reliability.

NACK-Oriented Reliable Multicast (NORM) is a transport layer Internet protocol designed to provide reliable transport in multicast groups in data networks. It is formally defined by the Internet Engineering Task Force (IETF) in Request for Comments (RFC) 5740, which was published in November 2009.

References

  1. 1 2 Len (October 20, 2011). "Out of band data, TCP Urgent mode and overlapped I/O". Serverframework.com. Retrieved 21 February 2014.
  2. ↑ "Chapter 11: Signaling Systems". George Mason University. Retrieved 21 February 2014.
  3. ↑ On the implementation of the TCP urgent mechanism. sec. 2.2. I-D draft-ietf-tcpm-urgent-data-01.
  4. ↑ TELNET PROTOCOL SPECIFICATION. doi: 10.17487/RFC0854 . RFC 854.
  5. ↑ Altera Corporation. "AN-635-1.0 Application Note Implementing SATA and SAS Protocols in Altera Devices" (PDF). Archived from the original (PDF) on 4 March 2016. Retrieved 21 February 2014.
  6. ↑ "TC Space Data Link Protocol" (PDF). CCSDS 232.0-B-1. Consultative Committee for Space Data Systems. Retrieved 21 February 2014.
  7. ↑ Stevens, W. Richard; Rago, Stephen A. (2005). "16.7". Advanced Programming in the Unix Environment: Second Edition. Addison-Wesley Professional. p. 960. ISBN   0201433079 . Retrieved 21 February 2014.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.