Network protocol design principles - Revision history

Xqbot: Bot: Fixing double redirect to Communication protocol

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Bot: Fixing double redirect to Communication protocol

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	#REDIRECT [[~~Communications~~ protocol]]		#REDIRECT [[Communication protocol]]

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	#~~redirect~~ [[~~network~~ protocol]		#REDIRECT [[Communications protocol]]

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			#redirect [[network protocol]
	<i>The topic of this entry is to describe the design principles which had been applied for specifying [[network protocol]]s. The entry needs rework and has been moved here from [[Systems engineering]].</i>

	== Protocol Layering ==

	In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.

	For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may detect and retry errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[Internet Protocol]]), another handles the encapsulation of that data into a stream of bits (for example, with the [[point-to-point protocol]]), and another handles the electrical encoding of the bits, (with a V.42 [[modem]], for example).

	Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.

	The reference model usually used for layering is the [[OSI seven layer model]], which can be applied to any protocol, not just the OSI protocols. In particular, the Internet Protocol can be analysed using the OSI model.

	== [[Error Detection]] and [[error correction\|Correction]] ==

	It is a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.

	In [[telephony]], failure rates of 10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).

	Communication systems correct errors by selectively resending bad parts of a [[message]]. For example, in TCP (the internet's Transmission Control Protocol), messages are divided into [[packet]]s, each of which has a checksum. When a [[checksum]] is bad, the packet is discarded. When a packet is lost, the receiver acknowledges all of the packets up to, but not including the failed packet. Eventually, the sender sees that too much time has elapsed without an acknowledgement, so it resends all of the packets that have not been acknowledged. At the same time, the sender backs off its rate of sending, in case the packet loss was caused by saturation of the path between sender and receiver. (Note: this is an over-simplification: see [[Transmission Control Protocol\|TCP]] and [[congestion collapse]] for more detail)

	In general, the performance of TCP is severely degraded in conditions of high packet loss (more than 0.1%), due to the need to resend packets repeatedly. For this reason, [[TCP/IP]] connections are typically either run on highly reliable fiber networks, or over a lower-level protocol with added error-detection and correction features (such as modem links with ARQ). These connections typically have uncorrected bit error rates of 10<sup>-9</sup> to 10<sup>-12</sup>, ensuring high TCP/IP performance.

	== Resiliency ==

	Another form of network failure is topological failure, which a communications link is cut. Most modern communication protocols periodically send messages to test a link. In phones, a framing bit is sent every 24 bits on [[T-carrier system\|T1]] lines. In phone systems, when "sync is lost", fail-safe mechanisms reroute the signals around the failing equipment.

	In [[packet switched]] networks, the equivalent functions are performed using [[router]] update messages to detect loss of connectivity.

	== Further reading ==

	* [[Radia Perlman]], ''Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2nd Edition)''. Addison-Wesley 1999. ISBN 0201634481. In particular Ch. 18 on "network design folklore".
	* [[Gerard J. Holzmann]], ''Design and Validation of Computer Protocols''. Prentice Hall, 1991. ISBN 0-13-539925-4. Also available online at http://spinroot.com/spin/Doc/Book91.html

Niteowlneils: =Protocol Layering= consistent caps, -rdndt link

2004-04-13T17:22:28Z

=Protocol Layering= consistent caps, -rdndt link

← Previous revision		Revision as of 17:22, 13 April 2004
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	In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.		In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.

	For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may detect and retry errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[~~internet~~ ~~protocol~~]]), another handles the encapsulation of that data into a stream of bits (for example, with the [[point-to-point protocol]]), and another handles the electrical encoding of the bits, (with a V.42 [[modem]], for example).		For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may detect and retry errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[Internet Protocol]]), another handles the encapsulation of that data into a stream of bits (for example, with the [[point-to-point protocol]]), and another handles the electrical encoding of the bits, (with a V.42 [[modem]], for example).

	Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.		Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.

	The reference model usually used for layering is the [[OSI seven layer model]], which can be applied to any protocol, not just the OSI protocols. In particular, the [[Internet ~~protocol]]~~ can be analysed using the OSI model.		The reference model usually used for layering is the [[OSI seven layer model]], which can be applied to any protocol, not just the OSI protocols. In particular, the Internet Protocol can be analysed using the OSI model.

	== [[Error Detection]] and [[error correction\|Correction]] ==		== [[Error Detection]] and [[error correction\|Correction]] ==

The Anome: see TCP and congestion collapse for more detail

2004-01-14T13:22:26Z

see TCP and congestion collapse for more detail

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	In [[telephony]], failure rates of 10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).		In [[telephony]], failure rates of 10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).

	Communication systems correct errors by selectively resending bad parts of a [[message]]. For example, in TCP (the internet's Transmission Control Protocol), messages are divided into [[packet]]s, each of which has a checksum. When a [[checksum]] is bad, the packet is discarded. When a packet is lost, the receiver acknowledges all of the packets up to, but not including the failed packet. Eventually, the sender sees that too much time has elapsed without an acknowledgement, so it resends all of the packets that have not been acknowledged. At the same time, the sender backs off its rate of sending, in case the packet loss was caused by saturation of the path between sender and receiver. (Note: this is an over-simplification: see [[Transmission Control Protocol\|TCP]] for more detail)		Communication systems correct errors by selectively resending bad parts of a [[message]]. For example, in TCP (the internet's Transmission Control Protocol), messages are divided into [[packet]]s, each of which has a checksum. When a [[checksum]] is bad, the packet is discarded. When a packet is lost, the receiver acknowledges all of the packets up to, but not including the failed packet. Eventually, the sender sees that too much time has elapsed without an acknowledgement, so it resends all of the packets that have not been acknowledged. At the same time, the sender backs off its rate of sending, in case the packet loss was caused by saturation of the path between sender and receiver. (Note: this is an over-simplification: see [[Transmission Control Protocol\|TCP]] and [[congestion collapse]] for more detail)

	In general, the performance of TCP is severely degraded in conditions of high packet loss (more than 0.1%), due to the need to resend packets repeatedly. For this reason, [[TCP/IP]] connections are typically either run on highly reliable fiber networks, or over a lower-level protocol with added error-detection and correction features (such as modem links with ARQ). These connections typically have uncorrected bit error rates of 10<sup>-9</sup> to 10<sup>-12</sup>, ensuring high TCP/IP performance.		In general, the performance of TCP is severely degraded in conditions of high packet loss (more than 0.1%), due to the need to resend packets repeatedly. For this reason, [[TCP/IP]] connections are typically either run on highly reliable fiber networks, or over a lower-level protocol with added error-detection and correction features (such as modem links with ARQ). These connections typically have uncorrected bit error rates of 10<sup>-9</sup> to 10<sup>-12</sup>, ensuring high TCP/IP performance.

The Anome: clarify; this stuff is riddled with imprecision

2003-10-13T11:58:35Z

clarify; this stuff is riddled with imprecision

← Previous revision		Revision as of 11:58, 13 October 2003
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	In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.		In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.

	For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may ~~correct~~ errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the ~~error~~ ~~detection~~ (with the ~~internet's~~ [[point-to-point protocol]]), and another handles the ~~physical~~ ~~form~~ of the bits, (with a V.42 [[modem]], for example).		For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may detect and retry errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the encapsulation of that data into a stream of bits (for example, with the [[point-to-point protocol]]), and another handles the electrical encoding of the bits, (with a V.42 [[modem]], for example).

	Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.		Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.

The Anome: removed redundant "1x"

2003-10-13T11:55:26Z

removed redundant "1x"

← Previous revision		Revision as of 11:55, 13 October 2003
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	It is a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.		It is a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.

	In [[telephony]], failure rates of ~~1x10~~<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while ~~1x10~~<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).		In [[telephony]], failure rates of 10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).

	Communication systems correct errors by selectively resending bad parts of a [[message]]. For example, in TCP (the internet's Transmission Control Protocol), messages are divided into [[packet]]s, each of which has a checksum. When a [[checksum]] is bad, the packet is discarded. When a packet is lost, the receiver acknowledges all of the packets up to, but not including the failed packet. Eventually, the sender sees that too much time has elapsed without an acknowledgement, so it resends all of the packets that have not been acknowledged. At the same time, the sender backs off its rate of sending, in case the packet loss was caused by saturation of the path between sender and receiver. (Note: this is an over-simplification: see [[Transmission Control Protocol\|TCP]] for more detail)		Communication systems correct errors by selectively resending bad parts of a [[message]]. For example, in TCP (the internet's Transmission Control Protocol), messages are divided into [[packet]]s, each of which has a checksum. When a [[checksum]] is bad, the packet is discarded. When a packet is lost, the receiver acknowledges all of the packets up to, but not including the failed packet. Eventually, the sender sees that too much time has elapsed without an acknowledgement, so it resends all of the packets that have not been acknowledged. At the same time, the sender backs off its rate of sending, in case the packet loss was caused by saturation of the path between sender and receiver. (Note: this is an over-simplification: see [[Transmission Control Protocol\|TCP]] for more detail)

	In general, the performance of TCP is severely degraded in conditions of high packet loss (more than 0.1%), due to the need to resend packets repeatedly. For this reason, [[TCP/IP]] connections are typically either run on highly reliable fiber networks, or over a lower-level protocol with added error-detection and correction features (such as modem links with ARQ). These connections typically have uncorrected bit error rates of ~~1x10~~<sup>-9</sup> to ~~1x10~~<sup>-12</sup>, ensuring high TCP/IP performance.		In general, the performance of TCP is severely degraded in conditions of high packet loss (more than 0.1%), due to the need to resend packets repeatedly. For this reason, [[TCP/IP]] connections are typically either run on highly reliable fiber networks, or over a lower-level protocol with added error-detection and correction features (such as modem links with ARQ). These connections typically have uncorrected bit error rates of 10<sup>-9</sup> to 10<sup>-12</sup>, ensuring high TCP/IP performance.

	== Resiliency ==		== Resiliency ==

The Anome: OSI model in own graf

2003-10-13T11:53:45Z

OSI model in own graf

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	== Protocol Layering ==		== Protocol Layering ==

	In modern protocol design, [[network protocol\|protocols]] are ~~[[OSI model\|~~layered]]. ~~This~~ divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.		In modern protocol design, [[network protocol\|protocols]] are "layered". Layering is a design principle which divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.

	For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may correct errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the error detection (with the internet's [[point-to-point protocol]]), and another handles the physical form of the bits, (with a V.42 [[modem]], for example).		For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may correct errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the error detection (with the internet's [[point-to-point protocol]]), and another handles the physical form of the bits, (with a V.42 [[modem]], for example).

	Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.		Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.

			The reference model usually used for layering is the [[OSI seven layer model]], which can be applied to any protocol, not just the OSI protocols. In particular, the [[Internet protocol]] can be analysed using the OSI model.

	== [[Error Detection]] and [[error correction\|Correction]] ==		== [[Error Detection]] and [[error correction\|Correction]] ==

The Anome: fmt, clarify layering

2003-10-13T11:51:04Z

fmt, clarify layering

← Previous revision		Revision as of 11:51, 13 October 2003
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	== Protocol Layering ==		== Protocol Layering ==

⚫	~~Usually, [[network protocol\|protocols]] are [[OSI model\|layered]].~~ For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may correct errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the error detection (with the internet's [[point-to-point protocol]]), and another handles the physical form of the bits, (with a V.42 [[modem]], for example).
			In modern protocol design, [[network protocol\|protocols]] are [[OSI model\|layered]]. This divides the protocol design into a number of smaller parts, each of accomplishes a particular sub-task, and interacts with the other parts of the protocol only in a small number of well-defined ways.

		⚫	For example, one layer might describe how to encode text (with [[ASCII]], say), while another describes how to inquire for messages (with the Internet's [[simple mail transfer protocol]], for example), while another may correct errors (with the Internet's [[transmission control protocol]]), another handles addressing (say with IP, the [[internet protocol]]), another handles the error detection (with the internet's [[point-to-point protocol]]), and another handles the physical form of the bits, (with a V.42 [[modem]], for example).

	Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.		Layering allows the parts of a protocol to be designed and tested without a combinatorial explosion of cases, keeping each design relatively simple. Layering also permits familiar protocols to be adapted to unusual circumstances. For example, the mail protocol above can be adapted to send messages to aircraft. Just change the V.42 modem protocol to the INMARS LAPD data protocol used by the international marine radio satellites.

	== [[Error Detection]] and [[error correction\|Correction]] ==		== [[Error Detection]] and [[error correction\|Correction]] ==

	It's a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.		It is a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.

	In [[telephony]], failure rates of 1x10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 1x10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).		In [[telephony]], failure rates of 1x10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 1x10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).
Line 16:		Line 20:

	== Resiliency ==		== Resiliency ==

	Another form of network failure is topological failure, which a communications link is cut. Most modern communication protocols periodically send messages to test a link. In phones, a framing bit is sent every 24 bits on [[T-carrier system\|T1]] lines. In phone systems, when "sync is lost", fail-safe mechanisms reroute the signals around the failing equipment.		Another form of network failure is topological failure, which a communications link is cut. Most modern communication protocols periodically send messages to test a link. In phones, a framing bit is sent every 24 bits on [[T-carrier system\|T1]] lines. In phone systems, when "sync is lost", fail-safe mechanisms reroute the signals around the failing equipment.

	In [[packet switched]] networks, the equivalent functions are performed using [[router]] update messages to detect loss of connectivity.		In [[packet switched]] networks, the equivalent functions are performed using [[router]] update messages to detect loss of connectivity.

	== ~~See~~ ~~Also~~ ==		== Further reading ==

	* [[Radia Perlman]], ''Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2nd Edition)''. Addison-Wesley 1999. ISBN 0201634481. In particular Ch. 18 on "network design folklore".		* [[Radia Perlman]], ''Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2nd Edition)''. Addison-Wesley 1999. ISBN 0201634481. In particular Ch. 18 on "network design folklore".
	* [[Gerard J. Holzmann]], ''Design and Validation of Computer Protocols''. Prentice Hall, 1991. ISBN 0-13-539925-4. Also available online at http://spinroot.com/spin/Doc/Book91.html		* [[Gerard J. Holzmann]], ''Design and Validation of Computer Protocols''. Prentice Hall, 1991. ISBN 0-13-539925-4. Also available online at http://spinroot.com/spin/Doc/Book91.html

24.91.22.174 at 19:59, 1 July 2003

2003-07-01T19:59:00Z

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	== [[Error Detection]] and [[error correction\|Correction]] ==		== [[Error Detection]] and [[error correction\|Correction]] ==
	It's a [[truism]] that communication media are ~~alway~~ faulty. The conventional measure of quality is ~~failing~~ bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.		It's a [[truism]] that communication media are always faulty. The conventional measure of quality is the number of failed bits per bit transmitted. This has the wonderful feature of being a dimensionless figure of merit that can be compared across any speed or type of communication media.

	In [[telephony]], failure rates of 1x10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 1x10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).		In [[telephony]], failure rates of 1x10<sup>-4</sup> bit per bit are faulty (they interfere with [[telephone]] conversations), while 1x10<sup>-5</sup> bit per bit or more should be dealt with by routine maintenance (they can be heard).