Application layer

An application layer is an abstraction layer that specifies the shared communications protocols and interface methods used by hosts in a communications network. The application layer abstraction is used in both of the standard models of computer networking: the Internet Protocol Suite (TCP/IP) and the OSI model. Although both models use the same term for their respective highest level layer, the detailed definitions and purposes are different.

In TCP/IP, the application layer contains the communications protocols and interface methods used in process-to-process communications across an Internet Protocol (IP) computer network. The application layer only standardizes communication and depends upon the underlying transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a client-server or peer-to-peer networking model. Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in RFC 1123) does rely on and recommend the robustness principle for application design.^[1]

In the OSI model, the definition of the application layer is narrower in scope. The OSI model defines the application layer as the user interface responsible for displaying received information to the user. In contrast, the Internet Protocol Suite does not concern itself with such detail. OSI also explicitly distinguishes additional functionality below the application layer, but above the transport layer at two additional levels: the session layer, and the presentation layer. OSI specifies a strict modular separation of functionality at these layers and provides protocol implementations for each layer.

Application layer protocols[edit]

(Session Layer under OSI model) The IETF definition document for the application layer in the Internet Protocol Suite is RFC 1123. It provided an initial set of protocols that covered the major aspects of functionality of the early Internet.^[1]

Remote login to hosts: Telnet
File transfer: File Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP)
Electronic mail transport: Simple Mail Transfer Protocol (SMTP)
Networking support: Domain Name System (DNS)
Host initialization: BOOTP
Remote host management: Simple Network Management Protocol (SNMP), Common Management Information Protocol over TCP (CMOT)

Design patterns for application layer protocols[edit]

There are commonly reoccurring problems that occur in the design and implementation of communication protocols that can be addressed by patterns from several different pattern languages: Pattern Language for Application-level Communication Protocols (CommDP^[2]),^[3]^[4] Service Design Patterns,^[5] Patterns of Enterprise Application Architecture,^[6] and Pattern-Oriented Software Architecture: A Pattern Language for Distributed Computing.^[7] The first of these pattern languages focuses on the design of protocols and not their implementations. The others address issues in either both areas or just the latter.

Other protocol examples[edit]

9P, Plan 9 from Bell Labs distributed file system protocol
AFP, Apple Filing Protocol
APPC, Advanced Program-to-Program Communication
AMQP, Advanced Message Queuing Protocol
Atom Publishing Protocol
BEEP, Block Extensible Exchange Protocol
Bitcoin
BitTorrent
CFDP, Coherent File Distribution Protocol
CoAP, Constrained Application Protocol
DDS, Data Distribution Service
DeviceNet
eDonkey
ENRP, Endpoint Handlespace Redundancy Protocol
FastTrack (KaZaa, Grokster, iMesh)
Finger, User Information Protocol
Freenet
FTAM, File Transfer Access and Management
Gopher, Gopher protocol
HL7, Health Level Seven
HTTP, HyperText Transfer Protocol
H.323, Packet-Based Multimedia Communications System
IRCP, Internet Relay Chat Protocol
IPFS, InterPlanetary File System
Kademlia
LDAP, Lightweight Directory Access Protocol
LPD, Line Printer Daemon Protocol
MIME (S-MIME), Multipurpose Internet Mail Extensions and Secure MIME
Modbus
MQTT Protocol
Netconf
NFS, Network File System
NIS, Network Information Service
NNTP, Network News Transfer Protocol
NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
NTP, Network Time Protocol
OSCAR, AOL Instant Messenger Protocol
POP, Post Office Protocol
PNRP, Peer Name Resolution Protocol
RDP, Remote Desktop Protocol
RELP, Reliable Event Logging Protocol
Rlogin, Remote Login in UNIX Systems
RPC, Remote Procedure Call
RTMP, Real Time Messaging Protocol
RTP, Real-time Transport Protocol
RTPS, Real Time Publish Subscribe
RTSP, Real Time Streaming Protocol
SAP, Session Announcement Protocol
SDP, Session Description Protocol
SIP, Session Initiation Protocol
SLP, Service Location Protocol
SMB, Server Message Block
SMTP, Simple Mail Transfer Protocol
SNTP, Simple Network Time Protocol
SSH, Secure Shell
SSMS, Secure SMS Messaging Protocol
TCAP, Transaction Capabilities Application Part
TDS, Tabular Data Stream
Tor (anonymity network)
Tox
TSP, Time Stamp Protocol
VTP, Virtual Terminal Protocol
Whois (and RWhois), Remote Directory Access Protocol
WebDAV
X.400, Message Handling Service Protocol
X.500, Directory Access Protocol (DAP)
XMPP, Extensible Messaging and Presence Protocol

References[edit]

↑ ^1.0 ^1.1 Robert Braden, ed. (October 1989). "RFC 1123: Requirements for Internet Hosts – Application and Support". Network Working Group of the IETF.
↑ CommDP
↑ Jorge Edison Lascano, Stephen Clyde, and Ali Raza. “Communication-protocol Design Patterns (CommDP) - COMMDP.” Accessed: 17-Mar-2017.
↑ J. E. Lascano and S. Clyde, “A Pattern Language for Application-level Communication Protocols,” presented at the ICSEA 2016, The Eleventh International Conference on Software Engineering Advances, 2016, pp. 22–30.
↑ R. Daigneau, Service Design Patterns: Fundamental Design Solutions for SOAP/WSDL and RESTful Web Services, 1 edition. Upper Saddle River, NJ: Addison-Wesley Professional, 2011.
↑ M. Fowler, Patterns of Enterprise Application Architecture, 1 edition. Boston: Addison-Wesley Professional, 2002.
↑ F. Buschmann, K. Henney, and D. C. Schmidt, Pattern-Oriented Software Architecture Volume 4: A Pattern Language for Distributed Computing, Volume 4 edition. Chichester England; New York: Wiley, 2007.

[rfc1123-1] 1.0 ^1.1 Robert Braden, ed. (October 1989). "RFC 1123: Requirements for Internet Hosts – Application and Support". Network Working Group of the IETF.

[2] CommDP

[3] Jorge Edison Lascano, Stephen Clyde, and Ali Raza. “Communication-protocol Design Patterns (CommDP) - COMMDP.” Accessed: 17-Mar-2017.

[4] J. E. Lascano and S. Clyde, “A Pattern Language for Application-level Communication Protocols,” presented at the ICSEA 2016, The Eleventh International Conference on Software Engineering Advances, 2016, pp. 22–30.

[5] R. Daigneau, Service Design Patterns: Fundamental Design Solutions for SOAP/WSDL and RESTful Web Services, 1 edition. Upper Saddle River, NJ: Addison-Wesley Professional, 2011.

[6] M. Fowler, Patterns of Enterprise Application Architecture, 1 edition. Boston: Addison-Wesley Professional, 2002.

[7] F. Buschmann, K. Henney, and D. C. Schmidt, Pattern-Oriented Software Architecture Volume 4: A Pattern Language for Distributed Computing, Volume 4 edition. Chichester England; New York: Wiley, 2007.

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