Application Layer

There are several well-known ports for #Transmission Control Protocol (TCP) and #User Datagram Protocol (UDP) authorised by Internet Assigned Numbers Authority (IANA) for #Application Layer protocols ranged from 0 to 1023. They are shown in the following table:

UDP is a widely used #Transport Layer Protocol# (defined by #Open Systems Interconnection (OSI) Model for the #Internet Protocol Suite (TCP/IP). Unlike Transmission Control Protocol (TCP), it is an unreliable and connectionless protocol which is great for real time communication such as voice chat or video streaming. UDP doesn’t guarantee that the packets or datagram (its Protocol Data Units (PDU))# will reach their destination or arrive in order as there is no mean to acknowledge such state. It has a rather small segment headers, with only 8 bytes, and provides fine application control over data transmission, which allow application-specific error recovery at Application Layer# for reliability.

Transport Layer is the forth layer in #Open Systems Interconnection (OSI) Model. It has the same name under #Internet Protocol Suite (TCP/IP). Its main purpose is to transfer the chunk of data from Application Layer onto the network. Sometimes, it will cut down the sizes of the data and send them as several packets (its #Protocol Data Units (PDU)). Their header will identify the Well-Known Ports# or socket numbers of the sender and receiver.

SNMP is a lightweight #Application Layer Protocol# allowing remote and local #management# of items or Network Device on the network. It is part of #Internet Protocol Suite (TCP/IP). SNMP comprises of two entities: agents who are running on managed node and collecting information about the node, and managers who are running on management workstation that requests information about devices on the network.

Session Layer is the fifth layer in the #Open Systems Interconnection (OSI) Model. It manages the connections between hosts. Sometimes, it will referred to as Application Layer with Presentation Layer and Application Layer.

S/MIME is an extension to the existing MIME# email infrastructure focus on security enhancements in Application Layer# which is supported in many mail agents such as MS Outlook, Mozilla, Mac Mail etc. It is similar to Pretty Good Privacy (PGP) which offers ability to sign and/or encrypt messages. The public keys are distributed in the form of Public-Key Certificate# which both parties have to obtain the cert.

PGP is a #Asymmetric Cryptographic program used to encrypt, decrypt and sign emails over insecure transmission channel such as Internet with Digital Signature# which is developed by Philip R. Zimmermann in 1991. It has become the de facto #standard for email security. It provides five services: Confidentiality#, Authentication#, compression, e-mail compatibility (encode raw binary to ASCII characters using Radix-64 Encoding#) and segmentation (if the message is too large). It guarantees the security in Application Layer#.

Presentation Layer is the sixth layer in the #Open Systems Interconnection (OSI) Model. It mainly provides formatting services to the Application Layer such as file encryption and format conversion. Session Layer, Application Layer and itself are commonly known as Application Layer as a whole in Internet Protocol Suite (TCP/IP).

Kerberos is a protocol utilising #Symmetric Cryptography to provide Security Service# in Application Layer#. It is done by authenticate the user in order to gain temporary access to internal or remote resources. There are currently two versions of Kerberos implementation: Version 4# and Version 5#. Regardless of the version, three components make up the structure of Kerberos which is used to guard the network: Authentication#, Accounting and Auditing. It has two main components servers: Authentication Server and Ticket Granting Server.

TCP/IP is a #Protocol Suite that is widely used for Internet or other computer networks connection. Internet Protocol (IP)# forms the foundation for it. It also comprises some Application Layer, Transport Layer and Network Layer protocols.

Hypertext Transfer Protocol is an #Application Layer protocol that is used to manage the request and distribution of the hypertext documents.

e2e occurs between the original source and the final destination, that is the encryption is happened in either Application Layer#, Presentation Layer#, Transport Layer# or Network Layer#. This implies that they have the shared keys. e2e only concerns about the encryption of the user data. If user’s privacy and security is desirable, then e2e is preferred. However, due to the translation limit when jumping between different network technology such as IPv4# and IPv6#, the data sent must be decrypted and then be transformed to an understandable form. This could be a huge compromise.