IP Suite and VoIP
The purpose of this article is to discuss the IP Suite and VoIP at a more technical level. The Internet Protocol Suite (IPS), is also known as the TCP/IP Protocol Suite after the most important protocols in it. The IPS consists of 5 layers; each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the higher layers. The higher layers are logically closer to the user and deal with more abstract data, relying on lower layers to translate data into forms that can eventually be physically manipulated.
The three top layers make connections between computers and two lowest layers is where data passes through to reach its destination; these are the actual physical components of a computer.
These are explained in more detail below.
Layer 5 - Application This layer gives an application access to the communication environment; in VoIP these can be the SoftPhones or Software. The most common application layer is SIP (Session Initiation Protocol) Layer 4 - Transport The transport layer provides an application layer delivery service. The two protocols found at the transport layer are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Either of these two protocols are used by the application layer process. The choice depends on the application's transmission reliability requirements. TCP is a reliable, connection-oriented protocol that provides error checking and flow control through a virtual link that it establishes and finally terminates. This gives a reliable service and is used for file transfer and email delivery. UDP is an unreliable, connectionless protocol that provides data transport with lower network traffic overheads than TCP - UDP does not error check or offer any flow control, this is left to the application process. |
Layer 3 - Network
This layer is responsible for the routing and delivery of data across networks. It allows communication across networks of the same and different types, and carries out translations to deal with dissimilar data addressing schemes. IP (Internet Protocol) is found at the Network layer, but offers no guarantee of data delivery or integrity, which is left to the upper layers (transport and application).
Layers 2 and 1 – Data Link and Physical
The combination of datalink and physical layers deals with pure hardware such as twisted-pair cable that connects the network card, routers, modems, Analog Telephone Adaptors (ATAs) and IP Phones.
Ethernet is used as the Data Link layer in VoIP. It provides reliability of data transmission by controlling and synchronizing the flow. The physical layer provides the pathway that transmits bits to the Data Link layer. In VoIP the physical layer is the twisted-pair cable that connects the network card, routers, modems, Analogue Telephone Adaptors (ATAs) and IP Phones.
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