Monday, March 9, 2020

Telephony terminologies

POTS (Plain-Old-Telephone-Service) was created in 1876.

ISDN (Integrated Services Digital Network) was introduced in 1988. ISDN comes in two forms: the basic rate interface (BRI) and the primary rate interface (PRI)

PRI can transfer more data, making it easier to transfer things like HD audio and video and more suitable for enterprises.

PSTN (public switched telephone network) is simply the global aggregate of all these interconnected copper telephone systems.

SIP (Session Initiation Protocol) was introduced in 2000.

Session Initiation Protocol is a set of communication standards that allow (for the most part) the setup and termination of voice or video calls. SIP allows voice traffic to be carried over data networks, including the internet. SIP is considered a type of VoIP.

VoIP (Voice over Internet Protocol) is an overarching term for the technology included in all IP based telephony.

Over-the-Top (OTT) VoIP, services such as WhatsApp, require both calling parties to have an active data connection and carry calls entirely over data networks.

The beauty of SIP is that it can be used to send calls to and from the PSTN, using media gateway.

A SIP Trunk is used to transfer a call between its origin and destination using the Public Switched Telephone Network (PSTN) or in the case of a Voice over Internet Protocol (VoIP) call, the internet. It describes the process of allowing multiple callers access to the same telephone service by sharing a line that can handle multiple calls instead of providing an individual line for each call.

Monday, March 2, 2020

CIDR notation

CIDR notation is a compact representation of an IP address and its associated routing prefix. The notation is constructed from an IP address, a slash ('/') character, and an integer. The integer is the count of leading 1 bits in the subnet mask. Larger values here indicate smaller networks.

Classful network design for IPv4 sized the network prefix as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses. IP address allocations were based on the bit boundaries of the four octets of an IP address. (The other two classes are used for other purposes – class D for multicast and class E for experimental purposes.)

Classless addressing is an IP address allocation method that is designed to replace classful addressing to minimize the rapid exhaustion of IP addresses.

Class A addresses allocate first 8 bits for the network and the remaining bits for the host.
Class B addresses allocate first 16 bits for the network and the remaining bits for the host.
Class C addresses allocate first 24 bits for the network and the remaining bits for the host.

What used to be class A is now '/8', B is '/16', C is '/24' and '/32' is the 'netmask' for a single host.
CIDR sees an IP address as a 32 bit rather than a 4 bytes address.
Classless Inter-Domain Routing (CIDR)
IP Calculator