Question

a. Critique on the switching techniques a) circuit switching and

b) packet switching with a scenario example. [5 Marks] b. Illustrate the Session Initiation Protocol (SIP) for VoIP in your own words with appropriate diagram. [5 Marks]

c. Explain the procedure and significance of the presence service elements with an appropriate usage case. [5 Marks]

Answer 1

a) Circuit switching:

Circuit switched networks are connection-oriented networks. Here, a dedicated route is established between the source and the destination and the entire message is transferred through it. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit. Circuit switching contrasts with message switching and packet switching. In circuit switching, the bit delay is constant during a connection (as opposed to packet switching, where packet queues may cause varying and potentially indefinitely long packet transfer delays). No circuit can be degraded by competing users because it is protected from use by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains reserved and protected from competing users.

b) Packet Switching: Packet switching is the transfer of small pieces of data across various networks. These data chunks or “packets” allow for faster, more efficient data transfer.

Often, when a user sends a file across a network, it gets transferred in smaller data packets, not in one piece. For example, a 3MB file will be divided into packets, each with a packet header that includes the origin IP address, the destination IP address, the number of packets in the entire data file, and the sequence number.

Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless systems are Ethernet, Internet Protocol (IP), and the User Datagram Protocol (UDP). Connection-oriented systems include X.25, Frame Relay, Multiprotocol Label Switching (MPLS), and the Transmission Control Protocol (TCP).

b. Session Initiation protocol: is one of the most widespread protocols used in VoIP technology. It is an application layer protocol that works in combination with other application layer protocols to control multimedia communication sessions over the Internet. VOIP is a technology that enables you to deliver voice or multimedia (videos, pictures) content over the Internet. It is one of the most inexpensive way to communicate anytime, anywhere with the Internet’s availability.

· Some advantages of VOIP include −

o Low cost

o Portability

o No extra cables

o Flexibility

o Video conferencing

· For a VOIP call, all that you need is a computer/laptop/mobile with internet connectivity. The following figure depicts how a VoIP call takes place.

Basically SIP is an application layer protocol. It is a simple network signalling protocol for creating and terminating sessions with one or more participants. The SIP protocol is designed to be independent of the underlying transport protocol, so SIP applications can run on TCP, UDP, or other lower-layer networking protocols.

c. Explain the procedure and significance of the presence service elements with an appropriate usage case. [5 Marks]

Ans: Presence service is a type of network service which accepts, stores and distributes presence information.

Presence service may be implemented as a single server or have an internal structure involving multiple servers and proxies. There may be complex patterns of redirection and proxying while retaining logical connectivity to a single presence service. Also presence service may be implemented as direct communication among presentity and watchers, i.e. server is not required.

The Presence Server, that reside in the presentity's home network, is able to receive and manage presence information. It is a SIP Application Server and is located using SIP URLs.

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