Pressing the number seven on the keypad will result in 1209Hz and 852Hz being sent at the same time.
The above shows In-channel and Common-channel Signalling.
A virtual circuit has a pre-planned route determined before the packets are sent. There is not a dedicated line as in circuit switching, as others can use the same circuit, so the packets may be queued. Each of the packets has a virtual circuit identifier or a VCI.
Advantages of a datagram are that the call time setup is avoided, datagrams can be routed away from any congestion, the delivery is more reliable, suitable when only a few packets need to be transmitted and if the node fails the datagrams will find another route.
Advantages of a virtual circuit are that a virtual circuit is suitable when packets are to be transmitted between 2 computers for a period of time, services can be provided for virtual circuit such as error control which is when if a packet arrives at one node with an error code it can be requested again, and virtual circuits are faster because there is no routing decision required at each node.
Next i will include som equestions and there answers that I have completed about Voice over IP (VoIP) and Voice over ATM (VoATM)
Voice over IP
1. State what VoIP is.
2. Discuss Voice Quality with VoIP.
3. List 4 different applications of VoIP
4. Describe one of those applications via diagram or text
Voice over ATM
5. What is ATM
6. Discuss the ATM Cell
7. Discuss VoATM
8. What are the advantages and disadvantages of ATM
1. VoIP enables data networks such as the internet, local area networks and wide area networks to be used for voice communication and it reduces the cost of communication.
2. Voice quality is very important in VoIP and the quality must be as good as the PSTN. There are 3 factors that affect voice quality in ViOP, transmission delay is the first which is the time it takes a packet from source to destination, the second is Jitter delay which is the difference in arrival time between packets and the third is packet loss which is when if a packet is dropped there is a gap in the conversation eg. You won’t be able to makeout the full word or sentence you are being told, packet loss with VoIP can cause big bits of a conversation to be lost.
3. Four applications of VoIP are computer to computer, computer to multiple sites, voice or internet via ISP and voice over intranet or LAN.
4. Computer to multiple sites is a traditional analog telephone attached to an IP telephony enabled PBX and this requires an expensive adapter.
5. ATM or asynchronous transfer mode is a connection-oriented, cell based technique for the transfer of information, ATM can be used for the transfer of audio, video and data. ATM is an extremely fast broadband switching technology eg high bandwidth.
6. ATM uses a uniform 53 byte cell, 5 bytes of addressing information, 48 bytes of payload. The benefit of the small cell size is reduced latency in transmitting through the network nodes. There is a disadvantage which is because of the small cell size it means that there is increased overhead.
7. Class A provides for Voice Over ATM and class A includes constant bit rate or CBR services for connection-oriented transfer with end-to-end synchronisation. Protocol AAL 1 supports services class A and some examples of this include PCM-coded voice, circuit-emulated connections having a bit rate of n x 64kbits/s or n x 2Mbits/s and video signals coded for constant bit rate.
8. The advantages of ATM are that it provides hardware switching, allows dynamic bandwidth of bursty traffic, it provides QoS for multimedia and voice, it scales in speed and network size, its used for LAN and WAN, has good network management capabilities and is used by 80-85% of internet backbone networks. But there are some disadvantages which are it has small cell size, has high overhead, has a high service cost, requires new equipment and requires new technical expertise.