(i)Packet switching
In packet switching, the data is split into small segments known as packets. Each packet has a label that contains information such as its source address and destination address. The packets are routed individually on different intermediate nodes. The Internet is the best example of a packet-switched network. Data from the source computer to the destination computer is routed in individual packets that take different routes. Each packet is sent using the best and shortest route.
Packet-switched networks use a routing algorithm to send the individual packets to their destination. Often a route with the shortest path (lowest cost) is selected for a packet. It is very possible that the next packet travels by a different route. The individual packets arrive at the destination in a random order. The destination node waits for all the packets to arrive, checks their sequence numbers, and then reconstructs the information.
(ii)Circuit switching
In circuit-switched networks, a dedicated physical circuit is established before the two nodes can communicate. Each circuit or communication channel is reserved and cannot be used by other nodes until the nodes already using the channel release it. The Plain Old Telephone System (POTS) is an example of a circuit switched network. An ISDN is another example where a separate channel is used for control and administrative purposes.
In packet switching, the data is split into small segments known as packets. Each packet has a label that contains information such as its source address and destination address. The packets are routed individually on different intermediate nodes. The Internet is the best example of a packet-switched network. Data from the source computer to the destination computer is routed in individual packets that take different routes. Each packet is sent using the best and shortest route.
Packet-switched networks use a routing algorithm to send the individual packets to their destination. Often a route with the shortest path (lowest cost) is selected for a packet. It is very possible that the next packet travels by a different route. The individual packets arrive at the destination in a random order. The destination node waits for all the packets to arrive, checks their sequence numbers, and then reconstructs the information.
(ii)Circuit switching
In circuit-switched networks, a dedicated physical circuit is established before the two nodes can communicate. Each circuit or communication channel is reserved and cannot be used by other nodes until the nodes already using the channel release it. The Plain Old Telephone System (POTS) is an example of a circuit switched network. An ISDN is another example where a separate channel is used for control and administrative purposes.
The advantages of circuit switching include reliable connection and guaranteed speed of data transmission. The disadvantage is that resources are wasted due to dedicated physical connections. Circuit switching is different from packet switching in which data is split into packets and sent over a shared network. Packet switching allows several nodes to communicate simultaneously over the same network.
(iii)Integrated Services Digital Network (ISDN)
ISDN is a packet-switched network that is designed to allow transmission of data and voice over the same copper wires used in telephone systems. This results in better quality and higher data transfer speeds than regular dial-up connections. ISDN is actually a set of protocols that define rules for establishing and terminating connections. It also provides several advanced features. At the same time, ISDN requires dedicated telephone lines and therefore is expensive.
As with a regular dial-up connection, an ISDN connection also uses a dial-up telephone number—but these telephone lines are considered leased lines. When the two ends need to communicate, one of them dials the specified ISDN number, and the connection is set up. When the communication between the two nodes is over, the user hangs up and the ISDN line becomes free. Computers using the ISDN line need the special network interface known as the ISDN adapter (or the terminal adapter).
ISDN communications use two types of channels: a bearer channel (B channel) that is used for data (or voice), and a delta channel (D channel) that is used for control signals. There are two main implementations of ISDN as follows:
(iii)Integrated Services Digital Network (ISDN)
ISDN is a packet-switched network that is designed to allow transmission of data and voice over the same copper wires used in telephone systems. This results in better quality and higher data transfer speeds than regular dial-up connections. ISDN is actually a set of protocols that define rules for establishing and terminating connections. It also provides several advanced features. At the same time, ISDN requires dedicated telephone lines and therefore is expensive.
As with a regular dial-up connection, an ISDN connection also uses a dial-up telephone number—but these telephone lines are considered leased lines. When the two ends need to communicate, one of them dials the specified ISDN number, and the connection is set up. When the communication between the two nodes is over, the user hangs up and the ISDN line becomes free. Computers using the ISDN line need the special network interface known as the ISDN adapter (or the terminal adapter).
ISDN communications use two types of channels: a bearer channel (B channel) that is used for data (or voice), and a delta channel (D channel) that is used for control signals. There are two main implementations of ISDN as follows:
Basic Rate Interface (BRI)
BRI ISDN uses 2 B channels of 64 Kbps each for data/voice, and a D channel of 16 Kbps. The total data transfer speed of BRI ISDN using two B channels is 128 Kbps. The two B channels can also be used separately with 64 Kbps speed.
Primary Rate Interface (PRI)
PRI ISDN uses 23 B channels of 64 Kbps each for data/voice, and a D channel of 64 Kbps. The total data transfer speed of PRI ISDN is up to 1.544 Mbps. The PRI ISDN is usually carried over dedicated (leased) T1 lines.
BRI ISDN uses 2 B channels of 64 Kbps each for data/voice, and a D channel of 16 Kbps. The total data transfer speed of BRI ISDN using two B channels is 128 Kbps. The two B channels can also be used separately with 64 Kbps speed.
Primary Rate Interface (PRI)
PRI ISDN uses 23 B channels of 64 Kbps each for data/voice, and a D channel of 64 Kbps. The total data transfer speed of PRI ISDN is up to 1.544 Mbps. The PRI ISDN is usually carried over dedicated (leased) T1 lines.
(iv)Fiber Distributed Data Interface (FDDI)
FDDI provides data transmissions in local area networks that can extend up to 200 kilometers (124 miles). It is primarily based on the Token Ring protocol and uses the token-passing media access method. Unlike Token Ring topology, FDDI uses two rings for providing fault tolerance. The nodes in an FDDI network are attached to two rings, and the two tokens rotate on the rings, each in the opposite direction. The first ring is used for carrying data while the second ring is used for fault tolerance.
FDDI provides data transmissions in local area networks that can extend up to 200 kilometers (124 miles). It is primarily based on the Token Ring protocol and uses the token-passing media access method. Unlike Token Ring topology, FDDI uses two rings for providing fault tolerance. The nodes in an FDDI network are attached to two rings, and the two tokens rotate on the rings, each in the opposite direction. The first ring is used for carrying data while the second ring is used for fault tolerance.
FDDI can support thousands of network nodes spread over wide geographical locations. Due to the increasing popularity of Gigabit Ethernet, FDDI is rarely used in modern networks. The following are some of the main characteristics of FDDI:
• It is resistant to electromagnetic and radio frequency interferences (EMI and RFI).
• It provides fault tolerance because of two rings.
• Fiber optic cables can have a maximum distance of 200 kilometers.
• It has a built-in error-detection mechanism known as beaconing.
• It is very expensive in terms of the cost associated with devices and media.
• It is difficult to implement and maintain.
• It is resistant to electromagnetic and radio frequency interferences (EMI and RFI).
• It provides fault tolerance because of two rings.
• Fiber optic cables can have a maximum distance of 200 kilometers.
• It has a built-in error-detection mechanism known as beaconing.
• It is very expensive in terms of the cost associated with devices and media.
• It is difficult to implement and maintain.
(v)T-Carrier
The T-carrier lines are high-speed, dedicated digital lines that can carry both data and voice signals. These lines can be leased from the local telephone company. The basic unit of T-carrier lines is the DS0, which has a transmission speed of 64 Kbps and is used for one voice circuit. Although dedicated T lines are expensive, they provide a consistent point-to-pint connection between two end systems. The European equivalent of T-carrier is the E-carrier, while in Japan the J-carrier is used. The most common of all T-carriers are T1 and T3 lines, with data transmission speeds of 1.544 Mbps and 44.736 Mbps respectively.
The T-carrier lines are high-speed, dedicated digital lines that can carry both data and voice signals. These lines can be leased from the local telephone company. The basic unit of T-carrier lines is the DS0, which has a transmission speed of 64 Kbps and is used for one voice circuit. Although dedicated T lines are expensive, they provide a consistent point-to-pint connection between two end systems. The European equivalent of T-carrier is the E-carrier, while in Japan the J-carrier is used. The most common of all T-carriers are T1 and T3 lines, with data transmission speeds of 1.544 Mbps and 44.736 Mbps respectively.
(vi)Optical Carrier (OC)
OC levels describe the range of digital signals (data, voice, and video) that can be carried over SONET. SONET is a fiber optic network developed by Bell Communications. The minimum speed of an optical carrier is 51.84 Mbps, and it can go up to 2.488 Gbps.
OC levels describe the range of digital signals (data, voice, and video) that can be carried over SONET. SONET is a fiber optic network developed by Bell Communications. The minimum speed of an optical carrier is 51.84 Mbps, and it can go up to 2.488 Gbps.
Note that the OC levels are expressed as OC-n, where n is a number. The speed of any given OC level is calculated by multiplying the level number n by 51.8 Mbps. For example, the speed of OC-3 is calculated as 3X51.84 Mbps, which is equal to 155.52 Mbps.
(vii)X.25
X.25 is a packet-switching WAN technology that uses telephone or ISDN hardware. It works at a maximum data transfer speed of 56 Kbps It is a globally accepted standard, but is slowly becoming obsolete due to newer and more efficient technologies. Since it is a packet-switching technique, the X.25 network works well when there is congestion on any part. It can route different packets on different routes. The packets are assembled at the destination using special devices known as Packet Assemblers/Dis-assemblers (PADs). Each end of the X.25 connection is attached to a PAD.
X.25 is a packet-switching WAN technology that uses telephone or ISDN hardware. It works at a maximum data transfer speed of 56 Kbps It is a globally accepted standard, but is slowly becoming obsolete due to newer and more efficient technologies. Since it is a packet-switching technique, the X.25 network works well when there is congestion on any part. It can route different packets on different routes. The packets are assembled at the destination using special devices known as Packet Assemblers/Dis-assemblers (PADs). Each end of the X.25 connection is attached to a PAD.
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