A switched network consists of a series of intermediate nodes called switches. Switches are H/W and/or S/W devices capable of creating temporary connections between two or more devices linked to the switch not to each other.
Circuit switching creates direct physical connection between two devices.—is a device with n inputs and m outputs that creates temporary connection between an input link and an output link—no of inputs does not have to match no of outputs An n by n folded switch can connect n lines in full duplex mode.
view / download: switching (size 665 KB)
Synchronous optical network (SONET) is ANSI standard whereas Synchronous digital hierarchy (SDH) is ITU-T standard. SONET/SDH is a synchronous network. Single clock is used to handle the timing of transmission and equipment across the entire network so it adds a level of predictability to the system.—improved speed and reducing cost. SONET/SDH contains recommendations for the standardization of fiber optic transmission equipment (FOTS). SONET/SDH physical specification and frame design include mechanism that allow it to carry signals from incompatible tributary systems (e.g. asynchronous services –DS-0 and DS-1) SONET is a multiplexed transport mechanism and can be a carrier for broadband services e.g. ATM and B-ISDN. SONET defines a hierarchy of signaling levels called synchronous transport signals (STSs). The physical links defined o carry each level of STS is called Optical Carriers (OCs). OC describe the conceptual and physical specification of the links required to support each level of signaling.
view / download: SONET-SDH (size 509 KB)
ISDN consists of following
Bearer Services: provide the means to transfer information between users without the network manipulating the contents of that
information. Belongs to first three layers.
Teleservices: the network may change or process the contents of the data. Correspond to 4-7 layers.
Supplementary services: provide additional functionality to the bearer services and teleservices.
view/download: ISDN (size 933KB)
The most important technical innovation to come out of the standardization work on broadband ISDN is asynchrounous transfer mode (ATM), is a cell relay uses fixed size cell transmission technique. It has less overhead than frame relay and designed to operate at significantly higher data rates than frame relay.
view / download: ATM(Asynchronous Transfer Mode) (size 600KB )
Frame Relay is a virtual circuit technology that provides low-level (physical and data link layers) services in response to following demands:
o Higher data rate at lower cost
o Bursty data—bandwidth on demand—bursty data requires different bandwidth allocation at different times.
o Less overhead due to improved transmission media
• The most technical innovation to come out of the standardization work on narrowband ISDN is the frame relay.
• Frame relay is a streamlined technique for packet switching that operates at the data link layer with much less overhead than packet switching X.25
• Standardization of the frame-mode bearer service, or frame relay, was done by both ITU-T and ANSI.
View / Download: Frame Relay (Size 928KB)
Data Link protocols
• Asynchronous Protocols
• Not complex and inexpensive to implement
• Data unit is transmitted with no timing co-ordination between sender and receiver.
• Receiver does not know when data unit is sent- only recognizes the beginning and ending of frame-accomplished by start and stop bit.
• Used primarily in modem, features start and stop bits and variable length gaps between characters.
• Synchronous Protocols
View / Download: Data Link Protocol (Size 1.24 MB)
Line Discipline: co-ordinates the link system-determines which device can send and when it can send.
• Flow Control: co-ordinates the amount of data that can be sent before receiving ack.
• Error Control: error detection/correction-allows receiver to inform the sender of any frame lost or damaged and co-ordinate the retransmission
View / Download : Data Link Layer Functions (Size 988 KB)
Learning material by
Prof.H. S. Jamadagni, CEDT, IISc, Bangalore
Topics in Digital Communications
- Digital communication system advantages and disadvantages
- Digital communication system classification
- Digitization of analog signals
- Digital transmission systems
- Data communication systems
- Integrated Services Digital Network and other advanced digital communication systems
View / download : DCN-LearningMaterial (size 1.44MB)