Long distance transmission is typically done over a network of switched nodes
Nodes not concerned with content of data
End devices are stations
Computer, terminal, phone, etc.
A collection of nodes and connections is a communications network
Data routed by being switched from node to node
A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link. Each link is normally divided into n channels by using FDM or TDM.
In message switching no physical path is established in advance between sender and receiver.
Instead, it is sent and stored in the first switching office (i.e., router) and then forwarded later,
one hop at a time. Each block is received in its entirety, inspected for errors, and then
Telegrams were message switching.
This technique needs routers with big buffers and also a single block may tie up a router-
router line for minutes, useless for interactive traffic. Packet switching gets round this problem. ...
Bài giảng Kỹ thuật chuyển mạch báo hiệu - Chương 1: Chuyển mạch kênh (Circuit Switching) gồm có những nội dung chính sau: Chuyển mạch kênh, chuyển mạch không gian tương tự, điều chế biên độ xung PAM, công nghệ PCM và chuyển mạch số. Mời tham khảo.
Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice.
GSM (Global System for Mobile Communications), is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe technologies for second generation digital cellular networks. Developed as a replacement for first generation analog cellular networks, the GSM standard originally described a digital, circuit switched network optimized for full duplex voice telephony. The standard was expanded over time to include first circuit switched data transport, then packet data transport via GPRS (General Packet Radio Services)....
The control system for a star delta contactor is
The star contactor and delta contactor are interlocked
relative to each other with a ‘either - or’ condition.
Switching from ‘star’ to ‘delta’ is done automatically
by means of a time relay.
In the circuit above, the star contactor is energised
first, then the mains contactor. Circuits in which the
mains contactor is energised first, followed by the star
contactor, are also common.
The first electronic device to be introduced is called the diode. It is the simplest ofsemiconductor devices but plays a very vital role in electronic systems, having char-acteristics that closely match those of a simple switch. It will appear in a range of ap-plications, extending from the simple to the very complex.
General Packet Radio Service (GPRS)
Packet data transmission has already been standardized in GSM phase 2, offering access to the Packet Switched Public Data Network (PSPDN); see Sections 9.5.3 and 9.6.2. However, on the air interface such access occupies a complete circuit switched traf®c channel for the entire call period. In case of bursty traf®c (e.g. Internet traf®c), such access leads to a highly inef®cient resource utilization. It is obvious that in this case, packet switched bearer services result in a much better utilization of the traf®c channels.
Navigating the migration of circuit switched to packet switched networks is a complex affair. In pursuit of improving overall network efficiency and making advanced data services available, service providers must simultaneously protect existing TDM revenue while investing in new packet-based technologies. The good news is that the circuit switched architecture, which accounts for the bulk of service provider revenues, is highly reliable. The bad news is that this massive centralized processing network is neither fully depreciated nor built for packet switching.
Similarities between ATM and packet switching
Transfer of data in discrete chunks
Multiple logical connections over single physical interface
In ATM flow on each logical connection is in fixed sized packets called cells
Minimal error and flow control
Data rates (physical layer) 25.6Mbps to 622.08Mbps
[ Team LiB ] 11.1 Switch-Modeling Elements Verilog provides various constructs to model switch-level circuits. Digital circuits at MOS-transistor level are described using these elements. Array of instances can be defined for switches.
[ Team LiB ] 11.2 Examples In this section, we discuss how to build practical digital circuits, using switch-level constructs. 11.2.1 CMOS Nor Gate Though Verilog has a nor gate primitive, let us design our own nor gate,using CMOS switches.
The Host Digital Terminal (HDT) comprises all of the “common equipment” functions of the voice and data
portion of the ADC Homeworx product line. Normally located in the center office/headend with direct
connection to a local digital switch (LDS) or digital network element (DNE).
Data transmitted in small packets
Typically 1000 octets
Longer messages split into series of packets
Each packet contains a portion of user data plus some control info
Routing (addressing) info
Packets are received, stored briefly (buffered) and past on to the next node
Store and forward
Although the previous chapters in this part are issues related to the physical layer or transmission media, Chapter 8 discusses switching, a topic that can be related to several layers. We have included this topic in this part of the book to avoid repeating the discussion for each layer.