25 terms

Circuit/Packet Switching LW

Stallings, Chapter 12
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circuit switching
A method of communi-cating in which a dedicated communi-cations path is established between two devices through one or more inter-mediate switching nodes. Unlike with packet switching, digital data are sent as a continuous stream of bits. Data rate is guaranteed, and delay is essen-tially limited to propagation time.
common channel signaling
Technique in which network control signals ( e. g., call request) are separated from the associated voice or data path by placing the signaling from a group of voice or data paths on a separate channel dedicated to signaling only.
control signaling
means by which the network is managed and by which calls are established, maintained, and terminated. Both call management and overall net-work management require that information be exchanged between subscriber and switch, among switches, and between switch and network management center.
datagram
In packet switching, a self-contained packet, independent of other packets, that carries information suffi-cient for routing from the originating data terminal equipment ( DTE) to the destination DTE without relying on earlier exchanges between the DTEs and the network.
exchange
The switching centers in the network. A switching center that di-rectly supports subscribers is known as an end office. Typically, an end office will support many thousands of subscribers in a localized area.
inchannel signaling
the same channel is used to carry control signals as is used to carry the call to which the control signals relate. Such signaling begins at the originating subscriber and follows the same path as the call itself.
integrated services digital network (ISDN)
WAN for data that offers both packet switching and traditional circuit switching in an integrated service.
local loop
A transmission path, generally twisted pair, between the individual subscriber and the nearest switching center of a public telecommunications network. Also referred to as a sub-scriber loop.
packet
A group of bits that includes data plus control information. Generally refers to a network layer ( OSI layer 3) protocol data unit.
packet switching
A method of transmitting messages through a communications network, in which long messages are subdivided into short packets. Each packet is passed from source to desti-nation through intermediate nodes. At each node, the entire message is received, stored briefly, and then passed on to the next node.
pubic data network (PDN)
public network owned or controlled by the government
softswitch
a general purpose computer running specialized software that turns it into a smart phone switch. cost significantly less than traditional circuit switches and can provide more functionality. In particular, in addition to handling the traditional circuit- switching functions, it can convert a stream of digitized voice bits into packets.
subscriber
The devices that attach to the network. It is still the case that most subscriber devices to public telecommunications networks are telephones, but the percentage of data traffic increases year by year.
subscriber line
The link between the subscriber and the network, also re-ferred to as the subscriber loop or local loop. Almost all local loop connections use twisted- pair wire. The length of a local loop is typically in a range from a few kilometers to a few tens of kilometers.
subscriber loop
The link between the subscriber and the network, typically in a range from a few kilometers to a few tens of kilometers.
trunk
The branches between exchanges. Trunks carry multiple voice-frequency circuits using either FDM or synchronous TDM. These are also re-ferred to as carrier systems.
value-added network (VAN)
the network provider owns a set of packet- switching nodes and links these together with leased lines provided by a carrier such as AT& T.
virtual circuit
A packet- switching mechanism in which a logical connection is established between two stations at the start of transmission. All packets follow the same route, need not carry a complete address, and arrive in sequence.
supervisory
control functions that have a binary character ( true/ false; on/ off), such as request for service, answer, alerting, and return to idle. They deal with the availability of the called subscriber and of the needed network resources
media gateway
physical switching functions in softswitch
media gateway controller
the call processing logic in a softswitch
circuit switching advantages
compatible with voice, commonality of calling procedures for voice and data, predictable data rate
circuit switching disadvantages
subject to blocking, requires subscriber compatibility, large processing and signal burden
packet switching advantages
provides speed conversion, appears nonblocking, efficiennt utilization, logical multiplexing
packet switching disadvantages
complex routing and control, delay can be long and varible