Monday, 19 March 2007


What is required to build a successful telecom business?

Need to understand competition, and regulation and win market share. Need to keep customers by satisfying them early and win new ones. On the financial side, need to keep investors satisfied by having good margins: this can be done by increasing revenues and/or reducing costs. Revenues come from services. New service time to market is important. Existing services quality, billing, price, ordering, customer support will influence their success. Examples of services that a carrier can offer with an optical network: dark fiber; wavelength service; bandwidth (E1 to 2.5G) leasing;
Hierarchy in a Network: found in all networks. Logical structure to interconnect Network Elements. Connect local equipment to higher level equipment. Idea is not to interconnect all the local NEs together (not transmission resource efficient and not scalable approach) but to connect to a higher level (say regional) NE, themselves connected via a connection to a higher level NE. Equipment at different levels have different function. For example a Central Office/Telephone exchange at the local level will have connections to customers whereas the higher level will do connections between CO only and to the higher level.

A hierarchy brings order to the way interconnections are made and also creates different functions – in the same way as people in an organization hierarchy have different responsibilities and the hierarchy allows people to understand how of how people communicate.
Where transmission fits: the first or last mile is called Access – the rest is transmission. Transmission is what connect Network Elements such as Switches (telephone or data) together.

Switch functionality – example: a telephone switch connects 2 ports under the end user command. The difference between a tel switch and a cross connect is in the control of this element: the end user controls/activates the telephone switch (and the future intelligent optical switch!) whereas the management system for a cross connect allows its control. The logic of connecting a telephone call: all the COs talk to each other with signaling to set-up the call – same principle as we are going to have with the future intelligent optical network!
Analog and digital signals: an analogue signal is continuous in time. A digital signal is a series of on/off signals or ‘1’ and ‘0’.

Types of networks: Circuit switching, Packet switching

In circuit switching, a circuit across the network is established before data can flow from one point to another. This circuit can be seen as a pipe (like plumbing) and the data will flow on it. The data does not need to have any indication of where it is going. It just flows on the stablished pipe. In packet switching, the data to be sent is chopped into packets, each packet has a destination address and the switch examines it to decide where to send it. In connectionless networks, there is no predetermined route for the data to flow along (such as in IP or Ethernet networks). Each switch does its own analysis of where the data needs to go to send it on. In connection oriented packet switching networks (such as MPLS or ATM), a route is established once for all and the switches are setup to recognize the data to go on one route. Hence all the packets follow the same route.
ISO 7 Layer Model
Complex function is split into layers to simplify the tasks and allow a modular implementation: A client layer simply uses the service of a server layer. This allows the implementation of the server layer to be hidden – just the service is visible, not how the job is done.
The transport layer segments the info to be transmitted into pieces, numbers them (and can do checking on this number to ensure they all get through) and pass them on to the Network layer.
The network layer has a view of the whole network and can see which hop a packet needs to go next and passes the packet to the data link layer.
The data link layer ensure the point to point communication and passes the data to the physical layer for actual transmission onto the physical medium..
IP is layer 3
ATM, Frame Relay are layer 2
SONET/SDH is layer 1/2
A synchronous transmission pipe at the physical layer is has a fixed size and is present whether data flows or not.
Nortel Networks

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