Modem
A hardware device, which allows a computer to transmit and receive information over telephone lines. It converts digital signals into analog signals and vise versa. It is Data Communication Equipment (DCE).
There are three types of DCE’s available in leased lines
1. V.35 modem
2. G703 modem
3. Converter
V.35
This modem will directly connect to the router’s interface, as it is having V.35 connector in it. It is also back-to-back connected to G703 modem. The pin out / signal description of V.35 is given below.
Name | Pin | Description | Type |
FG | A | Frame/Chassis Ground | - |
SG | B | Signal Ground | - |
SDA | P | Send Data A | Differential |
SDB | S | Send Data B | Differential |
RDA | R | Receive Data A | Differential |
RDB | T | Receive Data B | Differential |
RTS | C | Request To Send | Unbalanced |
CTS | D | Clear To Send | Unbalanced |
DSR | E | Data Set Ready | Unbalanced |
DTR | H | Data Terminal Ready | Unbalanced |
RLSD | F | Received Line Signal Detect | Unbalanced |
TCEA | U | Transmit Clock Ext A | Differential |
TCEB | W | Transmit Clock Ext B | Differential |
TCA | Y | Transmit Clock A | Differential |
TCB | AA | Transmit Clock B | Differential |
RCA | V | Receive Clock A | Differential |
RCB | X | Receive Clock B | Differential |
LL | J | Local Loop back | Unbalanced |
RLB | BB | Remote Loop back | Unbalanced |
TM | K | Test Mode | Unbalanced |
- | L | Test Pattern | Unbalanced |
G703
G.703 is a CCITT standard for transmitting voice over digital carriers such as T1 and E1. G.703 provides the specifications for pulse code modulation (PCM) at data rates from 64 Kbps to 2.048 Mbps. G.703 service is typically used for interconnecting data communications equipment such as bridges, routers, and multiplexers. G.703 is transported over balanced (120 ohm twisted pair) or unbalanced (dual 75 ohm coax) cable. Whether the G.703 is balanced or unbalanced depends on your geographic location and the carrier that supplies the service.
At data rates of 64 kbps over balanced wire, there are three ways of transmission:
co-directional
central directional
contra-directional
Co-directional uses four twisted wires, two to transmit and two to receive. The data and timing are sent in the same direction over the same wires. Central directional is rarely used. Here the clock signals are supplied on different wires from a centralized clock such as an atomic clock. Central directional can use six or eight wires to send a clock signal in both directions or in separate directions. The six-wire version uses two for the clock signals and four for the data signals, and the eight-wire version uses four for clock signals and the other four for data. The contra-directional is an eight-wire version that uses two wires each for transmitting and receiving and two pairs for the clock signals. (Clock signals originate at the Data Communications Equipment (DCE) and are sent to the Data Terminal Equipment (DTE).)
In the concept of leased line, there must be always even number of G703 modems. G703 modems not only transmit data to a large distance compared to V.35 but also encrypt data.
Converter
It will do both functions of V.35 and G.703 in the same equipment. This will be used in places where the local loop is less than 50 meters.
1.4 Router
In packet-switched networks such as the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway (where one network meets another), including each point-of-presence on the Internet.
A router may create or maintain a table of the available routes and their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network points with routers before arriving at its destination. Routing is a function associated with the Network layer (layer 3) in the standard model of network programming, the Open Systems Interconnection (OSI) model.
A router connects networks together, controlling the routing of packets from source to destination and providing alternate paths when necessary.
1.5 MUX
In communication transmission systems, mux (pronounce muks, sometimes spelled "MUX") is an abbreviation for multiplexing, a device that sends multiple signals on a carrier channel at the same time in the form of a single, complex signal to another device that recovers the separate signals at the receiving end. The receiver is sometimes called a demux (or "DEMUX").
1.6 Basic Service Operators (BSO)
At Sify, there are four Basic Service Operators who provide connectivity services. They are,
1. Bharat Sanchar Nigam Limited (BSNL)
2. Bharti Telecom Nigam Limited (BTNL)
3. Bharti Telesonic Limited (BTSOL)
4. Tata
1.7 Sample Connectivity of Leased Line
1.8 FEATURES OF LEASED LINES
2. Available in multiples of 64 Kbps.
3. Uses Time Division Multiplexing (TDM)
