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Layered tasks

OSI Model

Layers in OSI model

TCP/IP Suite

Addressing

Telephone and cable networks for data transmission,

Telephone networks

Dial up modem

DSL

Cable TV for data transmission.

Unit - 1

Overview

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Telephone and cable networks for data transmission,

Telephone networks

Dial up modem

DSL

Cable TV for data transmission.

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TELEPHONE NETWORKTELEPHONE NETWORK

Telephone networks use circuit switching. The Telephone networks use circuit switching. The telephone network had its beginnings in the late telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the 1800s. The entire network, which is referred to as the plain old telephone system (POTS),plain old telephone system (POTS), was originally an was originally an analog system using analog signals to transmit voice.analog system using analog signals to transmit voice.

PSTN: Public Switched Telephone Network

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Circuit Switching

Message Switching

Packet Switching.

Connection-Oriented versus Connectionless

Virtual Circuit versus Datagram Networks

Point-to-Point Network Switching

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Circuit Switching

Store-and -Forward Networks

• Message Switching

• Packet Switching• connection-oriented vs connectionless

• virtual circuit vs datagram

Circuit Switching:Seeking out and establishing a physical copper path from end-to-end [historic definition] .Circuit switching implies the need to first set up a dedicated, end-to-end path for the connection before the information transfer takes place.Once the connection is made the only delay is propagation time.

Point-to-Point Switching

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(a) Circuit switching. (b) Packet switching.

Circuit Switching

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Intermediate processors (IMPS, nodes, routers, gateways, switches) along the path store the incoming block of data.

Each block is received in its entirety, inspected for errors, and retransmitted along the path to the destination. This implies buffering at the router and one transmission time per hop.

A store-and-forward network where the block of transfer is a complete message.

Since messages can be quite large, this can cause:

• Buffering problems

• High mean delay times

Store-and-Forward Networks

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A store-and-forward network where the block of transfer is a complete packet. A packet is a variable length block of data with a tight upper bound.

Using packets improves mean message delay.

Packet Switching

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Connection-oriented Protocols

• A setup stage is used to determine the end-to-end path before a connection is established.

• Data flow streams are identified by some type of connection indicator .

Packet Switched Networks

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Connectionless Protocols

• No set up is needed.

• Each packet contains information which allows the packet to be individually routed hop-by-hop through the network.

Packet Switched Networks

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Datagram

• Each datagram packet may be individually routed.

Virtual Circuit

• Virtual circuit set up is required.

• All packets in a virtual circuit follow the same path.

Datagram v/s Virtual Circuit

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Event Timing

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Telephone and cable networks for data transmission

Telephone networks

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Endoffices

Local loop

Trunk

Tandemoffices Regional offices

Trunk

• • •

Major components of a telephone system

LOOPS, TRUNKS, SWITCHING OFFICES

The connection between end or local central office and the customer is the “local loop”

The first 3 digits of local telephone number define the office and the last 4 digits define the local loop number.

Trunks: are transmission media that handle the communication between offices.

To avoid permanent physical link between any two subscribers telephone company has switches located in a switching office.

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Advantages

• Available everywhere

• Reliable connectivity

• Low cost

• Easy setup

Disadvantages

• Only one session per circuit

• FCC limited transmission speed at 53 Kbps

• Most circuits will only reach 44 Kbps due to line noise

• Analog transmissions only

POTS advantages and disadvantages

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Intra-LATA services are provided by local exchange carriers.

Since 1996, there are two types of LECs: incumbent local exchange carriers and competitive

local exchange carriers.

Local Access Transport Areas (LATA): A LATA can be small or metropolitan area.

Small state have one single LATA and a large state may have several LATAs

The services offered by common carriers inside a LATA are called intra-LATA services.

The carrier that handles these services is called a local exchange carrier (LEC)

Local Access Transport Areas (LATA)

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Switching offices in a LATA

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Point of presences (POPs)

The services between LATAs are handled by interexchange carriers (IXCs)

The connection between Tandem office and IXCs are point of presence (POP).

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Signaling

The tasks of data transfer and signaling are separated in modern telephone

networks: data transfer is done by one network, signaling by another.

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Data transfer and signaling networks

Signal Point: Telephone or computer is connected to SP.

Signaling Network uses nodes called signal transport points (STPs).

SCP: Service Control Point controls the whole operation of the signaling network

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Signaling System No.7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world’s public switched telephone network (signaling network) telephone calls.

The main purpose is to set up and tear down telephone calls.

Other uses include number translation, prepaid billing mechanisms, short messages service(SMS), and a variety of other mass market services.

Signaling System No.7 (SS7)

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Types of Signaling

Signaling in Telecommunications Network

Channel Associated Signaling (CAS)

Common Channel Signaling (CCS)

Signaling System Number (SS7) is a form of Common Channel Signaling.

Channel Associated Signaling (CAS)

Used for In-Band Signaling

Signaling is transmitted in the same frequency band as used by voice.

Voice path is established when the call setup is complete, using the same path that the call setup signals used.

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Out of Band signaling

Employs separate, dedicated path for signaling.

Voice trunks are used only when a connection is established, not before.

Faster Call Setup.

Switch

A

Switch

B

Voice Trunks

Signaling Link

Common Channel Signaling

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Faster call setupNo interference between signaling tones by network and frequency of human speech pattern.Greater Trunking Efficiency:- CCS has shorter call set up and tear down times that result in less call holding time, thereby reducing the traffic on the network.Information Transfer:- CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification

Advantage of CCS over CAS

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Out of band SignalingHigher Signaling data rates (56Kbps & 64 Kbps)Signaling traffic is bursty and of short duration, hence operates in connectionless mode using packet switchingVariable length signal units with maximum size limitationOptimum use of bandwidthReliability and flexibility

SS7 Principle

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OSI SS7

SS7 Protocol Stack

MTP: Message transport level

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Message Transfer Part (MTP Level 1) Physical• Provides an interface to the actual physical channel over

which communication takes place• CCITT (Consultative Committee for International Telegraphy and Telephony) recommends

64Kbps transmission whereas ANSI recommends 56 Kbps

MTP Level 2 (Data Link)• Ensures accurate end-to-end transmission of a message

across a signaling link• Variable Length Packet Messages are defined here• Implements flow control, message sequence validation,

error checking and message retransmission• Monitor links and reports their status• Test links before allowing their use• Provides sequence numbers for outgoing messages

Protocols

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Layers in SS7

Similar to Internet model, is signaling system seven(SS7)

Physical Layer: uses several physical layer specifications such as T-1 (1.544 Mbps) and DC0 (64kbps)

Data link Layer: provides service such packetizing, packet header and CRC

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MTP Level 3 (Network)• Message routing between signaling points in the SS7 network• Signaling network management that provides traffic, links and

routing management, as well as congestion (flow) control• Re-routes traffic away from failed links and signaling points,

controls traffic when congestion occurs

Signaling Connection Control Part (SCCP)

• Provides connectionless and connection-oriented network services

• Provides more detailed addressing information than MTPs• Used as transport layer for TCAP (Transaction capabilities

applications part) based services

Protocols

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Transaction Capabilities Applications Part (TCAP)

Exchange of non-circuit related data

• Between applications across the SS#7 network

• Using the SCCP service

Queries and responses sent between Signaling Switching Point (SSPs) and Signaling Control Point (SCPs)

Sends and receives database information

• Credit card validation

• Routing information

Protocols

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Layers in SS7

Network Layer: Provides end to end connectivity by using the datagram approach to switching .

Routers and switches route the signal packets from the source to destination

Transport Layer: Signaling connection control points is used for special services such as 800 call processing

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Layers in SS7

Upper Layers: TUP, TCAP and ISUP. 3 protocols

Telephone User Port (TUP) is responsible for setting up voice calls, receives the dialed digits and routes the calls.

Transaction capabilities application port (TCAP) provides remote calls that let an application program on a computer invoke procedure on another computer

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Services provided by Telephone Networks

Telephone companies provide two types of services: Analog and Digital

Analog Services

Analog Switched Services

Analog Leased Services

Digital Services

Switched 56/ Service

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Services provided by Telephone Networks

Analog Switched Services:

This is dial up service, signal is of analog and the bandwidth is of between 0 to 4000 Hz.

Service is normally provided for a flat monthly rate or charged for each call or a set of call.

800 service: If a subscriber needs to provide free connections for other subscribers (customers) it request the 800 service. The call is free for the caller, but is paid by the callee (Tollfree).

Wide area telephone service (WATS): Outbound call (to the customer) paid by the organization, charges are based on the number of calls.

900 Service: Inbound service, call is paid by the caller and is normally more expensive than a normal call.

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Services provided by Telephone Networks

Analog Leased Service:

Customer can use leased line called a dedicated line. Permanently connected to another customer. Although connection passes through the switches in the network, but switch is always closed, no dialing is needed.

Digital Services:

Switched /56 Service: Digital version of an analog switched line. Provides data rate up to 56kbps. Subscribers do not need modems need a device called a digital service unit (DSU).

Digital Data Service: DDS is the digital version of an analog leased line, with a maximum data rate of 64 kbps.

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Dial up modem

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DIAL-UP MODEMSDIAL-UP MODEMS

Traditional telephone lines can carry frequencies Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz. All this range is used for transmitting voice, 3000 Hz. All this range is used for transmitting voice, where a great deal of interference and distortion can where a great deal of interference and distortion can be accepted without loss of intelligibility.be accepted without loss of intelligibility.

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Telephone line bandwidth

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(a) A binary signal

(b) Amplitude modulation(c) Frequency modulation

(d) Phase modulation

Modems

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(a) QPSK.

(b) QAM-16.

(c) QAM-64.

Modems

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(a) V.32 for 9600 bps.

(b) V32 bis for 14,400 bps.

(a) (b)

Modems

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Modulation/demodulation

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Modem Standards

V series standards

V.32 and V.32 bis

V.32 bis

V.90

V. 34 bit : Bit rate of 28,800 bps with a 960 point constellation and a bit rate of 33,600 bps with a 1664 point

V. 90 : Bit rate of 56,000 bps

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The V.32 and V.32bis constellation and bandwidth

V.32 uses combined modulation and coding technique: Trellis coded modulation

4 bit and 1 extra bit for error detection

32 QAM with baud rate of 2400. 4*2400=9600bps

V.32 bis uses 128-QAM :7 bits/baud with 1 bit for error detection

2400*6=14400bps

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Uploading and downloading in 56K modems

In uploading quantization noise limits the data rate to 33.6 kbps

In downloading data rate is 56 kbps

Sampling rate 8000 and 8 bits per sample, one bit is used for control purpose

8000*7=56kbps

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DIGITAL SUBSCRIBER LINEDIGITAL SUBSCRIBER LINE (DSL)

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DIGITAL SUBSCRIBER LINEDIGITAL SUBSCRIBER LINE

After traditional modems reached their peak data rate, After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. to provide higher-speed access to the Internet. Digital Digital subscriber line (DSL)subscriber line (DSL) technology is one of the most technology is one of the most promising for supporting high-speed digital promising for supporting high-speed digital communication over the existing local loops. communication over the existing local loops.

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DIGITAL SUBSCRIBER LINEDIGITAL SUBSCRIBER LINE

ADSL is an adaptive asymmetric communication technology designed for residential users; it is not suitable for businesses.

The existing local loops can handle bandwidths up to 1.1 MHz.

The system uses a data rate based on the condition of the local loop line.

Twisted pair cable is capable of handling BW up to 1.1 MHz, but filter installed at the end office of the telephone company which limits BW to 4 Khz, If the filter is removed entire 1.1 Mhz BW is available.

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Asymmetric DSL: provides higher speed (bit rate) in the downstream direction than in the upstream direction.

Discrete Multitone Technique (DMT): Modulation technique used in ADSL is called the discrete multitone technique which combines QAM and FDM.

Available bandwidth is 1.104 MHz is divided into 256 channels, each channel of 4.312 kHz

Voice: Channel 0 is reserved for Voice

Idle: 1 to 5

Upstream: 6 to 30(25 Channels), one for control channel and 24 channels for data transfer

24X4000(Hz)X15(bits)=1.44 Mbps (Normally below 500 kbps, some channels are deleted )

Downstream: 31 to 255 (225 Ch) 1 Ch for Contr,

224 X4000X15=13.4 Mbps (Normally below 8 Mbps)

ADSL

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Discrete multitone technique

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Bandwidth division in ADSL

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Customer site: ADSL modem

At the customer site, device is called a digital subscriber line access multiplexer (ADSL).

ADSL modem modulates and demodulates the data using DMT, and creates downstream and upstream channels.

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Telephone Company Site: DSLAM

At the telephone company site, device is called a digital subscriber line access multiplexer (DSLAM).

Its function is similar to ADSL modem, and in addition it packetizes the data to be sent to the Internet (ISP server)

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ADSL Lite: (Splitterless ADSL), Downstream is of 1.5Mbps and downstream of 512 kbps

Symmetric Digital Subscriber Line (SDSL)

is a Digital Subscriber Line (DSL) variant with T1/E1-like data rates (72 to 2320 kbit/s).

It runs over one pair of copper wires, with a maximum range of about 3 kilometers or 1.86 miles.

The main difference between ADSL and SDSL is that SDSL has the same upstream data rate as downstream (symmetrical), whereas ADSL always has smaller upstream bandwidth (asymmetrical).

However, unlike ADSL, it can't co-exist with a conventional voice service on the same pair as it takes over the entire bandwidth.

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HDSL (High bit-rate Digital Subscriber Line:

• Single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.

SDSL (Symmetric Digital Subscriber Line:)

• One twisted pair version of HDSL

• Full duplex symmetric communication upto 768 kbps in each direction

VDSL (Very High bit-rate Digital Subscriber Line)

• Uses coaxial, fiber optic, or twisted pair cable for short distances.

• DMT modulation technique is used

• 25 to 55 Mbps for downstream and 3.2 mbps for upstream

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Summary of DSL technologies

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CABLE TV NETWORKSCABLE TV NETWORKS

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CABLE TV NETWORKSCABLE TV NETWORKS

The The cable TV networkcable TV network started as a video service started as a video service provider, but it has moved to the business of Internet provider, but it has moved to the business of Internet access. access.

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Traditional cable TV network

HDSL (High bit-rate Digital Subscriber Line), Head end receives video signals feeds signal to coaxial cables.

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Hybrid fiber-coaxial (HFC) network

RCH: Regional cable head 400,000 subscribers.

Communication in an HFC cable TV network can be bidirectional.

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CABLE TV FOR DATA TRANSFERCABLE TV FOR DATA TRANSFER

Cable companies are now competing with telephone Cable companies are now competing with telephone companies for the residential customer who wants high-companies for the residential customer who wants high-speed data transfer. speed data transfer.

Bandwidth: Coax BW is of 5 to 750 MHz Bandwidth: Coax BW is of 5 to 750 MHz

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Downstream Video Band: 54 to 550 Mhz , Each TV Channel occupies 6 MHz this can accommodate more than 80 channels

Downstream Data Band: Occupies upper band, from 550 to 750 MHz, this band is divided into 6-Mhz channels, 64-QAM modulation technique.

Data rate: 6 bits/baud in 64 QAM. 1 bit is used for error detection 5 bits of data per baud. 5 bits/Hz* 6 Mhz=30 Mbps.

Upstream Data Band: Occupies upper band, from 5 to 42 MHz, this band is divided into 6-Mhz channels, QPSK modulation technique.

Data rate: 2 bits/baud in 64 QAM, 2 bits/Hz* 6 Mhz=12 Mbps. The theoretical upstream data rate is 12 Mbps

Division of coaxial cable band by CATV

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Cable modems transfer data across local cable TV lines, toggling between analog and digital signals with data transfer rates comparable to DSL.

Cable modem (CM)

The cable modem connects a computer to the cable company network through the same coaxial cabling that feeds cable TV (CATV) signals to a television set.

Uses Cable Modem at Home End and CMTS (Cable Modem Termination System) at Head End.

Characteristics: Shared bandwidth technology 10 Mbps to 30 Mbps downstream 128Kbps-3 Mbps upstream Maximum Distance from provider to customer site: 30 miles

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Cable Modems

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Coaxial TV cable

1 to 10 Mbps download speeds

Up to 2 Mbps upload speeds

Cable connects from NIC to a cable modem, which has an RJ-45 port

Many users connect a router to the cable modem to provide access to several PC’s or other network devices

Cable modem (CM)

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Cable modem transmission system (CMTS)

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Cable TV (CATV) Network serves as the Internet Service Provider (ISP)Cable Modem modulates/transmits and demodulates/receives to/from a CATV channelDownstream: data received at the modem is communicated to one or more PCs on a LAN via Ethernet, USB, PCI Bus, etc.Upstream: data requests from the PC are transmitted through the modem to the CATV network via coaxial cable, phone line or wireless. CATV data service interfaces to the Internet via Cable Modem Termination System (CMTS )

Cable modem transmission system (CMTS)

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June/July 2011With a neat diagram, explain the TCP/IP reference model, giving brief description of the protocols in each layer.Differentiate between CM and CMTSExplain the operation of ADSL using discrete muti tone modulation indicating the different channels, with a neat diagram

May/June 2010Explain OSI model, with a neat block diagram. Consider a source, destination machine and some intermediate nodes for discussion.How addresses employed (used) in internet employing TCP/IP protocol can be classifiedWhat is DSL technology List different DSLs available. Discuss salient features of ADSL.

Questions

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December 09/Jan 10Show the layer representation in the TCP/IP and the OSI model and explain.Give a brief overview of SS7 signalingMatch the following functions to the appropriate layers in the OSI model.• Dividing the transmitted bit stream into frames• Determining the route to be used through subnet• Reliable process to process message delivery• Accessing the World Wide Web

December 2010What are the levels of addresses that are used in an internet, employing the TCP/IP protocolWhat are different types of services provided by telephone networksName the major components of a telephone network

Questions