Unit - 1 Overview • 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.
Telephone and cable networks for data transmission, • Telephone networks • Dial up modem • DSL • Cable TV for data transmission.
TELEPHONE NETWORK 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. • PSTN: Public Switched Telephone Network
Point-to-Point Network Switching • Circuit Switching • Message Switching • Packet Switching. • Connection-Oriented versus Connectionless • Virtual Circuit versus Datagram Networks
Point-to-Point Switching • 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 upa 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.
Circuit Switching (a) Circuit switching. (b) Packet switching.
Store-and-Forward Networks • 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
Packet Switching • 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 Switched Networks 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 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.
Datagram v/s Virtual Circuit 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.
Telephone and cable networks for data transmission Telephone networks
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.
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
Local Access Transport Areas (LATA) 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) 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.
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).
Signaling The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another.
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
Signaling System No.7 (SS7) 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.
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.
Common Channel Signaling Voice Trunks Switch A Switch B Signaling Link • 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.
Advantage of CCS over CAS • Faster call setup • No 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
SS7 Principle • Out of band Signaling • Higher Signaling data rates (56Kbps & 64 Kbps) • Signaling traffic is bursty and of short duration, hence operates in connectionless mode using packet switching • Variable length signal units with maximum size limitation • Optimum use of bandwidth • Reliability and flexibility
SS7 Protocol Stack OSI SS7 MTP: Message transport level
Protocols 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
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
Protocols 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 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
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
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
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
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.
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.
DIAL-UP MODEMS Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz. All this range is used for transmitting voice, where a great deal of interference and distortion can be accepted without loss of intelligibility.
(a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation Modems
Modems (a) QPSK. (b) QAM-16. (c) QAM-64.
Modems (a) V.32 for 9600 bps. (b) V32 bis for 14,400 bps. (b) (a)
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
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
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
DIGITAL SUBSCRIBER LINE After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. Digital subscriber line (DSL) technology is one of the most promising for supporting high-speed digital communication over the existing local loops.
DIGITAL 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.
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