Networks are about Communication! What is a good model of communication?

A COMMUNICATION MODEL

DATA COMMUNICATION NETWORK comm.net comm net node net station i.e computer terminal or telephone

DATA COMMUNICATION NETWORKS Communication networks switched unswitched

Switched Circuit Switched Packet Switched DATA COMMUNICATION NETWORKS

Unswitched(broadcast nets) DATA COMMUNICATION NETWORKS packet radio satellite local Packet switched nets are store and forward nets.

ckt switched nets have dedicated communication paths (i.e. telephone) For example: DATA COMMUNICATION NETWORKS A Broadcast Comm. Net can be WAN, the media is unshared

DATA COMMUNICATION NETWORKS Dish LAN EXAMPLES:

DATA COMMUNICATION NETWORKS Ethernet with a bus topology:

DATA COMMUNICATION NETWORKS Ring topology net: Note: No switching nodes,media is shared in LAN For packet radio,every station can hear every other, the media is shared so this is a LAN technology

DATA COMMUNICATION NETWORKS Agent input devicetransmitterchannel channel receiver output device This course addresses the communication systems parts between the input and output devices.

Computer Communications Architecture The Three Layer Model Application run on computer which use networks network layer - xchange of data between computer and network transport layer - error detection and correction application layer - file xfer etc.

Computer Communications Architecture

Protocol Data Units TPDU1 = transport protocol data unit := transport hdr, chunk1 TPDU2 = transport hdr, chunk2 NPDU = network protocol data unit network hdr, TPDU

Protocol Data Units Application data = chunk1 + chunk Destination SAP (service access points) TPDU has destination SAP so that appropriate application obtains data

Protocol Data Units Sequence # TPDU’s may be sent in any order,and by different routes and may arrive at different times. TPDU may have error detection or correction codes built-in NPDU destination address (i.e. IP address) facilities requires (i.e. priority)

Transmission Terminology point-to-point :- guided transmission is unshared I.e. O(N**2) connectivity (completely connected) = number of links

Transmission Terminology Multipoint guided transmission allows shared medium

Transmission Terminology ANSI Defs: – simplex - one direction only – half-duplex - two-way but not at the same time. – full-duplex - simultaneous two way transmission

Transmission Terminology CCITT – CCITT vs ANSI – simplex = half-duplex – duplex = full-duplex CCITT = international telegraph and telephone consultive committee

Analog and Digital Data Transmission data - entities which convey meaning signals - encoding of data signaling - act of sending a signal transmission - communication of data by propagation and processing of signals

Analog and Digital Data Transmission digital data - takes on discrete values, i.e. text integers. analog data - takes on continuously varying patterns of intensity, i.e.. sound But what is digital? What is Analog? How do we defines these things?

Analog and Digital Data Transmission s(t) is continuous (i.e. analog) iff for all a

DATA and SIGNALS Modem (modulator/demodulator) modulation involves two waveforms: The modulating signal (the message) and the carrier wave which is altered by the modulating signal The complementary process is called demodulation Bits modem analog signal modem bits

ISO-OSI Model ISO= International Standards Organization OSI = Open Systems Interconnection OSI Model = a 7 layer model used to describe most networks today

1. Physical Layer This is a physical connection between machines. BITS

2. Data Link Layer Provides reliable transfer of information across the physical links. FRAMES/Packets or DLPDU

3. Network Layer Routing

4. Transport Layer error recovery and flow control

5. Session Layer Control for communication, close and open connections

6. Presentation Layer Data formatting and character code conversion

7. Application Layer file transfer, virtual terminals, electronic mail etc..