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

transcript

Networks are about Communication!

What is a good model of communication?

A COMMUNICATION MODEL

Source Channel

Destination

xmitted signal rcvd signal

DATA COMMUNICATION NETWORK

comm.net

comm net node

net station i.ecomputer terminal or telephone

DATA COMMUNICATION NETWORKS

Communication networks

switched unswitched

Switched

Circuit Switched Packet Switched

Unswitched(broadcast nets)

packet radio satellite local

Packet switched nets are store and forward nets.

ckt switched nets have dedicated communication paths (i.e. telephone)

For example:

net station

A Broadcast Comm. Net can be WAN, the media is unshared

LAN EXAMPLES:

Ethernet with a bus topology:

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

Agent input device transmitter channel

channel receiver output device

This course addresses the communication systems parts between the input and output devices.

Computer Communications Architecture

The Three Layer ModelApplication 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

Applications Applications

Transport layer 1 2 3

network access

network accessCom net

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 + chunk2 + ...

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)

(N 2 N ) = number of links

Multipoint guided transmission allows shared medium

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

– full-duplex - simultaneous two way transmission

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 meaningsignals - encoding of datasignaling - act of sending a signaltransmission

- communication of data by propagation and processing

of signals

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?

lim s(t) s(a)t a

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 ModelISO= 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 LayerData formatting and character code conversion

7. Application Layer

file transfer, virtual terminals, electronic mail

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

Documents