Chapter 7 Protocols
Protocols
For different devices on different networks to communicate requires a specific combination of hardware and software. This chapter describes the various ways that different manufacturers’ devices communicate and what is needed to allow them to talk to one another.
All machines on a network have software and hardware installed on them. Hardware has come a long way baby! Once hardware is installed, changes are needed only when the network is expanded, when a component fails, or when the network is upgraded. Devices on a network run some type of network software. Software tells them when data is coming in, when to send data out, error-checking and fixing, control the flow of data, terminal emulation. Software needs to be changed everytime a change occurs on the network.
A protocol is a set of rules that defines how two devices communicate with each other over a network. Example of placing a phone order(7-2). Three key elements that a protocol defines in order for devices to communicate:
1. syntax - describes the format of the data and the coding
schemes used for transmission.
2. semantics - the control information that is needed
by the network for establishing a connection and for error handling.
3. timing - describes the methods used to control the
flow of data on the network, to match the speed of devices on the network,
and provide sequencing techniques for the transmitted data.
Early protocols were proprietary, meaning manufactures developed them for use only on their computer equipment. Only computers from one manufacturer could communicate. More manufacturers - different equipment - need to talk - developed OSI model.
Open System Interconnection (OSI) model - suggested standard for communications developed by the International Standards Organization (ISO). 7 layers, each with a unique name and a specific funtion. Elevator analogy - 7-3.
7 layers:
Application - determines which data is transmitted, the message or form of the data, and the codes needed to identify the data; serves as the interface between the user and the communciation system and performs the actual information processing
Presentation - defines the format the data uses as it is transmitted on the communication line. Performs data compression and encryption. Performs protocol and file conversion to covert data from one type of code to another. Responsible for converting the data generated by the application program into a form compatible with terminals on the network.
Session - responsible for establishing and maintaining the connection
between two communication computers. A session is the
period of time between the establishment of the connection for the
transmission, the actual transmission of data, and the termination of the
connection. Responsible for the defining the rules of communicaiton
between two devices, know as
flow control. Flow control prevents a device from sending
two much data to a receiving machine.
Functions from the Transport layer and below are transparent to the users.
Transport - referred to the “end-to-end” layer, concerned with the transmission of the data between networks. Generates an address for the receiving computer and adds it to the data so all the networks know where the data should be sent.
Network- splits up long messages from the transport layer into
smaller groups of bits (usually 128 characters) called packets.
Adds destination addresses and routing information to the packets and moves
the packets between nodes on the network. Route-path data takes from
sender to receiver. The process of deciding which path to take is
called routing. The network
layer handles this. 2 types of routing:
1. adaptive or dynamic - network that
can changes routes based on network conditions.
2. static - data always takes the same
route from source to destination
Data Link - concerned w/ the transmission of characters; establishes and control the physical path of communication to the next network node. Prepares the packets created in the network layer for transmission by transforming them into frames - groups of data that the DL layer send out of the medium adding error-correction bits and control info to the packet received from the network layer. Responsible for implementing extensive error detection and correction procedures.
Physical - concerned with hardware; puts the individual
bits out onto the communication medium; Concerned with the elecrical
specification that define how the electrical signal transmits the 1 bits
and 0 bits so that the receiver recognizes the bits as the correct type.
Mainframe Protocols
1. character-oriented protocols (character synchronous)
- use an eight-bit byte to send control information, uses special
contol characters to show
header information and data
2. byte-count-oriented protocols - adds a count of the
number of bytes to be sent, a network address, and a block control
character at the end of
the clock to each block of data
3. bit-oriented protocols - data and its control information
are combined into a frame
4. X.25 protocols - international standard developed by
the CCITT for connecting devices to a packet-switching network.
Packet-switching referes
to the process of breaking messages into small parts, called packets, and
send them over the
fastest link to their destination.
5. Transmission Control Protocol/Internet Protocol (TCP/IP)
- originally designed to connect different networks but has
developed into a suite of
network protocols that support a number of communication needs, including
remote log-in
capabilities, file transfer,
e-mail, and routing. Actually two different protocols:
a. TCP - operates at the transport layer and is responsible
for end-to-end message delivery. Provides error
checking and detection, sequences packets in the correct order, and regulates
the flow of messages between
the source and the destination.
b. IP - operates at the network layer and breaks message into packets
and provides address for each packet.
6. X.400 and X.500 protocols - used to define standards
for e-mail. X.400 describes how e-mail should be sent so that messages
can be sent between e-mail systems worldwide. X.500 describes
how to create a directory containig every e-mail user;s name and e-mail
addresses.
Personal Computer Protocols
1. Interconnection Protocols -
a. X-ON / X-OFF -
when a device is available to receive data, it sends an X-ON signal to
the sender. If the receivers
buffer is full or it cannot accept dat afor other reasons, it sends an
X-OFF signal. Today is used to connect printer to
PC.
b. Xmodem - file
transfer protocol that allows users to move files between network nodes.
P.7-15
c.Kermit - FTP that
commonly is used to link a PC with a mainframe or minicomputer.
d. X.PC - developed
by Tymnet for converting asynchronours data into a form that can be sent
on a packet-switching
network.
2. Local Area Network Protocols -
a.Ethernet - allows
pcs to contend for access to the network. CSMA/CD (carrier sense multiple
access/collision
detection); 10Mbps. Fast Ethernet - 100Mbps
b. Token Passing -
MAU, FDDI
c.Manufacturing Automation
Protocol/Technical and office Protocol (MAP/TOP) - developed by the
Boeing Corp.
1. MAP - allows very different types of computer-related machinery
to interact with each other.
2. TOP - provides a way to integerate many devices from different manufacturers
onto a single network.
d. AppleTalk - Macintosh;
used CSMA/CA (carrier sense multiple access/collision aviodance)
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