1. Networks by Topology and Protocols
The Management of Telecommunications
Houston H. Carr and Charles A. Snyder
Networks by Topology and Protocols
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2. Introduction
Topology is the way networks are constructed and connected.
For a network, topology means how the connections are physically and electrically made.
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3. Point-to-Point (N=2) Network
Remember, a network is two or more nodes connected by one or more channels.
The simplest network is where there are only two nodes.
If both nodes are computers, it is a point-to-point topology.
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4. Relationships between nodes in an N=2 network
In a peer-to-peer relationship, both computers are of the same standing
Neither is a master
Neither is a slave or client
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5. Multipoint (N>2) Network
Topology where many computers are connected to common communication channel.
All connections are local.
The physical topology is how the wires are run, the electrical topology is how the wires are connected.
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6. How computers are connected to networks
Diagram of node with Network Interface Card (NIC) and cable
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7. Client/Server architecture
All but one of the computers are user workstations and one provides services to the rest.
Workstations are “clients” of the server.
The nodes on the network are not equal.
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8. Potential Benefits of Networks
Cost savings due to sharing
Reduced number of peripherals
Less storage space required per workstation
Reduced software cost
Cost savings due to the common channel
Single-network communications
Cost savings due to fewer applications
Savings in installation and maintenance
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9. Potential Benefits of Networks
Sharing of resources
Reduced cost per resource item
Potential availability of more expense peripherals
Greater use of resources
Reduced redundancy
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10. Potential Benefits of Networks
User Interface
Interface with network
Less or no involvement by users in operational tasks
Capability of sharing data and text for joint work
Added functionality
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11. Potential Benefits of Networks
Encourages Management Control
Control of the introduction of new technology
One network management environment
Equipment compatibility
Uniformity of communication and resources
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12. Protocol
A protocol is a standard, or a set of rules or guidelines, that governs the interaction
between people
between people and machines
between machines
Protocol determines how data move on the network.
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13. Consideration of Device-to-Device Handshaking
Communications startup –
communications initiated. B.
Character identification and framing -
determine text characters and which are control characters. C.
Message identification -
Separate characters into messages. D.
Line control -
Receiving unit says data were good, by turnaround, and requests next block. E.
Error control -
What to do in case of error (retransmit), what to do when communications breaks and is reestablished. F.
Termination -
Normal and abnormal.
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14. Collisions Collisions occur when two nodes transmit at the same time.
Collisions result in all communications being unintelligible.
Collisions cause everyone to lose, as all transmissions are destroyed.
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15. Collision control - Polling
Polling is the simplest method of collision control.
A central node has the ultimate control
Polling takes two forms
First, the central node asks each receiving node, in turn, if it has something to send.
Second, the central node waits for a signal from a node wishing to transmit and recognizes that node.
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16. Collision control – Ring topology
In a ring topology, nodes are connected to form a ring.
Any data are passed from one node to the next.
Everyone receives all messages
A node only reads messages destined for it
A data packet, called a token, is passed around the ring from one node to the next.
A node wishing to transmit must first take possession of the token. If another node possesses it, the node wishing to transmit must wait.
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17. Collision control
The final method of collision control is to react to, rather than avoid, collisions.
Method to recognize a collision has taken place.
Any node may transmit when it thinks it is permissible.
Nodes use carrier sense technology to listen to a common channel. When one believes all is quiet, it can transmit.
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18. Collision control
If more than one transmits at a time, a collision takes place.
The network protocol causes offending nodes to stop transmitting.
The nodes wait a random time and try again.
Primary method used by Ethernet bus network.
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19. Topology Topology is the electrical or channel configuration
There are two types of topology
Physical
Electrical (logical)
For local networks, the physical topology is always a star.
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20. Star network topology
The star is one of the simplest electrical topologies
All channels terminate into a computer (or switch). That is they radiate out from a central point, like a star.
The nodes at the end of the channels request the attention of the central node and communication takes place.
Although the simplest form, the overload or crashing of the central node causes the network to stop.
POTS is an example of an analog star.
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21. Logical Star Network
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22. Bus Topology
In a bus topology, all nodes are multipoint on a single shared channel.
In a bus, all wires are logically connected to a central wire, making a bus network.
Connections made through a hub.
Physical topology is still a star.
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23. Logical Bus Network
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24. Electrical Network Using a Hub
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25. Ring Network Token passing protocol Used primarily in ring networks
Transmission is only possible for node that captures token.
It then attaches the data to token and send it on its way.
Each node reads packet header, but only the designated recipient reads message.
The recipient then adds a message noting correct receipt and send it back to source.
All node read header but only the original sender reads the message.
It then clears the token and releases it.
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26. Ring Topology Third kind of local connectivity is the ring network.
Each computer is connected to those on either side of it on the ring.
All messages pass around the ring and each transited node will see part of each message, e. g. the token.
Physical topology is star with a hub or MSAU at the center, making it an electrical ring.
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27. Logical Ring Network
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28. Electrical Ring Network
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29. Physical (Star-Connected) Token-Passing Ring Architecture
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30. CSMA/CD protocol
Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
With an Ethernet bus, multiple access of many nodes is possible because each single node uses carrier sense to determine if the network is quiet.
If no signal is heard, the node in question broadcasts a message on the network that all nodes hear.
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31. CSMA/CD protocol
Under normal conditions, every node receives and reads the header of the message and only the named recipient reads the actual message.
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32. Protocol
An agreed-upon format for transmitting data between two devices
The primary function of the protocol is to control access and collisions
The protocol determines
The type of error checking to be used
Data compression method, if any
How the sending device will indicate that it has finished sending a message
How the receiving device will indicate that it has received a message.
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33. Synchronous communications
Synchronous communications protocols define the content of the packet, including a header that may include a large amount of information.
The actual content is protocol specific as well as connection dependent.
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34. Synchronous communications
Data that may be included in the header
Start of header (SOH) character
Address of the destination
Address of the sender
Block number of this block of data (e.g. sequence number)
Possibly the block number in reverse for reliability
Other administrative information such as a time stamp.
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35. Synchronous communications
The protocol will define header as fixed or variable length
If data field is variable length, a framing field notes the data length.
If data field is fixed length, this is not needed because it becomes positional in nature.
Trailer is after data field, containing the block check character (BCC) for error detection and possibly characters denoting end of transmission with a number of blocks.
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36. Synchronous Data Link protocols
Synchronous Data Link protocols have several formats
Character-oriented
Byte-count-oriented
Bit-oriented
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37. Synchronous Data Link Control (SDLC)
An example of a synchronous data link protocol used by IBM
Header and fields are of predefined length and the header is followed by data with no intervening control character.
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38. Internet Protocols
TCP/IP (transmission control protocol/Internet protocol)
IP is responsible for moving packets of data between nodes
TCP is responsible for verifying delivery from client to server.
Forms the basis for the Internet and is built into every common operating system.
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39. Internet Protocols SLIP (serial line Internet protocol)
Standard for connecting to the Internet with a modem over a phone line.
PPP (point-to-point protocol)
Internet standard for serial communications.
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40. Connectivity in Networks
A primary form of local (area) networks in the bus, using CSMA/CD protocol.
The trade name for this environment is Ethernet.
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41. Defining XBaseT
10BaseT means a speed of 10 Mbps, running on baseband, generally category 3 twisted-pair wire.
100BaseT is the same but faster, generally requiring a better grade of wire (type or category 5).
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42. LAN/WAN Interconnectivity
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43. The Management of Telecommunications:
Houston H. Carr and Charles A. Snyder
End of Chapter 6