1. Chapter 9 Computer Networks

2. Chapter 9 Computer Networks
Chapter Outline
Network Topology
Addressing and Routing
Media Access Control
Network Hardware
OSI Network Layers
TCP/IP
Focus – Voice over IP
Network Standards
Focus - Ethernet
Focus - Upgrading Network Capacity (Part II)

3. Chapter Goals
Compare and contrast bus, ring, and star network topologies
Describe packet routing across local and wide area networks
Describe the CSMA/CD media access control protocol
Describe network hardware devices, including network interface units, routers, and switches
Describe the OSI network model, the TCP/IP protocol suite, and IEEE network standards

4. Chapter 9 Computer Networks

5. Network Topology
Spatial organization of network devices, physical routing of network cabling, and flow of messages from one network node to another
Can be physical or logical
Three types – star, bus, ring – differentiated by
Length and routing of network cable
Type of node connections
Data transfer performance
Susceptibility of network to failure

6. Point-to-Point Network Topology
Impractical for all but very small networks

7. Point-to-Point Network Topology
Impractical for all but very small networks

8. Point-to-Point Network Topology
Impractical for all but very small networks

9. Advanced Network Topologies Improve practicality for most networks

10. Store and Forward System Centralizes the work of networking

11. Network Topologies Star
Uses a central node to which all end nodes are connected
Relatively simple wiring
Bus
Connects each end node to a common transmission line
Low susceptibility to failure
Ring
Connects each end node to two other end nodes
Long maximum network length
Low susceptibility to noise and distortion
Susceptible to failure and difficulty in adding, removing, or moving nodes

12. Star Topology Uses a central node to which all end nodes are connected
Relatively
simple
wiring

13. to a common transmission line
Bus Topology
Connects each
end node
to a common transmission line
Low susceptibility
to failure
Relatively
simple
wiring

14. Long maximum network length Low susceptibility to noise
Ring Topology
Connects each
end node
to two other end nodes
Long maximum network length
Susceptible to failure and difficulty in adding, removing, or moving nodes
Low susceptibility to noise
and distortion

15. Physical Star / Logical Bus Topology and another for message routing.
The strengths of two different topologies can be combined by using one topology for physical layout
and another for message routing.

16. Addressing and Routing
How messages sent by end nodes find their way through transmission lines and central nodes to their ultimate destination
Local area networks (LANs)
Interconnected to form WANs
Wide area networks (WANs)

17. Local Area Network Routing
Each central node maintains and uses a routing table to make routing decisions
LAN hub or switch usually handles packet routing
Logical network topology determines exact procedure for routing a message between two end nodes in the same LAN

18. Example of a WAN Includes end nodes LANs zone networks backbone
central
nodes

19. LAN Central Node Routing Decisions

20. Wide Area Network Routing
Packet routing uses a store and forward approach
Forwarding stations can be implemented using
Bridges
Routers
Switches

21. Media Access Control
Uses a protocol that specifies rules for accessing a shared transmission medium
Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
Commonly used in bus networks to detect and recover from collisions
Token passing MAC protocol
Used by ring network topologies

22. CSMA/CD Protocol Process Listen and wait for an idle state
Transmit a packet
Listen for a collision
If a collision is detected
First wait for a random period of time
Then retransmit the same packet
Primary Advantage
Simplicity
Primary Disadvantage
Potentially inefficient use of data transfer capacity

23. Token Passing MAC Protocol
Token passes from node to node
in a predetermined order
includes all nodes on network
in a specified time interval
Only the node that “possesses” the token is allowed to transmit messages
All others can only receive and repeat messages
No longer used in LANs; rarely in WANs

24. Effect of CSMA/CD Protocol
on Network Throughput

25. Network Hardware Devices

26. Network Interface Units (NIUs)
Interface between network node and network transmission medium
Scan destination address of all packets
In bus network
ignores packets not addressed to it
In ring network
retransmits all packets not addressed to it
Implement media access control functions

27. Hubs Connect nodes to form a LAN Most are Ethernet devices
Combine separate point-to-point connections between nodes and the hub into a single shared transmission medium by repeating all incoming packets to every connection point
Low-cost alternative for home and small office networks

28. Bridges
Connect two networks or network segments and copy packets between them
Look at source addresses and update internal tables of node addresses on each network segment
Common uses
Construct a virtual LAN from two separate LANs
Divide a network into segments in order to minimize congestion

29. Routers
Intelligently route and forward packets among two or more networks
Forward packets based on information other than destination address
Build internal “map” of the network
constantly scan the netework to monitor traffic patterns and network node changes

30. Switches
High-speed devices that create virtual LANs on a per-packet basis
Each input connection is treated as a separate LAN
Dramatically increase network performance
Connection decisions made by hardware are based only on destination address
Each virtual LAN has only one sending and one receiving node
eliminates congestion

31. Open System Interconnection (OSI) model
OSI Network Layers
Open System Interconnection (OSI) model
ISO conceptual model that divides network architecture into seven layers
Each layer uses services of layer below and is unaware of other layer’s implementations
Uses:
General model of networks
Framework for comparing networks
Architectural roadmap that enhances interoperability among network architectures and products

32. OSI Network Model

33. Application Layer Network service request and response
Contains programs that make and respond to high-level requests for network services
End-user network utilities
Network services embedded in the OS
Network service providers

34. Presentation Layer Converts and formats data
Ensures correct interpretation of transmitted data
Encryption and decryption
Compression and decompression
Converting data between EBCDIC and ASCII
Font substitution
Primarily used by applications that format data for user display

35. Session Layer Negotiates and implements high-level protocol parameters
timeout
half or full duplex
synchronization
quality of service
Establishes and manages communication sessions
Monitors communication to detect and resolve problems that arise once protocol has been established

36. Transport Layer
Formats messages into packets suitable for transmission over the network
Places messages within a packet data area and adds header/trailer information (network addresses, error detection data, packet sequencing data)
Gives packets to network layer for delivery
Examines packets for errors; requests retransmission if necessary (when receiving packets)

37. Network Layer Routes packets to their proper destination
Those within central node interact with one another to exchange routing information and update internal routing tables

38. Data Link Layer Transmits packets and bits
Interface between network software and hardware

39. Physical Layer Transmits bit streams
Where communication between devices actually takes place
Includes hardware devices that encode and decode bit streams and the transmission lines that transport them

40. OSI Network Model

41. TCP/IP The core Internet protocol suite
Delivers most services associated with the Internet
File transfer via FTP
Remote login via Telnet protocol
Electronic mail distribution via SMTP
Access to Web pages via HTTP
Predates and corresponds poorly to OSI model

42. IP Internet Protocol
Provides connectionless packet transport across LANs and WANs
Translates datagrams into format suitable for transport by physical network
IP layer can divide datagram into smaller units and transmit them individually
Attaches header information to each unit, including its sequence in the datagram

43. IP Internet Protocol
Assumes datagram will traverse multiple networks via nodes called gateways
Determines transmission routes via related protocols (ICMP, RIP)
IP nodes
Identified by unique 32-bit address (nnn.nnn.nnn.nnn)
Periodically exchange routing information to keep tables current

44. Only the IP layer is implemented within the gateways

45. TCP Transmission Control Protocol
Provides connection-oriented packet transport to higher-level Internet service protocols, including HTTP, FTP, and Telnet
Provides framework to check for lost messages; explicitly establishes connection with intended recipient before transmitting messages
Performs connection management functions (verifying receipt, verifying data integrity, controlling message flow, securing message content)

46. TCP Transmission Control Protocol
Sender and recipient TCP layers maintain information about one another (message routes, errors encountered, transmission delays, status of ongoing data transfers)
Uses positive acknowledgment protocol to ensure data delivery
Establishes connections through a port and an socket

47. VoIP Voice over IP
Technologies/standards that carry voice messages and data over single packet-switched network
Lower cost than traditional public switched telephone network (PSTN)
Complex and competing standards
Transmission quality problems
packet loss
latency
jitter

48. for many component protocols
H.323 is an umbrella
for many component protocols

49. Network Standards IEEE 802 standards
Describe network hardware, transmission media, transmission methods, and protocols
Help ensure compatibility among products from competing vendors
Developed by committees whose membership is drawn from industry, government, and academia
Ethernet standard (802.3) - very successful

50. IEEE 802 Network Standards

51. No provision for packet priorities or guarantees of quality of service
Ethernet
No provision for packet priorities
or guarantees of quality of service

52. 10 Gigabit Ethernet

53. Business Focus – Upgrading Network and Storage Capacity
Bradley Advertising Agency
The trade-off between short and long-range benefits of copper and fiber optic wiring
Copper is installed in most buildings, works well for current needs, and can be upgraded
Current technology pushes copper to its maximum
Fiber optic cable has far greater theoretical capacity than copper
Current optical products are expensive and not yet perfected
Fiber optic cable is the future
But when is it cost effective for a particular organization or need?

54. Summary Network topology Addressing and routing Media access control
Network hardware
OSI network layers
Network standards

55. Chapter Goals
Compare and contrast bus, ring, and star network topologies
Describe packet routing across local and wide area networks
Describe the CSMA/CD media access control protocol
Describe network hardware devices, including network interface units, routers, and switches
Describe the OSI network model, the TCP/IP protocol suite, and IEEE network standards