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Title: Intro%20to%20Course


1
Data Communications
  • Intro to Course
  • And
  • Architecture Models

2
Intro to TDC 460
  • Masters degree is now called Network Engineering
    and Management
  • Prereqs Java, TDC 311 or CSC 373, TDC 261, TDC
    363
  • Foundation TDC 460 (updated), TDC 463, TDC 464
    (updated)
  • Advanced TDC 477 (security), TDC 511
    (practicum), TDC 560, TDC 563
  • Electives 5 courses
  • Capstone TDC 594

3
System Architectures
  • We have already been introduced to the various
    types of communications systems
  • Telephone
  • Internet
  • Television
  • Cable TV and modems
  • LANs (wired and wireless)
  • Wireless WAN

4
System Architectures
  • Lets look at these system architectures in more
    detail
  • What are the models that support each
    architecture?
  • What type of code conversions must be performed?
  • What protocols support these models?
  • Where is the convergence?

5
What is a Protocol?
  • For two entities to communicate successfully,
    they must speak the same language.
  • What is communicated, how it is communicated, and
    when it is communicated must conform to some
    mutually acceptable conventions.
  • These conventions are referred to as a protocol.

6
Key Elements of a Protocol
  • Syntax
  • Data formats
  • Signal levels
  • Semantics
  • Control information for coordination
  • Error handling
  • Timing
  • Speed matching (between sender and receiver)
  • Sequencing (the right commands in the right order
    closely related to semantics)

7
Network Architecture
  • The task of communication is broken up into
    modules
  • For example, a file transfer could use many
    modules
  • The file transfer interface that the user runs
    (FTP)
  • The module that makes sure the file arrives at
    the destination exactly the same as when it left
    the source
  • The module that gets the packets from one router
    to another
  • The module that get each packet from the users
    computer to the network
  • The module that converts 1s and 0s to voltages

8
TCP/IP Protocol Suite
  • Dominant commercial protocol architecture
  • Specified and extensively used before OSI
  • Developed by research funded by U.S. Department
    of Defense
  • Used by the Internet

9
TCP/IP Suite Architecture
  • No official model, but a working one.
  • Application layer
  • Host to host or transport layer
  • Internet layer
  • Network access layer
  • Physical layer

10
TCP/IP Physical Layer
  • Physical interface between data transmission
    device (e.g. computer) and transmission medium or
    network
  • Characteristics of transmission medium
  • Signal levels
  • Data rates
  • etc.

11
TCP/IP Network Access Layer
  • Exchange of data between end system and network
  • Frame created
  • Destination address provided
  • Error checking code provided
  • Possible services like priority invoked

12
TCP/IP Internet Layer (IP)
  • Systems may be attached to different networks
  • Routing functions across multiple networks
  • Implemented in end systems and routers

13
TCP/IP Transport Layer (TCP)
  • Reliable delivery of data (error-free)
  • Ordering of delivery
  • Implemented in end systems only (not implemented
    in routers)

14
TCP/IP Application Layer
  • Support for user applications
  • e.g. HTTP, SMTP, FTP, SNMP

15
OSI Model
  • Open Systems Interconnection
  • Developed by the International Organization for
    Standardization (ISO)
  • Seven layers
  • A theoretical system delivered too late!
  • TCP/IP is the de facto standard

16
OSI - The Model
  • A layer model
  • Each layer performs a subset of the required
    communication functions
  • Each layer relies on the next lower layer to
    perform more primitive functions
  • Each layer provides services to the next higher
    layer
  • Changes in one layer should not require changes
    in other layers

17
OSI as Framework for Standardization
18
OSI Layers
  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data Link
  • Physical
  • What is the function of each OSI layer?

19
The OSI Environment
20
Figure 2.16 TCP/IP and OSI model
21
Questions
  • What TCP/IP layer handles addressing?
  • What OSI layer handles voltage conversions?
  • What TCP/IP layer handles email?
  • What OSI layer handles routing?
  • What TCP/IP layer handles end-to-end connections?
  • What OSI layer handles session connections?
  • What TCP/IP layer handles synchronization?

22
SNA
  • IBMs Systems Network Architecture
  • Created in the 1970s
  • Being replaced with TCP/IP but still out there a
    little bit
  • Seven layers which map fairly closely to OSI
  • Good website http//www.cisco.com/univercd/home/h
    ome.htm

23
Novell
  • Novell NetWares architecture used to rely
    heavily on IPX and SPX protocols
  • Starting with NetWare version 5, IP became the
    default protocol replacing IPX
  • NetWare protocol suite maps to the following OSI
    layers

24
(No Transcript)
25
Telephony Architecture
  • Subscribers
  • Lines
  • Central offices
  • Trunks
  • LATAs
  • SS7
  • Switching centers

26
Standards
  • Required to allow for interoperability between
    equipment
  • Advantages
  • Ensures a large market for equipment and software
  • Allows products from different vendors to
    communicate
  • Disadvantages
  • Freeze technology
  • May be multiple standards for the same thing

27
Standards Organizations
  • Internet Society
  • ISO
  • ITU-T (formally CCITT)
  • IEEE
  • ANSI

28
Functions of Standards
  1. Encapsulation
  2. Segmentation and reassembly
  3. Connection control
  4. Ordered delivery
  5. Flow control
  6. Error control
  7. Addressing
  8. Multiplexing
  9. Transmission services

29
Encapsulation
  • Addition of control information to data
  • Address information
  • Error-detecting code
  • Protocol control

30
Segmentation (Fragmentation)
  • Data blocks are of bounded size
  • Application layer messages may be large
  • Network packets may be smaller
  • Splitting larger blocks into smaller ones is
    segmentation (or fragmentation in TCP/IP)
  • ATM blocks (cells) are 53 octets long
  • Ethernet blocks (frames) are up to 1526 octets
    long
  • Checkpoints and restart/recovery

31
Why Fragment?
  • Advantages
  • More efficient error control
  • More equitable access to network facilities
  • Shorter delays
  • Smaller buffers needed
  • Disadvantages
  • Overheads
  • Increased interrupts at receiver
  • More processing time

32
Connection Control
  • Connection Establishment
  • Data transfer
  • Connection termination
  • May be connection interruption and recovery
  • Sequence numbers used for
  • Ordered delivery
  • Flow control
  • Error control

33
Connection Oriented Data Transfer
34
Ordered Delivery
  • Packets may traverse different paths through
    network
  • Packets may arrive out of order
  • Sequentially number packets to allow for ordering

35
Flow Control
  • Done by receiving entity
  • Limit amount or rate of data
  • Stop and wait
  • Credit systems
  • Sliding window
  • Needed at application as well as network layers

36
Error Control
  • Guard against loss or damage
  • Error detection
  • Sender inserts error detecting bits
  • Receiver checks these bits
  • If OK, acknowledge
  • If error, discard packet
  • Retransmission
  • If no acknowledge in given time, re-transmit
  • Performed at various levels

37
Addressing Level
  • Level in architecture at which entity is named
  • Unique address for each end system (computer) and
    router
  • Network level address
  • IP or internet address (TCP/IP)
  • Network service access point or NSAP (OSI)
  • Process within the system
  • Port number (TCP/IP)
  • Service access point or SAP (OSI)

38
Figure 2.18 Relationship of layers and addresses
in TCP/IP
39
Figure 2.19 Physical addresses
40
Example 2.3
Figure 2.20 shows a part of an internet with two
routers connecting three LANs. Each device
(computer or router) has a pair of addresses
(logical and physical) for each connection. In
this case, each computer is connected to only one
link and therefore has only one pair of
addresses. Each router, however, is connected to
three networks (only two are shown in the
figure). So each router has three pairs of
addresses, one for each connection.
41
Figure 2.20 IP addresses
42
Example 2.4
Figure 2.21 shows two computers communicating via
the Internet. The sending computer is running
three processes at this time with port addresses
a, b, and c. The receiving computer is running
two processes at this time with port addresses j
and k. Process a in the sending computer needs to
communicate with process j in the receiving
computer. Note that although physical addresses
change from hop to hop, logical and port
addresses remain the same from the source to
destination.
43
Figure 2.21 Port addresses
44
Addressing Mode
  • Usually an address refers to a single system
  • Unicast address
  • Sent to one machine or person
  • May address all entities within a domain
  • Broadcast
  • Sent to all machines or users
  • May address a subset of the entities in a domain
  • Multicast
  • Sent to some machines or a group of users

45
Multiplexing
  • Supporting multiple connections on one machine
  • Mapping of multiple connections at one level to a
    single connection at another
  • Carrying a number of connections on one fiber
    optic cable
  • Aggregating or bonding ISDN lines to gain
    bandwidth

46
Transmission Services
  • Priority
  • e.g. control messages
  • Quality of service
  • Minimum acceptable throughput
  • Maximum acceptable delay
  • Security
  • Access restrictions

47
Review Questions
  • What are the layers of the TCP/IP protocol suite?
    The OSI model?
  • What is meant by encapsulation?
  • Trace an FTP command as it moves down through the
    layers, across the medium, and up the layers on
    the receiving side.
  • What are the functions of standards?
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