1. Fast Packet Technology
ISOM 591
March 27, 2000 1

2. Global WANs Must Support Bandwidth Demands
How to Determine Broadband Needs?
Internet access
video-on-demand and multimedia
teleconferencing
CAD/CAM applications

3. Broadband in the Analog World
broadband in the analog world is the ability to stack frequencies on a single transmission medium, providing multiple channels on the same medium like radio or TV, using multiplexing techniques

4. Broadband in the Digital World
in the digital world, broadband loosely means any data rate greater than T-1 speeds (1.544 Mbps)

5. Broadband vs. Narrowband
narrowband communications channels provide a single channel for communications so that only one device can transmit at a time
ex: Ethernet LANs

6. Fast Packet Switching to Support Broadband
differs from conventional packet-switching in these ways paths are established dynamically bandwidth is dynamically assigned packets are rates
modern transmission media is highly reliable and needs less error-checking

7. Types of Communication Connections
connection-oriented
a connection path is established before data is transfered
this connection path is unavailable to other users while in use
ex: telephone calls 2

8. Types of Communication Connections
connectionless
no connection is established for a communication
packets associated with the communication are transmitted on the medium as they are generated 3

9. Bursty Data
traditional data applications are called “bursty” because the data transported between the application and the user is not transmitted at a fixed, predictable rate
this causes congestion at peak demand times
packet-switching serves bursty traffic well
note that voice and video need packets to arrive at a highly uniform rate 4

10. Protocols
for two devices to communicate, must agree on the same set of conventions, or protocols
protocols include decisions about how to structure a packet or frame, what is included in a packet header, how to do error detection, network management issues
during transmission, different nodes need to have different levels of information 5

11. OSI and Interconnection Devices
Application (gateway)
user application
Presentation
formats and converts data
Session
establishes the communications session
these three layers are not used for transport across the network 6

12. OSI (Open Systems Interconnection)
Transport
manages the end to end control of the communication
Network (routers)
routes the data to the correct destination
Data link (bridges)
transmits data to and from each node
Physical (repeater)
electrical connections 7

13. The Life of a Packet: Its Journey
FEP
Network Interface
Card
Global network 8

14. The Life of a Packet: Application Layer
A spreadsheet is to be sent from Chicago to London
the spreadsheet application program adds some information to the data identifying it as a spreadsheet so that the destination program knows what to do with it 9

15. The Life of a Packet: Presentation Layer
The combination of data and control information flows to the company gateway computer or front end processor
the bit stream is compressed or encrypted as necessary and a header is added to identify the application needed 10

16. The Life of a Packet: Session Layer
FEP divides the bit stream into segments, each of which is encapsulated into a packet
the packets are moved to a network interface device 11

17. The Life of a Packet: Transport Layer
A header is added that is needed for end-to-end error control and network management
TCP typically used at this layer 12

18. The Life of a Packet: Network Layer
Another header is added by the end node, which will be used by the intermediate nodes to determine routing and perform call setup and teardown
IP typically used at this layer 13

19. The Life of a Packet: Data Link Layer
Final header is added which includes necessary info on error checking in route, how the packet is constructed, how to handle time outs
HDLC typically used at this level 14

20. The Life of a Packet: Physical Layer
Procedures at this layer handle how the physical interface is achieved
hardware and driver software work together
for example, voltage levels and how the data pins carry specific signals are established 15

21. Packets and Protocol Data Units
Network
Header
Transport
Header
Session
Header
Data Link
Header
Raw data &
control info
Layer 2
Layer 3
Layer 4
Layer 5
Layers 6,7 16

22. The Packet Is Ready to Travel17

23. The Packet Travels Through the Network
At each intermediate node, bridge, or router, the lowest two layers of info are stripped off so the node knows how to
route the packet to its destination
perform error checking
manage the network
create reports on network conditions
when the packet arrives at the next gateway….. 18

24. Data Link and Network
At the data link layer, arrange the packets in sequence and passed up to the network link layer
gateway checks the destination address from the session layer
if gateway recognizes the destination address, layer 4 header information (transport) is read to determine if network and session layers need to exchange any info 19

25. Transport and Session Layer
End to end checking is done here
the PDU is sent on to the session layer
the receiver follows the instructions which might include error checking to be done at the session layer
corrupt packets are discarded, a NAK (negative acknowledgement) is sent requesting the packet be re-sent 20

26. Presentation and Application
Good packets move into the destination computer for de-encryption and decompression as needed
finally, all control information is stripped away and the destination computer is informed about the type of application which has been sent
this entire process takes less than one second! 21

27. Transmission Methods and Procedures
data communications standards
ex: X.25 is a standard protocol for packet switching
orderly rules for transferring information throughout the network
what is a protocol?
exchange of information to initiate a conversation and set up rules for conducting the conversation 36

28. Transmission Protocol: What Does It Do?
initiation of communication
character identification and grouping
message or conversation identification to determine where one ends and another begins
link control to regulate the flow of data
error detection and correction
termination of the communication 37

29. Communication Services
packet-switching services
data is transmitted, a packet at a time
each packet may take a different path through the network
no predefined virtual circuit
can route packets around broken or congested lines
handles bursty communications well
ex: X.25, frame relay 26

30. Communication Services
cell-switched services
smallest unit of data switched is a fixed-size cell rather than a variable sized packet
switching can be done in hardware
ex: ATM (asynchronous transfer mode), SMDS (switched multimegabit data service) 27

31. Network Connections
need to consider hardware devices, protocols supported, speed, cost, function
switching techniques
on-the-fly forwards each frame before it receives the entire packet
store-and-forward (buffered) places the data in storage until the entire packet is received 29

32. Switches
switches receive electronic signals and redirect them through the network to their final destination
switches route your telephone call
multiplexing (combining many slower speed messages into single messages to take advantage of high speed capacity lines)
intelligent switches route both voice and data traffic 28

33. Intelligence in Switches
error handling
accounting and control
message format conversion
analog-to-digital conversion
prevention of unauthorized access
fault detection and diagnosis 35

34. X.25
designed in the mid 1970s as a type of packet-switching for the public data network over copper twisted-pair wire
divides user data into packets sent from node to node through a network
extensive addressing and error checking between intermediate nodes
needed because of inherent unreliability of the communication lines in the 70s 22

35. X.25 works at the physical, data link, and network layers
requires special interface at subscriber premises
PBX or PAD (packet assembly/disassembly) device
bridges and routers contain PAD to support X.25
still an economical choice for business 23

36. Frame Relay
global WAN technology offered by most public and private carriers
AT&T, MCI, RBOCs
supports speeds of Mbps (E-1 speed)
virtual circuit packet switching
packet size is variable, up to 9000 bytes
uses twisted pair or above
single point of network access so that multiple LANs can have access to the frame relay network over a T-1 line to a central office 24

37. Frame Relay
lower overhead and higher throughput than X.25 because less error checking is done
standards set by CCITT, ANSI
world wide use
can transport other types of packets
major limitation is inability to deliver quality video since the variable length frames create variable delays between frames 25

38. Advantages of Frame Relay
higher performance than X.25 packet switching
simple software upgrade from most X.25 devices
supports applications like file transfer, high resolution graphics, CAD/CAM

39. Disadvantages of Frame Relay
time to correct errors may be higher
could be difficult to manage
may not work well for delay sensitive data like voice and vide

40. Web Sites for Frame Relay
frame-relay/resources.html

41. Cell Relay: ATM ATM is an example of this switching technology
breaks all data into cells and transmits them from one location to another on the network connected by switches
transfers data using fixed length packets of 53 bytes called cells
cells are always the same size and take up only as much bandwidth as they need
a string of cells with a destination stamp

42. ATM
high speed, cell-based transmission scheme which offers bandwidth-on-demand forvoice, data, and video applications
low latency making it good for video and voice which are time-sensitive
latency is the amount of delay experienced with a connection
fast transmission and switching over great distances

43. ATM
grown out of the need for a worldwide standard to allow interoperability
it is not based on a physical transport and ATM cells can be sent over twisted pair, coaxial cable, or fiber optic networks (different physical media)
the goal is one international standard
ATM equipment is available for purchase
expensive by the box, but cheaper by the byte!

44. Advantages of ATM supports the integration of LANs to WANs
evolving to a standard technology for local, campus backbone, and public and private wide area services (scalability)
many powerful players are making it happen: manufacturers, telcos

45. Advantages of ATM private wide area services (scalability)
many powerful players are making it happen: manufacturers, telcos
industry standardization is occuring at a fast pace