Fast Packet Technology ISOM 591 March 27, 2000 1

Global WANs Must Support Bandwidth Demands http://www.specialty.com/highband How to Determine Broadband Needs? Internet access video-on-demand and multimedia teleconferencing CAD/CAM applications

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The Packet Is Ready to Travel 17

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

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

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

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

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

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

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

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

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

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

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

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

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

Frame Relay global WAN technology offered by most public and private carriers AT&T, MCI, RBOCs supports speeds of 2.048 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

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

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

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

Web Sites for Frame Relay http://www.frforum.com/ http://www.mot.com/MIMS/ISG/tech/ frame-relay/resources.html

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

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

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!

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

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 http://www.atmforum.com http://cell-relay.indiana.edu/cell-relay