Ch 3: Underlying Technologies Exam 2 on Monday, March 5th 75 minutes and opened book FIB, MC, Short Questions and Short Problems Covers lectures 9 through 13 and associated book chapters and sections Dr. Clincy Lecture

Internet – Underlying Technologies Internet is comprised of LANs, Point-to-Point WANs and Switched WANs We have covered LANS: Ethernet, Token Ring (not in book), Wireless and FDDI Ring (not in book) We have covered Pt-to-Pt WANs: Telephony Modem, DSL, Cable/Modem, T-Lines and SONET We will cover Switched WANs: X.25, Frame Relay and ATM Dr. Clincy Lecture

SWITCHED WANS Switched WAN - a mesh of point-to-point networks connected via switches Unlike LANS – multiple paths are needed between locations Unlike LANS – no direct relationship between Tx and Rx Paths are determined upfront and theses paths are used to send and receive (multiple paths for reliability and restoration) – recall that LANS uses Tx/Rx addresses to make the connection Uses Virtual Circuit concept 3 well known Switch WANs: X.25, Frame Relay and ATM Dr. Clincy Lecture

X.25 Developed in 1970 – the first switch WAN – becoming more and more obsolete X.25 standard describes all of the functions necessary for communicating with a packet switching network Divided into 3 levels: (1) physical level – describes the actual interfaces (2) frame level – describes the error detection and correction (3) Packet level – provides network-level addressing (constant BW efficiency problem – but it worked) Because X.25 was developed before the Internet, the IP packets are encapsulated in the X.25 packet when you have an IP network on each side of a X.25 backbone Dr. Clincy Lecture

Frame Relay Network Designed to replace X.25 Have higher data rates than X.25 Can handle “bursty data” by allocating BW as needed versus dedicating constant chucks of BW Less error checking and overhead needed – more reliable and efficient DTE – data terminating equipment – devices connecting users to the network (ie routers) DCE – data circuit-terminating equipment – switches routing the frames through the network Frame Relay Switches in the yellow cloud Dr. Clincy Lecture

Switched WANs - ATM ATM – Asynchronous Transfer Mode – is a cell relay protocol Objectives of ATM (upfront initiative): Make better use of high data rate transmission (ie. fiber optics) WAN between various types of packet-switch networks that will not drive a change in the packet-switch networks Must be inexpensive (no barrier to use) – want it to be the international backbone Must be able to support the existing network hierarchies – local loops, long-distance carriers, etc..) Must be connection-oriented (high reliability) Make more hardware oriented versus software oriented in speeding up rates (explain this – circuit vs software) Cell – small unit of data of fixed size – basic unit of data exchange Different types of data is loaded into identical cells Cells are multiplexed with other cells and routed By having a static size, the delivery is more predictable and uniform Dr. Clincy Lecture

ATM multiplexing ATM uses asynchronous time-division multiplexing – cells from different channels are multiplexed Fills a slot with a cell from any channel that has a cell Dr. Clincy Lecture

Architecture of an ATM network User access devices (called end points) are through a user-to-network interface (UNI) to switches in the network The switches are connected through network-to-network interfaces (NNI) Dr. Clincy Lecture

Virtual circuits Connections between points are accomplished using transmission paths (TP), virtual paths (VP) and virtual circuits (VC). TP – all physical connections between two points VP – set of connections (a subset of TP) (ie. Highway) VC – all cells belonging to a single message follow the same VC and remain in original order until reaching Rx (ie. Lane) The virtual connection is defined by the VP and VC identifiers Dr. Clincy Lecture

An ATM cell Dr. Clincy Lecture

ATM layers ATM Standard defines 3 layers: Application Adaptation Layer, ATM Layer and Physical Layer Application Adaptation Layer – facilitates communications between ATM networks and other Packet-Switched Networks by taking the packets and fitting them into fixed-sized CELLS. At the Rx, cells are re-assembled back into packets Keep in mind that any type of transmission signal can be packaged into an ATM cell: data, voice, audio and video - makes ATM very powerful Application Adaptation Layer is divided into 4 parts: AAL1- handles the constant bit rate cases (ie. voice, real-video) AAL2- handles variable bit rate cases (ie. compressed voice, non-real-time video, data) AAL3/4 – handles connection-oriented data services (ie VoIP) AAL5 – handles connectionless-oriented protocols (ie. TCP/IP) Dr. Clincy Lecture

ATM layers ATM Layer in general – routing, flow control switching & multiplexing ATM Layer – going down – accepts bytes segments and translate to cells ATM Layer – going up – translate cells back into byte segments – keep in mind that a node can be acting as both an intermediate and Rx node (and Tx) ATM Physical Layer – translate cells into a flow of bits (or signals) and vice versa Dr. Clincy Lecture

ATM LAN architecture ATM LAN speeds: 155 Mbps and 622 Mbps 3 design approaches: (1) pure ATM LAN, (2) legacy ATM LAN and (3) combo of (2) and (3) Pure ATM LAN: ATM switch is used to connect the stations in a LAN (uses VPI/VCI versus destination/source addresses) Dr. Clincy Lecture

Legacy ATM LAN architecture Use an ATM LAN as a backbone – frames staying with in a certain network need not be converted Frames needing to cross to another LAN must be converted and ride the ATM LAN Dr. Clincy Lecture

Mixed ATM LAN Architecture Dr. Clincy Lecture

Internet – Underlying Technologies Recall that the Internet is comprised of LANs, Point-to-Point WANs and Switched WANs We covered LANS: Ethernet, Token Ring, Wireless and FDDI Ring We covered Switched WANs: X.25, Frame Relay and ATM We covered Pt-to-Pt WANs: Telephony Modem, DSL, Cable/Modem, T-Lines and SONET How are these networks connected ? Dr. Clincy Lecture

CONNECTING DEVICES Dr. Clincy Lecture

Repeater Operates at the physical layer – layer 1 Receives the signal and regenerates the signal in it’s original pattern A repeater forwards every bit; it has no filtering capability Is there a difference between a regen or repeater and an amp ?? Dr. Clincy Lecture

Repeaters d For the architecture above, will a signal ever traverse through more than 2 repeaters ? Dr. Clincy Lecture

Hubs Hub – multi-port repeater Typically used to create a physical star topology Also used to create multiple levels of hierarchy For bus technology type networks, hubs can be used to increase the collision domain Dr. Clincy Lecture

Bridge Operates at both the physical and data link layers At layer 1, it regenerates the signal. At layer 2, it checks the Tx/Rx physical address (using a bridge table) Example Below: If packet arrives to bridge-interface #1 for either of the 71….. stations, the packet is dropped because the 71…. Stations will see the packet If packet arrives to bridge-interface #2 for either of the 71….. stations, the packet is forwarded to bridge-interface #1 With such an approach, the “bridged” network segments will acted as a single larger network What is a “smart” bridge ?? Dr. Clincy Lecture

Routers Show example where a decision is needed d d Is a 3-layer device: (1) at layer 1, regen the signals, (2) at layer 2, check physical address and (3) at layer 3, check network addresses Routers are internetworking devices Routers contain a physical and logical/IP address for it’s interfaces (repeaters/bridges don’t) Routers only act on the packets needing to pass through Routers change the physical address of the packets needing to pass through (repeaters/bridges don’t change physical addresses) Show example where a decision is needed d d Dr. Clincy Lecture

Routing example LAN 1 LAN2 Routers can change the physical address of a packet Example: as a packet flow from LAN 1 to LAN 2 In LAN 1, the source address is the Tx’s address and the destination address is the Router’s interface address In LAN 2, the source address is the Router’s interface address and the destination address is the Rx’s address LAN 1 LAN2 Dr. Clincy Lecture

You are a High Priced Network Consultant Marketing Dept Engineering Dept (Super Computer) Manufacturing Dept (Robots) d They want all departments to communicate with one another; you want the network to maintain top performance – which design would you recommend ? Which devices would you recommend for empty circles ? – the least cost solution is the best solution Dr. Clincy Lecture