Enterprise and Wide Area Networks

1. Enterprise and Wide Area Networks ITEC 370 George Vaughan Franklin University

2. Sources for Slides • Material in these slides comes primarily from course text, Guide to Networking Essentials,Tomsho, Tittel, Johnson (2007). • Other sources are cited in line and listed in reference section.

3. TCP/IP and OSI Models

4. Creating Larger NetworksTomsho, Tittel, Johnson (2007) • Ways to stretch or expand network capabilities • Physically expanding to support additional computers • Segmenting the network into smaller pieces to filter and manage network traffic • Collision Domains • Broadcast Domains • Extending the network to connect separate LANs • Connecting two or more disjointed networking environments • Many devices can accomplish these tasks • Repeaters, bridges, switches, routers, and gateways

5. Repeaters and Hubs • Accepts a signal, and regenerates it. • Common Collision Domain • Common Broadcast Domain • Operates at OSI layer 1. • Operates at bit level • no frame knowledge. • Does not use Protocol Data Units (PDU). • Half-Duplex communication. • Can connect different media (i.e. Fiber to TP). • A Hub is a multi-port Repeater. • Only one device can transmit at a time • Collisions can occur between any connected device.

6. RepeatersTomsho, Tittel, Johnson (2007)

7. Bridges • Segments (divides) a network in two. • 2 separate Collision Domains • Common Broadcast Domain • Can filter frames • Operates at Layer 2 (PDU = Frame). • Full-Duplex communication. • Operates in software • If destination is in same segment as sender, bridge drops frame. • Transparent (learning) bridges: • Knows nothing upon boot. • Builds bridging table based on port, source MAC and destination MAC. • Learns which MACs (based on ports) are on which segment. • Slower than repeaters, hubs. • Broadcast frames sent to all other ports. • Can connect different types of networks (ring, Ethernet).

8. Switches • Switch = high-speed, multi-port bridge. • A switch with ‘n’ ports has: • ‘n’ separate Collision Domains • Common Broadcast Domain • Can filter frames. • Operates at Layer 2 (PDU = Frame). • Full-Duplex communication. • Operates in hardware (faster than bridges). • Each port provides a separate collision domain. • Full bandwidth available to communicating ports. • Broadcast frames are forwarded.

9. Switching Methods • Cut-Through • Fastest transmission • All errors forwarded • Reads just enough of frame to determine source and destination. • Fragment Free • Medium transmission • All errors, except frame fragments, are forwarded. • Read just enough of frame to guarantee frame is at least minimum size. • Store-and-Forward • Slowest transmission • No error frames forwarded • Entire frame is read and Frame Check Sequence (FSC) is checked.

10. VLANs • Switches can support Virtual LANs (VLANs) • Multiple logical LANs on one switch: • ‘n’ separate Collision Domains • ‘n’ Broadcast Domains • However, devices in one segment cannot talk to devices in another segment without adding a router. • Allows administrator to group logically devices instead of just by physical location. • Each VLAN is assigned a unique network number. • Router needed for VLANs to inter-communicate.

11. SwitchesTomsho, Tittel, Johnson (2007)

12. Routers • Operates at Layer 3 (PDU = Packets). • ‘n’ separate Collision Domains • ‘n’ Broadcast Domains • Used to create inter-network from different networks. • Broadcast frames are NOT forwarded. • Can be used to form multi-path networks (i.e. more than one path between source and destination). • Each network segment is assigned a network address.

13. Collision and Broadcast DomainsTomsho, Tittel, Johnson (2007) Broadcast Domain Broadcast Domain Collision Domains

14. Routers and Multi-path Networks • Routers determine path for each packet based on: • Network address of destination • Routing tables • Routers can send information from one network type to another. • Discards any broadcast packet or packet not understood.

15. RoutersTomsho, Tittel, Johnson (2007)

16. Routing Tables • Routing tables keep track of network addresses (IP Addresses) • Not hardware addresses (MAC addresses). • Distance to destination network (measured in ‘Hops’). • A hop indicates a router. • Example: If hops = 2, then packet must go through 2 more routers before reaching destination network. • Router may choose different paths to same destination for load balancing.

17. Populating Routing Tables • Static Routing • Routing tables manually populated. • Router always uses same path to destination. • Dynamic Routing • Uses discovery process to populate table. • Shares routing table with other routers.

18. Router ‘Best’ Path Algorithms • Distance-Vector Algorithm (DVA) • Calculates a route metric based on hops and bandwidth, network delays, etc. • DVAs share routing tables • Routing Information Protocol (RIP) is a DVA • Link-State Algorithm (LSA) • Metric is speed of link • A router sends status of its interfaces to other routers. • Requires more CPU, but is more efficient than DVA • ‘Open Shortest Path First’ (OSPF) is a LSA.

19. Gateways • Translates information between 2 different protocols or data formats (example TCP/IP). • Used to connect LANs to WANs • Gateways strip off all network information from the packet down to the raw data. • Raw data is repackaged in new protocol or format.

20. Digital ConnectivityTomsho, Tittel, Johnson (2007) • Because computers and LANs transmit data digitally, using digital techniques to connect LANs over long distances to form a WAN makes more sense than using digital-to-analog conversion • Digital Data Service (DDS) lines are direct or point-to-point synchronous communication links with 2.4, 4.8, 9.6, or 56 Kbps transmission rates • E.g., ISDN, T1, T3, and switched 56K • DDS uses a communication device called Channel Service Unit/Data Service Unit (CSU/DSU)

21. Digital Connectivity (continued)Tomsho, Tittel, Johnson (2007)

22. Digital ModemsTomsho, Tittel, Johnson (2007) • The interface for ISDN is sometimes called a digital modem • Consists of network termination (NT) device and terminal adapter (TA) equipment • Cable TV operators and telcos that offer digital connections for Small Office/Home Office also use the term modem • Technically, both uses of term “modem” are incorrect • Some CATV systems do indeed use analog signaling, so the term “cable modem” is correct in these cases

23. Digital Modems (continued)Tomsho, Tittel, Johnson (2007) • Cable modems transmit signals to/from Internet points of presence using broadband CATV network • Provide shared media access bandwidth • Security was a concern in early networks (users could eavesdrop other communication sessions) • DSL uses the same twisted-pair phone lines that deliver voice services • Connections are not shared (guaranteed bandwidth) • Disadvantage: distance limitation between the user’s location and the nearest central office • Most common types: ADSL (asynchronous digital subscriber line) and SDSL

24. T1Tomsho, Tittel, Johnson (2007) • T1 is a DDS technology that uses two two-wire pairs to transmit full-duplex data signals at a maximum rate of 1.544 Mbps • Digital link that organizations purchase or lease • Subscribing to one or more channels instead of an entire T1 is possible with fractional T1 • In some countries, the E1 technology is used • Multiplexing enables several communication streams to travel simultaneously over the same cable segment • Can increase DS-1 rates up to DS-4 speeds

25. T1 (continued)Tomsho, Tittel, Johnson (2007)

26. T3Tomsho, Tittel, Johnson (2007) • A T3 line has 28 T1s or 672 channels and supports a data rate of 44.736 Mbps • Many large service providers offer both T3 and fractional T3 leased lines with transmission rates of 6 Mbps and up • A single T3 commonly replaces several T1 lines

27. References Tomsho, Tittel, Johnson (2007). Guide to Networking Essentials. Boston: Thompson Course Technology. Odom, Knott (2006). Networking Basics: CCNA 1 Companion Guide. Indianapolis: Cisco Press Wikipedia (n.d.). OSI Model. Retrieved 09/12/2006 from http://en.wikipedia.org/wiki/OSI_Model