TCP/IP Protocol Suite 1 Chapter 3 Objectives Upon completion you will be able to: Underlying Technology Understand the different versions of wired Ethernet Understand wireless Ethernet Understand the types of point-to-point WANs Understand the types of switched WANs, especially ATM Differentiate between repeaters, bridges, routers, and hubs

TCP/IP Protocol Suite 2 Figure 3.1 Internet model

TCP/IP Protocol Suite Local Area Networks A local area network (LAN) is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographic area such as a single department, a single building, or a campus. A large organization may need several connected LANs.The most popular LANs are Ethernet and wireless LANs. We briefly review these technologies in this section. The topics discussed in this section include: Wired LANs: Ethernet Wireless LANs: IEEE

TCP/IP Protocol Suite 4 Ethernet Xerox (Bob Metcalfe) performed initial development of Ethernet in 1976 (2.94 Mbps over 100 personal workstations, 1-km long cable) and was later joined by the Digital Equipment Corporation (DEC) and Intel to define the Ethernet 1 specification in The same group subsequently released the Ethernet 2 specification in The Ethernet specification describes a packet switching CSMA/CD LAN.

TCP/IP Protocol Suite 5 Data link layer Physical layer Original Ethernet architecture 0.5 “ Coax tap BNC connector transceiver AUI cable station interface data encapsulation link management encoding and decoding transmission and receipt Network Interface Card ( NIC)

TCP/IP Protocol Suite Carrier sense: station listens to media before transmitting Multiple access: multiple stations may access at same time Carrier Sense Multiple Access Media idle? YES Transmit immediately NO -- wait Listen until the media is idle, then transmit

TCP/IP Protocol Suite Collision More than one station may send a frame during overlapping times. How does a station know that a collision occurred? What does the station do after a collision?

TCP/IP Protocol Suite 8

Collision Detection Rules 1.Stations must listen to the cable while transmitting in order to detect a collision. 2.A frame must be at least 64 bytes (512 bits, 51.2 msec) long to ensure sender “hears” a collision before he finishes. (The transmission time must be more than the RTT.) 3. If a collision is detected, send a brief jamming signal and then wait before retransmitting. Jamming signal

TCP/IP Protocol Suite 10 Worst Case Collision Timing Assume delay for repeater is 1 msec; for transceiver 0.5 msec. ComponentPropagation Time Microsecs Five 500 meter segments2500m/0.77c10.8 Four repeaters4 x 1 msec 4.0 Nine 50 meter AUI cables 450m/0.65c 2.3 Nine transceivers9 x 0.5 msec 4.5 Total one-way time21.6 2,500 meters 500 meters

TCP/IP Protocol Suite 11 Worst Case Collision Timing (cont.) Under these assumptions, the round trip time would be 43.2 microseconds. Allowing some tolerance for equipment, IEEE chose 51.2 microseconds, equal to 512 bit-times, as the collision detection interval. This is why all frames must be at least 512 bits (64 bytes) long microsecond RTT 500 meters

TCP/IP Protocol Suite How does a node detect a collision? Transceiver: A node monitors the media while transmitting. If the observed power is more than transmitted power + attenuated reflection of its own signal, it indicates a collision. Transmitted signal Observed signal Collision! Simultaneous input on two ports Output “ collision presence ” on all ports Hub: if input occurs simultaneously on two ports, it indicates a collision. Hub sends a collision presence signal on all ports.

TCP/IP Protocol Suite Late Collisions A late collision occurs when sender finishes transmission before detecting collision presence. Usual causes: cable too long too many repeaters between stations Solution: higher layer protocol must detect packet loss and retransmit.

TCP/IP Protocol Suite 14 Figure 3.3 Ethernet layers

TCP/IP Protocol Suite 15 Figure 3.4 Ethernet frame

TCP/IP Protocol Suite 16 Figure 3.5 Ethernet implementations

TCP/IP Protocol Suite 17 10Base5 tap : cable does not need to be cut tap : cable does not need to be cut transceiver : send/receive, collision transceiver : send/receive, collision detection, electronics isolation detection, electronics isolation AUI : Attachment Unit Interface AUI : Attachment Unit Interface Use for backbone networks Use for backbone networks 0.5“ Coax  0.5“ Coax vampire tap BNC connector transceiver AUI cable maximum segment length=500m maximum number of stations per segment=100 minimum distance between two stations = 2.5 m maximum network distance between two stations = 2.8km NIC

TCP/IP Protocol Suite 18 10Base “ Coax BNC T-connector NIC BNC connector No drop cable use for office LAN What is its benefit since length < 500m? maximum segment length=185m maximum number of stations per segment=30 minimum distance between two stations = 0.5 m maximum network distance between two stations = 925 m

TCP/IP Protocol Suite 19 A hub functions as a repeater UTP category 5 uses 2 pairs of wires terminated by an eight-bin (RJ-45 style) connector. This means that 4 pins of the 8-pin are used. The transmit and receive data signal on each pair of the segment are polarised, with one wire of the signal pair carrying the positive (+) signal and the other carrying the negative (-). 10BaseT NIC hub maximum segment length = 100m Medium Dependent Interface (MDI), RJ45

TCP/IP Protocol Suite 20 Half Duplex / Full Duplex Ethernet they were initially implemented in a half-duplex manner with the transceiver detecting a collision if an attempt was made to transmit and receive simultaneously and looping back data to the host so it could hear itself transmit (as it would on a shared medium). However if both ends of the link are not hubs, and the hardware supports it, the two channels can be split and used to make a full- duplex link. Unfortunately if autonegotiation is enabled on one end and forced full-duplex on the other, the end with autonegotiation will detect the link as half-duplex causing large numbers of errors due to duplex mismatch.full- duplexautonegotiationduplex mismatch Ethernet Charecteristics

TCP/IP Protocol Suite 21 Collision Domain - Segment Broadcast Domain – Subnet Hub Switch Ethernet Charecteristics

TCP/IP Protocol Suite 22 Figure 3.6 Fast Ethernet implementations

TCP/IP Protocol Suite 23 Figure 3.7 Gigabit Ethernet implementations

TCP/IP Protocol Suite 24 Wireless LAN (WLAN) A WLAN is a shared network. An access point is a shared device and functions like a shared Ethernet hub. Data is transmitted over radio waves. Two-way radio communications (half-duplex) are used. The same radio frequency is used for sending and receiving (transceiver).

TCP/IP Protocol Suite What Are WLANs? They are: Local In building or campus for mobile users Radio or infrared Not required to have RF licenses in most countries Using equipment owned by customers They are not: WAN or MAN networks Cellular phones networks Packet data transmission via celluar phone networks Cellular digital packet data (CDPD) General packet radio service (GPRS) 2.5G to 3G services

TCP/IP Protocol Suite 26 Similarities Between WLAN and LAN A WLAN is an 802 LAN. Transmits data over the air vs. data over the wire Looks like a wired network to the user Defines physical and data link layer Uses MAC addresses The same protocols/applications run over both WLANs and LANs. IP (network layer) IPSec VPNs (IP-based) Web, FTP, SNMP (applications)

TCP/IP Protocol Suite 27 Differences Between WLAN and LAN WLANs use radio waves as the physical layer. WLANs use CSMA/CA instead of CSMA/CD to access the network. Radio waves have problems that are not found on wires. Connectivity issues. Coverage problems Multipath issues Interference, noise Privacy issues. WLANs use mobile clients. No physical connection. Battery-powered. WLANs must meet country-specific RF regulations.

TCP/IP Protocol Suite 28 WLAN and LAN

TCP/IP Protocol Suite 29 Service Set Identifier (SSID) SSID is used to logically separate WLANs. The SSID must match on client and access point. Access point broadcasts one SSID in beacon. Client can be configured without SSID. Client association steps: 1. Client sends probe request. 2. A point sends probe response. 3. Client initiates association. 4. A point accepts association. 5. A point adds client MAC address to association table.

TCP/IP Protocol Suite WLAN Access Topology

TCP/IP Protocol Suite Wireless Repeater Topology

TCP/IP Protocol Suite 32 Workgroup Bridge Topology

TCP/IP Protocol Suite Alternative Peer-to-Peer Topology

TCP/IP Protocol Suite 34 Service Sets and Modes Ad hoc mode Independent Basic Service Set (IBSS) Mobile clients connect directly without an intermediate access point. Infrastructure mode Basic Service Set Mobile clients use a single access point for connecting to each other or to wired network resources. Extended Services Set Two or more Basic Service Sets are connected by a common distribution system.

TCP/IP Protocol Suite 35 Figure 3.9 ESS

TCP/IP Protocol Suite 36 Roaming Through Wireless Cells

TCP/IP Protocol Suite 37 Client Roaming Roaming without interruption requires the same SSID on all access points. Maximum data retry count exceeded Too many beacons missed Data rate shifted Periodic intervals

TCP/IP Protocol Suite b Standard Standard was ratified in September 1999 Operates in the 2.4-GHz band Specifies direct sequence spread spectrum (DSSS) Specifies four data rates up to 11 Mbps 1, 2, 5.5, 11 Mbps Provides specifications for vendor interoperability (over the air) Defines basic security, encryption, and authentication for the wireless link Is the most commonly deployed WLAN standard

TCP/IP Protocol Suite Channel Identifier Channel Center Frequency Channel Frequency Range [MHz] Regulatory Domain Americas Europe, Middle East, and Asia Japan MHz2401 – 2423XXX MHz2406 – 2428XXX MHz2411 – 2433XXX MHz2416 – 2438XXX MHz2421 – 2443XXX MHz2426 – 2448XXX MHz2431 – 2453XXX MHz2436 – 2458XXX MHz2441 – 2463XXX MHz2446 – 2468XXX MHz2451 – 2473XXX MHz2466 – 2478XX MHz2471 – 2483XX MHz2473 – 2495 X 2.4-GHz Channels

TCP/IP Protocol Suite GHz Channel Use Each channel is 22 MHz wide. North America: 11 channels. Europe: 13 channels. There are three nonoverlapping channels: 1, 6, 11. Using any other channels will cause interference. Three access points can occupy the same area.

TCP/IP Protocol Suite b/g (2.4 GHz) Channel Reuse

TCP/IP Protocol Suite b Access Point Coverage

TCP/IP Protocol Suite g Standard Standard was ratified June 2003 Operates in the 2.4-GHz band as b Same three nonoverlapping channels: 1, 6, 11 DSSS (CCK) and OFDM transmission 12 data rates of up to 54 Mbps 1, 2, 5.5, 11 Mbps (DSSS / b) 6, 9, 12, 18, 24, 36, 48, 54 Mbps (OFDM) Full backward compatiblity to b standard

TCP/IP Protocol Suite 44 Range Comparisons

TCP/IP Protocol Suite 45 Figure 3.10 Physical layer

TCP/IP Protocol Suite 46 Figure 3.11 FHSS Frequency Hopping Sequential use of multiple frequencies Hop sequence and rate will vary

TCP/IP Protocol Suite 47 Figure 3.12 DSSS Direct Sequence Each symbol is transmitted over multiple frequencies at the same time Very efficient (no overhead) Higher speed than FH at comparable distances System capacity (multiple channels) higher than FH

TCP/IP Protocol Suite 48 Figure 3.13 MAC layers in IEEE standard

TCP/IP Protocol Suite Collisions Avoidance Similar to CSMA/CD (Ethernet) Transmit when medium is idle, back off on collision Problem: medium is not fully shared ABCD

TCP/IP Protocol Suite Collisions Avoidance contd. Hidden node problem: A and C cannot hear each other If they both transmit to B at the same time, there will be a collision which won’t be detected by A or C

TCP/IP Protocol Suite Collisions Avoidance contd. Exposed node problem: C could send to D while B is sending to A C is blocked when B is sending

TCP/IP Protocol Suite “Hidden stations” the solution IEEE defines: MAC level RTS/CTS protocol (Request to Send / Clear to Send) Can be switched off to reduce overhead (when no hidden nodes exist) More robustness, and increased reliability No interruptions when large files are transmitted AB RTS: I want to send to B 500 bytes CTS: OK A, go ahead, so everybody quiet Data: the 500 bytes of data from A to B ACK: B received the data OK, so an ACK C

TCP/IP Protocol Suite 53 Figure 3.14 CSMA/CA

TCP/IP Protocol Suite 54 Figure 3.15 Frame

TCP/IP Protocol Suite 55 Table 3.1 Addresses in IEEE

TCP/IP Protocol Suite Point-to-Point WANs A second type of network we encounter in the Internet is the point-to- point wide area network. A point-to-point WAN connects two remote devices using a line available from a public network such as a telephone network. We discuss the physical and data link layers of these technologies here.. The topics discussed in this section include: Physical Layer Data Link Layer

TCP/IP Protocol Suite 57 Figure K modem

TCP/IP Protocol Suite 58 ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. Note:

TCP/IP Protocol Suite 59 Figure 3.17 Bandwidth division

TCP/IP Protocol Suite 60 Figure 3.18 ADSL and DSLAM

TCP/IP Protocol Suite 61 Figure 3.19 Cable bandwidth

TCP/IP Protocol Suite 62 Figure 3.20 Cable modem configurations

TCP/IP Protocol Suite 63 Table 3.2 T line rates

TCP/IP Protocol Suite 64 Table 3.3 SONET rates

TCP/IP Protocol Suite 65 Figure 3.21 PPP frame

TCP/IP Protocol Suite Switched WANs The backbone networks in the Internet are usually switched WANs. A switched WAN is a wide area network that covers a large area (a state or a country) and provides access at several points to the users. Inside the network, there is a mesh of point-to-point networks that connects switches. The switches, multiple port connectors, allow the connection of several inputs and outputs. The topics discussed in this section include: X.25 Frame Relay ATM

TCP/IP Protocol Suite 67 Figure 3.22 Frame Relay network

TCP/IP Protocol Suite 68 A cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-size block of information. Note:

TCP/IP Protocol Suite 69 Figure 3.23 ATM multiplexing

TCP/IP Protocol Suite 70 Figure 3.24 Architecture of an ATM network

TCP/IP Protocol Suite 71 Figure 3.25 Virtual circuits

TCP/IP Protocol Suite 72 Note that a virtual connection is defined by a pair of numbers: the VPI and the VCI. Note:

TCP/IP Protocol Suite 73 Figure 3.26 An ATM cell

TCP/IP Protocol Suite 74 Figure 3.27 ATM layers

TCP/IP Protocol Suite 75 The IP protocol uses the AAL5 sublayer. Note:

TCP/IP Protocol Suite 76 We will discuss IP over ATM in Chapter 23. Note:

TCP/IP Protocol Suite Connecting Devices LANs or WANs do not normally operate in isolation. They are connected to one another or to the Internet. To connect LANs or WANs, we use connecting devices. Connecting devices can operate in different layers of the Internet model. We discuss three kinds of connecting devices: repeaters (or hubs), bridges (or two-layer switches), and routers (or three-layer switches). Repeaters and hubs operate in the first layer of the Internet model. Bridges and two-layer switches operate in the first two layers. Routers and three-layer switches operate in the first three layers The topics discussed in this section include: RepeatersHubsBridgesRouter

TCP/IP Protocol Suite 78 Figure 3.28 Connecting devices

TCP/IP Protocol Suite 79 Figure 3.29 Repeater

TCP/IP Protocol Suite 80 A repeater connects segments of a LAN. Note:

TCP/IP Protocol Suite 81 A repeater forwards every bit; it has no filtering capability. Note:

TCP/IP Protocol Suite 82 A repeater is a regenerator, not an amplifier. Note:

TCP/IP Protocol Suite 83 Figure 3.30 Function of a repeater

TCP/IP Protocol Suite 84 A bridge has a table used in filtering decisions. Note:

TCP/IP Protocol Suite 85 Figure 3.31 Bridge

TCP/IP Protocol Suite 86 A bridge does not change the physical (MAC) addresses in a frame. Note:

TCP/IP Protocol Suite 87 Figure 3.32 Learning bridge

TCP/IP Protocol Suite 88 A router is a three-layer (physical, data link, and network) device. Note:

TCP/IP Protocol Suite 89 A repeater or a bridge connects segments of a LAN. A router connects independent LANs or WANs to create an internetwork (internet). Note:

TCP/IP Protocol Suite 90 Figure 3.33 Routing example

TCP/IP Protocol Suite 91 A router changes the physical addresses in a packet. Note: