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    • Computer Networks LMR WWW.AMARPANCHAL.COM
    • What is….. It ? • A computer network consists of end systems, which are sources of information, which are sources of information, which communicate through the transit systems interconnecting them. The transit system is also called an interconnect subsystem or a subnetwork.
    • Topology: – Topology refers to the way the network is laid out, either physically or logically. Two or more devices connect to a link, two or more links form a topology. A B A E E B B HUB Central Controller D D C A HUB HUB C C D D D D F F A A B A Ring interface unit A C D A A
    • The OSI Model
    • TCP/IP Protocol :
    • Asymmetrical DSL (ADSL) • ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. – Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit (most of the time).
    • Asymmetrical DSL (ADSL) • ADSL is an adaptive technology. • The system uses a data rate based on the condition of the local loop line. • Speed: Most existing local loops can handle bandwidths up to 1.1 MHz.
    • ADSL Modem
    • OTHER TYPES OF DSL: • Symmetric DSL (SDSL) • High-bit-rate DSL (HDSL) • Very high bit-rate DSL (VDSL)
    • Symmetric DSL (SDSL) • Used mainly by small businesses & residential areas • Bit rate of downstream is higher than upstream
    • High-bit-rate DSL (HDSL) • Used as alternative of T-1 line • Uses 2B1Q encoding • Less susceptible to attenuation at higher frequencies • Unlike T-1 line (AMI/1.544Mbps/1km), it can reach 2Mbps @ 3.6Km
    • Very high bit-rate DSL (VDSL) • Uses DMT modulation technique • Effective only for short distances(300-1800m) • Speed: downstream : 50 - 55 Mbps upstream : 1.5-2.5 Mbps
    • DATA LINK LAYER • chacter count
    • • Starting and ending characters with character stuffing
    • • Starting end ending flags with bit stuffing.
    • Error control : • Cyclic redundancy check : • If Original Data to be transmitted is 110101010 • Divisor is 10101 • The data is appended with 4 zeros and divided by the divisor. • The remainder is added to the dividend in order to obtain the data to be transmitted. • 1101010100000 • 1011 • 1101010101011 • Therefore, transmitted data : 1101010101011 10101 1101010100000 10101 11111 10101 10100 10101 11000 10101 11010 10101 11110 10101 1011 REMANIDER
    • Taxonomy of Networks • Communication networks can be classified based on the way in which the nodes exchange information: Communication Network Circuit-Switched Network Frequency Division Multiplexing Packet-Switched Network Datagram Network Time Division Multiplexing Wavelength Division © Jörg Liebeherr, Multiplexing CS757 Virtual Circuit Network
    • Circuit Switching • In a circuit-switched network, a dedicated communication path (“circuit”) is established between two stations through the nodes of the network • The dedicated path is called a circuit-switched connection or circuit • A circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuits • Data is not delayed at the switches © Jörg Liebeherr, CS757
    • Circuit Switching • Circuit-switched communication involves three phases: 1. Circuit Establishment 2. Data Transfer 3. Circuit Release • “Busy Signal” if capacity for a circuit not available • Most important circuit-switching networks: • • Telephone networks ISDN (Integrated Services Digital Networks) © Jörg Liebeherr, CS757
    • Circuit Switching circuit 2 C B D 1 2 3 5 4 A circuit 1 © Jörg Liebeherr, 7 CS757 6 E
    • Implementation of Circuit-Switching • There are two ways to implement circuits – Frequency Division Multiplexing (FDM) – Time Division Multiplexing (TDM) – Wavelength Division Multiplexing (WDM) • Example: Voice in (analog) telephone network: Needed bandwidth: 3000 Hz Allocated bandwidth: 4000 Hz Therefore, a channel with 64 kHz can carry 16 voice conversations © Jörg Liebeherr, CS757
    • Frequency Division Multiplexing (FDM)  Approach: Divide the frequency spectrum into logical channels and assign each information flow one logical channel Channel 1 (f1) Source 1 1 Source 2 Source 3 Source 4 Source 5 Source 6 © Jörg Liebeherr, Channel 2 (f2) S w i t c h Channel 3 (f3) Channel 4 (f4) Channel 5 (f5) Channel 6 (f6) CS757 2 S w i t c h 3 4 5 6
    • Frequency Division Multiplexing (FDM) Endsystem Endsystem Circuit Switch Circuit Switch Endsystem Endsystem • A circuit switch bundles (multiplexes) multiple voice calls on a high-bandwidth link • Frequency-Division-Multiplexing (FDM): Each circuit receives a fixed bandwidth. The frequency of each call is shifted, so that multiple calls do not interfere © Jörg Liebeherr, CS757
    • Time Division Multiplexing (TDM)  Approach: Multiple signals can be carried on a single transmission medium by interleaving portions of each signal in time Source 1 1 Source 2 Source 3 M M 3 Source 4 U Source 5 12345612 X U X Source 6 © Jörg Liebeherr, 2 4 5 6 CS757
    • Time Division Multiplexing (TDM) endsystem Circuit Switch endsystem endsystem slots Circuit Switch endsystem frames • Time is divided into frames of fixed length • Each frame has a fixed number of constant-sized “slots” • Each circuit obtains one or more “slots” per frame © Jörg Liebeherr, CS757
    • Circuit Switch switch fabric memory •A circuit switch relays a circuit from an input to an output link •A switch may reassign frequencies (FDM) or time slot allocation (TDM) •No queueing delays are experienced CS757 © Jörg Liebeherr,
    • Packet Switching • • Data are sent as formatted bit-sequences, so-called packets Packets have the following structure: Header Data Trailer • Header and Trailer carry control information • Each packet is passed through the network from node to node along some path (Forwarding/Routing) • At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks) • Packet transmission is never interrupted (no preemption) • No capacity is allocated for packets © Jörg Liebeherr, CS757
    • A Packet Switch input queues output queues switch fabric memory © Jörg Liebeherr, CS757
    • Statistical Multiplexing • Packet transmission on a link is referred to as statistical multiplexing – There is no fixed allocation of packet transmissions – Packets are multiplexed as they arrive Packets from different streams Transmission line 1 2 1 N 2 output buffer N © Jörg Liebeherr, CS757 1
    • Datagram Packet Switching • The network nodes process each packet independently If Host A sends two packets back-to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together In fact, the two packets can take different routes • Packets are called datagrams • Implications of datagram packet switching: • A sequence of packets can be received in a different order than it was sent • Each packet header must contain the full address of the destination © Jörg Liebeherr, CS757
    • Virtual-Circuit Packet Switching • Virtual-circuit packet switching is a hybrid of circuit switching and packet switching – All data is transmitted as packets – Emulates a circuit-switched network • All packets from one packet stream are sent along a pre-established path (=virtual circuit) – Guarantees in-sequence delivery of packets – Note: Packets from different virtual circuits may be interleaved © Jörg Liebeherr, CS757
    • Virtual-Circuit Packet Switching • Communication with virtual circuits (VC) takes place in three phases: 1. 2. 3. VC Establishment Data Transfer VC Disconnect • Note: Packet headers don’t need to contain the full destination address of the packet • Circuit-switched and virtual-circuit packet-switched networks are said to provide a connection-oriented service. © Jörg Liebeherr, CS757
    • Packet Forwarding and Routing • There are two parts to the routing problem: 1. How to pass a packet from an input interface to the output interface of a router (packet forwarding)? 2. How to calculate routes (routing algorithm)? • Packet forwarding is done differently in datagram and virtual-circuit packet networks • Route calculation is similar in datagram and virtual-circuit packet networks © Jörg Liebeherr, CS757
    • Datagram Packet Switching C B C.1 1 2 C.1 C.2 A.1 A.3 A.2 4 A A.1 C.1 A.2 C.2 A.3 C.2 A.1 A.2 A.3 © Jörg Liebeherr, 5 D 3 A.1 A.3 C.2 A.2 A.2 7 CS757 A.2 6 E
    • Virtual-Circuit Packet Switching C.2 VC 2 B C A.1 C.1 A.2 C.2 A.3 C.1 1 2 C.2 3 C.1 5 4 A A.1 VC 1 C.1 C.2 A.1 A.3 A.2 A.1 A.3 A.2 7 A.2 A.3 © Jörg Liebeherr, D CS757 6 E
    • Packet Forwarding of Datagrams • Recall: In datagram networks, each packet must carry the full destination address • Each router maintains a routing table which has one row for each possible destination address Routing Table of node v • The lookup yields the address of the next hop to (next-hop routing) w v n d via (next hop) x d n © Jörg Liebeherr, CS757
    • Packet Forwarding of Datagrams • When a packet arrives at an incoming link, ... 1. The router looks up the routing table 2. The routing table lookup yields the address of the next node (next hop) 3. The packet is transmitted onto the outgoing link that Table of node v Routing goes to the next hop to via (next hop) d w d v n x d n © Jörg Liebeherr, CS757 d
    • To A Next hop To Next hop Forwarding Datagrams - A A B B - C C D D C D D E B E E X C X D B C To E Next hop To Next hop E E E A C B C C C D C E C A A A B X - B - B B C D C C D D D - E D E B X E X C X © Jörg Liebeherr, C To D To Next hop CS757 Next hop B B B - X E B D E B E B A C A E B
    • Packet Forwarding with Virtual Circuits • Recall: In VC networks, the route is setup in the connection establishment phase • During the setup, each router assigns a VC number (VC#) to the virtual circuit • The VC# can be different for each hop • Routingis written into the packet headers VC# Table of node v path of virtual circuit from VC# to VC# 2 w 3 1 v n x w 2 © Jörg Liebeherr, d 3 CS757 d
    • Packet Forwarding of Virtual Circuits • When a packet with VCin in header arrives from router nin, ... 1. The router looks up the routing table for an entry with (VCin, nin) 2. The routing table lookup yields (VCout, nout) 3. The router updates the VC# of the header to VCout and transmits the packet to nout Routing Table of node v from VC# to 2 VC# 2 w 3 path of virtual circuit 1 3 1 v n x w 2 © Jörg Liebeherr, d 3 CS757 d
    • Forwarding with VCs Part 1: VC setup from X to E nin Vin nout - C Vin D 5 nout Vout E 3 A Vout - nin B E 5 nin Vin nout B X C nin X © Jörg Liebeherr, Vin 5 3 nout Vout B 5 D nout Vout D 3 CS757 nin C Vin 3 Vout - -
    • Forwarding with VCs Part 2: Forwarding the packet nin Vin nout - C Vin D 5 nout Vout E 2 A Vout - nin 2 B 5 5 5 X X © Jörg Liebeherr, Vin 5 nin Vin nout B 3 C nin E 3 nout Vout B 5 D nout Vout D 3 CS757 nin C Vin 3 Vout - -
    • Comparison Datagram Packet Switching Circuit Switching          Dedicated transmission path Continuous transmission Path stays fixed for entire connection Call setup delay Negligible transmission delay No queueing delay Busy signal overloaded network Fixed bandwidth for each circuit No overhead after call setup © Jörg Liebeherr,          No dedicated transmission path Transmission of packets Route of each packet is independent No setup delay Transmission delay for each packet Queueing delays at switches Delays increase in overloaded networks Bandwidth is shared by all packets Overhead in each packet CS757 VC Packet Switching          No dedicated transmission path Transmission of packets Path stays fixed for entire connection Call setup delay Transmission delay for each packet Queueing delays at switches Delays increase in overloaded networks Bandwidth is shared by all packets Overhead in each packet
    • HDLC Overview Broadly HDLC features are as follows: • Reliable protocol – selective repeat or go-back-N • Full-duplex communication – receive and transmit at the same time • Bit-oriented protocol – use bits to stuff flags occurring in data • Flow control – adjust window size based on receiver capability • Uses physical layer clocking and synchronization to send and receive frames
    • HDLC Overview • Defines three types of stations – Primary – Secondary – Combined • Defines three types of data transfer mode – Normal Response mode – Asynchronous Response mode – Asynchronous Balanced mode • Three types of frames – Unnumbered – information – Supervisory
    • HDLC • The three stations are : – Primary station • Has the responsibility of controlling the operation of data flow the link. • Handles error recovery • Frames issued by the primary station are called commands. – Secondary station, • Operates under the control of the primary station. • Frames issued by a secondary station are called responses. • The primary station maintains a separate logical link with each secondary station. – Combined station, • Acts as both as primary and secondary station. • Does not rely on other for sending data
    • HDLC Unbalanced Mode Commands Primary Responses Secondary Secondary Balanced mode Combined Combined commands/Responses
    • HDLC • The three modes of data transfer operations are – Normal Response Mode (NRM) • Mainly used in terminal-mainframe networks. In this case, • Secondaries (terminals) can only transmit when specifically instructed by the primary station in response to a polling • Unbalanced configuration, good for multi-point links – Asynchronous Response Mode (ARM) • Same as NRM except that the secondaries can initiate transmissions without direct polling from the primary station • Reduces overhead as no frames need to be sent to allow secondary nodes to transmit • Transmission proceeds when channel is detected idle , used mostly in point-to-point-links – Asynchronous Balanced Mode (ABM) • Mainly used in point-to-point links, for communication between combined stations
    • Data Link Control HDLC frame structure (a) Frame Format (b) Control field format
    • 11-7 POINT-TO-POINT PROTOCOL Although HDLC is a general protocol that can be used for both point-to-point and multipoint configurations, one of the most common protocols for point-to-point access is the Point-to-Point Protocol (PPP). PPP is a byte-oriented protocol.
    • Figure 11.32 PPP frame format 11.54
    • Note PPP is a byte-oriented protocol using byte stuffing with the escape byte 01111101. 11.55
    • Figure 11.33 Transition phases 11.56
    • Routing : • • • • 1) 2) 3) 4) Centralized Routing : Distributed Routing : Static Routing or Non-adaptive routing : Dynamic Routing or Adaptive Routing :
    • • 1.Shortest path routing algorithm:
    • • Distance Vector Routing :
    • • . The count-to-infinity problem.
    • • Link State Routing – Discover its neighbors and learn their network addresses. – Measure the delay or cost to each of its neighbors. – Construct a packet telling all it has just learned. – Send this packet to all other routers. – Compute the shortest path to every other router.
    • CIDR Addresses • Identifying a CIDR block requires both an address and a mask – Slash notation – for addresses – • Here the /21 indicates a 21 bit mask – All possible CIDR masks can easily be generated • /8, /16, /24 correspond to traditional class A, B, C categories • IP addresses are now arbitrary integers, not classes • Raises interesting questions about lookups – Routers cannot determine the division between prefix and suffix just by looking at the address • Hashing does not work well • Interesting lookup algorithms have been developed and analyzed CS 640 62
    • CIDR – A Couple Details • ISP’s can further subdivide their blocks of addresses using CIDR • Some prefixes are reserved for private addresses – 10/8, 172.16/12, 192.168/16, 169.254/16 – These are not routable in the Internet CS 640 63
    • Traffic Shaping
    • Congestion control • In Virtual-Circuit – Admission control • In Datagram Subnets – The Warning Bit – Choke Packets – Hop-by-Hop Choke Packets – Load Shedding – Jitter Control
    • IP Addresses
    • HEADER
    • T/TCP
    • Connecting Devices and the OSI Model
    • Connecting Devices
    • Connecting Devices Repeaters Hubs Bridges Two-Layer Switches
    • Connecting devices
    • Repeaters • A repeater (or regenerator) is an electronic device that operates on only the physical layer of the OSI model. • A repeater installed on a link receives the signal before it becomes too weak or corrupted, regenerates the original pattern, and puts the refreshed copy back on the link.
    • Repeaters • A repeater does not actually connect two LANS; it connects two segments of the same LAN. • A repeater forwards every frame; it has no filtering capability.
    • Hubs • A Hub is a multiport repeater. It is normally used to create connections between stations in a physical star topology.
    • Bridges • Bridges operate in both the physical and the data link layers of the OSI model.
    • Bridges • Bridges can divide a large network into smaller segments. They contain logic that allows them to keep the traffic on each segment separate. When a frame (or packet) enters a bridge, the bridge not only regenerates the signal but checks the destination address and forwards the new copy only to the segment the address belong.
    • Bridges • A bridge operates in both the physical and the data link layers. • As a physical layer device, it regenerates the signal it receives. • As a data link layer device, the bridge can check the physical (MAC) address (source and destination) contained in the frame. • A bridge has filtering capability. It can check the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port. • A bridge does not change the physical (MAC) addresses in a frame. • A bridge has a table used in filtering decisions.
    • Bridge
    • Types of Bridges • To select between segments, a bridge must have a look-up table that contains the physical addresses of every station connect to it. The table indicate to which segment each station belongs. Simple Bridge • The address table must be entered manually, before a simple bridge can be used. • Whenever a new station is added or removed, the table must modified. • Installation and maintenance of simple bridges are timeconsuming and potentially more trouble than the cost savings are worth.
    • Routers • Routers have access to network layer addresses and contain software that enables them to determine which of several possible paths between those addresses is the best for a particular transmission. • Routers operate in the physical, data link, and network layers of the OSI model.
    • • Routers relay packets among multiple interconnected networks. They route packets from one network to any of a number of potential destination networks on an internet.
    • Gateways • Gateways potentially operate in all seven layers of the OSI model.
    • Gateways • A gateway is a protocol converter. A router by itself transfers, accepts, and relays packets only across networks using similar protocols. A gateway can accept a packet formatted for one protocol (e.g. AppleTalk) and convert it to a packet for another protocol (e.g. TCP/IP).
    • Gateways • A gateway is generally software installed within a router. The gateway understands the protocols used by each network linked into the router and is therefore able to translate from one to another.
    • What is SONET? • Synchronous Optical Network standard SONET Network Element • • • • • Digital Tributaries SONET Network Element Digital Tributaries Defines a digital hierarchy of synchronous signals Maps asynchronous signals (DS1, DS3) to synchronous format Defines electrical and optical connections between equipment Allows for interconnection of different vendors’ equipment Provides overhead channels for interoffice OAM&P
    • SONET Rates Level Optical Designation Bit Rate (Mb/s) STS-1 OC-1 51.840 STS-3 OC-3 155.520 STS-12 OC-12 622.080 STS-48 OC-48 2,488.320 STS-192 OC-192 9,953.280 STS OC = SYNCHRONOUS TRANSPORT SIGNAL = OPTICAL CARRIER (“..result of a direct optical conversions of the STS after synchronous scrambling” - ANSI)
    • SONET Network Layers Services DS3, DS1, etc Path Line Section • Map Services & POH Into SPE • Path Protection/Restoration • Other Path OA&M Functions Path • Combine SPE & LOH • Sync & Mux For Path Layer • Line Protection/Restoration • Other Line OA&M Functions Section • Add SOH & Create STS Signal • Framing, Scrambling • Section OA&M Functions Physical • E/O Conversion (Photonic) • Line Code • Physical Signal [No additional overhead] Line Line DS3 etc MUX LTE Section Regen Section Regen SONET ADM Section LTE LTE MUX DS3 etc
    • Functional Description of SONET Layers Function Path Layer Information Payload Line OH Line Layer Section Layer Photonic Layer Path OH Section OH E/O Conversion Transmission over OC-N Payload Mapping Error Monitoring Synchronization Multiplexing Error Monitoring Line Maintenance Protection Switch Order Wire Framing Scrambling Error Monitoring Section Maintenance Orderwire E/O Conversion Pulse Shaping Power Level Wavelenght OH: Overhead
    • Internet Protocol (IP) • Features: – Layer 3 (Network layer) – Unreliable, Connectionless, Datagram – Best-effort delivery • Popular version: IPv4 • Major functions – Global addressing – Datagram lifetime – Fragmentation & Reassembly
    • IPv4 Header
    • IPv4 companion protocols (1) • ARP: Address Resolution Protocol – Mapping from IP address to MAC address • ICMP: Internet Control Message Protocol – Error reporting & Query • IGMP: Internet Group Management Protocol – Multicast member join/leave • Unicast Routing Protocols (Intra-AS) – Maintaining Unicast Routing Table – E.g. RIP, OSPF (Open Shortest Path First)
    • IPv4 companion protocols (2) • Multicast Routing Protocols – Maintaining Multicast Routing Table – E.g. DVMRP, MOSPF, CBT, PIM • Exterior Routing Protocols (Inter-AS) – E.g. BGP (Border Gateway Protocol) • Quality-of-Service Frameworks – Integrated Service (ISA, IntServ) – Differentiated Service (DiffServ)
    • Why IPv6? • Deficiency of IPv4 • Address space exhaustion • New types of service  Integration – Multicast – Quality of Service – Security – Mobility (MIPv6) • Header and format limitations
    • Advantages of IPv6 over IPv4 • • • • • • • Larger address space Better header format New options Allowance for extension Support for resource allocation Support for more security Support for mobility
    • Header: from IPv4 to IPv6 Changed Removed
    • IPv6 Header Format
    • Advantages of IPv6 over IPv4 (1) Feature Source and destination address IPSec Payload ID for QoS in the header Fragmentation Header checksum Resolve IP address to a link layer address IPv4 IPv6 32 bits 128 bits Optional required No identification Using Flow label field Both router and the sending hosts Only supported at the sending hosts included Not included broadcast ARP request Multicast Neighbor Solicitation message
    • Advantages of IPv6 over IPv4 (2) Feature IPv4 IPv6 Determine the address of the best default gateway ICMP Router Discovery(optional) ICMPv6 Router Solicitation and Router Advertisement (required) Send traffic to all nodes on a subnet Broadcast Link-local scope allnodes multicast address Configure address Manually or DHCP Autoconfiguration (IGMP) Multicast Listener Discovery (MLD) Manage local subnet group membership
    • Bluetooth Overview • Wireless technology for short-range voice and data communication • Low-cost and low-power • Provides a communication platform between a wide range of “smart” devices • Not limited to “line of sight” communication
    • Motivation Digital Camera Computer Scanner Inkjet Printer Home Audio System PDA Cell Phone Cordless Phone Base Station
    • Bluetooth Applications • Automatic synchronization between mobile and stationary devices • Connecting mobile users to the internet using bluetooth-enabled wire-bound connection ports • Dynamic creation of private networks
    • Ad Hoc Networks • Up to 8 devices can be actively connected in master/slave configuration • Piconets can be combined to form scatternets providing unlimited device connectivity
    • Bluetooth Radio • Uses 2.4 GHz ISM band spread spectrum radio (2400 – 2483.5 MHz) • Advantages – Free – Open to everyone worldwide • Disadvantages – Can be noisy (microwaves, cordless phones, garage door openers)
    • Frequency Hopping • • • • In order to mitigate interference, Bluetooth implements frequency hopping 1600 hops per second through 79 1MHz channels Spreads Bluetooth traffic over the entire ISM band All slaves in piconet follow the master for frequency hop sequence
    • Establishing Piconets • Whenever there is a connection between two Bluetooth devices, a piconet is formed • Always 1 master and up to 7 active slaves • Any Bluetooth device can be either a master or a slave • Can be a master of one piconet and a slave of another piconet at the same time (scatternet) • All devices have the same timing and frequency hopping sequence
    • Scatternets • Formed by two or more Piconets • Master of one piconet can participate as a slave in another connected piconet • No time or frequency synchronization between piconets
    • Berkeley Sockets The socket primitives for TCP.