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Networking Technologies Yelena Yesha Olga Streltchenko Presentation Overview Evolution of Networks. Networking Challenges. Types of Networks. Network Principles. Internet Protocols. Summary. The Network Built from Transmission media Wire, cable, fibre, wireless channels;

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yelena yesha olga streltchenko

Networking Technologies

Yelena Yesha

Olga Streltchenko

presentation overview
Presentation Overview
  • Evolution of Networks.
  • Networking Challenges.
  • Types of Networks.
  • Network Principles.
  • Internet Protocols.
  • Summary.
the network
The Network
  • Built from
    • Transmission media
      • Wire, cable, fibre, wireless channels;
    • Hardware devices
      • Routers, switches, bridges, hubs, repeaters, network interfaces;
    • Software components
      • Protocol stacks, communication handlers, drivers.
evolution of networking
Evolution of Networking
  • Batch Environment - 1950s
    • no direct interaction between users and their programs during execution.
  • Time Sharing - 1960s
    • Dumb terminals were connected to a central computer system.
    • Users were able to interact with the computer and could share its information processing resources.
    • Marked the beginning of computer communications.
evolution of networking cont d
Evolution of Networking (cont'd)
  • Distributed Processing: use of minicomputers - 1970s
    • Users demanded computing closer to their work areas.
    • Communication between neighbour processors and applications via networks.
  • WAN and LAN- 1980s
  • Internet, broadband and wireless communication, mobile code, ubiquitous computing, etc. - 1990s
  • 2000s - ?
networking challenges
Networking Challenges
  • Performance
  • Scalability
  • Reliability
  • Mobility
  • Security
  • QoS (Quality of Service)
performance
Performance
  • Parameters that determine the speed of message exchange between two nodes
    • Latency
      • Delay that occurs after a send operation and before the data becomes available at the target node, i.e. latency=time to transmit an empty message
    • Data transfer rate
      • The speed at which data can be transferred between two nodes (bits/sec).
  • If a message length does not exceed the max determined by the network technology, then Message transmission time=latency+length/data transfer rate
performance cont d
Performance (cont'd)
  • Transfer rate is primarily determined by physical characteristics of the network.
  • Latency is primarily determined by
    • software overheads,
    • routing delays,
    • load-dependent non-deterministic elements;
      • E.g., message collision on the Ethernet.
  • Total system bandwidth of a network
    • Measure of throughput;
    • Total volume of traffic that can be transferred across the network in a given time.
scalability
Scalability
  • A system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users.
  • Challenges in scalable system design:
    • Controlling the cost of physical resources as the demand for resources grows;
      • e.g., for a system with n users the quantity of physical resources should be at mostO(n).
    • Controlling the performance lost as the number of users/resources grows;
      • e.g., for a system with n objects the access time should be at mostO(log n).
scalability cont d
Scalability (cont'd)
  • Challenges in scalable system design (cont'd):
    • Preventing software resources running out
      • Example: 32-bit IP address of the 1970's ran out; current IP address uses 128 bits and is expected to be exhausted by early 2000's. - Keeping up is a serious challenge!
    • Avoiding performance bottlenecks
      • Use decentralized algorithms, caching, redundancy and replication;
      • Example: DNS table maintenance: tables are distributed and replicated.
scalability on the internet
Scalability on the Internet
  • Potential size of the Internet=world population.
  • Original network technologies did not anticipate this scope.
  • Changes to the addressing and routing.
  • Current average round-trip time= 100-150ms
    • Individual numbers vary widely.
  • The ability to scale will depend on the economics of use
    • Charges to the users
    • Patterns of communication.
reliability failure models
Reliability: Failure Models
  • Communication failures (vs process failures)
    • Omission failure: communication channel fails to perform prescribed actions;
      • e.g., loss of messages;
      • Easiest type of failure to detect and handle, e.g., retransmit the message.
    • Arbitrary failure: unintended actions occur (any type of error);
      • e.g., delivery of a corrupted message, delivery of a non-existent message, repeated delivery;
      • This type of error is rare since communications software is able to detect [and correct] it.
reliability failure models cont d
Reliability: Failure Models (cont'd)
  • Communication failures (cont'd)
    • Timing failure arises in synchronous application where time limits are set on message delivery;
      • Responses become unavailable to clients after timeout, e.g., ftp;
      • Asynchronous systems like WWW are not suseptible to this type of error since they do not provide any timing guarantees.
handling failures
Handling failures
  • Detecting
    • E.g., use checksum to detect a corrupted message;
    • Not always possible, e.g., a remote server crash.
  • Masking
    • Hide a failure
      • By means of service/data replication, etc.;
    • Convert a failure into another type of failure
      • e.g., dropping a corrupted message turns an arbitrary failure into anomission failure;
        • We know how to handle it.
handling failures cont d
Handling Failures (cont'd)
  • Tolerating
    • Impractical to detect and hide all the failures on the Internet;
    • Software informs users about failure;
    • Include redundant components into the system to tolerate failures, e.g.
      • at least two different routes between two routers;
      • DNS replication;
      • operational database replication.
handling failures cont d16
Handling failures (cont'd)
  • Recovery
    • Involves special software design that allows to recover the state of the permanent data.
reliability of communications requirements
Reliability of Communications Requirements
  • Validity
    • Any message in the outgoing buffer will be eventually delivered to the incoming message buffer.
  • Integrity
    • The message received is identical to the message sent, and no messages are delivered twice.
mobile code
Mobile Code
  • Code that can be sent from one computer to another;
    • e.g., Java applets;
    • Virtual Machine approach
      • A way of making code executable on any hardware;
      • VM is middleware, i.e. a layer of software whose purpose is to mask heterogeneity of hardware;
      • The compiler generates code for a VM;
      • Used by Java and is not necessarily extendable to other languages.
mobile code cont d
Mobile Code (cont’d)
  • The advantage of running downloaded code is network delay avoidance during interactions.
  • Potential security threat to the local resources.
mobile agents
Mobile Agents
  • A running program (code and data) that travels from one computer to another over the network carrying out a task on behalf of a user;
    • e.g., to perform information retrieval.
  • The advantage over client-server approach lies in the reduction of communication time and cost;
    • replaces remote invocations with local ones.
  • Potential security threat to the host.
  • MA are vulnerable themselves.
mobile devices
Mobile Devices
  • Proliferation of small and portable computer devices
    • e.g., laptops, PDAs, mobile phones, digital cameras, etc.
  • Enabled with wireless networking
    • Metropolitan or greater ranges
      • GSM (Global Mobile System), European standard;
      • CDPD (Cellular Digital Packet Data), in the USA and Canada.
    • Ranges of l 100m
      • BlueTooth;
      • Infra-red;
      • HomeRF.
spontaneous networking
Spontaneous Networking
  • The term best describes the integration of mobile devices into a given network.
    • Encompasses applications that involve connection of mobile and non-mobile devices to networks.
  • Challenge: enable universal interoperability between mobile devices and local non-mobile services:
    • e.g., laptops or palmpilots need to detect and be able to use available resources, like printers, fax machines, etc., when they move into different surroundings.
spontaneous networking cont d
Spontaneous Networking (cont’d)
  • Requirements
    • Easy connection to a local network:
      • Avoid the need of pre-installed cabling, inconvenience of plugs and sockets;
      • Transparently reconfigure a mobile device to obtain connectivity (avoid the need of manually installing drivers).
    • Easy integration with local services:
      • Automatic discovery of available services.
        • Active research area.
  • Challenge for IP addressing:
    • Classical IP addressing and routing assumes that computers are located on a particular subnetwork;
    • if a computer is moved to another subnet it is no longer accessible with its IP address;
    • Solution: MobileIP (discussed later)
spontaneous networking cont d24
Spontaneous Networking (cont’d)
  • Limited connectivity
    • Users are intermittently disconnected as they move;
    • Could be disconnected for long periods of time
  • Security and Privacy
    • Security attacks by mobile devices onto the host network or vice versa;
    • Tracking of physical location of the user;
    • Access to data otherwise protected by a firewall;
    • Many other scenarios.
discovery services
Discovery Services
  • Accept and store details of services that become available on the network and respond to queries from clients about them.
  • Offer two interfaces:
    • A registration service accepts registration requests from servers and records the details in the discovery service’s database;
    • A lookup service accepts and processes queries concerning available services; returns enough details to the client to enable it to choose among similar services and establish a connection.
  • Example: Jini (discussed later in class).
security requirements
Security Requirements
  • Confidentiality
    • protection against disclosure to unauthorized individuals.
  • Integrity
    • protection against alteration or corruption.
  • Availability
    • protection against interference with the means to access the resource (denial of service attack).
firewalls
Firewalls
  • Creates a protection boundary between the organization's intranet and the Internet.
  • Runs on a gateway - a computer that stands at the network entry point to the intranet.
  • Receives and filters all the incoming and outgoing messages according to the organization‘s security policy.
secure network environment
Secure Network Environment
  • Need to move beyond the restrictions imposed by firewalls.
  • Need to ensure authentication, privacy and security over unprotected channels.
  • Use of cryptographic techniques.
  • Virtual Private Network (VPN) concept:
    • Use encryption schemes to establish secure tunnels through the Internet.
time and data delivery
Time and Data Delivery
  • Most of the data can be delivered within a range of transfer rates;
    • E.g., e-mail, file transfer.
  • Time-critical data: streams of data that are required to be transferred at a certain rate.
    • Multimedia data require guaranteed bandwidth and bounded latency for the communication channels they use.
quality of service
Quality of Service
  • The ability to meet deadlines when transmitting and processing streams of real-time multimedia data;
    • provide computing and communication resources.
  • Currently network performance deteriorates fast with load growth:
    • no QoS support on the Internet.
types of networks
Types of Networks
  • Local area networks (LANs).
  • Wide area networks (WANs).
  • Metropolitan area networks (MANs).
  • Wireless networks.
  • Internetworks.
slide32
LANs
  • A collection of hosts connected by a high speed network of a single communication medium;
    • twisted pair, coaxial cable, optical fibre.
  • Designed and developed for communications and resource sharing in a local work environment;
    • room, campus, building.
lans cont d
LANs (cont'd)
  • A segment is a section of a cable serving a floor or a building:
    • no routing of messages is required since the medium provides direct connection between all of the nodes connected to it.
  • Larger LANs consist of several segments.
  • For a LAN, total system bandwidth is high and latency is low.
lan technologies
LAN Technologies
  • Ethernet as a dominant technology for wired LANs;
    • lacks latency and bandwidth guarantees needed by multimedia applications.
  • ATM networks were developed to fill the gap;
    • their high cost inhibited their adoption for LANs.
  • High-speed Ethernet
    • is deployed in a switched mode;
    • overcomes drawbacks of Ethernet;
    • not as effective as ATM for MM data.
slide35
WANs
  • Networks connecting remote communicating entities;
    • lower speed between nodes;
    • used to connect LANs.
  • The communication medium is a set of communication circuits linking a set of routers- dedicated computers that
    • manage the communication network;
    • rout messages or packets to their destinations.
wans cont d
WANs (cont'd)
  • Routing operations introduce a delay at each point of routing;
    • total latency for a transmission depends on the route taken and traffic encountered.
  • Lower bound on latency is set by physical properties of the medium;
    • the speed of electronic signals in most media is close to the speed of light.
slide37
MANs
  • Network based on the high-bandwidth copper and fibre optic cabling;
    • installed in metropolitan areas for transmission of video, voice, or other multimedia data over distances up to 50km.
  • Likely to meet requirements set for LANs while connecting more distant entities.
  • “Last mile” technology.
man technologies
MAN Technologies
  • DSL (digital subscriber line)
    • typically uses ATM switches located in telephone exchange to route digital data onto twisted pair;
    • limited range: 1.5km from the switch;
    • speed: 0.25-6.0Mbps.
  • Cable Modem
    • uses analog signalling over coaxial cable;
    • greater range than DSL;
    • speed: 1.5Mbps.
wireless networks
Wireless networks
  • Digital wireless communication technologies
    • WaveLAN (IEEE 802.11)
      • 2-11Mbps over 150m;
      • wireless local area network designed to replace wired LANs.
    • other technologies to connect mobile devices to other mobile or fixed devices in the immediate vicinity.
wpans
WPANs
  • Wireless personal area networks
    • infra-red links;
      • included in laptops and palmtops.
    • BlueTooth low-power radio network (www.bluetooth.com)
      • 1-2 Mbps over 10 m.
mobile phone networks
Mobile phone networks
  • Based on digital wireless network technologies.
  • Standards
    • GSM (global System for Mobile communications) used in Europe;
    • Most mobile phones in the US are based on the analog AMPS cellular radio network with CDPD (Cellular Digital Packet Data) layer over it.
  • Offer wide-area mobile connections to the Internet for portable devices;
    • low-data rates: 9.6-19.2 kbps;
    • successor networks are being designed for 128-384kbps over ~ km and 2Mbps for smaller cells.
internetworks
Internetworks
  • A communication subsystem in which several networks are linked together to provide common data communication facilities that conceal the technologies and protocols of the individual component networks and the methods used for their interconnection.
    • Built upon a variety of LAN and WAN technologies;
    • interconnected by routers (dedicated switching computers) and gateways (general-purpose computers)
    • a software layer supports addressing and data transmission.
      • Example: the Internet.
network principles
Network Principles
  • Packet transmission.
  • Data streaming.
  • Switching schemes.
  • Protocols.
  • Routing.
  • Congestion control.
  • Internetworking.
packet transmission
Packet transmission
  • Message: sequence of data items (binary).
  • Messages are subdivided into packets of bounded size
    • to manage the buffer storage;
    • to avoid long wait for a window of sufficient size on the communications channel.
data streaming
Data Streaming
  • Packet transmission is inappropriate for multimedia.
  • MM applications rely on the transmission of data stream at guaranteed rates with bounded latencies
  • QoS requirements:
    • bandwidth, latency, reliability;
    • availability of a channel from the source to the destination;
    • buffering where appropriate to cushion flow irregularities.
data streaming cont d
Data Streaming (cont'd)
  • ATM networks are designed to provide the necessary QoS for MM data.
  • IPv6 includes feature for recognition and special treatment of MM data packets.
switching schemes
Switching Schemes
  • Broadcast
    • no switching: everything is transmitted to every node;
    • Broadcast-based technologies:
      • Ethernet;
      • Wireless.
  • Circuit switching
    • a channel is created from the source to the destination;
    • telephone networks are based on circuit switching;
      • referred to as POST (plain old telephone system).
switching schemes cont d
Switching Schemes (cont'd)
  • Packet switching, or store-and-forward
    • no direct channel between the source and the destination;
    • packets are forwarded from node to node along the route and buffered if necessary.
  • Frame relay
    • switch very small packets (frames);
    • switching nodes base their decisions on the first few bits of the packet;
    • frames are not stored at nodes but streamed through them;
    • basis for ATM technology.
protocols
Protocols
  • Communication protocol: a set of rules and formats; it defines a specification of
    • the sequence of messages exchanged;
    • the format of the data in the messages.
  • Existence of open protocols enables component-based software development.
  • A protocol is implemented as a pair of software modules on the sender and receiver nodes.
    • Examples: transport protocol (implements process-to-process channel); network protocol (handles routing).
protocol layers
Protocol Layers
  • Network software=hierarchy of layers.
  • Each layer provides a service to the layer above it and utilizes the services of the layer below.
  • Each layer appears to communicate directly to its peer on the other side of the network.
  • Each layer communicates via local procedure calls to the adjacent layers

Layer n

Layer 2

Layer1

data encapsulation
Data Encapsulation
  • Peer protocol modules must communicate control information to each other
    • e.g., instructions on how to handle the message upon arrival, etc.
  • A special data structure is attached at either end of the message - a header or a tailer.
  • The rest of the message is called a body
    • info carried over from the layer above.
  • Data is encapsulated by a module.
protocol suits stacks
Protocol Suits/Stacks
  • A complete set of protocol layers.
    • Examples: OSI (open system interconnection), Internet protocol suit.
  • Protocol layering
    • simplifies and generalizes the software interfaces for access to the communication services of the networks;
    • induces performance cost:
      • N layers=N control transfers;
      • header/tailer data overhead.
    • actual transfer rates << available network bandwidth!
osi model
OSI Model

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

Network

Network

Network

Data link

Data link

Data link

Physical

Physical

Physical

physical layer
Physical Layer
  • The physical layer defines electrical signalling on the transmission channel; how bits are converted into electrical current, light pulses or any other physical form.
  • Specific functions:
    • connection establishment and termination;
    • encoding and transmission of bits;
    • Repeating or amplification to increase the range of transmission.
data link layer
Data Link Layer
  • Defines how the network layer packets are transmitted as bits.
  • Examples of data link layer protocols:
    • PPP (Point to Point Protocol) ;
    • Ethernet framing protocol.
  • Bridges work at this layer only.
  • Other functions:
    • Framing and Error detection
      • transmission might get corrupted, bits may be lost (parity, checksum);
      • may lose connection.
    • Flow control
      • may send data too fast for a modem;
      • data might get delayed a long time in the network.
the network layer
The Network Layer
  • Delivers packets from sending computer to receiving computer (host-to-host).
  • Defines how information from the transport layer is sent over networks and how different hosts are addressed.
  • Example of a network layer protocol: the Internet Protocol.
  • Device that takes care of the network level functions is router or sometimes a gateway .
  • Functions:
    • Addressing: Determines which machine to send the packet to;
    • Routing: Determines the best set of links;
    • Congestion Control: Routes the packets via a different route if one intermediate node gets flooded with packets.
the transport layer
The Transport Layer
  • Takes care of data transfer, ensuring the integrity of data if desired by the upper layers.
  • Provides end-to-end delivery.
  • Functions:
    • establishing and terminating connection;
    • flow control;
    • error detection and correction;
    • Multiplexing.
  • TCP and UDP operate at this layer.
the session layer
The Session Layer
  • Establishes and terminates connections and arranges sessions to logical parts.
  • Provides a means of controlling the dialogue between two end users;
    • Dialogue management (half versus full duplex);
    • Synchronization and recovery management.
  • This layer is not often used in existing systems.
  • TCP and RPC provide some functions at this layer.
the presentation layer
The Presentation Layer
  • Takes care of data type conversion
  • An example of protocol residing at this layer: XDR (External Data Representation), which is used by RPC applications to provide interoperability between heterogeneous computer systems
  • Presentation layer functions are, in most systems, handled elsewhere in the network protocols
the application layer
The Application Layer
  • Defines the protocols to be used between the application programs.
  • Examples of protocols at this layer are: protocols for electronic mail (e.g. SMTP), file transfer (e.g. FTP)and remote login, directory look up, http.
the internet model
The Internet Model
  • The implementation of the Internet does not follow the OSI model.
  • Also called TCP/IP model.
      • Evolved from ARPANET.
  • Note: the components are not strictly layered.

Application

Application

TCP/UDP

TCP/UDP

IP

IP

Network

Network

the internet model cont d
The Internet Model (cont'd)
  • Network layer:
    • a combination of hardware (network adapter, etc.) and software (network device driver).
  • Internet Protocol layer:
    • creates a logical network over multiple networking technologies.
  • Transmission Control Protocol and User Datagram Protocol layer:
    • alternative logical channels to application programs.
  • Application layer:
    • a set of application protocols to enable interoperability of popular applications.
the internet model cont d63
The Internet Model (cont'd)
  • Does not imply strict layering
    • programs are free to define new channel abstraction or applications that run on top of any of the existing protocols.
  • IP as a focal point of the model:
    • a variety of protocols above IP level and a number of implementations under it.
packet assembly
Packet Assembly
  • Function of the transport protocol.
  • Divides messages into packets and assigns sequence numbers to them before transmission.
  • Reassembles them after transmission according to the sequence numbers.
  • Encapsulation: header+body(data field).
  • Length(body) <=MTU
    • maximum transfer unit.
      • Ethernet MTU=1500 bytes, IP MTU=64kbytes.
ports
Ports
  • Software-definable destination points for communication within a host.
  • Attached to processes for interprocess communications.
  • Transport layer obtains a message at a port and delivers it to another port
    • port numbers are part of the header: transport address=network address+port number
addressing
Addressing
  • A network address is a unique numeric identifier of a host.
  • Used by routers to forward frames.
  • For the Internet model: IP address.
packet delivery
Packet Delivery
  • Datagram packet delivery (connectionless approach).
    • A message is not sent as a single unit, but broken down into small packets that are transmitted individually;
    • Every packet contains the full network address of the source and the destination;
      • enough information for any switch encountered en route to decide how to route the packet;
    • no circuit set-up is required;
    • the network retains no info about the packet;
    • packets may travel on different routes and may even arrive to the destination out of order;
    • delivery is not necessarily affected by failure of one or several links.
packet delivery cont d
Packet Delivery (cont'd)
  • Virtual circuit packet delivery (connection-oriented approach).
    • virtual connection from the source to the destination must be established (dynamically);
      • receives a virtual circuit identifier (VCI) to be used by the datagrams between the source and the destination;
      • each node maintains a table indicating which link should be used for each VC;
    • no addresses are required and the overhead (caused by VCI) is small;
    • several virtual circuits may use the same link at a time;
    • the connection is broken if a single link fails.
    • Example: ATM uses this technology.
routing
Routing
  • Adaptive routing:
    • the best way for communication is re-evaluated periodically;
    • routing decisions are made on hop-by-hop basis using locally held information.
  • A routing algorithm
    • makes decisions about the rout taken by each packet:
      • in circuit-switched networks all decisions are made when the connection is being established;
      • in packet-switched networks the route is determined independently for each packet;
    • updates its knowledge of the network
      • traffic intensity, failed links, etc.
routing cont d
Routing (cont'd)
  • A problem of graph theory
    • networks are representable by graphs.
  • Bellman's shortest path algorithm [1957].
  • A routing algorithm must be distributed
    • centralization is the enemy of scalability.
  • Extension to a distributed algorithm by Ford & Fulkerson [1962]
    • Bellman-Ford protocols.
routing table update
Routing table update
  • Distance vector algorithm
    • implemented in RIP (one of the Internet protocols);
    • each node maintenance/updates a vector of "distances" (costs) for each destination on the network.
  • Link state algorithm
    • implemented in OSPF (one of the Internet protocols);
    • every node maintains and disseminates information on how costly it is to reach its immediate neighbours;
    • each node updates its knowledge based on the information received from its neighbours;
    • each node eventually builds a map of the whole network.
congestion control
Congestion Control
  • Network capacity is limited by the performance of its communication links and switching nodes.
  • Queues are built at the hosts as the load approaches capacity.
  • Packets are dropped when buffers are full.
  • Dropped packets need to be resent.
  • Throughput deteriorates.
congestion control cont d
Congestion Control (cont'd)
  • Solution: increase delays, keep throughput at its maximum;
    • inform nodes along the route about the state of links and switches along the route;
    • reduce the transmission rate on the route;
      • buffer packets at the nodes encountered earlier on the route.
  • Congestion control is achieved by informing nodes along a route that congestion has occurred.
congestion control cont d74
Congestion Control (cont'd)
  • Congestion information is supplied by
    • Transmission of choke packets: special messages requesting a reduction in the transmission rate;
    • Special provisions in a transmission control protocol, e.g., TCP;
    • Observing occurrence of dropped messages.
  • In virtual circuit-based networks congestion information is received and acted on at each node;
    • QoS management.
internetworking
Internetworking
  • Internetwork=integrated network
    • Encompasses many subnets implemented over a number of technologies, like Ethernet, ATM, IDSN links and DSL connections.
    • Requirements
      • A unified internetwork addressing scheme;
      • A protocol defining the packet format and packet handling rules;
      • Internetworking components (hardware) to route packets to their destination.
    • For the Internet, I and II are provided by IP addresses; III is performed by Internet Routers.
subnets
Subnets
  • A portion of network that shares a common address component.
  • On TCP/IP networks, subnets are all devices whose IP addresses have the same prefix.
    • Networks are divided using a subnet mask (discussed later).
  • Subnetting facilitates security and performance.
interconnection devices
Interconnection Devices
  • Router: a general-purpose computer responsible for
    • forwarding the internetwork packets that arrive on any connection to the correct outgoing connection;
    • Maintaining routing tables for the above purpose.
    • Note: routing is not required for Ethernet, wireless, and other networks where hosts are connected to a single transmission medium.
  • Bridge: a link between networks of different types.
  • Bridge/Router links several networks and, therefore, perform routing.
interconnection devices cont d
Interconnection Devices (cont’d)
  • Hub: a simple connection for hosts on a broadcast network;
    • Provides means of connecting additional hosts;
    • Overcomes distance limitations (amplifies).
  • Switch: a router for a local network;
    • Interconnects several separate Ethernets by routing incoming packets onto an appropriate network connection;
    • Starts with no knowledge of the wider internetwork and builds up routing tables by observation of traffic and supplemental broadcast requests.
  • Switches vs hubs: the former reduce congestion by transmitting only to an appropriate network connection.
tunnelling
Tunnelling
  • Hiding of the underlying network protocol.
  • Necessary when a pair of nodes need to communicate over an alien protocol.
    • They construct a protocol tunnel or encapsulate the datagram.

Encapsulators

A

B

IP network

IP network

ATM

tunnelling cont d
Tunnelling (cont’d)
  • A protocol tunnel is a software layer that transmits packets through an alien network environment.
  • Examples:
    • MobileIP transmits IP packets to mobile hosts anywhere on the Internet by constructing a tunnel from their host base.
    • PPP protocol for dial-up line constructs a tunnel to transmit IP packets.
    • ATM Adaptation layer constructs a tunnel to transmit IP packets.
    • With the anticipated transition from IPv4 (current version to IPv6, IPv4 will constructs a tunnel to transmit IPv6 packets.