Managing Computer and Communication Networks Part1 Dr. Hamid Reza Naji

Motivation for Networks Information Access Sharing of Resources Facilitate Communications

What A Network Includes Transmission hardware Special-purpose hardware devices interconnect transmission media control transmission run software protocol Software Protocol encodes/decodes and formats data detects and corrects problems

What A Network Does Provides communication that is Reliable Fair Efficient From one application to another Automatically detects and corrects Data corruption Data loss Duplication Out-of-order delivery Automatically finds optimal path from source to destination

Issues we’ll be dealing with Point-to-point - Individual connections between pairs of machines. Broadcast Networks - Single channel with multiple machines connected to it. Packets - Messages - the "chunk" of data transmitted from one machine to the next. Addressing - One to one: Packet contains specific target address. Broadcasting: All machines on the network receive and process the packet. Multicasting: A subset of machines receive and process the packet.

transmission distance view messaging in terms of the transmission distance 100 meter Building -- Local area network 10 kilometer City -- Metropolitan area network 1K kilometer Country -- Wide area network 10K kilometer Continents -- Internet

Circuit Switching Dedicated fixed bandwidth route fixed at setup idle capacity wasted network state

Packet Switching Best Effort end-to-end control multiplexing technique re-route capability congestion problems

Network Hardware LOCAL AREA NETWORKS LANs are: Privately owned. Can be up to several kilometers long; Run at speeds of 10, 100, or more Mbps. Low delay. High reliability. Requires collision arbitration. Ethernet: IEEE 802.3. Bus based broadcast network with decentralized control at 10 or 100 Mbps. Token Ring: IEEE 802.5 Ring based broadcast network with token arbitration at 4 or 16 Mbps.

Network Hardware METROPOLITAN AREA NETWORKS MANS are: Larger version of LAN ("city" wide). Public or private / data or voice. Broadcast Can be distinguished from LANs based on wiring mechanism.

Network Hardware WIDE AREA NETWORKS WANS are: Networks spanning large distances. Hosts or End Systems - Machines running user applications. (Communication) Subnet - Connections between hosts - transmission lines + switches. A "locality" understanding each other's addresses. Circuits/Channels/Trunks - Transmission lines move the bits.

Network Hardware WIDE AREA NETWORKS Router - Generic term for switching computers. Point-to-point/Store-and-forward/Packet-switched - Moving through a series of routers, packets are received at a router, stored there, then forwarded to the next router.

Network Hardware Media Wireline String, Copper (Twisted Pair, Coax), Optical Fiber Wireless Sound, Light, Infrared, RF, Microwave Used where computer is mobile or far away from wires. Only few Mbps / higher error rates / interference.

PROTOCOL HIERARCHIES Layers - The concept that network software is organized functionally into levels. A level on one host talks to the same level on another host (its peer). Protocol - The protocol is the convention or standard that a layer uses to talk to the other layer. An agreement or standard on the conversation.

PROTOCOL HIERARCHIES

PROTOCOL HIERARCHIES Physical Medium - Underneath the layers is the wire or fiber or whatever. Interface - Defines the services that one layer offers another (either up or down.) Important that each layer perform specific actions.

PROTOCOL HIERARCHIES Network architecture - A set of layers and protocols. It contains details on what happens in the layer and what the layer says to its peer. Protocol stack - A list of protocols used by a system, one protocol per layer.

DESIGN ISSUES FOR THE LAYERS Both Directions Simultaneous Simplex No No Half duplex Yes No Full duplex Yes Yes o Number of logical channels per connection o Error control. o Flow control. o Breaking up messages into a smaller chunks (and reassembly.) o Multiplexing messages on same connection. o Routing - how to get from one host to another.

DESIGN ISSUES FOR THE LAYERS

INTERFACES AND SERVICES Purpose of each layer is to provide services to the layer above it. Entities / Peer entities - Active element in each layer (processor / IO chip). Peer entity = layer N entity <--> layer N entity. Layer N entity provides service for layer N + 1. Service providers and users - Layer N is a provider for user N + 1. SAPs (Service Access Points) - Entry points in N that layer N + 1 can access. Has an address that uniquely identifies it.

INTERFACES AND SERVICES IDUs (Interface Data Unit) - The information from N + 1 provided at the SAP. Made up of SDU + control information. SDUs (Service Data Unit) - The portion of the IDU that will be passed up to the peer entity. PDUs (Protocol Data Unit) - The SDU may be broken up into PDUs, that being the chunk size for further transmission.

INTERFACES AND SERVICES

CONNECTION-ORIENTED SERVICES Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in. Connection Setup Data Transfer Connection Termination

CONNECTIONLESS SERVICES Like the post office. Each message has the entire address on it. Each message may follow a different route to its destination. Ordering is not important

CONNECTION-ORIENTED / CONNECTIONLESS SERVICES: Quality of service - Will the message arrive?? A reliable connection-oriented service guarantees success. Message sequence - message boundaries and order are maintained. Byte streams - messages are broken up or combined; flow is bytes. Can pair mechanism with upper-layer requirements (matching).

CONNECTION-ORIENTED / CONNECTIONLESS SERVICES: Datagram Service – Like junk mail. It's not worth the cost to determine if it actually arrived. Needs a high probability of arrival, but 100% not required. Connectionless, no acknowledgment. Acknowledged datagram service - As above, but improved reliability via acknowledgment. Request-reply service - Acknowledgment is in the form of a reply.

CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:

SERVICE PRIMATIVES Primitives are: The operations available to an entity. Possibilities include: Request -- An entity want some work done. Indication -- An entity is told about an event. Response -- An entity wants to respond to an event. Confirm -- Response to earlier request has come back.

SERVICE PRIMATIVES Example of Connectionless Protocol: Data-request |--------->| Data-indication Data-indication |<---------| Data-request Example of Connection-oriented Protocol: (needs connection establishment) Connect-request |--------->| Connect-indication Connect-confirm |<---------| Data-request |--------->| Data-indication Data-indication |<---------| Data-request Disconnect-request |--------->| Disconnect-indication Disconnect-confirm |<---------|

SERVICE PRIMATIVES THE RELATIONSHIP OF SERVICES TO PROTOCOLS: Services are primitives that a layer provides for the layer above it. Protocols are rules governing the meaning of frames/packets/messages exchanged with the peer entity.

Layering

Headers, Data, and Trailers Reference Models Headers, Data, and Trailers Encapsulation

THE OSI REFERENCE MODEL OSI == Open Systems Interconnection Developed by ISO == International Standards Organization Principles used to develop OSI Layering: 1. Need a layer for each different level of operation. 2. Each layer performs a well defined function. 3. Each layer has a standard. 4. Layer boundaries should minimize data flow across those boundaries. 5. The right number of layers - don't put too many functions together, but not too many layers either.

THE OSI REFERENCE MODEL

THE OSI REFERENCE MODEL Physical Layer - Purpose -- Transmits raw bits across a medium. Electrical -- Concerns are voltage, timing, duplexing, connectors, etc.

THE OSI REFERENCE MODEL Data Link Layer - Framing -- Breaks apart messages into frames. Reassembles frames into messages. Error handling -- solves damaged, lost, and duplicate frames. Flow control -- keeps a fast transmitter from flooding a slow receiver. Gaining Access -- if many hosts have usage of the medium, how is access arbitrated.

THE OSI REFERENCE MODEL Network Layer - Routing -- What path is followed by packets from source to destination. Can be based on a static table, when the connection is created, or dynamic when each packet is sent. Congestion -- Controls the number packets in the subnet. Accounting -- Counts packets/bytes for billing purposes. Heterogeneity -- Interfacing so one type of network can talk to another.

THE OSI REFERENCE MODEL Transport Layer - Reliability -- Ensures that packets arrive at their destination. Reassembles out of order messages. Hides network -- Allows details of the network to be hidden from higher level layers. Service Decisions -- What type of service to provide; error-free point to point, datagram, etc. Mapping -- Determines which messages belong to which connections. Naming -- "Send to node xyz" must be translated into an internal address and route. Flow control -- keeps a fast transmitter from flooding a slow receiver.

THE OSI REFERENCE MODEL Session Layer – Sessions -- Provides services that guarantee a particular message. For instance, a login session could be logged. Synchronization-- Provide way to subdivide a long mechanism for reliability.

THE OSI REFERENCE MODEL Presentation Layer - Prettiness -- Syntax and semantics of information transmitted. --Understands the nature of the data being transmitted. --Converts ASCII / EBCDIC.

THE OSI REFERENCE MODEL Application Layer - Interfacing -- Terminal type translation. File transfer -- Programs able to understand directory structures and naming conventions and map them onto various systems.

Data Transmission in the OSI Model -

THE TCP/IP REFERENCE MODEL Used in the Internet. Common mechanism that is surpassing the OSI Model. Internet Layer - The IP (Internet Protocol) does delivery and congestion control.

THE TCP/IP REFERENCE MODEL Transport Layer - Allows peer entities to communicate. TCP -- Transmission Control Protocol provides a reliable connection oriented protocol that delivers a byte stream from one node to another. Guarantees delivery and provides flow control. UDP -- User Datagram Protocol provides an unreliable connection-less protocol for applications that provide their own. Application Layer - Terminal -- Telnet File transfer -- FTP The Web -- HTTP

COMPARISON OF REFERENCE MODELS LAYERS Transport Network OSI Connectionless Connection-Oriented Connection-Oriented TCP Connectionless Connectionless Connection-Oriented

Example Networks NOVELL NETWARE: Heavily used in PC world. Proprietary protocol stack Network layer -- IPX - unreliable connectionless Transport layer -- NCP (Network Core Protocol) - connection oriented Naming and Addressing -- SAP (Service Advertising Protocol) - Servers advertise their address to router machines. Clients, when booted, ask for location of nearest server.

Example Networks THE INTERNET: Growing exponentially. All nodes run TCP/IP. Means that all nodes have an IP address by which they can be contacted. Services provided include: o e-mail o news o remote login o file transfer o the web

Standards ISO (International Standards Organization) ANSI (American National Standards Institute) NIST (National Institute of Standards and Technology) IEEE (Institute of Electrical and Electronics Engineering) IAB (Internet Architecture Board)