Routing and Switching Principles. Lecture#01

Transcription

1 Routing and Switching Principles Lecture#01

2 Text Book

3 Companion website

4 Course Contents Understand the function of each OSI Model Layer, specifically Layers 1 through 3 Differentiate between token and contention protocols Configure station cash for learning transparent bridges Deploy the spanning tree given a specific bridged network Understand which specific source routing strategy to adopt Understand the differences between switches, hubs, bridges and routers Implement a VLAN solution (lecture, Lab4) Understand the Service Model and how to implement it Understand the use of X.25, ATM, TCP/IP, UDP, and ports Basic router set up and deployment (Labs 3 & 4) with hands on using a fully configurable router When to route using Distance Vector or Link State protocols Map the different routing technologies (ex: RIP, OSPF) to the routing protocols Basic usage of an industrial simulator to further understanding routing and switching

5 The OSI Reference Model

6 Physical layer Transmits information across a link. Deals with: Size and shape of connectors Assignment of functions to pins Conversion of bits to electrical signals Bit-level synchronization. Several different types of physical layers to exist within a network and even for multiple different types of physical layers to exist within a node, because each technology requires its own physical layer.

7 Data link layer: Checksumming to detect data corruption Coordinating the use of shared media (LAN) Addressing (when multiple systems are reachable, as in a LAN). It is common for different links to implement different data link layers and for a node to support several data link layer protocols, one for each of the types of links to which the node is attached.

8 Network layer: Enables any pair of systems in the network to communicate with each other. A fully connected network is one in which every pair of nodes has a direct link between its nodes, but this kind of topology does not scale beyond a few nodes. Typical network layer find a path through a series of connected nodes, and nodes along the path must forward packets in the appropriate direction. Deals with: Route calculation Packet fragmentation and reassembly Congestion control.

9 Transport layer: The transport layer establishes a reliable communication stream between a pair of systems. Deals with errors that can be introduced by the network layer, such as lost packets, duplicated packets, packet reordering, and fragmentation and reassembly Reacts to congestion in the network by sending data more slowly in response.

10 Session layer: ISO's session layer offers services beyond the simple fullduplex reliable communication stream provided by transport Such as dialogue control (enforcing a particular pattern of communication between systems) Chaining (combining groups of packets so that either all or none of the packets in the group gets delivered). Whatever this layer is, it's irrelevant for routing and switching.

11 Presentation layer: Goal: To agree on representations for data so that people defining structures don't have to worry about bit/byte order or what a floating point number looks like. ISO standardized on ASN.1 (Abstract Syntax Notation 1). Drawbacks: complex and inefficient in both space and processing IETF standards follows ASN.1.

12 Application layer: As fascinating as bridging and routing is, it's actually because of applications that people want any of this stuff. Applications include file transfer, virtual terminal, Web browsing, and so on. It is common for multiple applications to be running concurrently in a node.

13 Sender Receiver Data Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Header/trailer information is added or removed as data passes from layer to layer.

14 PDUs and SDUs Each layer communicates with its peer layer through a protocol data unit, or PDU. To make it clear which layer is being discussed, a single-letter prefix is added to PDU. The data link layer communicates with a peer data link layer by transmitting LPDUs. The network layer communicates with other network layers through NPDUs. The transport layer communicates with other transport layers through TPDUs.

15 PDUs and SDUs continued When upper layer gives information to lower layer for transmission, the information is known as an SDU, or service data unit. Single-letter prefix is added to eliminate ambiguity. When the transport layer wishes to transmit a TPDU to another transport layer, it must do so by giving the network layer an NSDU. Network layer takes the NSDU, adds an envelope and transmits it as an NPDU to data link layer

16 PDUs and SDUs continued

17 Connection-oriented Vs. Connectionless Connectionless Connection-oriented Transport Layer UDP TCP Network Layer CLNS CONS Datalink Layer LLC Type 1 LLC Type 2

18 Properties of Network Architecture 1. Scope 2. Scalability 3. Robustness 1. Alternative Routes 2. Safety barriers 3. Self-stabilization 4. Fault detection 5. Byzantine robustness 4. Autoconfigurability 5. Tweakability 6. Determinism 7. Migration

19 Scope Network Architecture should solve as general a problem as possible. Should be designed to support both a wide range of applications and a wide range of underlying technologies. If a network is designed with a specific application or upon particular technology, it may perform better for that one case. It is better to design a network that can handle a broad spectrum of applications and underlying technologies.

20 Scalability Ideal network design would work well with very large networks and also be efficient with small networks. Efficiency would not be sacrificed if the same design were used on a very small network

21 Robustness Robustness in the sense of computing alternative routes is not sufficient. Safety barriers: Networks should designed so that a fault does not spread beyond a safety barrier and therefore a disruption affects only a portion of the network Self-stabilization After any sort of database corruption, due to such causes as malfunctioning hardware or undetected data errors, the network will return to normal operation without human intervention within a reasonable time, provided that the faulty hardware is disconnected from the network or repaired and no further data corruption occurs (for some time). Fault detection All networks have some ability to detect faults, but none has a perfect ability to do so, and networks vary greatly in the degree to which faults can be identified Byzantine robustness A Byzantine failure is one in which a node fails not by simply ceasing operation but instead by acting improperly. Such failure can occur because of defective implementations, hardware faults, or active sabotage. Network with Byzantine robustness would be able to continue working properly even if some portion of the nodes had Byzantine failures.

22 Autoconfigurability Some network designs work well provided that very smart people do a lot of complex management and constantly tweak parameters. Such network designs greatly enhance the job security of the people who understand how to manage them. However in future people will be too dependent on networks to rely on a very few experts to keep them running. Users should not have to find the manager of other nodes to get information about their new node configured into databases.

23 Tweakability Networks should come with timers and other parameters that adventurous network managers can play with to optimize performance for specific conditions.

24 Determinism Identical conditions will yield identical results For example, in a deterministic network design, routes would always be identical given identical physical topologies In not deterministic, routes might differ depending on the order in which nodes were brought up in the network

25 Migration It is important to design network protocols so that new features can be added to nodes, one at a time, without disrupting current operations. It is also important to have a design that lets you make modifications, such as address changes, in a node-by-node fashion without disrupting network operations.