Notes On Networking 1

Notes on Communication (1): Some fundamentals Jean-Lou Dupont jl @ jldupont . com http://www.jldupont.com/

Story board - context setting Communication between a source and sink (s) requires one of more interconnected ( network ) medium to forward the information that constitutes the communication-instance . The process by which information is transported from a source to the destination sink(s) requires resources and addressing . The resources can either be dedicated to the a communication-instance or shared amongst communication-instances. Sharing resources (effectively) require coordination and thus protocols . In this presentation, we will not be focusing on the transport of information which is encoded in a physical structure (e.g. transport by plane of information contained in a book).

Key Points Communication requires Medium air/vacuum, metal strings , optical strings Medium is composed of Dimensions Time, Frequency, Power Dimension access is either dedicated or shared Information transport is structured stream of symbols, stream of packets (group of symbols) Sharing implies Coordination implies protocol

Definition Channel: (sometimes called communications channel ) refers to the medium used to convey information from a sender (or source, transmitter) to a receiver (or sink). Communication-instance : a specific communication between a source and a sink. Forwarding Process : a component of a system responsible for the transport of information. Partition: Generally, a partition is a splitting of something into parts. In communications we further assume that partitions can only interact with each other (i.e. exchange information) by established interfaces. Source : aka transmitter Sink : aka receiver

Resources Resource usage can either be dedicated or shared Dedicated : the client of the resource controls the said resource for a period of time (either bounded or un-bounded) Shared : multiple clients compete to access & use the said resource using a coordination protocol (or apparent lack thereof :-) Dedicated access is just a special case of Shared access: nothing is really dedicated for an unbounded time period, more likely "leased" for a bounded time period (by a master process).

Medium - Dimensions A medium consists of 3 domains: Frequency Domain Time Domain Power Domain ALL dimensions ALWAYS present Often, the power dimension is assumed and abstracted from diagrams Frequency: change in Time Domain change includes matter level change e.g. finger over braille text

Dimensions - Examples Example 1: Medium is divided in the frequency domain - total isolation between dimensions Example 2: ( CDMA ) Medium is divided using "codes" in the Freq+Power plane - no total isolation

Medium - Partitioning E.g. air/vacuum : can be spatially partitioned (see figure) can be temporally partitioned ( time domain multiplexed ) a combination of the above

Medium For communication to take place, one or several medium must be used between source (s) and sink (s). A medium can either be dedicated or shared Dedicated 1 source, m sinks (where m>=1) Special case of shared Shared n sources, m sinks Requires a coordination protocol (e.g. CS MA /CD)

Medium - Access Multiple Access (i.e. shared access) requires a coordination protocol active between the sources Manage Information Merging => Loss

Information 3 fundamental properties: Information can be copied Information can be modified Information can be measured Note: Erase ~ no copy

Information Property: Copy Medium: air/vacuum By nature broadcast Use of electro-magnetic wave => copy is natural Partitioning is possible ( spatial, temporal ) Medium: metal / fiber strings Can be used in "broadcast" configuration too Easier to dedicate

Information Property: Modify 2 fundamental types: Intentional => the usual purpose behind a communication Un-intentional => environmental cause etc. => yields to loss

Information Property: Measure Measurement: Information Entropy Algorithmic Entropy ( Kolmogorov ) Complexity of the algorithm that describes the Information

Information Copy: role of Power Distance => power @ each sink => power

Forwarding Forwarding can take place in 2 fundamental types of channel: Destination Un-Aware Destination Aware

Channel - Destination Un-aware Representation of a broadcast channel A) one source accessing the channel @ time t B) two sources accessing the channel @ time t => loss

Channel - Destination Aware Representation of a destination aware channel: A) Information copied to 1 egress B) Information copied to multiple egresses

Forwarding - Identifier Types 2 fundamental types: Address Label Ultimately, the forwarding process requires an unambiguous way of delivering the information Note : we are not concerned here with the trivial case "identifier-less broadcast"

Address Types Unicast ==> 1 destination Multicast ==> n destination(s) where n>=0 Broadcast ==> 'all' Anycast ==> 1 destination from a set

Label Type A "label" is meant to be interpreted : can refer to a sequence of hops to a destination can refer to a communication-instance (aka connection) Indirection towards a destination

Connection Types 2 types: Non-merging (aka Transport Connection) Merging Merging: when multiple sources merge their traffic Result: can't identify individual sources

Merging Merging is undesirable: Noise merges into channels ==> loss of information Requires additional information (e.g. overhead) to mitigate against merging ==> less efficient Root Cause analysis difficult ==> higher OPEX

Merging - Management Aspect In order to manage communication (e.g. in a network), it is highly desirable to have the capability to find the root cause of faults. Noise is always present If higher than usual , need to locate and mitigate Noise can (sometimes) have a signature ==> identifiable Packet Switching is prone to merging multipoint-to-point constructs configuration errors routing errors

Notes On Networking 1

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Notes On Networking 1