Reference Models and Standards

Reference Models (1) A reference model is the formal name for a protocol suite – a collection of protocols and layer definitions that provide network service We discuss a few models in this lesson –The 7-layer, Open Systems Interconnection (OSI) model created primarily by the phone companies –The 5-layer Transmission Control Protocol (TCP) / Internet Protocol (IP) model created by the Internet Engineering Task Force (IETF) –The ATM model –The Bluetooth model 2

Reference Models (2): OSI Conceptual objects are central to the OSI model –Services: define what the layer does, i.e., its semantics –Interfaces: describe how to access the services –Protocols: describe the interaction with the peer and implement the offered service described by the interface –The concepts are the only significant contributions of this reference model Designed without any thought of internetworking –Typical phone company arrogance: Everyone will use our technologies Therefore internetworking is not needed (WRONG!!!) 3

Reference Models (3): OSI The model was devised before the protocols – so there are problems with what service is put into each layer –Designers couldn’t agree whether there should be 6 or 8 layers, so they comprised and declared 7 layers –As a joke people now often talk about layers 8 and 9 - politics and economics - as two unspoken layers –The lower layer names are often still used OSI is complex - initial implementations were poor TCP/IP was already established and as a result TCP/IP became more popular 4

Reference Models (4): OSI 5 voltages, cabling framing routing end-to-end boundary synchronization “endian” issues

Reference Models (5): TCP/IP The principle TCP/IP design goals were internetworking capability and survivability –The US Department of Defense wanted connections to continue working as long as the source and destination machines continued to work Originally there were 4 layers with a Host-to- Network layer below the Internet layer –Now TCP/IP is a 5 layer model with a Network Interface layer and a Physical layer similar to the Data-Link layer and the Physical layer of the OSI model –The OSI names are often used at layer 2 and even sometimes at layer 3 without too much confusion... 6

Reference Models (6): TCP/IP 7 Also called the network-access layer

Reference Models (7): TCP/IP 8 Layer 3 is often called the network layer and Layer 2 the data-link layer – borrowing from the OSI model

Reference Models (8): TCP/IP At the transport layer there were originally two protocols –Transmission Control Protocol (TCP): a reliable, connection-oriented byte stream protocol –User Datagram Protocol (UDP): an unreliable connectionless protocol –Other transport layer protocols are emerging –Some “transport” protocols are constructed at the application layer as a shim on top of UDP Session and presentation layers were not included –The application must perform those roles in TCP/IP 9

Reference Models (9): TCP/IP The focal point of TCP/IP is the Internet layer – giving the protocol graph a “narrow waist” –This is the layer responsible for routing datagrams in an internetwork –It is also responsible for congestion control and fragmentation –The key to the design is an arbitrary number of transport protocols above and network technologies below this layer 10

Reference Models (10): TCP/IP 11 TCP/IP Initial protocol graph Application Transport Internet Network Interface

Reference Models (11): TCP/IP The descriptions provided in the OSI protocol stack slide for layers 1 to 4 generally apply here as well We will study Layers 3 and 4 particularly with Ethernet at Layer 2 Although ubiquitous, TCP/IP has its problems –TCP/IP did not initially distinguish between service, protocol, and interface – so its protocols are more coupled and therefore harder to replace –TCP/IP isn’t really a model – just a description of protocols that already had been created 12

Reference Models (12): ATM Asynchronous Transfer Mode (ATM) is a phone company promoted, packet-switched, connection- oriented technology with its own reference model –The model is 3-dimensional with a user plane and a control plane, and with layer and plane management functions at all layers During the late 1990s it was promoted as the “one- size fits all” technology but it has since been overtaken by the much simpler Ethernet for LAN use 13

Reference Models (13): ATM 14

Reference Models (14): Bluetooth Bluetooth is a Personal Area Network (PAN) technology for very small piconets It has its own protocol architecture that has been modified somewhat by the IEEE committee to make it compatible with other 802 networks Perhaps most interesting is that there is no layer corresponding to the network layer of the OSI model – the piconet is too small to need routing –But there has been interest in adding routing 15

Reference Models (15): Bluetooth 16

Reference Models (16): Hybrid Model The OSI model is useful but its protocols are not popular (although DECNET is based on OSI) The TCP/IP model was never used but its protocols are ubiquitous A hybrid reference model used by our textbook and others is shown below. 5Application layer 4Transport layer 3Network layer 2Data link layer 1Physical layer 17

Standards (1) ITU – International Telecommunication Union ISO – International Standards Organization –ANSI – American National Standards Institute is the US member, but it is not government sponsored IEEE – Institute of Electrical and Electronic Engineers –Lots of standards at networking layer 2 (and 1) – some now available for free due to sponsorship of vendors IETF – Internet Engineering Task Force –Lots of Request For Comments (RFCs) and standards at higher layers 18

Standards (2) –Free download of IEEE 802 standards –Well-written and the final word on most things layer 2 – but they can be difficult to digest –Searchable database of Requests For Comments (RFCs) –Building networks requires reading RFCs and understanding how to determine their status in the standardization process –The quality is variable – but the important standards have been revised several times and are generally readable –Briefly examine the RFCs published on April 1 for some networking humor 19