Services are performed by protocol(s) in layer N (server layer) for layer N+1 (client layer) across an interface. Protocols are used to implement services . Protocols can change without affecting service. A set of layers that defines a network is called a protocol stack (aka “architectures”, “suite”, or “models”) 34
TDC-463 Protocols Clients and servers must follow a set of rules called a protocol which determines Packet format Permissible requests and responses Format of header information and data Packet ordering and timing Protocol standards are documents that define protocols. Internet protocol standards are called Request for Comments (RFCs). 35
TDC-463 OSI Stack 36 Must know layer names and general services
TDC-463 Layer 1 – Physical layer Physical layer coordinates functions to transport traffic over physical medium Physical layer protocol specifies the following services to the data link client Physical characteristics of interfaces and media Supported transmission line rate (or channel bandwidth) Bit encoding method (e.g. NRZ, NR, QAM, PSK, etc) Block encoding methods (e.g. 8b10b) Bit, timeslot, frame synchronization Multiplexing (e.g. TDM, FDM, WDM) Line protection Operations, Administration, and Maintenance (OAM) for the physical layer 37
TDC-463 Layer 2 - Data Link Layer Key Services A Data Link layer protocol may support some or all of the following services to the network layer client 1. Framing 2. Client layer encapsulation 3. Physical addressing 4. Flow control 5. Error detection 6. Error control 7. Link management 8. Congestion notification 9. Switching (virtual circuit or datagram) 10.Media access control (for broadcast networks) 11.Traffic management (CoS, QoS, Policing, Shaping) Page 38
TDC-463 Layer 3 - Network Layer The network layer is responsible for the delivery of individual packets from the source host to the destination host. Network layer is responsible for the following services: Logical addressing Packet routing from source to destination Examples of network layer protocols? IP (Internet Protocol), Appletalk, IS-IS 39
TDC-463 Network Layer Source-to-destination delivery 40
TDC-463 Network and Underlying Layers Client-Server Abstraction Client Server layer abstraction example 41 Network layer Data Link layer Physical layer Router R1 Router R2 Router R3 Ethernet SW1 Ethernet SW2 Ethernet SW3 Ethernet SW4 SONET/WD network SONET/WD M Transport network Ethernet 100Base-FX
TDC-463 Layer 4 – Transport Layer The transport layer is responsible for the delivery of a message from one process to another process Transport layer is responsible for the following services: Service Point (aka process) addressing Service “Multiplexing” Connection control between source and destination Flow control between source and destination Error control between source and destination Segmentation and reassembly Network congestion control Examples of transport layer protocols Transmission Control Protocol (TCP), UDP 42
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- Fall '09