Computer Networks Chapter 6 Network Interface Service Models

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Computer Networks Chapter 6 – Network Interface: Service Models CEN 5501 C - Computer

Computer Networks Chapter 6 – Network Interface: Service Models CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 1

Network Layer • What is Network Layer? – Transfer data between indirectly connected nodes

Network Layer • What is Network Layer? – Transfer data between indirectly connected nodes (perhaps on different LANs) – Layer 3 – routing • Service Models – Reliability (datagram or best-effort) – Connection orientation (VC or DG) CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 2

Reliability • Ordering – Delivered in same order sent or not • Losses –

Reliability • Ordering – Delivered in same order sent or not • Losses – Omissions allowed or not • Duplicates – Duplicates removed or not CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 3

Connection Orientation • Virtual Circuit (VC) – VC must first be set up (path,

Connection Orientation • Virtual Circuit (VC) – VC must first be set up (path, identifier) – Once set up, packets flow over VC path – VC must be torn down (release state info) – Small VCID compared to NSAP pair • Datagram (DG) – Datagrams are sent independently – DGs from S to D may take different route – Each DG must have all relevant info in it CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 4

Performance Guarantees • End node expression of requirements – Capacity – data rate (avg,

Performance Guarantees • End node expression of requirements – Capacity – data rate (avg, max, etc. ) – CBR, VBR, ABR – Latency, jitter – Packet loss tolerance – Priority, TOS • Network restrictions – Call admission control (CAC) & reservations – Traffic policing, marking CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 5

Service Model Combinations Datagram Connectionless Connection. Oriented IP, IPX, CLNP, DECnet, Appletalk ATM Reliable

Service Model Combinations Datagram Connectionless Connection. Oriented IP, IPX, CLNP, DECnet, Appletalk ATM Reliable Not possible X. 25, CONP CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 6

Connection-Oriented Pros • Faster Routers possible (smaller tables) • If service is guaranteed, there

Connection-Oriented Pros • Faster Routers possible (smaller tables) • If service is guaranteed, there needs to be CAC (continue service to existing calls) • Uniform service easier for transport layer • Interfacing easier (layer 4 less complex) • Transport breaks in DG network if network path is disrupted anyway CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 7

Connectionless Pros • Full transport layer needed anyway • Simpler interface, N/W layer code

Connectionless Pros • Full transport layer needed anyway • Simpler interface, N/W layer code • Service may be overkill, depending on application • Network traffic is bursty – reservations are wasteful • Democratic degradation • Stateless CEN 5501 C - Computer Networks - Spring 2007 - UF/CISE - Newman 8