Networking Protocols John R. Durrett ISQS 6343 #1

Introduction Protocol –set of rules –software –facilitate inter-computer communication OSI Seven Layer Model –model not reality –facilitate understanding –representative of different aspects of inter-networking –no direct correspondence with commercial implementations

The OSI Model 7 - Application 6 - Presentation 5 - Session 4 - Transport 3 - Network 2 - Data Link 1 - Physical

Physical Layer Bits over media electrical signals computers, NIC, “wire”, etc. “black box” interface assumptions with upper layers

Data-Link Assumes physical layer frames - groups of bits ensures only delivery not accuracy Examples: –Token Ring –Ethernet IEEE model –LLC (logical link control) –MAC (Media Access Control)

Network Assumes data-link layer packets routing of packets –therefore addresses necessary network optimization congestion handling No error checking

Transport Relies on network layer Frequently combined with network layer in protocols Messages Error checking –UDP & TCP NetBEUI, TCP/IP, IPX/SPX

Session Assumes Transport layer Sessions between computers based on names of other computers NetBIOS - Windows Sockets - TCP/IP

Presentation Assumes session layer based on services provided –encryption, compression, translation

Application Assumes session exists RPC –procedural –distributed –locations required –relatively static pipes FTP protocol

Windows Networking Transport Device Interface (TDI) Network Device Interface Specification (NDIS) Allows support of multiple transport protocols interface between transport & session layers

NetBEUI Compact LAN based not routable ubiquitous limits size limits choice of clients/servers

TCP/IP UBIQUITIOUS performance & reliability based standards arrived before implementations IETF RFCs flexibility == difficult to manage IPs

Dotted quad – Classes –C, B, A –subnets Limits of current IPs –IPv6 or IPng Domain Names –reversed version of IPs –DNS

Protocol choice Clients –Windows NT –Windows 95… –DOS –OS/2 –Un*x –Macs Network Structure –Similar servers –LCD

Interoperability Hub - very simple relay Switch - virtual circuits Router - makes pathway choice based on IPs Bridge - passes data unchanged Gateway - translation Proxy Server - security