CE 536 - Networking and Microcomputer Systems
Day 7: Network Architectures Models, Network Protocols, and Internetworking
Models of Network Architectures
Proprietary - different vendors, different architectures
IBM - SNA/SDLC - Systems Network Architecture/Synchronous Data Line Control
Digital Equipment Corporation - DECnet
Open Systems - architecture adheres to published standards with defined interfaces
ISO/OSI - Open Systems Interconnection Reference Model
TCP/IP - Transmission Control Protocol/Internet Protocol
Protocol - standard - a formal set of rules setting the format and control of data exchange
The OSI Reference Model
Seven Layer Network Architecture
Connectivity is provided in layers 1-3 (communications subnet)
Interoperability is provided in layers 5-7 (host process)
Regardless of equipment vendor
Transport Layer 4 acts as a buffer between connectivity and interoperability
Peer protocols used between corresponding layers on communicating systems
Each layer communicates or passes data to adjacent layers
Application Layer - provides end-user services - user applications interact with this layer and with each other through this layer
Presentation Layer - establishes a common syntax in which data is exchanged between the two hosts
Session Layer - establishes and terminates process-to-process communication sessions
synchronizes flow of data
can have multiple session connections
Transport Layer - lets processes at each end transmit and receive data reliably (i.e., end-to-end transparency)
Segments long messages into smaller packets prior to transmission and assures the reassembly of those packets at the receiving end
Sequentially handles multiple sessions
Allows each protocol to use its own Service Access Point (also referred to as a Port or Socket)
Network Layer - establishes a path (route) for the data packets along the communication subnet from the source node to the destination node
Routing is not standard on LANs; use standard protocols
RIP - Routing Information Protocol - assumes that the path with the smallest hop count (number of routers through which a packet must pass) will be the shortest and least expensive (STD 34)
OSPF - Open Shortest Path First - least-cost routing - allows load balancing
IP - Internet Protocol
RIP-IP
Data Link Layer - maintains a reliable communication link between adjacent nodes
Media Access Control
Logical Link Control
Physical Layer - handles the electrical and mechanical interface and transmission of signals from one system to another
Logical Link Control
Defined by IEEE 802.2
Common to multiple access methods
IEEE 802.3 Ethernet
IEEE 802.5 Token-passing
FDDI
Passes outbound application data to Media Access Control (i.e., places data on the LAN)
Sends the received data to the correct protocol stack (i.e., delivers data to its correct destination)
Messages pass from the LAN to the LLC sublayer through a Service Access Point (also called a Port or Socket)
Each protocol has its own Service Access Point
Provides a standard software interface to higher level protocols
TCP/IP - Transmission Control Protocol/Internet Protocol
IPX - Novell's Internetwork Packet Exchange
Insulates higher layers from any network tasks or problems
Different types of Service Connections
Connectionless - most commonly used by LANs (TCP/IP, IPX)
No pre-existing logical connection is needed
Each data unit is sent independently
Flow control does not exist (at the LLC level)
Error detection is implemented
Error recovery is not (at the LLC level)
Connection-oriented (IBM's SNA/SDLC)
Error detection, retransmission, and flow control
A logical connection must be built before data can be exchanged
Data can only be sent to one address at a time
TCP/IP - Transmission Control Protocol/Internet Protocol
Four Layer Network Architecture
Developed by the Department of Defense in the 1970's (ARPA - Advanced Research Projects Agency)
Protocols used on the Internet
World-wide collection of interconnected networks
Network Access and Internet layers communicate with routers
Host to Host layer for reliable communications
Process layer is for actual communications
Internet information is published in documents known as Request for Comments or RFC
Comparing the OSI and TCP/IP Models
Process (Application) Layer - protocols for actual communications
File Transfer - FTP or File Transfer Protocol (STD 9)
Terminal Emulation - TELNET Protocol (STD 8)
Electronic Mail - SMTP or Simple Mail Transfer Protocol (STD 10)
Network Management - SNMP or Simple Network Management Protocol (STD 15)
Host to Host (Transport) Layer - assures reliable communication between hosts since neither the Network Access or Internet protocols are of an end-to-end nature - makes sure data is accurate, in sequence, complete, and free of duplication
TCP or Transmission Control Protocol (STD 7)
Data passed down from higher levels is broken into pieces and given a header with a sequence number
This segment is then passed to the other system which re-assembles the data and verifies the data
Internet (Network) Layer - handles the routing of data
IP or Internet Protocol (STD 5)
Internet addresses are of the form
147.106.xxx.xxx (Allentown College)
147.106.1.5 (Allentown College's WWW Server)
128.180.xxx.xxx (Lehigh University)
Network Access Layer - controls access to the LAN
Ethernet
Token Ring
Internetworking
Internetworking Devices
Repeaters
Bridges
Routing Bridges
Routers
Gateways
Internetworking Links
Repeaters - signal regenerators that extend cable distances
Work at the Physical Level
Ethernet (IEEE 802.3) can have no more than 4 interrepeater links (i.e., links between any two stations)
Token Ring (IEEE 802.5) cards repeat the signal inherently (i.e., they are repeaters)
Bridges - connect similar LAN segments
Work at the Data Link Layer
Operate in simple, single-site internetworks
Not appropriate in larger environments
Ethernet (IEEE 802.3) Bridges
Need the addresses of all stations on each network
Tables entered manually
Learn Mode - watches the traffic on the LAN
Work as address filters - checks destination address to see if it is on the same LAN; if not, passes packet to another port on the bridge (to another LAN segment)
Store and Forward Devices - look like any other station on the network
Transparent - do nothing but filter and forward packets
Token Ring (IEEE 802.5) Bridges
Source Routing - checks each frame's source address field for routing indicator bit followed by routing information
Routing Bridges - combine the functions of bridging and routing in a single box (could be a high-end hub)
Routers - used to connect dissimilar types of LANs which use the same communications architecture and protocols
Centerpiece of interconnected LANs
Work at the Network Layer
Checks the network layer destination address in each packet
Checks routing table to determine whether to send it off
Protocol specific - packets are not forwarded; only the data within the packets is forwarded
Some Routers handle multiple protocols
TCP/IP - Transmission Control Protocol/Internet Protocol
IPX/SPX -Internetwork Packet Exchange/Sequenced Packet Exchange
Determines best path (route) for information flow
Routing Protocols
RIP - Routing Information Protocol
OSPF - Open Shortest Path First
IP - Internet Protocol
RIP-IPX - Routing Information Protocol/Internetwork Packet Exchange
Data Link Protocols - tie together bridges and routers
PPP - Point-to-Point Protocol
Connects multiprotocol routers
Encapsulates data frames
TCP/IP
OSI
IPX
Workhorse for remote users
IPX - Internetwork Packet Exchange
Interoperability - routers from different vendors can work together if both use the same routing protocols and data link protocols
Gateways - match totally dissimilar networks (i.e., those with totally different protocol stacks)
The most sophisticated internetworking tool
Used to connect networks which utilize completely different protocol stacks (e.g., TCP/IP to SNA)
Work at the Application Layer
For each frame, removes all header information from each layer of the first protocol leaving just raw data at the Application Layer; then, rebuilds the frame with headers from the other protocol
Internetwork Links - leased lines
Analog Service - via modem
Download speeds to 56kbit/second
Uploads at up to 33.6k
Fractional T-1 Service - speeds from 56 kbit/second up to 1.344 Mbit/second in 56 kbit/second increments
ISDN - Integrated Services Digital Network - 128 kbit/second
Full T-1 Service - 1.5 Mbit/second (actually 1.544)
T-3 Service - 45 Mbit/second (actually 44.736)
SMDS - Switched Multimegabit Data Service - speeds from 1.5 Mbit/second up to 45 Mbit/second
Migration path to 155 Mbit/second and ATM (Asynchronous Transfer Mode)
SONET - Synchronous Optical Network - fiber-optic network operating at speeds up to 2.5 Gbit/second
Assignment for Class 8 ...
Read and be prepared to discuss:
Chapter 11 skim