CS457/557 - Computer Networks: Chapter 9 - Connecting LANs: Inter-Networking

Objectives

Understand the rationale, methodology, technology, and business analysis for standalone PCs accessing a LAN remotely for either use of LAN services or LAN management purposes.
Understand the rationale, methodology, technology, and business analysis for standalone PCs accessing a mainframe remotely.
Understand the rationale, methodology, technology, and business analysis for connecting two or more local area networks.
Understand the additional consequences, advantages, and limitations involved when connecting LANs of differing topologies, network operating systems, media, or protocols.
Understand how micro-mainframe PC connectivity solutions may vary in different technological environments
Understand major characteristics of IBM SNA and the direction of the architecture in terms of integration with the LAN environment.
Understand the current state of internetworking technology as well as future trends in internetworking.
Understand the importance of the OSI model to effective internetworking analysis and design.

Introduction

internetworking - transmitting data into and out of a LAN

Dialing into and out of a LAN
LAN-to-LAN connections
Micro-to-mainframe / minicomputer connectivity

Internetworking Category 1: Dialing Into and Out of the LAN

Business Uses of Remote Computing

telecommuting - working and accessing the LAN from home
mobile computing
technical support - dial-in to client systems

Needs Analysis

Exchange e-mail
Upload/download files
Run interactive applications remotely
Utilize LAN attached resources

Physical Topology

Modem connection of a LAN attached PC
Communications server
LAN modem

Logical Topology

Remote Operation Mode: Where does the Processing Occur?

Remote client operation mode
Modem remote control operation mode

Technology

Hardware	Software
Modems Communications servers LAN modems Redirector hardware	Remote control software Comm server software Redirector software

ACCESS POINT 1: REMOTE PC TO LOCAL LAN-ATTACHED PC

remote control software(RAS)
both guest and host computers must be running the same software
other types of software: PcAnywhere, Carbon Copy

ACCESS POINT 2: COMMUNICATIONS SERVERS

remote control software is loaded on to the LAN-attached access server
may have multiple users and multiple protocols

ACCESS POINT 3: LAN MODEM OR DIAL-IN SERVER

modem attaches directly to the network

Dialing Out from the LAN

requires a modem server and a redirector to route traffic via network card to modem

Internetworking Category 2: LAN-to-LAN Connections

Overall Internetworking Design Strategies

segmentation - fewer workstations per segment -> less contentation for the shared bandwidth
microsegmentation (switch) - one workstation per LAN segment
server isolation
hierarchical networking

LANs can differ in

Network architecture
Media
NOS
OS

InterLAN devices:

Repeaters
Bridges
Switches
Routers
Brouters
Gateways

Bridging

80/20 rule: 80% of all LAN traffic should stay local with 20% being forwarded across the bridge

Addressing

bridge receives every frame broadcast on each LAN it is connected to
bridge only processes data-link layer (MAC) addresses and only allows data frames with "nonlocal" destination addresses to cross the bridge
bridge adds source addresses to the known local nodes table

Advantages

bridges are easy to install and configure, providing quick, cost-effective relief for overburdened network segments.
bridges can extend network segment lengths by repeating, retiming and regenerating signals
bridges can connect different network architectures and different network media

Limitations

only know to forward all packets that are addressed to nonlocal nodes
improperly addressed frames can be infinitely perpetuated or flooded onto all bridged LANs (broadcast storm)

Routing

routers only reads data packets addressed to it, confirms the existence of the destination address, and chooses the best path for the data packet to reach its destination

Addressing

routers use addresses from the network layer
router has its own MAC address
router consults its routing table to determine the best path on which to forward the data packet, looking at
1. network number of the destination network
2. MAC address of the next router along the path to this target network
3. port on this router out of which the frame should be sent
4. number of hops to the destination network
5. age of this entry to avoid routing based on outdated information
uses forward-if-proven-remote logic

Advantages

Creates firewalls to protect connected LANs.
Filters unwanted broadcast packets from the internetwork.
Discriminates and prioritizes rpocessing of packets according to the network layer protocol.
Provides secruity by filtering packetrs by either data-link or network layer addresses.
Provides transparent interconnection between LANs.

Limitations

- more complicated to configure and manage

Switching

used in microsegmentation by creating point-to-point connections using ASIC (application-specific integrated circuit) chips

Addressing

uses MAC addresses to build a switched connection

Advantages

produces dramatic increases in bandwidth; used in virtual LANs

Limitations

more complicated to manage; more expensive than simple bridging

The OSI Model and Internetworking Devices

Repeaters: Layer 1 -- The Physical Layer

Repeat signal by regenerating, retiming, and amplifying the signal
Pass all signals between attached segments
notread destination addresses of data packets
allow for the connection of different types of media
extend overall LAN distance effectively by repeating signals between LAN segments

Bridges: Layer 2 -- The Data Link Layer

bridges are more discriminating (bridge reads the destination addressof each data frame and decides whether the destination is local or remote and only allows packets with remote addresses to "cross the bridge"

bridges also check the source address of each frame and adds it to a table of known local addresses

forward-if-not-local

MAC Sublayer Protocol: Types of Bridges

Transparent bridges (both LANs must be the same type)
Translating bridges (multiprotocol bridges contain a format converter)
Encapsulation bridges (bridges Ethernet & FDDI)
Source routing bridges (source routing Token Ring to Ethernet)

Source Routing - data contains path instructions for bridge

Data Storms - can result in a looping topology (requires IEEE 802.1 -spanning tree algorithm)

Bridge performance can be measuered by the filtering rate (packets/sec) and the forwarding rate (packets/sec)

Wireless Bridges

Preamble Address (64 bit)	Destination Address(48 bit)	Source Address(48 bit)	Type(16 bit)	Data(46-1500 bytes)	32 bit CRC
used for timing / synchronization	bridges uses to determine which side of the bridge	bridge uses to build "known local nodes"	identifies type of network layer protocol	data packets	error detection

Routers: The Network Layer Processors

(Network layer establishes, maintains, and terminates the link between two points on the network

Functionality

router only examines packets addressed to it
router must first confirm the existence of the destination and the available network paths to get there
router chooses the best path
router has its own destination address
router maintains a routing table used to determine the best path
router is a forward-if-proven-remote

Data link header

Network Layer header

Source Address

Destination Address

Data field

Data link trailer

Determining the Best Path

number of intermediate hops
speed/condition of the communications circuits
NOS protocol

Network Layer Protocol	NOS or Protocol Stack Name
IPX	Netware
IP	TCP/IP
VIP	Vines
AFP	Appletalk
XNS	3Com
OSI	Open Systems

Data-link control protocols processed by some routers:

LAT	DecNet
SNA/SDLC	IBM SNA
NetBEUI	Windows-based LANs

Routing Protocols

Routing Protocol Acronym	Routing Protocol Name	Associated Protocol Suites
RIP	Routing Information Protocol	XNS, IPX, TCP/IP
OSPF	Open Shortest Path First	TCP/IP
IS-IS	Intermediate System to Intermediate System	DECNET, OSI
RTMP	Routing Table Maintenance Protocol	Appletalk
PPP	Point-to-Point Protocol	Internet standard that replaces SLIP
RTP	Router Table Protocol	Vines

Internetworking Category 3: LAN-to-Mainframe/Minicomputer Connectivity

gateway - hardware device used to connect different types of networks

Micro-Mainframe Hierarchical Network

Classic SNA Architecture

SNA - systems network architecture
Front-end processor (FEP) (IBM3745) - compuer that offloads the communications processing from the mainframe; also known as a communications controller
Cluster Controller (IBM 3174, 3274) - device that allows connection of 3270 terminals and LANs
PCs as 3270 Terminals requires a 3270 protocol conversion controller (can be emulated with software & a modem)
3270s are connected using RG-62 coax cable
Coax muxes (multiplexer) is required to connect large numbers of terminals to the cluster controller
Balun - used to convert BNC connector to UTP RJ-45 connector

SNA Architecture

Layer Number

Layer Name

Function

Transaction Services

provides network management services. controls document exchange

Presentation Services

Formats data, data compression & data transformation

Data Flow Control

synchronous exchange of data supports communications session for end-user applications. (assures reliability)

Transmission Control

Matches the data exchange rate, establishes, maintains, and terminates sessions. Guarantees reliable delivery of data between end-points. Error control, flow control

Path Control

	Overall layer: creates the link between two end-points for the transmission control protocols to manage
Virtual Route Control	Create virual route, manages end-to-end flow control
Explicit Route Control	Determines actual end-to-end route for link between end nodes via intermediate nodes
Transmission Group Control	manages to use multiple lines to assure reliability and load balancing

Data Link Control

Establishes, maintains, and terminates data transmission between two adjacentnodes. uses SDLC

Physical Control

provides physical connections specifications from nodes to shared media

SDLC (synchronous data link control) - nonroutable protocol (has no network layer address)

Three SNA/LAN Integration Challenges

reduce unnecessary traffic
find way to prioritize SNA traffice to avoid time-outs
find way to allow internetwork protocols to transport, or route, SDLC frames

Four Possible SNA/LAN Integration Solutions

Attach token ring LAN to the Cluster controller (only handles #3)
encapsulation (passthrough, tunneling) - stuff each SDLC frame into an IP "envelope"
SDLC conversion - uses a SDLC converter to change SDLC frames into token ring frames
use protocol independent routers - adds a MAC layer address to each frame received

APPN (advanced peer-to-peer network)

allows all attached devices to talk directly with each other without going through the mainframe

New SNA

Applications	Conversion (CPI-C) Remote Procedure Call (RPC) Message Queueing (MQI) Standard applications Distributed services
Multivendor application support	APPC OSI/TP OSF DCE FTAM X.400, TELNET, FTP Data directory, security, recovery time
Common Transport Semantics
Multiprotocol transport networking	SNA, APPN TCP/IP OSI NetBIOS, IPX
Network Architecture	LANs frame relay X.25 cell packet
Media	physical

DECNET

based on Ethernet network architecture
NOS - Pathworks (licensed version of MS's LAN Manager)
uses terminal servers
terminals use transport layer protocol (LAT - local area transport) to interface with data link layer
LAT traffic must be bridged

Internetworking Category 4: Integration of LANs and the UNIX Environment

TCP/IP - Transmission Control Protocol / Internet Protocol

Layer	OSI	INTERNET	Data Format	Protocols
7	Application	Application	Messages / Streams	TELNET FTP TFTP SMTP SNMP CMOT MIB
6	Presentation	"	"	"
5	Session	"	"	"
4	Transport	Transport or Host-Host	Transport Protocol Packets	TCP, UDP
3	Network	Internet	IP Datagrams	IP
2	Data Link	Network Access	Frames
1	Physical	"	"

Multiple Protocol Stacks - loading multiple network & transport layer protocols in a single client PC
requirres multiple protocol device drivers (NDIS (network driver interface specification) or ODI (open data-link interface))

NOS	Transport Protocol
UNIX	TCP/IP or UDP/IP
MS Windows	NETBEUI
Netware	SPX/IPX
DECNET	LAT
VINES	VIPC/VIP
DOS based LANs	NETBIOS
APPLETALK	ATP

TCP/IP Gateway - place multiprotocol software on the server
ex. Netware NFS

Important Features and Options for Multiprotocol Software

Which Protocols Need Supporting?
What is the Client Operating Environment?
What NICs and Device Drivers are available?
Ease of Use/Transparency?
Cross-Platform E-mail Support?
Terminal Emulation?

Internetworking Category 5: Macintosh Integration

Needs:

file sharing
printer sharing
file transfer
E-mail

Compatability Issues

data formatting & stoage
applications software
Internetworking

Network Architecture

Localtalk - 230.6 Kbps using DIN plugs [used mainly for peer-to-peer networks]
AppleTalk - suite of protocols compliant with OSI Model
AppleTalk can run over Ethernet or Token ring

7-Application

AppleTalk Filing protocol(AFP)

Postscript

6-Presentation

AppleTalk Filing protocol(AFP)

Postscript

5-Session

AppleTalk Data Stream protocol(ADSP)

Zone Information Protocol (ZIP)

Appletalk Session Protocol (ASP)

Printer Access Protocol (PAP)

4-Transport

Routing table Maintenance Protocol (RTMP)

AppleTalk Echo Protocol (AEP)

AppleTalk Transaction Protocol (ATP)

Name Binding Protocol (NBP)

3-Network

Datagram Delivery Protocol (DDP)

2-DataLink

TokenTalk Link Access Protocol (TLAP)

EtherTalk Link Access Protocol (ELAP)

LocalTalk Link Access Protocol (LLAP)

1-Physical

token ring hardware

ethernet hardware

Localtalk hardware

Router supports Appletalk Protocols while Gateways translate AppleTalk protocols into SNA / DECNET

10BASET Hubs support Appletalk over Localtalk and Ethernet

Netware, Vines & Windows include features for Macintosh integration

Internetworking in Perspective

Internetwork Design
Business Motivation
Application and Data Layers: Deliver Business Interoperability Requirements
1. Where is the data?
2. Where is the user of the data?
3. In what format is the required data?
4. How much data needs to be transported?
The Network Layer
The Technology Layer

Slides

CS457/557 - Computer Networks: Chapter 9 - Connecting LANs: Inter-Networking

Objectives

Introduction

Internetworking Category 1: Dialing Into and Out of the LAN

Business Uses of Remote Computing

Needs Analysis

Physical Topology

Logical Topology

Technology

ACCESS POINT 1: REMOTE PC TO LOCAL LAN-ATTACHED PC

ACCESS POINT 2: COMMUNICATIONS SERVERS

ACCESS POINT 3: LAN MODEM OR DIAL-IN SERVER

Dialing Out from the LAN

Internetworking Category 2: LAN-to-LAN Connections

Overall Internetworking Design Strategies

Bridging

Addressing

Advantages

Limitations

Routing

Addressing

Advantages

Limitations

Switching

Addressing

Advantages

Limitations

The OSI Model and Internetworking Devices

Repeaters: Layer 1 -- The Physical Layer

Bridges: Layer 2 -- The Data Link Layer

MAC Sublayer Protocol: Types of Bridges

Source Routing - data contains path instructions for bridge

Data Storms - can result in a looping topology (requires IEEE 802.1 -spanning tree algorithm)

Wireless Bridges

Routers: The Network Layer Processors

Functionality

Determining the Best Path

Routing Protocols

Internetworking Category 3: LAN-to-Mainframe/Minicomputer Connectivity

Micro-Mainframe Hierarchical Network

Classic SNA Architecture

SNA Architecture

Three SNA/LAN Integration Challenges

Four Possible SNA/LAN Integration Solutions

APPN (advanced peer-to-peer network)

New SNA

DECNET

Internetworking Category 4: Integration of LANs and the UNIX Environment

Important Features and Options for Multiprotocol Software

Internetworking Category 5: Macintosh Integration

Compatability Issues

Network Architecture

10BASET Hubs support Appletalk over Localtalk and Ethernet

Netware, Vines & Windows include features for Macintosh integration

Internetworking in Perspective

Review Questions(due Nov. 10): 7, 34