1. Review of WAN Protocol Basics

2. Lesson 1 - Agenda Data Communications Fundamentals
Introduction to Network Protocols
Physical Interfaces
Bit Oriented Protocols
Basic Analysis with the Internet Advisor

3. Lesson 1 - Objectives
On Completion of this lesson you will be able to:
List and explain data communications fundamentals as they apply to wide area networks.
Define the term network protocol.
Explain the OSI seven-layer protocol model, peer-to-peer communications and protocol encapsulation.
Explain bit oriented protocol and give examples.
Identify and describe the different interfaces and components of the Internet Advisor.
Demonstrate how to connect the Internet Advisor to a network under test.

4. Data Communications Fundamentals
Communications Modes
DTE/DCE Terminology
Wide Area Analog/Digital Transmission
Multiplexing
Private Leased Lines
Public Switched Data Networks

5. Communication Mode Simplex Half Duplex Full Duplex
one direction always
alternate one direction
and then the other
both directions always
Communication from point to point can be either simplex, half duplex or full duplex:
simplex: one direction only, all the time. Example: data connections from an airline scheduling computer to each of the TV monitors located throughout an airport.
half duplex: one direction at a time. Example: a telephone conversation between two polite people, each person takes his turn to talk and then listen, but both do not talk at the same time.
full duplex: both directions simultaneously. Example: high speed WAN connections between local area network routers provide for simultaneous communication in both directions.
Half Duplex
Full Duplex

6. Data Circuit-Terminating
DTE/DCE Terminology
Data Circuit-Terminating
Equipment (DCE)
Data Terminal
Equipment (DTE)
Line (DCE)
EQPT (DTE)
Full Duplex
Full duplex WAN connections involve two separate (though related) data channels. The following labels are used to distinguish between these two separate data streams at the user-to-network interface:
Line or DCE: Data which is transmitted from the wide area network to the customer site is labeled “Line” or “DCE” data. DCE stands for Data Circuit-terminating Equipment.
EQPT or DTE: Data which is transmitted from the customer site to the wide area network is labeled “EQPT” [Equipment] or “DTE” [Data Terminal Equipment].
When monitoring WAN links within the wide area network itself, or in cases where data terminal equipment is connected together directly with no intervening WAN, it becomes unclear which direction is DTE and which is DCE. While “modem eliminator” or data swapping cables can be used to physically interconnect nodes in such configurations, from a protocol perspective one station must function as a logical DCE and the other as a logical DTE in order to communicate.
Customer Premise
Wide Area Network

7. Wide Area Analog/Digital Transmission
analog transmission
typically asynchronous
typically low speed (<=56kbps)
modem
modem
Wide area networks themselves employ either an analog or a digital transmission process.
Analog transmission was first used as a method for interconnecting computers on existing telephone links using modems to encode the digital bit streams on analog transmission lines. Analog transmission continues to be widely used for dial-up connections at low speed [<= 56kbps] using asynchronous data transmission (i.e. no clock provided).
Digital transmission allows the two end nodes to communicate completely digitally from end to end. Signal conditioning devices called CSU and DSU are used to translate between physical protocols used on the customer premise (like RS-232C/V.24 or V.35) and physical protocols used by the network service provider:
CSU (Channel Service Unit): a device which terminates the common carrier’s digital circuit on the customer premise
DSU (Digital Service Unit): a device connected between the user’s DTE and the common carrier’s digital circuits, which are typically terminated by a channel service unit.
Very often the CSU and DSU functions are combined into one physical device. Combined DSU/CSU devices can be built on cards and plugged into the chassis of other data comm equipment.
digital transmission
typically synchronous
typically high speed (>=56kbps)
DSU/CSU
DSU/CSU

8. Multiplexing
Transmission of more than one signal on a single communications line
Increases the number of communications sessions that can be maintained at one time
Various types
Time Division Multiplexing
Statistical Multiplexing
Frequency Division Multiplexing
Due to the ever growing demand for telecommunications services, there is a constant need for increasing the amount of information that can be transmitted across a network line. The growing demand for telecommunications speed (bandwidth) is a force that has driven the expansion of telecommunications technology from its first days to today’s internet revolution. Multiplexing is an important means of increasing bandwidth.
Multiplexing is a general term that describes the transmission of more than one information-carrying signal over the same physical conductor. Various types of multiplexing exist, but they all allow multiple signals to be carried on the same physical conductor. Time division multiplexing is the most common type of multiplexing. Early techniques for multiplexing voice channels used frequency division multiplexing.

9. Time Division MultiplexingA B C D

10. Private Leased Lines Point to Point Point to Multipoint Fully Meshed
Private wide area networks can be implemented by leasing individual circuits from the network provider.
While this method works well for a small number of connected sites, when that number grows then the number of private leased lines needed to interconnect every site directly with every other site grows exponentially. The growth formula is n(n-1) where ‘n’ is the number of nodes
Point to Multipoint
Fully Meshed

11. Public Switched Data Networks
X.25
Frame Relay
ATM
SMDS
ISDN
Public switched data networks provide the interconnections as needed between user end nodes, which are also referred to as network subscribers.
There are several different public switched data networks available today, the most common of which are listed above.

12. Summary of Data Communications Fundamentals
Binary communications
Most often serial in networks
Full duplex communications occurs in both directions
DTE on customer site while DCE on WAN
Multiplexing allows more than one communications channel on the same line
Time division multiplexing
WAN cover large distances
Computers function through the use of binary communications which may be transmitted as a serial stream of bits on a single conductor or as a parallel stream of bits transmitted simultaneously over several different conductors.
The signals transmitted over networks are usually serial and can be transmitted and/or received in several communications modes. The simplex communications mode allows communication in one direction only over a single conductor. The half duplex communications mode allows communication in one direction only over a single conductor -- but only if each end of the network takes turns transmitting their data. The full duplex communications mode allows simultaneous communication in both directions using a pair of conductors.
Data Terminal Equipment (DTE) is found at the customer site while Data Communications Terminating Equipment (DCE) is often a part of the telecommunications provider’s network such as a Wide Area Network which traverses distances more than 8 km. Individual communications sessions are often multiplexed over these lines, allowing more than one session to exist on a single conductor.

13. Introduction to Network Protocols
Definition
Protocol Functions
ISO Reference Model
Peer to Peer Communications
Data Encapsulation from Higher Layers
The last section described the basic concepts of data communications over networks. Because different computers use different operating systems, languages, and infrastructures, network protocols were developed to allow these diverse systems to communicate with one another. This section discusses these protocols.

14. Definition of Communications Protocol
Set of communications rules
Defines addressing
Defines syntax and semantics
Allows communications between disparate systems
Communication rules
Connection control
There are many different types of computers that need to connect to one another and transmit information on networks. Because these computers often operate in fundamentally different ways due to different types of construction and operating systems, network protocols that allow common function, at least at the physical media layer, are employed to allow communication.
This section will define protocols and how they function in a layered fashion to create common communications processes from widely differing equipment.
A protocol is a set of rules that allows computer systems to communicate with each other using the same physical media. Protocols exist in coordinated layered architectures -- sometimes called “protocol stacks” -- that allow a common transmission at the lowest layer (the physical layer) to be transparently communicated to differing types of computer equipment. Once at the target device, information encoded in the bit stream allows the computer to pass data up the stack. The ISO (International Standards Organization) reference model is the standard derived from this layered approach to networking.

15. Radio Communications Protocol
HQ, One Adam 12.
I’m going at
DD for a cuppa java.
Over.
One Adam 12, HQ.
What’s your 10-22?
Over.
This radio communications protocol example shows protocol addressing (One Adam 12, HQ), message content (What is your 10-22?) and flow control (Over).
It also shows that arbitrary groups of numbers can have specific meanings (10-22 == physical location).

16. ISO Reference Model Provides access to the network for the end user or
Application
Provides access to the network for the end user or
software application.
Responsible for format and code conversion. Includes
formatting the syntax of data.
Presentation
Responsible for establishing, maintaining and terminating
logical connections.
Session
Responsible for moving data between nodes; providing
reliable or unreliable data transfer. Includes packet
fragmentation, error detection, and retransmission.
Transport
The ISO protocol reference model defines seven separate protocol layers for computer-to-computer communications:
physical - the transmission of bits. Includes the mechanical, electrical and functional physical interface.
data link - controls the flow of data cross a physical link.
network - end-to-end connectivity through the network. Includes routing and flow control.
transport - moves data between nodes, providing reliable or unreliable data transfer. Includes packet fragmentation or segmentation, error detection, and retransmission.
session - establishes, maintains and terminates logical connections.
presentation - formatting and conversion of code. Includes formatting the syntax of data.
application - access to the network for the end user or software application.
Responsible for end-to-end connectivity through the
network. Includes routing and flow control.
Network
Responsible for ensuring error-free, reliable flow of data
acrossa physical link.
Data Link
Responsible for the transmission of bits. Includes the
mechanical, electrical and functional physical interface.
Physical

17. Protocol Functions Addressing Connection control
Ordered delivery and sequencing
Flow control
Error control
Segmentation and reassembly
Encapsulation (control plus data)
Multiplexing
Message
Other protocols
All complete protocol stacks must in one way or another perform the communication functions listed above.
Even though these functions are assigned to various layers explicitly by the OSI model, each stack implementation makes pragmatic assignments of these functions to various layers that may differ from the OSI model itself. Additionally, these functions may be partitioned and assigned by parts to different layers in a given stack, and some layers of the stack may not be required in certain protocols. It is also important to recognize that there may be more than one protocol present at each particular layer.
To efficiently learn and understand data communication, one must recognize implementations of these basic functions whenever and wherever they occur without regard to layer assignment, task partitioning, implementation details, or variations in terminology.

18. Peer-to-Peer Communications
Physical
Application
Presentation
Session
Transport
Network
Data Link
Application
Presentation
Session
Transport
Physical
Network
Data Link
Each protocol layer communicates with a peer layer on another machine. Each protocol layer relies on the layers beneath it to handle lower level protocol tasks, as outlined on the previous page.
Although there are exceptions, most of the time the upper protocol layers communicate on an end-to-end basis; that is, the end nodes communicate with each other transparently over the network.
The lower layer protocols in most cases are used to communicate between each pair of physical devices encountered all the way along the route. In the diagram above, a multiprotocol router is used to connect together two end nodes. Each of the end nodes communicates with the router on the lower protocol layers, but on the higher protocol layers the end nodes communicate directly with each other.
Physical
Network
Data Link

19. Each Protocol Layer Encapsulates Data from the Layer Above
The Open Systems Interconnect model attempts to divide the various tasks required for data communications into modular layers of functionality that are not implementation dependent. A total system is a stack of modules which pass data up to and down from a user. This data communication philosophy has been widely accepted but not widely implemented to exact OSI specifications. This leaves us with many different protocol implementations that all take a stack of layers approach. Unfortunately, the exact division of duties between layers seldom follows the OSI model exactly. Nevertheless, a knowledge of the lower several protocol layers is invaluable for a general discussion of data communications.
Each layer asserts its functions by means of a header containing bit fields whose values have significance. The header and data from the next upper layer is encapsulated in the data portion of each layer below. Headers typically align on 8 bit boundaries so data characters are always aligned as bytes. Of course, padding is often required, and exceptions are possible.

20. Protocol Layers and Stacks
WAN protocol analysis focuses on the lower three layers
Physical, Data Link and Network
Different protocol stacks often share the same lower three layers
For example, IP, IPX and SNA over Frame Relay

21. Protocol Summary
Protocols are sets of rules that allow computer with different characteristics to communicate with one another
Protocol stacks share common lower layers for actual communication
Peer-to-Peer communication occurs between upper layers
Lowest three layers often involved in network analysis and troubleshooting
The ISO model is a way of describing sets of communications rules that exist in stacks and allow different kinds of computers to share information and resources over common physical media. While the upper layers of the protocol stack perform peer-to-peer communication, problems in the lower layers of the network can prevent this communication and disrupt the function of the network. The most common faults in WAN networks occur in the lower three layers.

22. Physical Interfaces
Physical interfaces are hardware components that attach to the physical media that transmit and receive network signals
Physical interfaces are associated with one or more protocols that utilize the interface to perform the function of the lower layers of the ISO reference model
Physical interface standards are sets of common features that manufacturers use to produce products that operate with one another
Physical interface standards allow different manufacturers to produce products that will work together. Familiarization with the particular standard under analysis is extremely important to the isolation and troubleshooting of problems.

23. Typical WAN Physical Interfaces
RS-232/V.24
V.35
RS-449/V.36 T1 E1
ISDN Basic Rate Interface (BRI)
ISDN Primary Rate Interface (PRI)
There are a wide variety of physical media which can transmit network information. Physical interfaces are the hardware components of the Internet Advisor that actually attach to the physical medium of the network. In addition, different types of physical layer protocols can use the same type of physical interface.
Physical layer protocols are designed to handle all of the physical aspects of communication. These include the transmission media, the physical connectors, voltage levels, line codes and other physical aspects of networking.
Examples of physical layer protocols include RS-232C/V.24, V.35, X.21, RS-449/V.36, T1, T3, E1, E3, OC-3, OC-12 and many others.

24. Introduction to Bit-Oriented Protocols
Definition
Data Communications Today: Bit-Oriented Protocols
Examples of Bit-Oriented Protocols
The Control Field Specifies the Frame Type
Point-to-Point Protocol
Bit-Oriented Protocols Summary
Bit-oriented protocols such as frame relay can transmit a wide variety of information in the form of binary numbers transmitted as bits. Unlike character-oriented protocols where transmissions always represent text or character-based control codes, bit-oriented protocol bit streams can communicate anything from text, to graphics, to voice, to video. Freed from the use of characters as a protocol medium, bit-oriented protocols are much more flexible and more powerful than character-oriented protocols.

25. Data Communications Today: Bit-Oriented Protocols01 E3
The quick brown fox...
FCS
Data
Control
Flag
Address
FCS
It has been recognized that many functions in data transmission can be communicated with just a few bits and sometimes with only one bit. With this in mind, many protocols have been proposed and implemented using bit fields rather than entire characters to provided communication information and control. These protocols are collectively called Bit Oriented Protocols (BOPs). Standards organizations have provided extensive specifications of BOP protocols to perform a wide variety of tasks in both Wide Area Networks (WAN) and Local Area Networks (LAN).

26. Examples of Bit-Oriented Protocols
SDLC (Synchronous Data Link Control)
HDLC (High-level Data Link Control)
LAP-B (Link Access Procedure-Balanced)
ADCCP (Advanced Data Communications Control Procedures)
And many others
Data
Control
Flag
Address
FCS
In a bit-oriented protocol, each frame begins and ends with a “flag”, which is the bit pattern “ ” (=7E hex). The flags serve to synchronize the receiver to the beginning and ending boundaries of the frame, and to the bytes boundaries within the frame. Interframe spacing is typically filled with flags to maximize transitions and maintain receiver clock synchronization.
The start flag is followed by the address field and then by the control field. Both of these fields can be either one or two bytes long, depending on the protocol and the implementation. Two-byte implementations of either field is referred to as “extended” addressing or extended control.
Care must be taken to avoid the 7E hex bit pattern from occurring randomly anywhere within the frame, lest the receiver would falsely interpret a premature frame end boundary. To prevent this, a process called “bit stuffing” will automatically insert an extra 0 bit whenever five consecutive 1s occur within the frame. The receiver will automatically remove this 0.
8 bits 8 or 16 bits 8 or 16 bits optional (multiple of 8 bits) 16 bits 8 bits
payload (next protocol)
Frame
delineation
frame type identification, frame numbering
link level addressing

27. The Control Field Specifies the Frame Type
Information frames carry user data
numbered by N(S) and N(R)
Supervisory frames acknowledge receipt of info frames and communicate receiver busy/ready state
numbered by N(R)
include RR, RNR and REJ
Unnumbered frames establish and terminate the data link, report errors and sometimes transfer data
include SNRM, SABM, UA, DISC, FRMR, XID, UI and others
There are three types of frames defined by the control field in a bit-oriented protocol:
information frames carry user data.
supervisory frames acknowledge receipt of information frames and communicate receiver busy and receiver ready states.
unnumbered frames establish and terminate the data link, detect and recover from transmission errors and sometimes transfer user data.

28. Point-to-Point Protocol (PPP)
Synchronous PPP
Asynchronous PPP
Multilink PPP
Information
Control
Flag
Address
FCS
8 bits 8 bits bits bits optional (multiple of 8 bits) 16 bits 8 bits
next protocol type field
03 hex identifies PPP information frame
not used (FF hex)
Type Field
payload (next protocol)
Synchronous PPP frame format:
The Point-to-Point Protocol (PPP) was developed as a standard data link layer for multivendor router communications. The PPP frame format is similar to other bit-oriented protocols, except that the address and control fields are fixed at FF and 03 hex, respectively. A two-byte type field is added to identify the protocol type of the payload.
Note: The two-byte type field values defined for PPP are NOT CONSISTENT with the two-byte type field values used in Ethernet.

29. Bit-Oriented Protocol Summary
Bit oriented protocols can transmit more types of data than can character oriented protocols
Fields within the protocols (not control characters) manage network overhead and physical layer maintenance
Bit-oriented protocols are inherently more flexible than character-oriented protocols because they can carry many different types of traffic. Bit-oriented protocols employ fields within the protocol for overhead and control functions.

30. Connecting the Agilent Technologies Internet Advisor to the Network Under Test
modem
Asynchronous
RS-232C/V.24
(RS-449/V.36
or V.35)
To monitor asynchronous WAN connections on analog transmission facilities, the Agilent Technologies Internet Advisor must be connected between the DTE and the modem using a Y-cable at the points shown above. It is not possible to connect the analyzer to the analog transmission facility between the modems.

31. Connecting the Agilent Technologies Internet Advisor to the Network Under Test
Synchronous
DSU/CSU
T1 DSX
CEPT - E1
RS-232C/V.24
RS-449/V.36
X.21
or V.35
T1 network,
or DDS 4-wire R
Connection of the Agilent Technologies Internet Advisor to monitor a synchronous data network can be done on either side of the CSU/DSU as shown. The signal levels (T1 network vs. T1 DSX) and in some cases the physical interface (DDS 4-wire vs. V.35) will differ for these connections.

32. Interface Configuration
V-series interfaces include:
RS-232C/V.24
RS-449/V.36
V.35
Interface configuration:
DTE clock source: DTE or DCE (default)
Data sense: normal, inverted, NRZI-external
To configure the Agilent Technologies Internet Advisor to monitor V-series interfaces (like RS-232C/V.24, V.35, etc.), the user must specify the clock source [either DCE or DTE], the data sense [normal, inverted or NRZI] and/or the line bit rate. or
Bits/second

33. Agilent Technologies Internet Advisor Configuration Menu
Interface/Protocols
Data source
Monitor options
Protocols
Decode Table
Filters/Counters
Log
Disk logging options
Disk logging configuration
Configuring the Agilent Technologies Internet Advisor to monitor a WAN data stream is done in the Config View. In order to monitor data, the selections under the Interface/Protocols tab must correctly match the conditions of the interface to be monitored.

34. Lesson 1 - Review You should be able to:
List and explain data communications fundamentals as they apply to wide area networks.
Define the term network protocol.
Explain the OSI seven-layer protocol model, peer-to-peer communications and protocol encapsulation.
Explain bit oriented protocol and give examples.
Identify and describe the different interfaces and components of the Internet Advisor.
Demonstrate how to connect the Internet Advisor to a network under test.