Much More Idle Chatter About Reference Models


Jim Stevens (Stevens@A.ISI.EDU)
Fri 18 Dec 87 14:59:11-EST


                  DISCUSSION OF LAYERED PROTOCOL MODEL
                    Jim Stevens (Stevens@A.ISI.EDU)
                            18 December 1987

                              INTRODUCTION

Recently CMC has distributed a nice multi-colored wall chart showing
the DoD Internet Architecture and the protocols at each layer.

I only list CMC as reference because their chart caused a flurry of
e-mail messages on TCP-IP. Note that their chart is just the latest of
many papers and reference-type-material to contain the same type of
problems. Since many of you may not have seen the CMC chart, it is
included for reference as Figure 1 at the end of this message.

There are 2 problems with this chart:
  (1) Location of EGP, GGP, and HMP and
  (2) Incorrect Physical and Data Link protocols under some networks
       (especially radio networks).

                LOCATION OF NETWORK MANAGEMENT PROTOCOLS

The location of EGP, GGP, and HMP have caused a flurry of e-mail
messages on TCP-IP. These 3 protocols are network management
protocols. There has been a lot of work in the last decade on protocol
architectures which include network management that provide an answer
to the question of the network management protocol location. Some of
the efforts include ISO (reference ISO 7498 Part 4), CCITT (ISDN, see
recommendation I.320), and AT&T (J.W. Timko, AT&T Technology, Vol 2, No
3). I intend to locate EGP, GGP, HMP, and ICMP within the ISDN
protocol stack using the OSI management structure categories.

All three of the above named efforts basically came up with the same
architecture. These architectures just added a new dimension to the
current the 7-layer OSI reference model. The 7-layer OSI model
contains only 1 dimension, which I'll call the X dimension. The X
dimension described the different services performed upon User data as
it is sent from one host to another. The new architectures added a Y
dimension which showed the different functions which must be performed
at each layer. The three different functions that are performed are:

   1. The (N)-layer performs some service upon user data and send the
       data onward. (This function is identical to that described in
       the original X dimension.)
   2. The (N)-layer performs signaling between the different layers.
       (For packet switched networks this signaling is typically
       provided in the packet headers.)
   3. The (N)-layer performs internal management decisions.

Figure 2 shows the ISDN protocol stack and the 2 dimensions of their
model. The user service function is the vertical stack of layers
labeled with a U. The signaling function is the vertical stack of
layers labeled with a C. The management function is the vertical stack
of layers labeled with an M.

The OSI management framework describes 3 management structure
categories:

   1. Systems Management
         System Management Application-Process (SMAP)
         System Management Application-Entity (SMAE)
   2. (N)-layer management
         coordinates multiple instances of communications
   3. (N)-layer operation
         coordinates single instance of communications

The Systems Management is an application process which can use the
entire protocol stack when communicating. The difference between a
Systems Management application process and another user application
process (such as Terminal Emulation) is that the Systems Management
application has access to the control/management data within each of
the protocol layers. EGP, GGP, and HMP are system management
applications.

The (N)-layer management/operation are processes within the (N)-layer.
Thus these processes can only use the protocols which lie under them.
ICMP is a Network-layer management process.

     INCORRECT PHYSICAL AND DATA LINK PROTOCOLS UNDER SOME NETWORKS

The CMC chart has confused the Physical and Data Link protocols used
within some networks and the Physical and Data Link protocols used to
interface to these networks. This has been a common problem and has
shown up in several different papers. Figure 3 shows a layered
protocol chart which did not have this problem.

Since I have worked on the DARPA Packet Radio Program and its follow on
Survivable Adaptive Networks (SURAN) Program, I will use older fielded
Improved Packet Radio (IPR generation Packet Radios) as an example to
explain how the confusion arises.

Normally, the 7 protocol layers are implemented in a single box. The
protocol drivers are then contained within either the OS kernel or
applications residing above the OS. This is not true however in Packet
Radio, where the 7 protocol layers are implemented in 3 different boxes
interconnected via a BBN 1822 line. Figure 4 shows how the DOD
protocols stack is implemented in 3 boxes interconnected together with
BBN 1822.

The Hosts interface to the Packet Radio Network via a Host Interface
Unit (HIU). The actual interface between the HIU and the Hosts is a
defined host access protocol running on top of BBN 1822. The hosts
implements the Session and higher layer protocols such as FTP and mail.

The HIU interface to the actual Packet Radios (PRs) using a defined
device access protocol running on top of BBN 1822. The HIUs implement
the Internet and Transport protocols such as IP and TCP.

The PRs communicate to each other using the PR Channel Access Protocol
(CAP) at the network and upper data link layers, CSMA at the lower data
link layer, and spread spectrum at the physical layer. The PRs thus
implement the Network, Link, and Physical layers.

There is often confusion between the host or device interface to Packet
Radio and the actual protocols used within Packet Radio. That is why
the CMC chart shows BBN 1822 as the Packet Radio Network Physical
protocol instead of spread spectrum.

It is fairly easy to catch this type of error for radio networks, since
the radio network physical layer must be some sort of RF transmission
scheme such as Spread Spectrum (SS) or Amplitude Modulation (AM).

------------------------------------------------------------------------------

                                Figure 1

                         Layered Protocol Model
                    Taken from CMC chart, Fall 1987

DOD
MODEL

        +-------+ +------+ +-------+ +--------------------------+ +-------+
Appli- | File | | Mail | | Term- | | User Programs | | Name |
cation | Trans-| | Text | | inal | | | | Server|
        | fer | | RFC | | Emul- | | | | |
        | Server| | 822 | | ation | | | | |
        +-------+ +------+ +-------+ +--------------------------+ +-------+
           ^ ^ ^ ^ ^ ^ ^
           . . . . . . .
           . . . . . . .
           v v v v v v v
        +-------+ +------+ +-------+ +-----------+ +------+ +-----+ +-------+
Util- | FTP | | SMTP | |Telnet | | NETBIOS | | TFTP | | NFS | | NSP |
ity | MIL | | MIL- | | MIL- | | RFC | | | | | | |
        | STD | | STD | | STD | | 1001/ | | | | | | RFC |
        | 1780 | | 1781 | | 1782 | | 1002 | | | | | | 882 |
        +-------+ +------+ +-------+ +-----------+ +------+ +-----+ +-------+
           ^ ^ ^ ^ ^ ^ ^ ^
           . . . . . . . .
           .............................. ............................
                                        . .
                                        v v
         +-----+ +-----+ +-----+ +------------------+ +-------+
Trans- | EGP | | GGP | | HMP | | TCP | | UDP |
port | | | | | | | MIL-STD 1778 | | RFC |
         | | | | | | | | | 768 |
         +-----+ +-----+ +-----+ +------------------+ +-------+
           ^ ^ ^ ^ ^
           . . . . .
           . . . . .
           ....................................................
                                          .
                                          v
Inter- +------------------------------------+----------------+
net- | Internet Protocol (IP) | ICMP |
work | MIL-STD 1777 | RFC 792 |
               +------------------------------------+----------------+
                                         ^
                                         .
                                         .
        ..............................................
        . . . . .
        . . . . .
        v v v v v
     +-----+ +-------+ +---------+ +------------+ +--------------+
Net- | Pkt | | BBN | | Pkt | | CCITT X.25 | | Ethernet ARP |
Work |Radio| | 1822 | |Satellite| |Packet Layer| | RFC 826 |
     +-----+ +-------+ +---------+ +------------+ +--------------+
        ^ ^ ^ ^ ^ ^
        . . . . . .
        . . . . . .
        ....... ......... ....... .
        . . . . . .
        . . . . . .
        . v v v v v
        . +------+ +-----+ +-----+ +-----+ +--------------+ +-------+
Data . | BBN | | BBN | |LAPB | |LAPB | |IP / Ethernet | | IEEE |
Link . | HDH | | VDH | | BSC | |HDLC | | RFC 894 | | 802.2
        . | | | | | | | | +--------------+ +-------+
        . | | | | | | | | ^ ^
        . | | | | | | | | . .
        . | | | | | | | | . .......................
        . | | | | | | | | . . . . .
        . | | | | | | | | v v v v v
        . | | | | | | | | +------+ +-----+ +-----+ +----+
        . +------+ +-----+ +-----+ +-----+ | | | | | | | |
        . ^ ^ ^ ^ | | | | | | | |
        . . . . . | | | | | | | |
        . .......................... | | | | | | | |
        . . . . . | | | | | | | |
        v v v v v | | | | | | | |
      +----+ +-----+ +-----+ +------+ +------+ | | | | | | | |
Phys- |BBN | |CCITT| | EIA | | EIA | |MilStd| | IEEE | |IEEE | |IEEE | |FDDI|
ical |1822| |V.35 | |RS449| |RS232C| | 188C | |802.3 | |802.4| |802.5| | |
      +----+ +-----+ +-----+ +------+ +------+ +------+ +-----+ +-----+ +----+

------------------------------------------------------------------------------

                               FIGURE 2.

                          ISDN Protocol Stack
                         Taken from CCITT I.320

       Control User Data System Management
        ________ ________ ________
       | \ \ | \ \ | \ \
       | \ \ | \ \ | \ \
         \ \ ______\ \ \ ______\ \ \ ______\
            \ | | \ | | o \ | |
               \|______| \|______| o \|______|
                      @ @ o o @
                      @ @ o o @
                      @ @ oooooo@ooooooooo o @
                      @ o @ o @
                      @ o @ ooooooooooo @
                ______@____ _o_____@_ o @
               | \ @ \o @ \o @@@@@@@@@
               | \ C o \ @ o \ @
               | \ ________\@ o \ @
               | \ |\ @ \ o M @\
               | \ | \ U o\ @ \
               | \ | \ _________\_________\
               | \ |\ | | |
               | \ | \ | 7 - Appl | |
               | \ | \|__________| |
               | \ |\ | | |
               | \ | \ | 6 - Pres | |
               | \ | \|__________| |
               | \ |\ | | |
               | \ | \ | 5 - Sess | |
               | \ | \|__________| |
               | \ |\ | | |
               | \ | \ | 4 - Tran | |
               | \ | \|__________| |
               | \ |\ | | |
               | \ | \ | 3 - Netw | |
 ______________| \ | \|__________| |
. \ |\ | | |
   . \ | \ | 2 - Link | |
. . \ | \|__________| |
   . . \ | | |
      . . \ | 1 - Phys | |
         . . _______________\|__________|_________|
            . Physical Media |
               . ___________________________|

------------------------------------------------------------------------------

                               Figure 3.

                  Layered DOD Reference Model Chart
       Taken from "Tactical Information Exchange (TIE) Framework
          Development (For the 1990s Time Frame" October 1981

                       +-----+ +----------+ +------------+
Application | MTP | |Multimedia| | Conference |
                       | | |Message | | |
                       +-----+ +----------+ +------------+
                            ^ ^ ^ ^
                            . . . .
                            . . . .
                            . . . .
             +------+ +---+ . . +----+ +------+ . .
Utility |TELNET| |FTP| . . |TFTP| |Name | . .
             | | | | . . | | |Server| . .
             +------+ +---+ . . +----+ +------+ . .
                ^ ^ . . ^ ^ . .
                . . . . . . . .
                . . . . . . . .
                ................. ....... . .
                        . . . .
                        . . . .
                        v v v .
              +------------------+ +---------+ +-----+ +--------+ .
Transport | TCP | | UDP | | GGP | | NVP II | .
              +------------------+ +---------+ +-----+ +--------+ .
                       ^ ^ ^ ^ .
                       . . . . .
                       . . . . .
                       ................................ .........
                                            . .
                                            . .
                                            v v
          +-----------------------------------------------+ - - - - - - - - -
Internet | Internet Protocol | Stream Protocols !
          +-----------------------------------------------+ - - - - - - - - -
                                            ^
                                            .
                                            .
                    ......................................................
                    . . . . . .
                    . . . . . .
                    v v v v v v
               +----------+ +------+ +------+ +-----+ +-----+ +------+
Network | ARPANET | |SATNET| |CCITT | |PRNET| |JTIDS| | DIN |
               | HOST/IMP | | | | X.25 | | | | | |2 SIP |
               +----------+ +------+ +------+ +-----+ +-----+ +------+
                    ^ ^ ^ ^ ^ ^
                    . . . . . .
                    . . . . . .
             .............. ......... . . . .
             . . . . . . . . .
             . . . . . . . . .
             v v . v v v v v v
          +----+ +----+ . +-----+ +----+ +-----+ +-----+ +-----+ +------+
Link |HDH | |VDH | . | VDH | |HDH | |HDLC | |CSMA | |TDMA | |ADCCP |
          |HDLC| |RTP | . | RTP | |HDLC| | | | | | | | |
          +----+ +----+ . +-----+ +----+ +-----+ +-----+ +-----+ +------+
             ^ ^ . ^ ^ ^ ^ ^ ^
             . . . . . . . . .
             . . . . . . . . .
             v v v v v v v v v
          +---+ +-----+ +----+ +-----+ +----+ +-----+ +-----+ +-----+ +------+
Physical |M/W| |Modem| |BBN | |Modem| |M/W | |X.21 | | SS | |SS/FH| | M/W |
          | | | | |1822| | | | | | | | | | | | |
          +---+ +-----+ +----+ +-----+ +----+ +-----+ +-----+ +-----+ +------+

Key:

ADCCP Advanced Data Communications Control Procedures
DIN 2 SIP AUTODIN II Segment Interface Protocol
FH Frequency Hop
HDH HDLC Distant host
JTIDS Joint Tactical Information Distribution System
MTP Mail-Transport Protocol
M/W Modem / Wire
NVP II Network Voice Protocol
PRNET Packet Radio Network
RTP Real Time Protocol
SATNET (Experimental) Satellite Network
SS Spread Spectrum
TDMA (Synchronous) Time Division Multiple Access
VDH Very Distant Host

----------------------------------------------------------------------------

                                Figure 4
                     Host Interface to Packet Radio

                  +---------------+
                  | | Host
Application |FTP, Mail, etc.|
                  | |
Utility | |
                  +---------------+
                      ^
                      . BBN 1822 and defined host access protocol
                      .
                      v
                  +---------------+
                  | | Host
Transport | TCP | Interface
                  | | Unit
                  | |
Internetwork | IP |
                  | |
                  +---------------+
                      ^
                      . BBN 1822 and defined device access protocol
                      .
                      v
                  +---------------+
                  | | Packet
Network | Channel | Radio
                  | Access |
                  | Protocol |
                  | |
                  | |
Link | CSMA |
                  | |
                  | |
Physical | Spread |
                  | Spectrum |
                  | |
                  +---------------+

----------------------------------------------------------------------------
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