latest connectivity draft

Gene Hastings <hastings@psc.edu> Thu, 01 April 1993 04:31 UTC

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From: Gene Hastings <hastings@psc.edu>
Subject: latest connectivity draft
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I've incorporated comments from and since the last meeting, and expanded
some parts of the narrative. I would greatly appreciate pointers to
relevant citations.

I will have a handful of hardcoopies Thursday, and try to get more copies.

Gene
 -------------------------------

Draft v1.9     Connectivity Models for Internet Access   Gene Hastings

[Introductory boilerplate here]





Models for Connections to Internet MANs

                Models for Connections to Internet MANs

  This document describes a number of models for the
  interconnection of remote Local Area Networks to a larger TCP/IP
  (or similar) datagram internetwork. All of the models presuppose
  IP transport, no contention for hub ports, permanent connections,
  either physical or virtual(even on fabrics which support switched
  connections). and connections to remote networks, not remote
  hosts, thus mandating the support of updated routing protocols
  over the links.

  My orientation in this context is that of a network operator of
  both very high performance networking and high ubiquity
  networking. I believe that the history of the access for
  researchers to scientific resources is being mirrored in the more
  recent experience of other communities, including Education,
  Libraries and Museums.



(0)  As this is a discussion of network connectivity, ASCII access to host
accounts is outside the scope of this document. See [document reference?]1

(1)  Dialup packet connections on voice telephone lines.
Description
 High speed compressing modems, used with routers providing dialup
   asynchronous PPP or SLIP connections .
    Routers capable of performing dynamic point-to-point TCP/IP
      connections over the PSTN are configured with high speed
      compressing modems (V.32bis/V.42bis or a higher performance
      successor) to create a low cost transport fabric. All remote
      site routers dial into central or metro hub(s). In some areas,
      prevailing tariffs allow the use of dialup services as
      permanent circuits.
 The choice of PPP versus SLIP will often be based more on
   availability and implementation details than on fundamental
   differences between the protocols. PPP is in general preferable,
   due to more powerful options negotiation and therefore better
   interoperability and the ability to support some degree of pre-
   configuration. PPP also supports multiple network protocols, while
   SLIP supports IP only (exclusive of arbitrary encapsulation or
   tunneling). Unfortunately, PPP is not available on all potential
   platforms of interest as clients, and where it is available may
   not be attractively priced for the K12 community.
Modems
 Modems can be used on voice grade dial-up lines to provide
   connectivity to a network hub. Instead of running ASCII terminal
   sessions over these connections, TCP/IP is used with either the
   SLIP or PPP encapsulations  Running TCP/IP imposes an overhead of
   40B/packet (with remote echo and a medium to slow typist, this
   means 40B per character). This requires either high speed modems
   or IP Header Compression or both to achieve acceptable
   performance.
Compression
 V.32 modems can send uncompressed data at up to 9600 bps. V.32bis
   modems extend this to  14,400 bps (this base rate capability is
   also referred to as the "data pump"). The new interim proposal for
   V.32terbo is expected to run at 19,200 bps, and the forthcoming
   V.fast is expected to run at over 28,000 bps.
 V.42bis compression can achieve effective speeds of up to 4x the
   data pump speed, depending on the compressibility of the data. and
   the maximum data rate of the serial interface on the modem.
   Current modems have asynchronous port speeds of up to 38.4 kbps
   for V.32/V.42bis modems, and 57.6 kbps for V.32bis/V.42bis modems.
   In order for the systems (routers or hosts) to fully utilize the
   compression, however, the ports must be capable of performing
   hardware flow control, as in-band software flow control can cause
   problems.
Asynchronous Routers/Low Cost Async Router/host port
 SLIP or PPP connections can be made between general purpose
   computers or workstations, which provided an early model for
   networking in that manner. There are now specialized routers with
   multiple asynchronous lines providing a cost-effective way to
   provide a bank of dialups for this purpose. these routers also
   have much in common with (and are often descended from) terminal
   servers, and various router models  are suited to different
   connection models the TeleBit NetBlazer or Livingston Portmaster
   (among others in an expanding market segment) are suited to dialup
   access from remote LANs, and have powerful dialup management
   features. Products like the Annex terminal server can provide
   cheaper per-port costs if the remote connections are from single
   hosts. In some cases a workstation can be used as an Asynchronous
   router, but may lack a serial interface with sufficient
   performance, and will likely lack advanced link management
   features.
Tariffs
 Telephone tariffs in some regions (like Metro Pittsburgh) have
   institutional  rates which provide measured but untimed calls in
   the calling area. This means that there is a charge per call, but
   that call costs the same whether it is one minute or all month.
   With the base rate of about $20/month for such service, it makes
   an extremely attractive model for low-end (but still highly
   useful) connectivity.
Cost
 Central Router
    NetBlazer
    Livingston Portmaster
    Rockwell/CMC NetHopper (limited number of ports)
    NEC Dr. Bond
    Annex xxxx
    Cisco xxxx
 Remote Router
    NetBlazer
    Personal NetBlazer
    Livingston Portmaster
     B. Lloyd: The Portmaster has a list price of $2,495 for a 10 port
     device.  We use them at BARRNet and are very pleased with the
     product.
    Rockwell/CMC NetHopper
    NEC Dr. Bond
    Networks Northwest Breeze 1000
    Datability
    Annex
    Cisco CS-500
     B. Lloyd: The Cisco CS-500 is not a great solution right now
     because the PPP is not well integrated (a port can run either PPP
     or SLIP/ASCII-terminal but not both).
    Workstation or Desktop Computer
     B. Lloyd: PPP/SLIP for most UNIX workstations is available from
     Morning Star Technologies.  PPP for PC is available from FTP
     Software.  Larry Blunk of Merit (lbk@merit.edu) is just finishing
     up a PPP driver for MacTCP that should run on just about any
     Macintosh.  Intercon includes SLIP with their TCP/Connect II
     product for the Mac.

 Modems
    B. Lloyd: A key factor for modem selection is low latency (time
      from when you put a character into the sending modem before it
      comes out of the receiving modem).  Latency in modems varies
      greatly from vendor to vendor.  Check modem reviews for latency
      numbers.
    TeleBit T3000
    TeleBit T1600
    Supra
    Zoom
    Practical Peripherals
    USRobotics Courier V.32
    AT&T/Paradyne
 Link - see your local phone company for rates for regular telephone
   service. Be sure to ask if calls to your hub will be timed, and
   compare the price of "metro area flat rate" and "foreign exchange"
   service, if available.

Advantages:
 Very low link cost (as low as $15/mo.)
 Low router cost
 Can be used anywhere there is POTS.
 Hardware is reusable (components can be migrated to bootstrap sites,
   or maintained as terminal server)
 Can be used for host as well as LAN connections
 Uses tested routing protocols and topologies
Disadvantages
 Low speed
 Performance dependent on  compressibility of data
 Links can be unreliable
 Does not take advantage of developing Telephone Company FastPacket
   services/infrastructure
 Lacks link & transit diversity for reliability

(2)  Dialup  Synchronous PPP on voice telephone lines [is there any
point to this one?]
Description
 [comment from B. Lloyd: If you are running dial-up sync using
   V.32bis modems you do not get to use compression so performance
   will be less than async (V.42 performs async to sync conversion
   within the modem so there is no advantage to sync over async at
   any time).]
 V.32bis/V.42bis modems. NetBlazer/NAT/Livingston/Cisco IGS
    Entry level routers with interfaces for leased, Synchronous lines
      can be combined with the modems cites in section (1) to provide
      similar connectivity, but at slightly higher throughput. The
      most compelling reason for this option is where market
      pressures make such a router cheaper than the Asynchronous
      router in section (1) or it is desirable to allow for an
      upgrade to a leased Synchronous connection.
 As #1, possibly marginally higher performance, higher per-port cost
   at the central hub.

Link Terminating Equipment
 Modems as in section #(1).
Link Data Formatting
 CCITT standard high speed modems with error correction and
   compression, as in section (1)
Routers
 Entry level tail circuit routers with synchronous data interfaces,
   typically well under $10k. In many cases the synchronous
   interfaces are capable of signaling rates up to T1 and higher,
   which allows for future link upgrade without the necessity of
   purchasing new router hardware. In some cases there is also
   support (current or planned for the near future) for MAN packet
   services like Frame Relay or SMDS.
Tariffs/Link Costs
 As in section (1)
Advantages:
 Very low link cost
 Medium-low router cost
 Hardware is reusable (can be migrated to bootstrap sites)
 Uses tested routing protocols and topologies
Disadvantages
 Low speed.
 Performance dependent on  compressibility of data
 Links can be unreliable.
 Link interface and hardware does not take advantage of developing
   Telephone Company FastPacket services and infrastructure.
 Lacks link and transit diversity for reliability.
 Synchronous interfaces are more expensive than asynchronous.

Cost
 Central Router
    Matching unit to remote router
    Cisco MGS/AGS/AGS+
    Wellfleet
    B. Lloyd: Livingston has a four-sync-port router, the IR-4, with
      a list price of $3,295.  I suspect that they can be talked into
      an educational discount.
 Remote Router
    NetBlazer                  $3500 for 1 Sync.. Can also be used as
      terminal server
    Livingston xxxx
    NAT
     B. Lloyd: NAT offers educational/non-profits a discount.  We also
     use these in BARRNet and are generally pleased (you must use
     their SNMP management station to manage the NAT router after it
     is initially configured).
    Cisco IGS
 Modems
 Link

(3)  ISDN point-to-point using Permanent Virtual Circuits
Description
 ISDN Virtual circuits permanently configured.
    Asynchronous or Synchronous routers connected to a strict ISDN
      fabric, with Permanent Virtual Circuits configured. With a
      Basic Rate Interface (BRI) can be asynchronous, 64kb
      synchronous, or 128 kbps synchronous at remote site. At the
      central hub, this requires either individual lines, an inverse
      multiplexer, or a hub router which can internally demultiplex
      multiple ISDN channels on one PRI interface.
Link Terminating Equipment
 ISDN Terminal Adapter.
Link Data Formatting
 not yet formalized
Routers
 NetBlazer at BRI
 ?
Tariffs/Link Costs
 Currently in development. Estimates are connections for ~ $40/month,
   but the application (or not) of usage charges is ambiguous, and
   estimates vary widely. Usage charges range from $.01/minute to
   $.10/minute.
Advantages:
 Lower Link cost (~$40/mo.). Depending on usage charges, may be
   higher, or MUCH higher in some areas.
 Better speed than voice dialup (Basic Rate = 2 64kb channels)
 Does not (at present) use compression, so there is no data
   sensitivity in performance.
 Many Local Exchange Carriers are promising wide availability.
Disadvantages
 Is not available everywhere.
 Link Adapters still expensive, but falling. More of their
   functionality is being incorporated into host/router interfaces.
 Encapsulation not well defined/deployed. *****
 Does not (at present) use compression, so there is no improvement in
   performance over the native data rate for any data type.
 Dearth of hub port equipment
Cost
 Host/Router
 Site Link Adapter
 Hub Router
 Hub Multiplexer?
 Link(s)

(4)  ISDN pipes to LATA WAN packet (F-R, SMDS, etc.)
Description
 Utilizing ISDN "Local Loops" to site premises, very low cost local
   loop connections can be made to FastPacket switches in the Central
   Office. Router vendors are supporting both SMDS and Frame Relay on
   current platforms. Using ISDN bit transport technology (2B1Q?)
   could dramatically reduce the cost of providing higher speed
   digital service to customer premises. (See previous estimates of
   $40/month for an ISDN BRI local loop.)
 Frame Relay is a service which provides multiple vitual circuits
   over the same physical access link. The most common anticipated
   usage model is though statically configured Permanent Virtual
   Circuits (PVCs), which can have variable abandwidth, depending
   upon traffic needs. Access rates for Frame Relay are from 56 Kbps
   at least to T1, and possibly (depending upon which marketeer
   you've just talked to) to T3.
 SMDS is a Metro Area connectionless packet service. There are no
   virtual circuits, so everything is based on an SMDS MAC address.
   To this degree, SMDS resembles a Metro Area Ethernet. Access rates
   for SMDS are from T1 to T3.
Link Terminating Equipment
 ISDN Terminal Adapter.
Link Data Formatting
 Yet to be determined.
Routers
 The same set of routers of interest in section (3) should be
   suitable here, but there is not at present support for this kind
   of usage.
Tariffs/Link Costs

Advantages:
 Lowest cost digital packet services to premises.
 Only requires physical ISDN at remote site, as FastPacket connection
   to hub can be traditional leased line at a higher aggregate
   bandwidth.
 Conserves hub ports and aggregate price (one T1 port on a hub can
   serve many remote sites).
 Provides multiplexing and traffic aggregation in the Telephone
   Company Fabric.
Disadvantages
 No clear commitment to mix ISDN and Fastpacket fabrics. (see
   Northern Telecom DataSpan)
 Is not available everywhere.
 Link Adapters still expensive.

Cost
 Host/Router
 Site Link Adapter
 Hub Router
 Hub CSU
 Link(s)

(4.5)     Analog leased lines
"3002"?
Description
 Leased point to point voice grade circuit, suitable for the use of
   dialup and leased line modems. In some regions, dialup analog
   phone service is usage sensitive, so that the breakpoint for a
   leased line is reached in short order. Analog leased lines are in
   general cheaper than digital leased lines, and in some areas may
   be the only sort of leased line available at all.
Link Terminating Equipment
 modem
Link Data Formatting
 varies
Routers

Tariffs/Link Costs

Advantages:
 Depending on regional tariffs, may be cheaper than permanently
   dialed up switched voice connection. Will very likely be cheaper
   than leased point-to-point digital service.
 May be the only leased line service available in a region.
Disadvantages
 low speed
Cost
 Remote router
    see async dialup
 modem
    see async dialup
 Hub router
    see async dialup
 Maintenance



(5)  Digital leased lines
Description
 Leased data lines forming a tree or mesh network of point-to-point
   links. Uses off-the shelf routers at a wide range of data rates
   (56 kbps to 45 Mb). Uses off-the-shelf CSU/DSUs. (There was a time
   when this model included rates as low as 9.6 kbps, but those rates
   are frequently not economical anymore, having been supplanted
   either by 56 kbps leased lines or with 9.6 kbps and up dialup
   lines.)
Link Terminating Equipment
 CSU/DSU, a device to terminate a digital connection from the
   telephone company. It provides a termination interfae to the
   telephone company's wires and provides a digital
   datacommunications interface to the customer's equipment. It may
   also have line testing and supervisory functions, such as loopback
   and fault isolation.
Link Data Formatting
 Originally data lines were for the transmission of digitized voice
   channels, with each channel assigned 56 kbps of bandwidth (64 kbps
   minus synchronization and formatting overhead).  Contemporary
   CSU/DSUs will perform or ensure the proper formatting of the data
   presetned to the telephone company, and can present an apparently
   unformatted ("clear channel") to the customer's equipment at the
   line rate minus overhead.
 There is an additional level of formatting imposed upon the signal.
   The data from the CSU to the customer's equipment looks like
   another piece of computer equipment. There still remains the task
   of encapsulating TCP/IP (or other higher level transport protocol)
   packets on that link. Originally, each vendor used a different
   proprietary protocol. As this was not satisfactory to network
   operators, the Point to Point Protocol (PPP) was developed. It is
   now possible for different vendors' equipment to be used on
   opposite ends of a leased link.
Routers
 Almost all of the usual suspects, and more. Cisco, Wellfleet,
   Proteon, Network Systems, TeleBit, NAT, 3Com, , , , ,
Tariffs/Link Costs
 Installation
 base rate
 mileage
Advantages:
 Familiar, proven technology
 Many vendors support it.
Disadvantages
 Expensive. Line is more expesive than analog facilities, and line
   termination equipment (DSU) is often more expensive than modems.
 Requires one hub port for every directly connected remote site.
 If sites cross LEC boundaries, every link requires two local loops
 Simple (and less expensive) topologies sensitive to cable cuts.
Cost
 Remote Router
 Hub router
 CSU
 Leased Line

(6)  Leased lines to LATA WAN packet (F-R, SMDS, etc.)
Description
 Leased data lines to Telephone Company FastPacket switches. This is
   the current model for the use of FastPacket technologies. It
   utilizes off-the shelf router products and new CSU technology, as
   well as new Telephone Company transport services.. Range of speeds
   is 56 kbps to 45 Mb.
 Frame Relay is a service which provides multiple vitual circuits
   over the same physical access link. The most common anticipated
   usage model is though statically configured Permanent Virtual
   Circuits (PVCs), which can have variable abandwidth, depending
   upon traffic needs. Access rates for Frame Relay are from 56 Kbps
   at least to T1, and possibly (depending upon which marketeer
   you've just talked to) to T3.
 SMDS is a Metro Area connectionless packet service. There are no
   virtual circuits, so everything is based on an SMDS MAC address.
   To this degree, SMDS resembles a Metro Area Ethernet. Access rates
   for SMDS are from T1 to T3.

Link Terminating Equipment
 CSU/DSU, similar to that for leased P-P links, save that in some
   cases (like SMDS) the CSU currently also participates in the link
   protocol and is consequently more expensive.
Link Data Formatting
 Standard, according to F-R, SMDS, etc. standards.
Routers
 A number of the major router manufacturers are supporting Frame
   Relay, or SMDS, or both. See your salescritter.
Tariffs/Link Costs

Advantages:
 Easiest path to FastPacket fabric
 Most components available now, others soon.
 Pilot services available now, production services soon
 Wide range of speeds
 Aggregation of traffic
 diversity in switching fabric
Disadvantages
 Has no cost advantage over (5) for small configurations
 Tariffs unsettled. Some may be structured to be prohibitive for IP
   usage models.
 Only Pilot services available now
 Components and management still subject to debugging.
 Not available everywhere
Cost
 Remote Router
 Hub router
 CSU
 Leased Line

(7)  CATV Ethernet (Applitek LANCity)
Description
 Providing MAN or Point-to-Point services over channels in a CATV
   environment. It requires a CATV system capable of bidirectional
   (not just broadcast) communications.
 As distinguished from LAN technologies, like Broadband Ethernet,
   CATV services must be well-behaved and coexist with the other CATV
   services. IT must be able to operate within the ~4.5 Mhz bandwidth
   that CATV channels have available, be able to use arbitrary
   channel frequencies, and have good attenuation outside of its
   channel assignment.
Link Terminating Equipment
 Proprietary
Link Data Formatting
 Proprietary
Routers
 Additional.
Tariffs/Link Costs
 CATV services are not tarriffed. Your mileage may vary.
Advantages:
 High Speed
Disadvantages
 Unusual, may not scale.
Cost
 Head End Translator
 Site Adapter
 Site Router
 Channel Charge

(8)  MAN FDDI
Description
 Since the FDDI design allows for a ring circumference of 100 km, and
   the availability of FDDI drivers for Single Mode Fiber, some
   Operating Companies and Bypass Operators have begun to offer FDDI
   services in metropolitan areas.
Link Terminating Equipment

Link Data Formatting

Routers

Tariffs/Link Costs

Advantages:

Disadvantages
Cost
 Router/ Host
 Single Mode to MM FDDI adapter and Mulitimode host adapter, or
   Single Mode FDDI interface
 Hub Router
 Single Mode Applique
 Bandwidth charge


(9)  MAN ATM
Description

 Host or router connections directly to a Metro Area ATM fabric.
   Speeds are not yet determined, but may start at 50 Mbps.
   Interfaces are not yet determined, but may be SONET or DS3. IBM
   has recently (March '93) proposed "low speed" (25Mb) ATM.
 ATM will potentially be the underlying fabric for other FastPacket
   Services like Frame Relay or SMDS.
Link Terminating Equipment
 Undetermined
Link Data Formatting

Routers

Tariffs/Link Costs

Cost
 Router/ Host
 Physical Link adapter
 Hub Router
 Connect/usage charge
Advantages:

Disadvantages

(10) P-P Laser
Description

Link Terminating Equipment

Link Data Formatting

Routers

Tariffs/Link Costs

Advantages:
 High speed
Disadvantages
 Sensitivity to weather and wildlife.
Cost
 Remote router
 Remote Transceiver
 Hub router
 Hub Transceiver
 Maintenance


(11) P-P Microwave
Description

Link Terminating Equipment

Link Data Formatting

Routers

Tariffs/Link Costs

Advantages:
 High speed
Disadvantages
 Sensitivity to weather and wildlife.
Cost
 Remote router
 Remote Transceiver
 Hub router
 Hub Transceiver
 Maintenance

(12) Dark Fiber (bypass or tarrifed)
Description

Link Terminating Equipment

Link Data Formatting

Routers

Tariffs/Link Costs

Advantages:

Disadvantages
Cost
 Remote router
 Remote Link adapter
 Hub router
 Hub link adapter
 Maintenance

(13) SONET Point-to-point (bypass or tarrifed)
Description

Link Terminating Equipment

Link Data Formatting

Routers

Tariffs/Link Costs

Advantages:
 high speeds
 will likely be available intra LATA sooner than ATM, and may have
   higher access rates available sooner.
Disadvantages
 $$$$
Cost
 Remote router
 Remote Transceiver
 Hub router
 Hub Transceiver
 Maintenance

(14) Amateur Packet Radio
Description

Link Terminating Equipment
Link Data Formatting
Routers
other hardware
Tariffs/Link Costs

Advantages:
Disadvantages
Cost

(15) Commercial Packet Radio
Description

Link Terminating Equipment
Link Data Formatting
Routers
other hardware
Tariffs/Link Costs

Advantages:
Disadvantages
Cost

Glossary entries
ASCII 1
asynchronous 1
Basic Rate Interface 6
BRI 6
compressing 1
CSU 8
datagram 1
Dialup 1
DSU 8
dynamic 1
Encapsulation 6
FastPacket 7, 10
internetwork 1
ISDN 6
Link Adapter 6
Local Area Networks 1
Local Exchange Carriers 6
Local Loop 7
MAC 7
MANs 1
modems 1
Permanent Virtual Circuits 7
PPP 1
PSTN 1
PVC 7
routers 1
SLIP 1
SMDS 7
T1 10
tariffs 1
TCP/IP 1
Terminal Adapter 6
V.32 1
V.32bis 1
V.42bis 1



_______________________________
1    Reference to access to host accounts.