Internet-D. co/cl ip over atm
Hiroshi Esaki <hiroshi@ctr.columbia.edu> Thu, 02 March 1995 04:02 UTC
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From: Hiroshi Esaki <hiroshi@ctr.columbia.edu>
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To: rsvp@isi.edu, int-serv@isi.edu, ip-atm@matmos.hpl.hp.com, rolc@maelstrom.timeplex.com, colip-atm@necom830.cc.titech.ac.jp
Subject: Internet-D. co/cl ip over atm
Hi all,
The attached Internet-Draft will be soon put in IETF directry.
We intend to discuss this Internet-Draft at colip-BoF in April
meeting, as one of discussion items.
>> Tuesday, April 4, 1995
>> 1300-1500
>> TSV CO and CL IP Transport over ATM BOF
The proposed architectural framework will be able to work over
all of architectural models discussed in IETF associated with ATM.
Though this proposal is an other alternative for NHRP approach,
this approach will also work for the routers in NHRP-based NBMA
platform.
Regards,
Yasuhiro Katsube
Hiroshi Esaki
(Toshiba Corp.)
----------------- included Internet-Draft -----------------
Internet Draft Yasuhiro Katsube
Ken-ichi Nagami
Hiroshi Esaki
(Toshiba R&D Center)
March 1st, 1995
Router Architecture Extensions for ATM : Overview
<draft-katsube-router-atm-overview-00.txt>
Status of this memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
To learn the current status of any Internet-Draft, please check the
"1id-abstract.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
Abstract
This memo describes new internetworking architecture which makes
better use of the property of ATM. IP datagrams are transferred
along hop-by-hop path via routers similar to the Classical IP Model
[RFC1577], but datagram assembly/disassembly and IP header processing
are not necessarily carried out at individual routers in the proposed
architecture. A concept of "Cell Switch Router (CSR)" is introduced
as a new internetworking equipment, which has ATM cell switching
capabilities in addition to conventional IP datagram forwarding.
CSR can concatenate one incoming VC and another outgoing VC in order
to provide a certain communication with an ATM level connectivity
even when its endpoints do not share a common IP address prefix.
Proposed architecture can provide applications with desired QOS and
as much bandwidth as current ATM switch networks provide while
retaining current router-based internetworking concept. In addition,
it is interoperable with IP level resource reservation protocol such
as RSVP.
Katsube, et al. Expires Sept. 1st, 1995 [Page 1]
Internet Draft March 1st, 1995
1. Introduction
The Internet is growing both in its size and its traffic volume.
In addition, recent applications often require guaranteed bandwidth
and QOS rather than best effort. Such changes make the current
hop-by-hop datagram forwarding paradigm inadequate, then accelerate
investigations on new internetworking architectures.
Roughly two distinct approaches can be seen as possible solutions;
the use of ATM to convey IP datagrams, and the revision of IP to
support flow concept and resource reservation. Both approaches do
not seem to take each other's approach into account although
integration or interworking of them may be necessary to provide end
hosts with high throughput and QOS guaranteed internetworking
services over any datalink platforms as well as ATM.
New internetworking architecture proposed in this draft is based on
"Cell Switch Router" which has the following properties.
- It makes the best use of ATM's property while retaining current
router-based internetworking and routing architecture.
- It takes into account intereoperability with future IP that
supports flow concept and resource reservations.
Section 2 of this draft explains background and motivations of our
proposal. Section 3 describes an overview of the proposed
internetworking architecture and its several remarkable features.
Section 4 discusses various issues which would have close
relationship to the design of the detailed architecture.
2. Backgrounds and Motivations
It is considered that the current hop-by-hop best effort datagram
forwarding paradigm will not be adequate to support future large
scale Internet which accommodates huge amount of traffic with certain
desired quality. Two major schools of investigations can be seen in
IETF whose main purpose is to improve ability of the Internet with
regard to its throughput and QOS. One is to utilize ATM technology
as much as possible, and the other is to introduce the concept of
resource reservation and flow into IP.
1) Utilization of ATM
Although basic properties of ATM; necessity of connection setup,
necessity of traffic contract, etc.; is not necessarily suited to
conventional IP datagram transmission, its excellent throughput and
Katsube, et al. Expires Sept. 1st, 1995 [Page 2]
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delay characteristics let us to investigate the realization of IP
datagram transmission over ATM.
A typical internetworking architecture specified by IETF IPoverATM WG
is "Classical IP Model"[RFC1577]. This model allows direct ATM
connectivities only between nodes that share the same IP address
prefix. IP datagrams should traverse routers whenever they go beyond
IP subnet boundaries even though their source and destination are
accommodated in the same ATM cloud. Although an ATMARP is introduced
which is not based on legacy datalink broadcast but on centralized
ATMARP servers, this model does not require drastic changes to the
legacy internetworking architectures with regard to the IP datagram
forwarding process. This model still has problems of limited
throughput and large latency due to IP header processing at every
router. It will become more critical when multimedia applications
that require much larger bandwidth and smaller latency will become
dominant in the near future.
Another internetworking model is currently under discussion in IETF
ROLC WG[KAT94] and the ATM Forum Multiprotocol-over-ATM SWG. The
model, that we call "NHRP (Next Hop Resolution Protocol) Model" here,
aims at resolving throughput and latency problems in the Classical IP
Model and making the best use of the ability of ATM. ATM connections
can be directly established from an ingress point to an egress point
of an ATM cloud even when they do not share the same IP address
prefix. In order to enable it, the entity of Next Hop Server[KAT94]
(or Route Server) is introduced which can find an egress point of the
ATM cloud nearest to the given destination and resolves its ATM
address. A sort of query/response protocols between the server(s)
and clients and possibly server and server will be specified. After
the ATM address of a desired egress point is resolved, the client
establishes a direct ATM connection to that point through ATM
signaling procedures.[ATM3.1] IP datagram forwarding function and
routing protocol processing function, both of which are provided by
conventional routers, are distributed to the ATM cloud and server(s)
respectively. Once a direct ATM connection has been set up through
this procedure, IP datagrams do not have to experience hop-by-hop IP
processing but can be transmitted over the direct ATM connection.
Therefore, high throughput and low latency communications become
possible even if that go beyond IP subnet boundaries.
In this model, ATM is utilized not only as a datalink function but
also as a replacement of current hop-by-hop IP forwarding function.
However, it should be noted that the provision of such direct ATM
connections does not mean disappearance of legacy routers which
interconnect distinct ATM-based IP subnets. For example, hop-by-hop
IP datagram forwarding function would still be required in the
following cases:
Katsube, et al. Expires Sept. 1st, 1995 [Page 3]
Internet Draft March 1st, 1995
- When you want to transmit IP datagrams before direct ATM connection
from an ingress point to an egress point of the ATM cloud is
established
- When you neither require a certain QOS nor transmit large amount of
IP datagrams for some communication[REK95]
- When the direct ATM connection is not allowed by security or policy
reasons
2) IP level resource reservation and flow support
Apart from investigation on specific datalink technology such as ATM,
resource reservation technologies for desired IP level flows have
been studied and are still under discussion. Their typical examples
are STII[STII] and RSVP[RSVP].
STII is regarded as a connection oriented IP which requires
connection setup process from a sender to a receiver (or receivers)
before transmitting datagrams. STII-capable routers along the path
of the requested connection reserve their resources for datagram
forwarding according to its flow spec.
RSVP itself is not a connection oriented technology since datagrams
can be transmitted regardless of the result of resource reservation
process. After a resource reservation process from a receiver to a
sender (or senders) is successfully completed, RSVP-capable routers
along the path of the flow reserve their resources for datagram
forwarding according to its flow spec.
Neither STII nor RSVP restrict underlying datalink networks since
their primary purpose is to let routers provide each IP flow with
desired forwarding quality (by controlling their datagram scheduling
rules). Since various datalink networks will coexist as well as ATM
datalink in the future, these IP level resource reservation
technologies would be necessary in order to provide end-to-end IP
flow with desired bandwidth and QOS.
Taking these backgrounds into consideration, we should be aware of
several issues which motivate our proposal.
- ATM specific internetworking architecture proposed as NHRP model
[KAT94] does not take into account an interoperability with IP
level resource reservation or connection setup protocols.
Especially emulating RSVP in the NHRP-based ATM cloud seems to
require much effort since RSVP is soft-state, receiver-oriented
Katsube, et al. Expires Sept. 1st, 1995 [Page 4]
Internet Draft March 1st, 1995
protocol.
- Although STII or RSVP-based routers will provide each IP flow with
a desired bandwidth and QOS, they have some native throughput
limitations due to processor-based IP forwarding mechanism compared
with the switching mechanism of ATM.
Main objective of our proposal is to resolve above issues. Proposed
internetworking architecture makes the best use of the property of
ATM by extending legacy routers which can also handle future IP such
as flow support and resource reservation in the future.
3. Internetworking Architecture Based On Cell Switch Router
3.1 Overview
Cell Switch Router (CSR) is a key network element of the proposed
internetworking architecture. The CSR provides cell switching
function in addition to conventional IP datagram forwarding.
Communications with high throughput and small latency, that are
native property of ATM, become possible by using this cell switching
function even when the communications pass through IP subnetwork
boundaries. In an ATM Internet composed of CSRs, VPI/VCI-based cell
switching which bypasses datagram assembly/disassembly and IP header
processing is possible at every CSR for communications which are
worth doing that (e.g., communications which require certain amount
of bandwidth and QOS), while hop-by-hop datagram forwarding based on
IP header is also possible at every CSR for other conventional
communications.
By using such cell-level switching capabilities, the CSR is able to
concatenate incoming and outgoing VPI/VCIs, although the
concatenation in this case is controlled outside the ATM cloud unlike
conventional ATM switch nodes. By carrying out such VPI/VCI
concatenations at multiple CSRs consecutively, native ATM pipe
composed of multiple ATM connections, each of which connects adjacent
CSRs (and CSR and hosts/routers), can be provided. We call such an
ATM pipe "ATM Bypass-pipe" to differentiate it from "ATM VCC (VC
connection)" provided by a single ATM datalink cloud.
Example network configurations based on CSRs are shown in figure 1.
An ATM datalink network may be a large cloud which accommodates
multiple IP subnets X, Y and Z. Or several distinct ATM datalinks
may accommodate single IP subnet X, Y and Z respectively. The latter
configuration is referred as "Conventional Model" in [OHTA94]
[ESAKI94] which would be straightforward in discussing CSR, but CSR
is also applicable to the former configuration as well.
Katsube, et al. Expires Sept. 1st, 1995 [Page 5]
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Two different kinds of ATM VCs are defined between adjacent CSRs or
between CSR and ATM-attached hosts/routers.
1) Default-VC
It is general purpose VC used by any communications which select
conventional hop-by-hop IP processed route. All incoming cells
received from this VC are assembled to IP datagrams and handled based
on their IP headers. VCs set up in the Classical IP Model are
classified into this category.
2) Dedicated-VC
It is used to be concatenated with other Dedicated-VCs and
constitutes ATM Bypass-pipe for certain communications. The number
of Dedicated-VCs necessary between adjacent two nodes is the same as
the number of Bypass-pipes which pass through these nodes.
Ingress/egress nodes of the Bypass-pipe can be either CSRs or ATM-
attached routers/hosts which understand a Bypass-pipe control
protocol. (we call that "Bypass-capable nodes")
On the other hand, intermediate nodes of the Bypass-pipe should be
CSRs since they need to have cell switching capabilities as well as
to understand Bypass-pipe control protocol.
Route for a Bypass-pipe is determined when it is set up based on IP
routing table in each CSR. In figure 1, IP datagrams from source
host or router X.1 to destination host or router Z.1 are transferred
over the route X.1 -> CSR1 -> CSR2 -> Z.1 regardless of whether the
communication is hop-by-hop basis or Bypass-pipe basis. Routes for
individual Dedicated-VCs which constitutes the Bypass-pipe X.1 -->
Z.1 (X.1 -> CSR1, CSR1 -> CSR2, CSR2 -> Z.1) would be determined
based on ATM routing protocol [IISP][PNNI], and would be independent
of IP level routing.
An example of an IP datagram transmission mechanism is as follows.
o The host/router X.1 checks an identifier of each IP datagram,
which may be "destination IP address (prefix)",
"source/destination IP address (prefix) pair", "destination IP
address and port ID", "source IP address and Flow label (in
IPv6)", and so on. Based on either of those identifier, it
determines over which VC the datagram should be transmitted.
o The CSR checks the VPI/VCI value of each incoming cell. When the
mapping from the incoming interface/VPI/VCI to outgoing
interface/VPI/VCI is found in an ATM routing table, it is directly
Katsube, et al. Expires Sept. 1st, 1995 [Page 6]
Internet Draft March 1st, 1995
forwarded to the specified interface through ATM switch module.
When the mapping in not found in the ATM routing table (or the
table shows an IP module as an output interface), the cell is
assembled to an IP datagram then forwarded to an appropriate
outgoing interface/VPI/VCI.
IP subnet X IP subnet Y IP subnet Z
<---------------------> <-----------------> <--------------------->
+-------+ Default +-------+ Default +-------+ Default +-------+
| | -VC | CSR 1 | -VC | CSR 2 | -VC | |
| Host +=============+ +===============+ +=============+ Host |
| X.1 +-------------+++++---------------+++++-------------+ Z.1 |
| +-------------+++++---------------+++++-------------+ |
| +-------------+++++---------------+++++-------------+ |
| |Dedicated | | Dedicated | |Dedicated | |
+-------+ -VCs +-------+ -VCs +-------+ -VCs +-------+
<--------------------------------------------------->
Bypass-pipe
Figure 1 Internetworking Architecture based on CSR
3.2 Features
Main feature of the proposed CSR-based internetworking architecture
is the same as that of NHRP-based architecture in the sense that
they both provide direct ATM level connectivity beyond IP subnet
boundaries. There are, however, several remarkable differences in
the CSR-based architecture from NHRP-based architecture as follows.
1) Relationship between IP routing and ATM routing
In NHRP model, an egress point of the ATM network is first determined
in the next hop resolution phase based on IP level routing
information. Then the actual route for an ATM-VC to the obtained
egress point is determined in the ATM connection setup phase based on
ATM level routing information. Both kinds of routing information
would be calculated according to factors such as network topology and
available bandwidth for the large ATM cloud. The ATM routing will be
based on IISP[IISP] or PNNI phase1[PNNI] while the IP routing will be
based on conventional one such as OSPF/BGP. We need to manage two
Katsube, et al. Expires Sept. 1st, 1995 [Page 7]
Internet Draft March 1st, 1995
different routing protocols over the large ATM cloud until
Integtrated-PNNI[IPNNI] which takes both ATM level metric and IP
level metric into account will be phased in.
In CSR model, IP level routing determines an egress point of the ATM
cloud as well as determines inter-subnet level path to the point that
shows which CSRs it should pass through. ATM level routing
determines intra-subnet level path for ATM-VCs (both Dedicated-VC and
Default-VC) only between adjacent nodes (CSRs or ATM-attached
hosts/routers). Since roles of routing are hierarchically subdevided
into IP level (router level) and ATM level (ATM SW level), ATM
routing does not have to manage all over the ATM cloud but only
individual IP subnets independent from each other. This will
decrease the amount of information for ATM routing protocol handling.
2) Dynamic routing and redundancy support
CSR-based network can dynamically change routes for Bypass-pipes when
related IP level routing information changes. Ingress points of
these Bypass-pipes (ATM-attached sender hosts or routers) do not have
to be aware of such dynamic change of routes since CSRs related to IP
routing changes can follow them and change routes for related Bypass-
pipes by themselves.
The same things apply when some error or outage happens in any ATM
nodes/links/routers on the route of a Bypass-pipe. CSRs that have
noticed such error or outage would change routes for related Bypass-
pipes by themselves.
3) Support of hard-state and soft-state control
Although direct ATM-VCs in NHRP model are controlled by ATM signaling
which is hard-state protocol, Bypass-pipes provided by CSR-based
network are controlled by dedicated protocols which can be both
hard-state and soft-state. A motivation of the support of soft-state
in Bypass-pipe control is an interworking with RSVP protocol.
Soft-state protocol will be much more suited to the realization of
dynamic routing described in 2).
4) Support of sender-initiated and receiver-initiated control
Although setup of direct ATM-VCs in NHRP model is sender-initiated
only, setup of Bypass-pipes in CSR model can be either sender-
initiated or receiver-initiated. Detailed procedures for receiver-
initiated protocol will be designed to handle RSVP messages.
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4. Discussions for Designing Detailed Architecture
Several issues that need further investigations in order to design
detailed architecture are discussed in this section.
4.1 Network Reference Model
In order to help understanding discussions in this section, the
following network reference model are assumed. Source hosts S1, S2,
and destination hosts D1, D2 are attached to Ethernet, while S3 and
D3 are attached to ATM. Routers R1 and R5 are attached to Ethernet
only, while R2, R3 and R4 are attached to ATM. ATM datalink for
subnet #3 and subnet #4 can either be physically separated datalinks
or be the same datalink.
Bypass-pipes can be set up [S3 or R2]-->R3-->[D3 or R4]. That means
that S3, D3, R2, R3 and R4 need to speak Bypass-pipe control protocol
described later, and means that R3 needs to be a CSR. We use term
"Bypass-capable nodes" for hosts/routers which can speak Bypass-pipe
control protocol but are not necessarily CSRs.
As shown in this reference model, Bypass-pipe can be set up from host
to host (S3-->R3-->D3), router to host (R2-->R3-->D3), host to router
(S3-->R3-->R4), and router to router (R2-->R3-->R4).
Ether Ether ATM ATM Ether Ether
| | +-----+ +-----+ | |
| | | | | | | |
S1--| S2---| S3---| | | |---D3 |---D2 |--D1
| | | | | | | |
|---R1---|---R2---| |--R3--| |---R4---|---R5---|
| | | | | | | |
| | +-----+ +-----+ | |
subnet subnet subnet subnet subnet subnet
#1 #2 #3 #4 #5 #6
Figure 2 Network Reference Model
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4.2 Ways of Providing Dedicated-VCs
There are roughly three alternatives regarding the way of providing
Dedicated-VCs in individual IP subnets as components of a Bypass-
pipe.
a) On-demand SVC setup
Dedicated-VCs are set up in individual IP subnets each time you want
to set up a Bypass-pipe through the ATM signaling procedure. Each
Dedicated-VC is released when the corresponding Bypass-pipe is
released.
b) Picking up one from a bunch of (semi-)PVCs
Several Dedicated-VCs are set up beforehand between CSR and CSR, or
CSR and other ATM-attached nodes (hosts/router) in each IP subnet.
Unused VC is picked up as a Dedicated-VC from these PVCs in each IP
subnet when a Bypass-pipe is set up. A sort of "Unused VC list" will
be managed by a peer nodes which share these PVCs.
c) Picking up one VCI in PVP/SVP
A PVPs or SVPs are set up between CSR and CSR, or CSR and other ATM-
attached nodes (hosts/routers) in each IP subnet. PVPs would be set
up as a kind of router/host initialization procedure, while SVPs, on
the other hand, would be set up through ATM signaling when the first
VC (either Default- or Dedicated-) setup request is initiated by
either of some peer nodes. Then, Unused VCI value is picked up as a
Dedicated-VC in the PVP/SVP in each IP subnet when a Bypass-pipe is
set up. A sort of "Unused VC list" will be managed by the peer nodes
which share the PVP/SVP. The SVP can be released through ATM
signaling when no VCI value is active state. That may require some
revision to RFC1577.
The best choice will be a) with regard to efficient network resource
usage. However, you may go through three steps, ATMARP (in each IP
subnet), SVC setup (in each IP subnet) and Bypass-pipe setup in this
case. Whether a) is practical choice or not will depend on whether
you can allow larger Bypass-pipe setup time due to three-step
procedure mentioned above, or whether you can send datagrams over
Default-VCs in a hop-by-hop manner while waiting for Bypass-pipe set
up.
In the case of b) or c), the issue of Bypass-pipe setup time will be
improved since SVC setup step can be skipped. In b), each node (CSR
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or ATM-attached host/router) should specify some traffic descriptors
even for unused VCs, and the ATM datalink should reserve its resired
resource (such as VCI value and bandwidth) for them. In addition,
the ATM datalink may have to carry out UPC functions for those unused
VCs. In c), on the other hand, traffic descriptors which should be
specified by each node for the ATM datalink is not each VC's but VP's
only. Resource reservations for individual VCs will be carried out
not as a function of the ATM datalink but of each CSR or ATM-attached
host/router if necessary. Only function which need to be provided by
the ATM datalink is control of VPs' bandwidth such as UPC and dynamic
bandwidth negotiation if necessary.
As a result of the above observations, we will implement c) as a
preliminary protocol specification, but may add a) in the future
version if it is desirable.
4.3 Channels for Bypass-pipe Control Message Transfer
There are several alternatives regarding the protocol for managing
(setting up and releasing) a Bypass-pipe. This subsection explains
these alternatives and discusses their properties from various
viewpoints.
Among alternatives of how to provide Dedicated-VCs described in 4.2,
"picking up an unused VCI in PVP/SVP" is assumed. When we use "on-
demand SVC setup", Dedicated-VC setup in each subnet through ATM
signaling (and possibly ATMARP before that) will be added to the
following procedures. An alternative described in iii), however,
investigates a possibility of managing Bypass-pipes by only extending
ATM signaling messages, and of excluding the necessity of additional
control messages.
Three alternatives are discussed, Inband message protocol, Outband
message protocol, and ATM signaling extension.
i) Inband Control Message
When setting up a Bypass-pipe, control messages are transmitted over
an unused Dedicated-VC which will eventually be used as a component
of the Bypass-pipe. These messages are handled at each CSR and
forwarded over an unused Dedicated-VC along the selected route
(based on IP routing table) for the requested Bypass-pipe. Unlike
outband message protocol described in ii), each message does not have
to indicate VCI value used as a Dedicated-VC since the message itself
is carried by that VC. That leads to a possibility that existing
messages such as STII, RSVP, or NHRP messages itself can be utilized
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as a Bypass-pipe control message with no modification. However,
there are following shortcomings;
- Bypass-pipe control messages transmitted after a Bypass-pipe has
been set up (e.g., Bypass-pipe release) cannot be identified at
intermediate CSRs since those messages are forwarded at cell level
there.
- Bypass-incapable routers (routers which does not understand Bypass-
pipe control protocol) would not receive and process cells
transmitted over "unknown VCI". That means that Bypass-pipe
management massages will be discarded by Bypass-incapable routers.
We can manage to find solutions for the former issue. That is,
intermediate CSRs can identify Bypass-pipe control messages by
marking cell headers, e.g., PTI bit on indicating F5 OAM cell. It
would be difficult, however, to find solutions for the latter issue.
As a result of these observations, Inband message will not be
adequate as a Bypass-pipe control.
ii) Outband Control Message
When both setting up and releasing a Bypass-pipe, control messages
are transmitted over VCs which are different from Dedicated-VCs used
as components of the Bypass-pipe. Although each message has to
indicate VCI value used as a Dedicated-VC, which means that STII or
RSVP messages received from conventional routers/hosts cannot be
utilized as a Bypass-pipe control messages as they are, the
shortcomings in inband case do not exist.
Three alternatives are possible regarding how to convey Bypass-pipe
control messages hop-by-hop over ATM datalink networks.
1) Defines VC for Bypass-pipe control messages only.
2) Uses Default-VC and discriminates Bypass-pipe control messages
from user datagrams by an LLC/SANP value in RFC1483 encapsulation.
3) Uses Default-VC and discriminates Bypass-pipe control messages
from user datagrams by a protocol field value in IP header.
When we take into account interoperability with Bypass-incapable
routers, 1) will not be a good choice. Whether we select 2) or 3)
depends on whether we should consider multiprotocol rather than IP
only. We select 3) as a preliminary protocol specification.
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iii) Use of ATM Signaling Message
Supposing that ATM signaling messages can convey IP addresses (and
possibly port IDs) of source and destination, it may be possible that
ATM signaling messages be used as Bypass-pipe control messages also.
In that case, an ATM Call Setup message indicates a setup of a
Dedicated-VC to an ATM address of a desirable next-hop IP node, and
also indicates a setup of a Bypass-pipe to an IP address (and
possibly port ID) of a target destination node. Information elements
for the Dedicated-VC setup (ATM address of a next-hop node,
bandwidth, QOS, etc.) are handled at ATM nodes, while information
elements for the Bypass-pipe setup (source and destination IP
addresses, and possibly their port IDs, etc.) are transparently
transferred to the next-hop IP node. The next-hop IP node accepts
Dedicated-VC setup and handles such IP level information elements.
Then it transmits an ATM signaling message to the ATM network in
order to forward Bypass-pipe setup request to the next-hop IP node as
well as to request Dedicated-VC setup to that.
Examples of Bypass-pipe setup procedure are shown in figure 3.
ATM ATM
+----------+ +----------+
| | | |
S3---| ATM-SW | | ATM-SW |---D3
| |X| | | |X| |
---R2---| |----R3----| |---R4---
+----------+ +----------+
subnet subnet
#3 #4
Setup Setup Setup Setup
(S3-R3) (S3-R3) (R3-D3) (R3-D3)
(Trg)|------>|-|------>|---|------>|-|------>|
|<------|-|-------|---|<------|-|-------|
Conn Conn Conn Conn
Setup Setup Setup Setup
(S3-R3) (S3-R3) (R3-D3) (R3-D3)
(Trg)|------>|-|------>|-+-|------>|-|------>|
|<------|-|-------|-+ |<------|-|-------|
Conn Conn Conn Conn
(Trg) : Trigger event for
Bypass-pipe setup
Figure 3 Use of ATM Signaling Messages
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A difference of the two examples is whether a CONNECT message means
confirmation of Bypass-pipe setup or confirmation of Dedicated-VC
setup. The problems of this method are,
- Information elements which specify IP level (and port level)
information need to be defined, e.g., B-HLI or B-UUI, as an ATM
signaling standard.
- It would be difficult to support soft-state operation since ATM
signaling is naturally a hard-state protocol.
As a result of above observations, we will select ii) as a
preliminary protocol specification, while the possibility of iii)
will be further study issue.
4.4 Triggers for Bypass-pipe Setup/Release
This subsection discusses several possible events which triggers a
node to set up or release a Bypass-pipe.
4.4.1 Triggers for Bypass-pipe Setup
As of now, following two cases should be taken into account as
triggers for Bypass-pipe setup.
1) Request by IP layer or upper layers of an end host
2) Decision by a Bypass-capable router based on the measurement of IP
datagrams transmitted.
The case 1) is further classified into the cases in which the request
is initiated by a sender-host or a receiver-host, and the cases in
which the request is initiated by a Bypass-capable host or a Bypass-
incapable host. Therefore we should take the following four cases
into account. (see figure 2)
1-1) Request by Bypass-capable sender-host (S3)
1-2) Request by Bypass-incapable sender-host (S1, S2)
1-3) Request by Bypass-capable receiver-host (D3)
1-4) Request by Bypass-incapable receiver-host (D1, D2)
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For simplicity, we mean that the Bypass-(in)capable node is equal to
ATM-(non)attached node in figure 2, but there may be the case that an
ATM-attached node does not support Bypass-pipe control protocol.
In the case of 1-1) or 1-3), sender-host(S3) or receiver-host(D3)
itself executes Bypass-pipe setup protocol. IP layer or upper layers
in S3 or D3 requests Bypass-pipe setup to its own Bypass management
entity directly, or via other QOS/Resource management entity such as
STII (in the case of sender-host) or RSVP (in the case of receiver-
host). Resulting Bypass-pipe will finally be S3-->R3-->D3 in this
case.
In the case of 1-2) or 1-4), neither sender-host(S1, S2) nor
receiver-host (D1, D2) has Bypass management entity. IP layer or
upper layers in S1/S2 or D1/D2 requests resource reservation to its
own QOS/Resource management entity such as STII or RSVP. Then it
transmits IP level resource reservation messages over whatever
datalink network (Ethernet in figure 2). A Bypass-capable router R2
or R4 which has received those messages either translates those IP
level resource reservation messages to Bypass-pipe control messages
or encapsulates those messages in Bypass-pipe control messages. In
any case, Bypass-pipe management entities in R2 or R4 initiates
Bypass-pipe setup procedures triggered by IP level resource
management messages from S1/S2 or D1/D2. Resulting Bypass-pipe will
finally be R2-->R3-->R4 in this case.
In the case of 2), a Bypass-capable router R2 initiates Bypass-pipe
setup procedures with its own decision based on the measurement of IP
datagrams transmitted toward a certain destination host or network.
Unlike case 1), the purpose of setting up Bypass-pipe in case 2) is
to reduce IP processing burden at intermediate CSRs rather than to
provide end hosts or applications with desired bandwidth/QOS. For
example, when R2 detects large amount of datagrams bound for IP
subnet #6, it may initiates Bypass-pipe setup with its destination
set to subnet#6. Resulting Bypass-pipe will finally be R2-->R3-->R4
in this case. Whether the use of this Bypass-pipe is limited to the
communication destined to subnet#6 or is open to communications
destined to other networks (e.g., subnet#5) depends on whether the
information about the Bypass-pipe is advertized as a routing
information, and requires further study.
4.4.2 Triggers for Bypass-pipe Release
The same items as the case of Bypass-pipe setup applies to Bypass-
pipe release, 1) and 2). However, 1) will have variations of whether
IP level resource reservation protocol which is running in Bypass-
incapable hosts is hard-state (STII) or soft-state (RSVP). Bypass-
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pipe release can be initiated at R2 or R4 by the reception of
explicit IP level resource release messages in both cases, and by the
detection of "no resource keep message" for a predetermined timeout
period in the case of soft-state. Detailed discussion will be given
later.
It should be noted that the trigger for setup/release of Bypass-pipe
is not limited to examples given in this subsection although we
assume them in specifying version 1 protocol. Actual Bypass-pipe
control protocol, therefore, should not be dependent on what the
trigger is.
4.5 Bypass-pipe Control Protocol
It is desirable that the Bypass-pipe can be set up in response to
triggers at least described in 4.4. That is, a Bypass-capable node
(host or router) should initiate Bypass-pipe setup when,
- It (router) has received IP level resource reservation messages
from its upstream (e.g., STII) or downstream (e.g., RSVP) node.
[1-2) or 1-4) in 4.4]
- It (host) has received IP level resource reservation primitives
from its own IP level resource reservation entities such as STII
or RSVP.
[1-1) or 1-3) in 4.4]
- It (router) has decided to set up a Bypass-pipe for a
communication to a certain host or network based on the result of
IP level traffic measurement.
[2) in 4.4]
Taking them into account, the protocol should be designed to support
- both hard-state (STII) and soft-state (RSVP) control
- both sender-initiated (STII) and receiver-initiated (RSVP) control
Since currently available IP level protocols are sender-initiated
hard-state (STII) and receiver-initiated soft-state (RSVP), we
investigate brief examples of those two as a preliminary protocol
specification.
4.5.1 Sender-Initiated Hard-State Control
Examples of sender-initiated hard-state control protocol are shown in
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figure 4. A Bypass-capable node (R2 or S3) which has been triggered
by an upstream node (S1 or S2) or by an internal entity (S3)
transmits a Bypass-pipe setup message (BP-Setup) toward target
destination node which may or may not be Bypass-capable.
BP-Setup includes at least target host or network address, identifier
of a Bypass-pipe which is being set up, identifier of a Dedicated-VC
which is being used as a component of the Bypass-pipe, and desirable
bandwidth. A node which has received BP-Setup from the previous node
obtains next-hop node based on IP routing table, decides whether
requested bandwidth is available to the obtained node, and picks up
an available Dedicated-VC to the node when the bandwidth is
available. Then it transmits BP-Setup to the next-hop node over a
Default-VC. This procedure is repeated all the way to the target
node until whether the BP-Setup reaches the target node or some
intermediate node recognizes that it cannot extend Bypass-pipe
anymore (e.g., by the policy restriction or bandwidth shortage).
Such a node creates a Bypass-pipe setup ack message (BP-SetupAck)
over the reverse route toward the requesting node. Bypass-pipe setup
procedure completes when the BP-SetupAck has returned to the
requesting node.
ATM ATM
+---------+ +---------+
| | | |
S3---| | | |---D3
| | | |
---R2---| |---R3---| |---R4---
| | | |
+---------+ +---------+
subnet subnet
#3 #4
[Setup] BP-Setup BP-Setup
(Trg)|-------------->|--|-------------->|
|<--------------|--|<--------------|
BP-SetupAck BP-SetupAck
[Release] BP-Release BP-Release
(Trg)|-------------->| |-------------->|
|<--------------| |<--------------|
BP-RelAck BP-RelAck
(Trg): Trigger event for
Bypass-pipe setup
Figure 4 Sender-Initiated Hard-State Control
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With regard to Bypass-pipe release, BP-Release message is issued by
either of nodes on the route of the Bypass-pipe by its own trigger or
by the indirect trigger (e.g., the reception of STII Disconnect from
Bypass-incapable host which uses the Bypass-pipe).
4.5.2 Receiver-Initiated Soft-State Control
Examples of receiver-initiated soft-state control protocol are shown
in figure 5. In soft-state, sender node periodically transmits Path
messages (BP-Path) over the Default-VC forward along the route
specified by the IP routing table. These BP-Path messages are
necessary in order that the resource reservation messages (BP-Resv)
transmitted by the receiver node are routed in the reverse direction
toward the sender node.
A Bypass-capable node which has been triggered by a downstream node
or by an its internal entity transmits a resource reservation message
(BP-Resv) toward the sender node along the reverse route given by the
BP-Path.
Contents of the BP-Resv message will be the same as that of the RSVP
Resv message with the addition of Bypass-pipe specific information
such as an identifier of a Dedicated-VC which is being used as a
component of the Bypass-pipe. A node which has received BP-Resv from
the downstream node obtains previous-hop node based on the Path state
given by the BP-Path messages, decides whether requested bandwidth to
the previous node is available, and picks up an available Dedicated-
VC to that node. Then it transmits the BP-Resv to that node over a
Default-VC. This procedure is repeated all the way to the sender
node. If the BP-Resv message fails to be transmitted at an
intermediate node, that node would become an ingress point of the
Bypass-pipe or send back an error message.
After setting up a Bypass-pipe, the sender node still continues to
send BP-Path messages, and the receiver node continues to send BP-
Resv messages periodically. When individual nodes along the Bypass-
pipe route have not received BP-Resv messages for a predetermined
timeout period, they would decide that the Bypass-pipe can be
released. The Bypass-pipe can be released by an explicit Teardown
message as well as the above-mentioned timeout-based release.
When some IP routing change happens to nodes related to a Bypass-
pipe, BP-Path messages will be automatically transferred along the
new route. BP-Resv messages from the receiver node then will be sent
back along the new route, that will lead to removal of the Bypass-
pipe from old route and creation of the Bypass-pipe over the new
route.
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ATM ATM
+---------+ +---------+
| | | |
S3---| | | |---D3
| | | |
---R2---| |---R3---| |---R4---
| | | |
+---------+ +---------+
subnet subnet
#3 #4
[Setup] BP-Path BP-Path
|-------------->|--|-------------->|
|<--------------|--|<--------------|(Trg)
| BP-Resv | | BP-Resv |
| | | |
%%% Communications over Bypass-pipe %%%
[Keep] | | | |
| BP-Path | | BP-Path |
|-------------->|--|-------------->|
|<--------------|--|<--------------|
| BP-Resv | | BP-Resv |
(Trg): Trigger event for
Bypass-pipe setup
Figure 5 Receiver-Initiated Soft-State Control
5. Security Considerations
Security issues are not discussed in this memo.
6. Open Issues
o Detailed protocol sequences and proposed message formats.
It should be interoperable with conventional IP level resource
management protocols such as STII and RSVP.
o Mapping of IP level filter specs to ATM cell level control
mechanisms, especially in multicast cases.
o Do we support any combination of both hard-state/soft-state and
sender-initiated/receiver-initiation control?
o Support of source route option on the CSR-based network.
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7. References
[ATM3.1] The ATM-Forum, "ATM User-Network Interface Specification,
v.3.1", Sept. 1994.
[ESAKI94] H. Esaki, et al., "Connection Oriented and Connectionless
IP Forwarding over ATM Networks", IETF Internet Draft (work in
progress), draft-esaki-co-cl-ip-forw-atm-01.txt, Oct. 1994.
[IISP] The ATM-Forum, "Interim Inter-switch Signaling Protocol (IISP)
Protocol Specification, Version 1.0", Dec. 1994.
[IPNNI] R. Callon, "Integrated PNNI for Multi-Protocol Routing", The
ATM Forum Contribution No. 94-0789, Sept. 1994.
[KAT94] D. Katz and D. Piscitello, "NBMA Next Hop Resolution
Protocol(NHRP)", IETF Internet Draft (work in progress), draft-ietf-
rolc-nhrp-03.txt, Nov. 1994.
[OHTA94] M. Ohta, et al., "Conventional IP over ATM", IETF Internet
Draft (work in progress), draft-ohta-ip--over-atm-01.txt, July 1994.
[PNNI] The ATM-Forum, "P-NNI Draft Specification R5", Jan. 1995.
[REK95] Y. Rekhter and D. Kandlur, "IP Architecture Extensions over
ATM", IETF Internet Draft (work in progress), draft-rekhter-ip-atm-
architecture.txt, Jan. 1995.
[RFC1483] J. Heinanen, "Multiprotocol Encapsulation over ATM
Adaptation Layer 5", IETF RFC 1483, July 1993.
[RFC1577] M. Laubach, "Classical IP and ARP over ATM", IETF RFC 1577,
Oct. 1993.
[RSVP] L. Zhang, et al., "Resource ReSerVation Protocol (RSVP),
Version 1 Functional Specification", IETF Internet Draft (work in
progress), draft-ietf-rsvp-spec-04.ps, Nov. 1994.
[STII] L. Delgrossi and L. Berger, "Internet STream Protocol Version
2(STII)", Internet Draft (work in progress),
draft-ietf-st2-spec-02.ps, Feb. 1995.
8. Authors' Address
Yasuhiro Katsube
R&D Center, Toshiba
1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210
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Japan
Phone : +81-44-549-2238
Email : katsube@isl.rdc.toshiba.co.jp
Ken-ichi Nagami
R&D Center, Toshiba
1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210
Japan
Phone : +81-44-549-2238
Email : nagami@isl.rdc.toshiba.co.jp
Hiroshi Esaki
R&D Center, Toshiba
801 Schapiro Research Building, c/o CTR, Columbia Univ.
530 West, 120th St., New York, NY 10027
Phone : 212-854-2365
Email : hiroshi@ctr.columbia.edu
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- Internet-D. co/cl ip over atm Hiroshi Esaki