VIP: A Protocol Providing Host Mobility

41 Pages·1994·1.8 MB·English

by  Teraoka, F., Uehara, K., Sunahara, H., Murai, J.

Fumio Teraoka, Keisuke Uehara, Hideki Sunahara, and Jun Murai
VIP: A Protocol
Providing Host Mobility
Computer networks such as the This article proposes a protocol transparency in the application layer,
Imi'iiK'i have spread worldwide, that provides host mobility in the the transport layer, or the network
(.ompuiers are getting smaller and Internet, VIP (Virtual Internet Proto- layer. In case oflhe application layer
smaller. Such an environment rol). In contrast lo oilier schemes, approach, name server emries Im¬
allows users to carry portable com¬ VIP introduces logical identifiers im¬ migrating hosts are updated every
puters and use them to access net¬ mobile hosts. VIP was first proposed movement. A host that wants to coui-
works. "Mobile Computing" has in 1991 [18. 14] anti improved in niuuicate with a migrating host
become a buzzword in the area of 1998 [15]. VIP is defined as an in¬ knows the destination address by ac¬
computer communications. A vital stance of the Virtual Network Protocol, a cessing die name server. In this ap¬
issue in the Held of mobile comput¬ network layer protocol that provides proach, however, on-line migration
ing is how to communicate with the transport layer with host migra¬ cannot be achieved because commu¬
hosts that move between subnet¬ tion transparency anti which is appli¬ nication channels are broken after
works.' In conventional network cable to any connectionless-mode movement.
architectures such as TCP/IP and network protocol such as IP [7], In case of the transport layer ap¬
the OSI seven-layer model, the net¬ CLNP [5], and Xerox Internet Data¬ proach. the transport layer reestab¬
work address of a host denotes its gram [17], VIP has the following fea¬ lishes communication channels every
identification as well as its location. tures (discussed later): movement with the assistance of the
Since host migration results in a application layer approach. In this
• VIP is scalable lo the scale of the
change of its network address, net¬ network anti the total number of approach, if a host detects its move¬
work addresses returned by name mobile hosts. ment. it notifies corresponding hosts
servers cannot identify migrating • VIP is free from routing loops with of its new network address, and then
hosts. Additionally, communication all packets, except for the lirsi packet, the communication channels between
channels cannot be preserved after traversing the optimum route, and these hosts are reestablished. In gen¬
migration. eral, communication channel man¬
• VIP is also tolerant ol the loss of
There are several candidate proto¬ control packets. agement is complicated. This ap¬
cols for supporting host mobility in proach makes ii more complicated,
the Internet [4. 8, 10, 16]. In addition The Key Services for Host besides the overhead of this ap¬
to the schemes for the Internet, a Migration Transparency proach increases in proportion to the
scheme is proposed for ISO CLNP Types of Host Migration number of active communication
(Connectionless-mode Network Pro¬ Host migration can be classified into channels. Additionally, this approach
tocol) networks [2], while another two types: off-line and on-line. In on¬ cannot provide host migration
scheme uses learning bridges [9]. line migration, the host is discon¬ transparency in connectionless
Packet radio networks also support nected from the network before mov¬ communication.
host mobility otflj^wjthiiV a subnet¬ ing. In contrast, on-line migration al¬ In contrast with these approaches,
work [6]. However/tfiftse protocols all lows a host to access die network even adding only two new services to the
suffer various problems, e-g-. [4] an£^ during actual movement. In conven¬ network layer allows host migration
[9] cannot scale to the size of the net¬ tional wiled networks, only oil-line transparency as described later. From
work: network partitioning might migration is possible due to physical a protocol-layering viewpoint, it is
disable communications between two restrictions. However, wireless net¬ suitable that the network layer pro¬
hosts on the same Ethernet when at works such as digital cellular tele¬ vides host migration transparency
least one of the hosts is mobile in [16]; phone systems allow on-line migra¬ because it is responsible to host-to-
the schemes proposed in [8] and [10] tion. In this ariicle, hosts that can host communication. In other words,
cannot be applied to datagram com¬ migrate on-line are called mobile hosts, the transport and higher layers do
munication in the transport layer. while those that can migrate off-line not perceive the notion of host, and it
Also, a fundamental problem of these only are called portable hosts. The gen¬ is up to the network layer to inaimaiii
schemes is the requirement for a net¬ eral term migrating host is used to de¬ host location.
work address to identify the location
note these two host types.
of mobile hosts. _ Key Services in the Network Layer
11» lliis uilicit, u network rders lo >he overallnet" The Layer To Provide Host Migration End-to-end communication services
work. A \nlmeaoork rders to an individual conl- Transparency are provided by the transport and
ponem network. An oiternel rders m a nctwor
From a user's viewpoint, it can be lower lavers. To offer host migration
on whir It Inicmel Protocol (IP) is running as a
nelwoik hitit [trolmol. possible to adiieve host migration transparency in end-to-end commu-
mention services, die billowing four are supported bs N-l. N-2. N-ll. and matter where the program is located
services ill ilie transport liner mnsi be N-f). 1-4 is supported bs N-2, N-4. in physical memory. .Similarly. a host
t
migration transparent. anti N-6. can Ik- indicated by its VN-address no
In the network laser. N-‘.f through mailer where the host migrates in die
• Cl'-!) iranspori eniiiy addressing.
N-C> are supported by the data link physical network. From another
The iranspori layer mnsi provide die r
layer. Therefore. N-l and N-2. i.e., viewpoint, the virtual network con¬
session layer wiili a migration-inde¬
migration Irnnsjiarrut host addressing cept introduces host identifiers in addi¬
pendent idemilier lor die iranspori
and niigratmn-trausfuirrut connection¬ tion to host addresses. The host iden¬
eniiiy.
less-mode communication. are peculiar tifier specifies "what it is," whereas t
• (T-2) tonneciionless-niode conimu-
to the netsvork layer and can be die host address specifies “where it
nicalion. The irans|)on layer inusi
thought of as being key services in is."
provide iranspori-level cnnneciioii-
achieving host migration transpar¬ Layering. Since die iranspori layer i
less-mode communication (datagram i
ency. Ihe relationships beisveen uses die VN-address in the packet
service), regardless of migration.
these services are depicted in figure transmission request to die network
• (T-b) eonneciion esiablislnneni.
I [II]. lay er, lo deliver packets, the network
The iranspori layer mnsi be able 10
layer must resolve the VN-address of
establish transpori-level connections,
The Virtual Network a host into the corresponding I’N-
regardless of migration.
The previous section defined two nct- address. The network layer is respon¬
• (1—4) connection-oriented commu¬
svork layer services that are key to sible for host-to-host eonnimnicaiion,
nication. The iranspori laser must be
liosi inobilitv: 1) migration-transpar¬ including packet relaving, routing
able lo preserve iranspori-lcvel com¬
ent host addressing and 2) migiaiion- control, and so on. Since it is not ap¬
munication during actual moveineni,
t runs parent eonneciion less-mode propriate tu classify this address reso¬
ollcring irans|iori-level connection-
coininunicaiion. In order lo achieve lution into the traditional categories
orienlecl eonnimnicaiion.
llic former, the concept of a virtual of basic network layer fin id ions, die
Oil-line migration transparency, network is iiuroduced. To achieve the network layer should be divided iiuii
which mnsi be provided lo boili pori- latter, the propagating-cochc method is two snblavers. as follows (see Figure
able and mobile liosls, can be sup¬ proposed. 2):
ported by services '/'-/ through T-j. The concept. The virtual network is
• The virtual artwork sublayer (l '.V-
On-line migration transparency, re¬ a logical netsvork that exists on top of
sidiluyrr) conceals the physical location
quired by mobile hosts, requires all the actual, or physical, network. Only
o( hosts in die phvsical subnetworks.
four services. die virtual neisvork is visible to die
A host is assigned a VN-address.
To support these services in the iranspori layer, bach host is regarded
which tile VN-snblaycr resolves into
iranspori layer, die network layer as ulsvnvs being connected lo die
the corresponding I’N-address.
must have the hollowing six services. same virtual subnetwork, called die
• The physical artwork sublayer fl’iV-
home subnetwork of the host even il it
• (A’-/) Migralioa-traasjaireat host tul- suhlayrr) is the conventional network
migrates to another physical .subnet¬
drrssiug: provides die transport laser laser. According to the OSI layering
work. A host has both a virtual network
with a migration-independent idenii- model, this sublayer consists of die
address (I A ’-address) and a physitai net-
lier Ibr die host. snbuei work-independent suhlavcr.
work address tl’X-addiess). Since a host
• t.X-2) Migratioa-trua\p(ireut roaaee- the subnetwork-depending sublayer,
never migrates in the virtual net¬
tioaless-auule roanuaidcatioa: oilers uel- and the subnetwork access sublayer.
work. iis VN-address never changes.
svork-level connectionless-mode com¬ The 1’N-sublaver is responsible Ibr
The I’N-athiress of a host indicates
munication regardless of migration. packet relaving, routing iulnriuaiiou
the location of the host in the phvsiea!
• (A'-j) Disconnect request: prepares exchange, and so on. A host is as¬
network and is used for packet rout¬
lor a host to leave a subnetwork when signed a l’N-address in the l’N-
ing. The iranspori layer specifics the
it is to be disconnected. snblayer.
target host bv its YN-address, no mai¬
• (A---/) Disconnect indication: called by
ler where it migrates to in the physi¬ This protocol layering a fleets die
the data link layer to prej>aflcu> lease
cal network, basically, the l’N- packet header formal. According lo
die current subnetworkemer
address is invisible to tile transport this division..the- VN-sublavcr header
another in on-line migration;..
layer. The VN-address and l’N- is added'between the (physical) net¬
• (X-5) Conner! request: prepares lor
address have the same formal. For a work laser and iranspori layer head¬ i
joining to a subnetwork svhen a host
host, the tallies of both addresses are ers. if the (physical) network layer
is 10 be connected.
the same when the host is connected header of an incoming packet speci¬
• f.V-fi) Cunnrrl indication: called by
to its home subnetwork. fies the VN-sublaver as the next i
the data link layer lo prepare lbr join¬
The relationship between the VN- higher layer, the packet is passed to
ing a host lo anew subnetwork in on¬
address and the I’N-address of a host the VN-sublayer. Otherwise, the
line migration.
is analogous to that between the vir¬ packet bypasses the VN-sublayer and
The services required in tile trans¬ tual and physical addresses in a vir¬ is passed to tile transport lay er. Thus, i
port layer are supported by the ser¬ tual memory system. In a virtual the VN-sublayer can be bypassed if
vices in the netsvork layer as follows: memory system, the virtual address ;m incoming packet does not have the
T-l is supported by N-I. T-2 and T-.S used in a program never changes, no VN-sublayer header, or if the receiv-
68
AugUll lt*t>4/Vi,1.37. Nu.B COMMUNICATIONS OP VMli JtCM
ncd
jjBpBB35BBBB8S85SI
iio.st
.
s MO off-line':.. " on-line -
; die tisnan&xwtm J-c tramnisgpraartieonnc ~y I _■nuynjMT_OS!g! :sasss*i ^?StaSunai^nig^igW>gff«igm™amg 1 tramnisgpraartieonnc y
diei* ' J rt»» if application level^
Dll-
♦atesEWffl^Ks&a
ddi-
len-
1__ WWggggwf-
tVilS mig. tret nsprnt. -mig.transprnt.^ mig. tra nsprnt. • -.mig. tra: nsprnt-
■e it transpci rt entity conn.iess comm. conn, e stablish conn, c iomm. -
addret ssing
iver transport level
ker 5
A.
ork
< >rk
*> oI‘ mig. transprnt. mig. transprnt disconn. disconn. CO nn. conn.
host addr conn.iess comm. request Ind." req nest ind.
i **-y- i/V
• >11- t
on, Concept of a * ^ Propagating _
:l\£ Virtual Network 13B Cache Method
*I>"
M )-
ies
'^ipipgi^..
lie
ito
ire
Figure i. Relationships between services
ing host does not support the VN-
stibliiver and silently ignores the VN-
.V-
<»n stihlaver header.
ks.
The Propagating-Cache Method Transport Layer . Transport Layer
'VS,
Tile basic idea of the propagating-
no Virtual Network Sublayer
cache method takes advantage of a _ Network Laver.l’fgT
V- cache mechanism for address resolu¬ Physical Network Sublayer
rk tion, i.e., each router or host holds a v*£z Data Link Layer^^l Data Link Layer
cache for address resolution. Address
]kr
resolution is executed either on the ... .... ..
IC
source host or an intermediate ‘^SfePhysicaitay^^» Physical Layer
•r,
T. router. If the source host does not
•r. know the I’N-address of the destina¬ Figure 2. protocol layering fora virtual network
tion host, it assumes the destination
>r
host is phvsically connected to its
>n
home subiie(w<irL_i-e., the sender routing to ;i migrating host becomes cols. The VN-piotocol exploits the.
assumes the PhfeutetTess of the desti¬ more ellicicnt as communication be¬ virtual .network concept and the,
nation host to be regnal to its VN* tween migrating hosts occurs. propagating-cache method to achieve
address. Then^'-dte.' transmitted A host is called a family host on its the two key services defined earlier.
packet travels to the home subnet¬ home subnetwork. The relationship The cache in (lie propagating-cache
work of the destination host. How¬ between the VN-address and the PN- method is called the Address Mapping
ever. if a router on the path holds a address of a family host is always Table (AMT). The AMT consists of
cache entry for the destination host, it maintained by the hosts or routers in entries, each of which corresponds to
its
resolves the VN-address of the desti honte subnetwork. In practice, a migrating host. The VN-proioco!
nation host into the PN-address. hav 'ng routers in the home subnet- has two control packet types: CAMT
Then, the packet is forwarded to the work maintain the relationship for (create an AMT entry) and InvAMT
actual physical location of the destina *he family hosts is sufficient for ad¬ (invalidate tin AMT entry). A data
tion host without traveling the entlf? dress resolution. packet as well as the CAMT packet
route to the home subnetwork. creates or updates an AMT entry
cache is created or updated using * e 7,16 Virtual Network Protocol when relayed or received. A router
packets received. Cache information 77le Virtual Network Protocol (VN-prolo- that executes address resolution is
propagates across the wide area net col) is a general protocol that provides called an address resolver. Address
work along the communication pa* s host mobility on the top of connec¬ resolution for a packet destined
between migrating hosts, such * a tionless-mode network layer prof¬ *o a migrating host is executed by
remain on other routers. When a
’ <home subne>woi1{^s^*«Oteiag^'di&^«tfai«^sa;,^v,s^fei^Sfecy«^i.'*^w,.v .• :•
router receives such an InvAMT
■:^^—1W.p"MW m m CAMTw'^*,‘l‘,tl*‘*14' '*■*»•*«*>*■■.. [jacket, if it holds an obsolete AMT
■ InvAMT,'; entry, it invalidates that entry and
0. ’vr-wc-*^ O "primary resolverS^v"- broadcasts the InvAMT packet. Note
L^.^_ 3t;? fc-»,a:~fci.a^fc.8rS'3.~&'> | [ se1c.*o*n-d.?a*r*y# *re*s- orl.v*e#rm ^i hj"&- that (lie InvAMT packet is not broad¬
cast throughout since a host or router
|E53?JS^.V.V^aSteK;^' ^ (temporary proxy)—££2-^ does not forward an InvAMT [jacket
~. SO ml
9ra,in9***&%% if it rloes not have the corresponding
entry or holds a newer entry. 3)
When a primary address resolver of
^ » »>**-* l.£oV».i» li .t-im I ■J'* the migrating host receives this
IH» • w : .’^■S^ScV'T' —r- -■—:. ('.AMT packet, it also creates or up¬
<previous subnetwork^;; <current subnetwork - ^ ..^.w- .„vr •
dates the AMT entry for die migrat¬
ing host. If it holds an obsolete AMT
Fieure s. Host connection
entry for the migrating host, it trans¬
mits another CAMT packet to the
• v» = • ••— - -w ■»• i -<*,
subnetwork to which the migrating
primary resolver™ host was previously eoimected. As a
«-:* ■-. toiacrvaftifs:' | [ secondary resolver’;nrir;: result, the previous subnetwork holds
rr* secondary resolver the most recent AMT entry lot- the
<home subnetworks L£J (temporary proxy) '•/•:'• . migrating host until it times out, i.e.,
I I resolver holding,; .rr*-.-••-
fr~ 1—1 obsolete entry •='-> ' ' the previous subnetwork becomes a
temporary proxy lor the migrating
O source host.-.-.:::.-.i■: - ...
host. 4) On the path of the CAMT
'tSSTiijj' (Q) destination host---;..";.
packet transmitted by a primary ad¬
dress resolver, the same processing as
— - T -- ‘ f " “" ”’ ''" -' ' "'
2) is executed.
Data Communication
i f sucbcnuertrwenotr k-^. . s■:- \’ -• ;| ; □f -■”■•■”'■’-* r* ss<uuPbbpnrnreeeevvtt*iwi o oursk > '•'■~2ri Figure 4 depicts the possible How of
!■'£*»£f packets in data communication.
,.>';.'P4,.
t - OOOO . There are lour eases: a) If the source
%. (a) (b) (c) (d) ' host has the AMT entry for the desti¬
nation host, it executes address reso¬
Figure «. Data communication lution. The [jacket will traverse the
optimum route, b) If the smiree host
eillier the source Iiosi or an address remapping of [jackets that suffered does not have the AM'F entry for the
resolver. incorrect mapping for the destination destination host, it assumes that the
host by an obsolete AMT entry. I’N-address of the destination host is
Address Resolvers ei|uu! to its VN-address. "Fite packet
There are three types of" address re¬ Connecting to a Subnetwork heads for the home subnet work of
solvers for each migrating host: )m- Figure 3 depicts the packet flow when the destination host. If an intermedi¬
wan address re\nl\>er. serondan address a migrating host connects to a subnet¬ ate router holds an AM'F entry for
resolver, and Irw/unan /irnxx. A pri¬ work. I) Tbe migrating host trans¬ the destination host, it executes ad¬
mary address resolver is an address mits a CAMT packet to its home sub¬ dress resolution and forwards the
resolver in die home su.lyngTfdrkmf a network. On relaying this CAMT. packet, r) A primary address resolver
migrating host. The pritwarySaddress packet, intermediate routers create receives ultimately the packet head¬
resolvers for a migrating~hmi,always or update the AMT entry for the mi¬ ing for the home .subnetwork of the
hold the most recent AMT'entry lor grating host, i.e., such intermediate destination host. It executes address
tlie migrating host. A secondary ad¬ routers become secondary address re¬ resolution and forwards the packet,
dress resolver is an address resolver solvers for the migrating host. While d) A router that holds an obsolete
in the subnetworks other than the connected to a subnetwork other AM'F entry for the destination host
home subnetwork of die migrating than the home subnetwork, the mi¬ executes address resolution for the
host. Obsolete AMT entries might grating host continues to transmit a packet heading for the home subnet¬
remain on secondary address resolv¬ ("AMT packet periodically. 2) If an work of the destination host. 'Fite
ers. A temporary proxy is a kind of intermediate router holds an obsolete [jacket is forwarded to tbe previous
secondary address resolver in the AMT entry for the migrating host, it subnetwork of the destination host. A
subnetwork to which the migrating broadcasts an InvAMT packet to all temporary proxy of the destination
host was previously connected. The the connected subnetworks to invali¬ host in the previous subnetwork exe¬
temporary proxy was introduced (or date any obsolete entries that might cutes address resolution and for-
70
Atiuust lWH/Vol,117. Nw.H communications o*tm* *cm
wards the packet to the correct loca¬ address/Address-Version, and Target entry for the source host, it creates or
tion. Note that once the source host Holding Time. The Flugx field speci¬ updates a valid entry. In the valid
receives a packet from the destination fies the packet type and other infor¬ state, the entry holds a valid mapping
host, it creates the AMT entry for the mation. There are three packet types: between a VN-address and a PN-
destination host. data, CAMT, and InvAMT. The address. A valid entry overwrites the
If a host does not have the func¬ Holding Time field in the data packet destination PN-address field when
tions for the VN-protocoI. it transmits specifies the timeout value of the relaying a packet which holds an
conventional network layer packets. AMT entry created or updated by older mapping for the destination
When a router relays such a packet, if this packet. The Resolver PN-acldress host. When the entrv times-out. it re¬
it has tile AMT entry for the destina¬ field in the data packet specifies the turns to the free state. A valid entry
tion host of the packet, it adds the PN-address of the address resolver changes its slate to invalid when re¬
VN-sublayer header to the packet that executed address resolution for ceiving an InvAMT packet which has
and forwards it. In the worst case, this packet. The Target VN-address/ an equal or newer version number
such a packet reaches the primary ; PN-address/Address-Version fields in than the entry. A valid or invalid
address resolver of the destination the CAMT/InvAMT packet indicate entry detects an obsolete mapping Tor
host and is converted into a VN- those values of the target machine of the destination host which might be
protocol packet. When such a host the AMT entry to be updated. On the caused by an obsolete AM I' entrv on
receives a VN-protocoI packet, if it si¬ other hand, in case of the data packet, another machine. Invalid entries are
lently ignores tile header of the VN- the Source VN-address/PN-address/ used not for address resolution hut
sublayer, it correctly recognizes the Address-Version fields are used for for detecting packets that have an
VN-address of the source host. (Such AMT update. obsolete mapping between the desti¬
a case in the II’ environment is dis¬ nation VN/PN-addresses. When a
cussed later.) AMT Entry host or router delects an obsolete
The AMT must hold the information mapping in a packet, it transmits an
Disconnecting from a subnetwork that enables 1) resolution of the VN- InvAMT packet to the address re¬
Figure 5 depicts the packet flow when address of the destination host into solver indicated by the Resolver PN-
a migrating host disconnects from a the corresponding PN-address, 2) address field of the packet. The rea¬
subnetwork or is powered off. I) The keeping the entry consistent with the son why the invalid state was intro¬
migrating host may transmit an In- most recent information, and 3) dele¬ duced is to increase the probability of
vAMT packet to its home subnet¬ tion of itself when it has not been re¬ detecting obsolete mappings. An in¬
work. Note that the migrating host freshed for a certain period. Thus, an valid entry times-out also, and then
can omit this procedure. 2) On the AMT entry must have the following changes its state to free. Such deletion
path of the InvAMT packet, if an in¬ five fields: Virtual Network Address, of the AMT entry (valid —► invalid —►
termediate router hits an obsolete Physical Network Address, Address free) is called the lu'ii-jilwsril tlrlrlinn.
AMT entry for the migrating host, Version Number, Status, and Hold¬ Figure 6 depicts the state transition
the router broadcasts another In¬ ing Time. diagram of an AMT entry.
vAMT packet to all connected subnet¬ An AMT entry takes one of three
works. When a. router receives such states: free, valid, and invalid. In the VIP: Virtual internet Protocol
an InvAMT packet, if it holds an ob¬ free state, the entry does not hold any VIP is derived from IP by applying
solete AMT entry, it invalidates that information. When relaying or re¬ the VN-protocoI. VIP /iil/lirssfx are
entry and broadcasts the InvAMT ceiving a packet, if the host does not introduced as VN-addresses in the
packet, 3) When a primary address have an AMT entry for the source VN-proiocol, while IP addresses are
resolver of the migrating host re¬ host of the packet or it has an older thought of as PN-addresses. Table 1
ceives the I nvAMTjtacket, it if has an shows the correspondence of the VN-
obsolete AMT entry? for the host, it prottKoI to VI.P.
broadcasts anothref~I.nvAMT packet
to all connected subnetworks. VIP Header and AMT Entry
Figure 7 depicts the VIP header for¬
The VN-Protocol Header mats. Figure 8 shows tile format of an
As mentioned earlier, the network AMT entry for VIP. Since the length
layer header includes both the VN- of the VIP header becomes too great
sublayer header and the PN-sublayer if it includes all mandatory fields for
header. The PN-sublayer header is the VN-sublayer header, the control
equal to the conventional networ packet is separated from the data
layer header. The VN-sublayer packet. To ensure backward compati¬
header must have the following bility with IP, the VIP header is im¬
fields: Flags, Source VN-address/P plemented as an IP option, instead ol
address/Atldress-Version, Destination the higher-sublaver header oflP[I2].
VN - address/PN - address/Address- In Figures 7(a) and (b), the top-20
Waure s. Host disconnection or
Version, Holding Time, Resolver PN- octets construct the IP header, while
address. Target VN-address/PN- Power off the remainder is the VIP header as
'UMieanoMa IMUVY.,1 C V..K 71
Table i. Correspondence of the VN-protocoi to viP Host:C'.-b transmits an IP packet to
liosl:A-a with the VIP address of
Host:A-a as the destination IP ad¬
VN-prolocol VIP
dress. This IP packet is converted
into a VIP packet by G\V:BB-ab and
VN-addresses VIP addresses
I’N-addresses IP addresses forwarded to Nct.B-a. Note that once
home subnetwork the subnetwork indicated by the network HoscC-a receives a VIP packet from
number of the VIP address Host-A-a, it creates the AMT entry for
primary address resolvers routers connected to the home subnetwork
Hosi:A-a. such that it executes ad¬
of a migrating host (home routers)
secondary address resolvers routers connected to the subnetworks other dress resolution at the transmission
than the home subnetwork of a migra¬ time. However, packets transmitted
ting host by Hosi:C-b always travel the redun¬
temporary proxies routers connected to the previous subnet¬ dant route.
work of a migrating host
Suppose that Hosr.A-a moves
again from Net:B-a to Nei:A-c (2) and
that its home routers and GW:D hold
an AMT entry for Host:A-a, which
;in II’ option. In accortlunce with the Examples indicates tbiti the current subnetwork
il’ option format, the VII’ header in¬ Figure !) shows a simple Internet con¬ of Host:A-a is Nei:B-a. When Ht>si:A-
cludes the Option Type and Length sisting of both VIP and IP machines. a transmits a CAMT packet to its
fields. Note that the Source VII’ Ad¬ In the figure, a VIP host Hnst:A-a home subnetwork, C\V:A-ltc also
dress held is included in the 11’ moves from its home subnetwork transmits another CAMT packet to
header and that the Source II’ Ad¬ Net:A-b to Nci.B-a (I). 'File VIP ad¬ Nci:B-a because G\\’:A-bc held an
dress field is included in the VII’ dress of Hosr.A-a remains unchanged obsolete AMT entry. As a result,
header to ensure backward compati¬ while it temporary IP address is as¬ GW'.B updates the AMT entry for
bility with IP. signed to the host by, say, DHCP (Dy¬ Host:A-a. i.e., it becomes the tempo¬
To control address resolution and namic Host Configuration Protocol) rary proxy of Hosr.A-a. However, an
the manipulation of AM T entries, |.‘ij. Hnxi:A-a transmits a GAMT obsolete AM'F entry for Host:A-a
VII’ defines four more Hags in the packet to its home subnetwork Net:A- remains on G\\':D. Consider the
Flags field of the VIP header in addi¬ b, so that intermediate VIP routers packet transmission from a VIP host
tion to the Hags indicating the packet (CWtlL GU':BB-ab. and C\\':A) and Host:I)-a to Hosr.A-a. The VIP
type (see Figure 7(c)). If the don't its borne routers (G\V:A-ab and [Jacket transmitted by Host:D-a is for¬
cache Hag is set. routers other than G\V:A-he) create an AMT entry for warded to Net:B-a because OW-D hits
the home routers of the source host Hosn.A-a. Consider packet transmis¬ an obsolete AM’F entry for Hnsi:A-a.
do not create the AMT entry for the sion front a VIP host HoscC-a to Since G\V:B has the must recent AM'F
source host. If the don't resolve Hag is Host:A-a. Since Host:C-a does not entry for Hosi:A-a. it executes correct
set, routers other than the home have the AMT entry litr Hosr.A-a. it address resolution and forwards the
routers of the destitution host do not assumes that the IP and VIP ad¬ [jacket to NcnA-c. G\V:B also trans¬
execute address resolution for the dresses of Hosi:A-;i are the same. mits an InvAMT [jacket to G\\’:l> to
destination host. II the aniheniicaiion Therefore, the VIP packet heads for invalidate the obsolete AMT entry. A
flag is set. the packet includes authen¬ Net:A-h. On relaying the packet on new. correct AM'F entry will he cre¬
tication dam. If the broadcast In- G\\':BB-ab, since it lias the AMT ated at G\V:D if Hosr.A-a sends a
vAMT Hag is not set. routers do not entry for Host:A-a, it executes ad¬ reply to Hosr.D-a.
broadcast an InvAMT packet on de¬ dress resolution and forwards the
tecting obsolete AMT entries. VIP packet to Net:B-a. An IP host Discussion of VIP Features
Scalability on Memory usage
Although .VIP- makes use of a cache
called-the--A'MT for-address resolu¬
tion. the number of AMT entries a
host or router must maintain is inde¬
pendent of the scale of the internet or
the total number of migrating hosts.
S receive old data packet receive old data packet It is suHicicnt for a host to have AM'F
r ... sencd InvAMmT receive new CAMT ... send lnvAMT_^ ;~ entries for oilier hosts with which the
or new data packet
K ■ O host communicates. If a Host commu¬
O nicates with up to 100 hosts simulta¬
I receive new InvAMT
neously, it is enough for the host to
receive CAMT or rreecceeii ve old CAMT have 100 AMT entries, which occupy
data packet oorr IInnvi AMT • •
only 2,800 octets.’’
The number of AMT entries a
Figure 6. State transition diagram of an AMT entry router must maintain is equal to the
72
Augim J9V4/V*iJ,37, Ntt.ft COMMUNICATIONS OPTMI ACM

Site A Host: A-a f~""' O VIP host numbers compared on address reso¬
* Site B
---L GW:A.hi» I Sv* O lution and AMT entry update a. ecre-
lp hositt ated by the same host, the coinpari-
\^jet:A-a^—□——f~i—?'NenA^c
[) CNel.B^a) n VIP rouutteerr SC)n ()l version numbers always works
I I IP routteerr l'‘>n ectl>'. provided eadi Iiost ensures
■ hat its address version number in¬
QGW:B
creases monotonically.
—^w£B-b5—sGw:BB,d I Gw:b^-
Routing Loops
Backbone network "1 ^ -r-—' VIP is a protocol which resolves a
^ ^ addiess into a corresponding II’
address. Packet routing is calculated
in the IP layer. VIP never affects the
-»GW;C-ab —L^C3W:C-bc "'l fsiteD |
routing calculation in the IP layer.
^3>-0<Ne^ (g^
Since the comparison of version
numbers works correctly as men¬
SlteC Host:C-a(j Host:C-b O p) * tioned earlier, the destination IP ad¬
--' [ Host:D-a dress of the packet is updated moms
tomcally as the packet is relayed by
Figure 9. a sample network
routers. Therefore, the packet
reaches a host regardless of whether
r ,l,e 'c-ceiving bos. is the correct desti¬
j" — •- -.1::'-L^L.V'lCilL I£P^DP layer ^t :
nation host. Consequently, as long as
v ihe routing control in the IP laver is
; free from routing loops, VIP will
c never exhibit routing loops.
Kx fenpul iff:1' >r^tJpdatefr^:maods, I ^SKf
p’iTxJ— •’ ■ -j—; r^l: • ; I i I . Loss of Control Packets
■ 4-vf i ■ ‘•'■'’* ,. r*:rr»• •*• . .Tr*^
1 here are two control packet types
|. I Ly p-C0nv I | vjp_error *| { vip_output |
for VIP: (.'AMT and InvAMT. VIP is
tolerant of losing control packets.
Since a migrating host continues to
L;:; L-'p'nlr 1 <; j^QipjonTl—. • \| iP_0UtpUt j "x-
transmit CAMT packets to its home
subnetwork periodically, the loss of a
, V^T; V- " | Vip_forw I
single CAMT packet is not fatal. An
_:
IitvAMI packet is transmitted when¬
(; .-. V -- V. interface layer ’...’ ’ ever an obsolete AMT entry is found.
It may be transmitted also when a
Iiost is about u> disconnect from a
Figure 10. Block diagram subnetwork or when the host is pow¬
ered off. If an InvAMT packet is lost,
obsolete AMT entries will time-out.
Kven il an obsolete AMI entry deliv-
.transmission? eis a \ IP packet loan incorrect host,
‘Stviwc u»«a,v bwX.
I 205 (127) the receiving host can detect the mis¬
delivery because the destination VIP
address of the packet does not match
the VIP address of the host.
I 389 (89X
KgW^eWcMep JIt i9oUn,V^ rI Network Partitioning
128 (62) There is the possibility that network
partitioning disables coiiimuiiicaiion
with a migrating host even if an avail¬
^^p0^^p 200 V. . 300 ..... 400 500
able physical link exists. Suppose that
MBwrs^WgST^r- time (p. sec)
the network is partitioned between a
host that is about to send a packet to a
Figure 11. Comparison of processing time migrating host and the home subnet¬
work of the migrating host. If neither
the sending host nor intermediate
routers have the AMT entry for the
migrating host, the transmitted
Au«u" 'W«/V"l.«. Vo 8 cewMuw{u.now* n_
' I'OSO- packet will be lost. However, if the BSD/386 on PCs with Intel 386/486). separate logical identifiers from phys¬
I'e cre- migrating host sends packets, AMT The VIP functions were added io the ical identifiers. In the conventional
npari- entries lor the migrating host propa¬ IP layer in the kernel. The added network architecture, each host is
works gate along the communication path. functionality requires approximately identified by its location in (lie net¬
nsiircs Thus, network partitioning is not 900 lines of C code. Figure 10 shows a work. i.e.. bv a physical identifier.
■er in- fatal to VIP. hnt VIP is not tolerant of block diagram of the code. In tile However, each host should be recog¬
all forms of network partitions. figure, thin boxes indicate IP mod¬ nized by a logical identifier because it
Compatibility with IP ules while thick boxes indicate VIP is no longer stationary. This is the
Suppose that a VIP subnetwork is modules. base of the virtual network concept.
!ves ;i The VIP processing time was mea¬ Such a notion should be applied to
connected to a traditional IP network
111; I i» sured by using a special timer board other identifiers such as group identi¬
anti that a VIP host, whose home sub¬
ilmccl with a I-/isec granularity. Our lest fiers for multicast communications.
network is the VIP subnetwork, mi¬
is (lie environment consists of seven SONY Currently. VIP is running on a lest
grates to an IP subnetwork. The VIP
Inver. NEWS workstations and four Ether¬ network. We plan to deploy VIP in
host can communicate with any IP
I'siotl nets. Each workstation has a the WIDE internet'1 and in a campus
host with its VIP address. VVhen the
uten- MC68030/25MHz CPU and 4 io 8MB network of Keio University1 to deter¬
VIP host transmits a VIP packet to an
I’ ad- of main memory. mine tile optimum values for param¬
IP host, the values in the Destination
11)110- Figure 11 shows the processing eters such as tile interval time of the
IP and VIP fields of the VIP packet
d by time required for the transmission, CAMT packet transmission, the num¬
will he the same. The VIP packet
u'ket relay, and reception of IP and VIP in ber of AMT entries, and the value of
travels the optimal route to the desti¬
■t her the stable state. "Stable state" means the Holding Time field of the VIP
nation IP host. IP routers and IP
ic.sti- that I) the source host has the AMT header.
hosts ignore the VIP header as an
ig ;is entry for the destination host, 2) in¬ Some problems still remain un¬
unknown IP option [Ij. IP routers
er is termediate routers have the AMT solved however. One is security. To
relay the VIP packet correctly, and IP
will entry for the source host and l«>r the prevent malicious hosts from imper¬
hosts handle the VIP packet cor¬
destination host, and 3) the destina¬ sonating others. a host auihenticiUion
rectly. Additionally, since the Source
tion host has the AMT entry for the mechanism must be implemented in
IP Address field of the VIP packet
source host. Therefore, the IP ad¬ VIP. Security is an area for future
holds the VIP address of the source
pes dress for the destination host is re¬ study. Also, we plan to apply the
VIP host instead of its temporary IP
I* is solved at the source host. Intermedi¬ mechanisms of VIP to oilier connec¬
address, the destination IP host rec¬
eis. ate routers and the destination hosts tionless-mode network laver proto¬
ognizes the correct source address of
■ to update only the Holding Time field cols such as ISO CI.NP. □
the VIP packet.
me of the entry for the source host. Inter¬
When the IP host transmits an IP
>1 ;i mediate routers do not modify any Acknowledgments
packet to the VIP host, the Destina¬
An header field related to the destination We express our thanks to Mario
tion IP Address held of the IP packet
■II- host, although they search the AMT Tokoro of Sony Computer Science
is assigned the VIP address of the
id. for the entry for the destination host. Laboratory Inc./Keio University and
VIP host. This packet heads for the
i a The numbers in parentheses repre¬ Hideyuki Tokuda of Keio University/
home subnetwork of the VIP host. If
n sent the overhead relative to that of Carnegie Mellon University, for giv¬
an intermediate router has an AMT
The host-to-host overhead of VIP ing ns many valuable suggestions on
entry of the VIP host, it converts the
st. can be formulated as a function of the the basic concept of the virtual net¬
IP packet into a VIP packet. In the
it. hop count, ;l.s follows. work protocol. We acknowledge the
worst case, the IP packet reaches the
assistance of the members of Sony
home subnetworks off the VIP host,
’t. oi'erhead = 89A,';,„,„ 4- 189 (pisec) Computer Science Laboratory Inc.
then is converted^nfif-a VIP packet. ^
and the WIDE project, especially the
Thus, packets fronnih IP host to a
P The VIP overhead is approxi¬ members of the WIDE VIP working
VIP host might travel'along redun¬
h mately 0.6 ms if M/,,,!, is 5, 1.0 ms if group, for their contributions to the
dant routes. — Nat * is 10, and 2.0 ms if is 20. design of the protocols of VIP.
implementation and r ;Since IP transmission in the Internet
Performance . . takes time on the order of 100 ms. the References
1. Braden. R. Requirements for Inter¬
k In general, there are two ways of in¬ P data packet transmission over-
net busts—Communication layers.
corporating a new protocol into exist¬ _ca 's negligible from the user's
ing systems: l) to write programs viewpoint. RKCl 122. Oct. 1989.
from scratch and 2) to modify exist- . The WtllK inlcriiei is an academic internet in
ing programs. For the sake of ease o Conclusions Japan. i< is die mtrasmicuire network ol (he
WtOK project, a research project lor a widely
implementation and future software TTiis article proposed VIP. a protocol (lisirilnned environment.
distribution, the latter was chosen to . h ^osts. VIP is an instance of
implement VIP. VIP was imp.e ^ ^-protocol, the general proto- Alosl Modems (more than 2.(1(111) have portable
computers.
mented by modifying 4.3BSD Unix = co Providing host migration trans¬
based operating systems (NEWS- parency [0 t|)e transport layer. The
and
SONY NEWS workstations ey P<)ini of t|le VN-pnitocol is to CONTINUED ON PACE 113