PARC Universal Packet
Encyclopedia
The PARC Universal Packet (commonly abbreviated to PUP, although the original documents usually use Pup) was one of the two earliest internetwork protocol suites; it was created by researchers at Xerox PARC
in the mid-1970s. (Technically, the name "PUP" only refers to the internetwork-level protocol, but it is also applied to the whole protocol suite.) The entire suite provided routing
and packet delivery, as well as higher level functions such as a reliable byte stream
, along with numerous applications.
), and the creation of the Ethernet
local area network
at PARC. However, the development of PUP split off because Xerox PARC wished to move ahead with implementation, for in-house use. The fundamental design of the PUP suite was substantially complete by 1974.
In the 1980s Xerox
used PUP as the base for the Xerox Network Systems (XNS) protocol suite; some of the protocols in the XNS suite (such as the Internetwork Datagram Protocol) were lightly modified versions of the ones in the PUP suite, but others are quite different, reflecting the experience gained with PUP and IP.
(IP) layer in TCP/IP. A full PUP network address
consisted of an 8-bit network number, an 8-bit host number, and a 16-bit socket number. The network number had a particular special value which meant 'this network', for use by hosts which did not (yet) know their network number.
Unlike TCP/IP, socket fields were part of the full network address in the PUP header, so that upper-layer protocols did not need to implement their own demultiplexing; PUP also supplied packet types (again, unlike IP). Also, an optional 2-byte checksum covered the entire packet.
PUP packets were up to 554 bytes long (including the 20 byte PUP header
), and the checksum. This was a smaller packet size than IP, which requires all hosts to support at least 576 (but supports packets of up to 65K bytes, if the hosts support them); individual PUP host pairs on a particular network might use larger packets, but no PUP router was required to handle them. Larger packets could be fragmented.
A protocol named the Gateway Information Protocol (a remote ancestor of RIP
) was used as both the routing protocol
, and for hosts to discover routers.
PUP also included a simple echo protocol at the internetwork layer, similar to IP's ping
, but operating at a lower level.
.
Once RTP had started the connection, BSP took over and managed the data transfer. Like TCP, BSP's semantics and operation were in terms of bytes; this was discarded in favour of packets for the equivalent protocol in XNS, Sequenced Packet Protocol.
and File Transfer Protocol
, were basically the same protocols as used on the ARPANET
(much as occurred with the TCP/IP suite).
Others were novel, including protocols for printer spooling, copying disk packs, page-level remote access to file servers, name lookup, remote management, etc (although some of these capabilities had been seen before, e.g. the ARPANET already made heavy use of remote management for controlling the Interface Message Processors which made it up).
model first demonstrated at Xerox PARC; that demonstration would not have been anything like as powerful as it was without all the capabilities that a working internetwork provided.
The Gateway Information Protocol's descendant, RIP, (somewhat modified to match the syntax of addresses of other protocol suites), remains in wide use today in other protocol suites. One version of RIP served as one of the initial so-called interior gateway protocol
s for the growing Internet
, before the arrival of the more modern OSPF and IS-IS
. It is still in use as an interior routing protocol, in small sites with simple requirements.
Xerox PARC
PARC , formerly Xerox PARC, is a research and co-development company in Palo Alto, California, with a distinguished reputation for its contributions to information technology and hardware systems....
in the mid-1970s. (Technically, the name "PUP" only refers to the internetwork-level protocol, but it is also applied to the whole protocol suite.) The entire suite provided routing
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
and packet delivery, as well as higher level functions such as a reliable byte stream
Reliable byte stream
A reliable byte stream is a common service paradigm in computer networking; it refers to a byte stream in which the bytes which emerge from the communication channel at the recipient are exactly the same, and in exactly the same order, as they were when the sender inserted them into the channel.The...
, along with numerous applications.
History
The origins of the PUP suite lie in two developments; in the same events in the early 1970s as the very earliest stage of the development of TCP/IP (see History of the InternetHistory of the Internet
The history of the Internet starts in the 1950s and 1960s with the development of computers. This began with point-to-point communication between mainframe computers and terminals, expanded to point-to-point connections between computers and then early research into packet switching...
), and the creation of the Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
at PARC. However, the development of PUP split off because Xerox PARC wished to move ahead with implementation, for in-house use. The fundamental design of the PUP suite was substantially complete by 1974.
In the 1980s Xerox
Xerox
Xerox Corporation is an American multinational document management corporation that produced and sells a range of color and black-and-white printers, multifunction systems, photo copiers, digital production printing presses, and related consulting services and supplies...
used PUP as the base for the Xerox Network Systems (XNS) protocol suite; some of the protocols in the XNS suite (such as the Internetwork Datagram Protocol) were lightly modified versions of the ones in the PUP suite, but others are quite different, reflecting the experience gained with PUP and IP.
Basic internetwork protocol
The main internetwork layer protocol was PUP, which roughly corresponds to the Internet ProtocolInternet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) layer in TCP/IP. A full PUP network address
Network address
Network address may refer to:*Base address*Classful address*IP address*IPX address*Logical address*Network layer address,*X.25/X.21 address*MAC address-See also:*Autonomous system *Host address*Link layer*Subnet mask...
consisted of an 8-bit network number, an 8-bit host number, and a 16-bit socket number. The network number had a particular special value which meant 'this network', for use by hosts which did not (yet) know their network number.
Unlike TCP/IP, socket fields were part of the full network address in the PUP header, so that upper-layer protocols did not need to implement their own demultiplexing; PUP also supplied packet types (again, unlike IP). Also, an optional 2-byte checksum covered the entire packet.
PUP packets were up to 554 bytes long (including the 20 byte PUP header
Header (information technology)
In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the header are sometimes called the payload or body....
), and the checksum. This was a smaller packet size than IP, which requires all hosts to support at least 576 (but supports packets of up to 65K bytes, if the hosts support them); individual PUP host pairs on a particular network might use larger packets, but no PUP router was required to handle them. Larger packets could be fragmented.
A protocol named the Gateway Information Protocol (a remote ancestor of RIP
Routing Information Protocol
The Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops allowed for RIP is 15....
) was used as both the routing protocol
Routing protocol
A routing protocol is a protocol that specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network, the choice of the route being done by routing algorithms. Each router has a priori knowledge only of...
, and for hosts to discover routers.
PUP also included a simple echo protocol at the internetwork layer, similar to IP's ping
Ping
Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...
, but operating at a lower level.
Transport layer protocols
To establish a transport connection, two protocols came into play. The first, the Rendezvous and Termination Protocol (RTP), which was used to initiate communication between two entities, as well as manage and terminate the connection. The second was the primary transport layer protocol, Byte Stream Protocol (BSP), which was analogous to TCPTransmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
.
Once RTP had started the connection, BSP took over and managed the data transfer. Like TCP, BSP's semantics and operation were in terms of bytes; this was discarded in favour of packets for the equivalent protocol in XNS, Sequenced Packet Protocol.
Application protocols
PUP supported a large number of applications. Some of them, such as TelnetTELNET
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...
and File Transfer Protocol
File Transfer Protocol
File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...
, were basically the same protocols as used on the ARPANET
ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...
(much as occurred with the TCP/IP suite).
Others were novel, including protocols for printer spooling, copying disk packs, page-level remote access to file servers, name lookup, remote management, etc (although some of these capabilities had been seen before, e.g. the ARPANET already made heavy use of remote management for controlling the Interface Message Processors which made it up).
Impact
In showing that internetworking ideas were feasible, in being influential in the early work on TCP/IP, and as the foundation for the later XNS protocols, PUP was very influential. However, its biggest impact was probably as a key component of the office of the futureOffice of the future
The office of the future is a concept dating from the 1940s. It is also known as the "paperless office". After sixty years of unfulfilled prophecies the phrase "paperless office" has been discredited somewhat...
model first demonstrated at Xerox PARC; that demonstration would not have been anything like as powerful as it was without all the capabilities that a working internetwork provided.
The Gateway Information Protocol's descendant, RIP, (somewhat modified to match the syntax of addresses of other protocol suites), remains in wide use today in other protocol suites. One version of RIP served as one of the initial so-called interior gateway protocol
Interior gateway protocol
An interior gateway protocol is a routing protocol that is used to exchange routing information within an autonomous system ....
s for the growing Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
, before the arrival of the more modern OSPF and IS-IS
IS-IS
Intermediate System To Intermediate System , is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices....
. It is still in use as an interior routing protocol, in small sites with simple requirements.
Further reading
- Michael A. Hiltzik, Dealers of Lightning: Xerox PARC and the Dawn of the Computer Age (HarperBusiness, New York, 1999), pp. 291-293