Client Server Middleware Tools

• Network components:
  • LANs
  • WANs
• Pipes:
  • general:
    • distributed directories
    • authentication services
    • peer-to-peer communication:
      • transport independent API
      • remote procedure calls (RPCs)
      • message-oriented middleware (MOM)
      • publish and subscribe
    • transport stacks
    • data representation protocols
  • specific:
    • database-specific
    • OLTP-specific
    • groupware-specific
    • object-specific
    • internet-specific
    • system management specific
• Platforms:
  • transaction monitors
  • object transaction monitors
  • web application servers
• see also:
  • Delphi Programming Main Index
  • Relational database management systems
  • Two-tier client server
  • Multi-tiered client server
  • Web Services

Network components:

• LANs:
  • network operating systems (NOS):
    • NOS vendors:
      • Unix-based
      • PC LAN based:
        • Novell NetWare
        • MS NT
      • Enterprise-based:
        • Distributed Computing Environment (DCE):
          • from Open Software Foundation (OSF) in 1992
          • provides DCE RPCs, naming services, time synchronisation service, network security service & a threads package
      • Internet-based:
        • most players are converging technology onto open Internet standards forming an intergalactic NOS derived from tecnologies from both Unix, PC & Internet aspects.
        • Netscape (now AOL) - web browser, HTTP servers, LDAP directories, SSL security, certificate servers, CORBA IIOP
        • JavaSoft
    • NOS-independent directory systems:
      • X.500 DAP:
        • too bulky & overly complicated
      • Lightweight Distributed Access Protocol (LDAP):
        • designed by Netscape to provide a simplified version of the X.500 DAP that could also run on TCP/IP networks
        • Netscape's Directory Server 3.0 (Feb1998) - a native LDAP server
    • Object Request Brokers (ORBs):
      • will subsume NOSs & expand their scope
      • an object bus that lets components interoperate across address spaces, languages, operating systems & networks
      • also provides mechanisms that let components exchange metadata & discover each other
      • examples:
        • CORBA
        • COM+
  • protocols with their own network adapter cards such as:
    • Token Rings
    • Ethernets
    • ISDN
  • logical network drivers:
    • interfaces protocol stacks to network adapter cards
      • NDIS
      • ODI
  • protocol transport stacks:
    • TCP/IP, IPX/SPX, NetBIOS, SNA
  • transport-independent API:
    • sit on top of transport stacks & allow developers to plug their programs into a single interface that supports multiple protocols
    • Sockets interface is becoming the main interface
    • Others:
      • Transport Layer Interface (TLI) - used in NetWare & many Unix implementations
      • CPI-C: the modern SNA peer-to-peer API that can now run over both SNA & TCP/IP stacks
      • Named Pipes: runs on top of TCP/IP, IPX/SPX, NetBIOS
  • protocol matchmakers:
    • allow applications designed to run over one protocol, run over a different protocol without re-writing code
  • bridges:
    • are computers or devices that interconnect LANs using a link-layer routing information & physical addresses
    • protocols that require bridges include NetBIOS as it does not support inter-networking
  • routers:
    • interconnect LANs using protocol-dependent routing information
    • create & maintain dynamic routing tables of the destinations they know
    • used with protocols that support a network layer eg. TCP/IP, IPX/SPX, APPN, XNS, AppleTalk, OSI
    • LAN to WAN connection:
      • router connects to WAN via dedicated leased lines (usually T1 or T3 line type)
      • switcher technology is typically Frame Relay, X.25 or just point-to-point (PPP)
  • multi-protocol routers:
    • support different combinations of network layer protocols
  • bridge/routers:
    • are single devices that combine functions of bridges & routers so that netBIOS LAN's can be connected to TCP/IP LANs
  • gateways:
    • devices that perform brute force translations between protocols
• WAN public & private packet-switched networks:
  • X.25:
    •  
  • Frame Relay:
    • uses virtual circuits to allocate bandwidth on demand
    • the current LAN-toWAN connection technology
  • Asynchronous Transfer Mode (ATM):
    • the ultimate isochronous technology
    • allocates LAN/WAN bandwidth on demand via virtual circuits
    • uses high-speed, hardware-based, circuit-switching technology that is potentially capable of unleashing an awesome amount of bandwidth at very low cost (every node is given its own dedicated LAN segment into the switch)
    • up to 2.4Gb/s

Pipes:

• provide the intercomponent & interapplication communication services
• general pipes:
  • provide substrate for most C/S interactions
  • include:
    • communication stacks
    • network time - synchronisation of clocks across the network
    • queuing services
    • network operating system extensions such as distributed file & print services
  • examples:
    • distributed directories:
      • LDAP
      • X.500
    • authentication services:
      • firewalls
      • certificate servers
      • SSL
    • peer-to-peer interfaces that let apps communicate using close-to-the-wire send/receive semantics:
      • low-level, conversational, protocols (hard to code & maintain):
        • transport-independent API:
          • NetWare's Transport Layer Interface (TLI):
            • introduced by AT&T in 1986, similar to Sockets but more network independent - a cleaner version of Sockets
          • NetWare's Named Pipes:
            • file-like programming API that abstracts a session-based two-way exchange of data
            • built-in to NT, Win 95/98 & is supported in Unix via LAN Manager/X
          • Sockets:
            • introduced in 1981 as the Unix BSD 4.2 generic interface
            • Sun introduced NFS & RPC over sockets in 1985
            • supported on virtually every OS (eg. Winsock for TCP/IP in Windows)
            • socket address = IP address + Port address
              • Oracle & Sybase DBMSs have their own well-known ports!
          • Common Programming Interface for Communications (CPI-C):
            • IBM product that builds on top of APPC & masks its complexities & irregularities, thereby allowing porting of programs to all SNA platforms
          • NetBIOS:
            • the premier protocol for LAN-based, program-to-program communications
            • introduced by IBM & Sytek in 1984 for the IBM PC Network
            • used by NetWare as an interface to both TCP/IP & IPX/SPX
            • used by MS as an interface to both TCP/IP & NetBEUI
      • remote procedure calls (RPCs):
        • synchronous, telephone-like, call-return style fast messaging
        • 1970's:
          • HTTP:
            • internet messaging protocol which is plain text based & layers request-response communications over TCP
            • HTTP requests:
              • a HTTP request may be as simple as:
                • POST /foobar HTTP/1.1
                • Host: 209.110.197.12
                • Content-Type: text/plain
                • Content-Length: 12
                • {blank line needed here}
                • Hello, world
              • 1st line must be: HTTP method (eg. GET/POST) Target URI HTTP version
              • 2nd line must be Host IP address
              • 3rd line must be the MIME type of the content being sent
              • 4th line must be length of content being sent in bytes
              • optionally next line can be Connection: Keep-Alive to maintain TCP connection
              • header must be separated from content by a blank line
              • finally the content
            • HTTP responses:
              • the web server then returns a HTTP text response as follows:
                •  200 0K (the HTTP error message, this one means all went well)
                • Content-Type: text/plain
                • Content-Length: response content length
                • {blank line needed here}
                • response content
            • Uniform Resource Identifier (URI):
              • is simply a formatted string that uniquely identifies a resource and come in 2 flavours:
                • Uniform Resource Locator (URL):
                  • encode the underlying protocol needed to locate the resource being identified & have the syntax:
                    • protocol:// <host> [":" <port>] [<path> ["?" <qry>]]
                    • where host = IP address of the server, port is the TCP port number, path is the absolute URI to be passed as the Request-URI
                • Uniform Resource Name (URN):
                  • are location-independent and in no way imply any protocol or mechanism for locating the resource
                  • the syntax is structured so that URN's are unique across disparate organisations:
                    • "urn:" <NID> ":" <NSS>
                    • where NID is the namespace identifier and NSS is the namespace-specific string
        • 1980's:
          • SUN RPC:
            •  its most popular application is the Network File System used by most Unix systems 
          • DCE RPC:
            • its most popular application is Windows NT which uses it for a number of its system services
            • most use NDR as its data representation protocol
          • MS-RPC
        • Object RPC's (ORPCs):
          • attempted to marry object orientation with network protocols with the main difference from earlier RPC protocols being the codification of the mapping of a communication endpoint to a language-level object.
          • 1990's:
            • Microsoft's DCOM:
              • only runs on Wintel machines, not good for internet applicability; problems with firewalls
              • instead of HTTP's URI, it has a DCOM IPID
            • CORBA's Internet Inter-ORB Protocol (IIOP) flavour of the General Inter-ORB Protocol (GIOP) :
              • compatibility problems between vendors, not good for internet applicability
              • problems with firewalls
              • instead of HTTP's URI, it has a IIOP/GIOP object_key
          • 2000:
            • Microsoft's SOAP:
              • XML-based, readily passes firewalls & able to communicate with either DCOM or CORBA
              • the HTTP payload of a SOAP request is simply an XML document that contains the values of the [in] and [in,out] parameters of the method. These values are encoded as child elements of a distinguished call element that shares the method name and namespace URI of the SOAPMethodName HTTP header.
              • thus the HTTP request is as for usual EXCEPT:
                • content type = text/xml
                • additional header: SOAPMethodName: URN
                • the content must have:
                  •  the SOAP tags <Envelope> and at end </Envelope>
                  • the 1st child element under <Body> must match the SOAPMethodName
      • message-oriented middleware (MOM):
        • asynchronous, post-office like, queued & thus slow messaging
        • MS NT5.0 MSMQ
        • IBM's MQSeries
        • BEA's MessageQ
        • PeerLogic's Pipes
        • TIBCO's TIB/Rendezvous
        • CORBA Messaging
      • publish-and-subscribe:
        •  
    • transport stacks:
      • TCP/IP:
        •  
      • Novell NetWare's IPX/SPX:
        • an implementation of Xerox Network Services (XNS) transport & network protocol
        • on the decline?
      • NetBEUI:
        • the original transport for NetBIOS commands
        • offers powerful datagram & connection-oriented services
        • lacks a network layer & security
    • data representation protocols:
      • a protocol that specifies how the data is structured in a data packet being sent
      • MIME - specifies various types of multimedia formatting of data 
      • NDR
      • CDR
      • XML:
        • a text-based, extremely flexible object oriented data structure specification
        • to support extensibility, every element and attribute in XML has a namespace URI associated with it
• Service-specific pipes:
  • Database-specific middleware:
    • SQL API's:
      • ODBC
      • JDBC
      • SQLJ
      • DRDA
      • EDA/SQL
      • SAG/CLI
      • OLE DB
      • OQL
      • Oracle SQL*Net
  • OLTP-specific:
    • Tuxedo's ATMI & /WS
    • Encina's Transactional RPC
    • X/Open's TxRPC & XATMI
    • CORBA's OTS
    • MS DTC & TIP
  • Groupware-specific:
    • MAPI
    • VIM
    • JavaMail
    • SMTP
    • Web/NNTP
    • S/MIME
    • POP3
    • IMAP
    • Workflow
    • Lotus Notes calls
  • Object-specific:
    • OMG's CORBA/IIOP
    • MS COM+
    • JavaSoft's RMI-over-IIOP
  • Internet-specific:
    • CGI
    • SET
  • System management-specific:
    • SNMP
    • CMIP
    • RMON
    • DMTF
    • WFM
    • JMAPI
    • WEBEM
    • ORBs

Platforms:

• the application servers that run the server-side components (NOT the client side)
• examples:
  • TP monitors
  • Object Transaction Monitors:
    • MS MTS
  • Web Application Servers