sna

SNA Networking: 

SNA Networking ...connecting the dots ...many of them

SNA history: 

SNA history Before OSI model...handle all functions Mainframe to terminal application use Move characters only to dumb terminals Central control of network Specialists to pre-define and maintain Complex responsibilities Understanding programs/databases Understanding peripheral devices

SNA Node Roles (subarea): 

SNA Node Roles (subarea) Heirarchy is defined in Nodes Subarea nodes Peripheral nodes Subarea nodes control action of Peripheral nodes

SNA Node Roles (subarea): 

SNA Node Roles (subarea)

SNA hardware entities (subarea): 

SNA hardware entities (subarea) Mainframe Front-end processor Cluster controller 3270 terminal

SNA software entities (subarea): 

SNA software entities (subarea) VTAM NCP SSCP

SNA Network Accessible Units (subarea): 

SNA Network Accessible Units (subarea) PU LU CP (earlier edition showed “session” here, which is incorrect)

Network Activation (subarea): 

Network Activation (subarea) Done by mainframe operator Heirarchical Careful sequence of nodes and links Must correspond to network gen When the T5 Network node comes up, most (if not all) of the remainder of the network is brought up as well

Establishing Routes (subarea): 

Establishing Routes (subarea) Links along a physical path are statically predefined in subarea network tables Characteristics determines Class of Service Reliability Performance Class of Service is important When LU wants to initiate a session, it petitions SSCP SSCP will establish permanent routing between requested LUs based on class of service requested and class of service available Once session is established (routing is established) the route cannot be changed If the route goes down, the session goes down

Transmission Groups in a Heirarchical Network: 

Transmission Groups in a Heirarchical Network

SNA after the PC and AS/400: 

SNA after the PC and AS/400 Smart device, simple message Binary data Offload complex responsibilities programs and databases peripheral devices Exchange by peer over token-ring central control not needed

OSI model corresponds to SNA: 

OSI model corresponds to SNA Layer 7 Transaction CPI-C Layer 6 Presentation APPC Layer 5 Data flow LU6.2 Layer 4 Transmission LU6.2 Layer 3 Path APPN Layer 2 Data link Token Ring Layer 1 Physical Token Ring

APPN Goal: 

APPN Goal Handle diversity Platforms, topologies, applications Heirarchical and APPN simultaneously Older dependent LUs can use APPN Intelligent technology Present throughout the network Dynamic (automatic) response to changes Local or wide-area Fast or slow links

SNA software entities with APPN: 

SNA software entities with APPN

SNA hardware entities: 

SNA hardware entities Mainframe Front-end processor Cluster controller 3270 terminal AS/400 minicomputer PC microcomputer Token-ring LAN

APPN functions: 

APPN functions Keep track of resources in network Dynamic exchange of information between nodes Paths between nodes Resources within node Select best path for data route Handle mix of traffic Class of Service routing Enhance reliability Non-disruptive path switch

SNA Node Roles (APPN): 

SNA Node Roles (APPN) Low-entry networking node Passive interaction with Network node Relies on Network node for all network services APPN End node No pass-thru traffic Active interaction with Network node Network node (intermediate routing network) Handles pass-thru traffic (routing) Finds location of partner node and exchanges information Places resource information in Central Directory Reduce broadcast searches Computes potential routes to partner Selects best route from among those computed

SNA Node Roles (APPN Interchange): 

SNA Node Roles (APPN Interchange) Interchange node (specialized for this function) Both heirarchical and peer-oriented functionality Handle search requests between subarea node and APPN node Speaks SSCP-SSCP on one side (CDINIT) Speaks CP-CP on other side (LOCATE) Allow gradual migration from heirarchical to peer-oriented APPN Permits routing that passes through intervening heirarchical node

SNA Node Roles (APPN Interchange): 

SNA Node Roles (APPN Interchange)

SNA Node Roles (APPN Composite): 

SNA Node Roles (APPN Composite) Mainframe node Handling heirarchical and peer-oriented functions)

SNA Node Roles (APPN Composite): 

SNA Node Roles (APPN Composite)

Links and Transmission Groups: 

Links and Transmission Groups Link connects adjacent nodes Link station at each end handles communication across data line Lower layers of communications protocol Typically SDLC or Token-Ring Links are formally known as Transmission Groups There may be several transmission groups between nodes Increase reliability Increase bandwith

APPN Control Points: 

APPN Control Points CP in a Network node handles routing and resource management Dynamic configuration Reveal its resources Discover other resources Initial route determination Pass thru routing

APPN Control Points: 

APPN Control Points CP in an End node handles resource management Dynamic configuration Reveals its resource to it adjacent Network node Requests help from Network node for initial route determination Controls only its local resources

APPN Control Points: 

APPN Control Points

APPN Network Accessible Units: 

APPN Network Accessible Units Components that establish a session Establish routing for data between end users Physical Unit (PU) Logical Unit (LU) Control Point (CP)

PU duties in APPN: 

PU duties in APPN PU’s activate and de-activate links between nodes Between APPN nodes this function is handled by the CP

LU duties in APPN: 

LU duties in APPN Work on behalf of end users Application programs Terminal users Pass user data into network Send session-activation requests directly to their LU partners This was handled by SSCP in heirarchical APPN LUs are Independent LU Not handled by CP or SSCP

CP duties in APPN: 

CP duties in APPN Entirely dynamic Manage resources in its domain Does not maintain sessions with LUs APPN LUs are Independent LUs Talk directly with their partner LUs Session setup and control Share resource data with CP in adjacent node Routing data Directory services

Network Activation (APPN): 

Network Activation (APPN) Local operator decides when APPN node becomes active network component Any node can be “first” or “last” or in-between No node is subordinate to any other node Local operator gives command to CP to bring up links Automatic Topology Database Update when a network node comes up New Network node reveals its resources to adjacent Network node Propagated among all Network nodes in network Cached in the Central Directory Services database

Phases of Link Activation: 

Phases of Link Activation Connect Dialup Modem “training” Pre-negotiation (is adjacent node active?) Link level poll APPN uses XID-XID pairs “pre-negotiation flag” Contact (link stations negotiate by exchanging XID pairs) Link station roles Which link station is primary and which is secondary The primary link station controls the links and the secondary link station Link characteristics Maximum BTU (basic transmission unit) sizes allowed on the link Node capabilities End node or Low-entry end node or Network node capability Segmentation and re-assembly capability of the node

Node connection example: 

Node connection example

Node connection example: 

Node connection example CP activates local LS (link station) CP commands LS to connect to adjacent LS LS sends successful connect reply CPs exchange identifications and protocol commands CPs establish sessions between them CPs exchange information on their capabilities List of resources (LUs) Topology database is updated

Node connection example: 

Node connection example

Activating CP-CP sessions: 

Activating CP-CP sessions CPs establish sessions after link has been established to adjacent node Both CP’s initiate a session between them The initiator of a LU6.2 session is the contention winner “Send” via the contention-winner session “Receive” via the contention-loser session Request capabilities of partner CP Management services capabilities Entry-point or focal-point Kinds of directory objects which can be searched Exchange directory or network topology information Reveal LUs to be cached in Network Directory

Session setup services: 

Session setup services Central Directory Server Locate partner LUs One Network nodes used by others After local searches have failed Network Topology Database Calculate route to partner LU Every Network node can do this Has its own copy of the database

Session setup sequence: 

Session setup sequence Locate the destination LU Local node table search Network node table search Central Directory server database search Directed search of neighbor Network nodes Broadcast search Calculate the best route Network node’s topology database

Route Selection Control Vector: 

Route Selection Control Vector Components of a route Chain of network nodes From origin to destination Conforms to Class of Service requested Is appended to the BIND request

Session Protocols between LUs (APPN): 

Session Protocols between LUs (APPN) Partner LUs at both ends must use same protocol Response requirements Message size requirements Number of multiple simultaneous requests Called the BIND request There is a particular protocol used for peer-oriented LU-to-LU communication LU6.2 Advanced-Program-to-Program Communcation (APPC)

LU6.2 or APPC Overview: 

LU6.2 or APPC Overview Designed for peer-oriented LU-to-LU communication Program-to-program Program-to-device Device-to-device Application Programming Interface to encapsulate product platform details of LU6.2 CPI-C Common Programming Interface-Communications

Establishing Routes for LUs (APPN): 

Establishing Routes for LUs (APPN) Uses Class of Service Locate the session partner Not predefined in a static table like subarea Find it in real-time since it is dynamic Determine the route between the session partners When the session partner is found CP in Network node server can determine route

Routing in APPN Networks: 

Routing in APPN Networks Session identifier in Transmission Header Matching session identifier stored at intermediate node Only for duration of session

Automatic Network Routing: 

Automatic Network Routing Reduces overhead at intermediate nodes Packet’s header contains path that packet is to take through the network Sequence of transmission groups No session table lookups

APPN Application Support: 

APPN Application Support Can now “push” from both ends of network API (application program interfaces) technical details required to “talk” across network Called CPI-C Dynamic definition of LUs Independent LUs

APPN node connection: 

APPN node connection CP-a activates LS-a1 CP-a issues CONNECT_OUT Command that requests LS-a1 to connect with LS-b1 LS-a1 informs CP-a that is has successfully connected with LS-b1 CP-a and CP-b exchange identifications and data link protocol commands necessary to activate the link CP-a and CP-b activate two CP-CP sessions between them CP-a and CP-b exchange information on their respective capabilities

APPN node connection: 

APPN node connection CP-a sends CP-b a list of its resources For example, a list of its LUs CP-b updates its local directory

Initiating LU-LU session example: 

Initiating LU-LU session example

Initiating LU-LU session: 

Initiating LU-LU session SESSION-INITIATION request from LU-a to CP-a Identify the two LUs that are to participate in the session Specify the MODE name for the session MODE name identifies CLASS of SERVICE CP-a checks directory to see if LU-c is a local resource LOCATE request from CP-a to CP-b CP-b is CP-a’s Network Node Server Finds partner LU-c Calculate route based on MODE (CLASS of SERVICE) Build Route-Selection-Control-Vector LOCATE-REPLY from CP-b to CP-a Contains Route-Selection-Control-Vector

Initiating LU-LU session: 

Initiating LU-LU session CONTROL-INITIATE (CINT) from CP-a to LU-a CINT enables LU-a to activate session with LU-c CP-a includes Route-Selection-Control-Vector SESSION-ACTIVATION (BIND) from LU-a to LU-c Include Route-Selection-Control-Vector in BIND CP-a CP-b CP-c use transmission group vectors in RSCV to route the BIND along consecutive transmissions groups to LU-c As the BIND flows from node to node, half-sessions are initialized in partner LU-a and LU-c as well as session connectors in intermediate routing node B Half-sessions and session-connectors built in reverse direction when LU-c sends BIND response to LU-a

Example Startup Script: 

Example Startup Script open $tw1 allow errors on log twh1aa add line tw1,tndm $twh1,protocol SDLC,type SECONDARY add pu putwh1,address %H01, line tw1,xid YES add mode LU62,maxsess 32,minconwin 31,minconlos 1,rcvw 7, sendw 7 add appl twqa,open #twqa,llu UMAG002,prot CPIC add appl twqb,open #twqb,llu UMAG002,prot CPIC add appl twqc,open #twqc,llu UMAG002,prot CPIC add appl twqd,open #twqd,llu UMAG002,prot CPIC add appl twqe,open #twqe,llu UMAG002,prot CPIC add appl twqf,open #twqf,llu UMAG002,prot CPIC add appl twqg,open #twqg,llu UMAG002,prot CPIC

Example Startup Script: 

Example Startup Script add RLU TRW1.CICSCVP1,pu putwh1,parsess yes add RLU TRW1.trw1bbp1,pu putwh1,parsess yes add RLUALIAS twqa,RLU TRW1.CICSCVP1 add RLUALIAS twqb,RLU TRW1.CICSCVP1 add RLUALIAS twqc,RLU TRW1.CICSCVP1 add RLUALIAS twqd,RLU TRW1.CICSCVP1 add RLUALIAS twqe,RLU TRW1.CICSCVP1 add RLUALIAS twqf,RLU TRW1.CICSCVP1 add RLUALIAS twqg,RLU TRW1.CICSCVP1 start line tw1,sub all start cnos LU62,llu UMAG002,rlu TRW1.CICSCVP1 start cnos LU62,llu UMAG002,rlu TRW1.TRW1BBP1

Congestion Causes: 

Congestion Causes Network sized for typical peak data flow Excessive data flow will choke network to a standstill Response times lengthen without ceasing Buffers are depleted This happens very rapidly Remains choked while network is at capacity Remains choked until data flow falls below network capacity

Congestion Solutions: 

Congestion Solutions Message repackaging Larger or smaller units Blocking Segmentation Accommodate efficiency of link Message pacing Number of end-to-end messages that source can send to destination without acknowledgement Session level pacing Intermediate session connectors pace their adjacent links as well Pacing back-pressure lowers message rate by propagating backwards toward sender LU

References: 

References www.cisco.com http://publibfp.boulder.ibm.com www.oreilly.com www.interskill.com www.navdesign.com www.support.3com.com Insession Labs Pty. Ltd: “ICE Intersystem Communications Environment Product Summary”